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Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..9c24686 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #69025 (https://www.gutenberg.org/ebooks/69025) diff --git a/old/69025-0.txt b/old/69025-0.txt deleted file mode 100644 index e0056d6..0000000 --- a/old/69025-0.txt +++ /dev/null @@ -1,13907 +0,0 @@ -The Project Gutenberg eBook of The filtration of public -water-supplies, by Allen Hazen - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: The filtration of public water-supplies - Third edition, revised and enlarged. - -Author: Allen Hazen - -Release Date: September 21, 2022 [eBook #69025] - -Language: English - -Produced by: Charlene Taylor, Brian G. Wilcox and the Online Distributed - Proofreading Team at https://www.pgdp.net (This file was - produced from images generously made available by The - Internet Archive/American Libraries.) - -*** START OF THE PROJECT GUTENBERG EBOOK THE FILTRATION OF PUBLIC -WATER-SUPPLIES *** - - -Transcriber’s Notes: - -The spelling, hyphenation, punctuation and accentuation are as the -original, except for apparent typographical errors which have been -corrected. - - Italic text is denoted _thus_. - Bold text is denoted =thus=. - -See further notes at the end of the book. - - - - -[Illustration: GENERAL VIEW OF FILTERS AT HAMBURG. - - [_Frontispiece._] -] - - - - - THE FILTRATION - - OF - - PUBLIC WATER-SUPPLIES. - - - BY - ALLEN HAZEN, - -MEMBER OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS, THE BOSTON SOCIETY -OF CIVIL ENGINEERS, THE AMERICAN WATER-WORKS ASSOCIATION, THE NEW -ENGLAND WATER-WORKS ASSOCIATION, THE AMERICAN CHEMICAL SOCIETY, THE -AMERICAN PUBLIC HEALTH ASSOCIATION, ETC. - - - _THIRD EDITION, REVISED AND ENLARGED._ - SECOND THOUSAND. - - - NEW YORK: - JOHN WILEY & SONS. - LONDON: CHAPMAN & HALL, LIMITED. - 1905. - - - Copyright, 1900, - BY - ALLEN HAZEN. - - - ROBERT DRUMMOND, ELECTROTYPER AND PRINTER, NEW YORK. - - - - -PREFACE TO FIRST EDITION. - - -The subject of water-filtration is commencing to receive a great deal -of attention in the United States. The more densely populated European -countries were forced to adopt filtration many years ago, to prevent -the evils arising from the unavoidable contaminations of the rivers -and lakes which were the only available sources for their public -water-supplies; and it has been found to answer its purpose so well -that at the present time cities in Europe nearly if not quite equal in -population to all the cities of the United States are supplied with -filtered water. - -Many years ago, when the whole subject of water-supply was still -comparatively new in this country, filtration was considered as a means -for rendering the waters of our rivers suitable for the purpose of -domestic water-supply. St. Louis investigated this subject in 1866, -and the engineer of the St. Louis Water Board, the late Mr. J. P. -Kirkwood, made an investigation and report upon European methods of -filtration which was published in 1869, and was such a model of full -and accurate statement combined with clearly-drawn conclusions that, up -to the present time, it has remained the only treatise upon the subject -in English, notwithstanding the great advances which have been made, -particularly in the last ten years, with the aid of knowledge of the -bacteria and the germs of certain diseases in water. - -Unfortunately the interest in the subject was not maintained in -America, but was allowed to lag for many years; it was cheaper to use -the water in its raw state than it was to purify it; the people became -indifferent to the danger of such use, and the disastrous epidemics -of cholera and typhoid fever, as well as of minor diseases, which so -often resulted from the use of polluted water, were attributed to other -causes. With increasing study and diffusion of knowledge the relations -of water and disease are becoming better known, and the present state -of things will not be allowed to continue; indeed at present there is -inquiry at every hand as to the methods of improving waters. - -The one unfortunate feature is the question of cost. Not that the cost -of filtration is excessive or beyond the means of American communities; -in point of fact, exactly the reverse is the case; but we have been so -long accustomed to obtain drinking-water without expense other than -pumping that any cost tending to improved quality seems excessive, thus -affording a chance for the installation of inferior filters, which by -failing to produce the promised results tend to bring the whole process -into disrepute, since few people can distinguish between an adequate -filtration and a poor substitute for it. It is undoubtedly true that -improvements are made, and will continue to be made, in processes of -filtration; so it will often be possible to reduce the expense of the -process without decreasing the efficiency, but great care must be -exercised in such cases to maintain the conditions really essential to -success. - -In the present volume I have endeavored to explain briefly the nature -of filtration and the conditions which, in half a century of European -practice, have been found essential for successful practice, with a -view of stimulating interest in the subject, and of preventing the -unfortunate and disappointing results which so easily result from the -construction of inferior filters. The economies which may possibly -result by the use of an inferior filtration are comparatively small, -and it is believed that in those American cities where filtration is -necessary or desirable it will be found best in every case to furnish -filters of the best construction, fully able to do what is required of -them with ease and certainty. - - - - -PREFACE TO THIRD EDITION. - - -There have been several distinct epochs in the development of water -purification in the United States. The first may be said to date -from Kirkwood’s report on the “Filtration of River Waters,” and the -second from the inauguration of the Lawrence Experiment Station by -the Massachusetts State Board of Health, and the construction of -the Lawrence city filter, with the demonstration of the wonderful -biological action of filters upon highly polluted waters. - -The third epoch is marked by the experiments at Louisville, Pittsburg -and Cincinnati, which have greatly increased our knowledge of the -treatment of waters containing enormous quantities of suspended matter, -and have reduced to something like order the previously existing -confused mass of data regarding coagulation and rapid filtration. - -The first edition of this book represented the earlier epochs -before the opening of the third. In the five years since it was -written, progress in the art of water purification has been rapid -and substantial. No apology is needed for the very complete revision -required to treat these newly investigated subjects as fully as were -other matters in the earlier editions. - -In the present edition the first seven chapters remain with but few -additions. Experience has strengthened the propositions contained -in them. New data might have been added, but in few cases would the -conclusions have been altered. The remaining chapters of the book have -been entirely rewritten and enlarged to represent the added information -now available, so that the present edition is nearly twice as large as -the earlier ones. In the appendices, also, much matter has been added -relating to works in operation, particularly to those in America. - - NEW YORK January, 1900. - - - - -CONTENTS. - - - PAGE - - Chapter I. INTRODUCTION. 1 - II. CONTINUOUS FILTERS AND THEIR CONSTRUCTION 5 - Sedimentation-basins 8 - Size of Filter-beds 10 - Form of Filter-beds 11 - Covers for Filters 12 - III. FILTERING-MATERIALS 20 - Sand 20 - Sands Used in European Filters 24 - Effect of Size of Grain Upon Efficiency of Filtration 30 - Effect of Grain Size Upon Frequency of Scraping 32 - Selection of Sand 33 - Thickness of the Sand Layer 34 - Underdraining 35 - Gravel Layers 35 - Underdrains 39 - Depth of Water on Filters 45 - IV. RATE OF FILTRATION AND LOSS OF HEAD 47 - Effect of Rate Upon Cost of Filtration 48 - Effect of Rate Upon Efficiency of Filtration 50 - The Loss of Head 52 - Regulation of the Rate and Loss of Head in the - Older Filters 52 - Apparatus For Regulating the Rate and Loss of Head 55 - Apparatus For Regulating the Rate Directly 57 - Apparatus For Regulating the Height of Water Upon - Filters 59 - Limit to the Loss of Head 60 - V. CLEANING FILTERS 68 - Frequency of Scraping 72 - Quantity of Sand to Be Removed 74 - Wasting the Effluents After Scraping 74 - Sand-washing 76 - VI. THEORY AND EFFICIENCY OF FILTRATION 83 - Bacterial Examination of Waters 93 - VII. INTERMITTENT FILTRATION 97 - The Lawrence Filter 100 - Chemnitz Water-Works 107 - Application of Intermittent Filtration 111 - VIII. TURBIDITY AND COLOR, AND THE EFFECT OF MUD UPON - SAND FILTERS 113 - The Measurement of Color 114 - Amount of Color in American Waters 115 - Removal of Color 117 - Measurement of Turbidity 117 - Relation of Platinum-wire Turbidities to Suspended - Matters 122 - Source of Turbidity 123 - The Amounts of Suspended Matters in Water 129 - Preliminary Processes to remove Mud 133 - Effect of Mud upon Sand Filters 137 - Effect of Turbidity Upon the Length of Period 137 - Power of Sand Filters to Produce Clear Effluents - from Muddy Water 139 - Effect of Mud Upon Bacterial Efficiency of Filters 141 - Limits to the Use of Subsidence for the Preliminary - Treatment of Muddy Waters 142 - IX. COAGULATION OF WATERS 144 - Substances used for Coagulation 145 - Coagulants Which Have Been Used 150 - Amount of Coagulant required to remove Turbidity 150 - Amount of Coagulant required to remove Color 153 - Successive Applications of Coagulant 154 - The Amount of Coagulant which Various Waters will - receive 155 - X. MECHANICAL FILTERS 159 - Providence Experiments 159 - Louisville_Experiments 161 - Lorain Tests 161 - Pittsburg Experiments 162 - Wasting Effluent After Washing Filters 163 - Influence of Amount of Sulphate of Alumina on - Bacterial Efficiency of Mechanical Filters 165 - Influence of Degree of Turbidity upon Bacterial - Efficiency of Mechanical Filters 167 - Average Results Obtained with Various Quantities of - Sulphate of Alumina 171 - Types of Mechanical Filters 172 - Efficiency of Mechanical Filters 179 - Pressure Filters 180 - XI. OTHER METHODS OF FILTRATION 181 - Worms Tile System 181 - The Use of Asbestos 181 - Filters Using High Rates of Filtration Without - Coagulants 182 - Household Filters 183 - XII. REMOVAL OF IRON FROM GROUND-WATERS 186 - Amount of Iron Required to Render Water Objectionable 186 - Cause of Iron in Ground-waters 187 - Treatment of Iron-containing Waters 189 - Iron-removal Plants in Operation 192 - XIII. TREATMENT OF WATERS 197 - Cost of Filtration 200 - What Waters Require Filtration 207 - XIV. WATER-SUPPLY AND DISEASE—CONCLUSIONS 210 - Appendix I. RULES OF THE GERMAN GOVERNMENT IN REGARD TO THE - FILTRATION OF SURFACE-WATERS USED FOR PUBLIC - WATER-SUPPLIES 221 - II. EXTRACTS FROM “BERICHT DES MEDICINAL-INSPECTORATS - DES HAMBURGISCHEN STAATES FÜR DAS JAHR 1892” 226 - III. METHODS OF SAND-ANALYSIS 233 - IV. FILTER STATISTICS 241 - Statistics of Operation of Sand Filters 241 - Partial List of Cities Using Sand Filters 244 - List of Cities and Towns Using Mechanical Filters 247 - Notes Regarding Sand Filters in the United States 251 - Capacity of Filters 254 - V. LONDON’S WATER-SUPPLY 255 - VI. THE BERLIN WATER-WORKS 261 - VII. ALTONA WATER-WORKS 265 - VIII. HAMBURG WATER-WORKS 269 - IX. NOTES ON SOME OTHER EUROPEAN WATER-SUPPLIES 272 - The Use of Unfiltered Surface-waters. 275 - The Use of Ground-water. 276 - X. LITERATURE OF FILTRATION 277 - XI. THE ALBANY WATER-FILTRATION PLANT 288 - Description of Plant. 289 - Capacity of Plant and Means of Regulation. 308 - Results of Operation. 314 - Cost of Construction. 314 - INDEX 317 - - - - -UNITS EMPLOYED. - - -The units used in this work are uniformly those in common use in -America, with the single exception of data in regard to sand-grain -sizes, which are given in millimeters. The American units were not -selected because the author prefers them or considers them particularly -well suited to filtration, but because he feared that the use of the -more convenient metric units in which the very comprehensive records -of Continental filter plants are kept would add to the difficulty of -a clear comprehension of the subject by those not familiar with those -units, and so in a measure defeat the object of the book. - - -TABLE OF EQUIVALENTS. - - Unit. Metric Equivalent. Reciprocal. - Foot 0.3048 meter 3.2808 - Mile 1609.34 meters 0.0006214 - Acre 4047 square meters 0.0002471 - Gallon[1] 3.785 liters 0.26417 - 1 million gallons 3785 cubic meters 0.00026417 - Cubic yard 0.7645 cubic meters 1.308 - 1 million gallons per } { meter in depth } - acre daily } 0.9354 { of water daily } 1.070 - - - - -ACKNOWLEDGMENT. - - -I wish to acknowledge my deep obligation to the large number of -European engineers, directors, and superintendents of water-works, and -to the health officers, chemists, bacteriologists, and other officials -who have kindly aided me in studying the filtration-works in their -respective cities, and who have repeatedly furnished me with valuable -information, statistics, plans, and reports. - -To mention all of them would be impossible, but I wish particularly to -mention Major-General Scott, Water-examiner of London; Mr. Mansergh, -Member of the Royal Commission on the Water-supply of the Metropolis; -Mr. Bryan, Engineer of the East London Water Company; and Mr. Wilson, -Manager of the Middlesborough Water-works, who have favored me with -much valuable information. - -In Holland and Belgium I am under special obligations to Messrs. Van -Hasselt and Kemna, Directors of the water companies at Amsterdam and -Antwerp respectively; to Director Stang of the Hague Water-works; to -Dr. Van’t Hoff, Superintendent of the Rotterdam filters; and to my -friend H. P. N. Halbertsma, who, as consulting engineer, has built many -of the Dutch water-works. - -In Germany I must mention Profs. Frühling, at Dresden, and Flügge, at -Breslau; Andreas Meyer, City Engineer of Hamburg; and the Directors of -water-works, Beer at Berlin, Dieckmann at Magdeburg, Nau at Chemnitz, -and Jockmann at Liegnitz, as well as the Superintendent Engineers -Schroeder at Hamburg, Debusmann at Breslau, and Anklamm and Piefke at -Berlin, the latter the distinguished head of the Stralau works, the -first and most widely known upon the Continent of Europe. - -I have to acknowledge my obligation to City Engineer Sechner at -Budapest, and to the Assistant Engineer in charge of water-works, -Kajlinger; to City Engineer Peters and City Chemist Bertschinger at -Zürich; and to Assistant Engineer Regnard of the Compagnie Générale des -Eaux at Paris. - -On this side of the Atlantic also I am indebted to Hiram F. Mills, -C.E., under whose direction I had the privilege of conducting -for nearly five years the Lawrence experiments on filtration; to -Profs. Sedgwick and Drown for the numerous suggestions and friendly -criticisms, and to the latter for kindly reading the proof of this -volume; to Mr. G. W. Fuller for full information in regard to the -more recent Lawrence results; to Mr. H. W. Clark for the laborious -examination of the large number of samples of sands used in actual -filters and mentioned in this volume; and to Mr. Desmond FitzGerald -for unpublished information in regard to the results of his valuable -experiments on filtration at the Chestnut Hill Reservoir, Boston. - - ALLEN HAZEN. - - BOSTON, April, 1895. - - - - -FILTRATION OF PUBLIC WATER-SUPPLIES. - - - - -CHAPTER I. - -INTRODUCTION. - - -The rapid and enormous development and extension of water-works in -every civilized country during the past forty years is a matter which -deserves our most careful consideration, as there is hardly a subject -which more directly affects the health and happiness of almost every -single inhabitant of all cities and large towns. - -Considering the modern methods of communication, and the free exchange -of ideas between nations, it is really marvellous how each country has -met its problems of water-supply from its own resources, and often -without much regard to the methods which had been found most useful -elsewhere. England has secured a whole series of magnificent supplies -by impounding the waters of small streams in reservoirs holding enough -water to last through dry periods, while on Continental Europe such -supplies are hardly known. Germany has spent millions upon millions in -purifying turbid and polluted river-waters, while France and Austria -have striven for mountain-spring waters and have built hundreds of -miles of costly aqueducts to secure them. In the United States an -abundant supply of some liquid has too often been the objective point, -and the efforts have been most successful, the American works being -entirely unrivalled in the volumes of their supplies. I do not wish -to imply that quality has been entirely neglected in our country, for -many cities and towns have seriously and successfully studied their -problems, with the result that there are hundreds of water-supplies -in the United States which will compare favorably upon any basis with -supplies in any part of the world; but on the other hand it is equally -true that there are hundreds of other cities, including some among -the largest in the country, which supply their citizens with turbid -and unhealthy waters which cannot be regarded as anything else than a -national disgrace and a menace to our prosperity. - -One can travel through England, Belgium, Holland, Germany, and large -portions of other European countries and drink the water at every city -visited without anxiety as to its effect upon his health. It has not -always been so. Formerly European capitals drank water no better than -that so often dispensed now in America. As recently as 1892 Germany’s -great commercial centre, Hamburg, having a water-supply essentially -like those of Philadelphia, Pittsburg, Cincinnati, St. Louis, New -Orleans, and a hundred other American cities, paid a penalty in one -month of eight thousand lives for its carelessness. The lesson was a -dear one, but it was not wasted. Hamburg now has a new and wholesome -supply, and other German cities the qualities of whose waters were open -to question have been forced to take active measures to better their -conditions. We also can learn something from their experience. - -There are three principal methods of securing a good water-supply for a -large city. The first consists of damming a stream from an uninhabited -or but sparsely inhabited watershed, thus forming an impounding -reservoir. This method is extensively used in England and in the United -States. In the latter most of the really good and large supplies are so -obtained. It is only applicable to places having suitable watersheds -within a reasonable distance, and there are large regions where, owing -to geological and other conditions, it cannot be applied. It is most -useful in hilly and poor farming countries, as in parts of England and -Wales, in the Atlantic States, and in California. It cannot be used to -any considerable extent in level and fertile countries which are sure -to be or to become densely populated, as is the case with large parts -of France and Germany and in the Middle States. - -The second method is to secure ground-water, that is, spring or well -water, which by its passage through the ground has become thoroughly -purified from any impurities which it may have contained. This was the -earliest and is the most widely used method of securing good water. -It is specially adapted to small supplies. Under favorable geological -conditions very large supplies have been obtained in this manner. In -Europe Paris, Vienna, Budapest, Munich, Cologne, Leipzig, Dresden, a -part of London, and very many smaller places are so supplied. This -method is also extensively used in the United States for small and -medium-sized places, and deserves to be most carefully studied, and -used whenever possible, but is unfortunately limited by geological -conditions and cannot be used except in a fraction of the cases where -supplies are required. No ground-water supplies yet developed in the -United States are comparable in size to those used in Europe. - -The third process of securing a good water-supply is by means of -filtration of surface waters which would otherwise be unsuitable for -domestic purposes. The methods of filtration, which it is the purpose -of this volume to explain, are beyond the experimental stage; they -are now applied to the purification of the water-supplies of European -cities with an aggregate population of at least 20,000,000 people. In -the United States the use of filters is much less common, and most of -the filters in use are of comparatively recent installation. - -Great interest has been shown in the subject during the last few -years, and the peculiar character of some American waters, which differ -widely in their properties from those of many European streams, has -received careful and exhaustive consideration. In Europe filtration has -been practised with continually improving methods since 1829, and the -process has steadily received wider and wider application. It has been -most searchingly investigated in its hygienic relations, and has been -repeatedly found to be a most valuable aid in reducing mortality. The -conditions under which satisfactory results can be obtained are now -tolerably well known, so that filters can be built in the United States -with the utmost confidence that the result will not be disappointing. - -The cost of filtration, although considerable, is not so great as to -put it beyond the reach of American cities. It may be roughly estimated -that the cost of filtration, with all necessary interest and sinking -funds, will add 10 per cent to the average cost of water as at present -supplied. - -It may be confidently expected that when the facts are better -understood and realized by the American public, we shall abandon the -present filthy and unhealthy habit of drinking polluted river and -lake waters, and shall put the quality as well as the quantity of our -supplies upon a level not exceeded by those of any country. - - - - -CHAPTER II. - -CONTINUOUS FILTERS AND THEIR CONSTRUCTION. - - -Filtration of water consists in passing it through some substance -which retains or removes some of its impurities. In its simplest form -filtration is a straining process, and the results obtained depend upon -the fineness of the strainer, and this in turn is regulated by the -character of the water and the uses to which it is to be put. Thus in -the manufacture of paper an enormous volume of water is required free -from particles which, if they should become imbedded in the paper, -would injure its appearance or texture. Obviously for this purpose the -removal of the smaller particles separately invisible to the unaided -eye, and thus not affecting the appearance of the paper, and the -removal of which would require the use of a finer filter at increased -expense, would be a simple waste of money. When, however, a water is -to be used for a domestic water supply and transparency is an object, -the still finer particles which would not show themselves in paper, but -which are still able, in bulk, to render a water turbid, should be as -far as possible removed, thus necessitating a finer filter; and, when -there is reason to think that the water contains the germs of disease, -the filter must be fine enough to remove with certainty those organisms -so extraordinarily small that millions of them may exist in a glass of -water without imparting a visible turbidity. - -It is now something over half a century since the first successful -attempts were made to filter public water-supplies, and there are -now hundreds of cities supplied with clear, healthy, filtered water. -(Appendix IV.) While the details of the filters used in different -places present considerable variations, the general form is, in -Europe at least, everywhere the same. The most important parts of a -filter are shown by the accompanying sketch, in which the dimensions -are much exaggerated. The raw water is taken from the river into a -settling-basin, where the heaviest mud is allowed to settle. In the -case of lake and pond waters the settling-tank is dispensed with, but -it is essential for turbid river-water, as otherwise the mud clogs -the filter too rapidly. The partially clarified water then passes to -the filter, which consists of a horizontal layer of rather fine sand -supported by gravel and underdrained, the whole being enclosed in a -suitable basin or tank. The water in passing through the sand leaves -behind upon the sand grains the extremely small particles which were -too fine to settle out in the settling-basin, and is quite clear as it -goes from the gravel to the drains and the pumps, which forward it to -the reservoir or city. - -[Illustration: FIG. 1.—SKETCH SHOWING GENERAL ARRANGEMENT OF FILTER -PLANTS.] - -The passages between the grains of sand through which the water must -pass are extremely small. If the sand grains were spherical and 1/50 of -an inch in diameter, the openings would only allow the passage of other -spheres 1/320 of an inch in diameter, and with actual irregular sands -much finer particles are held back. As a result the coarser matters -in the water are retained on the surface of the sand, where they -quickly form a layer of sediment, which itself becomes a filter much -finer than the sand alone, and which is capable of holding back under -suitable conditions even the bacteria of the passing water. The water -which passes before this takes place may be less perfectly filtered, -but even then, the filter may be so operated that nearly all of the -bacteria will be deposited in the sand and not allowed to pass through -into the effluent. - -As the sediment layer increases in thickness with continued filtration, -increased pressure is required to drive the desired volume of water -through its pores, which are ever becoming smaller and reduced in -number. When the required quantity of water will no longer pass with -the maximum pressure allowed, it is necessary to remove, by scraping, -the sediment layer, which should not be more than an inch deep. This -layer contains most of the sediment, and the remaining sand will then -act almost as new sand would do. The sand removed may be washed for use -again, and eventually replaced when the sand layer becomes too thin -by repeated scrapings. These operations require that the filter shall -be temporarily out of use, and as water must in general be supplied -without intermission, a number of filters are built together, so that -any of them can be shut out without interfering with the action of the -others. - -The arrangement of filters in relation to the pumps varies with local -conditions. With gravity supplies the filters are usually located below -the storage reservoir, and, properly placed, involve only a few feet -loss of head. - -In the case of tidal rivers, as at Antwerp and Rotterdam, the quality -of the raw water varies with the tide, and there is a great advantage -in having the settling-basins low enough so that a whole day’s supply -can be rapidly let in when the water is at its best, without pumping. -At Antwerp the filters are higher, and the water is pumped from the -settling basins to them, and again from the reservoir receiving the -effluents from the filters to the city. In several of the London -works (East London, Grand Junction, Southwark and Vauxhall, etc.) the -settling-basins are lower than the river, and the filters are still -lower, so that a single pumping suffices, that coming between the -filter and the city, or elevated distributing reservoir. - -In many other English filters and in most German works the -settling-basins and filters are placed together a little higher than -the river, thus avoiding at once trouble from floods and cost for -excavation. The water requires to be pumped twice, once before and once -after filtration. At Altona the settling-basins and filters are placed -upon a hill, to which the raw Elbe water is pumped, and from which it -is supplied to the city after filtration by gravity without further -pumping. The location of the works in this case is said to have been -determined by the location of a bed of sand suitable for filtration on -the spot where the filters were built. - -When two pumpings are required they are frequently done, especially in -the smaller places, in the same pumping-station, with but one set of -boilers and engines, the two pumps being connected to the same engine. -The cost is said to be only slightly greater than that of a single -lift of the same total height. In very large works, as at Berlin and -Hamburg and some of the London companies, two separate sets of pumping -machinery involve less extra cost relatively than would be the case -with smaller works. - - -SEDIMENTATION-BASINS. - -Kirkwood[2] found in 1866 that sedimentation-basins were essential -to the successful treatment of turbid river-waters, and subsequent -experience has not in any way shaken his conclusion. The German works -visited by him, Berlin (Stralau) and Altona, were both built by English -engineers, and their settling-basins did not differ materially from -those of corresponding works in England. Since that time, however, -there has been a well-marked tendency on the part of the German -engineers to use smaller, while the English engineers have used much -larger sedimentation-basins, so that the practices of the two countries -are now widely separated, the difference no doubt being in part at -least due to local causes. - -Kirkwood found sedimentation-basins at Altona with a capacity of -2-1/4 times the daily supply. In 1894 the same basins were in use, -although the filtering area had been increased from 0.82 acre to 2.20 -acres, and still more filters were in course of construction, and -the average daily quantity of water had increased from 600,000 to -4,150,000 gallons in 1891-2, or more than three times the capacity of -the sedimentation-basins. In 1890 the depth of mud deposited in these -basins was reported to be two feet deep in three months. At Stralau in -Berlin, also, in the same time the filtering area was nearly doubled -without increasing the size of the sedimentation-basins, but the Spree -at this point has such a slow current that it forms itself a natural -sedimentation-basin. At Magdeburg on the Elbe works were built in 1876 -with a filtering area of 1.92 acres, and a sedimentation-basin capacity -of 11,300,000 gallons, but in 1894 half of the latter had been built -over into filters, which with two other filters gave a total filtering -surface of 3.90 acres, with a sedimentation-basin capacity of only -5,650,000 gallons. The daily quantity of water pumped for 1891-2 was -5,000,000 gallons, so that the present sedimentation-basin capacity is -about equal to one day’s supply, or relatively less than a third of the -original provision. The idea followed is that most of the particles -which will settle at all will do so within twenty-four hours, and that -a greater storage capacity may allow the growth of algæ, and that the -water may deteriorate rather than improve in larger tanks. - -[Illustration: PAVED EMBANKMENT BETWEEN TWO FILTERS, EAST LONDON.] - -[Illustration: FILTERS AND CHANNELS FOR RAW WATER, ANTWERP.] - - [_To face page 10._] - -At London, on the other hand, the authorities consider a large storage -capacity for unfiltered water as one of the most important conditions -of successful filtration, the object however, being perhaps as much to -secure storage as to allow sedimentation. In 1893 thirty-nine places -were reported upon the Thames and the Lea which were giving their -sewage systematic treatment before discharging it into the streams -from which London’s water is drawn. These sewage treatments are, with -hardly an exception, dry-weather treatments, and as soon as there is -a considerable storm crude sewage is discharged into the rivers at -every point. The rivers are both short, and are quickly flooded, and -afterwards are soon back in their usual condition. At these times of -flood, the raw water is both very turbid and more polluted by sewage -than at other times, and it is the aim of the authorities to have the -water companies provide reservoir capacity enough to carry them through -times of flood without drawing any water whatever from the rivers. This -obviously involves much more extensive reservoirs than those used in -Germany, and the companies actually have large basins and are still -adding to them. The storage capacities of the various companies vary -from 3 to 18 times the respective average daily supplies, and together -equal 9 times the total supply. - -In case the raw water is taken from a lake or a river at a point where -there is but little current, as in a natural or artificial pond, -sedimentation-basins are unnecessary. This is the case at Zürich (lake -water), at Berlin when the rivers Havel and Spree spread into lakes, at -Tegel and Müggel, and at numerous other works. - - -SIZE OF FILTER-BEDS. - -The total area of filters required in any case is calculated from the -quantity of water required, the rate of filtration, and an allowance -for filters out of use while being cleaned. To prevent interruptions -of the supply at times of cleaning, the filtering area is divided into -beds which are operated separately, the number and size of the beds -depending upon local conditions. The cost per acre is decreased with -large beds on account of there being less wall or embankment required, -while, on the other hand, the convenience of operation may suffer, -especially in small works. It is also frequently urged that with large -filters it is difficult or impossible to get an even rate of filtration -over the entire area owing to the frictional resistance of the -underdrains for the more distant parts of the filter. A discussion of -this point is given in Chapter III, page 41. At Hamburg, where the size -of the single beds, 1.88 acres each, is larger than at any other place, -it is shown that there is no serious cause for anxiety; and even if -there were, the objectionable resistance could be still farther reduced -by a few changes in the under-drains. The sizes of filter-beds used at -a large number of places are given in Appendix IV. - -At a number of places having severe winters, filters are vaulted over -as a protection from cold, and in the most important of these, Berlin, -Warsaw, and St. Petersburg, the areas of the single beds are nearly -the same, namely, from 0.52 to 0.59 acre. The works with open filters -at London (seven companies), Amsterdam, and Breslau have filter-beds -from 0.82 to 1.50 acres each. Liverpool and Hamburg alone use filters -with somewhat larger areas. Large numbers of works with both covered -and open filters have much smaller beds than these sizes, but generally -this is to avoid too small a number of divisions in a small total area, -although such works have sometimes been extended with the growth of the -cities until they now have a considerable number of very small basins. - - -FORM OF FILTER-BEDS. - -The form and construction of the filter-beds depend upon local -conditions, the foundations, and building materials available, the -principles governing these points being in general the same as for the -construction of ordinary reservoirs. The bottoms require to be made -water-tight, either by a thin layer of concrete or by a pavement upon -a puddle layer. For the sides either masonry walls or embankments are -used, the former saving space, but being in general more expensive in -construction. Embankments must, of course, be substantially paved near -the water-line to withstand the action of ice, and must not be injured -by rapid fluctuations in the water-levels in the filters. - -Failure to make the bottoms water-tight has perhaps caused more -annoyance than any other single point. With a leaky bottom there -is either a loss of water when the water in the filters is higher -than the ground-water, or under reverse conditions, the ground-water -comes in and mixes with the filtered water, and the latter is rarely -improved and may be seriously damaged by the admixture. And with very -bad conditions water may pass from one filter to another, with the -differences in pressure always existing in neighboring filters, with -most unsatisfactory results. - - -COVERS FOR FILTERS. - -The filters in England and Holland are built open, without protection -from the weather. In Germany the filters first built were also open, -but in the colder climates more or less difficulty was experienced -in keeping the filters in operation in cold weather. An addition to -the Berlin filters, built in 1874, was covered with masonry vaulting, -over which several feet of earth were placed, affording a complete -protection against frost. The filters at Magdeburg built two years -later were covered in the same way, and since that time covered filters -have been built at perhaps a dozen different places. - -[Illustration: INTERIOR VIEW OF COVERED FILTER, ASHLAND, WIS. - -When in use the water rises nearly to the springing line of the arches.] - -[Illustration: COVERED FILTER IN COURSE OF CONSTRUCTION, SHOWING WOODEN -CENTERS FOR MASONRY VAULTING, SOMERSWORTH, N. H.] - - [_To face page 12._] - -It was found at Berlin that, owing to the difficulty of properly -cleaning the open filters in winter, it was impossible to keep the -usual proportion of the area in effective service, and as a result -portions of the filters were greatly overtaxed during prolonged -periods of cold weather. This resulted in greatly decreased bacterial -efficiency, the bacteria in March, 1889, reaching 3000 to 4000 per -cc. (with 100,000 in the raw water), although ordinarily the effluent -contained less than 100. An epidemic of typhoid fever followed, and was -confined to that part of the city supplied from the Stralau works, -the wards supplied from the covered Tegel filters remaining free from -fever. Open filters have since been abandoned in Berlin. - -At Altona also, where the water is taken from an excessively polluted -source, decreased bacterial efficiency has repeatedly resulted in -winter, and the occasional epidemics of typhoid fever in that city, -which have invariably come in winter, appear to have been directly due -to the effect of cold upon the open filters. The city has just extended -the open filters, and hopes with an increased reserve area to avoid -the difficulty in future without resource to covered filters. (See -Appendices II and VII.) - -Brunswick, Lübeck, and Frankfort on Oder with cold winters have open -filters, but draw their water-supplies from less polluted sources, and -have thus far escaped the fate of Berlin and Altona. The new filters -at Hamburg also are open. At Zürich, where open and covered filters -were long used side by side, the covered filters were much more -satisfactory, and the old open filters have recently been vaulted over. - -Königsberg originally built open filters, but was afterward obliged to -cover them, on account of the severe winters; and at Breslau, where -open filters have long been used, the recent additions are vaulted over. - -The fact that inferior efficiency of filtration results with open -filters during prolonged and severe winter weather is generally -admitted, although there is some doubt as to the exact way in which -the disturbance is caused. In some works I am informed that in cutting -the ice around the edges of the filter and repeatedly piling the -loose pieces upon the floating cake, the latter eventually becomes so -thickened at the sides that the projecting lower corners actually touch -the sand, with the fluctuating levels which often prevail in these -works, and that in this way the sediment layer upon the top of the sand -is broken and the water rapidly passes without adequate purification at -the points of disturbance. - -This theory is, however, inadequate to account for many cases where -such an accumulation of ice is not allowed. In these cases the poor -work is not obtained until after the filters have been scraped. The -sand apparently freezes slightly while the water is off, and when water -is brought back and filtration resumed, normal results are for some -reason not again obtained for a time. - -In addition to the poorer work from open filters in cold weather, the -cost of removing the ice adds materially to the operating expenses, and -in very cold climates would in itself make covers advisable. - -I have arranged the European filter plants, in regard to which I have -sufficient information, in the table on page 15, in the order of the -normal mean January temperatures of the respective places. This may not -be an ideal criterion of the necessity of covering filters, but it is -at least approximate, and in the absence of more detailed comparisons -it will serve to give a good general idea of the case. I have not -found a single case where covered filters are used where the January -temperature is 32° F. or above. In some of these places some trouble is -experienced in unusually cold weather, but I have not heard of any very -serious difficulty or of any talk of covering filters at these places -except at Rotterdam, where a project for covering was being discussed. - -Those places having January temperatures below 30° experience a great -deal of difficulty with open filters; so much so, that covered filters -may be regarded as necessary for them, although it is possible to keep -open filters running with decreased efficiency and increased expense by -freely removing the ice, with January temperatures some degrees lower. - -Where the mean January temperature is 30° to 32° F. there is room for -doubt as to the necessity of covering filters, but, judging from the -experience of Berlin and Altona, the covered filters are much safer at -this temperature. - -TABLE OF PLACES HAVING OPEN AND COVERED FILTERS. - -ARRANGED ACCORDING TO THE MEAN JANUARY TEMPERATURES. - - ------------+------------------+-------------------------------------- - Normal Mean | | - January | Place. | Kind of Filters and Results. - Temperature.| | - Degrees F. | | - ------------+------------------+-------------------------------------- - 37-40° |All English cities|Open filters only are used, and no - | | great difficulty with ice is - | | experienced. - 33-35° |Cities in Holland |All filters are open, and there is - | | little serious trouble with ice; - | | but at Amsterdam and Rotterdam - | | the bacteria in effluents are said - | | to be higher in winter than at - | | other times. - 32° | Bremen |Open filters. - 31° | Altona |Much difficulty with ice in open - | | filters (see Appendices II and VII). - 31° | Brunswick |Open filters. - 31° | Hamburg |Open filters. - 31° | Lübeck |Open filters. - 31° | Berlin |Open filters were formerly used, but - | | owing to decreased efficiency in - | | cold weather they have been - | | abandoned for covered ones. - 31° | Magdeburg |Covered filters, but a recent addition - | | is not covered. - 30° |Frankfort on Oder |Open filters. - 30° | Stuttgart |Part of the filters are covered. - 30° | Stettin |Part of the filters are covered. - 29° | Zürich |Covered filters were much the most - | | satisfactory, and the open ones were - | | covered in 1894. The raw water has a - | | temperature of 35°. - 29° | Liegnitz |Open filters. - 29° | Breslau |Open filters have been used, but - | | recent additions are covered. - 29° | Budapest |Covered filters only. - 29° | Posen |Covered filters only. - 26° | Königsberg |The original filters were open, but it - | | was found necessary to cover them. - 24° | Warsaw |Covered filters only. - 16° | St. Petersburg |Covered filters only. - ------------+------------------+-------------------------------------- - -In case the raw water was drawn from a lake at a depth where its -minimum temperature was above 32°, which is the temperature which must -ordinarily be expected in surface-waters in winter, open filters might -be successfully used in slightly colder places. - -The covers are usually of brick or concrete vaulting supported by -pillars at distances of 11 to 15 feet in each direction, the whole -being covered by 2 or 3 feet of earth; and the top can be laid out as -a garden if desired. Small holes for the admission of air and light -are usually left at intervals. The thickness of the masonry and the -sizes of the pillars used in some of the earlier German vaultings are -unnecessarily great, and some of the newer works are much lighter. For -American use, vaulting like that used for the Newton, Mass., covered -reservoir[3] should be amply strong. - -Roofs have been used at Königsberg, Posen, and Budapest instead of -the masonry vaulting. They are cheaper, but do not afford as good -protection against frost, and even with great care some ice will form -under them. - -Provision must be made for entering the filters freely to introduce and -remove sand. This is usually accomplished by raising one section of -vaulting and building a permanent incline under it from the sand line -to a door above the high-water line in the filter. - -The cost of building covered filters is said to average fully one half -more than open filters. - -Among the incidental advantages of covered filters is that with the -comparative darkness there is no tendency to algæ growths on the -filters in summer, and the frequency of scraping is therefore somewhat -reduced. At Zürich, in 1892, where both covered and open filters were -in use side by side, the periods between scrapings averaged a third -longer in the covered than in the open filters. - -It has been supposed that covered filters kept the water cool in summer -and warm in winter, but owing to the large volume of water passing, the -change in temperature in any case is very slight; Frühling found that -even in extreme cases a change of over 3° F. in either direction is -rarely observed. - -[Illustration: REMOVING ICE FROM A FILTER, EAST LONDON. - -This represents the greatest accumulation of ice in the history of the -works. - - [_To face page 16._]] - -At Berlin, where open and covered filters were used side by side at -Stralau for twenty years, it was found that, bacterially, the open -filters were, except in severe winter weather, more efficient. It was -long supposed that this was caused by the sterilizing action of the -sunlight upon the water in the open filters. This result, however, was -not confirmed elsewhere, and it was finally discovered, in 1893, that -the higher numbers were due to the existence of passages in corners -on the columns of the vaulted roof and around the ventilators for the -underdrains, through which, practically, unfiltered water found its -way into the effluent. This at once removes the evidence in favor of -the superior bacterial efficiency of open filters and suggests the -necessity of preventing such passages. The construction of a ledge all -around the walls and pillars four inches wide and a little above the -gravel, as shown in the sketch, might be useful in this way, and the -slight lateral movement of the water in the sand above would be of no -consequence. The sand would evidently make a closer joint with the -horizontal ledge than with the vertical wall. - -[Illustration: FIG. 2.] - -In regard to the probable requirement or advisability of covers for -filters in the United States, I judge, from the European experience, -that places having January temperatures below the freezing-point will -have considerable trouble from open filters, and would best have -covered filters. Places having higher winter temperatures will be -able to get along with the ice which may form on open filters, and -the construction of covers would hardly be advisable except under -exceptional local conditions, as, for instance, with a water with an -unusual tendency to algæ growths. - -I have drawn a line across a map of the United States on this basis -(shown by the accompanying plate) and it would appear that places far -north of the line would require covered filters, and that those south -of it would not, while for the places in the immediate vicinity of the -line (comparable to Hamburg and Altona) there is room for discussion. - -In the United States covered filters have been constructed at St. -Johnsbury, Vt., Somersworth, N. H., Albany, N. Y., Ashland, Wis., and -Grand Forks, N. Dak., all of these places being considerably north of -the above-mentioned line. - -The filter at Lawrence, Mass., with a mean January temperature of -about 25°, is not covered, but serious difficulty and expense have -been experienced at times from the ice, so much so that it has been -repeatedly recommended to cover it. Open filters have also been in use -for many years at Hudson and Poughkeepsie, N. Y., with mean January -temperatures about 24°; and although considerable difficulty has been -experienced from ice at times, these filters, particularly the ones -at Poughkeepsie, have been kept in very serviceable condition at all -times, notwithstanding the ice. - -At Mount Vernon, N. Y., with a mean January temperature of about -31°, and with a reservoir water, no serious difficulty has been -experienced with ice; and at Far Rockaway, L. I., with a slightly -higher temperature and well-water, no difficulty whatever has been -experienced with open filters. Filters at Ilion, N. Y., with a mean -January temperature of about 23°, are not covered, and are fed from a -reservoir. No serious difficulty has been experienced with ice, which -is probably due to the fact that the water applied to them is taken -from near the bottom of the reservoir, and ordinarily has a temperature -somewhat above the freezing-point throughout the winter. - -[Illustration: Map showing - -Normal Mean January Temperatures - -IN THE UNITED STATES - -and the Area in which Filters should be covered] - -The cost of removing ice from filters depends, among other things, -upon the amount of reserve filter area. When this reserve is small -the filters must be kept constantly at work nearly up to their rated -capacity; the ice must be removed promptly whenever the filters -require cleaning, and under some conditions the expense of doing this -may be considerable. If, on the other hand, there is a considerable -reserve area, so that when a filter becomes clogged in severe weather, -the work can be turned upon other filters and the clogged filter -allowed to remain until more moderate weather, or until a thaw, the -expense of ice removal may be kept at a materially lower figure. - -In case open filters are built near or north of this line, I would -suggest that plenty of space between and around the filters for piling -up ice in case of necessity may be found advantageous, and that a -greater reserve of filtering area for use in emergencies should be -provided than would be considered necessary with vaulted filters or -with open filters in a warmer climate. - - - - -CHAPTER III. - -FILTERING MATERIALS. - - -SAND. - -The sand used for filtration may be obtained from the sea-shore, from -river-beds or from sand-banks. It consists mainly of sharp quartz -grains, but may also contain hard silicates. As it occurs in nature it -is frequently mixed with clayey or other fine particles, which must be -removed from it by washing before it is used. Some of the New England -sands, however, as that used for the Lawrence City filter, are so clean -that washing would be superfluous. - -The grain size of the sand best adapted to filtration has been -variously stated at from 1/8 to 1 mm., or from 0.013 to 0.040 inch. -The variations in the figures, however, are due more to the way that -the same sand appears to different observers than to actual variations -in the size of sands used, which are but a small fraction of those -indicated by these figures. - -As a result of experiments made at the Lawrence Experiment Station[4] -we have a standard by which we can definitely compare various sands. -The size of a sand-grain is uniformly taken as the diameter of a sphere -of equal volume, regardless of its shape. As a result of numerous -measurements of grains of Lawrence sands, it is found that when the -diameter, as given above, is 1, the three axes of the grain, selecting -the longest possible and taking the other two at right angles to it, -are, on an average, 1.38, 1.05, and 0.69, respectively and the mean -diameter is equal to the cube root of their product. - -It was also found that in mixed materials containing particles of -various sizes the water is forced to go around the larger particles and -through the finer portions which occupy the intervening spaces, so that -it is the finest portion which mainly determines the character of the -sand for filtration. As a provisional basis which best accounts for the -known facts, the size of grain such that 10 per cent by weight of the -particles are smaller and 90 per cent larger than itself, is considered -to be the _effective size_. The size so calculated is uniformly -referred to in speaking of the size of grain in this work. - -[Illustration: FIG. 3.—APPARATUS USED FOR MEASURING THE FRICTION OF -WATER IN SANDS.] - -Another important point in regard to a material is its degree of -uniformity—whether the particles are mainly of the same size or whether -there is a great range in their diameters. This is shown by the -_uniformity coefficient_, a term used to designate the ratio of the -size of the grain which has 60 per cent of the sample finer than itself -to the size which has 10 per cent finer than itself. - -The frictional resistance of sand to water when closely packed, with -the pores completely filled with water and in the entire absence of -clogging, was found to be expressed by the formula - - _v_ = _cd_^2(_h_/_l_)(_t_ Fah. + 10°)/60, - - where _v_ is the velocity of the water in meters daily in a solid column - of the same area as that of the sand, or approximately in - million gallons per acre daily; - _c_ is an approximately constant factor; - _d_ is the effective size of sand grain in millimeters; - _h_ is the loss of head (Fig. 3); - _l_ is the thickness of sand through which the water passes; - _t_ is the temperature (Fahr.). - - -TABLE SHOWING RATE AT WHICH WATER WILL PASS THROUGH EVEN-GRAINED AND -CLEAN SANDS OF THE STATED GRAIN SIZES AND WITH VARIOUS HEADS AT A -TEMPERATURE OF 50°. - - -------+-------------------------------------------------------------- - | Effective Size in Millimeters 10 per cent finer than: - _h_/_l_+------+------+-------+--------+--------+--------+-------+----- - | 0.10 | 0.20 | 0.30 | 0.35 | 0.40 | 0.50 | 1.00 | 3.00 - -------+------+------+-------+--------+--------+--------+-------+----- - | | | Million Gallons per Acre daily. | | - .001 | .01 | .04 | .10 | .13 | .17 | .27 | 1.07 | 9.63 - .005 | .05 | .21 | .48 | .65 | .85 | 1.34 | 5.35 |48.15 - .010 | .11 | .43 | .96 | 1.31 | 1.71 | 2.67 | 10.70 |96.30 - .050 | .54 | 2.14 | 4.82 | 6.55 | 8.55 | 13.40 | 53.50 | - .100 | 1.07 | 4.28 | 9.63 | 13.10 | 17.10 | 26.70 |107.00 | - 1.000 |10.70 |42.80 | 96.30 | 131.00 | 171.00 | 267.00 | | - -------+------+------+-------+--------+--------+--------+-------+----- - -The above table is computed with the value _c_ taken as 1000, this -being approximately the values deduced from the earliest experiments. -More recent and extended data have shown that the value of _c_ is not -entirely constant, but depends upon the uniformity coefficient, upon -the shape of the sand grains, upon their chemical composition, and upon -the cleanliness and closeness of packing of the sand. The value may be -as high as 1200 for very uniform, and perfectly clean sand, and maybe -as low as 400 for very closely packed sands containing a good deal -of alumina or iron, and especially if they are not quite clean. The -friction is usually less in new sand than in sand which has been in use -for some years. In making computations of the frictional resistance -of filters, the average value of _c_ may be taken at from 700 to 1000 -for new sand, and from 500 to 700 for sand which has been in use for a -number of years. - -The value of _c_ decreases as the uniformity coefficient increases. -With ordinary filter sands with uniformity coefficients of 3 or less -the differences are not great. With mixed sands having much higher -uniformity coefficients, lower and less constant values of _c_ are -obtained, and the arrangement of the particles becomes a controlling -factor in the increase in friction. - -The friction of the surface layer of a filter is often greater than -that of all the sand below the surface. It must be separately computed -and added to the resistances computed by the formula, as it depends -largely upon other conditions than those controlling the resistance of -the sand. - -While the value of _c_ is thus not entirely constant, it can be -estimated with approximate accuracy for various conditions, from a -knowledge of the composition, condition, and cleanliness of the sand, -and closeness of packing. - -The following table shows the quantity of water passing sands at -different temperatures. This table was computed with temperature -factors as given above, which were based upon experiments upon the -flow of water through sands, checked by the coefficients obtained from -experiments with long capillary tubes entirely submerged in water of -the required temperature. - - -RELATIVE QUANTITIES OF WATER PASSING AT DIFFERENT TEMPERATURES. - - 32° 0.70 - 35° 0.75 - 38° 0.80 - 41° 0.85 - 44° 0.90 - 47° 0.95 - 50° 1.00 - 53° 1.05 - 56° 1.10 - 59° 1.15 - 62° 1.20 - 65° 1.25 - 68° 1.30 - 71° 1.35 - 74° 1.40 - 77° 1.45 - -The effect of temperature upon the passage of water through sands and -soils has been further discussed by Prof. L. G. Carpenter, _Engineering -News_, Vol. XXXIX, p. 422. This article reviews briefly the literature -of the subject, and refers at length to the formula of Poiseuille, -published in the _Memoires des Savants Etrangers_, Vol. XI, p. 433 -(1846). This formula, in which the quantity of water passing at 0.0° -Cent., is taken as unity, is as follows: - - Temperature factor = 1 + 0.033679_t_ + 0.000221_t_^2. - -The results obtained by this formula agree very closely with those -given in the above table throughout the temperature range for -which computations are most frequently required. At the higher and -lower temperatures the divergencies are greater, as is shown in a -communication in the _Engineering News_, Vol. XL, p. 26. - -The quantity of water passing at a temperature of 50° Fahr. is in many -respects more convenient as a standard than the quantity passing at the -freezing-point. Near the freezing-point, owing to molecular changes in -the water, the changes in its action are rapid, and the results are -less certain, and also 50° Fahr. is a much more convenient temperature -for precise experiments than is the freezing point. - - -SANDS USED IN EUROPEAN FILTERS. - -To secure definite information in regard to the qualities of the sands -actually used in filtration, a large number of European works were -visited in 1894, and samples of sand were collected for analysis. These -samples were examined at the Lawrence Experiment Station by Mr. H. W. -Clark, the author’s method of analysis described in Appendix III being -used. In the following table, for the sake of compactness, only the -leading points of the analyses, namely, effective size, uniformity -coefficient, and albuminoid ammonia, are given. On page 28 full -analyses of some samples from a few of the leading works are given. - -ANALYSES OF SANDS USED IN WATER FILTRATION. - - ---------------------+---------+--------+--------+-------------------- - |Effective| | Albu- | - |Size; 10%| Uni- | minoid | - | Finer |formity | Ammo- | - Source. | than | Coeffi-| nia. | Remarks. - |(Milli- | cient. |Parts in| - | meters).| |100,000.| - ---------------------+---------+--------+--------+-------------------- - London, E. London Co.| 0.44 | 1.8 | 0.45 |New sand, never - | | | | used or washed. - London, E. London Co.| 0.39 | 2.1 | 26.20 |Dirty sand, very - | | | | old. - London, E. London Co.| 0.37 | 2.0 | 8.60 |Same, washed by - | | | | hand. - London, Grand Junc. | 0.26 | 1.9 | 1.90 |Sand from rough - | | filter. - London, Grand Junc. | 0.40 | 3.5 | 10.00 |Old sand in final - | | | | filter. - London, Grand Junc. | 0.41 | 3.7 | 2.70 |Freshly washed old - | | | | sand. - London, Southw’k & V.| 0.38 | 3.5 | 5.00 |Freshly washed old - | | | | sand. - London, Southw’k & V.| 0.30 | 1.8 | 2.80 |Freshly washed new - | | | | sand. - London, Lambeth | 0.36 | 2.3 | 2.60 |Freshly washed old - | | | | sand. - London, Lambeth | 0.36 | 2.4 | 0.35 |New unused sand, - | | | washed. - London, Lambeth | 0.25 | 1.7 | 0.70 |New extremely fine - | | | | sand. - London, Chelsea | 0.36 | 2.4 | 2.10 |Freshly washed old - | | | | sand. - Middlesborough | 0.42 | 1.6 | 17.60 |Dirty sand, ordinary - | | | | scraping. - Middlesborough | 0.43 | 1.6 | 7.30 |Same, after washing. - Birmingham | 0.29 | 1.9 | 33.20 |Dirty sand. - Birmingham | 0.29 | 1.9 | 7.20 |Sand below surface - | | | | of filter. - Reading | 0.30 | 2.5 | 4.00 |Dirty sand. - Reading | 0.22 | 2.0 | 1.50 |Same, after washing. - Antwerp | 0.38 | 1.6 | 7.80 |Dirty sand. - Antwerp | 0.39 | 1.6 | 3.40 |Same, after washing. - Hamburg | 0.28 | 2.5 | 8.50 |Dirty sand. - Hamburg | 0.31 | 2.3 | 0.80 |Same, after washing. - Hamburg | 0.34 | 2.2 | 7.90 |Dirty sand, another - | | | | sample. - Hamburg | 0.30 | 2.0 | 0.90 |Same, after washing - | | | | drums. - Hamburg | 0.34 | 2.3 | 1.50 |Same, after washing - | | | | ejectors. - Altona | 0.32 | 2.0 | 9.00 |Dirty sand, old - | | | | filters. - Altona | 0.37 | 2.0 | 1.50 |Same, after washing. - Altona | 0.33 | 2.8 | 0.50 |Washed sand for new - | | | | filters. - Berlin, Stralau | 0.33 | 1.9 | 12.20 |Dirty sand-pile. - Berlin, Stralau | 0.35 | 1.7 | 4.50 |Filter No. 6, - | | | | 3″ below surface. - Berlin, Stralau | 0.34 | 1.7 | 6.30 |Filter No. 7, - | | | | 3″ below surface. - Berlin, Stralau | 0.35 | 1.7 | 4.00 |Filter No. 10, - | | | | 3″ below surface. - Berlin, Tegel | 0.38 | 1.6 | 11.00 |Dirty sand, old - | | | | filters. - Berlin, Tegel | 0.38 | 1.5 | 2.80 |Same, after washing, - | | | | old filters. - Berlin, Tegel | 0.35 | 1.6 | 3.20 |Same, after washing, - | | | | new filters. - Berlin, Müggel | 0.35 | 1.8 | 0.80 |Sand from filters - | | | | below surface. - Berlin, Müggel | 0.33 | 2.0 | 6.30 |Dirty sand, ordinary - | | | | scraping. - Berlin, Müggel | 0.34 | 2.0 | 15.30 |Dirty sand, another - | | | | sample. - Charlottenburg | 0.40 | 2.3 | 7.20 |Dirty sand. - Chemnitz | 0.35 | 2.6 | 0.20 |New sand not yet - | | | | used. - Magdeburg | 0.39 | 2.0 | 9.50 |Dirty sand. - Magdeburg | 0.40 | 2.0 | 2.80 |Same, after washing. - Breslau | 0.39 | 1.8 | 1.40 |Normal new sand. - Budapest | 0.20 | 2.0 | 0.80 |New washed Danube - | | | | sand. - Zürich | 0.28 | 3.2 | 6.20 |Dirty sand. - Zürich | 0.30 | 3.1 | 1.50 |Same, after washing. - Hague | 0.19 | 1.6 | 0.70 |Dune-sand used for - | | | | filtration. - Schiedam | 0.18 | 1.6 | 5.60 |Dune-sand used for - | | | | filtration; dirty. - Schiedam | 0.31 | 1.5 | 13.50 |River-sand; dirty. - Amsterdam | 0.17 | 1.6 | 2.40 |Dune-sand. - Rotterdam | 0.34 | 1.5 | 2.30 |River-sand; new. - Liverpool, Rivington | 0.43 | 2.0 | 0.76 |Sand from bottom of - | | | | filter. - Liverpool, Rivington | 0.32 | 2.5 | 1.00 |New sand unwashed - | | | | and unscreened. - Liverpool, Rivington | 0.43 | 2.7 | 4.10 |Washed sand which - | | | | has been in use - | | | | 30 to 40 years. - Liverpool, Oswestry | 0.30 | 2.6 | 9.40 |Dirty sand. - Liverpool, Oswestry | 0.31 | 4.7 | 2.20 |Same, after washing. - ---------------------+---------+--------+--------+-------------------- - - NOTE.—It is obvious that in case the sands used at any place are not - always of the same character, as is shown to be the case by different - samples from some of the works, the examination of such a limited - number of samples as the above from each place is entirely inadequate - to establish accurately the sizes of sand used at that particular - place, or to allow close comparisons between the different works, and - for this reason no such comparisons will be made. The object of these - investigations was to determine the sizes of the sands commonly used - in Europe, and, considering the number and character of the different - works represented, it is believed that the results are ample for this - purpose. - -The English and most of the German sands are washed, even when entirely -new, before being used, to remove fine particles. At Breslau, however, -sand dredged from the river Oder is used in its natural state, and -new sand is used for replacing that removed by scraping. At Budapest, -Danube sand is used in the same way, but with a very crude washing, and -it is said that only new unwashed sand is used at Warsaw. - -In Holland, so far as I learned, no sand is washed, but new sand is -always used for refilling. At most of the works visited dune-sand -with an effective size of only 0.17 to 0.19 mm. is used, and this is -the finest sand which I have ever found used for water filtration on -a large scale. It should be said, however, that the waters filtered -through these fine sands are fairly clear before filtration, and are -not comparable to the turbid river-waters often filtered elsewhere, -and their tendency to choke the filters is consequently much less. At -Rotterdam and Schiedam, where the raw water is drawn from the Maas, as -the principal stream of the Rhine is called in Holland, river-sand of -much larger grain size is employed. It is obtained by dredging in the -river and is never washed, new sand always being employed for refilling. - -The average results of the complete analyses of sands from ten leading -works are shown in the table on page 28. These figures are the average -of all the analyses for the respective places, except that one sample -from the Lambeth Co., which was not a representative one, was omitted. - -The London companies were selected for this comparison both on -account of their long and favorable records in filtering the polluted -waters of the Thames and Lea, and because they are subject to close -inspection; and there is ample evidence that the filtration obtained is -good—evidence which is often lacking in the smaller and less closely -watched works. For the German works Altona was selected because of -its escape from cholera in 1892, due to the efficient action of its -filters, and Stralau because of its long and favorable record when -filtering the much-polluted Spree water. These two works also have -perhaps contributed more to the modern theories of filtration than all -the other works in existence. The remaining works are included because -they are comparatively new, and have been constructed with the greatest -care and attention to details throughout, and the results obtained are -most carefully recorded. - -Some of the most interesting of these results are shown graphically on -page 29. The method of plotting is that described in Appendix III. - - -TABLE SHOWING THE AVERAGE PER CENT OF THE GRAINS FINER THAN VARIOUS -SIZES IN SANDS FROM LEADING WORKS. - - --------------+---------------------------------------------------- - | Per Cent by Weight Finer than - +------+------+------+-----+-----+-----+-----+------- - |0.106 |0.186 |0.316 |0.46 |0.93 |2.04 |3.89 |5.89 - | mm. | mm. | mm. | mm. | mm. | mm. | mm. | mm. - --------------+------+------+------+-----+-----+-----+-----+------- - East London | 0.2 | 0.5 | 3.6 |22.2 |69.7 |89.8 |95.0 |99.0 - Grand Junction| 0 | 0.2 | 3.1 |17.4 |47.1 |68.2 |84.7 |93.6 - Southwark and | | | | | | | | - Vauxhall | | 0.7 | 8.0 |34.1 |69.7 |83.5 |90.0 |94.0 - Lambeth | 0 | 0.5 | 5.5 |26.6 |63.0 |79.2 |88.0 |94.3 - Chelsea | 0 | 0.1 | 5.0 |28.6 |63.0 |76.7 |86.0 |93.6 - Hamburg | 0.2 | 1.5 |10.9 |33.2 |74.4 |95.7 |99.5 | - Altona | 0.1 | 1.1 | 7.8 |28.7 |72.1 |92.1 |95.8 | - Stralau | | 0.3 | 7.0 |37.3 |86.9 |95.4 |97.6 | - Tegel | | 0.2 | 4.5 |35.4 |94.3 |98.5 |99.1 | - Müggel | 0.1 | 0.5 | 7.9 |33.6 |79.7 |94.3 |98.5 | - +------+------+------+-----+-----+-----+-----+------- - Average of all| 0.06 | 0.56 | 6.33 |29.71|71.99|87.34|93.42|(97.45) - --------------+------+------+------+-----+-----+-----+-----+------- - - -AVERAGE EFFECTIVE SIZE, UNIFORMITY COEFFICIENT, AND ALBUMINOID AMMONIA -IN SANDS FROM TEN LEADING WORKS. - - I. LONDON FILTERS. - ----------------------+--------------+------------+------------------- - | Effective | Uniformity |Albuminoid Ammonia. - | Size; 10% |Coefficient.+------------+------ - | Finer than | | Dirty Sand.|Washed - |(Millimeters).| | | Sand. - ----------------------+--------------+------------+------------+------ - East London | 0.40 | 2.0 | 26.00 | 8.60 - Grand Junction | 0.40 | 3.6 | 10.00 | 2.70 - Southwark and Vauxhall| 0.34 | 2.5 | | 3.90 - Lambeth | 0.36 | 2.4 | | 2.60 - Chelsea | 0.36 | 2.4 | | 2.10 - +--------------+------------+------------+------ - Average | 0.37 | 2.6 | 18.00 | 3.98 - ----------------------+--------------+------------+------------+------ - - II. GERMAN WORKS. - ----------------------+--------------+------------+------------+------ - Stralau | 0.34 | 1.7 | 12.20 | 4.00 - Tegel | 0.37 | 1.6 | 11.00 | 3.00 - Müggel | 0.34 | 2.0 | 10.80 | 0.80 - Altona | 0.34 | 2.3 | 9.00 | 1.50 - Hamburg | 0.31 | 2.3 | 8.20 | 1.07 - +--------------+------------+------------+------ - Average | 0.34 | 2.0 | 10.25 | 2.07 - ----------------------+--------------+------------+------------+------ - -[Illustration: PLACING SAND IN A FILTER, HAMBURG. - -[_To face page 28._]] - -The averages show the effective size of the English sands to be -slightly greater than that of the German sands—0.37 instead of 0.34 -mm.—but the difference is very small. The entire range for the ten -works is only from 0.31 to 0.40 mm., and these may be taken as the -ordinary limits of effective size of the sands employed in the best -European works. The average for the other sixteen works given above, -including dune-sands, is 0.31 mm., or, omitting the dune-sands, 0.34 mm. - -[Illustration: FIG. 3_a_.—SAND ANALYSIS SHEET, WITH ANALYSES OF SEVERAL -EUROPEAN FILTER SANDS.] - -It is important that filter sands should be free from lime. When water -is filtered through such sands, no increase in hardness results. When, -however, water is filtered through sand containing lime, some of it -is usually dissolved and the water is made harder. The amount of lime -taken up in this way depends both upon the character of the sand, and -upon the solvent power of the water; and it does not necessarily follow -that a sand containing lime cannot be used for filtration, but a sand -nearly free from lime is to be preferred. - -The presence of lime in sand can usually be detected by moistening it -with hydrochloric acid. The evolution of gas shows the presence of -lime. Some idea of the amount of lime can be obtained from the amount -of gas given off, and the appearance of the sample after the treatment, -but chemical analysis is necessary to determine correctly the amount. - -Experiments with filters at Pittsburg were made with sand containing -1.3 per cent of lime, the result being that the hardness of the water -was increased about one part in 100,000; but the amount of lime in the -sand was so small that it would be washed out after a time, and then -the hardening effect would cease. Larger amounts of lime would continue -their action for a number of years and would be more objectionable. - -Turning to the circumstances which influence the selection of the -sand size, we find that both the quality of the effluent obtained by -filtration and the cost of filtration depend upon the size of the -sand-grains. - -With a fine sand the sediment layer forms more quickly and the removal -of bacteria is more complete, but, on the other hand, the filter clogs -quicker and the dirty sand is more difficult to wash, so that the -expense is increased. - - -EFFECT OF SIZE OF GRAIN UPON EFFICIENCY OF FILTRATION. - -It is frequently stated that it is only the sediment layer which -performs the work of filtration, and that the sand which supports -it plays hardly a larger part than does the gravel which carries -the sand, and under some circumstances this is undoubtedly the case. -Nevertheless sand in itself, without any sediment layer, especially -when not too coarse and not in too thin layers, has very great -purifying powers, and, in addition, acts as a safeguard by positively -preventing excessive rates of filtration on account of its frictional -resistance. As an illustration take the case of a filter of sand with -an effective size of 0.35 mm. and the minimum thickness of sand allowed -by the German Board of Health, namely, one foot, and let us suppose -that with clogging the loss of head has reached two feet to produce -the desired velocity of 2.57 million gallons per acre daily. Suppose -now that by some accident the sediment layer is suddenly broken or -removed from a small area, the water will rush through this area, -until a new sediment layer is formed, at a rate corresponding to the -size, pressure, and depth of the sand, or 260 million gallons per -acre daily—a hundred times the standard rate. Under these conditions -the passing water will not be purified, but will pollute the entire -effluent from the filter. Under corresponding conditions, with a deep -filter of fine sand, say with an effective size of 0.20 mm. and 5 feet -deep, the resulting rate would be only 17 million gallons per acre -daily, or less than seven times the normal, and with the water passing -through the full depth of fine sand, the resulting deterioration in the -effluent before the sand again became so clogged as to reduce the rate -to nearly the normal, would be hardly appreciable. - -The results at Lawrence have shown that with very fine sands 0.09 and -0.14 mm., and 4 to 5 feet deep, with the quantity of water which can -practically be made to pass through them, it is almost impossible to -drive more than an insignificant fraction of the bacteria into the -effluent. Even when the sands are entirely new, or have been scraped or -disturbed in the most violent way, the first effluent passing, before -the sediment layer could have been formed, is of good quality. Still -finer materials, 0.04 to 0.06 mm., as far as could be determined, -secured the absolute removal of all bacteria, but the rates of -filtration which were possible were so low as to preclude their -practical application. - -With coarser sands, as long as the filter is kept at a steady rate of -filtration, without interruptions of any kind, entirely satisfactory -results are often obtained, although never quite so good as with -the finer sands. Thus at Lawrence the percentages of bacteria (_B. -prodigiosus_) appearing in the effluents under comparable conditions -were as follows: - - 1892 1893 - With effective grain size 0.38 mm .... 0.16 - With effective grain size 0.29 mm .... 0.16 - With effective grain size 0.26 mm .... 0.10 - With effective grain size 0.20 mm 0.13 0.01 - With effective grain size 0.14 mm 0.04 0.03 - With effective grain size 0.09 mm 0.02 0.02 - -We may thus conclude that fine sands give normally somewhat better -effluents than coarser ones, and that they are much more likely to -give at least a tolerably good purification under unusual or improper -conditions. - - -EFFECT OF GRAIN SIZE UPON FREQUENCY OF SCRAPING. - -The practical objection to the use of fine sand is that it becomes -rapidly clogged, so that filters require to be scraped at shorter -intervals, and the sand washing is much more difficult and expensive. -The quantities of water filtered between successive scrapings at -Lawrence in millions of gallons per acre under comparable conditions -have been as follows: - - 1892 1893 - Effective size of sand grain 0.38 mm .... 79 - Effective size of sand grain 0.29 mm .... 70 - Effective size of sand grain 0.26 mm .... 57 - Effective size of sand grain 0.20 mm 58 .... - Effective size of sand grain 0.14 mm 45 49 - Effective size of sand grain 0.09 mm 24 14 - -The increase in the quantities passed between scrapings with increasing -grain size is very marked. - -With the fine sands, the depth to which the sand becomes dirty is much -less than with the coarse sands, but as it is not generally practicable -to remove a layer of sand less than about 0.6 inch thick, even when the -actual clogged layer is thinner than this, the full quantity of sand -has to be removed; and the quantities of sand to be removed and washed -are inversely proportional to the quantities of water filtered between -scrapings. On the other hand, with very coarse sands the sediment -penetrates the sand to a greater depth than the 0.6 inch necessarily -removed, so that a thicker layer of sand has to be removed, which -may more than offset the longer interval. This happens occasionally -in water-works, and a sand coarse enough to allow it occur is always -disliked by superintendents, and is replaced with finer sand as soon as -possible. It is obvious that the minimum expense for cleaning will be -secured with a sand which just does not allow this deep penetration, -and I am inclined to think that the sizes of the sands in use have -actually been determined more often than otherwise in this way, and -that the coarsest samples found, having effective sizes of about 0.40 -mm., represent the practical limit to the coarseness of the sand, -and that any increase above this size would be followed by increased -expense for cleaning as well as by decreased efficiency. - - -SELECTION OF SAND. - -In selecting a sand for filtration, when it is considered that repeated -washings will remove some of the finest particles, and so increase -slightly the effective size, a new sand coarser than 0.35 mm. would -hardly be selected. Perhaps 0.20 might be given as a suitable lower -limit. For comparatively clear lake- or reservoir-waters a finer -sand could probably be used than would be the case with a turbid -river-water. A mixed sand having a uniformity coefficient above 3.0 -would be difficult to wash without separating it into portions of -different sizes, and, in general, the lower the coefficient, that is, -the more uniform the grain sizes, the better. Great pains should be -taken to have the sand of the same quality throughout, especially in -the same filter, as any variations in the grain sizes would lead to -important variations in the velocity of filtration, the coarser sands -passing more than their share of water (in proportion to the square of -the effective sizes) and with reduced efficiency. - -At Lawrence a sufficient quantity of natural sand was found of the -grade required; but where suitable material cannot be so obtained it -is necessary to use other methods. A mixed material can be screened -from particles which are too large, and can be washed to free it from -its finer portions, and in this way a good sand can be prepared, if -necessary, from what might seem to be quite unpromising material. The -methods of sand-washing will be described in Chapter V. - - -THICKNESS OF THE SAND LAYER. - -The thickness of the sand layer is made so great that when it is -repeatedly scraped in cleaning the sand will not become too thin for -good filtration for a considerable time. When this occurs the removed -sand must be replaced with clean sand. The original thickness of the -sand in European filters is usually from 24 to 48 inches, thicknesses -between 30 and 40 inches being extremely common, and this is reduced -before refilling to from 12 to 24 inches. The Imperial Board of Health -of Germany has fixed 12 inches as a limit below which the sand should -never be scraped, and a higher limit is recommended wherever possible. - -A thick sand layer has the same steadying action as a fine sand, and -tends to prevent irregularities in the rate of filtration in proportion -to its frictional resistance, and that without increasing the frequency -of cleaning; but, on the other hand, it increases the necessary height -of the filter, throughout, and consequently the cost of construction. - -In addition to the steadying effect of a deep sand layer, some -purification takes place in the lower part of the sand even with a good -sediment layer on the surface, and the efficiency of deep filters is -greater than that of shallow ones. - -Layers of finer materials, as fine sand or loam, in the lower part -of a filter, which would otherwise give increased efficiency without -increasing the operating expenses, cannot be used. Their presence -invariably gives rise sooner or later to sub-surface clogging at the -point of junction with the coarser sand, as has been found by repeated -tests at Lawrence as well as in some of the Dutch filters where such -layers were tried; and as there is no object in putting a coarser sand -under a finer, the filter sand is best all of the same size and quality -from top to bottom. - - -UNDERDRAINING. - -The underdrains of a filter are simply useful for collecting the -filtered water; they play no part in the purification. One of the first -requirements of successful filtration is that the rate of filtration -shall be practically the same in all parts of the filter. This is most -difficult to secure when the filter has just been cleaned and the -friction of the sand layer is at a minimum. If the friction of the -water in entering and passing through the underdrains is considerable, -the more remote parts of the filters will work under less pressure, -and will thus do less than their share of the work, while the parts -near the outlet will be overtaxed, and filtering at too high rates will -yield poor effluents. - -To avoid this condition the underdrains must have such a capacity -that their frictional resistance will be only a small fraction of the -friction in the sand itself just after cleaning. - - -GRAVEL LAYERS. - -The early filters contained an enormous quantity of gravel, but the -quantity has been steadily reduced in successive plants. Thus in 1866 -Kirkwood, as a result of his observations, recommended the use of a -layer four feet thick, and in addition a foot of coarse sand, while -at the present time new filters rarely have more than two feet of -gravel. Even this quantity seems quite superfluous, when calculations -of its frictional resistance are made. Thus a layer of gravel with an -effective size of 20 mm.[5] (which is much finer than that generally -employed) only 6 inches thick will carry the effluent from a filter -working at a rate of 2.57 million gallons per acre daily for a distance -of 8 feet (that is, with underdrains 16 feet apart), with a loss of -head of only 0.001 foot, and for longer distances tile drains are -cheaper than gravel. To prevent the sand from sinking into the coarse -gravel, intermediate sizes of gravel must be placed between, each grade -being coarse enough so that there is no possibility of its sinking into -the layer below. The necessary thickness of these intermediate layers -is very small, the principal point being to have a layer of each grade -at every point. Thus on the 6 inches of 20 mm. gravel mentioned above, -three layers of two inches each, of 8 and 3 mm. gravel and coarse -sand, with a total height of six inches, or other corresponding and -convenient depths and sizes, would, if carefully placed, as effectually -prevent the sinking of the filter sand into the coarse gravel as the -much thicker layers used in the older plants. - -The gravel around the drains should receive special attention. Larger -stones can be here used with advantage, taking care that adequate -spaces are left for the entrance of the water into the drains at a low -velocity, and to make everything so solid in this neighborhood that -there will be no chance for the stones to settle which might allow the -sand to reach the drains. - -[Illustration: RECONSTRUCTING THE UNDERDRAINAGE SYSTEM OF A FILTER -AFTER 25 YEARS OF USE, BREMEN.] - -[Illustration: PLACING SAND IN A FILTER, CHOISY LE ROI (PARIS). - -[_To face page 36._]] - -At the Lawrence filter, at Königsberg in Prussia, at Amsterdam and -other places, the quantity of gravel is reduced by putting the drains -in trenches, so that the gravel is reduced from a maximum thickness -at the drain to nothing half way between drains. The economy of the -arrangement, however, as far as friction is concerned is not so great -as would appear at first sight, and the cost of the bottom may be -increased; but on the other hand it gives a greater depth of gravel for -covering the drains with a small total amount of gravel. - -As even a very small percentage of fine material is capable of -getting in the narrow places and reducing the carrying power of the -gravel, it is important that all such matters should be carefully -removed by washing before putting the gravel in place. In England and -Germany gravel is commonly screened for use in revolving cylinders of -wire-cloth of the desired sizes, on which water is freely played from -numerous jets, thus securing perfectly clean gravel. In getting gravel -for the Lawrence filter, an apparatus was used, in which advantage was -taken of the natural slope of the gravel bank to do the work, and the -use of power was avoided. The respective grades of gravel obtained were -even in size, and reasonably free from fine material, but it was deemed -best to wash them with a hose before putting them in the filter. - -To calculate the frictional resistance of water in passing gravel, we -may assume that for the very low velocities which are actually found in -filters the quantity of water passing varies directly with the head, -which for these velocities is substantially correct, although it would -not be true for higher rates, especially with the coarser gravels.[6] -In the case of parallel underdrains the friction from the middle point -between drains to the drains may be calculated by the formula: - -Total head = (1/2)[(Rate of filtration × (1/2 distance between -drains)^2)/(Average depth of gravel × discharge coefficient)]. - -The discharge coefficient for any gravel is 1000 times the quantity - -of water which will pass when _h_/_l_ is 1/1000 expressed in million -gallons per acre daily. The approximate values of this coefficient for -different-sized gravels are as follows: - - -VALUES OF DISCHARGE COEFFICIENT. - - For gravel with effective size 5 mm _c_ = 23,000 - For gravel with effective size10 mm _c_ = 65,000 - For gravel with effective size15 mm _c_ = 110,000 - For gravel with effective size20 mm _c_ = 160,000 - For gravel with effective size25 mm _c_ = 230,000 - For gravel with effective size30 mm _c_ = 300,000 - For gravel with effective size35 mm _c_ = 390,000 - For gravel with effective size40 mm _c_ = 480,000 - -Example: What is the loss of head in the gravel at a rate of filtration -of 2 million gallons per acre daily, with underdrains 20 feet apart, -where the supporting gravel has an effective size of 35 millimeters, -and is uniformly 1 ft. deep? - -Total head = (1/2)[(2 × 10^2)/(1 × 390,000)] = .000256 ft. - -The total friction would be the same with the same average depth of -gravel whether it was uniformly 1 foot deep, or decreasing from 1.5 at -the drains to 0.5 in the middle, or from 2.0 to 0. The reverse case -with the gravel layer thicker in the middle than at the drains does not -occur and need not be discussed. - -The depth of gravel likely to be adopted as a result of this -calculation, when the drains are not too far apart, will be much less -than that actually used in most European works, but as the two feet or -more there employed are, I believe, simply the result of speculation, -there is no reason for following the precedent where calculations show -that a smaller quantity is adequate. - -The reason for recommending a thin lower layer of coarse gravel, which -alone is assumed to provide for the lateral movement of the water, -is that if more than about six inches of gravel is required to give a -satisfactory resistance, it will almost always be cheaper to use more -drains instead of more gravel; and the reason for recommending thinner -upper layers for preventing the sand from settling into the coarse -gravel is that no failures of this portion of filters are on record, -and in the few instances where really thin layers have been used the -results have been entirely satisfactory. In Königsberg filters were -built by Frühling,[7] in which the sand was supported by five layers -of gravel of increasing sizes, respectively 1.2, 1.2, 1.6, 2.0, 3.2, -or, together, 9.2 inches thick, below which there were an average of -five inches of coarse gravel. These were examined after eight years of -operation and found to be in perfect order. - -At the Lawrence Experiment Station filters have been repeatedly -constructed with a total depth of supporting gravel layers not -exceeding six inches, and among the scores of such filters there has -not been a single failure, and so far as they have been dug up there -has never been found to have been any movement whatever of the sand -into the gravel. The Lawrence city filter, built with corresponding -layers, has shown no signs of being inadequately supported. In -arranging the Lawrence gravel layers care has always been taken that no -material should rest on another material more than three or four times -as coarse as itself, and that each layer should be complete at every -point, so that by no possibility could two layers of greater difference -in size come together. And it is believed that if this is carefully -attended to, no trouble need be anticipated, however thin the single -layers may be. - - -UNDERDRAINS. - -The most common arrangement, in other than very small filters, is to -have a main drain through the middle of the filter, with lateral -drains at regular intervals from it to the sides. The sides of the main -drain are of brick, laid with open joints to admit water freely, and -the top is usually covered with stone slabs. The lateral drains may be -built in the same way, but tile drains are also used and are cheaper. -Care must be taken with the latter that ample openings are left for the -admission of water at very low velocities. It is considered desirable -to have these drains go no higher than the top of the coarsest gravel; -and this will often control the depth of gravel used. If they go -higher, the top must be made tight to prevent the entrance of the fine -gravels or sand. Sometimes they are sunk in part or wholly (especially -the main drain) below the floor of the filter. With gravel placed in -waves, that is, thicker over the drains than elsewhere, as mentioned -above, the drains are covered more easily than with an entirely -horizontal arrangement. When this is done, the floor of the filter is -trenched to meet the varying thickness of gravel, so that the top of -the latter is level, and the sand has a uniform thickness. - -Many filters (Lambeth, Brunswick, etc.) are built with a double bottom -of brick, the upper layer of which, with open joints, supports the -gravel and sand, and is itself supported by numerous small arches or -other arrangements of brick, which serve to carry the water to the -outlet without other drains. This arrangement allows the use of a -minimum quantity of gravel, but is undoubtedly more expensive than the -usual form, with only the necessary quantity of gravel; and I am unable -to find that it has any corresponding advantages. - -The frictional resistance of underdrains requires to be carefully -calculated; and in doing this quite different standards must be -followed from those usually employed in determining the sizes -of water-pipes, as a total frictional resistance of only a few -hundredths of a foot, including the velocity head, may cause serious -irregularities in the rate of filtration in different parts of the -filter. - -The sizes of the underdrains differ very widely in proportion to the -sizes of the filters in European works, some of them being excessively -large, while in other cases they are so small as to suggest a doubt as -to their allowing uniform rates of filtration, especially just after -cleaning. - -I would suggest the following rules as reasonably sure to lead to -satisfactory results without making an altogether too lavish provision: -In the absence of a definite determination to run filters at some -other rate, calculate the drains for the German standard rate of a -daily column of 2.40 meters, equal to 2.57 million gallons per acre -daily. This will insure satisfactory work at all lower rates, and -no difficulty on account of the capacity of the underdrains need be -then anticipated if the rate is somewhat exceeded. The area for a -certain distance from the main drain depending upon the gravel may be -calculated as draining directly into it, provided there are suitable -openings, and the rest of the area is supposed to drain to the nearest -lateral drain. - -In case the laterals are round-tile drains I would suggest the -following limits to the areas which they should be allowed to drain: - - Diameter of Drain. To Drain an Area not Corresponding Velocity of - Exceeding Water in Drain. - 4 inches 290 square feet. 0.30 foot. - 6 inches 750 square feet. 0.35 foot. - 8 inches 1530 square feet. 0.40 foot. - 10 inches 2780 square feet. 0.46 foot. - 12 inches 4400 square feet. 0.51 foot. - -And for larger drains, including the main drains, their cross-sections -at any point should be at least 1/6000 of the area drained, giving a -velocity of 0.55 foot per second with the rate of filtration mentioned -above. - -The total friction of the underdrains from the most remote points -to the outlet will be friction in the gravel, plus friction in the -lateral drains, plus the friction in main drain, plus the velocity head. - -[Illustration: FIG. 4.—PLAN OF ONE OF THE HAMBURG FILTERS, SHOWING -FRICTIONAL RESISTANCE OF THE UNDERDRAINS.] - -I have calculated in this way the friction of one of the Hamburg -filters for the rate of 1,600,000 gallons per acre daily at which it -is used. The friction was calculated for each section of the drains -separately, so that the friction from intermediate points was also -known. Kutter’s formula was used throughout with _n_ = 0.013. On -the accompanying plan of the filter I have drawn the lines of equal -frictional resistance from the junction of the main drain with the last -laterals. My information was incomplete in regard to one or two points, -so that the calculation may not be strictly accurate, but it is nearly -so and will illustrate the principles involved. - -[Illustration: CONSTRUCTING THE UNDERDRAINAGE SYSTEM OF A FILTER, -HAMBURG. - - [_To face page 42._] -] - -The extreme friction of the underdrains is 11 millimeters = 0.036 foot. - -The frictional resistance of the sand 39 inches thick, effective size -0.32 mm. and rate 1.60 million gallons per acre daily, when absolutely -free from clogging, is by the formula, page 21, 15mm., or .0490 -foot, when the temperature is 50°. Practically there is some matter -deposited upon the surface of the sand before filtration starts, and -further, after the first scraping, there is some slight clogging in the -sand below the layer removed by scraping. We can thus safely take the -minimum frictional resistance of the sand including the surface layer -at .07 foot. The average friction of the underdrains for all points -is about .023 foot and the friction at starting will be .07 + .023 = -.093 foot (including the friction in the last section to the effluent -well where the head is measured, .100 foot, but the friction beyond the -last lateral does not affect the uniformity of filtration). The actual -head on the sand close to the outlet will be .093 and the rate of -filtration .093/.070 · 1.60 = 2.12. The actual head at the most remote -point will be .093 - .036 = .057, and the rate of filtration will there -be .057/.070 · 160 = 1.30 million gallons per acre daily. The extreme -rates of filtration are thus 2.12 and 1.30, instead of the average rate -of 1.60. As can be seen from the diagram, only very small areas work -at these extreme rates, the great bulk of the area working at rates -much nearer the average. Actually the filter is started at a rate below -1.60, and the nearest portion never filters so rapidly as 2.12, for -when the rate is increased to the standard, the sand has become so far -clogged that the loss of head is more than the .07 foot assumed, and -the differences in the rates are correspondingly reduced. Taking this -into account, it would not seem that the irregularities in the rate of -filtration are sufficient to affect seriously the action of the filter. -They could evidently have been largely reduced by moderately increasing -the sizes of the lower ends of the underdrains, where most of the -friction occurs with the high velocities (up to .97 foot) which there -result. - -The underdrains of the Warsaw filters were designed by Lindley to have -a maximum loss of head of only .0164 foot when filtering at a rate of -2.57, which gives a variation of only 10 per cent in the rates with the -minimum loss of head of .169 foot in the entire filter assumed by him. -The underdrains of the Berlin filters, according to my calculations, -have .020 to .030 foot friction, of which an unusually large proportion -is in the gravel, owing to the excessive distances, in some cases over -80 feet, which the gravel is required to carry the water. In this case, -using less or finer gravel would obviously have been fatal, but the -friction as well as the expense of construction would be much reduced -by using more drains and less gravel. - -The underdrains might appropriately be made slightly smaller, with a -deep layer of fine sand, than under opposite conditions, as in this -case the increased friction in the drains would be no greater in -proportion to the increased friction in the sand itself. - -The underdrains of a majority of European filters have water-tight -pipes connecting with them at intervals, and going up through the sand -and above the water, where they are open to the air. These pipes were -intended to ventilate the underdrains and allow the escape of air when -the filter is filled with water introduced from below. It may be said, -however, that in case the drains are surrounded by gravel and there is -an opportunity for the air to pass from the top of the drain into the -gravel, it will so escape without special provision being made for it, -and go up through the sand with the much larger quantity of air in the -upper part of the gravel which is incapable of being removed by pipes -connecting with the drains. - -These ventilator pipes where they are used are a source of much -trouble, as unfiltered water is apt to run down through cracks in the -sand beside them, and, under bad management, unfiltered water may even -go down through the pipes themselves. I am unable to find that they -are necessary, except with underdrains so constructed that there is -no other chance for the escape of air from the tops of them, or that -they serve any useful purpose, while there are positive objections to -their use. In some of the newer filters they have been omitted with -satisfactory results. - - -DEPTH OF WATER ON THE FILTERS. - -In the older works with but crude appliances for regulating the rate of -filtration and admission of raw water, a considerable depth of water -was necessary upon the filter to balance irregularities in the rates -of filtration; the filter was made to be, to a certain extent, its own -storage reservoir. When, however, appliances of the character to be -described in Chapter IV are used for the regulation of the incoming -water, and with a steady rate of filtration, this provision becomes -quite superfluous. - -With open filters a depth of water in excess of the thickness of any -ice likely to be formed is required to prevent disturbance or freezing -of the sand in winter. It is also frequently urged that with a deep -water layer on the filter the water does not become so much heated in -summer, but this point is not believed to be well taken, for in any -given case the total amount of heat coming from the sun to a given area -is constant, and the quantity of water heated in the whole day—that -is, the amount filtered—is constant, and variations in the quantity -exposed at one time will not affect the average resulting increase in -temperature. If the same water remained upon the filter without change -it would of course be true that a thin layer would be heated more than -a deep one, but this is not the case. - -It is also sometimes recommended that the depth of water should be -sufficient to form a sediment layer before filtration starts, but this -point would seem to be of doubtful value, especially where the filter -is not allowed to stand a considerable time with the raw water upon it -before starting filtration. - -It is also customary to have a depth of water on the filter in excess -of the maximum loss of head, so that there can never be a suction in -the sand just below the sediment layer. It may be said in regard to -this, however, that a suction below is just as effective in making the -water pass the sand as an equal head above. At the Lawrence Experiment -Station filters have been repeatedly used with a water depth of only -from 6 to 12 inches, with losses of head reaching 6 feet, without the -slightest inconvenience. The suction only commences to exist as the -increasing head becomes greater than the depth of water, and there is -no way in which air from outside can get in to relieve it. In these -experimental filters in winter, when the water is completely saturated -with air, a small part of the air comes out of the water just as it -passes the sediment layer and gets into reduced pressure, and this -air prevents the satisfactory operation of the filters. But this is -believed to be due more to the warming and consequent supersaturation -of the water in the comparatively warm places in which the filters -stand than to the lack of pressure, and as not the slightest trouble -is experienced at other seasons of the year, it may be questioned -whether there would be any disadvantage at any time in a corresponding -arrangement on a large scale where warming could not occur. - -The depths of water actually used in European filters with the full -depth of sand are usually from 36 to 52 inches. In only a very few -unimportant cases is less than the above used, and only a few of the -older works use a greater depth, which is not followed in any of the -modern plants. As the sand becomes reduced in thickness by scraping, -the depth of water is correspondingly increased above the figures given -until the sand is replaced. The depth of water on the German covered -filters is quite as great as upon corresponding open filters. Thus the -Berlin covered filters have 51, while the new open filters at Hamburg -have only 43 inches. - - - - -CHAPTER IV. - -RATE OF FILTRATION AND LOSS OF HEAD. - - -The rate of filtration recommended and used has been gradually reduced -during the past thirty years. In 1866 Kirkwood found that 12 vertical -feet per day, or 3.90 million gallons per acre daily, was recommended -by the best engineers, and was commonly followed as an average rate. -In 1868 the London filters averaged a yield of 2.18 million gallons[8] -per acre daily, including areas temporarily out of use, while in 1885 -the quantity had been reduced to 1.61. Since that time the rate has -apparently been slightly increased. - -The Berlin filters at Stralau constructed in 1874 were built to filter -at a rate of 3.21 million gallons per acre daily. The first filters at -Tegel were built for a corresponding rate, but have been used only at -a rate of 2.57, while the more recent filters were calculated for this -rate. The new Hamburg filters, 1892-3, were only intended to filter -at a rate of 1.60 million gallons per acre daily. These in each case -(except the London figures) are the standard rates for the filter-beds -actually in service. - -In practice the area of filters is larger than is calculated from -these figures, as filters must be built to meet maximum instead of -average daily consumptions, and a portion of the filtering area usually -estimated at from 5 to 15 per cent, but in extreme cases reaching 50 -per cent, is usually being cleaned, and so is for the time out of -service. In some works also the rate of filtration on starting a filter -is kept lower than the standard rate for a day or two, or the first -portion of the effluent, supposed to be of inferior quality, is - -wasted, the amount so lost reaching in an extreme case 9 to 14 per -cent of the total quantity of water filtered.[9] In many of the older -works also, there is not storage capacity enough for filtered water to -balance the hourly fluctuations in consumption, and the filters must be -large enough to meet the maximum hourly as well as the maximum daily -requirements. For these reasons the actual quantity of water filtered -in a year is only from 50 to 75 per cent of what would be the case if -the entire area of the filters worked constantly at the full rate. A -statement of the actual yields of a number of filter plants is given in -Appendix IV. The figures for the average annual yields can be taken as -quite reliable. The figures given for rate, in many cases, have little -value, owing to the different ways in which they are calculated at -different places. In addition most of the old works have no adequate -means of determining what the rate at any particular time and for a -single filter really is, and statements of average rates have only -limited value. The filters at Hamburg are not allowed to filter faster -than 1.60 or those at Berlin faster than 2.57 million gallons per acre -daily, and adequate means are provided to secure this condition. Other -German works aim to keep within the latter limit. Beyond this, unless -detailed information in regard to methods is presented, statements of -rate must be taken with some allowance. - - -EFFECT OF RATE UPON COST OF FILTRATION. - -The size of the filters required, and consequently the first cost, -depends upon the rate of filtration, but with increasing rates the cost -is not reduced in the same proportion as the increase in rate, since -the allowance for area out of use is sensibly the same for high and low -rates, and in addition the operating expenses depend upon the quantity -filtered and not upon the filtering area. Thus, to supply 10 million -gallons at a maximum rate of 2 million gallons per acre daily we should -require 10 ÷ 2 = 5 acres + 1 acre reserve for cleaning = 6 acres, while -with a rate twice - -as great, and with the same reserve (since the same amount of cleaning -must be done, as will be shown below), we should require 10 ÷ 4 + 1 -= 3.5 acres, or 58 per cent of the area required for the lower rate. -Thus beyond a certain point increasing the rate does not effect a -corresponding reduction in the first cost. - -The operating cost for the same quantity of water filtered does not -appear to be appreciably affected by the rate. It is obvious that -at high rates filters will became clogged more rapidly, and will -so require to be scraped oftener than at low rates, and it might -naturally be supposed that the clogging would increase more rapidly -than the rates, but this does not seem to be the case. At the Lawrence -Experiment Station, under strictly parallel conditions and with -identically the same water, filters running at various rates became -clogged with a rapidity directly proportional to the rates, so that -the quantities of water filtered between scrapings under any given -conditions are the same whether the rate is high or low. - -The statistics bearing upon this point are interesting, if not entirely -conclusive. There were eleven places in Germany filtering river waters, -from which statistics were available for the year 1891-92. Of these -there were four places with high rates, Lübeck, Stettin, Stuttgart, and -Magdeburg, yielding 3.70 million gallons per acre daily, which filtered -on an average 59 million gallons per acre between scrapings. Three -other places, Breslau, Altona, and Frankfurt, yielding 1.85, passed -on an average 55 million gallons per acre between scrapings, and four -other places, Bremen, Königsberg, Brunswick and Posen, yielding 1.34 -million gallons per acre daily, passed only 40 million gallons per -acre between scrapings. The works filtering at the highest rates thus -filtered more water in proportion to the sand clogged than did those -filtering more slowly, but I cannot think that this was the result of -the rate. It is more likely that some of the places have clearer waters -than others, and that this both allows the higher rate and causes less -clogging than the more turbid waters. - - -EFFECT OF RATE UPON EFFICIENCY OF FILTRATION. - -The effect of the rate of filtration upon the quality of the effluent -has been repeatedly investigated. The efficiency almost uniformly -decreases rapidly with increasing rate. Fränkel and Piefke[10] first -found that with the high rates the number of bacteria passing some -experimental filters was greatly increased. Piefke[11] afterward -repeated these experiments, eliminating some of the features of the -first series to which objection was made, and confirmed the first -results. The results were so marked that Piefke was led to recommend -the extremely low limit of 1.28 million gallons per acre daily as the -safe maximum rate of filtration, but he has since repeatedly used 2.57 -million gallons. - -Kümmel,[12] on the other hand, in a somewhat limited series of -experiments, was unable to find any marked connection between the rate -and the efficiency, a rate of 2.57 giving slightly better results than -rates of either 1.28 or 5.14. - -The admirably executed experiments made at Zürich in 1886-8 upon this -point, which gave throughout negative results, have but little value in -this connection, owing to the extremely low number of bacteria in the -original water. - -At Lawrence in 1892 the following percentages of bacteria (_B. -prodigiosus_) passed at the respective rates: - - --------+--------+-----------+--------------------------------------- - No. of | Depth. | Effective | Rate. Millions gallons per acre daily. - Filter. | | Size of +-------+-------+-------+-------+------- - | | Sand. | 0.5 | 1.0 | 1.5 | 2.0 | 3.0 - --------+--------+-----------+-------+-------+-------+-------+------- - | | | | | | | - 33A | 60 | 0.14 | 0.002 | | | 0.040 | - 34A | 60 | 0.09 | 0.001 | 0.005 | | 0.020 | - 36A | 60 | 0.20 | | | 0.050 | | 0.050 - 37 | 60 | 0.20 | | | 0.010 | 0.130 | - 38 | 24 | 0.20 | 0.018 | | 0.140 | 0.110 | 0.310 - 39 | 12 | 0.20 | 0.014 | 0.070 | | 0.080 | 0.520 - 40 | 12 | 0.20 | | 0.070 | | 0.090 | - 42 | 12 | 0.20 | 0.016 | | | 0.150 | 0.550 - --------+--------+-----------+-------+-------+-------+-------+------- - Average | 0.010 | 0.048 | 0.067 | 0.088 | 0.356 - -----------------------------+-------+-------+-------+-------+------- - -These results show a very marked decrease in efficiency with -increasing rates, the number of bacteria passing increasing in general -as rapidly as the square of the rate. The 1893 results also showed -decreased efficiency with high rates, but the range in the rates -under comparable conditions was less than in 1892, and the bacterial -differences were less sharply marked. - -While the average results at Lawrence, as well as most of the European -experiments, show greatly decreased efficiency with high rates, there -are many single cases, particularly with deep layers of not too coarse -sand, where, as in Kümmel’s experiments, there seems to be little -connection between the rate and efficiency. An explanation of these -apparently abnormal results will be given in Chapter VI. - -It is commonly stated[13] that every water has its own special rate of -filtration, which must be determined by local experiments, and that -this rate may vary widely in different cases. Thus it is possible that -the rate of 1.60 adopted at Hamburg for the turbid Elbe water, the rate -of 2.57 used at Berlin, and about the same at London for much clearer -river-waters, and the rate of 7.50 used at Zürich for the almost -perfectly clear lake-water are in each case the most suitable for the -respective waters. In other cases however, where rates much above 2.57 -are used for river-waters, as at Lübeck and Stettin, there is a decided -opinion that these rates are excessive, and in these instances steps -are now being taken to so increase the filtering areas as to bring the -rates within the limit of 2.57 million gallons per acre daily. - -From the trend of European practice it would seem that for American -river-waters the rate of filtration should not exceed 2.57 in place of -the 3.90 million gallons per acre daily recommended by Kirkwood, or -even that a somewhat lower rate might be desirable in some cases. Of -course, in addition to the area - -necessary to give this rate, a reserve for fluctuating rates and for -cleaning should be provided, reducing the average yield to 2.00, 1.50, -or even less. In the case of water from clear lakes, ponds, or storage -reservoirs, especially when they are not subject to excessive sewage -pollution or to strong algæ growths, it would seem that rates somewhat -and perhaps in some cases very much higher (as at Zürich) could be -satisfactorily used. - - -THE LOSS OF HEAD. - -The loss of head is the difference between the heads of the waters -above and below the sand layer, and represents the frictional -resistance of that layer. When a filter is quite free from clogging -this frictional resistance is small, but gradually increases with the -deposit of a sediment layer from the water filtered until it becomes so -great that the clogging must be removed by scraping before the process -can be continued. After scraping the loss of head is reduced to, or -nearly to, its original amount. With any given amount of clogging the -loss of head is directly proportional to the rate of filtration; that -is, if a filter partially clogged, filtering at a rate of 1.0, has a -frictional resistance of 0.5 ft., the resistance will be doubled by -increasing the rate to 2.00 million gallons per acre daily, provided -no disturbance of the sediment layer is allowed. This law for the -frictional resistance of water in sand alone also applies to the -sediment layer, as I have found by repeated tests, although in so -violent a change as that mentioned above, the utmost care is required -to make the change gradually and prevent compression or breaking of the -sediment layer. From this relation between the rate of filtration and -the loss of head it is seen that the regulation of either involves the -regulation of the other, and it is a matter of indifference which is -directly and which indirectly controlled. - - -REGULATION OF THE RATE AND LOSS OF HEAD IN THE OLDER FILTERS. - -In the older works, and in fact in all but a few of the newest works, -the underdrains of the filters connect directly through a pipe with a -single gate with the pure-water reservoir or pump-well, which is so -built that the water in it may rise nearly or quite as high as that -standing upon the filter. - -[Illustration: FIG. 5.—SIMPLEST FORM OF REGULATION: STRALAU FILTERS AT -BERLIN.] - -A typical arrangement of this sort was used at the Stralau works at -Berlin (now discontinued), Fig. 5. With this arrangement the rate of -filtration is dependent upon the height of water in the reservoir or -pump-well, and so upon the varying consumption. When the water in the -receptacle falls with increasing consumption the head is increased, -and with it the rate of filtration, while, on the other hand, with -decreasing draft and rising water in the reservoir, the rate of -filtration decreases and would eventually be stopped if no water were -used. This very simple arrangement thus automatically, within limits, -adjusts the rate of filtration to the consumption, and at the same time -always gives the highest possible level of water in the pump-well, thus -also economizing the coal required for pumping. - -In plants of this type the loss of head may be measured by floats -on little reservoirs built for that purpose, connected with the -underdrains; but more often there is no means of determining it, -although the maximum loss of head at any time is the difference between -the levels of the water on the filter and in the reservoir, or the -outlet of the drain-pipe, in case the latter is above the water-line -in the reservoir. The rate of filtration can only be measured with this -arrangement by shutting off the incoming water for a definite interval, -and observing the distance that the water on the filter sinks. The -incoming water is regulated simply by a gate, which a workman opens or -closes from time to time to hold the required height of water on the -filter. - -The only possible regulation of the rate and loss of head is effected -by a partial closing of the gate on the outlet-pipe, by which the -freshly-cleaned filters with nearly-closed gates are kept from -filtering more rapidly than the clogged filters, the gates of which -are opened wide. Often, however, this is not done, and then the fresh -filters filter many times as rapidly as those which are partially -clogged. - -A majority of the filters now in use are built more or less upon this -plan, including most of those in London and also the Altona works, -which had such a favorable record with cholera in 1892. - -The invention and application of methods of bacterial examination in -the last years have led to different ideas of filtration from those -which influenced the construction of the earlier plants. As a result -it is now regarded as essential by most German engineers[14] that -each filter shall be provided with devices for measuring accurately -and at any time both the rate of filtration and the loss of head, and -for controlling them, and also for making the rate independent of -consumption by reservoirs for filtered water large enough to balance -hourly variations (capacity 1/4 to 1/3 maximum daily quantity) and low -enough so that they can never limit the rate of filtration by causing -back-water on the filters. These points are now insisted upon by the -German Imperial Board of Health,[15] and all new filters are built in -accordance with them, while most of the old works are being built over -to conform to the requirements. - - -APPARATUS FOR REGULATING THE RATE AND LOSS of HEAD. - -Many appliances have been invented for the regulation of the rate and -loss of head. In the apparatus designed by Gill and used at both Tegel -and Müggel at Berlin the regulation is effected by partially closing -a gate through which the effluent passes into a chamber in which the -water-level is practically constant (Fig. 6). The rate is measured -by the height of water on the weir which serves as the outlet for -this second chamber into a third connecting with the main reservoir, -while the loss of head is shown by the difference in height of floats -upon water in the first chamber, representing the pressure in the -underdrains, and upon water in connection with the raw water on the -filter. From the respective heights of the three floats the attendant -can at any time see the rate of filtration and the loss of head, and -when a change is required it is effected by moving the gate. - -[Illustration: FIG. 6.—REGULATION APPARATUS AT BERLIN (TEGEL).] - -In the apparatus designed in 1866 by Kirkwood for St. Louis and never -built (Fig. 7) the loss of head was directly, and the rate indirectly, -regulated by a movable weir, which was to have been lowered from time -to time by the attendant to secure the required results. This plan is -especially remarkable as it meets the modern requirements of a regular -rate independent of rate of consumption and of the water-level in the -reservoir, and also allows continual measurements of both rate (height -of water on the weir) and head (difference in water-levels on filter -and in effluent chamber) to be made, and control of the same by the -position of the weir. Mr. Kirkwood found no filters in Europe with such -appliances, and it was many years after his report was published before -similar devices were used, but they are now regarded as essential. - -[Illustration: FIG. 7.—REGULATION APPARATUS AND SECTION OF FILTER -RECOMMENDED FOR ST. LOUIS BY KIRKWOOD IN 1866.] - -[Illustration: FIG. 8.—REGULATION APPARATUS USED AT HAMBURG.] - -The regulators for new filters at Hamburg (Fig. 8) are built upon the -principle of Kirkwood’s device, but provision is made for a second -measurement of the water if desired by the loss of head in passing a -submerged orifice. Both the rate and loss of head are indicated by a -float on the first chamber connecting directly with the underdrain, -which at the same time indicates the head on a fixed scale, the zero of -which corresponds to the height of the water above the filter, and the -rate upon a scale moving with the weir, the zero of which corresponds -with the edge of the weir. The water on the filter is held at a -perfectly constant level. - -The regulators in use at Worms and those recently introduced at -Magdeburg act upon the same principle, but the levels of the water on -the filters are allowed to fluctuate, and the weirs and in fact, the -whole regulating appliances are mounted on big floats in surrounding -chambers of water connecting with the unfiltered water on the filters. -I am unable to find any advantages in these appliances, and they are -much more complicated than the forms shown by the cuts. - - - -APPARATUS FOR REGULATING THE RATE DIRECTLY. - -[Illustration: FIG. 9.—LINDLEY’S REGULATION APPARATUS AT WARSAW, -RUSSIA.] - -The above-mentioned regulators control directly the loss of head, -and only indirectly the rate of filtration. The regulators at Warsaw -were designed by Lindley to regulate the rate directly and make it -independent of the loss of head. The quantity of water flowing away -is regulated by a float upon the water in the effluent chamber, -which holds the top of the telescope outlet-pipe a constant distance -below the surface and so secures a constant rate. As the friction of -the filter increases the float sinks with the water until it reaches -bottom, when the filter must be scraped. A counter-weight reduces the -weight on the float, and at the same time allows a change in the rate -when desired. This apparatus is automatic. All of the other forms -described require to be occasionally adjusted by the attendant, but -the attention they require is very slight, and watchmen are always on -duty at large plants, who can easily watch the regulators. The Warsaw -apparatus is reported to work very satisfactorily, no trouble being -experienced either by leaking or sticking of the telescope-joint, -which is obviously the weakest point of the device, but fortunately a -perfectly tight joint is not essential to the success of the apparatus. -Regulators acting upon the same principle have recently been installed -at Zürich, where they are operating successfully. - -Burton[16] has described an ingenious device designed by him for the -filters at Tokyo, Japan. It consists of a double acting valve of gun -metal (similar to that shown by Fig. 11), through which the effluent -must pass. This valve is opened and closed by a rod connecting with -a piston in a cylinder, the opposite sides of which connect with the -effluent pipe above and below a point where the latter is partially -closed, so that the valve is opened and closed according as the loss -of head in passing this obstruction is below or above the amount -corresponding to the desired rate of filtration. - -The use of the Venturi meter in connection with the regulation of -filters would make an interesting study, and has, I believe, never been -considered. - -[Illustration: REGULATOR-HOUSE, SHOWING RATE OF FILTRATION AND LOSS OF -HEAD ON THE OUTSIDE, BREMEN.] - -[Illustration: INLET FOR ADMISSION OF RAW WATER TO A FILTER, EAST -LONDON. - - [_To face page 58._] -] - - -APPARATUS FOR REGULATING THE HEIGHT OF WATER UPON FILTERS. - -It will be seen by reference to the diagrams of the Berlin and Hamburg -effluent regulators (Figs. 6 and 8) that their perfect operation -is dependent upon the maintenance of a constant water-level upon -the filters. The old-fashioned adjustment of the inlet-gate by the -attendant is hardly accurate enough. - -The first apparatus for accurately and automatically regulating the -level of the water upon the filters was constructed at Leeuwarden, -Holland, by the engineer, Mr. Halbertsma, who has since used a similar -device at other places, and improved forms of which are now used at -Berlin and at Hamburg. - -At Berlin (Müggel) the water-level is regulated by a float upon the -water in the filter which opens or shuts a balanced double valve on -the inlet-pipe directly beneath, as shown in Fig. 10. It is not at all -necessary that this valve should shut water-tight; it is only necessary -that it should prevent the continuous inflow from becoming so great as -to raise the water-level, and for this reason loose, easily-working -joints are employed. The apparatus is placed in a little pit next to -the side of the filter, and the overflowing water is prevented from -washing the sand by paving the sand around it for a few feet. - -[Illustration: FIG. 10.—REGULATION OF INFLOW USED AT MÜGGEL, BERLIN.] - -At Hamburg the same result is obtained by putting the valve in a -special chamber outside of the filter and connected with the float by a -walking-beam (Fig. 11). - -[Illustration: FIG. 11.—REGULATION OF INFLOW USED AT HAMBURG.] - -The various regulators require to be protected from cold and ice by -special houses, except in the case of covered filters, where they can -usually be arranged with advantage in the filter itself. In regard to -the choice of the form of regulator for both the inlets and outlets of -filters, so far as I have been able to ascertain, each of the modern -forms described as in use performs its functions satisfactorily, and in -special cases any of them could properly be selected which would in the -local conditions be the simplest in construction and operation. - - - -LIMIT TO THE LOSS OF HEAD. - -The extent to which the loss of head is allowed to go before filters -are cleaned differs widely in the different works, some of the newer -works limiting it sharply because it is believed that low bacterial -efficiency results when the pressure is too great, although the -frequency of cleaning and consequently the cost of operation are -thereby increased. - -At Darlington, England, I believe as a result of the German theories, -the loss of head is limited to about 18 inches by a masonry weir built -within the last few years. At Berlin, both at Tegel and Müggel, the -limit is 24 inches, while at the new Hamburg works 28 inches are -allowed. At Stralau in 1893 an effort was made to not exceed a limit -of 40 inches, but previously heads up to 60 inches were used, which -corresponds with the 56 inches used at Altona; and, in the other old -works, while exact information is not easily obtained because of -imperfect records, I am convinced that heads of 60 or even 80 inches -are not uncommon. At the Lawrence Experiment Station heads of 70 inches -have generally been used, although some filters have been limited to 36 -and 24 inches. - -In 1866 Kirkwood became convinced that the loss of head should not go -much above 30 inches, first, because high heads would, by bringing -extra weight upon the sand, make it too compact, and, second, because -when the pressure became too great the sediment layer on the surface of -the sand, in which most of the loss of head occurs, would no longer be -able to support the weight and, becoming broken, would allow the water -to pour through the comparatively large resulting openings at greatly -increased rates and with reduced efficiency. - -In regard to the first point, a straight, even pressure many times -that of the water on the filter is incapable of compressing the sand. -It is much more the effect of the boots of the workmen when scraping -that makes the sand compact. I have found sand in natural banks at -Lawrence 70 or 80 feet below the surface, where it had been subjected -to corresponding pressure for thousands of years, to be quite as porous -as when packed in water in experimental filters in the usual way. - -The second reason mentioned, or, as I may call it, the breaking-through -theory, is very generally if not universally accepted by German -engineers, and this is the reason for the low limit commonly adopted by -them. - -A careful study of the results at Lawrence fails to show the slightest -deterioration of the effluents up to the limit used, 72 inches. Thus -in 1892, taking only the results of the continuous filters of full -height (Nos. 33A, 34A, 36A, and 37), we find that for the three days -before scraping, when the head was nearly 72 inches, the average -number of bacteria in the effluents was 31 per cc., while for the -three days after scraping, with very low heads, the number was 47. The -corresponding numbers of _B. prodigiosus_[17] were 1.1 and 2.7. This -shows better work with the highest heads, but is open to the objection -that the period just after scraping, owing to the disturbance of the -surface, is commonly supposed to be a period of low efficiency. - -To avoid this criticism in calculating the corresponding results for -1893, the numbers of the bacteria for the intermediate days which could -not have been influenced either by scraping or by excessive head are -put side by side with the others. Taking these results as before for -continuous filters 72 inches high, and excluding those with extremely -fine sands and a filter which was only in operation a short time toward -the end of the year, we obtain the following results: - - Water B. - Bacteria Prodigiosus - per cc. per cc. - Average 1st day after scraping, low heads 79 6.1 - Average 2d day after scraping, low heads 44 4.1 - Average 3d day after scraping, low heads 45 3.6 - Intermediate days, medium heads 59 4.5 - Second from last day, heads of nearly 72 inches 66 2.7 - Next to the last day, heads of nearly 72 inches 56 3.2 - Last day, heads of nearly 72 inches 83 2.5 - -These figures show a very slight increase of the water bacteria in the -effluent as the head approaches the limit, but no such increase as -might be expected from a breaking through of the sediment layer, and -the _B. prodigiosus_ which is believed to better indicate the removal -of the bacteria of the original water, actually shows a decrease, the -last day being the best day of the whole period. - -The Lawrence results, then, uniformly and clearly point to a conclusion -directly opposite to the commonly accepted view, and I have thus -been led to examine somewhat closely the grounds upon which the -breaking-through theory rests. - -The two works which have perhaps contributed most to the theories -of filtration are the Stralau and Altona works. After examining the -available records of these works, I am quite convinced that at these -places there has been, at times at least, decreased efficiency with -high heads. For the Stralau works this is well shown by Piefke’s -plates in the _Zeitschrift für Hygiene_, 1894, after page 188. In both -of these works, however, the apparatus (or lack of apparatus) for -regulating the rate is that shown by Fig. 5, page 49, and the rate -of filtration is thus dependent upon the rate of consumption and the -height of water in the reservoir. At the Stralau works, at the time -covered by the above-mentioned diagrams, the daily quantity of water -filtered was 27 times the capacity of the reservoir, and the rate -of filtration must consequently have adapted itself to the hourly -consumptions. The data which formed the basis of Kirkwood’s conclusions -are not given in detail, but it is quite safe to assume that they were -obtained from filters regulated as those at Altona and Stralau are -regulated, and what is said in regard to the latter will apply equally -to his results. - -Piefke[18] shows that among the separate filters at Stralau, all -connected with the same pure-water reservoir, those connected through -the shorter pipes gave poorer effluents than the more remote filters, -and he attributes the difference to the frictional resistance of the -connecting pipes, which helped to prevent excessive rates in the -filters farthest away when the water in the reservoir became low, and -thus the fluctuations in the rates in these filters were less than in -those close to the reservoir. He - -does not, however, notice, in speaking of the filters in which the -decreased efficiencies with high heads were specially marked, that they -follow in nearly the same order, and that of the four open filters -mentioned three were near the reservoir and only one was separated by -a comparatively long pipe, indicating that the deterioration with high -heads was only noticeable, or at least was much more conspicuous, in -those filters where the rates fluctuated most violently. - -It requires no elaborate calculation to show that of two filters -connected with the same pure-water reservoir, as shown by Fig. 5, -with only simple gates on the connecting pipes, one of them clean and -throttled by a nearly closed gate, so that the normal pressure behind -the gate is above the highest level of water in the reservoir, and the -other clogged so that the normal pressure of the water in the drain is -considerably below the highest level of the water in the reservoir, -the latter will suffer much the more severe shocks with fluctuating -water-levels; and the fact being admitted that fluctuating levels are -unfavorable, we must go farther and conclude that the detrimental -action will increase with increasing loss of head. I am inclined to -think that this theory is adequate to explain the Stralau and Altona -results without resource to the breaking-through theory. - -While the above does not at all prove the breaking-through theory to be -false, it explains the results upon which it rests in another way, and -can hardly fail to throw so much doubt upon it as to make us refuse to -allow its application to those works where a regular rate of filtration -is maintained regardless of variations in the consumption, until proof -is furnished that it is applicable to them. - -I have been totally unable to find satisfactory European results in -regard to this point. The English works can furnish nothing, both on -account of the lack of regulating appliances and because the monthly -bacterial examinations are inadequate for a discussion of hourly or -daily changes. The results from the older Continental works are also -excluded for one or the other, or more often for both, of the above -reasons. The Hamburg, Tegel, and Müggel results, so far as they go, -show no deterioration with increased heads, but the heads are limited -to 24 or 28 inches by the construction of the filters, and the results -thus entirely fail to show what would be obtained with heads more than -twice as high. - -I am thus forced to conclude that there is no adequate evidence of -inferior efficiency with high heads in filters where the rates are -independent of the water-level in the pure-water reservoir, the -only results directly to the point—the Lawrence results mentioned -above—indicating that the full efficiency is maintained with heads -reaching at least 72 inches. - -The principal reason for desiring to allow a considerable loss of head -is an economical one; the period will then be lengthened, while the -frequency of scraping and the volume of sand to be washed and replaced -will be correspondingly reduced. There may be other advantages in long -periods, such as less trouble with scraping and better work in cold -winter weather, but the cost is the most important consideration. - -It is the prevalent idea among the German engineers that the loss of -head after reaching 24 to 30 inches would increase very rapidly, so -that the quantity of water filtered, in case a much higher head was -allowed, would not be materially increased. No careful investigations, -however, have been made, and indeed they are hardly possible with -existing arrangements, as in the older filters the loss of head -fluctuates with varying rates of filtration in such a way that only -results of very doubtful value can be obtained, and in the newer works -the loss of head is too closely limited, and the curves which can be -drawn by extrapolation are evidently no safe indications of what would -actually happen if the process was carried farther. - -On the other hand, I was told by the attendant at Darlington, England, -that since the building of the weir a few years ago, which now limits -the loss of head to about 18 inches instead of the 5 feet or more -formerly used, the quantity of sand to be removed has been three times -as great as formerly. No records are kept, and this can only be given -as the general impression of the man who superintends the work. - -At Lawrence the average quantities of water filtered between scrapings -with sand of an effective size of 0.20 mm. have been as follows: - - Maximum Loss of Million Gallons per Acre filtered - Head. between Scrapings. - - 1892. 1893. Average. - - 70 inches 58 88 73 - 34 foot 32 22 27 - 22 foot 17 16 16 - -With sand of an effective size of 0.29 mm. the results were: - - 1893. - - 70 inches 70 - 22 foot 29 - -These results indicate a great increase in the quantity of water -filtered between scrapings with increasing heads, the figures being -nearly proportional to the maximum heads used in the respective -cases. It is, of course, quite possible that the results would differ -in different places with the character of the raw water and of the -filtering material. - -The depth of sand to be removed by scraping at one time is, within -limits, practically independent of the quantity of dirt which it has -accumulated, and any lengthening of the period means a corresponding -reduction in the quantity of sand to be removed, washed and replaced -and consequently an important reduction in the operating cost, as well -as a reduction in the area of filters out of use while being cleaned, -and so, in the capital cost. - -Among the minor objections to an increased loss of head are the -greater head against which the water must be pumped, and the possible -increased difficulty of filling filters with filtered water from below -after scraping, but these would hardly have much weight against the -economy indicated by the Lawrence experiments for the higher heads. - -High heads will also drive an increased quantity of water through any -cracks or passages in the filter. Such leaks have at last been found to -be the cause of the inferior work of the covered filters at Stralau, -the water going down unfiltered in certain corners, especially at high -heads; but with careful construction there should be no cracks, and -with the aid of bacteriology to find the possible leaks this ought not -to be a valid objection. - -In conclusion: the trend of opinion is strongly in favor of limiting -the loss of head to about 24 to 30 inches as was suggested by Kirkwood, -but I am forced to conclude that there is reason to believe that -equally good results can be obtained with lower operating expenses by -allowing higher heads to be used, at least in the case of filters with -modern regulating appliances, and, I would suggest that filters should -be built so as not to exclude the use of moderately high heads, and -that the limit to be permanently used should be determined by actual -tests of efficiency and length of period with various losses of head -after starting the works. - - - - -CHAPTER V. - -CLEANING FILTERS. - - -When a filter has become so far clogged that it will no longer pass -a satisfactory quantity of water with the allowable head it must be -cleaned by scraping off and removing the upper layer of dirty sand. - -To do this without unnecessary loss of time the unfiltered water -standing upon the filter is removed by a drain above the sand provided -for that purpose. The water in the sand must then be lowered below the -surface of the sand by drawing water from the underdrains until the -sand is firm enough to bear the weight of the workmen. By the time -that this is accomplished the last water on the surface should have -soaked away, and the filter is ready to be scraped. This is done by -workmen with wide, sharp shovels, and the sand removed is taken to -the sand-washing apparatus to be washed and used again. Special pains -are given to securing rapid and cheap transportation of the sand. In -some cases it is wheeled out of the filter on an inclined plane to the -washer. In other cases a movable crane is provided which lifts the sand -in special receptacles and allows it to fall into cars on a tram-line -on which the crane also moves. The cars as filled are run to the washer -and also serve to bring back the washed sand. When the dirty sand has -been removed, the surface of the sand is carefully smoothed and raked. -This is especially necessary to remove the effects of the workmen’s -boots. - -It is customary in the most carefully managed works to fill the sand -with filtered water from below, introduced through the underdrains. In -case the ordinary level of the water in the pure-water canal is higher -than the surface of the sand in the filters, this is accomplished -by simply opening a gate provided for the purpose, which allows the -water to pass around the regulating apparatus. Otherwise filters can -be filled from a special pipe taking its water from any filter which -at that time can deliver its effluent high enough for that purpose. -The quantity of water required for filling the sand from below is -ordinarily but a fraction of one per cent of the quantity filtered. - -Formerly, instead of filling from below, after cleaning, the raw water -was brought directly onto the surface of the filter. This was said to -only imperfectly fill the sand-pores, which still contained much air. -If, however, the water is not brought on too rapidly it will sink into -the sand near the point where it is applied, pass laterally through the -sand or underlying gravel to other parts of the filter, and then rise, -so that even in this case all but a little of the filter will be really -filled from below. This is, however, open to the objection that however -slowly the water is introduced, the sand which absorbs it around the -inlet filters it at a very high rate and presumably imperfectly, so -that the water in the underdrains at the start will be poor quality -and the sand around the inlet will be unduly clogged. The practice of -filling from below is therefore well founded. - -As soon as the surface of the sand is covered with the water from -below, raw water is introduced from above, filling the filter to -the standard height, care being taken at first that no currents -are produced which might wash the surface of the sand. It has been -recommended by Piefke and others that this water should be allowed -to stand for a time up to twenty-four hours before starting the -filtration, to allow the formation of a sediment layer, and in some -places, especially at Berlin and the works of some of the London -companies, this is done; but varying importance is attached to the -procedure, and it is invariably omitted, so far as I can learn, when -the demand for water is heavy. - -The depth of sand removed by scraping must at least equal the -depth of the discolored layer, but there is no sharp dividing line, -the impurities gradually decreasing from the surface downward. -Fig. 12 shows the relative number of bacteria found in the sand at -various depths in one of the Lawrence experimental filters, and is a -representative result, although the actual numbers vary at different -times. In general it may be said that the bulk of the sediment is -retained in the upper quarter inch, but it is desirable to remove also -the less dirty sand below and, in fact, it is apparently impossible -with the method of scraping in use to remove so thin a layer as one -fourth inch. Practically the depth to which sand is removed is stated -to be from 0.40 to 1.20 inch. Exact statistics are not easily obtained, -but I think that 2 centimeters or 0.79 inch may be safely taken as -about the average depth usually removed in European filters, and it is -this depth which is indicated on Fig. 12. - -[Illustration: FIG. 12.—DIAGRAM SHOWING ACCUMULATION OF BACTERIA NEAR -THE SURFACE OF THE SAND.] - -At the Lawrence Experiment Station, the depth removed is often much -less than this, and depends upon the size of grain of the sand -employed, the coarser sands requiring to be more deeply scraped than -the finer ones. The method of scraping, however, which allows the -removal of very thin sand layers, is only possible because of the -small size of the filters, and as it is incapable of application on a -large scale, the depths thus removed are only interesting as showing -the results which might be obtained in practice with a more perfect -method of scraping. - -The replacing of the washed sand is usually delayed until the filter -has been scraped quite a number of times—commonly for a year. The last -scraping before refilling is much deeper than usual, because the sand -below the depth of the ordinary scraping is somewhat dirty, and might -cause trouble if left below the clean sand. - -In England it is the usual if not the universal practice to replace the -washed sand at the bottom between the old sand and the gravel. This is -done by digging up the entire filter in sections about six feet wide. -The old sand in the first section is removed clear down to the gravel, -and the depth of washed sand which is to be replaced is put in its -place. The old sand from the next six-foot section is then shovelled -upon the first section of clean sand, and its place is in turn filled -with fresh sand. With this practice the workmen’s boots are likely to -disturb the gravel each year, necessitating a thicker layer of the -upper and finest grade than would otherwise be required. - -In Germany this is also sometimes done, but more frequently the upper -layer of slightly clogged sand below the regular scraping is removed -as far as the slightest discoloration can be seen, perhaps 6 inches -deep. The sand below is loosened for another 6 inches and allowed to -stand dry, if possible, for some days; afterwards the washed sand is -brought on and placed above. The washed sand is never replaced without -some such treatment, because the slightly clogged sand below the layer -removed would act as if finer than the freshly washed sand,[19] and -there would be a tendency to sub-surface clogging. - - -FREQUENCY OF SCRAPING. - -The frequency of scraping depends upon the character of the raw water, -the thoroughness of the preliminary sedimentation, the grain-size of -the filter sand, the rate of filtration, and the maximum loss of head -allowed. With suitable conditions the period between scrapings should -never be less than one week, and will but rarely exceed two months. -Under exceptional conditions, however, periods have been recorded as -low as one day and as high as one hundred and ten days. Periods of less -than a week’s duration are almost conclusive evidence that something -is radically wrong, and the periods of one day mentioned were actually -accompanied by very inadequate filtration. In 1892 the average periods -at the German works varied from 9.5 days at Stettin (with an excessive -rate) to 40 days at Brunswick, the average of all being 25 days.[20] - -The quantity of water per acre filtered between scrapings forms the -most convenient basis for calculation. The effect of rate (page -49), loss of head (page 65), and size of sand grain (page 32) have -already been discussed, and it will suffice to say here that the total -quantity filtered between scrapings is apparently independent of the -rate of filtration, but varies with the maximum loss of head and with -the grain-size of the sand, and apparently nearly in proportion to -them. Eleven German filter-works in 1892, drawing their waters from -rivers, filtered on an average 51 million gallons of water per acre -between scrapings, the single results ranging from 28 at Bremen to 71 -at Stuttgart, while Zürich, drawing its water from a lake which is -but very rarely turbid, filtered 260 million gallons per acre between -scrapings. Unfortunately, the quantities at Berlin, where (in 1892 two -thirds and now all) the water is drawn from comparatively large ponds -on the rivers, are not available for comparison. - -At London, in 1884, the average quantities of water filtered - -between scrapings varied from 43 to 136 million gallons per acre with -the different companies, averaging 85, and in 1892 the quantities -ranged from 73 to 157, averaging 90 million gallons per acre. The -greater quantity filtered at London may be due to the greater sizes of -the sedimentation-basins, which for all the companies together hold a -nine days’ supply at London against probably less than one day’s supply -for the German works. - -There is little information available in regard to the frequency -of scraping with water drawn from impounding reservoirs. In some -experiments made by Mr. FitzGerald at the Chestnut Hill reservoir, -Boston, the results of which are as yet unpublished, a filter with -sand of an effective size of only .09 mm. averaged 58 million gallons -per acre between scrapings for nine periods, the rate of filtration -being 1.50 million gallons per acre daily, while another filter, with -sand of an effective size of .18 mm., passed an average of 93 million -gallons per acre for ten periods at the same rate. These experiments -extended through all seasons of the year, and taking into account the -comparative fineness of the sands they show rather high quantities of -water filtered between scrapings. - -The quantity of water filtered between scrapings is usually greatest -in winter, owing to the smaller quantity of sediment in the raw water -at this season, and is lowest in times of flood, regardless of season. -In summer the quantity is often reduced to a very low figure in waters -supporting algæ growths, especially when the filters are not covered. -Thus at Stralau in 1893 during the algæ period the quantity was reduced -to 14 million gallons per acre for open filters,[21] but this was quite -exceptional, the much-polluted, though comparatively clear, Spree water -furnishing unusually favorable conditions for the algæ. - - -QUANTITY OF SAND TO BE REMOVED. - -In regard to the quantity of sand to be removed and washed, if we -take the average result given above for the German works filtering -river-waters of 51,000,000 gallons per acre filtered between scrapings, -and the depth of sand removed at two centimeters or 0.79 inch, we -find that one volume of sand is required for every 2375 volumes of -water filtered, or 2.10 cubic yards per million gallons. At Bremen, -the highest average result, the quantity would be 3.80 yards, and at -Stralau during the algæ season 7.70 yards. At Zürich, on the other -hand, the quantity is only 0.41 yard, and at London, with 87,000,000 -gallons per acre filtered between scrapings, the quantity of sand -washed would be 1.24 yards per million gallons; assuming always that -the layer removed is 0.79 inch thick. - -These estimates are for the regular scrapings only, and do not include -the annual deeper scraping before replacing the sand, which would -increase them by about one third. - - -WASTING THE EFFLUENTS AFTER SCRAPING. - -It has already been stated that an important part of the filtration -takes place in the sediment layer deposited on top of the sand from -the water. When this layer is removed by scraping its influence is -temporarily removed, and reduced efficiency of filtration may result. -The significance of this reduced efficiency became apparent when the -bacteria in the water were studied in their relations to disease, and -Piefke suggested[22] that the first effluent after scraping should -be rejected for one day after ordinary scrapings and for one week -after replacing the sand. In a more recent paper[23] he reduces these -estimates to the first million gallons of water per acre filtered after -scraping - -for open and twice as great a quantity for covered filters, and to six -days after replacing the sand, which last he estimates will occur only -once a year. Taking the quantity of water filtered between scrapings at -13.9 million gallons per acre, the quantity observed at Stralau in the -summer of 1893, he finds that it is necessary to waste 9 per cent of -the total quantity of effluent from open and 13.8 per cent of that from -covered filters. - -The eleven German water-works[24] filtering river-waters, however, -filtered on an average 51.0 instead of 13.9 million gallons per acre -between scrapings, and applying Piefke’s figures to them the quantities -of water to be wasted would be only about one fourth of his estimates -for Stralau. - -The rules of the Imperial Board of Health[25] require that every German -filter shall be so constructed “that when an inferior effluent results -it can be disconnected from the pure-water pipes and the filtrate -allowed to be wasted.” The drain-pipe for removing the rejected water -should be connected below the apparatus for regulating the rate and -loss of head, so that the filter can be operated exactly as usual, -and the effluent can be turned back to the pure-water pipes without -stopping or changing the rate. The works at Berlin and at Hamburg -conform to this requirement, and most of the older German works have -been or are being built over to make them do so. - -In regard to the extent of deterioration after scraping, Piefke’s -experiments have always shown much larger numbers of bacteria both of -the ordinary forms and of special applied forms on the first day after -scraping, the numbers frequently being many times as high as at other -times. - -At the Lawrence Experiment Station it was found in 1892 that on an -average the number of water bacteria was increased by 70 per cent -(continuous filters only) for the three days following scraping, while -_B. prodigiosus_ when applied was increased 140 per - -cent, the increase being most marked where the depth of sand was -least, and with the highest rate of filtration. - -The same tendency was found in 1893, when the increase in the water -bacteria on the first day after scraping was only 19 per cent and _B. -prodigiosus_ 64 per cent, but for a portion of the year the difference -was greater, averaging 132 and 262 per cent, respectively. These -differences are much less than those recorded by Piefke, and with the -high efficiencies regularly obtained at Lawrence they would hardly -justify the expensive practice of wasting the effluent. - -The reduction in efficiency following scraping is much less at low -rates, and if a filter is started at much less than its normal rate -after scraping, and then gradually increased to the standard after -the sediment layer is formed, the poor work will be largely avoided. -Practically this is done at Berlin and at Hamburg. The filters are -started at a fourth or less of the usual rates and are gradually -increased, as past experience with bacterial results has shown it can -be safely done, and the effluent is then even at first so well purified -that it need not be wasted. - -Practically in building new filters the provision of a suitable -connection for wasting the effluents into the drain which is necessary -for emptying them involves no serious expense and should be provided, -but it may be questioned how often it should be used for wasting the -effluents. If the raw water is so bad that a good effluent cannot be -obtained by careful manipulation even just after scraping, the course -of the Berlin authorities in closing the Stralau works and seeking a -less polluted supply would seem to be the only really safe procedure. - - - -SAND-WASHING. - -[Illustration: CLEANING A FILTER, EAST LONDON.] - -[Illustration: WASHING DIRTY SAND WITH HOSE, ANTWERP.] - - [_To face page 76._] - -The sand-washing apparatus is an important part of most European -filtering plants. It seldom happens that a natural sand can be found -clean enough and sufficiently free from fine particles although such -a sand was found and used for the Lawrence filter. Most of the sand in -use for filtration in Europe was originally washed. In the operation of -the filters also, sand-washing is used for the dirty sand, which can -then be used over and over at a much lower cost than would be the case -if fresh sand was used for refilling. The methods used for washing sand -at the different works present a great variety both in their details -and in the underlying principles. Formerly boxes with double perforated -bottoms in which the sand was placed and stirred by a man as water from -below rose through them, and other similar arrangements were commonly -used, but they are at present only retained, so far as I know, in some -of the smaller English works. The cleansing obtained is apparently -considerably less thorough than with some of the modern devices. - -[Illustration: FIG. 13.—HOSE-WASHING FOR DIRTY SAND.] - -Hose-washing is used in London by the Southwark and Vauxhall, Lambeth -and Chelsea companies, and also at Antwerp. For this a platform is -constructed about 15 feet long by 8 feet wide, with a pitch lengthwise -of 6 to 8 inches (Fig. 13). The platform is surrounded by a wall -rising from one foot at the bottom to three feet high at the top, -except the lower end, which is closed by a removable plank weir 5 or 6 -inches high. From two to four cubic yards of the sand are placed upon -this platform and a stream of water from a hose with a 3/4 or 7/8-inch -nozzle is played upon it, moving it about from place to place. The sand -itself is always kept toward the upper end of the platform, while the -water with the dirt removed flows down into the pond made by the weir, -where the sand settles out and the dirt overflows with the water. When -the water comes off clear, which is usually after an hour or a little -less, the weir is removed, and, after draining, the sand is removed. -These arrangements are built in pairs so that the hose can be used in -one while the sand is being changed in the other. They are usually -built of brick laid in cement, but plank and iron are also used. The -corners are sometimes carried out square as in the figure, but are more -often rounded. The washing is apparently fairly well done. - -In Germany the so-called “drum” washing-machine, drawings of which have -been several times published,[26] has come to be almost universally -used. It consists of a large revolving cylinder, on the bottom of the -inside of which the sand is slowly pushed up toward the higher end by -endless screw-blades attached to the cylinder, while water is freely -played upon it all the way. The machine requires a special house for -its accommodation and from 2 to 4 horse-power for its operation. It -washes from 2.5 to 4 yards of sand per hour most thoroughly, with a -consumption of from 11 to 14 times as large a volume of water. The -apparatus is not patented or made for sale, but full plans can be -easily secured. - -A machine made by Samuel Pegg & Sons, Leicester, Eng., pushes the -sand up a slight incline down which water flows. It is very heavy and -requires power to operate it. The patent has - -expired. A machine much like it but lighter and more convenient and -moved by water-power derived from the water used for washing instead of -steam-power is used at Zürich with good results. - -In Greenway’s machine the sand is forced by a screw through a long -narrow cylinder in which there is a current of water in the opposite -direction. The power required is furnished by a water-motor, as with -the machine at Zürich. The apparatus is mounted on wheels and is -portable; it has an appliance for piling up the washed sand or loading -it onto cars. It is patented and is manufactured by James Gibb & Co., -London. - -Several of the London water companies are now using ejector washers, -and such an apparatus has been placed by the side of the “drum” washers -at Hamburg. This apparatus was made by Körting Brothers in Hannover, -and combines the ejectors long made by that firm with hoppers from -designs by Mr. Bryan, engineer of the East London Water Company. An -apparatus differing from this only in the shape of the ejectors and -some minor details has been patented in England, and is for sale by -Messrs. Hunter, Frazer & Goodman, Bow, London. - -Both of these forms consist of a series of conical hoppers, from the -bottom of each of which the sand and water are forced into the top of -the next by means of ejectors, the excess of dirty water overflowing -from the top of each hopper. The apparatus is compact and not likely -to get out of order, but is not portable. It can be easily arranged to -take the sand at the level of the ground, or even lower if desired, and -deliver it washed at some little elevation, thus minimizing hand-labor. -The washing is regular and thorough. The objection most frequently -raised against its use is the quantity of water required, but at -Hamburg I was informed that the volume of water required was only about -15 times that of the sand, while almost as much (13-14 volumes) were -required for the “drum” washers, and the saving in power much more -than offset the extra cost for water. - -In addition to the above processes of sand-washing, Piefke’s method -of cleaning without scraping[27] might be mentioned, although as -yet it has hardly passed the experimental stage, and has only been -used on extremely small filters. The process consists of stirring -the surface sand of the filter with “waltzers” while a thin sheet of -water rapidly flows over the surface. This arrangement necessitates a -special construction of the filters, providing for rapidly removing -the unfiltered water from the surface, and for producing a regular and -rapid movement of a thin sheet of water over the surface. In the little -filters now in use, one of which I saw in a brewery in Berlin, the -cleaning is rapidly, cheaply, and apparently well done. - -In washing dirty sand it is obvious that any small sand-grains will -be removed with the dirt, and in washing new sand the main object is -to remove the grains below a certain size. It is also apparent that -the sizes of grains which will and those which will not be removed -are dependent upon the mechanical arrangements of the washer, as, for -example, with the ejectors, upon the sizes of the hoppers, and the -quantity of water passing through them, and care should be taken to -make them correspond with the size of grain selected for the filter -sand. This can only be done by experiment, as no results are available -on this point. - -In some places filtered water is used for sand-washing, although this -seems quite unnecessary, as ordinary river-water answers very well. -It is, however, often cheaper, especially in small works, to use the -filtered water from the mains rather than provide a separate supply for -the washers. - -The quantity of water required for washing may be estimated at 15 times -the volume of the sand and the sand as 0.04 per cent of the volume of -the water filtered (page 74), so that - -0.6 per cent of the total quantity of water filtered will be required -for sand-washing. - -The cost of sand-washing in Germany with the “drum” washers is said -to be from 14 to 20 cents per cubic yard, including labor, power, and -water. In America the water would cost no more, but the labor would be -perhaps twice as dear. With an ejector apparatus I should estimate the -cost of washing dirty sand as follows: The sand would be brought and -dumped near to the washer, and one man could easily feed it in, as no -lifting is required. Two men would probably be required to shovel the -washed sand into barrows or carts with the present arrangements, but I -think with a little ingenuity this handling could be made easier. - - -ESTIMATED COST OF OPERATING EJECTOR WASHERS 9 HOURS. - - Wages of 3 men at $2.00 $6.00 - 110,000 gals, water (15 times the volume of sand) - at 0.05 a thousand gals. 5.50 - ----- - Total cost of washing 36 cubic yards $11.50 - or 32 cents a cubic yard. - -The cost of washing new sand might be somewhat less. The other costs of -cleaning filters, scraping, transporting, and replacing the sand are -much greater than the washing itself. Lindley states that at Warsaw 29 -days’ labor of 10 hours for one man are required to scrape an acre of -filter surface, and four times as much for the annual deep scraping, -digging up, and replacing the sand. The first expense occurs in general -monthly, and the second only once a year. At other places where I have -secured corresponding data the figures range from 19 to 40 days’ labor -to scrape one acre, and average about the same as Lindley estimates. - -Under some conditions sand-washing does not pay, and in still others -it is almost impossible. No apparatus has yet been devised which will -wash the dirt out of the fine dune-sands used in Holland without -washing a large part of the sand itself away, and in these works fresh -sand, which is available in unlimited quantities and close to the -works, is always used. At Breslau the dirty sand is sold for building -purposes for one third of the price paid for new sand dredged from the -river, delivered at the works, and no sand is ever washed. Budapest, -Warsaw, and Rotterdam also use fresh river-sand without washing, except -a very crude washing to remove clay at Budapest. - - - - -CHAPTER VI. - -THEORY AND EFFICIENCY OF CONTINUOUS FILTRATION. - - -The first filters for a public water-supply were built by James -Simpson, engineer of the Chelsea Water Company at London in 1829. They -were apparently intended to remove dirt from the water in imitation -of natural processes, and without any very clear conception of either -the exact extent of purification or the way in which it was to be -accomplished. The removal of turbidity was the most obvious result, and -a clear effluent was the single test of the efficiency of filtration, -as it remains the legal criterion of the work of the London filters -even to-day, notwithstanding the discovery and use of other and more -delicate tests. - -The invention and use of methods for determining the organic matters -in water by Wanklyn and Frankland, about 1870, led to the discovery -that the proportion of organic matters removed by filtration was -disappointingly low, and as, at the time, and for many years afterward, -an exaggerated importance was given to the mere quantities of organic -matters in water, it was concluded that filtration had only a limited -influence upon the healthfulness of the filtered water, and that -practically as much care must be given to securing an unpolluted water -as would be the case if it were delivered direct without filtration. -This theory, although not confirmed by more recent investigation, -undoubtedly has had a good influence upon the English works by causing -the selection of raw waters free from excessive pollutions, and, in -cases like the London supplies, drawn from the Thames and the Lea, in -stimulating a most jealous care of the watersheds and the purification -of sewage by the towns upon them. - -It was only after the discovery of the bacteria in water and their -relations to health that the hygenic significance of filtration -commenced to be really understood. Investigations of the bacteria in -the waters before and after filtration were carried out at Berlin -by Plagge and Proskauer, at London by Dr. Percy Frankland, and also -at Zürich, Altona, and on a smaller scale at other places. These -investigations showed that the bacteria were mainly removed by -filtration, the numbers in the effluents rarely exceeding two or three -per cent of those in the raw water. This gave a new aspect to the -problem. - -It was further observed, especially at Berlin and Zürich, that the -numbers of bacteria in effluents were apparently quite independent -of the numbers in the raw water, and the theory was formed that all -of the bacteria were stopped by the filters, and that those found in -the effluents were the result of contamination from the air and of -growths in the underdrains. The logical conclusion from this theory was -that filtered water was quite suitable for drinking regardless of the -pollution of its source. - -It was, however, found that the numbers of bacteria in the effluents -were higher immediately after scraping than at other times, and it was -concluded that before the formation of the sediment layer some bacteria -were able to pass the sand, and it was therefore recommended that the -first water filtered after scraping should be rejected. - -Piefke at Berlin gave the subject careful study, and came to the -conclusion that it was almost entirely the sediment layer which -stopped the bacteria, and that the bacteria themselves in the sediment -layer formed a slimy mass which completely intercepted those in the -passing water. When this layer was removed by scraping, the action -was stopped until a new crop of bacteria had accumulated. In support -of this idea he stated that he had taken ordinary good filter-sand -and killed the bacteria in it by heating it, and that on passing -water through, no purification was effected—in fact, the effluent -contained more bacteria than the raw water. After a little, bacteria -established themselves in the sand, and then the usual purification -was obtained. Piefke concluded that the action of the filter was a -biological one; that simple straining was quite inadequate to produce -the results obtained; that the action of the filter was mainly confined -to the sediment layer, and that the depth of sand beyond the slight -depth necessary for the support of this layer had no appreciable -influence upon the results. The effect of this theory is still seen in -the shallow sand layers used at Berlin and some other German works, -although at London the tendency is rather toward thicker sand layers. - -Piefke’s deductions, however, are not entirely supported by his data -as we understand them in the light of more recent investigation. -The experiment with sterilized sand has been repeatedly tried at -the Lawrence Experiment Station with results which quite agree with -Piefke’s, but it has also been found that the high numbers, often many -times as high as in the raw water, do not represent bacteria which pass -in the ordinary course of filtration, but instead enormous growths of -bacteria throughout the sand supported by the cooked organic matter in -it. It has been repeatedly found that ordinary sand quite incapable of -supporting bacterial growths, after heating to a temperature capable -of killing the bacteria will afterwards furnish the food for most -extraordinary numbers. A filter of such sand may stop the bacteria of -the passing water quite as effectually as any other filter, but if so, -the fact cannot be determined without recourse to special methods, on -account of the enormous numbers of bacteria in the sand, a small part -of which are carried forward by the passing water, and completely mask -the normal action of the filter. - -The theory that all or practically all of the bacteria are intercepted -by the sediment layer, and that those in the effluent are the result -of growths in the sand or underdrains, received two hard blows in 1889 -and 1891, when mild epidemics of typhoid fever followed unusually -high numbers of bacteria in the effluents at Altona and at Stralau in -Berlin, with good evidence in each case that the fever was directly due -to the water. Both of these cases came during, and as the result of, -severe winter weather with open filters and under conditions which are -now recognized as extremely unfavorable for good filtration. - -As a result of the first of these epidemics a series of experiments -were made at Stralau by Fränkel and Piefke in 1890. Small filters were -constructed, and water passed exactly as in the ordinary filters. -Bacteria of special kinds not existing in the raw water or effluents -were then applied, and the presence of a very small fraction of them -in the effluents demonstrated beyond a doubt that they had passed -through the filters under the ordinary conditions of filtration. These -experiments were afterwards repeated by Piefke alone under somewhat -different conditions with similar results. The numbers of bacteria -passing, although large enough to establish the point that some do -pass, were nevertheless in general but a small fraction of one per cent -of the many thousands applied. - -This method of testing the efficiency of filters had already been -used quite independently by Prof. Sedgwick at the Lawrence Experiment -Station in connection with the purification of sewage, and has since -been extensively used there for experiments with water-filtration. - -Kümmel also found at Altona that while in the regular samples for -bacterial examination, all taken at the same time in the day, there -was no apparent connection between the numbers of bacteria in the raw -water and effluents, by taking samples at frequent intervals throughout -the twenty-four hours, as has been done in a more recent series of -experiments, and allowing for the time required for the water to pass -the filters, a well-marked connection was found to exist between the -numbers of bacteria in the raw water and in the effluents. - -[Illustration: FIG. 14.—SHOWING BACTERIA SUPPOSED TO COME THROUGH -FILTERS AND FROM THE UNDERDRAINS.] - -The subject has more recently been studied in much detail at the -Lawrence Experiment Station, and it now appears that the bacteria -in the effluent from a filter are from two sources: directly from -the filtered water, and from the lower layers of the filter and -underdrains. Thus we may say: - - Bacteria in effluent = Bacteria from underdrains + _a_/100 × bacteria - in raw water, - -where _a_ is the per cent of bacteria actually passing the filter. - -Both of these terms depend upon a whole series of complex and but -imperfectly understood conditions. In general the bacteria from the -underdrains are low in cold winter weather, often almost _nil_, while -at Lawrence with water temperatures of 70 to 75 degrees, and over, in -July and August, the numbers from this source may reach 200 or 300, -but for the other ten months of the year rarely exceed 50 under normal -conditions. In summer especially it seems to be greater at low than -at high rates of filtration (although a high rate for a short time -only increases it), and so varies in the opposite way from the numbers -actually passing the filters. This subject is by no means clearly -understood; it is difficult, almost impossible, to separate the numbers -of bacteria into the two parts—those which come directly through and -may be dangerous, and those which have other origins and are harmless. -The sketch, Fig. 14, is drawn to represent my idea of the way they may -be divided. It has no statistical basis whatever. The light unshaded -section shows the percentage number of bacteria which I conceive to -be coming through a filter under given conditions at various rates of -filtration, while the shaded section above represents the bacteria from -other sources, and the upper line represents the sum of the two, or -the total number of bacteria in the effluent. The relative importance -of the two parts would probably vary widely with various conditions. -With the conditions indicated by the sketch the number of bacteria in -the effluent is almost constant: for a variation of only from 1.4 to -2.5 per cent of the number applied for the whole range is not a wide -fluctuation for bacterial results, but the number in the lower and -dangerous section is always rapidly increasing with increasing rate. - -This theory of filtration accounts for many otherwise perplexing facts. -The conclusion reached at Zürich and elsewhere that the efficiency of -filtration is independent of rate may be explained in this way. This is -especially probable at Zürich, where the number of bacteria in the raw -water was only about 200, and an extremely large proportion relatively -would have to pass to make a well-marked impression upon the total -number in the effluent. - -These underdrain bacteria are, so far as we know, entirely harmless; -we are only interested in them to determine how far they are capable -of decreasing the apparent efficiency of filtration below the actual -efficiency, or the per cent of bacteria really removed by the filter. - -This efficiency is dependent upon a large number of conditions many -of which have already been discussed in connection with grain-size -of filter sand, underdrains, rate of filtration, loss of head, etc., -and a mere reference to them here will suffice. Perhaps the most -important single condition is the rate, the numbers of bacteria passing -increase rapidly with it. Next, fine sand and in moderately deep -layers tends to give high efficiency. The influence of the loss of -head, often mentioned, is not shown to be important by the Lawrence -results, nor can I find satisfactory European results in support of -it. Uniformity in the rate of filtration on all parts of the filtering -area and a constant rate throughout the twenty-four hours are regarded -as essential conditions for the best results. Severe winter weather -has indirectly, by disturbing the regular action of open filters, an -injurious influence, and has been the cause of most of the cases where -filtered waters have been known to injure the health of those who have -drunk them. This action is excluded in filters covered with masonry -arches and soil, and such construction is apparently necessary for the -best results in places subject to cold winters. - -The efficiency of filtration under various conditions has been studied -by a most elaborate series of experiments at Lawrence with small -filters to which water has been applied containing a bacterium (_B. -prodigiosus_) which does not occur naturally in this country and is -not capable of growing in the filter, so that the results should -represent only the bacteria coming through the filter and not include -any additions from the underdrains. These results, which have been -published in full in the reports of the Massachusetts State Board of -Health, especially for the years 1892 and 1893, show that the number -of bacteria passing increases rapidly with increasing rate, and slowly -with decreasing sand thickness and increased size of sand-grain. - -Assuming that the number of bacteria passing is expressed by the formula - - 1 [(rate)^2 × effective size of sand] - Per cent bacteria passing = — ———————————————————————————————————————— - 2 ([sqrt](thickness of the sand in inches)) - -where the rate is expressed in million gallons per acre daily, and -calculating by it the numbers of bacteria for the seventy-three months -for which satisfactory data are available from 11 filters in 1892 and -1893, we find that - - In 14 cases the numbers observed were 4 to 9 times as great as the - calculated numbers; - - In 6 cases they were 2 to 3 times as great; - - In 35 cases they were between 1/2 and 2 times the calculated numbers. - - In 17 cases they were 1/2 to 1/3 of them. - - In 11 cases they were less than 1/3 the calculated numbers. - -The agreement is only moderately good, and in fact no such formula -could be expected to give more than very rough approximations, because -it does not take into consideration the numerous other elements, such -as uniformity and regularity of filtration, the influence of scraping, -the character of the sediment in the raw water, etc., which are known -to affect the results. Perhaps the most marked general difference is -the tendency of new or freshly-filled filters to give higher, and -of old and well-compacted filters to give lower, results than those -indicated by the formula. - -Comparing this formula with Piefke’s results given in his “Neue -Ermittelungen”[28] the formula gives in the first series (0.34 mm. -sand, 0.50 m. thick, and rate 100 mm. per hour), 0.25 per cent passing, -while the average number of _B. violacious_ reported, excluding the -first day of decreased efficiency after scraping, was 0.26 per cent. In -the second series, with half as high a rate the numbers checked exactly -the calculated 0.06 per cent. - -In other experiments,[29] however, in 1893, when the calculated per -cent was also 0.25, only 0.03, 0.04, and 0.07 per cent were observed in -the effluents. - -Comparing the results from the actual filters, (which numbers also -include the bacteria from the underdrains and should therefore be -somewhat higher) with the numbers calculated as passing through, -I find that for the 46 days, Aug. 20 to Oct. 4, 1893, for which -detailed results of the Stralau works are given by Piefke, the average -calculated number passing is 0.20 per - -cent, while twice as many were observed in the effluents; although -three of the filters gave better effluents than the other eight, and -the numbers from them approximated closely the calculated numbers. If -we calculate the percentages of bacteria passing a number of filters, -using the maximum rate of filtration allowed for the German filters -where this is accurately determined, and for the English filters -taking the maximum rate at one and one-half times the rate obtained by -dividing the daily quantity by the area of filters actually in use, we -obtain: - - ----------------------+--------+---------+-----------+-------------- - |Average |Effective| Maximum | Per cent - |Depth of| Size of | Rate of | Bacteria - | Sand, | Sand- |Filtration.| passing - | Inches.| grain. | | 1 r^2d - | | | |= - ---------- - | | | | 2 [sqrt]sand - ----------------------+--------+---------+-----------+-------------- - Hamburg | 32 | 0.31 | 1.60 | 0.07 - Altona | 28 | 0.34 | 2.57 | 0.21 - Berlin, Stralau | 20 | 0.34 | 2.57 | 0.25 - Berlin, Müggel | 20 | 0.34 | 2.57 | 0.25 - Berlin, Tegel | 20 | 0.37 | 2.57 | 0.27 - London, Southwark & | | | | - Vauxhall | 36 | 0.34 | 2.81 | 0.22 - London, West Middlesex| 39 | 0.37 | 2.81 | 0.23 - London, Chelsea | 54 | 0.36 | 3.27 | 0.26 - London, Grand Junction| 30 | 0.40 | 3.27 | 0.39 - London, Lambeth | 36 | 0.36 | 3.75 | 0.42 - Middlesborough | 20 | 0.42 | 5.85 | 1.58 - Zürich | 26 | 0.35 | 7.50 | 1.90 - ----------------------+--------+---------+-----------+-------------- - -The numbers actually observed are in every case higher than the -calculated per cents passing, as indeed they should be on account of -those coming from the underdrains, accidental contamination of the -samples, etc. - -It may be said that filtration now practised in European works under -ordinary conditions never allows over 1 or 2 per cent bacteria of the -raw water to pass, and ordinarily not over one fourth to one half -of one per cent, although exact data cannot be obtained owing to -masking effect of the bacteria which come from below and which bear -no relation to those of the raw water. By increasing the size of the -filters, fineness and depth of sand (as at Hamburg), the efficiency -can be materially increased above these figures. At the same time -it must be borne in mind that the effectiveness of a filter may be -greatly impaired by inadequate underdraining, by fluctuating rates of -filtration where these are allowed, by freezing in winter in the case -of open filters in cold climates, and by other irregularities, all of -which can be prevented by careful attention to the respective points. - -The action of a continuous filter throughout is mainly that of an -exceedingly fine strainer, and like a strainer is mainly confined to -the suspended or insoluble matters in the raw water. The turbidity, -sediment, and bacteria of the raw water are largely or entirely -removed, while hardness, organic matter, and color, so far as they are -in solution, are removed to only a slight extent, if at all. Hardness -can be removed by the addition of lime in carefully determined quantity -before filtration (Clark’s process), by means of which the excess of -carbonic acid in the water is absorbed and the lime added, together -with that previously in the water, is precipitated. - -Ordinary filtration will remove from one fourth to one third of the -yellow-brown color of peaty water. A larger proportion can be removed -by the addition of alum, which by decomposing forms an insoluble -compound of alumina with the coloring matter, while the acid of the -alum goes into the effluent either as free acid, or in combination with -the lime or other base in the water, according to their respective -quantities. Freshly precipitated alumina can be substituted for the -alum at increased expense and trouble, and tends to remove the color -without adding acid to the water. These will be discussed more in -detail in connection with mechanical filters. Alum is but rarely used -in slow sand filtration, the most important works where it is used -being in Holland with peaty waters. - -After all, the most conclusive test of the efficiency of filtration is -the healthfulness of the people who drink the filtered water; and the -fact that many European cities take water-supplies from sources which -would not be considered fit for use in the United States and, after -filtering them, deliver them to populations having death-rates from -water-carried diseases which are so low as to be the objects of our -admiration, is the best proof of the efficiency of carefully conducted -filtration. - -It is only necessary to refer to London, drawing its water from the -two small and polluted rivers, the Thames and the Lea; to Altona, -drawing its water from the Elbe, polluted by the sewage of 6,000,000 -people, 700,000 of them within ten miles above the intakes; to Berlin, -using the waters of the Havel and the Spree; to Breslau, taking its -water from the Oder charged with the sewage of mining districts in -Silicia and Galicia, where cholera is so common; to Lawrence, with its -greatly decreased death-rate since it has had filtered water, and to -the hundred other places which protect themselves from the infectious -matters in their raw waters by means of filtration. A few of these -cases are described more in detail in Appendices V to IX, and many -others in the literature mentioned in Appendix X. - -An adequate presentation of even those data which have been already -worked up and published would occupy too much space. I think every one -who has carefully studied the recent history of water filtration in -its relation to disease has been convinced that filtration carefully -executed under suitable and normal conditions, even if not an absolute, -is at least a very substantial protection against water-carried -diseases, and the few apparent failures to remove objectionable -qualities have been without exception due to abnormal conditions which -are now understood and in future can be prevented. - - -BACTERIAL EXAMINATION OF WATERS. - -Every large filter-plant should have arrangements for the systematic -bacterial examination of the water before and after filtration, -especially where the raw water is subject to serious pollution. Such -examinations need not be excessively expensive, and they will not -only show the efficiency of the plant as a whole, but may be made to -show the relative efficiencies of the separate filters, the relative -efficiencies at different parts of the periods of operation, the effect -of cold weather, etc., and will then be a substantial aid to the -superintendent in always securing good effluents at the minimum cost. - -In addition a complete record of the bacteria in the water at different -times may aid in determining definitely whether the water was connected -with outbreaks of disease. Thus if an outbreak of disease of any -kind were preceded at a certain interval by a great increase in the -number of bacteria,—as has been the case, for example, with the -typhoid epidemics at Altona and Berlin (see Appendices II and VII),—a -presumption would arise that they might have been connected with -each other, and each time it was repeated the presumption would be -strengthened, while, on the other hand, outbreaks occurring while the -bacteria remained constantly low would tend to discredit such a theory. - -Bacterial investigations inaugurated after an epidemic is recognized, -as has frequently been done, seldom lead to results of value, both -because the local normal bacterial conditions are generally unknown at -the commencement of the investigation, and because the most important -time, the time of infection, is already long past before the first -samples are taken. The fact that such sporadic activities have led -to few definite results should throw no discredit upon continued -observations, which have repeatedly proved of inestimable value. - -Considerable misconception of the use of bacterial examinations -exists. The simple bacterial count ordinarily used, and of which I -am now speaking, does not and cannot show whether a water contains -disease-germs or not. I object to the Chicago water, not so much -because a glass of it contains a hundred thousand bacteria more -or less, as because I am convinced, by a study of its source in -connection with the city’s death-rate, that it actually carries -disease-germs which prove injurious to thousands of those who drink -it. Now the fact being admitted that the water is injurious to health, -variations in the numbers of bacteria in the water drawn from different -intakes and at different times probably correspond roughly with varying -proportions of fresh sewage, and indicate roughly the relative dangers -from the use of the respective waters. If filters should be introduced, -the numbers of bacteria in the effluents under various conditions would -be an index of the respective efficiencies of filtration, and would -serve to detect poor work, and would probably suggest the measures -necessary for better results. - -I would suggest the desirability of such investigations where -mechanical filters are used, quite as much as in connection with -slow filtration; and it would also be most desirable in the case of -many water-supplies which are not filtered at all. Such continued -observations have been made at Berlin since 1884; at London since 1886; -at Boston and Lawrence since 1888; and recently at a large number -of places, including Chicago, where observations by the city were -commenced in 1894. They are now required by the German Government in -the case of all filtered public water-supplies in Germany, without -regard to the source of the raw water. The German standard requires -that the effluent from each single filter, as well as the mixed -effluent and raw water, shall be examined daily, making at some works -10 to 30 samples daily. This amount of work, however, can usually be -done by a single man; and when a laboratory is once started, the cost -of examining 20 samples a day will not be much greater than if only -20 a week are taken. In England and at some of the Continental works -drawing their waters from but slightly polluted sources, much smaller -numbers of samples are examined. - -The question whether the examinations should be made under the -direction of the water-works company or department, or by an -independent body—as, for instance, by the Board of Health—will depend -upon local conditions. The former arrangement gives the superintendent -of the filters the best chance to study their action, as he can himself -control the collection of samples in connection with the operation -of the filters, and arrange them to throw light upon the points he -wishes to investigate; while examination by a separate authority -affords perhaps greater protection against the possible carelessness or -dishonesty of water-works officials. An arrangement being adopted in -many cases in Germany is to have a bacterial laboratory at the works -which is under the control of the superintendent, and in which the very -numerous compulsory observations are made, while the Board of Health -causes to be examined from time to time by its own representatives, -who have no connection with the water-works, samples taken to check -the water-works figures, as well as to show the character of the water -delivered. - -It seems quite desirable to have a man whose principal business is to -make these examinations; as in case he also has numerous other duties, -the examinations may be found to have been neglected at some time when -they are most wanted. Such a man should have had thorough training in -the principles of bacterial manipulation, but it is quite unnecessary -that he should be an expert bacteriologist, especially if a competent -bacteriologist is retained for consultation in cases of doubt or -difficulty. - - - - -CHAPTER VII. - -INTERMITTENT FILTRATION. - - -By intermittent nitration is understood that filtration in which the -filtering material is systematically and adequately ventilated, and -where the water during the course of filtration is brought in contact -with air in the pores of the sand. In continuous filtration, which -alone has been previously considered, the air is driven out of the sand -as completely as possible before the commencement of filtration, and -the sand is kept continuously covered with water until the sand becomes -clogged and a draining, with an incidental aeration, is necessary to -allow the filter to be scraped and again put in service. - -In intermittent filtration, on the other hand, water is taken over the -top of the drained sand and settles into it, coming in contact with -the air in the pores of the sand, and passes freely through to the -bottom when the water-level is kept well down. After a limited time the -application of water is stopped, and the filter is allowed to again -drain and become thoroughly aerated preparatory to receiving another -dose of water. - -This system of treating water was suggested by the unequalled -purification of sewage effected by a similar treatment. It has been -investigated at the Lawrence Experiment Station, and applied to the -construction of a filter for the city of Lawrence, both of which are -due to the indefatigable energy of Hiram F. Mills, C.E. - -In its operation intermittent differs from continuous filtration in -that the straining action is less perfect, because the filters yield -no water while being aerated, and must therefore filter at a greater -velocity when in use to yield the same quantity of water in a given -time, and also on account of the mechanical disturbance which is -almost invariably caused by the application of the water; but, on the -other hand, the oxidizing powers of the filter, or the tendency to -nitrify and destroy the organic matters, are stronger, and in addition, -if the rate is not too high, the bacteria die more rapidly in the -thoroughly aerated sand than is the case with ordinary filters. - -It was found at Lawrence in connection with sewage filters that when -nitrification was actively taking place the numbers of bacteria were -much lower than under opposite conditions, and it was thought that -nitrification in itself might cause the death of the bacteria. Later -experiments, however, with pure cultures of bacteria of various kinds -applied to intermittent filters with water to which ammonia and salts -suitable for nitrification were added, showed that bacteria of all -the species tried were able to pass the filter in the presence of -nitrification, producing at least one thousand times as much nitrates -as could result in any case of water-filtration, as freely as was -the case when the ammonia was not added and there was but little -nitrification. These results showed conclusively that nitrification -in itself is not an important factor in bacterial removal, although -nitrification and bacterial purification do to some extent go together; -perhaps in part because the nitrification destroys the food of the -bacteria and so starves them out, but probably much more because the -conditions of aeration, temperature, etc., which favor nitrification -also favor equally, and even in its absence, the death of the bacteria. - -The rate at which water must pass through an intermittent filter -is, on account of the intervals of rest, considerably greater than -that required to give a corresponding total yield from a continuous -filter, and its straining effect is reduced to an extent comparable to -this increase in rate; and if other conditions did not come in, the -bacterial efficiency of an intermittent filter would remain below that -of a continuous one. - -As a matter of fact the bacterial efficiency has usually been found -to be less with intermittent filters at the Lawrence Experiment -Station, when they have been run at rates such as are commonly used for -continuous filters in Europe, say from one and one half to two million -gallons and upwards per acre daily. With lower rates, and especially -with rather fine materials, the bacterial efficiency is much greater; -but it may be doubted whether it would ever be greater than that of a -continuous filter with the same filtering material and the same total -yield per acre. The number of bacteria coming from the underdrains is -apparently generally less, and with very high summer temperatures much -less, than in continuous filters, and this often gives an apparent -bacterial superiority to the intermittent filters. - -The effluents from intermittent often contain less slightly organic -matter than those from continuous filters; but, on the other hand, -hardly any water proposed for a public water-supply has organic matter -enough to be of any sanitary significance whatever, apart from the -living bodies which often accompany it; and if the latter are removed -by straining or otherwise, we can safely disregard the organic matters. -In addition, the water filtered will in a great majority of cases have -enough air dissolved in itself to produce whatever oxidation there is -time for in the few hours required for it to pass the filter, and it is -only at very low rates of filtration that intermittent filters produce -effluents of greater chemical purity than by the ordinary process. The -yellow-brown coloring matter present in so many waters appears to be -quite incapable of rapid nitrification; and where it is to some extent -removed by filtration, the action is dependent upon other and but -imperfectly understood causes which seem to act equally in continuous -and intermittent filters. - -The peculiarities of construction involved by this method of filtration -will be best illustrated by a discussion of the Lawrence city filter -designed by Hiram F. Mills, C.E., which is the only filter in existence -upon this plan.[30] - - -THE LAWRENCE FILTER. - -The filter consists of a single bed 2-1/2 acres in area, the bottom of -which is 7 feet below low water in the river, and filled with gravel -and sand to an average depth of 4-1/2 feet. The filter is all in a -single bed instead of being divided into the three or four sections -which would probably have been used for a continuous filter of this -size. The water-tight bottom also was dispensed with, and the gravel -was prevented from sinking into the silt by thin intermediate layers -of graded materials. The saving in cost was considerable; but, on the -other hand, a considerable quantity of ground-water comes up through -the bottom and increases the hardness of the water from 1.5 to 2.6 -parts of calcium carbonate in 100,000; and while the water when -compared with many other waters is still extremely soft, the addition -cannot be regarded as desirable. The ground-water also contains iron, -which increases the color of the water above what it would otherwise be. - -The underdrains have a frictional resistance ten times as great as -would be desirable for a continuous filter, the idea being to check -extreme rates of filtration in case of unequal flooding, and also to -limit the quantity of water which could be gotten through the filter to -that corresponding to a moderate rate of filtration. - -The sand, instead of being all of the same-sized grain, is of two -grades, with effective sizes respectively 0.25 and 0.30 mm., the -coarser sand being placed farthest away from the underdrains, where -its greater distance is intended to balance its reduced frictional -resistance and make all parts filter at an equal rate. - -The surface instead of being level is waved, that is, there are ridges -thirty feet apart, sloping evenly to the valleys one foot deep half -way between them, to allow water to be brought on rapidly without -disturbing the sand surface. For the same reason, as well as to secure -equality of distribution, a system of concrete carriers for the raw -water goes to all parts of the filter, reducing the effective filtering -area by 4 or 5 per cent. The filter is scraped as necessary in -sections, the work being performed when the filter is having its daily -rest and aeration. Owing to the difference in frictional resistance -before and after scraping, and to the fact that it is impossible to -scrape the entire area in one day, considerable variations in the rate -of filtration in different parts of the filter must occur. The heavy -frictional resistance of the underdrains when more than the proper -quantity of water passes them tends to correct this tendency especially -for the more remote parts of the filter, but perhaps at the expense of -those near to the main drain. - -The filter is not covered as the suggestions in Chapter II would -require, but this is hardly on account of its being an intermittent -filter. - -The annual report of the Massachusetts State Board of Health for 1893 -states that during the first half of December, 1893, the surface -remained covered, that is, it was used continuously, and after December -16th it was so used when the temperature was below 24°, and was drained -only when the temperature was 24° or above. The days on which the -filter was drained during the remainder of December are not given, but -during January and February, 1894, the filter remained covered 29 days -and was drained 30 days. Bacterial samples were taken on 44 of these -days, 22 days when it was drained and 22 when it was not. The average -number of bacteria on the days when it was not drained was 137 and on -those days when it was drained 252 per cubic centimeter. - -From February 24th to March 12th the number of bacteria were unusually -high, averaging 492 per cubic centimeter, or 5.28 per cent of the 9308 -applied. During this period the filter was used intermittently; there -was ice upon it, and parts of the surface were scraped under the ice, -and high rates of filtration undoubtedly resulted on the scraped areas. -After March 12th the ice had disappeared and very much better results -were obtained. - -While there may be some question as to the direct cause of this -decreased efficiency with continued cold weather and ice, the results -certainly are not such as to show the advisability of building open -filters in the Lawrence climate. - -The cost of building the filter in comparison with European filters -was extraordinarily low—only $67,000, or $27,000 per acre of filter -surface. To have constructed open continuous filters of the same area -with water-tight bottoms, divided into sections with separate drains -and regulating apparatus, with the necessary piping, would have cost at -least half as much more, and with the masonry cover which I regard as -most desirable in the Lawrence climate the cost would have been two or -three times the expenditure actually required. - -It was no easy matter to secure the consent of the city government to -the expenditure of even the sum used; there was much skepticism as to -the process of filtration in general, and it was said that mechanical -filters could be put in for about the same cost. Insisting upon the -more complete and expensive form might have resulted either in an -indefinite postponement of action, or in the adoption of an inferior -and entirely inadequate process. Still I feel strongly that in the -end the greater expense would have proved an excellent investment in -securing softer water and in the greater facility and security of -operating the filter in winter. - -In regard to the effect of the Lawrence filter upon the health of -the city, I can best quote from Mr. Mills’ paper in the Report of -the Massachusetts State Board of Health for 1893, and also published -in the Journal of the New England Water-works Association. Mr. Mills -says: “In the following diagram [Fig. 15] the average number of deaths -from typhoid fever at Lawrence for each month from October to May, in -the preceding five years, are given by the heavy dotted line; and the -number during the past eight months are given by the heavy full line. - -“The total number for eight months in past years has been forty-three, -and in the present year seventeen, making a saving of twenty-six. Of -the seventeen who died nine were operatives in the mills, each of whom -was known to have drunk unfiltered canal water, which is used in the -factories at the sinks for washing. - -[Illustration: FIG. 15.—TYPHOID FEVER IN LAWRENCE.] - -“The finer full line shows the number of those who died month after -month who are not known to have used the poisoned canal water. The -whole number in the eight months is eight. - -“It is evident from the previous diagram [not reproduced] that the -numbers above the fine full line, here, follow after those at Lowell in -the usual time, and were undoubtedly caused by the sickness at Lowell; -but we have satisfactory reason to conclude that the disease was not -propagated through the filter but that the germs were conveyed directly -into the canals and to those who drank of the unfiltered canal water. -Among the operatives of one of the large corporations not using the -canal water there was not a case of typhoid fever during this period. -Warnings have been placed in the mills where canal water is used to -prevent the operatives from drinking it. - -“We find, then, that the mortality from typhoid fever has, during the -use of the filter, been reduced to 40 per cent of the former mortality, -and that the cases forming nearly one half of this 40 per cent were -undoubtedly due to the continued use of unfiltered river water drawn -from the canals.” - -The records of typhoid fever in Lawrence before and after the -introduction of filters are as follows: - - -DEATHS FROM TYPHOID FEVER IN LAWRENCE, 1888-98. - - --------+----------+-------------+------------------------------------ - | | | Persons who are known to have been - Years. | Total | Deaths | exposed to infection. - | Number | per +--------------+--------------------- - | of | 10,000 | | While living out - | Deaths. | of | By drinking | of town just before - | | Population. | Canal Water. | falling sick in - | | | | Lawrence. - --------+----------+-------------+--------------+--------------------- - 1888 | 48 | 11.36 | | - 1889 | 55 | 12.66 | | - 1890 | 60 | 13.44 | | - 1891 | 55 | 11.94 | | - 1892 | 50 | 10.52 | | - 1893 | 39 | 7.96 | | - 1894 | 24 | 4.75 | 12 | - 1895 | 16 | 3.07 | 9 | 2 - 1896 | 10 | 1.86 | 2 | 4 - 1897 | 9 | 1.62 | | - 1898 | 8 | 1.39 | 1 | - --------+----------+-------------+--------------+--------------------- - Filter put in operation September, 1893. - Average rate before the introduction of filtered water (1888-92) 11.31 - Average rate afterward (1894-98) 2.54 - -These results show a striking reduction in the deaths from typhoid -fever with the introduction of filtered water, which has been most -gratifying in every way. - -The more recent history of the underdrains of the Lawrence filter -is particularly instructive. Owing to the absence of a water-tight -bottom to the filter, and its low position, a certain amount of water -constantly entered the filter from the ground below. This water -contained iron in solution as ferrous carbonate. When this water came -in contact with the filtered water in the gravel and underdrains, the -iron was oxidized by the dissolved oxygen carried in the filtered water -and precipitated. This was accompanied by a growth of crenothrix in -the gravel and underdrains, which gradually reduced their carrying -capacity. This reduction in carrying capacity first became apparent -in cold weather when the yield from the filter was less free than -formerly. There was difficulty in maintaining the supply during the -winter of 1896-7 and more difficulty in the following winter. - -[Illustration: FIG. 16.—TYPHOID FEVER IN LAWRENCE, 1888 TO 1898.] - -The sand of the filter was as capable of filtering the full supply -of water as it ever had been, and the efficiency was as good; but -the underdrains were no longer able to collect the filtered water -and deliver it. As the filtering area was ample for the supply, it -was desired to avoid construction of additional filtering area. The -underdrains were dug up and cleaned during the periods when the filter -was drained. As the filter is all in one bed, the times when the filter -could be allowed to remain drained, and when the work could proceed, -were limited. Great care was taken to leave the work in good condition, -and free from passages, at the end of each day’s work, but the numbers -of bacteria in the effluent nevertheless increased somewhat. Some -weeks afterward the number of cases of typhoid fever in the city -increased. The numbers did not become as high as they had been prior to -the introduction of filtered water, but they were much higher than they -had been since that time, and they pointed strongly to the disturbance -of the underdrains as the cause of the increase. - -The numbers of bacteria in the applied water and in the effluent from -the Lawrence filter by months, from the time the filter was put in -operation, compiled from the reports of the State Board of Health, as -far as available, are as follows: - - -BACTERIA IN WATER APPLIED TO AND EFFLUENT FROM LAWRENCE FILTER. - - - RAW WATER. - - ----------------+--------+--------+--------+--------+--------+-------- - | 1893. | 1894. | 1895. | 1896. | 1897. | 1898. - ----------------+--------+--------+--------+--------+--------+-------- - January | | 7,700 | 18,700 | 7,500 | 13,314 | 6,519 - February | | 7,600 | 15,040 | 12,600 | 13,113 | 4,653 - March | | 6,500 | 20,770 | 5,900 | 12,055 | 3,748 - April | | 11,200 | 8,420 | 3,800 | 6,904 | 2,320 - | | | | | | - May | | 6,000 | 7,000 | 9,600 | 4,625 | 2,050 - June | | 8,300 | 9,000 | 6,400 | 4,650 | 6,775 - July | | 2,400 | 10,000 | 3,900 | 6,240 | 2,840 - August | | 3,100 | 5,000 | 2,700 | 10,700 | 8,575 - | | | | | | - September | 57,500 | 6,500 | 5,000 | 12,300 | 27,300 | 6,100 - October | 22,200 | 25,300 | 19,000 | 5,300 | 13,200 | 5,120 - November | 10,800 | 16,600 | 8,700 | 5,600 | 6,644 | 4,310 - December | 8,100 | 23,800 | 6,700 | 9,695 | 5,581 | 5,200 - +--------+--------+--------+--------+--------+-------- - Average | 24,650 | 10,417 | 11,111 | 7,108 | 10,360 | 4,850 - - EFFLUENT. - - January | | 129 | 206 | 166 | 91 | 39 - February | | 244 | 283 | 315 | 79 | 45 - March | | 455 | 405 | 133 | 67 | 34 - April | | 281 | 84 | 40 | 47 | 21 - | | | | | | - May | | 134 | 68 | 56 | 35 | 48 - June | | 110 | 68 | 22 | 56 | 50 - July | | 25 | 50 | 39 | 106 | 22 - August | | 36 | 38 | 146 | 72 | 28 - | | | | | | - September | 6,850 | 42 | 40 | 37 | 98 | 67 - October | 1,216 | 116 | 60 | 30 | 33 | 28 - November | 161 | 175 | 64 | 37 | 27 | 122 - December | 111 | 364 | 84 | 67 | 24 | - +--------+--------+--------+--------+--------+-------- - Average | 2,084 | 176 | 121 | 91 | 61 | 46 - | | | | | | - Average | | | | | | - efficiency | 91.55 | 98.31 | 98.91 | 98.72 | 99.41 | 98.95 - - -CHEMNITZ WATER-WORKS. - -The only other place which I have found where anything approaching -intermittent filtration of water is systematically employed is -Chemnitz, Germany. The method there used bears the same relation to -intermittent filtration as does broad irrigation of sewage to the -corresponding method of sewage treatment; that is, the principles -involved are mainly the same, but a much larger filtering area is used, -and the processes take place at a lower rate and under less close -control. - -[Illustration: FIG. 17.—PLAN OF AREA USED FOR INTERMITTENT FILTRATION -AT CHEMNITZ.] - -The water-works were built about twenty years ago by placing -thirty-nine wells along the Zwönitz River, connected by siphon pipes, -with a pumping-station which forced the water to an elevated reservoir -near the city (Fig. 17). The wells are built of masonry, 5 or 6 feet in -diameter and 10 or 12 feet deep, and are on the rather low bank of the -river. The material, with the exception of the surface soil, and loam -about 3 feet deep, is a somewhat mixed gravel with an effective size of -probably from 0.25 to 0.50 mm., so that water is able to pass through -it freely. The wells are, on an average, about 120 feet apart, and the -line is seven eighths of a mile long. - -It was found that in dry times the ground-water level in the entire -neighborhood was lowered some feet below the level of the river without -either furnishing water enough or stopping the flow of the river below. -The channel of the river was so silted that, notwithstanding the porous -material, the water could not penetrate it to go toward the wells. - -A dam was now built across the river near the pumping-station, and -a canal was dug from above the dam, crossing the line of wells and -running parallel to it on the back side for about half a mile. Later a -similar canal was dug back of the remaining upper wells. Owing to the -difference in level in the river above and below, the canals can be -emptied and filled at pleasure. They are built with carefully prepared -sand bottoms, and the sand sides are protected by an open paving, to -allow the percolation of as much water as possible, and the sand is -cleaned by scraping, as is usual with ordinary sand filters, once a -year or oftener. - -The yield from the wells was much increased by these canals, but the -water of the river is polluted to an extent which would ordinarily -quite prevent even the thought of its being used for water-supply, and -it was found that the water going into the ground from the canals, -and passing through the always saturated gravel to the wells, without -coming in contact with air at any point, after a time contained iron -and had an objectionable odor. - -To avoid this disagreeable result the meadow below the pumping-station -was laid out as an irrigation field (Fig. 16). The water from above the -dam was taken by a canal on the opposite side of the river through a -sedimentation pond (which, however, is not now believed to be necessary -and is not always used), and then under the river by a siphon to a -slightly elevated point on the meadow, from which it is distributed -by a system of open ditches, exactly as in sewage irrigation. The -area irrigated is not exactly defined and varies somewhat from time -to time; the rate of filtration may be roughly estimated at from -100,000 to 150,000 gallons per acre daily, although limited portions -may occasionally get five times these quantities for a single day. The -water passes through the three feet of soil and loam, and afterward -through an average of six feet of drained coarse sand or gravel in -which it meets air, and afterward filters laterally through the -saturated gravel to the wells. The water so obtained is invariably of -good quality in every way, colorless, free from odor and from bacteria. -The surface of the irrigated land is covered with grass and has -fruit-trees (mostly apple) at intervals over its entire area. - -This first system of irrigation is entirely by gravity. On account -of natural limits to the land it could not be conveniently extended -at this point, and to secure more area, the higher land above the -pumping-station was being made into an irrigation field in 1894. This -is too high to be flooded by gravity, and will be used only for short -periods in extremely dry weather. The water is elevated the few feet -necessary by a gas-engine on the river-bank. In times of wet weather -enough water is obtained from the wells without irrigation, and the -land is only irrigated when the ground-water level is too low. - -During December, January, and February irrigation is usually impossible -on account of temperature, and the canals are then used, keeping them -filled with water so that freezing to the bottom is impossible; but -trouble with bad odors in the filtered water drawn from the wells is -experienced at these times. - -The drainage area of the Zwönitz River is only about 44 square miles, -and upon it are a large number of villages and factories, so that the -water is excessively polluted. The water in the wells, however, whether -coming from natural sources, or from irrigation, or from the canals, -has never had as many as 100 bacteria per cubic centimeter, and is -regarded as entirely wholesome. - -In extremely dry weather the river, even when it is all used for -irrigation so that hardly any flows away below, cannot be made to -supply the necessary daily quantity of 2,650,000 gallons, and to supply -the deficiency at such times, as well as to avoid the use of the canals -in winter, a storage reservoir holding 95,000,000 gallons has recently -been built on a feeder of the river. This water, which is from an -uninhabited drainage area, is filtered through ordinary continuous -filters and flows to the city by gravity. Owing to the small area of -the watershed it is incapable of supplying more than a fraction of the -water for the city, and will be used to supplement the older works. - -This Chemnitz plant is of especial interest as showing the successful -utilization of a river-water so grossly polluted as to be incapable of -treatment by the ordinary methods. Results obtained at the Lawrence -Experiment Station have shown that sewage is incapable of being -purified by continuous filtration, the action of air being essential -for a satisfactory result. With ordinary waters only moderately -polluted this is not so; for they carry enough dissolved air to effect -their own purification. In Chemnitz, however, as shown by the results -with the canals, the pollution is so great that continuous filtration -is inadequate to purify the water, and the intermittent filtration -adopted is the only method likely to yield satisfactory results in such -cases. - -Intermittent filtration is now being adopted for purifying brooks -draining certain villages and discharging into the ponds or reservoirs -from which Boston draws its water-supply. The water of Pegan Brook -below Natick has been so filtered since 1893 with most satisfactory -results, and affords almost absolute protection to Boston from any -infection which might otherwise enter the water from that town. A -similar treatment is soon to be given to a brook draining the city of -Marlborough. The sewage from these places is not discharged into the -brooks, but is otherwise provided for, but nevertheless they receive -many polluting matters from the houses and streets upon their banks. - -The filtration used resembles in a measure that at Chemnitz, and I am -informed by the engineer, Mr. Desmond FitzGerald, that it was adopted -on account of its convenience for this particular problem, and not -because he attaches any special virtue to the intermittent feature. - - -APPLICATION OF INTERMITTENT FILTRATION. - -In regard to the use of waters as grossly polluted as the Zwönitz, -the tendency is strongly to avoid their use, no matter how complete -the process of purification may be; but in case it should be deemed -necessary to use so impure a water for a public supply, intermittent -filtration is the only process known which would adequately purify -it. And it should be used at comparatively low rates of filtration. -I believe that an attempt to filter the Zwönitz at the rate used for -the Merrimac water at Lawrence, which is by comparison but slightly -polluted, would result disastrously. - -The operation in winter must also be considered. Intermittent -filtration of sewage on open fields in Massachusetts winters is only -possible because of the comparatively high temperature of the sewage -(usually 40° to 50°), and would be a dismal failure with sewage at -the freezing-point, the temperature to be expected in river-waters in -winter. - -It is impossible to draw a sharp line between those waters which are -so badly polluted as to require intermittent filtration for their -treatment and those which are susceptible to the ordinary continuous -filtration. Examples of river-waters polluted probably beyond the -limits reached in any American waters used for drinking purposes and -successfully filtered with continuous filters are furnished by Altona, -Breslau, and London. - -Intermittent filtration may be considered in those cases where it -is proposed to use a water polluted entirely beyond the ordinary -limits, and for waters containing large quantities of decomposable -organic matters and microscopical organisms; but in those cases where -a certain and expeditious removal of mud is desired, and where -waters are only moderately polluted by sewage, but still in their raw -state are unhealthy, it is not apparent that intermittent filtration -has any advantages commensurate with the disadvantages of increased -rate to produce the same total yield and of the increased difficulty -of operation, particularly in winter; and in such cases continuous -filtration is to be preferred. - -In the removal of tastes and odors from pond or reservoir waters which -are not muddy, but which are subject to the growths of low forms of -plants, which either by their growth or decomposition impart to the -water disagreeable tastes and odors, intermittent filtration may have a -distinct advantage. In such cases there is often an excess of organic -matter to be disposed of by oxidation, and the additional aeration -secured by intermittent filtration is of substantial assistance in -disposing of these matters. - - - - -CHAPTER VIII. - -TURBIDITY AND COLOR, AND THE EFFECT OF MUD UPON SAND-FILTERS. - - -The ideal water in appearance is distilled water, which is perfectly -clear and limpid, and has a slight blue color. When other waters are -compared with it, the divergences in color from the color of distilled -water are measured, and not the absolute colors of the waters. Many -spring waters and filtered waters are indistinguishable in appearance -from distilled water. - -Public water-supplies from surface sources contain two substances or -classes of substances which injure their appearance, namely, peaty -coloring matters, and mud. Waters discolored by peaty matters are most -common in New England and in certain parts of the Northwest, while -muddy waters are found almost everywhere, but of different degrees of -muddiness, according to the physical conditions of the water-sheds from -which they are obtained. - -Muddy waters are often spoken of as colored waters, and in a sense this -is correct where the mud consists of clays or other materials having -distinct colors; but it is more convenient to classify impurities of -this kind as turbidities only, and to limit the term colored waters to -those waters containing in solution vegetable matters which color them. - -The removal of either color or turbidity may be called clarification. - -Colored waters are usually drawn from water-sheds where the underlying -rock is hard and does not rapidly disintegrate, and where the soils are -firm and sandy, and especially from swamps. The water here comes in -contact with peat or muck, which colors it, but is so firm as not to -be washed by flood flows, and so does not cause turbidity. - -Large parts of the United States have for rock foundations shales or -other soft materials which readily disintegrate when exposed, and -which form clayey soils readily washed by hard rains. Waters from -such watersheds are generally turbid and very rarely colored. In fact -a water carrying much clay in suspension is usually found colorless -when the clay is removed, even if it were originally colored. It thus -happens that waters which are colored and turbid at the same time -hardly exist in nature. - -Color-producing matters and turbidity-producing matters are different -in their natures, and the methods which must be used to remove them are -different. - - -THE MEASUREMENT OF COLOR. - -The colors of waters are measured and recorded by comparing them with -colors of solutions or substances which are permanent, or which can be -reproduced at will. One of the earliest methods of measuring colors of -waters was to compare them with the colors of the Nessler standards -used for the estimation of ammonia in water analysis. The Nessler -standards were similar in appearance to yellow waters, and their colors -depended upon the amounts of ammonia which had been used in preparing -them, and a record was made of the standard which most closely -resembled the water under examination. - -The method was open to the serious objections that the hues of the -standards did not match closely the hues of the waters; that the colors -produced with different lots of Nessler reagent differed considerably, -and therefore the exact values of results were more or less uncertain; -and further, that the numbers obtained for color were not even -approximately proportional to the amounts of coloring matter present. -Because of this peculiarity, in filtration the percentage of color -removal, as determined by the use of these standards, is not even -approximately correct, but is much above the truth. - -In the Lovibond tintometer, which has been extensively used in England, -the standards of color are based upon the colors of certain glass -slips, which are in turn compared with standard originals kept for -that purpose. This process answers quite well, but is open to some -objections because of possible uncertainties in the standardization of -the units. - -Another method of measuring colors is to compare them with dilute -solutions of platinum and cobalt. The ratio of cobalt to platinum can -be varied to make the hue correspond very closely with the hues of -natural waters, and the amount of platinum required to match a water -affords a measure of its color, one part of metallic platinum in 10,000 -parts of water forming the unit of color. - -This standard has the advantages that it can be readily prepared with -absolute accuracy in any laboratory, and that by varying the ratio of -platinum to cobalt the hues of various waters can be most perfectly -matched. It is important that the observations should not be made in -too great a depth, as the discrepancy in hues increases much more -rapidly than the depth of color. - -For further information regarding colors the reader is referred to -articles in the American Chemical Journal, 1892, vol. xiv, page 300; -Journal of the American Chemical Society, vol. ii, page 8; vol. xviii, -1896, pp. 68, 264, and 484; Journal of the Franklin Institute, Dec. -1894, p. 402; Journal of the New England Water Works Association, vol. -xiii, 1898, p. 94. - - -AMOUNT OF COLOR IN AMERICAN WATERS. - -New England surface-waters have colors ranging from almost nothing -up to 2.00. The colors of the public water-supplies of Massachusetts -cities have been recorded in the reports of the State Board of Health -for some ten years. The figures given were recorded first upon the -Nessler standard, and afterwards upon a modification of the same, known -as the natural water standard. The figures given are approximately -equal to those for the platinum color standard, the relations between -the two having been frequently determined by various observers and -published in the above-mentioned papers. The accompanying diagram shows -the colors in several Massachusetts supplies, as plotted from the -figures given in the published reports. - -[Illustration: FIG. 18.—COLORS OF WATERS. - -(Analyses of the Mass. State Board of Health.)] - -In Connecticut also the colors of many public water-supplies have been -recorded in the reports of the State Board of Health on the platinum -color-standard. - -The waters of the Middle States, with rare exceptions, are almost free -from color. In the Northwest waters are obtained often with very high -colors, even considerably higher than the New England waters, and some -of the Southern swamps also yield highly colored waters. - - -REMOVAL OF COLOR. - -Peaty coloring-matter is almost perfectly in solution, and only a -portion of it is capable of being removed by any form of simple -filtration. In order to remove the coloring-matter it is necessary to -change it chemically, or to bring it into contact with some substance -capable of absorbing it. For this reason sand filtration with ordinary -sands, having no absorptive power for color, commonly removes only from -one fourth to one third of the color of the raw water. - - -MEASUREMENT OF TURBIDITY. - -The amount of mud or turbidity in a water is often expressed as the -weight of the suspended matters in a given weight of the water. Most -of the data relating to turbidities of waters are stated in this -way, because this was the only method recognized by the earlier -investigators. - -This method of statement has some disadvantages: it fails to take -into account the different sizes of particles which are carried in -suspension by different waters, and at different times. Thus the -Merrimac River in a great flood may carry 100 parts in 100,000 of -fine sand in suspension, and still it could hardly be called muddy; -while another stream carrying only a fraction of this amount of fine -clay would be extremely muddy. Further, an accurate determination of -suspended matters is a very troublesome and tedious operation, and -cannot be undertaken as frequently as is necessary for an adequate -study of the mud question. - -Turbidity is principally important as it affects the appearance of -water, and it would seem that optical rather than gravimetric methods -should be used for its determination. Various optical methods of -measuring turbidity have been proposed. The general method employed -is to measure the thickness of the layer of water through which some -object can be seen under definite conditions of lighting. The most -accurate results can probably be obtained in closed receptacles and -with artificial light. Such a method has been used by Mr. G. W. Fuller -at Louisville and Cincinnati in connection with his experiments, and is -described by Parmelee and Ellms in the Technology Quarterly for June, -1899. This apparatus is called by Mr. Fuller a diaphanometer. - -At the Lawrence Experiment Station of the Massachusetts State Board of -Health as early as 1889 it became necessary to express the turbidities -of various waters approximately, and the very simple device of -sticking a pin into a stick, and pushing it down into the water under -examination as far as it could be seen, was adopted. Afterwards a -platinum wire 0.04 of an inch in diameter was substituted for the pin, -and the stick was graduated so that the turbidities could be read from -it directly. The figures on the stick were inversely proportional to -their distances from the wire. When the wire could be seen one inch -below the surface, the turbidity was reported as 1.00; when the wire -could be seen two inches, the turbidity was 0.50, and when it could -be seen ten inches the turbidity was 0.10, etc. This scale is much -more convenient than a scale showing the depth at which the wire can -be seen; and within certain limits the figures obtained with it are -directly proportional to the amount of the elements which obstruct -light in the water. Thus, if a water having a turbidity of 1.00 is -mixed with an equal volume of clear water, the mixture will have a -turbidity of 0.50. Advantage is taken of this fact for the measurement -of turbidities so great that they cannot be accurately determined -by direct observation. For turbidities much above 1.00 it is very -difficult to read the depth of wire with sufficient accuracy, and such -waters are diluted with one, two, or more times their volume of clear -water in a pail or other receptacle, the turbidity of the diluted water -is taken, and multiplied by the appropriate factor. - -For the greatest accuracy it is necessary that the observations should -be taken in the open air and not under a roof. They should preferably -be made in the middle of the day when the light is strongest, and in -case the sun is shining, the wire must be kept in shadow and not in -direct sunlight. - -The turbidities of effluents are usually so slight that they cannot -be taken in this manner; in fact, turbidities of less than 0.02, with -the wire visible 50 inches below the surface, cannot be conveniently -read in this way. For the estimation of lower turbidities a water is -taken having a turbidity of 0.03 or 0.04 and as free as possible from -large suspended particles. The turbidity of this water is measured by -a platinum wire in the usual way, and the water is then diluted with -clear water to make standards for the lower turbidities. - -The comparisons between standards and waters are best made in bottles -of perfectly clear glass, holding at least a gallon, and the comparison -is facilitated by surrounding the bottles with black cloth except at -the point of observation, and lighting the water by electric lights so -arranged that the light passes through the water but is hidden from -the observer. In case the water under examination is colored, the -comparison is rendered difficult, and it is often advisable to add a -small amount of methyl orange to the standards to make the colors equal. - -Instead of diluting a water of known turbidity for the standards, a -standard can be made by precipitating a known amount of silver chloride -in the water. For this purpose about one per cent of common salt is -dissolved in clear water and small measured amounts of silver nitrate -added, until the turbidity produced is equal to that of the water under -examination. The relation of the amount of silver nitrate used to the -turbidity is entirely arbitrary, and is established by comparisons of -standards made in this way with waters having turbidities from 0.02 to -0.04, the turbidities of which are measured with the platinum wire, and -which afterwards serve to rate the standards. The silver chloride has a -slight color, which is an objection to its use, and perhaps some other -substance could be substituted for it with advantage. The standards -have to be made freshly each day. - -One disadvantage of the platinum-wire method of observing turbidities -in the open air, as compared with the diaphanometric method using -artificial light, is that observations cannot be made in the night. To -get the general character of the water in a stream, daily observations -taken about noon will generally be sufficient; but for some purposes it -is important to know the turbidity at different hours of the day, and -in such cases the platinum-wire method is at a distinct disadvantage. -Variations in the amount of light, within reasonable limits, do not -affect the results materially, although extreme variations are to be -avoided. The size of the wire also influences the results somewhat. The -wire commonly used is 0.04 of an inch or one millimeter in diameter. -A wire only four tenths of this size in some experiments at Pittsburg -gave results 25 per cent higher; with a wire twice as large the -results were lower, but the differences were much less. Wire 0.04 of -an inch in diameter was adopted as being very well adapted to rather -turbid river-waters. For very clear lake or reservoir waters, usually -transparent to a great depth, a much larger object is preferable. -Within certain limits the results obtained with an object of any size -can be converted into corresponding figures for another object, or -another light, by the use of a constant factor. Thus the turbidities -obtained with a platinum wire always have approximately the same ratio -to the turbidities of the same waters determined by the diaphanometer. - -The platinum-wire method has been used in many cases with most -satisfactory results. If it lacks something in theoretical accuracy -as compared with more elaborate methods, it more than makes up for it -by its simplicity; and reliable observations can be taken with it by -people who would be entirely incompetent to operate more elaborate -apparatus; and it can thus be used in many cases where other methods -would be impossible. - -Upon this scale the most turbid waters which have come under the -observation of the author have turbidities of about 2.50, although -waters much more turbid than this undoubtedly exist. A water with -a turbidity of 1.00 is extremely muddy, and only one tenth of this -turbidity would cause remark and complaint among those who use it for -domestic purposes. In an ordinary pressed-glass tumbler a turbidity of -0.02 is just visible to an ordinary observer who looks at the water -closely, but it is not conspicuous, nor would it be likely to cause -general complaint; and this amount may be taken as approximately the -allowable limit of turbidity in a good public water-supply. In a -carefully polished, and perfectly transparent glass a turbidity of 0.01 -will be visible, and in larger receptacles still lower turbidities may -be seen if the water is examined carefully. In gallon bottles of very -clear glass, under electric light and surrounded by black cloth, a -turbidity of 0.001 can be distinguished, but a turbidity even several -times as large as this could hardly be detected except by the use of -special appliances, or where water is seen in a depth of several feet. - - -RELATION OF PLATINUM-WIRE TURBIDITIES TO SUSPENDED MATTERS. - -The relation of turbidity to the weight of suspended matters is -approximately constant for waters from which the coarser matters have -been entirely removed by sedimentation. For these waters the suspended -matters in parts per 100,000 are about 16 times the turbidity. For -river-waters the ratios are always larger. With very sluggish rivers -the ratio is only a little larger than for settled waters. For average -river-waters the ratio is considerably higher, and increases with the -turbidity, and for very rapid rivers and torrents the ratio is much -wider, as the suspended matters consist largely of particles which are -heavy but do not increase very much the turbidity. - -The following table gives the amounts of suspended matters for various -classes of waters corresponding to the turbidities stated, which have -been deduced from the experience of the author. It is very likely that -ratios different from the above would be obtained with waters in which -the sediment was of different character. - - --------------+----------------------------------------------- - | Suspended Matters: Parts in 100,000. - Turbidity, +----------------------------------------------- - Platinum-wire | | River | River | River - Standard. | Settled | Waters, | Waters, | Waters, - | Waters. | Finest | Average | Coarsest - | | Sediment. | Sediment. | Sediment. - --------------+-----------+-----------+-----------+----------- - 0.01 | 0.16 | | | - 0.05 | 0.80 | 0.85 | 1.30 | 2.40 - 0.10 | 1.60 | 1.75 | 2.60 | 4.90 - 0.20 | 3.20 | 3.60 | 5.50 | 10.00 - 0.30 | 4.80 | 5.70 | 8.50 | 15.00 - 0.40 | 6.40 | 7.80 | 11.60 | 21.00 - 0.50 | 8.00 | 10.00 | 15.00 | 26.00 - 1.00 | 16.00 | 23.00 | 36.00 | 59.00 - 1.50 | 24.00 | 40.00 | 62.00 | 97.00 - 2.00 | 32.00 | 61.00 | 94.00 | 140.00 - 3.00 | 48.00 | 110.00 | 175.00 | 250.00 - --------------+-----------+-----------+-----------+----------- - - -SOURCE OF TURBIDITY. - -Much turbidity originates in plowed fields of clayey soil, or in -fields upon which crops are growing. If it has not rained for some -days, and the surface-soil is comparatively dry, the first rain that -falls upon such land is absorbed by the pores of the soil until they -are filled. If the rain is not heavy, but little runs off over the -surface. If, however, the rain continues rapidly after the surface-soil -is saturated, the excess runs off over the surface to the nearest -watercourse. The impact of the rain-drops upon the soil loosens -the particles, and the water flowing off carries some of them in -suspension, and the water is said to be muddy. - -The particles carried off in this way are extremely small. Mr. George -W. Fuller, in his report upon water purification at Louisville, -estimates that many of them are not more than a hundred thousandth of -an inch in diameter, and not more than a tenth as large as common water -bacteria. - -The turbidity of the water flowing from a field of loose soil may be -2.00 or more; that is to say, the wire is hidden by a depth of half an -inch of water or less. When the water reaches the nearest watercourse -it meets with water from other kinds of land, such as woodlands and -grassed fields, and these waters are less turbid. The water in the -first little watercourse is thus a mixture and has a turbidity of -perhaps 1.00. - -The conditions which control the turbidity of any brook are numerous -and complicated. The turbidity of a stream receiving various brooks -depends upon the turbidities of all the waters coming into it. -Generally speaking, the turbidity of a river depends directly upon the -turbidities of its feeders, and is not affected materially by erosion -of its bed or by sedimentation in it. There are, of course, some -streams which in times of great floods cut their banks, and all streams -pick up and move about from place to place more or less of the sand and -other coarse materials upon their bottoms. The materials thus moved, -however, have but little influence upon the turbidity. - -After the rain is over some of the water held by the soil will find -its way to the watercourses by underground channels, and will prevent -the stream from drying up between rains, but the average volume of the -stream-flows between rains will be much less than the volumes during -the rains when the water is most turbid. - -[Illustration: FIG. 19.—FLUCTUATIONS IN TURBIDITY OF THE WATER OF THE -ALLEGHENY RIVER AT PITTSBURG DURING 1898.] - -These conditions are well illustrated by a few data upon the turbidity -of three Pennsylvania streams, recently collected by the author. One -of these streams is a small brook having a drainage area of less than -three square miles. The observations extended over a period of 47 days. -During this time there were five floods, or an average of one flood in -ten days. The duration of floods was less than twenty-four hours in -each case. Selecting the days when the turbidity was the highest, to -the number of one tenth of the whole number of days, the sum of the -turbidities for these days was 67 per cent of the aggregate turbidities -for the whole period. That is to say, 67 per cent of the whole amount -of mud was in the water of only a tenth of the days; the water of the -other nine tenths of the days contained only 33 per cent of the whole -amount of turbidity. The average turbidity of the water for the flood -days was eighteen times as great as the average turbidity for the -remaining days. - -The next stream is a considerable creek having a drainage area of -350 square miles. The observations extended over 117 days, during -which time there were seven floods, or an average of one flood in 19 -days. The floods lasted in each case one or two days, and the sum of -the turbidities for the one tenth of the whole number of days when -the water was muddiest was 55 per cent of the aggregate of all the -turbidities for the period. - -The last case is that of a large river, with a drainage area of over -11,000 square miles. The observations extended over a full year. In -this period there were sixteen floods, each lasting from one to six -days, and the sum of the turbidities for the one tenth of the whole -number of days when the water was muddiest is 45 per cent of the -aggregate turbidities for the year. The floods occurred on an average -of once in 22 days, and the average duration was two and one half days. - -The results are very striking as showing that a very large proportion -of the mud is carried by the water in flood flows of comparatively -short duration. They also show that in small streams the proportion of -mud in the flood-flows is greater, and the average duration of floods -is shorter, than in larger streams. In other words, the differences -between flood- and low-water flows are greatest in small streams, and -gradually become less as the size of the stream increases. - -When a stream is used for water-works purposes in the usual way, a -certain quantity of water is taken from the stream each day, which -quantity is nearly constant, and is not dependent upon the condition -of the stream, or the volume of its flow. The proportions of the -total flows taken at high- and low-water stages are very different, -and it thus happens that the average quality of the water taken for -water-works purposes is different from the average quality of all the -water flowing in the stream. - -Let us assume, for example, a stream having a watershed of such a -size that in times of moderate floods water from the most distant -points reaches the water-works intake in twenty-four hours. Let us -assume further that rainfalls of sufficient intensity to cause floods -and muddy water occur, on an average, once in ten days, and that the -turbidity of the water at these times reaches 1.00, and that for the -rest of the time the turbidity averages 0.10. Let us assume further -that at times of storms the average flow of the stream is 100 units -of volume, and for the nine days between storms the average flow is -10 units of volume. We shall then have in a ten days’ period, for one -day, 100 volumes of water with a turbidity of 1.00, and nine days with -10 volumes each, or a total of 90 volumes of water with a turbidity -of 0.10. The total discharge of the stream will then be 190 volumes, -and the average turbidity 0.57. The turbidity of 0.57 represents the -average turbidity all the water flowing in the stream, or, in other -words, the turbidity which would be found in a lake if all the water -for ten days should flow into it and become thoroughly mixed without -other change. - -Now let us compute the average turbidity of the water taken from the -stream for water-works purposes. The water-works require, let us -say, one volume each day, and we have for the first day water with a -turbidity of 1.00, and then for nine days water with a turbidity of -0.10. The average turbidity of the water taken by the water-works for -the period is thus only 0.19 in place of 0.57, the average turbidity of -the whole run-off. - -The average turbidity of all the water flowing in the stream is thus -three times as great as that of the water taken from the stream for -water-works purposes. - -It is often noted that with long streams the water becomes muddier -farther down, and it may naturally be thought that it is because of the -added erosion of the stream upon its bed in its longer course. This, of -course, may be a cause, or the lower tributaries may be muddier than -the upper ones, but the fact that the water taken at the lower point is -more muddy than farther up is not an indication of this. - -Let us take, for example, a watershed of twice the size of that assumed -above, that is, so long that 48 hours will be required for the water -from the most remote feeders to reach the water-works intake. Let us -divide this shed into two parts, which we will assume to be equal, one -of which furnishes water reaching the intake within 24 hours, and the -other water reaching the intake between 24 and 48 hours. Now suppose -a storm upon the watershed producing turbidities equal to those just -assumed for the smaller stream. On the first day the water from the -lower half of the shed, namely, 100 volumes having a turbidity of 1.00, -passes the intake, but this is mixed with 10 volumes of water from -the upper half of the watershed, having a turbidity of 0.10, and the -total flow is thus 110 volumes of water having a turbidity of 0.92. -On the second day the water from the lower half of the watershed has -returned to its normal condition, and the flood-flow of the upper half -of the watershed, 100 volumes with a turbidity of 1.00, is passing, -and mingles with the 10 volumes from the lower half with a turbidity -of 0.10, and the total flow is again 110 volumes having a turbidity of -0.92. The following eight days, until the next rain, will have flows -of 20 volumes each, with turbidities of 0.10. The average turbidity of -all of the water flowing off is 0.57 as before, but the water taken -for water-works purposes will consist of 2 volumes of water with -turbidities of 0.92, and 8 volumes with turbidities of 0.10 making 10 -volumes with an average turbidity of 0.26. - -By doubling the length of the watershed we have thus doubled the length -of time during which the water is turbid, and have increased the -average turbidity of the water taken for water-works purposes from 0.19 -to 0.26, although the average turbidity of all the water running off -remains exactly the same. - -If now we assume a watershed so long that three days are required -for the water from the most remote points to reach the intake, with -computations as above, water taken for water-works purposes will have -an average turbidity of 0.32; and with still longer watersheds this -amount will increase, until with a watershed so long that ten days, -or the interval between rains, are required for the water from the -upper portions to reach the intake, the average turbidity of the water -taken for water-works purposes will reach the average turbidity of the -run-off, namely, 0.57. - -In the above computations the numbers taken are round ones, and of -course do not represent closely actual conditions. They do serve, -however, to illustrate clearly the principle that the larger the -watershed, other things being equal, the more muddy will be the water -obtained from it for water-works purposes, and the longer will be the -periods of muddy water, and the shorter the periods of clear water -between them. - -It cannot be too strongly emphasized that the period of duration of -muddy water is, in general, dependent upon the length of time necessary -for the muddy water to run out of the stream system after it is once in -it, and be replaced by clear water; and that the settling out of the -mud in the river has very little to do with it. - -Muddy waters result principally from the action of rains upon the -surface of ground capable of being washed, and the turbidities of the -stream at any point below will occur at the times when the muddy waters -reach it in the natural course of flow, and will disappear again when -the muddy waters present in the stream system at the end of the rain -have run out, and have been replaced with clear water from underground -sources, or from clearer surface sources. - - -THE AMOUNTS OF SUSPENDED MATTERS IN WATER. - -There is a large class of waters, including most lake and reservoir -waters, and surface-waters from certain geological formations, which -are almost free from suspended matters and turbidities. That is to say, -the average turbidities are less than 0.10, and the average suspended -matters are less than 2 parts in 100,000, and are often only small -fractions of these figures. This class includes the raw waters of the -supplies of many English cities drawn from impounding reservoirs, and -also the waters of the rivers Thames and Lea at London, and the raw -waters used by both of the Berlin water-works, and in the United States -the waters of the great lakes except at special points near the mouths -of rivers, nearly all New England waters, and many other waters along -the Atlantic coast and elsewhere where the geological formations are -favorable. - -Data regarding the suspended matters in these waters are extremely -meagre. The official examinations of the London waters contain no -records of suspended matters, although the clearness of filtered -waters is daily reported. Dibden, in his analytical investigations of -the London water-supply, mentioned in his book upon “The Purification -of Sewage and Water,” reports the average suspended matters in the -water of the Thames near the water-works intakes as 0.77 part in -100,000. No figures are available for the raw waters used by the Berlin -water-works, but both are taken from lakes, and are generally quite -clear. Even in times of floods of the rivers feeding the lakes, the -turbidities are not very high, because the gathering grounds for the -waters are almost entirely of a sandy nature, yielding waters with low -turbidities, and further, the streams flow through successions of lakes -before finally reaching the lakes from which the waters are taken. It -is safe to assume that the suspended matters and turbidities do not -exceed those of the London waters. Even at times when somewhat turbid -water is obtained, due to agitation by heavy winds, the suspended -matter is mainly of a sandy nature, readily removed by settling, and -it does not seriously interfere with filtration. - -The examinations of the Massachusetts State Board of Health, with a -very few exceptions, contain no statements of suspended matters. This -is due to the fact that the suspended matters, in most of the waters, -are so small in amount as to make them hardly capable of determination -by the ordinary gravimetric processes, and the determinations if made -would have but little value. The Merrimac River at Lawrence, at the -time of the greatest flood in fifty years, carried silt to the amount -of about 111 parts in 100,000. This was for a very short time, and the -suspended matter consisted almost entirely of sand, which deposited -in banks, the deposited sand having an effective size of 0.04 or 0.05 -millimeter. No clayey matter is ever carried in quantity by the river. - -The reports of the Connecticut State Board of Health also contain no -records of suspended matters for the same reason. It may be safely said -that the average suspended matters of New England waters are almost -always less than 1 part in 100,000. - -Lake waters are generally almost entirely free from sediment. At -Chicago the city water drawn from Lake Michigan has slightly more than -1 part in 100,000 of suspended matters, as determined by Professor Long -in 1888-9, and by Professor Palmer in 1896. The suspended matter in -this case is probably due to the nearness of the intake to the mouth of -the Chicago River, and to mud brought up from the bottom in times of -storms. The lake-water further away from the shore would probably give -much lower results. - -Turning now to waters having considerable turbidities, at Pittsburg the -average suspended matters in the Allegheny River water, as shown by -the weekly or semi-weekly analyses of the Filtration Commission during -1897-8, were 4 parts in 100,000. During a large part of the time the -suspended matters were so small that it was not deemed worth while -to determine them, and the results are returned as zero. This is not -quite correct, and a recomputation of the amount of suspended matters, -based on the observed amounts, and the amounts calculated from the -turbidities when they were very low, leads to an average of a little -less than 5 parts in 100,000, which is probably more accurate than the -direct average. The average turbidity on the platinum-wire scale was -0.16. - -At Cincinnati the suspended matters are about 23 parts in 100,000, -and at Louisville about 35 parts, both of these figures being from -Mr. Fuller’s reports. In all these cases the enormous and rapid -fluctuations in the turbidity of the water is a most striking feature -of the results. - -Observations on the Mississippi River above the Ohio have been -made by Professor Long in 1888-9, and by Professor Palmer in 1896. -These results are not as full and systematic as could be desired, -but indicate averages of 20 to 30 parts in 100,000 at the different -points. Professor William Ripley Nichols, in his work on water-supply, -states the amount of suspended matter in the water of the Mississippi, -probably referring to the lower river, as 66.66 parts. - -Investigations of Professor Long and Professor Palmer for numerous -interior Illinois streams extending over considerable periods give -average results ranging from 1 to 8 parts in 100,000. The very much -lower results for the interior streams as compared with the Mississippi -and Ohio rivers may be due to the relative sizes and lengths of the -streams, or in part to other causes. - -Regarding muddy European rivers there are but few data. The Maas, used -for the water-supply of Rotterdam, is reported by Professor Nichols as -having from 1.40 to 47.61 and averaging 10 parts of suspended matters -in 100,000. More recent information is to the effect that the raw water -has at most 30 parts of suspended matters, and that that quantity is -very seldom reached. - -At Bremen the Weser often becomes quite turbid. The turbidity of the -water is noted every day by taking the depth at which a black line on a -white surface can be seen. Assuming that this procedure is equivalent -to the platinum-wire procedure, the depths at which the wire can be -seen, namely, from 15 to 600 millimeters, correspond to turbidities of -from 0.04 to 1.70, a result not very different from the conditions at -Pittsburg. - -At Hamburg and Altona the water is generally tolerably clear, but at -times of flood the Elbe becomes very turbid, and the amount of mud -deposited in the sedimentation-basins is considerable. At Dresden, -several hundred miles up the river, I have repeatedly seen the -river-water extremely turbid with clayey matter, the color of the clay -varying from day to day, corresponding to the color of the earth from -which it had been washed. - -At Budapest, where filters were used temporarily, the Danube water -was excessively muddy with clayey material. At first very high rates -of filtration were employed and the results were not satisfactory. -Afterward the rate of filtration was limited to 1.07 million gallons -per acre daily, and good results were secured. There was no preliminary -sedimentation. Professor Nichols reports the average suspended matters -in the Danube at 32.68 parts in 100,000, but does not state at what -place. - -Many of the French and German rivers drain prairie country not -different in its general aspect from the Mississippi basin, and the -soil is probably in many places similar. There is no reason to suppose -that the turbidities of these streams in general are materially -different from those of corresponding streams in the United States, -although it is true that, other things being equal, the average -turbidity of water taken for water-works purposes will increase with -the size of the stream; and it may be that some American streams, -especially the Ohio, Missouri, and Mississippi rivers, are of larger -size than European streams, and consequently that the turbidity of the -water taken from them for water-works purposes may be greater. - -The following are the drainage areas of a number of European and -American streams yielding more or less muddy waters at points where -they are used for public water-supplies after filtration, with a few -other American points for comparison. The results are obtained in most -cases from measurements of the best available maps. - - ---------------------+------------------------+---------------- - | | Drainage Area, - Place. | River. | Square Miles. - ---------------------+------------------------+---------------- - New Orleans, La. | Mississippi | 1,261,000 - St. Louis, Mo. | Mississippi | 700,000 - St. Petersburg | Neva | 108,000 - Louisville, Ky. | Ohio | 90,000 - Rock Island, Ill. | Mississippi | 88,000 - Budapest | Danube | 79,000 - Cincinnati, O. | Ohio | 75,700 - Dordrecht | Maas | 68,000 - Rotterdam | Maas | 68,000 - Schiedam | Maas | 68,000 - Altona | Elbe | 52,000 - Hamburg | Elbe | 52,000 - Stettin | Oder | 40,000 - Magdeburg | Elbe | 36,000 - Warsaw | Weichsel | 34,000 - Odessa | Dneister | 26,000 - Worms | Rhine | 25,000 - Grand Forks, N. Dak. | Red River of the North | 22,000 - Frankfort on Oder | Oder | 21,000 - Bremen | Weser | 15,000 - Suburbs of Paris | Seine | 12,000 - Poughkeepsie, N. Y. | Hudson | 11,600 - Pittsburg, Penn. | Allegheny | 11,400 - Posen | Wartha | 9,400 - Hudson, N. Y. | Hudson | 9,200 - Albany, N. Y. | Hudson | 8,200 - Breslau | Oder | 8,200 - Brieg | Oder | 7,500 - Lawrence, Mass. | Merrimac | 4,634 - Stuttgart | Neckar | 1,660 - Brunswick | Ocker | 650 - Somersworth, N. H. | Salmon | 171 - ---------------------+------------------------+---------------- - - -PRELIMINARY PROCESSES TO REMOVE MUD. - -With both sand and mechanical filtration the difficulty and expense -of treatment of a water increase nearly in direct proportion to the -turbidity of the water as applied to the filter; and it is thus highly -important to secure a water for filtration with as little turbidity -as possible, and thus to develop to their economical limits the -preliminary processes for the removal of mud. One of the most important -of these processes is the use of reservoirs. - -Reservoirs serve two purposes in connection with waters drawn -from streams: they allow sedimentation, and they afford storage. -If a water having a turbidity of 1.00 is allowed to remain in a -sedimentation-basin for 24 hours, its turbidity may be reduced by -as much as 40 per cent, or to 0.60. If it is held a second day the -additional reduction is much less. - -If samples are taken of the water in the reservoir before and after -settling and sent to the chemist for analysis, he will probably report -that from 70 to 80 per cent of the suspended matters have been removed -by the process. The suspended matters are removed in much larger ratio -than the turbidity. This arises from the fact that there is a certain -proportion of comparatively coarse material in the water as it is -taken from the river. This coarse material increases the weight of the -suspended matters without increasing the turbidity in a corresponding -degree. In 24 hours the coarser materials are removed completely, and -at the end of that time only the clayey or finer particles remain in -suspension. It is these clayey particles, however, that constitute the -turbidity, which are most objectionable in appearance, and which are -most difficult of removal by filtration or otherwise. - -Sedimentation thus removes the heavier matters from the water, -but it does not remove the finer matters which principally affect -the appearance of the water and are otherwise most troublesome. A -sedimentation of 24 hours removes practically all of the coarser -matters, and the clayey material remaining at the end of that time -can hardly be removed by further sedimentation. The economic limit of -sedimentation is about 24 hours. - -Sedimentation has practically no effect upon the clearer waters between -flood periods. - -Let us consider the effect of a sedimentation-basin, or reservoir -holding a 24-hours’ supply of water, into which water is constantly -pumped at one end, and from which an equal quantity is constantly -withdrawn from the other, upon the water of a stream of such size -that the time of passage of water from the feeders to the intake is -less than 24 hours. During the period between storms the water is -comparatively clear and passes through the sedimentation basin without -change. When a storm comes the water in the stream promptly becomes -muddy, and muddy water is supplied to the reservoir; but owing to -the time required for water to pass through it, the outflowing water -remains clear for some hours. There is a gradual mixing, however, and -long before the expiration of 24 hours somewhat muddy water appears -at the outlet. The turbid-water period rarely lasts in streams of -this size more than 24 hours, and at the expiration of that time the -water in the sedimentation-basin is as muddy or muddier than the water -flowing in the stream. After the height of the flood the stream clears -itself by the flowing away of the turbid water much more rapidly than -the water clears itself by sedimentation in the reservoir. That is to -say, if at the time of maximum turbidity we take a certain quantity of -water from the stream and put it aside to settle, at no time will the -improvement by settling equal the improvement which has taken place in -the stream from natural causes. Generally the improvement in the stream -is several times as rapid as in the sedimentation-basin, and the water -from it will at times have only a fraction of the turbidity of the -water in the basin. - -Let us now consider what the sedimentation has done to improve the -water. During the period of clear water, that is for most of the -time, it has done nothing. For the first day of each flood period -very much clearer water has been obtained from it than was flowing -in the stream. For the first days following floods the water in the -sedimentation-basin has been more muddy than the water in the stream. -The only time when the sedimentation-basin has been of use is during -the first part of floods, that is, when the turbidity of the water in -the stream is increasing. During this period it has been of service -principally because of its storage capacity, yielding up water received -from the stream previously, when it was less muddy. Such sedimentation -as has been secured is merely incidental and generally not important in -amount. - -It will be obvious from the above that for these conditions storage -is much more important than sedimentation. This brings us back to -the old English idea of having storage-reservoirs large enough to -carry water-works over flood periods without the use of flood-waters. -Reservoirs of this kind were, and still are, considered necessary for -the successful utilization of waters of many English rivers, although -these waters do not approach in turbidity the waters of some American -streams. This idea of storage has been but little used in the United -States. - -In the above case, if we use our reservoir for storage instead of as a -sedimentation-basin, the average quality of the water can be greatly -improved. The reservoir should ordinarily be kept full, and pumping to -it should be stopped whenever the turbidity exceeds a certain limit, -to be determined by experience; and the reservoir is then to be drawn -upon for the supply until the turbidity again falls to the normal. In -the case assumed above, with a stream in which all of the water reaches -the intake in 24 hours, a reservoir holding a 24-hours’ supply, or in -practice, to be safe, a somewhat larger one, would yield a water having -a very much lower average turbidity than would be obtained with water -pumped constantly from the stream without a reservoir. - -With a river having a watershed so long that 48 hours are required to -bring the water down from the most remote feeders, a reservoir twice as -large would be required, and would result in a still greater reduction -in the average turbidity. - -As the stream becomes larger, and the turbid periods longer, the size -of a reservoir necessary to utilize this action rapidly becomes larger, -and the times during which it can be filled are shortened, and thus the -engineering difficulties of the problem are increased. For moderately -short streams, cost for cost, storage is far more effective than -sedimentation, and we must come back to the old English practice of -stopping our pumps during periods of maximum turbidity. - - -EFFECT OF MUD UPON SAND FILTERS. - -There are two aspects of the effect of mud upon the operation of sand -filters which require particular consideration. The first relates to -the rapidity of clogging, and consequently the frequency of scraping -and the cost of operation; while the second relates to the ability of -the filters to yield well-clarified effluents. - - -EFFECT OF TURBIDITY UPON THE LENGTH OF PERIOD. - -The amount of water which can be filtered between scrapings is directly -dependent upon the turbidity of the raw water. The greater the -turbidity, the more frequently will filters require to be scraped. In -the experiments of the Pittsburg Filtration Commission, with 4 feet of -sand of an effective size of about 0.30 millimeter, and with rates of -filtration of about three million gallons per acre daily, and with the -loss of head limited to 4 feet, sand filters were operated as follows: -For five periods the turbidities of the raw water ranged from 0.035 to -0.062, and averaged 0.051, and the corresponding periods ranged from -102 to 136, and averaged 113 million gallons per acre filtered between -scrapings. For ten periods the turbidities of the raw water ranged from -0.079 to 0.128, and averaged 0.102, and the periods averaged 78 million -gallons per acre between scrapings. For fifteen other periods the -turbidities of the raw water ranged from 0.134 to 0.269, and averaged -0.195, and the periods averaged 52 million gallons per acre between -scrapings. In two other periods the turbidities of the raw water -averaged 0.67, and the periods between scrapings averaged 16 million -gallons. In all cases the turbidity is taken as that of the water -applied to the filter. Usually this was the turbidity of the settled -water, but in some cases raw water was applied, and in these case the -turbidity of the raw water is taken. These results are approximately -represented by the formula - - Period between scrapings, } = 12/(turbidity + 0.05). - million gallons per acre } - -Except for very clear waters the amount of water passed between -scrapings is nearly inversely proportional to the turbidity. With twice -as great an amount of turbidity, filters will have to be cleaned twice -as often, the reserve area for cleaning will require to be twice as -great, and the cost of scraping filters and of washing and replacing -sand, which is the most important element in the cost of operation, -will be doubled. - -With waters having turbidities of 0.20 upon this basis, the average -period will be about 51 million gallons per acre between scrapings. -This is about the average result obtained at the German works filtering -river waters, and there is no serious difficulty in operating filters -which require to be scraped with this frequency. With more turbid -waters the period is decreased. With an average turbidity of 0.50 the -average period is only 24 million gallons per acre between scrapings, a -condition which means very difficult operation and a very high cost of -cleaning. With much more turbid waters the difficulties are increased, -and if the duration of turbid water should be long-continued, the -operation of sand filters would clearly be impracticable, and the -expense, also, would be prohibitive. - -In applying these figures to actual cases it must be borne in mind -that the turbidity is only one of the several factors which control -the length of period; and that the turbidity of a water of a given -stream is never constant, but fluctuates within wide limits; and that -raw water can be applied to filters for a short time without injurious -results, even though it is so turbid that its continued application -would be fatal. - -It is very likely also that the suspended matters in different streams -differ in their natures to such an extent that equal turbidities would -give quite different periods, although the Pittsburg results were so -regular as to give confidence in their application to other conditions -within reasonable limits, and when so applied they afford a most -convenient method of computing the approximate cost of operation of -filters for waters of known or estimated turbidities. - - -POWER OF SAND FILTERS TO PRODUCE CLEAR EFFLUENTS FROM MUDDY WATER. - -When the turbidity of the applied water is not too great it is entirely -removed in the course of filtration. With extremely muddy raw waters, -however, turbid effluents are often produced with sand filters. -The conditions which control the passage of the finest suspended -matters through filters have been studied by Mr. Fuller at Cincinnati -at considerable length. They are similar in a general way to the -conditions which control the removal of bacteria. That is to say, the -removal is more complete with fine filter sand than with coarse sand; -with a deep sand layer than with a shallow sand layer; and with low -rates of filtration than with high rates. The practicable limits to -the size of sand grain, depth of sand layer, and rate of filtration -are established by other conditions, and the question remains whether -within these limits a clear effluent can be produced. - -At Pittsburg the turbidity of the effluent from a sand filter operated -as mentioned above, which received water which had passed through a -sedimentation-basin holding about a 24-hours’ supply, but without -taking any advantage of storage to avoid the use of muddy water, was -nearly always less than 0.02, which may be taken as the admissible -limit of turbidity in a public water-supply. This limit was exceeded on -less than 20 days out of 365, these days being during the winter and -spring freshets, and on these days the excess was not such as would be -likely to be particularly objectionable. For the water of the Allegheny -River, then, sand filtration with one day’s sedimentation is capable -of yielding a water not absolutely clear, but sufficiently clear to be -quite satisfactory for the purpose of municipal water-supply. - -At Cincinnati, on the other hand, where the amount of suspended matters -was five times as great as at Pittsburg, the effluents which could be -obtained by sand filtration without recourse to the use of alum, even -under most favorable conditions, were very much more turbid than those -obtained at Pittsburg, and were, in fact, so turbid as to be seriously -objectionable for the purpose of public water-supply. - -With rivers no more turbid than the Allegheny River at Pittsburg, and -rivers having floods of such short duration that the use of flood-flows -can be avoided by the use of reservoirs, sand filters are adequate for -clarification. For waters which are much muddier than the Allegheny, -as, for instance, the Ohio at Cincinnati and at Louisville, sand -filtration alone is inadequate. Mr. Fuller,[31] as a result of his -Cincinnati experiments, has stated the case as follows: - -“For the sake of explicitness it is desired to show, with the data -of the fairly normal year of 1898, the proportion of the time when -English filters (that is, sand filters) would be inapplicable in the -purification of the unsubsided Ohio River water at Cincinnati. This -necessitates fixing an average limit of permissible suspended matter in -this river water, and is a difficult matter from present evidence. - -“In part this is due to variations in the character and in the relative -amounts of the suspended silt, clay, and organic matter; and in part -it is due to different amounts of clay stored in the sand layer, which -affects materially the capacity of the filter to retain the clay of the -applied water. During these investigations the unsubsided river-water -was not regularly applied to filters; and, with the exception of -the results of tests for a few days only, it is necessary to depend -upon general information obtained with reference to this point. So -far as the information goes, it appears that an average of 125 parts -per million is a conservative estimate of the amount of suspended -matters in the unsubsided river-water, which could be regularly and -satisfactorily handled by English filters. But at times this estimated -average would be too low, and at other times too high.... - -“While English filters are able to remove satisfactorily on an - -average about 125 parts of silt and clay of the unsubsided water, -actual experience shows that they can regularly handle suspended -clay in subsided water in amounts ranging only as high as from 30 to -70 parts (depending upon the amount of the clay stored in the sand -layer), and averaging about 50 parts per million. But it is true that -for two or three days on short rises in the river, or at the beginning -of long freshets, the retentive capacity of the sand layer allows of -satisfactory results with the clay in the applied water considerably in -excess of 70 parts. If this capacity is greatly overtaxed, however, the -advantage is merely temporary, as the stored clay is washed out later, -producing markedly turbid effluents.” - -Translating Mr. Fuller’s results into terms of turbidity, the 125 -parts per million of suspended matters in the raw water represent a -turbidity of about 0.40, and the 30 to 70 parts of suspended matters in -the settled water represent turbidities from 0.20 to 0.40, the average -of 50 parts of suspended matters corresponding to a turbidity of about -0.30. - -Upon this basis, then, sand filters are capable of treating raw waters -with average turbidities up to 0.40, or settled waters with average -turbidities up to 0.30, but waters more turbid than this are incapable -of being successfully treated without the use of coagulants or other -aids to the process. These results are in general accordance with -the results of the experiments at Pittsburg, and demonstrate that -while sand filters as generally used in Europe are adequate for the -clarification of many, if not most, river waters in the United States, -there are other waters carrying mud in such quantities as to make the -process inapplicable to them. - - -EFFECT OF MUD UPON BACTERIAL EFFICIENCY OF FILTERS. - -The question is naturally raised as to whether or not the presence of -large quantities of mud in the raw water will not seriously interfere -with the bacterial efficiency of filters. Experiments at Cincinnati -and Pittsburg have given most conclusive and satisfactory information -upon this point. Up to the point where the effluents become quite -turbid, the mud in the raw water has no influence upon the bacterial -efficiency; and even somewhat beyond this point, with effluents so -turbid that they would hardly be suitable for the purpose of a public -water-supply, the bacterial efficiency remains substantially equal to -that obtained with the clearest waters. Only in the case of excessive -quantities of mud, where, for other reasons, sand filters can hardly -be considered applicable, is there a moderate reduction in bacterial -efficiency. As mentioned above, particles constituting turbidity are -often much smaller than the bacteria, and in addition, the bacteria -probably have an adhesive power far in excess of that of the clay -particles. For these reasons clay particles are able to pass filters -under conditions which almost entirely prevent the passage of bacteria. - -On the other hand, it does not necessarily follow that the removal -of turbidity is accompanied by high bacterial efficiency. Although -this is often the case, there are marked exceptions, particularly in -connection with the use of coagulants, where very good clarification is -obtained, and notwithstanding this, effluents are produced containing -comparatively large numbers of bacteria. - - -LIMITS TO THE USE OF SUBSIDENCE FOR THE PRELIMINARY TREATMENT OF MUDDY -WATERS. - -When water is too muddy to be applied directly to filters, the most -obvious treatment is to remove as much of the sediment as possible by -sedimentation. Sedimentation-basins are considered as essential parts -of filtration plants for the treatment of muddy waters. The effect of -sedimentation, as noted above, is to remove principally the larger -particles in the raw water. By doing this the deposit upon the surface -of the filters and the cost of operation are greatly reduced. - -These larger particles are mainly removed by a comparatively short -period of sedimentation, and the improvement effected after the first -24 hours is comparatively slight. The particles remaining in suspension -at the end of this time consist almost entirely of very fine clay, and -the rate of their settlement through the water is extremely slow; and -currents in the basin, due to temperature changes, winds, etc., almost -entirely offset the natural tendency of the sediment to fall to the -bottom. - -There is thus a practical limit to the effect of sedimentation which is -soon reached, and it has not been found feasible to extend the process -so as to allow much more turbid waters to be brought within the range -which can be economically treated by sand filtration. - - - - -CHAPTER IX. - -THE COAGULATION OF WATERS. - - -The coagulation of water consists in the addition to it of some -substance which forms an inorganic precipitate in the water, the -presence of which has a physical action upon the suspended matters, and -allows them to be more readily removed by subsidence or filtration. - -The most common coagulant is sulphate of alumina. When this substance -is added to water it is decomposed into its component parts, sulphuric -acid and alumina, the former of which combines with the lime or other -base present in the water, or in case enough of this is lacking, it -remains partly as free acid and partly undecomposed in its original -condition; while the alumina forms a gelatinous precipitate which draws -together and surrounds the suspended matters present in the water, -including the bacteria, and allows them to be much more easily removed -by filtration than would otherwise be the case. In addition, the -alumina has a chemical attraction for dissolved organic matters, and -the chemical purification may be more complete at very high rates than -would be possible with sand filtration without coagulant at any rate, -however low. - -Coagulants have been employed in connection with filtration from -very early times. As early as 1831 D’Arcet published in the “Annales -d’hygiène publique,”[32] an account of the purification of Nile water -in Egypt by adding alum to the water, and afterwards filtering it -through small household filters. More recently alum has been repeatedly -used in connection with sand filters, particularly - -at Leeuwarden, Groningen, and Schiedam in Holland, where the river -waters used for public supplies are colored by peaty matter which -cannot be removed by simple filtration. - - -SUBSTANCES USED FOR COAGULATION. - -Mr. Fuller[33] has given a very full account of the substances which -can be used for the clarification of waters. Without taking up all of -the unusual substances which have been suggested, the most important of -the coagulants will be briefly described below. - -_Lime._—Lime has been extensively used in connection with the -purification of sewage, and also for softening water. Lime is first -slaked and converted into calcium hydrate, which is afterwards -dissolved in water, and applied to the water under treatment. The -amount of lime to be used is fixed by the amount of carbonic acid in -the water. So much lime is always used as will exactly convert the -whole of the carbonic acid of the water into normal carbonate of lime. -This substance is but slightly soluble in water and it precipitates. -The precipitate is crystalline rather than flocculent, and is not as -well adapted to aid in the removal of clayey matters as some other -substances, although its action in this respect is considerable. The -precipitate is quite heavy, and is largely removed by sedimentation, -although filtration must be used to complete the process. Water which -has been treated with lime is slightly caustic; that is to say, there -is a deficiency of carbonic acid in it, and it deposits lime in the -pipes, in pumps, etc.; and although the precipitated calcium carbonate -is much softer than steel, it rapidly destroys pumps used for lifting -it. - -Principally for these reasons it is necessary to supply carbonic acid -to water which has been treated in this way, and this is done by -bringing it in contact with flue-gases, or by the direct addition of -carbonic acid. - -The use of lime for softening waters is known as Clark’s process. It -was patented in England many years ago, and the - -patent has now expired. Various ingenious devices have been constructed -for facilitating various parts of the operation. The process has hardly -been used in the United States, but there is a large field for it in -connection with the softening of very hard waters, and where such -waters also contain iron or clay, these substances will be incidentally -removed by the process. - -Larger quantities of lime have an action upon the suspended matters -which is entirely different from that secured in Clark’s process, and -the action upon bacteria is particularly noteworthy. This action was -noted in experiments at Lawrence,[34] where it was found that sewage -was almost completely sterilized by the application of considerable -quantities of lime. An extremely interesting series of experiments upon -the application of large quantities of lime to water was made by Mr. -Fuller in 1899.[35] The bacterial results were extremely favorable, -although the necessity for removing the excess of lime afterward is a -somewhat serious matter, and in these experiments it was not entirely -accomplished. - -_Aluminum Compounds._—Sulphate of alumina is most commonly employed. -It can be obtained in a state of considerable purity at a very -moderate price, and important improvements in the methods used for its -manufacture have been recently introduced. Potash and soda alums have -no advantage over sulphate of alumina, and, in fact, are less efficient -per pound, while their costs are greater. Chloride of alumina is -practically equivalent to the sulphate in purifying power, but is more -expensive. - -_Sodium Aluminate_ has been examined by Mr. Fuller, who states that -experience has shown that its use is impracticable in the case of the -Ohio River water. - -_Compounds of Iron._—Iron forms two classes of compounds, namely, -ferrous and ferric salts. When the ferrous salts are applied to water, -under certain conditions, ferrous hydrate is precipitated, but this -substance is not entirely insoluble in water containing carbonic acid. -Under some conditions the precipitated ferrous hydrate is oxidized -by oxygen present in the water to ferric hydrate, and so far as this -is the case, good results can be obtained. Ferrous sulphate is not -as readily oxidized when applied to water as is the ferric carbonate -present in many natural waters, and for this reason ferrous sulphate -has not been successfully used in water purification. In the treatment -of sewage, where the requirements are somewhat different, it has been -one of the most satisfactory coagulants. - -Ferric sulphate acts in much the same way as sulphate of alumina, -and is entirely suitable for use where sulphate of alumina could be -employed, but it has not been used in practice, due probably to its -increased cost as compared with its effect, and to the practical -difficulties of applying it in the desired quantities due to its -physical condition. - -_Metallic Iron: The Anderson Process._—The use of metallic iron for -water purification in connection with a moderately slow filtration -through filters of the usual form is known as Anderson’s process -(patented), and has been used at Antwerp and elsewhere on a large -scale, and has been experimentally examined at a number of other places. - -The process consists in agitating the water in contact with metallic -iron, a portion of which is taken into solution as ferrous carbonate. -Upon subsequent aeration this is supposed to become oxidized and -precipitate out as ferric hydrate, with all the good and none of the -bad effects which follow the use of alum. The precipitate is partially -removed by sedimentation, while filtration completes the process. -The process is admirable theoretically, and in an experimental way -upon a very small scale often gives most satisfactory results, muddy -waters very difficult of filtration, and colored peaty waters yielding -promptly clear and colorless effluents. - -In applying the process on a larger scale, however, with peaty waters -at least, it seems impossible to get enough iron to go into solution -in the time which can be allowed, and the small quantity which is -taken up either remains in solution or else slowly and incompletely -precipitates out, without the good effects which follow the sudden and -complete precipitation of a larger quantity, and in this case the color -is seldom reduced, and may even be increased above the color of the raw -water by the iron remaining in solution. - -The ingenuity of those who have studied the process has not yet found -any adequate means of avoiding these important practical objections; -and even at Antwerp a great extension of the filtering area, as well -as the use of alum at times of unusual pollution, is good evidence -that simple filtration, in distinction from the effect of the iron, is -relied upon much more than formerly. - -At Dordrecht also, where the process has been long in use, the rate of -filtration does not exceed the ordinary limits; nor is the result, so -far as I could ascertain, in any way superior to that obtained a few -miles away at Rotterdam, by ordinary filtration, with substantially the -same raw water. - -The results obtained at Boulogne-sur-Seine, near Paris, have been -closely watched by the public chemist and bacteriologist of Paris, -and have been very favorable, and a number of new plants of very -considerable capacity have been built, to supply some of the suburbs of -Paris, but even in these cases only moderate rates of filtration are -employed which would yield excellent effluents without the iron. - -_Compounds of Manganese._—Manganese forms compounds similar to those -of iron, that is to say manganous and manganic salts, but their use -in connection with water filtration has not been found possible. In -addition, manganese forms a series of compounds, known as manganates -and permanganates, quite different in their structure and action from -the others. These compounds contain an excess of oxygen which they -give up very readily to organic matters capable of absorbing oxygen, -and because of this power, they have been extensively used in the -treatment of sewage. Applied to the treatment of waters their action is -very slight, and the compounds are so expensive that they have not been -employed for this purpose. Theoretically the action is very attractive, -as the oxygen liberated by their decomposition oxidizes some of the -organic matter of the water, thereby purifying it in part, while the -manganese is precipitated as a flocculent precipitate having all of -the advantages pertaining to a precipitate of hydrate of alumina, and -without the disadvantage of adding acid to the water, as is the case -with the compounds of alumina and iron. These chemicals, when used in -comparatively concentrated condition, have powerful germicidal actions, -but in water purification the amounts which can be used are so small -that no action of this kind results. The amount which can be applied to -a water is limited to the amount which can be decomposed by the organic -matters present in the water, and is not large. - -_The Use of Metallic Iron and Aluminum, with the Aid of -Electricity._—Elaborate experiments were made at Louisville with -metallic iron and aluminum oxidized and made available by the aid of -electric currents. The use of iron with electric currents was tried -in sewage purification some years ago, under the name of the Webster -process, but was never put to practical use. The theory is to oxidize -the iron or aluminum in contact with the water, with the formation -of flocculent hydrates, by the aid of an electric current, thereby -securing the advantages of the application of salts of these metals to -the water without the disadvantage of the addition of acid. - -_Other Chemicals Employed._—A solution containing chlorine produced -by electrical action has been suggested. Chlorine is a powerful -disinfectant, and when used in large quantities kills bacteria. It is -not possible to use enough chlorine to kill the bacteria in the water -without rendering it unfit for human use. The nature of this treatment -has been concisely described by Dr. Drown,[36] who shows that the -electrically prepared fluids do not differ in their action in any way -from well-known chemicals, the use of which would be hardly considered. - -The use of ozone and peroxide of hydrogen have also been suggested, but -I do not know that they have been successfully used on a large scale. -The same is true of many other chemicals, the consideration of which is -hardly necessary in this connection. - - -COAGULANTS WHICH HAVE BEEN USED. - -In actual work sulphate of alumina is practically the only coagulant -which has been employed, excepting the alums, which are practically its -equivalent in action, differing only in strength. Nearly all important -experiments upon the coagulation of water have been made with sulphate -of alumina, and in the further discussion of this subject only this -coagulant will be considered. - - -AMOUNT OF COAGULANT REQUIRED TO REMOVE TURBIDITY. - -In the coagulation of turbid waters a certain definite amount of -coagulant must be employed. If less than this amount is used either no -precipitate will be formed, or it will not be formed in sufficient bulk -to effect the desired results. It is necessary that the precipitate -should be sufficient, and that it should be formed practically all at -one time. The amount of coagulant necessary to accomplish this purpose -is dependent upon the turbidity of the raw water. With practically -clear waters sulphate of alumina of the ordinary commercial strength, -that is to say, with about 17 per cent soluble oxide of aluminum, -used in quantities as small as 0.3 or 0.4 of a grain per gallon, will -produce coagulation. As the turbidity increases larger amounts must be -employed. - -A special study was made of this point in connection with the Pittsburg -experiments.[37] As an average of these results it was found that two -grains per gallon of sulphate of alumina were - -required to properly coagulate waters having turbidities of 1.00, so -that they could be filtered by the Jewell filter, and 2.75 grains were -required for the Warren filter. - -[Illustration: FIG. 20.—AMOUNT OF COAGULANT REQUIRED TO REMOVE -TURBIDITY.] - -Aside from the amount required to produce a precipitate in the clearest -waters, the amount of coagulant required was proportional to the -turbidity. As an average for the two filters the required quantity was -approximately 0.30 of a grain, and in addition 0.02 of a grain for each -0.01 of turbidity. Thus a water having a turbidity of 0.20 requires -0.70 of a grain per gallon; a water having a turbidity of 0.50 requires -1.30 grains; of 1.00, 2.30 grains; of 2.00, 4.30 grains, etc. These are -average minimum results. Occasionally clear effluents were produced -with smaller quantities of coagulant, while at other times larger -quantities were necessary for satisfactory results. - -The amount of coagulant required for clarification at Cincinnati has -been stated by Mr. Fuller in his report. A number of his results are -brought together in the following table, to which has also been added a -column showing approximately the corresponding results at Pittsburg. - - -ESTIMATED AVERAGE AMOUNTS OF REQUIRED CHEMICAL FOR DIFFERENT GRADES OF -WATER. - - ----------+--------------------------------------------- - | Chemical Required, Grains per Gallon. - +----------+----------+----------+------------ - Suspended | Raw | Subsided | Subsided |Minimum for - Matter, |Water for |Water for |Water for |Raw Water - Parts in | Sand | Sand |Mechanical| for - 100,000. | Filters. | Filters. | Filters. |Mechanical - |Cincinnati|Cincinnati|Cincinnati| Filters. - | Report, | Report, | Report, | - |Page 290. |Page 290. |Page 341. | Pittsburg. - ----------+----------+----------+----------+------------ - 1.0 | 0 | 0 | 0.75 | 0.40 - 2.5 | 0 | 0 | 1.25 | 0.50 - 5.0 | 0 | 0 | 1.50 | 0.70 - 7.5 | 0 | 1.30 | 1.95 | 0.90 - 10.0 | 1.50 | 1.60 | 2.20 | 1.00 - 12.5 | 1.60 | 1.80 | 2.45 | 1.15 - 15.0 | 1.70 | 2.00 | 2.65 | 1.30 - 17.5 | 1.80 | 2.10 | 2.85 | 1.40 - 20.0 | 1.95 | 2.20 | 3.00 | 1.60 - 30.0 | 2.25 | 2.45 | 3.80 | 2.00 - 40.0 | 2.50 | 2.75 | 4.40 | 2.50 - 50.0 | 2.80 | | | - 60.0 | 3.05 | | | - 75.0 | 3.40 | | | - 100.0 | 4.00 | | | - 120.0 | 4.75 | | | - ----------+----------+----------+----------+------------ - -Mr. Fuller’s results seem to show that a greater amount of coagulant -is required for the preparation of water for mechanical filters than -is necessary in connection with sand filters. The results with sand -filters indicate that settled waters and raw waters containing equal -amounts of suspended matters are about equally difficult to treat. The -results at Pittsburg indicate that the raw waters required much smaller -quantities of coagulant for given amounts of suspended matters than was -the case with subsided waters at Cincinnati, the results agreeing more -closely with the amounts required to prepare raw water for sand filters -at Cincinnati. - - -AMOUNT OF COAGULANT REQUIRED TO REMOVE COLOR. - -The information upon this point is, unfortunately, very inadequate. In -some experiments made by Mr. E. B. Weston at Providence in 1893 with a -mechanical filter,[38] with quantities of sulphate of alumina averaging -0.6 or 0.7 of a grain per gallon, the removal of color was usually -from 70 to 90 per cent. The standard used for the measurement of color -is not stated, and there is no statement of the basis of the scale, -consequently no means of determining the absolute color of the raw -water upon standards commonly used. - -At Westerly, R. I., with a New York filter, the actual quantity of -potash alum employed from Oct. 10, 1896, to March 1, 1897, was 1.94 -grains per gallon, the amount being regulated to as low a figure as it -was possible to use to secure satisfactory decolorization. There is no -record of the color of the raw water. A very rough estimate would place -it at 0.50 upon the platinum scale. The chemical employed in this case -was alum, and two thirds as large a quantity of sulphate of alumina -would probably have done corresponding work, had suitable apparatus for -applying it been at hand. - -At Superior, Wisconsin, the water in the bay coming from the St. -Louis River, having a color of 2.40 platinum scale, was treated -experimentally with quantities of sulphate of alumina up to 4 grains -per gallon, by Mr. R. S. Weston in January, 1899, but even this -quantity of coagulant utterly failed to coagulate and decolorize it. - -At Greenwich, Conn., during 1898 the average amount of sulphate of -alumina employed, as computed from quantities stated in the annual -report of the Connecticut State Board of Health for 1898, was about -0.44 of a grain per gallon, and this quantity sufficed to reduce the -color of the raw water from 0.40 to 0.30, platinum standard. This -reduction is very slight, and it is obvious that this quantity of -coagulant was not enough for decolorization. - -Some experiments bearing on color removal were made at East Providence, -R. I., by Mr. E. B. Weston, and are described in the Proceedings of the -American Society of Civil Engineers for September, 1899. In this case -the color is reported to have been reduced from 0.58 to 0.10 platinum -standard by the use of one grain of sulphate of alumina, containing 22 -per cent of effective alumina, equivalent to about 1.30 grains of the -ordinary article per gallon. - -The various experiments seem to indicate that a removal from 80 to -90 per cent of the color can be effected by the use of a quantity of -sulphate of alumina equal to rather more than two grains per gallon -for waters having colors of 1.00, platinum standard, and proportionate -quantities for more and less deeply colored waters. With much less -sulphate of alumina decolorization is not effected, and even larger -quantities do not remove all of the color. - -The data are much less complete than could be desired, and it is to be -hoped that experiments will be undertaken to throw more light upon this -important subject. - - -SUCCESSIVE APPLICATION OF COAGULANT. - -Mr. Fuller, in his experiments at Louisville, has ascertained that when -sulphate of alumina is added to extremely muddy water the sediment -absorbs some of the chemical before it has time to decompose, and -carries it to the bottom, and so far as this is the case, no benefit -is derived from that part of the coagulant which is absorbed. In other -words, it is necessary to add more coagulant than would otherwise be -necessary because of this action. The data showed that different kinds -of suspended matters took up very different amounts of coagulant in -this way. With only moderately turbid waters the loss of chemical -from this source is unimportant. Hardly any trace of it was found at -Pittsburg with the Allegheny River water. At Louisville, however, it -was an important factor, as shown by Mr. Fuller’s results. - -To avoid this loss of chemical Mr. Fuller has suggested the removal of -the greater part of the suspended matters by sedimentation, without -chemicals, or with the aid of a small quantity of chemical, followed by -the application of the final coagulant prior to filtration. With the -worst waters encountered at Louisville the saving in coagulant to be -effected in this way is very great. - -Mr. Fuller states in “Water Purification at Louisville,” p. 417: “The -practical conclusions to be drawn from this experience are that with -preliminary coagulation, followed by subsidence for a period of about -three hours, the application of coagulants may be divided to advantage, -and a considerable portion of the suspended matter kept off the filter, -when the total amount of required coagulant ranges from 2 to 2.5 -grains or more of ordinary sulphate of alumina per gallon. In the case -of a water requiring more than this amount of coagulating treatment, -a proper division of the application would increase the saving of -coagulants and would diminish the frequency of washing the filter.” - -In his final summary and conclusions, page 441, Mr. Fuller estimates -the amount of sulphate of alumina required for the clarification of the -Ohio River at Louisville at 3.00 grains per gallon of water filtered -if all applied at one point, or at 1.75 grains by taking advantage of -subsidence to its economical limit prior to the final coagulation. The -saving to be effected in this way is sufficient to justify the works -necessary to allow it to be carried out. With less turbid waters, or -waters highly turbid for only short intervals, the advantages of double -coagulation would be less apparent. - - -THE AMOUNT OF COAGULANT WHICH VARIOUS WATERS WILL RECEIVE. - -The amount of coagulant which can be safely used is dependent upon -the alkalinity of the raw water. When sulphate of alumina is added -to water it is decomposed, as explained above, with the formation -of alumina, which is alone useful in the work of purification, and -sulphuric acid, which combines with the calcium carbonate or lime -present in the water. There should always be an excess of alkalinity or -lime in the raw water. If for any reason there is not, there is nothing -to combine with the liberated sulphuric acid, and the decomposition of -the coagulant is not complete, and a portion of it goes undecomposed -into the effluent. The effluent then has an acid reaction, and is unfit -for domestic supply. When distributed through iron pipes, it attacks -the iron, rusting the pipes, and giving rise to all the disagreeable -consequences of an iron containing water. - -The amount of lime in a water available to combine with the sulphuric -acid can be determined by a very simple chemical operation, namely, -by titration with standard acid with a suitable indicator. The amount -of coagulant corresponding to a given quantity of lime can be readily -and accurately calculated, but it is not regarded safe to use as -much sulphate of alumina as corresponds to the lime. The quantity of -coagulant used is not susceptible to exact control, but fluctuates -somewhat, and if the exact theoretical quantity should be employed -during 24 hours, there would surely be an excess during some portion of -that time from which bad results would be experienced. It is therefore -considered only prudent to use three quarters as much sulphate of -alumina as corresponds to the lime in the water. With sulphate of -alumina containing 17 per cent of soluble aluminum oxide and the -corresponding amount of sulphuric acid, the amount which can be applied -to a water in grains per gallon is slightly less than the alkalinity -expressed in terms of parts in 100,000 of calcium carbonate. - -Many waters contain sufficient lime to combine with the acid of all -the coagulant which is necessary for their coagulation. Others will -not, and it thus becomes an important matter to determine whether a -given water is capable of decomposing sufficient coagulant for its -treatment. It is usually the flood-flows of rivers which control in -this respect. The water at such times requires much larger quantities -of coagulant for its clarification, and it also usually contains much -less lime than the low-water flows. The reason for this is obviously -that the water of the flood-flows is largely rain-water which has come -over the surface without coming into very intimate contact with the -soil, and consequently without having taken from it much lime, while -the low-water flows contain a considerable proportion of water which -has percolated through the soil and has thus become charged with lime. - -In some parts of the country, as, for instance, in New England, the -soil and underlying rock are almost entirely free from lime, and -rivers from such watersheds are capable of receiving only very small -quantities of coagulant without injurious results. - -The deficiency of alkalinity in raw water can be corrected by the -addition to it of lime or of soda-ash. Lime has been used for this -purpose in many cases. When used only in moderate amounts it hardens -the water, and is thus seriously objectionable. The use of so large a -quantity as would precipitate out, as in Clark’s process, has not been -employed in practice. If it should be attempted, the amount of lime -would require to be very accurately controlled, and the effluent would -have to be treated with carbonic acid to make it suitable for supply. - -Waters so hard as to require the use of the Clark process almost always -have sufficient alkalinity, and do not require to be treated with lime -in connection with the use of sulphate of alumina. - -The use of soda-ash is free from the objections to the use of lime, -but is more expensive, and would require to be used with caution. Its -use has often been suggested, but I do not know that it has ever been -employed in practice. In small works the use of a filtering material -containing marble-dust, or other calcareous matter, would seem to have -some advantages in case of deficiency of alkalinity, although it would -harden the water so treated. - -The alkalinities of a number of waters computed as parts in 100,000 of -calcium carbonate (approximately equal to the safe doses of sulphate to -alumina in grains per gallon) are as follows: - - -------------------------------------+--------+--------+-------- - |Maximum.|Minimum.|Average. - -------------------------------------+--------+--------+-------- - Boston water, 1898 | 2.87 | 0.33 | 1.08 - Conestoga Creek, Lancaster, Penn. | 12.20 | 3.70 | 6.80 - Allegheny River, Pittsburg | 8.00 | 1.02 | 2.90 - Mahoning River and tributaries, 1897 | 20.00 | 2.20 | 10.00 - Scioto River and tributaries, 1897 | 35.00 | 10.00 | 20.00 - Ohio River, Cincinnati, 1898 | 7.00 | 2.00 | 4.50 - Ohio River, Louisville | 10.87 | 2.12 | 6.70 - Lake Erie, Lorain, Ohio | | | 9.50 - Lake Michigan, Chicago | | | 11.50 - -------------------------------------+--------+--------+-------- - - - - -CHAPTER X. - -MECHANICAL FILTERS. - - -The term mechanical filters is used to designate a general class of -filters differing in many respects quite radically from the sand -filters previously described. They had their origin in the United -States, and consisted originally of iron or wooden cylinders filled -with sand through which the water was forced at rates of one to two -hundred million gallons per acre daily, or from fifty to one hundred -times the rates usually employed with sand filters. These filters were -first used in paper-mills to remove from the large volumes of water -required the comparatively large particles, which would otherwise -affect the appearance and texture of the paper; and in their earlier -forms they were entirely inadequate to remove the finer particles, -such as the bacteria, and the clay particles which constitute the -turbidity of river waters. Various improvements in construction have -since been made, and, in connection with the use of coagulants, much -more satisfactory results can now be obtained with filters of this -class; and their use has been extended from manufacturing operations to -municipal supplies, in many cases with most satisfactory results. - -The information gathered in regard to the conditions essential to the -successful design and operation of these filters in the last few years -is very great, and may be briefly reviewed. - - -PROVIDENCE EXPERIMENTS.[39] - -The first data of importance were secured from a series of experiments -conducted by Mr. Edmund B. Weston of Providence, R. I., in 1893 and -1894, upon the Pawtuxet river water used by - -that city. The experimental filter was 30 inches in diameter, and had -a layer of sand 2 feet 10 inches deep. The sand was washed by the use -of a reverse current, the sand being stirred by a revolving rake at the -same time. The amount of coagulant employed was about 0.7 of a grain -per gallon. The raw water was practically free from turbidity, and the -filter was operated to remove color and bacteria. - -The removal of color, as stated in Mr. Weston’s report, amounted to -from 70 to 90 per cent. The experiments extended over a period of -ten months. The rate of filtration employed was about 128 million -gallons per acre daily. The bacterial results of the first six months’ -operations were rejected by Mr. Weston on account of defective methods -of manipulation. - -During the period from November 17, 1893, to January 30, 1894, the -average bacterial efficiency of filtration was about 95 per cent, and -the manipulation was considered to be in every respect satisfactory. -The efficiency was occasionally below 90 per cent, but for four -selected weeks was as high as 98.6 per cent. The average amount of -sulphate of alumina used, as calculated from Mr. Weston’s tables, was -two thirds of a grain per gallon. The highest efficiency followed the -application of a solution of caustic soda to the filtering material. -The first day following this treatment the bacterial efficiency was -above 99 per cent. Afterwards it decreased until January 30, when the -experiments were stopped. The high bacterial efficiency following the -use of caustic soda was of such short duration as to suggest very -grave doubts as to its practical value. It is extremely unfortunate -that the experiments stopped only a week after this experiment, and -the results were never repeated. I consider that the average bacterial -efficiency of about 95 per cent obtained for the period of October 17 -to January 30, when the manipulation was considered to be in every way -satisfactory, more nearly represents what can be obtained under these -conditions than the results for certain periods, particularly after the -use of the caustic soda. - - -LOUISVILLE EXPERIMENTS.[40] - -These experiments were inaugurated by the Louisville Water Company -in connection with the manufacturers of certain patented filters. -Mr. Charles Hermany, Chief Engineer of the Company, had general -charge of the experiments. Mr. George W. Fuller was Chief Chemist and -Bacteriologist and had direct charge of the work and has made a most -elaborate report upon the same. In these examinations many devices were -investigated; but the two which particularly deserve our attention are -the filters known as the Warren Filter and the Jewell Filter. - -These filters were operated for two periods, namely, from October -18, 1895, to July 30, 1896, and from April 5 to July 24, 1897. The -investigations were directed toward the clarification of the river -water from the mud, and to the removal of bacteria. The water was -substantially free from color. The character of the water at this -point was such that in its best condition at least three fourths of -a grain of sulphate of alumina were necessary for its coagulation, -and with this and with larger quantities of coagulant fair bacterial -purification was nearly always obtained. The problem studied -therefore was principally that of clarification from mud. The average -efficiencies, as shown by the total averages, (page 248,) were as -follows: Warren filter, bacterial efficiency, 96.7 per cent; Jewell -filter, 96.0 per cent. - - -LORAIN TESTS.[41] - -These tests were made by the author of a set of Jewell filters at -Lorain, Ohio. The filters were six in number, each 17 feet in diameter, -having an effective filtering area of 226 square feet each, or 1356 -square feet in all. The construction of the filters was in all respects -similar to the Jewell filter used at Louisville. The raw water was from -Lake Erie, and during the examination was - -always comparatively clear, but contained considerable numbers of -bacteria. The problem was thus entirely one of bacterial efficiency. -The question of clarification hardly presented itself. Although -the water became turbid at times it did not approach in muddiness -the condition of the Ohio River water, and an amount of coagulant -sufficient for a tolerable bacterial efficiency in all cases was more -than sufficient for clarification. - -A summary of the results obtained is as follows: - - -----------+--------------+-----------+--------+---------+---------- - | Average Rate |Sulphate of| | |Bacterial - Week Ending|of Filtration,| Alumina, |Bacteria|Bacteria |Efficiency - 6:00 P.M. | Gallons per |Grains per | in Lake| in |per cent. - | Sq. Ft. Min. |Gallon. | Water. |Effluent.| - -----------+--------------+-----------+--------+---------+---------- - June 19 | 1.06 | 2.58 | 1441 | 16 | 98.9 - 26 | 1.10 | 2.50 | 385 | 6 | 98.4 - July 3 | 1.11 | 2.27 | 367 | 9 | 97.5 - 10 | 1.28 | 1.07 | 154 | 14 | 90.9 - 17 | 1.14 | 0.94 | 189 | 26 | 86.3 - +--------------+-----------+--------+---------+---------- - Average | 1.14 | 1.83 | 507 | 14 | 96.4 - -----------+--------------+-----------+--------+---------+---------- - -The average bacterial efficiency was 96.4 per cent with 1.83 grains of -sulphate of alumina per gallon. - - -PITTSBURG EXPERIMENTS.[42] - -The Pittsburg experiments were inaugurated by the Pittsburg Filtration -Commission. The operation of the filters extended from January to -August, 1898. A Jewell and a Warren filter were used similar in design -to those used at Louisville. The raw water contained large numbers of -bacteria, and was also often very turbid, although less turbid than at -Louisville. At times more coagulant was necessary for clarification -than was required for bacterial efficiency; while as a rule more was -required for satisfactory bacterial purification than was necessary for -clarification. The opportunities were therefore favorable for the study -of both of these conditions. The amount of coagulant necessary for -clarification has been mentioned in connection with coagulation. - -The results secured upon the relation of the quantity of - -coagulant to the number of bacteria in the effluent were more complete -than any other experiments available, and are therefore here reproduced -from the Pittsburg report nearly in full. - -It was found that the amount of sulphate of alumina employed was -more important than any other factor in determining the bacterial -efficiency, and special experiments were made to establish the effect -of more and of less coagulant than used in the ordinary work. These -experiments were made upon the Warren filter during May, and with -the Jewell filter during June. The monthly averages for these months -are thus abnormal and are not to be considered. The remaining six -months for each filter may be taken as normal and as representing -approximately the work of these filters under ordinary careful working -conditions. - -During the six months when the Warren filter was in normal order the -raw water contained 11,531 bacteria and the effluent 201, the average -bacterial efficiency being 98.26 per cent. The bacterial efficiency was -very constant, ranging only, by months, from 97.48 to 98.96 per cent. -During the same period a sand filter receiving the same water yielded -an effluent having an average of 105 bacteria per cubic centimeter. - -The Jewell filter, for the six months in which it was in normal order, -received raw water containing an average of 11,481 bacteria and yielded -an effluent containing an average of 293, the bacterial efficiency -being 97.45 per cent, and ranging, in different months, from 93.23 to -98.61 per cent. - - -WASTING EFFLUENT AFTER WASHING FILTERS. - -After washing a mechanical filter the effluent for the first few -minutes is often inferior in quality to that obtained at other times, -and if samples are taken at these times and averaged with other samples -taken during the run, an apparent efficiency may be obtained inferior -to the true efficiency. To guard against this source of error, whenever -samples have been taken at such times, the average work for the day -has been taken, not as the numerical average of the results, but each -sample has been given weight in proportion to the amount of time which -it could be taken as representing; so that the results represent as -nearly as possible the average number of bacteria in the effluent for -the whole run. As a matter of fact, however, comparatively few samples -were taken during these periods of reduced efficiency, and thus most of -the results represent the normal efficiency exclusive of this period. A -study has been made, however, of the results of examinations of samples -taken directly after washing, somewhat in detail. The following is a -tabular statement of the average results obtained from each filter by -months, including only the results obtained on those days when samples -were taken within twenty minutes after washing, the results of other -days being excluded. - - -AVERAGE NUMBER OF BACTERIA IN EFFLUENT. - - --------------+------------+-------------+-------------+------------- - | Shown by | Within Ten | 11 to 20 | More than - | Record |Minutes after|Minutes after| Twenty - | Sheets. | Washing. | Washing. |Minutes after - | | | | Washing. - --------------+------------+-------------+-------------+------------- - WARREN FILTER.| | | | - February | 115 | | 118 | 114 - March | 316 | 50 | 515 | 301 - April | 79 | 417 | 207 | 75 - May | (Special experiments, omitted.) - June | 197 | 493 | 272 | 170 - July | 300 | | 546 | 207 - August | 174 | 356 | 601 | 223 - | | | | - JEWELL FILTER.| | | | - February | 2453 | 2425 | | 2099 - March | 455 | 657 | 958 | 354 - April | 99 | 665 | 462 | 165 - May | 144 | 998 | 346 | 127 - June | (Special experiments, omitted.) - July | 279 | 1330 | 272 | 274 - August | 344 | 612 | 323 | 376 - --------------+------------+-------------+-------------+------------- - -The time of inferior work very rarely exceeded twenty minutes. It -will be seen from the tables that the results as shown by the record -sheets are never very much higher, and are occasionally lower than the -results of samples taken on corresponding days more than twenty minutes -after washing; and thus while a decrease in bacterial efficiency was -noted after washing, no material increase in the average bacterial -efficiency of the mechanical filters would have been obtained if these -results had been excluded. The results for the whole time would be -affected much less than is indicated by the table, because the table -includes only results of those days when samples were taken just after -washing, while the much larger number of days when no such samples were -taken would show no change whatever. - -It has been suggested that these inferior effluents after washing -should be wasted. Such a procedure would mean wasting probably on -an average two per cent of the water filtered, and a corresponding -increase in the cost of filtering. Mr. Fuller[43] in his Louisville -report comes to the conclusion that with adequate washing and -coagulation it is unnecessary to waste any effluent, and that inferior -results after washing usually indicate incomplete washing. While our -experiments certainly indicate a reduction in efficiency after washing -so regular and persistent as to make it doubtful whether incomplete -washing can be the cause of it, it may be questioned whether or -not wasting the effluent would be necessary or desirable in actual -operation. At any rate the results as given in this report are not -materially influenced by this factor. - - -INFLUENCE OF AMOUNT OF SULPHATE OF ALUMINA ON BACTERIAL EFFICIENCY OF -MECHANICAL FILTERS. - -The number of bacteria passing a mechanical filter is dependent -principally upon the amount of sulphate of alumina used; and by using -a larger quantity of sulphate of alumina than was actually used in the -experiments the bacterial efficiency could be considerably increased. -To investigate this point, the results obtained each day with each -of the mechanical filters were arranged in the order of the sulphate -of alumina quantities used, and averaged by classes. In this and the -following tables a few abnormal results were omitted.[44] A summary of -the results is as follows: - - -SUMMARY OF RESULTS WITH WARREN MECHANICAL FILTER, ARRANGED ACCORDING TO -SULPHATE OF ALUMINA QUANTITIES. - - ------------+----------+--------------------+----------+--------+----------- - Number | | Bacteria. | | |Sulphate of - of Days |Turbidity.+----------+---------+ Per cent |Per cent| Alumina - Represented.| |Raw Water.|Effluent.|remaining.|removed.|used Grains - | | | | | |per Gallon. - ------------+----------+----------+---------+----------+--------+----------- - 7 | 0.05 | 4,773 | 1713 | 35.89 | 64.11 | 0.00 - 2 | 0.08 | 2,785 | 850 | 30.52 | 69.48 | 0.12 - 4 | 0.10 | 5,109 | 726 | 14.21 | 85.79 | 0.26 - 2 | 0.20 | 8,713 | 214 | 2.45 | 97.55 | 0.36 - 8 | 0.06 | 3,224 | 112 | 3.47 | 96.53 | 0.44 - 19 | 0.06 | 3,488 | 123 | 3.53 | 96.47 | 0.55 - 11 | 0.06 | 5,673 | 154 | 2.71 | 97.29 | 0.64 - 10 | 0.10 | 6,100 | 112 | 1.84 | 98.16 | 0.74 - 8 | 0.09 | 8,647 | 148 | 1.71 | 98.29 | 0.85 - 5 | 0.16 | 5,645 | 142 | 2.52 | 97.48 | 0.93 - 13 | 0.12 | 10,397 | 200 | 1.92 | 98.08 | 1.07 - 10 | 0.08 | 12,778 | 121 | 0.95 | 99.05 | 1.13 - 13 | 0.14 | 13,397 | 164 | 1.22 | 98.78 | 1.25 - 19 | 0.13 | 10,462 | 160 | 1.53 | 98.47 | 1.34 - 10 | 0.12 | 12,851 | 107 | 0.83 | 99.17 | 1.46 - 4 | 0.27 | 16,015 | 77 | 0.48 | 99.52 | 1.57 - 7 | 0.53 | 12,262 | 191 | 1.18 | 98.82 | 1.64 - 4 | 0.58 | 26,950 | 347 | 1.29 | 98.71 | 1.74 - 5 | 0.29 | 14,570 | 86 | 0.59 | 99.41 | 1.84 - 3 | 0.23 | 13,833 | 153 | 1.11 | 98.89 | 1.92 - 19 | 0.40 | 18,222 | 92 | 0.50 | 99.50 | 2.48 - 5 | 0.45 | 29,300 | 1119 | 3.82 | 96.18 | 3.37 - 5 | 1.06 | 33,030 | 535 | 1.62 | 98.38 | 8.06 - ------------+----------+----------+---------+----------+--------+----------- - - -SUMMARY OF RESULTS WITH JEWELL MECHANICAL FILTER, ARRANGED ACCORDING TO -SULPHATE OF ALUMINA QUANTITIES. - - ------------+----------+----------+---------+----------+--------+----------- - Number | | Bacteria. | | |Sulphate of - of Days |Turbidity.+----------+---------+ Per cent |Per cent| Alumina - Represented.| |Raw Water.|Effluent.|remaining.|removed.|used Grains - | | | | | |per Gallon. - ------------+----------+----------+---------+----------+--------+----------- - 6 | 0.03 | 14,037 | 6217 | 44.29 | 55.71 | 0.00 - 5 | 0.07 | 4,267 | 680 | 15.93 | 84.07 | 0.24 - 14 | 0.06 | 2,613 | 170 | 6.50 | 93.50 | 0.35 - 10 | 0.06 | 2,446 | 113 | 4.62 | 95.38 | 0.44 - 9 | 0.11 | 7,303 | 234 | 3.20 | 96.80 | 0.55 - 20 | 0.09 | 6,979 | 220 | 3.15 | 96.85 | 0.65 - 9 | 0.08 | 5,191 | 130 | 2.50 | 97.50 | 0.75 - 16 | 0.12 | 8,504 | 242 | 2.84 | 97.16 | 0.83 - 22 | 0.16 | 8,506 | 99 | 1.16 | 98.84 | 0.96 - 12 | 0.11 | 11,998 | 246 | 2.05 | 97.95 | 1.05 - 14 | 0.18 | 18,982 | 423 | 2.23 | 97.77 | 1.16 - 5 | 0.14 | 13,981 | 224 | 1.60 | 98.40 | 1.23 - 9 | 0.27 | 19,806 | 325 | 1.64 | 98.36 | 1.34 - 14 | 0.27 | 16,549 | 324 | 1.96 | 98.04 | 1.45 - 9 | 0.29 | 12,194 | 96 | 0.79 | 99.21 | 1.54 - 6 | 0.25 | 13,483 | 51 | 0.38 | 99.62 | 1.65 - 7 | 0.53 | 24,243 | 220 | 0.91 | 99.09 | 1.72 - 3 | 0.90 | 20,953 | 602 | 2.88 | 97.12 | 1.90 - 5 | 0.43 | 25,958 | 307 | 1.19 | 98.81 | 2.19 - 4 | 0.84 | 21,017 | 228 | 1.09 | 98.91 | 3.71 - ------------+----------+----------+---------+----------+--------+----------- - -These results are shown graphically by Fig. 21. - -[Illustration: FIG. 21.—BACTERIAL EFFICIENCIES OF MECHANICAL FILTERS.] - - -INFLUENCE OF DEGREE OF TURBIDITY UPON BACTERIAL EFFICIENCY OF -MECHANICAL FILTERS. - -It will be noticed by referring to the tables that as the sulphate of -alumina quantities increased the turbidities increased and the numbers -of bacteria increased, as well as the bacterial efficiencies. That -is to say, with the less turbid waters, small sulphate of alumina -quantities have been used, the numbers of bacteria in the raw water -have been low, and the bacterial efficiencies have also been low. With -turbid waters much larger quantities of sulphate of alumina have been -used, the raw water has contained more bacteria, and the bacterial -efficiencies have been higher. It may be then that the increased -efficiencies with increased quantities of sulphate of alumina are not -due alone to the increased sulphate of alumina, but in part also to -other conditions. Thus it may be easier to remove a large percentage of -bacteria from a water containing many than from a water containing only -a few. - -To investigate this matter and eliminate the influence of turbidity and -numbers of bacteria in the raw water, the results were first classified -with reference to turbidity. The results with waters having turbidities -of 0.10 or less, and called for convenience turbid waters, are arranged -by alum quantities as before. Afterwards the results obtained with -turbidities from 0.11 to 0.50, and called for convenience muddy -waters, are grouped; and finally the results with turbid water having -turbidities of 0.51 and over, and called for convenience thick waters. -The results thus arranged are as follows: - - - SUMMARY OF RESULTS WITH WARREN MECHANICAL FILTER, ARRANGED ACCORDING - TO TURBIDITIES AND SULPHATE OF ALUMINA QUANTITIES. - - ------------+----------+--------------------+----------+--------+----------- - | | | | |Sulphate of - Number | | Bacteria. | Per cent |Per cent| Alumina - of Days |Turbidity.+----------+---------+remaining.|removed.|used Grains - Represented.| |Raw Water.|Effluent.| | |per Gallon. - ------------+----------+----------+---------+----------+--------+----------- - 7 | 0.05 | 4,773 | 1713 | 35.89 | 64.11 | 0.00 - 2 | 0.07 | 2,785 | 850 | 30.52 | 69.48 | 0.12 - 12 | 0.06 | 3,209 | 224 | 7.00 | 93.00 | 0.42 - 31 | 0.06 | 4,238 | 119 | 2.81 | 97.19 | 0.60 - 9 | 0.06 | 7,953 | 130 | 1.64 | 98.36 | 0.84 - 16 | 0.04 | 11,265 | 137 | 1.22 | 98.78 | 1.11 - 29 | 0.06 | 11,500 | 158 | 1.37 | 98.63 | 1.58 - | | | | | | - 5 | 0.17 | 8,783 | 416 | 4.73 | 95.27 | 0.36 - 10 | 0.16 | 6,535 | 165 | 2.54 | 97.46 | 0.85 - 13 | 0.19 | 13,253 | 186 | 1.40 | 98.60 | 1.13 - 15 | 0.22 | 10,944 | 93 | 0.85 | 99.15 | 1.36 - 13 | 0.29 | 14,089 | 112 | 0.80 | 99.20 | 1.73 - 10 | 0.35 | 18,088 | 102 | 0.57 | 99.43 | 2.38 - 5 | 0.29 | 25,580 | 540 | 2.11 | 97.89 | 4.30 - | | | | | | - 6 | 0.87 | 25,433 | 369 | 1.45 | 98.55 | 1.74 - 6 | 0.73 | 26,566 | 79 | 0.30 | 99.70 | 2.64 - 4 | 1.35 | 42,037 | 1388 | 3.30 | 96.70 | 8.16 - ------------+----------+----------+---------+----------+--------+----------- - - SUMMARY OF RESULTS WITH JEWELL MECHANICAL FILTER, ARRANGED ACCORDING - TO TURBIDITIES AND SULPHATE OF ALUMINA QUANTITIES. - - ------------+----------+--------------------+----------+--------+----------- - | | | | |Sulphate of - Number | | Bacteria. | | | Alumina - of Days |Turbidity.+----------+---------+ Per cent |Per cent|used Grains - Represented.| |Raw Water.|Effluent.|remaining.|removed.|per Gallon. - ------------+----------+----------+---------+----------+--------+----------- - 6 | 0.03 | 14,037 | 6217 | 44.29 | 55.71 | 0.00 - 3 | 0.07 | 5,170 | 991 | 19.15 | 80.85 | 0.21 - 25 | 0.05 | 2,403 | 143 | 5.95 | 94.05 | 0.38 - 20 | 0.06 | 6,531 | 185 | 2.84 | 97.16 | 0.64 - 27 | 0.06 | 5,811 | 122 | 2.10 | 97.90 | 0.88 - 14 | 0.06 | 14,978 | 412 | 2.75 | 97.25 | 1.11 - 10 | 0.06 | 15,787 | 390 | 2.47 | 97.53 | 1.37 - 10 | 0.05 | 10,847 | 47 | 0.43 | 99.57 | 2.17 - | | | | | | - 14 | 0.16 | 7,525 | 256 | 3.40 | 96.60 | 0.60 - 17 | 0.24 | 11,310 | 208 | 1.84 | 98.16 | 0.91 - 15 | 0.24 | 15,441 | 262 | 1.70 | 98.30 | 1.13 - 10 | 0.28 | 17,842 | 232 | 1.30 | 98.70 | 1.43 - 8 | 0.29 | 9,556 | 59 | 0.62 | 99.38 | 1.59 - 4 | 0.29 | 20,212 | 135 | 0.67 | 99.33 | 2.00 - | | | | | | - 5 | 0.66 | 23,680 | 336 | 1.42 | 98.58 | 1.42 - 7 | 0.96 | 30,200 | 475 | 1.57 | 98.43 | 1.74 - 4 | 1.25 | 37,587 | 496 | 1.32 | 98.68 | 2.81 - ------------+----------+----------+---------+----------+--------+----------- - -The following table shows the bacterial efficiencies with turbid, -muddy, and thick waters, with substantially equal quantities of -sulphate of alumina: - - -------------------------------+------------------------------------- - Grains of Sulphate of Alumina.|Corresponding Bacterial Efficiencies. - ----------+----------+---------+-----------+----------+-------------- - Turbid. | Muddy. | Thick. | Turbid. | Muddy. | Thick. - ----------+----------+---------+-----------+----------+-------------- - WARREN FILTER. - 0.42 | 0.36 | | 93.00 | 95.27 | - 0.84 | 0.85 | | 98.36 | 97.46 | - 1.11 | 1.13 | | 98.78 | 98.60 | - 1.58 | 1.73 | 1.74 | 98.63 | 99.20 | 98.55 - | 2.38 | 2.64 | | 99.43 | 99.70 - | 4.30 | 8.16 | | 97.89 | 96.70 - - JEWELL FILTER. - 0.64 | 0.60 | | 97.16 | 96.60 | - 0.88 | 0.91 | | 97.90 | 98.16 | - 1.11 | 1.13 | | 97.25 | 98.30 | - 1.37 | 1.43 | 1.42 | 97.53 | 98.70 | 98.58 - 2.17 | 1.59 | 1.74 | 99.57 | 99.38 | 98.43 - | 2.00 | 2.81 | | 99.33 | 98.68 - ----------+----------+---------+-----------+------------------------- - -It appears from this table that waters of various degrees of turbidity -give substantially equal bacterial efficiencies with equal quantities -of sulphate of alumina, the results varying as often in one direction -as the other. Within certain limits it may thus be said that turbidity -is without influence upon the bacterial efficiency obtained in -mechanical filtration. - -It must be borne in mind, however, that the quantities of sulphate -of alumina, with very few exceptions, were sufficient to produce -full coagulation. Mr. Fuller has shown in his Louisville report that -considerable quantities of sulphate of alumina may be added to turbid -waters without producing appreciable coagulation; and therefore if -a quantity of sulphate of alumina sufficient to produce a certain -bacterial efficiency in a clear water should be added to a water so -turbid that it was unable to coagulate it, scarcely any effect would -be produced. The above statement therefore only applies in those cases -where sufficient sulphate of alumina is used to adequately coagulate -the water. - -As the numbers of bacteria often vary with the turbidity, the variation -in the numbers of bacteria in the different classes is much less than -in the first tables; but to further investigate the question of whether -the numbers of bacteria in the raw water have an important influence -upon the bacterial efficiencies, each of the two largest classes in the -foregoing tables was divided into two parts, according to the bacterial -numbers in the raw water, namely, the results from the Jewell filter -with turbid waters and with sulphate of alumina quantities ranging from -0.75 to 1.00 grain per gallon, and the results from the Warren filter -with turbid waters and with sulphate of alumina quantities of 1.25 -grains per gallon and upward. The results are as follows: - - ------------+----------+--------------------+----------+--------+----------- - | | | | |Sulphate - Number | | Bacteria. | | |of Alumina - of Days |Turbidity.+----------+---------+ Per cent |Per cent|used Grains - Represented.| |Raw Water.|Effluent.|remaining.|removed.|per Gallon. - ------------+----------+----------+---------+----------+--------+----------- - JEWELL FILTER. - 14 | 0.05 | 3,938 | 81 | 2.06 | 97.94 | 0.88 - 13 | 0.07 | 7,827 | 167 | 2.13 | 97.87 | 0.87 - WARREN FILTER. - 15 | 0.06 | 3,545 | 59 | 1.66 | 98.34 | 1.67 - 14 | 0.06 | 20,022 | 265 | 1.32 | 98.68 | 1.48 - ------------+----------+----------+---------+----------+--------+----------- - -It will be observed that the bacterial efficiencies are substantially -the same, with the lower and with the higher numbers of bacteria in -the raw water. That is to say, other things being equal, as the number -of bacteria increase in the raw water the number of bacteria in the -effluent increase in the same ratio. A further analysis of other groups -of results would perhaps show variations in one direction or the other, -but on the whole it is believed that the comparison is a fair one, and -that there is no well-marked tendency for bacterial efficiencies of -mechanical filters to increase or decrease with increasing numbers of -bacteria. - - -AVERAGE RESULTS OBTAINED WITH VARIOUS QUANTITIES OF SULPHATE OF ALUMINA. - -As it appears that neither the turbidity nor the number of bacteria in -the raw water has a material influence upon the percentage bacterial -efficiency obtained, we can take the results given above, which -include all the results obtained (except a very few abnormal ones) for -computing the various efficiencies obtained with various quantities of -sulphate of alumina. These results are graphically shown by Fig. 21, p. -167, on which lines have been drawn indicating the normal efficiencies -from various quantities of sulphate of alumina as deduced from our -experiments. - -In computing the amount of sulphate of alumina which it would be -necessary to use in operating a plant at a given place to give these -efficiencies, the quantities of sulphate of alumina shown by the -diagram can be taken as those which it would be necessary to use during -those days in the year when the raw water was clear, or sufficiently -clear, so that the amounts of sulphate of alumina mentioned would -suffice to properly coagulate it. - - -TYPES OF MECHANICAL FILTERS. - -Sections of the Warren and Jewell filters used at Pittsburg are -presented herewith. The filters here shown are practically identical -with those used at Lorain and Louisville, and nearly all the exact -information regarding mechanical filters relates to filters of these -types. These sections show clearly the constructions used at Pittsburg -and Louisville, but there are some points in connection with the -designs of these filters which require to be considered more in detail. - -The simplest idea of a mechanical filter is a tub, with sand in the -bottom and some form of drainage system. Water is run over the sand, -passes through it, and is collected by the drainage system. When the -sand becomes clogged it is washed by the use of a reverse current of -water. This reverse current of water is so rapid as to preclude the use -of a drainage system consisting of gravel, tile-drains, etc., such as -are used in sand filters operated at lower rates, and instead metallic -strainers in some form are used. The sand comes directly against these -strainers, which are made as coarse as it is possible to have them, -without allowing the sand to pass. - -The rate of washing is usually from five to seven gallons per square -foot per minute. In the Warren filter the openings in the strainers at -the bottom are 6 to 8 per cent of the total area, and during washing -the water has an average velocity of 0.20 foot per second upward -through them. This velocity is so slow that the friction of the water -in passing through the openings in the screen is practically nothing. -A result of this is that if there is any unequal resistance of the -sand to the water, the bulk of the water goes up at the points of least -resistance in the sand. - -[Illustration: FIG. 22.—SECTION OF JEWELL MECHANICAL FILTER USED IN -PITTSBURG EXPERIMENTS.] - -This tendency would be fatal were it not for the revolving rake which -loosens and mixes the sand and largely corrects it. The correction, -however, is imperfect, and some parts of the filter are washed more -than others. - -The rake is also necessary to prevent the separation of sand into -coarser and finer particles. It is practically impossible to get -filter sand the grains of which are all of the same size. When a filter -is washed the tendency is for the wash water to go up in limited areas. -The larger sand grains tend to collect at these points while the -finer grains collect in places where there is no upward current, or -where it is less rapid. In many filters this tendency is very strong. -The revolving rake is necessary to correct it, and to keep the sand -thoroughly mixed, otherwise when a filter is put in operation after -washing, the frictional resistance through the coarse sand being less, -the bulk of the water goes through it, with the result that a part of -the area, and the part which is least efficient as a filter, passes -nearly all of the water, and with inferior results. - -In the Jewell filter provision is made for the distribution of the wash -water over the whole area in another way. The strainers have areas at -the surface amounting to 1.2 to 1.4 per cent of the whole area, but -the water before reaching them passes through throats much smaller in -size than the strainer outlets, and amounting in the aggregate to only -about 0.07 per cent of the filter area. When washing at a rate of seven -gallons per square foot per minute, water passes through these necks -at a velocity of 22 feet per second. The friction and velocity head in -passing these necks is estimated to be about 30 vertical feet, and is -so much greater than the friction of the outlets proper, and of the -sand, that the water passes through each strainer with approximately -the same velocity, and the wash water is equally distributed over the -whole area of the bottom of the filter. - -This result is accomplished, however, at a great loss of head in the -wash water. When a filter is washed from the pressure-mains without -separate pumping, the pressure is usually sufficient and there is no -disadvantage in the arrangement. When, however, the water is specially -pumped for washing, the required head is much greater than would -otherwise be necessary. - -[Illustration: MECHANICAL FILTERS AT ELMIRA, N. Y. OUTLET TO FILTERS -WITH CONTROLLER AND PURE-WATER FLUME. - - [_To face page 174._] -] - -It would not be possible to increase the size of the necks, thereby -decreasing the friction, without increasing very largely the size -of the pipes in the underdrainage system into which the strainers are -fastened. These pipes are so small that during washing the velocity in -them is about 13 feet per second, and if the throats of the necks were -increased without also enlarging these pipes, the friction would be so -reduced that most of the water would go through the necks nearest the -supply, thus failing to reach the object to be attained. - -A more rational system would be to increase the sizes of all the -waterways in the outlet and wash-water system. The Jewell filter is -also provided with a rake to keep the sand mixed during washing, as -this is necessary even with the complete distribution of wash-water -over the area of the filter. - -Both the Warren and the Jewell filters are provided with receptacles -through which the water passes after receiving the coagulant, and -before entering the filter. In the Jewell filter the receptacle, called -a sedimentation-basin, is of such size as to hold as much water as is -filtered in 15 minutes. In the Warren filter the receptacle is entirely -independent and larger, holding about an hour’s supply. - -The rates of filtration used in the experiments have ranged from less -than 100 to about 130 million gallons per acre daily. To employ a rate -much higher than this involves the use of a much coarser sand, or an -increase in the height of water upon the filter to an impracticable -extent. There would seem to be no material advantage in the use of -lower rates within certain limits, while the cost of filters would be -greatly increased. - -The sand used in the Warren filters has been crushed quartz. In the -Jewell filters a silicious sand from Red Wing, Minn., with rounded -grains has been used. These sands are somewhat coarser than are -commonly used in sand filters, and the uniformity coefficients are -very low. It is necessary to use sand with the very lowest uniformity -coefficients to avoid the separation of sand particles according to -sizes as mentioned above, and for this reason the sand must be -selected with much greater care than is required for sand filters. - -[Illustration: PLAN JUST ABOVE COPPER. - -SECTION SHOWING FILTER DURING ORDINARY OPERATION. - -FIG. 23.—WARREN FILTER: PITTSBURG EXPERIMENTS. SECTION NO. 1.] - -[Illustration: PLAN OF AGITATOR, GUTTER CASTINGS, ETC. - -SECTION SHOWING FILTER DURING OPERATION OF WASHING. - -FIG. 24.—WARREN FILTER: PITTSBURG EXPERIMENTS. SECTION NO. 2.] - -The round-grained sand is more readily and completely washed than the -angular crushed quartz. It has been claimed that the crushed quartz is -more efficient as a filtering material, but the evidence of this is not -very clear. - -The amount of water filtered by a filter between washings is, in a -general way, about the same as that filtered by a sand filter between -scrapings, in relation to its area. The amount of water required for -washing is, on an average, about equal to a vertical column 5 or 6 -feet high equal in area to the area of the filter, exclusive of water -on the top of the filter wasted before the current is reversed. With -clear waters, as for instance, the Allegheny at low water, the amount -of washing is almost directly proportional to the amount of sulphate -of alumina used. With muddy waters the sulphate of alumina required is -proportional to the mud, and the frequency of washing and the amount of -wash-water are proportional to both. The amount of wash-water required -averages about five per cent; with very muddy waters more is required. -At Louisville, with the worst waters, the per cents of wash-water rose -at times to 30 per cent of the total quantity of water filtered. - -The rate of filtration with mechanical filters should be kept as -constant as possible, and can be regulated by devices similar to -those described in connection with sand filters. Owing to the smaller -areas and capacities, the amounts of water to be handled in the units -are smaller, and the regulating devices are thus smaller, and have -always been made of metal, either cast iron or copper. None of the -devices employed in the above-mentioned experiments has been entirely -satisfactory in this respect. The devices employed have been too small, -and the water has gone through at too high velocities to allow close -adjustment. - -[Illustration: MECHANICAL FILTERS AT ELMIRA, N. Y. UPPER PLATFORM AND -GENERAL ARRANGEMENT OF FILTERS. - - [_To face page 178._] -] - -As between the two types of filters, the Jewell filter requires a large -loss of head. The water has to be pumped at a sufficient elevation -to reach the top of a tank about 18 feet high, while the effluent -must be drawn off at the extreme bottom. The Warren filter is much -more economical in head, the plants at Pittsburg and Louisville only -requiring about 9 feet from the inlet to the outlet. - -The earlier mechanical filters were usually constructed of wrought -iron or steel plates. More recently wooden tanks have been commonly -employed, although steel is regarded as preferable. Concrete or masonry -tanks have been suggested, but they have not as yet been employed. - - -EFFICIENCY OF MECHANICAL FILTERS. - -The efficiency of mechanical filters depends entirely upon the use of -coagulants. Without coagulants they can only be used to remove very -large particles. The efficiency of the filtration depends much more -upon the kind, and amount, and method of application of coagulant than -upon the arrangement of the filter. In fact, the arrangements of the -filter are more directed to the convenience and economy of operation -and washing than towards the efficiency of the results. - -The conditions which control the efficiency of mechanical filters -have been discussed in connection with coagulation. With sufficient -coagulant the removal of turbidity or mud is complete. Color also can -be removed with these filters. The bacterial efficiencies secured with -them have been discussed at length in connection with the Pittsburg -experiments. - -With careful coagulation and manipulation it is possible to get 98 per -cent bacterial efficiency without difficulty. The results are somewhat -irregular, for reasons not as yet fully understood. On some occasions -higher bacterial efficiencies are secured with smaller quantities of -coagulant, while at other times the efficiencies are less without -apparent reason. There seems to be a limit to the bacterial efficiency -which can be secured with any amount of sulphate of alumina and -rapid filtration, and it is doubtful if a plant could be operated to -regularly secure as high a bacterial efficiency as 99 per cent with any -amount of sulphate of alumina. - - -PRESSURE FILTERS. - -Pressure mechanical filters are constructed in entirely closed -receptacles, through which the water is forced under pressure and not -by gravity. Many of the earlier mechanical filters were of this type. -In small plants this system has the distinct advantage that the water -can be pumped from a river or other source of supply through a filter -direct to the reservoir or into the mains, while any other system would -involve a second pumping. Pressure filters are extensively used for -hotel supplies, etc., where, from the conditions, gravity filters are -impossible. The practical objections to this system have been found -to be so great that it is rarely used under other conditions. Some -experiments were made at Louisville with a filter of this type, but -they were not long continued, and aside from them there is no precise -information as to what can be accomplished with filters of this type. - - - - -CHAPTER XI. - -OTHER METHODS OF FILTRATION. - - -WORMS TILE SYSTEM. - -This system, invented and patented by Director Fischer of the Worms -water-works, consists of the filtration of water through artificial -hollow sandstone tiles, made by heating a mixture of broken glass -and sand, sifted to determined sizes, to a point just below the -melting-point of the glass, in suitable moulds or forms. The glass -softens and adheres to the sand, forming a strong porous substance -through which water can be passed. These tiles are made hollow and -are immersed in the water to be treated, the effluent being removed -from the centre of each tile. They are connected together in groups -corresponding in size to the units of a sand-filtration plant. They -are washed by a reverse current of filtered water. These tiles have -been used for some years at Worms, Germany, and at a number of smaller -places, and were investigated experimentally at Pittsburg. Some -difficulty has been experienced in getting tiles with pores small -enough to yield an effluent of the desired purity, and at the same time -large enough to allow a reasonable quantity of water to pass. In fact, -with other than quite clear waters, it has not been found feasible to -accomplish both objects at the same time, and it has been necessary -to treat the water with coagulants and preliminary sedimentation or -filtration before applying it to the tiles. The problem of making the -joints between the tiles and the collection-pipes water-tight when -surrounded by the raw water also is a matter of some difficulty. - - -THE USE OF ASBESTOS. - -It has been suggested by Mr. P. A. Maignen that the surface of sand -filters should be covered with a thin layer of asbestos, applied in -the form of a pulp, with the first water put onto the filter after -scraping. The asbestos forms a sort of a paper on the sand which -intercepts the sediment of the passing water. The advantage of the -process is in the cleaning. When dried to the right consistency this -asbestos can be rolled up like a carpet, and taken from the filter -without removing any of the sand. - -This procedure is almost identical with that which has occurred -naturally in iron-removal plants, where algæ grow in the water upon the -filters, and form a fibrous substance with the ferric oxide removed -from the water, which can be rolled up and removed in the same way -as the asbestos. The advantages of the process, from an economical -standpoint, are less clear. - - -FILTERS USING HIGH RATES OF FILTRATION WITHOUT COAGULANTS. - -Numerous filters have been suggested, and a few have been constructed -for the use of much higher rates of filtration than are usually -employed with sand filters, but without the use of coagulants. The -results obtained depend upon the requirements and upon the character -of the raw water. If a reservoir water contains an algæ growth, it can -often be removed by a coarse and rapid filter. The organisms in this -case are many times larger than the bacteria, and many times larger -than the clay particles which constitute turbidity. The requirements in -this case are rather in the nature of straining than of filtration. - -The conditions necessary for the removal of bacteria and turbidity are -very well understood, and it can be stated with the utmost confidence -that no system of filtration through sand at rates many times as -high as are used in ordinary sand filtration, and without the use of -coagulants, will be satisfactory where either bacterial efficiency -or clarification is required. The application of such systems of -filtration would therefore seem to be somewhat limited. - -[Illustration: REMOVING DIRTY ASBESTOS COVERING FROM AN EXPERIMENTAL -FILTER. MAIGNEN SYSTEM. - - [_To face page 182._] -] - - -HOUSEHOLD FILTERS. - -The subject of household filters is a somewhat broad one, as the -variety in these filters is even greater than in the larger filters, -and the range in the results to be expected from them is at least as -great. I shall only attempt to indicate here some of the leading points -in regard to them. - -Household filters may be used to remove mud or iron rust from the tap -water, or to remove the bacteria in case the latter is sewage-polluted, -or to do both at once. Perhaps oftener they are used simply because -it is believed to be the proper thing, and without any clear -conception either of the desired result or the way in which it can -be accomplished. I shall consider them only in their relations to -the removal of bacteria, as I credit the people who employ them with -being sufficiently good judges of their efficiency in removing visible -sediment. - -In the first place, as a general rule, which has very few if any -exceptions, we may say that all small filters which allow a good stream -of water to pass do not remove the bacteria. The reason for this is -simply that a material open enough to allow water to pass through it -rapidly is not fine enough to stop such small bodies as the bacteria. -The filters which are so often sold as “germ-proof,” consisting of -sand, animal charcoal, wire-cloth, filter-paper, etc., do not afford -protection against any unhealthy qualities which there may be in the -raw water. Animal charcoal removes color without retaining the far more -objectionable bacteria. - -The other household filters have filtering materials of much finer -grain, unglazed porcelain and natural sandstone being the most -prominent materials, while infusorial earth is also used. The smaller -sizes of these filters allow water to pass only drop by drop, and when -a fair stream passes them the filters have considerable filtering -area (as a series of filter-tubes connected together). On account of -their slow action, filters of this class are, as a rule, provided with -storage reservoirs so that filtered water to the capacity of the -reservoir can be drawn rapidly (provided the calls do not come too -often). Some of these filters are nearly germ-proof, and are comparable -in their efficiency to large sand-filters. There is no sharp line -between the filters which stop and which do not stop the bacteria; but -in general the rule that a filter which works rapidly in proportion to -its size does not do so, and _vice versa_, will be found correct. - -In thinking of the efficiency of household filters we must distinguish -between the filter carefully prepared for an award at an exhibition -and the filter of the same kind doing its average daily work in the -kitchen. If we could be sure in the latter case that an unbroken layer -of fine sandstone or porcelain was always between ourselves and the raw -tap-water we could feel comparatively safe. The manufacturers of the -filters claim that leaky joints, cracked tubes, etc., are impossible; -but I would urge upon the people using water filtered in this way that -they personally assure themselves that this is actually the case with -their own filters, for in case any such accident should happen the -consequences might be most unpleasant. The increased yield of a filter -due to a leaky joint is sure not to decrease it in favor with the cook, -who is probably quite out of patience with it because it works so -slowly, that is, in case it is good for anything. - -The operation of household filters is necessarily, with rare -exceptions, left to the kitchen-girl and luck. Scientific supervision -is practically impossible. With a large filter, on the other hand, -concentrating all the filters for the city at a single point, a -competent man can be employed to run them in the best-known way; and -if desired, and as is actually done in very many places, an entirely -independent bacteriologist can be employed to determine the efficiency -of filtration. With the methods of examination now available, and -a little care in selecting the times and places of collecting the -samples, it is quite impossible for a filter-superintendent to -deliver a poor effluent very often or for any considerable length of -time without being caught. The safety of properly-conducted central -filtration is thus infinitely greater than that from even the best -household filters. Further, it may be doubted whether an infected water -can be sent into every house in the city to be used for washing and all -the purposes to which water is put except drinking, without causing -disease, although less than it would if it were also used for drinking. - -The use of household filters must be regarded as a somewhat desperate -method of avoiding some of the bad consequences of a polluted -water-supply, and they are adopted for the most part by citizens who -in some measure realize the dangers from bad water, but who cannot -persuade their fellow-citizens to a more thorough and adequate solution -of the problem. Such citizens, by the use of the best filters, and by -carefully watching their action, or by having their drinking-water -boiled, can avoid the principal dangers from bad water, but their -vigilance does not protect their more careless neighbors. - - - - -CHAPTER XII. - -REMOVAL OF IRON FROM GROUND-WATERS. - - -The filtration of ground-waters is a comparatively recent development. -Ground-waters are filtered by their passage through soil generally -much more perfectly than it is possible to filter other waters, and -any further filtration of them is useless. Such waters, however, -occasionally contain iron in solution as ferrous carbonate. - -Waters containing iron have been used as mineral waters for a very long -time. Such waters have an astringent taste, and have been esteemed -for some purposes. As ordinary water-supplies, however, they are -objectionable. The iron deposits in the pipes when the current is -slow, and is flushed out when it is rapid, and makes the water turbid -and disagreeable; and still worse, the iron often gets through the -pipe-system in solution, and deposits in the wash-tub, coloring the -linen a rusty brown and quite spoiling it. - -An organism called crenothrix grows in pipes carrying waters containing -iron, and after a while this organism dies, and decomposes, and -gives rise to very disagreeable tastes and odors. It thus happens -that ground-waters containing iron are unsatisfactory as public -water-supplies, and are sources of serious complaint. - - -AMOUNT OF IRON REQUIRED TO RENDER WATER OBJECTIONABLE. - -Three hundredths of a part in 100,000 of metallic iron very rarely -precipitate or cause any trouble. Five hundredths occasionally -precipitate, and this amount may be taken as about the allowable -limit of iron in a satisfactory water. One tenth of a part is quite -sure to precipitate and give rise to serious complaint. Two or three -tenths make the water entirely unsuitable for laundry purposes, and -are otherwise seriously objectionable, and will hardly be tolerated -by a community. Under some conditions ground-waters carry as much -as 1 part in 100,000 of iron, and such waters are hardly usable. In -iron-removal plants an effluent containing less than 0.05 is regarded -as satisfactory. One containing less than 0.02, as is the case with -many plants, is all that can be desired. The percentage of removal is -of no significance, but only the amount left in the effluent. - - -CAUSE OF IRON IN GROUND-WATERS. - -Natural sands, gravels, and rocks almost always contain iron, often in -considerable amount. The iron is usually combined with oxygen as ferric -oxide, and in this condition it is insoluble in water. Water passing -through iron containing materials will not ordinarily take up iron. -When, however, the water contains a large amount of organic matter in -solution, this organic matter takes part of the oxygen away from the -iron, and reduces the ferric oxide to ferrous oxide. The ferrous oxide -combines with carbonic acid, always present under these conditions, -forming ferrous carbonate, which is soluble and which goes into -solution. - -Surface-waters nearly always carry free oxygen, and when such waters -enter the ground they carry oxygen with them, and the organic matters -in the water use up the free oxygen before they commence to take oxygen -away from the iron of the ground. It is thus only in the presence of -organic matters, and in the absence of free oxygen, that the solution -of iron is possible. It sometimes happens that the organic matters -which reduce the iron are contained in the soil itself, in which -case iron may be taken up even by water originally very pure, as for -instance, by rain-water. - -Generally speaking, iron is everywhere present in sufficient quantity -in the strata from which ground-waters are obtained, and wherever the -conditions of the organic matters and oxygen necessary for solution -occur, iron-containing waters are secured, and the iron is usually -present in the earth in such quantity that the water can dissolve as -much as it will take up for a long series of years, or for centuries, -without exhausting the supply. There is thus little prospect of -improvement of such waters from exhaustion of the supply of iron. - -The circumstances which control the solution of iron are very -complicated and difficult to determine. Wells near a river, and drawing -their water largely from it by seepage, are apt to yield a water -containing iron sooner or later, especially where the river-water -carries a large amount of organic matter in solution. Waters drawn from -extensive gravel deposits, in which the water is renewed principally by -the rainfall upon the surface of the deposits themselves, often remain -entirely free from iron indefinitely. The rain-water is almost free -from organic matter, and the air is able to take care of decomposing -organic matters in the surface soil, and below this there are no -accumulations of organic matter sufficient to cause the solution of -iron. Under other conditions there are subterranean sources of organic -matter which result in the solution of iron under conditions which, on -the surface, appear most favorable for securing good water. Wells are -often used for many years without developing iron, when suddenly iron -will appear. This appearance of iron is often connected with increasing -consumption of water. In some cases it may result from drawing water -from areas not previously drawn upon. - -When iron once makes its appearance in a water, it seldom disappears -completely afterward, although it often fluctuates widely at different -seasons of the year and under different conditions of pumping. In some -cases a decrease in the quantity of iron is noted after a number of -years, but in other cases this does not happen. - -In a few cases manganese has been found in ground-waters. Manganese in -water behaves much like iron, but there are some points of difference, -so that the possibility of the presence of this substance should be -borne in mind. - -Iron-containing waters are generally entirely free from oxygen, and -when first drawn from the ground they are bright and clear and do not -differ in appearance from other ground-waters. On exposure to the air -they quickly become turbid from the oxidation of the iron, and its -precipitation as ferric hydrate. At West Superior, Wisconsin, a water -was found containing both iron and dissolved oxygen. It was turbid -as pumped from the well. This condition of affairs seemed abnormal, -but was repeatedly checked, and the theory was advanced by Mr. R. S. -Weston, who made the observations, that it resulted from a mixture in -the wells of two entirely different waters, namely, a water resulting -from the rainfall on sand deposits back of the wells, containing -dissolved oxygen and no iron, and water from the lake which had seeped -through the sand, and which contained a considerable amount of iron -in solution but no dissolved oxygen. The wells thus drew water from -opposite directions, and the two waters were entirely different in -character, and the mixture thus had a composition which would not have -been possible in a water all of which came from a single source. - -TREATMENT OF IRON-CONTAINING WATERS. - -The removal of iron from ground-water is ordinarily a very simple -procedure. It is simply necessary to aerate the water, by which process -the ferrous carbonate is decomposed, and oxidized with the formation -of ferric hydrate, which forms a flocculent precipitate and is readily -removed by filtration. The aeration required varies in different cases. -The quantity of oxygen required to oxidize the iron is only a small -fraction of the amount which water will dissolve, and allowing water to -simply fall through the air for a few feet in fine streams will usually -supply several times as much oxygen as is necessary for this purpose. - -Aerating devices of this kind have proved sufficient in a number of -cases, as at Far Rockaway, L. I., and at Red Bank, N. J. In some cases, -however, a further aeration is necessary, not for the purpose of -getting more oxygen into the water, but to get the excess of carbonic -acid out of it. Carbonic acid seems to retard in some way the oxidation -of the iron, and it is occasionally present in ground-waters in -considerable quantity, and quite seriously interferes with the process. -It can be removed sufficiently by aeration, but the necessary amount of -exposure to air is much greater than that required to simply introduce -oxygen. - -Coke-towers have sometimes been used for this purpose. The towers are -filled with coarse coke and have open sides, and water is sprinkled -over the tops of them and allowed to drip through to the bottoms. In -general the simple exposure of water to the air for a sufficient length -of time, in any form of apparatus or simply in open channels, will -accomplish the desired results. - -Mr. H. W. Clark[45] has called attention to the fact that in some cases -coke seems to have a direct chemical action upon the water which is -entirely independent of its aerating effect. In his experiments there -seemed to be some property in the coke which caused the iron to oxidize -and flocculate in many cases when it refused to do so with simple -aeration and filtration. - -When the right conditions are reached the oxidation of the iron is -very rapid, and it separates out in flakes of such size that they can -be removed by filtration at almost any practicable rate. Mechanical -filters have been used for this purpose, with rates of filtration -of 100 million gallons per acre daily. In Germany, where plants for -the removal of iron are quite common, modified forms of sand filters -have usually been employed which have been operated at rates up to 25 -million gallons per acre daily. - -In experiments made by the Massachusetts State Board of Health rates -from 10 to 25 million gallons per acre daily have been employed. - -The sand used for filtration may appropriately be somewhat coarser than -would be used for treating surface-waters, and the thickness of the -sand layer may be reduced. Owing to the higher - -rates the underdrainage system must be more ample than is otherwise -necessary. - -The rate of filtration employed is usually not a matter of vital -importance, but by selecting a rate that is not too high it is possible -to use a moderate loss of head. It is thus not necessary to clean the -filters too often, and the expenses of operation are not as high as -with an extreme rate. In some cases it is desired to accomplish other -results than the removal of iron by filtration, and this may lead to -the selection of a rate lower than would otherwise be used. - -Under normal conditions of operation all of the iron separates on the -top of the sand. No appreciable amount of it penetrates the sand at -all. With open filters at Far Rockaway and at Red Bank there is an algæ -growth in the water upon the filters which, with the iron, forms a -mat upon the surface of the filter; and when the filter is put out of -service and allowed to partially dry, this mat can be rolled up like a -carpet and thrown off without removing any sand, and the filters have -been in use for several years without renewing any sand and without any -important decrease in the thickness of the sand layer. - -Some waters contain iron in such a form that it cannot be successfully -removed in this manner. Thus at Reading, Mass., it was reported by -Dr. Thomas M. Drown that the iron was present in the form of ferrous -sulphate instead of ferrous carbonate, and that it was not capable of -being separated by simple aeration and filtration. A Warren mechanical -filter was installed, and the water is treated by aeration and with -the addition of lime and alum. The cost of the process is thereby much -increased, and the hardness of the water is increased threefold. - -Several other cases have been reported where it was believed that -simple aeration and filtration were inadequate; but the advantages of -the simple procedure are so great as to make it worth a very careful -study to determine if more complete aeration, or the use of coke-towers -and perhaps slower filtration, would not serve in these cases without -resorting to the use of chemicals and their attendant disadvantages. - - -IRON-REMOVAL PLANTS IN OPERATION. - -Iron-removal plants are now in use at Amsterdam and The Hague in -Holland, at Copenhagen in Denmark, at Kiel, Charlottenburg, Leipzig, -Halle, and many other places in Germany; at Reading, Mass.; Far -Rockaway, L. I.; Red Bank, Asbury Park, Atlantic Highlands, and -Keyport, N. J. - -Among the earliest plants for the removal of iron were the filters -constructed at Amsterdam and The Hague in Holland. At Amsterdam the -water is derived from open canals in the dunes draining a large area. -The water has its origin in the rain-water falling upon the sand. The -sand is very fine and contains organic matter in sufficient amount -so that the ground-water is impregnated with iron. In flowing to a -central point in the open canals the water becomes aerated and the iron -oxidized. There are also algæ growths in the water which perhaps aid -the process. Sand filters of ordinary construction are used, and remove -both the iron and the algæ, and the rate of filtration is not higher -than is usually used in the treatment of river-waters, although it -could probably be largely increased without detriment to the supply. - -The works at The Hague are very similar to those at Amsterdam, but -covered collectors are used to supplement the open canals. Both -of these plants were built before much was known about iron in -ground-waters and the means for its removal, but they have performed -their work with uniformly satisfactory results. In the more recent -German works various aerating devices are employed, and filters similar -in general construction to ordinary sand filters, but with larger -connections suited to very high rates of filtration, are employed. - -The plant at Asbury Park was the first of importance constructed in -America. The water is raised from wells from 400 to 1100 feet deep -by compressed air by a Pohle lift. It is delivered into a square -masonry receiving-basin holding some hours’ supply. The aeration of -the water by this means is very complete. It is afterwards pumped -through Continental pressure filters direct into the service-pipes. The -reservoir for the aerated water was not a part of the original plant, -but was added afterwards to facilitate operation, and to give more -complete aeration before filtration. - -At Far Rockaway, L. I., the water is lifted from wells by a Worthington -Pump, and is discharged over the bell of a vertical 16-inch pipe, -from which it falls through the air to the water in a receiving -chamber around it. The simple fall through the air aerates the water -sufficiently. From the receiving-chamber the water is taken to either -or both of two filters, each with an area of 20,000 square feet. These -filters are open, with brick walls and concrete bottoms, three feet -of sand and one foot of gravel, and the underdrains are of the usual -type. The water flows through regulator-chambers to a well 25 feet in -diameter and 12 feet deep, from which it is pumped to a stand-pipe in -the town. The plant was built to treat easily three million gallons -per day, and has occasionally treated a larger quantity. Either filter -yields the whole supply while the other is being cleaned. The rate of -filtration in this case was made lower than would have otherwise been -necessary, as there was an alternate supply, namely, the water from -two brooks, which could be used on occasions, and to purify which a -lower rate of filtration was regarded necessary, than would have been -required for the well-water. The removal of iron is complete. - -[Illustration: FIG. 25.] - -The plant of the Rumson Improvement Company at Red Bank, N. J., is -quite similar to that at Far Rockaway, but is much smaller. The outlet -is a 6-inch pipe perforated with 1/4-inch holes which throws the water -out in a pine-tree shape to the receiving-tank, thoroughly aerating -it. Each of the two filters has 770 square feet of area. The filtering -material is three feet of beach sand. From the regulator-chamber the -water flows to a circular well 18 feet in diameter, covered by a brick -dome and holding 17,000 gallons, from which it is pumped to the -stand-pipe. Either of the filters will treat ten thousand gallons of -water per hour, which is equal to the capacity of the pumps; and as -the consumption is considerably less than this figure, they are only -in use for a part of each day, the number of hours depending upon the -consumption. These filters are shown by the accompanying plan. The cost -of the work was as follows: - - Filters and pure-water reservoir, with piping - and drains complete $3,799.47 - New pump and connections 492.68 - Engineering and superintendence 992.91 - --------- - Total cost of plant $5,285.06 - -The engineer who operates the pumps takes care of the filters, and no -additional labor has been required. The entire cost of operation is -thus represented by the additional coal required for the preliminary -lift from the wells to the filters. The effluent is always free from -iron. - -The plant at Reading,[46] Mass., was installed by the Cumberland -Manufacturing Company, and combines aeration, treatment with lime and -sulphate of alumina and rapid filtration. The aeration is effected -by pumping air through the water, after the water has received the -lime. It afterwards receives sulphate of alumina and passes to a -settling-tank holding 40,000 gallons, in which the water remains for -about an hour. There are six filters of the Warren type, each with an -effective filtering area of 54 square feet. - -The cost of coagulant is considerable. The chief disadvantage of the -process is that it hardens the water, which is naturally soft. From -the completion of the plant in July, 1896, to the end of the year the -hardness of the water was increased, according to analyses of the State -Board of Health, from 4.1 to 11.3 parts in 100,000, and for the year -1897 the increase was from 4.0 to 12.7. The iron, which is present in -the raw water to the extent of about 0.26 part in 100,000, is removed -sufficiently at all times. - -Prior to the erection of this plant Mr. Desmond FitzGerald advised -aeration followed by sedimentation in two reservoirs holding half a -million gallons each, and by rapid filtration. Mr. Bancroft states that -in his opinion, if the reservoir recommended by Mr. FitzGerald had been -built, the filters could be run with very little or no coagulation, and -consequently without increase in hardness, which is the most obvious -disadvantage to the procedure. The nominal capacity of the plant is -one million gallons, and the average consumption about 200,000 gallons -daily. - -The plant at Keyport, N. J., is similar, but smaller. - - - - -CHAPTER XIII. - -TREATMENT OF WATERS. - - -Having now reviewed the most important methods in use for the treatment -of waters, we may take a general view of their application to various -classes of waters. Different raw waters vary so much, and the -requirements of filtration are so different, that it is not possible -to outline any general procedure or combination of procedures, but -each problem must be taken up by itself. Nevertheless, some general -suggestions may be of service. - -In the first place, we may consider the case of waters containing very -large quantities of oxidizable organic matter. Such waters are obtained -from some reservoirs containing very active vegetable and animal -growths, or from rivers receiving large amounts of sewage. Waters -of both of these classes are, if possible, to be avoided for public -water-supplies. When circumstances require their use, they can best be -treated by intermittent filtration, this process being best adapted to -the destruction by oxygen of excessive quantities of organic matter. - -Where the pollution is less, so that the dissolved oxygen contained -in the raw water is sufficient for the oxidation of the organic -matters, continuous filtration will give substantially as good results -as intermittent filtration, and in other respects it has important -advantages. The application of intermittent filtration for the -treatment of public water-supplies is thus somewhat limited, and, as a -matter of fact, it has been used in only a few cases. - -For the treatment of very highly polluted waters double filtration has -been used in a number of cases, notably by the Grand Junction Company -at London, at Schiedam in Holland, and at Bremen and Altona in Germany. -At the two first-mentioned places two separate systems of filters are -provided differing somewhat in construction, the first filters being at -a higher level than the after filters. The first filters supply water -of comparative purity, and very constant composition, to the after -filters, which are able to treat it with great efficiency and at very -low operating cost. - -This procedure is probably the most perfect which has been used for the -removal of disease-producing qualities from highly polluted waters; and -the cost of the process may not be as much greater than that of simple -filtration as would at first appear, because the cost of cleaning the -after filters is merely nominal, and the attendance, pumping, etc., -are practically common to both sets of filters, and are not materially -greater than they would be for a single set. - -For very bad waters the first filters might appropriately be -intermittent, while the after filters should be continuous. This was -the procedure originally intended for Lawrence, but the intermittent -filter first constructed yielded such very good results that it has not -been considered necessary to complete the plant as originally projected. - -At Bremen and at Altona a different procedure has been adopted. The -filters are all upon the same level, and of the same construction. -When a filter is put in service the effluent from it, instead of being -taken to the pure-water reservoir, is taken to another filter which -has already been some time in service. After the first filter has been -in operation for some time its effluent is taken to the pure-water -reservoir, and in turn it is supplied with the effluent from a filter -more recently cleaned. The loss of head of water passing a freshly -cleaned filter is comparatively slight, and the water of the second -filter is allowed to fall a few inches below the high-water mark, -at which level it will take the effluent from the other filter. The -connections between the filters are made by siphons of large pipe, the -summits of which are considerably above the high-water line. These -siphons are filled by exhausting the air, and when opened to the air -there is no possibility of a flow of water through them. The process -has given extremely good results in practice, yielding effluents of the -very greatest purity and at a quite moderate cost of operation. - -An objection to the method is the possible filling of a siphon some -time when the water standing upon the after-filter is higher than that -in the pure-water well of the fore-filter, and while the fore-filter is -connected with the pure-water reservoir. Such a connection would send -unfiltered water into the pure-water reservoir direct. I do not know -that any trouble of this kind has ever been experienced at Bremen or at -Altona; and the objection to this system is perhaps not well founded -where the management is careful and conscientious. The fact that an -unscrupulous attendant can make the connection at any time to help out -a deficiency of supply, or simply through carelessness, is certainly -objectionable. - -For the treatment of river-waters and lake-waters containing only -a small quantity of sediment, and where the removal of bacteria or -disease-producing qualities is the most important object of filtration, -sand filters can be used. Where the rivers are subject to floods and -moderate amounts of muddy water, sedimentation-basins or storage -reservoirs for raw water will often be found advantageous. - -For the treatment of extremely muddy waters, and waters which are -continuously muddy for long periods of time, and for the removal -of color from very highly colored waters, resource must be had to -coagulants. The coagulants which are necessary in each special case and -which can be used without injury to the water must be determined by -most careful investigation of the raw water. - -For the filtration of these waters after coagulation either sand or -mechanical filters can be employed. As the principal work in this -case is done by the coagulant, the kind of filtration employed is -of less consequence than where filtration alone is relied upon, -and the cheapest form of filter will naturally be employed. Under -present conditions mechanical filters will usually be cheaper than -sand filters for use in this way; but where waters, in addition to the -mud, carry bacteria in such large numbers as to make high bacterial -efficiency a matter of importance, sand filters may be selected, as the -bacterial efficiency obtained with them is not dependent upon the use -of coagulant; and is therefore less subject to interruptions from the -failure to apply coagulant in the right proportion. - -Mechanical filters have also been used for the treatment of -comparatively clear waters where bacterial efficiency was the principal -object of filtration. For this purpose the efficiencies obtained with -them are usually inferior to those obtained with sand filters, while -the cost of coagulants is so great as to make their use often more -expensive than that of sand filters. - -In the case of many streams which are comparatively clear for a part of -the year, but occasionally are quite turbid, the use of sand filters -has this advantage, that the use of coagulants can be stopped and the -cost of operation reduced whenever the water is clear enough to allow -of satisfactory treatment by them; and that coagulant can be employed -on those days when otherwise insufficient clarification would be -obtained. - -In this case the high bacterial efficiency is secured at all times, -while the cost of coagulant is saved during the greater part of the -time. In such cases, also, the preliminary process of sedimentation and -storage should be developed as far as possible. - -The application of other processes of filtration to special problems -are not sufficiently well understood to allow general discussion, and -must be taken up separately with reference to the requirements of each -special situation. - - -COST OF FILTRATION. - -The cost of filtration of water depends upon the character of the raw -water, upon the nature of the plant employed, upon its size, and -upon the skill and economy of manipulation. These conditions affect -the cost to such an extent as to make any accurate general estimate -quite impossible. Nevertheless a little consideration of the subject, -although not leading to exact results, may be helpful as furnishing a -rough idea of the probable cost before estimates for local conditions -are made. - -Open sand filters, with masonry walls, with reasonably favorable -conditions of construction, and not too small in area, have averaged -to cost in the United States within the last few years perhaps about -thirty thousand dollars per acre. The relative cost of small plants is -somewhat greater, and with embankments instead of masonry walls, the -cost is somewhat reduced. The cost is less where natural deposits of -sand can be made use of practically in their original condition, and is -increased where the filtering materials have to be transported by rail -for long distances, or where the sites are difficult to build upon. -Covered filters cost about a half more than open filters. Mechanical -filters at current prices cost about $20 per square foot of filtering -area, to which must be added the cost of foundations and buildings, -which perhaps average to cost half as much more, but are dependent upon -local conditions and the character of the buildings. - -To these figures must be added the costs of pumps, reservoirs, -sedimentation-basins, and pipe-connections, which are often greater -than the costs of the filters, but which differ so widely in different -cases as to make any general estimate impossible. - -Filters must be provided sufficient to meet the maximum and not the -average consumption. The excess of maximum over average requirements -varies greatly in different cities, and depends largely upon reservoir -capacities and arrangements. - -As a result of a considerable number of estimates made by the author -for average American conditions, the cost of installing filters may -be taken very roughly as five dollars per inhabitant, but the amounts -differ widely in various cases. - -The cost of operation of sand filters in England probably averages -about one dollar per million gallons of water filtered. The following -table shows the costs of operation of the filters of the seven London -companies for fifteen years, compiled in the office of Mr. W. B. Bryan, -Chief Engineer of the East London Water Company. The results have been -computed to dollars per million U. S. gallons, and include the cost of -all labor, sand, and supplies for the filters, but do not include any -pumping or interest costs. - - -COST OF FILTRATION, LONDON WATER COMPANIES. - -(Computed from data furnished Wm. B. Bryan, C.E., East London Water -Works.) - -Dollars per Million U. S. Gallons. - - --------+-------+------+--------+-------+-----+---------+---------+-------- - | | East | Grand | | New |Southwark| West | - |Chelsea|London|Junction|Lambeth|River| & |Middlesex|Average. - | Co. | Co. | Co. | Co. | Co. |Vauxhall | Co. | - | | | | | | Co. | | - --------+-------+------+--------+-------+-----+---------+---------+-------- - 1880-1 | 1.16 | 1.16 | 1.00 | 0.83 |1.34 | 1.16 | 1.67 | 1.19 - 1881-2 | 1.19 | 1.39 | 0.95 | 0.82 |1.15 | 1.37 | 1.54 | 1.20 - 1882-3 | 1.10 | 1.23 | 1.39 | 0.96 |1.40 | 1.47 | 1.74 | 1.33 - 1883-4 | 1.00 | 1.06 | 1.73 | 0.92 |1.11 | 1.62 | 1.67 | 1.30 - 1884-5 | 1.06 | 1.06 | 1.82 | 0.90 |1.02 | 1.40 | 1.30 | 1.22 - 1885-6 | 1.15 | 1.16 | 1.35 | 0.90 |1.00 | 1.15 | 1.07 | 1.11 - 1886-7 | 0.80 | 0.96 | 1.39 | 0.87 |0.98 | 1.43 | 1.70 | 1.16 - 1887-8 | 1.07 | 1.22 | 1.74 | 0.90 |0.92 | 1.28 | 1.00 | 1.16 - 1888-9 | 0.83 | 1.28 | 1.55 | 0.95 |0.98 | 1.52 | 0.83 | 1.13 - 1889-90 | 0.66 | 1.50 | 1.22 | 0.88 |0.90 | 1.70 | 3.56 | 1.49 - 1890-1 | 0.72 | 1.42 | 1.32 | 0.85 |1.02 | 1.16 | 1.00 | 1.07 - 1891-2 | 0.75 | 1.54 | 1.23 | 1.00 |0.92 | 1.15 | 0.96 | 1.08 - 1892-3 | 0.67 | 1.42 | 1.30 | 1.19 |1.16 | 1.26 | 1.42 | 1.20 - 1893-4 | 1.15 | 2.63 | 2.00 | 1.46 |1.43 | 1.52 | 0.95 | 1.59 - 1894-5 | 0.60 | 1.68 | 1.67 | 2.53 |1.03 | 1.34 | 0.96 | 1.40 - --------+-------+------+--------+-------+-----+---------+---------+-------- - Average | 0.93 | 1.38 | 1.44 | 1.06 |1.09 | 1.37 | 1.43 | 1.24 - --------+-------+------+--------+-------+-----+---------+---------+-------- - - Average of seven companies for 15 years, $1.24 per million gallons. - - Variations from year to year are caused by differences in the amounts - of ice, and in the quantities of new sand purchased. Wages average - about $1.00 per day. At Liverpool for 1896 the cost was $1.08 per - million U. S. gallons. - -In Germany, with more turbid river-waters, the costs of operation are -somewhat higher than the London figures, while at Zürich, where the -water is very clear, they are lower. - -In the United States the data regarding the cost of operation of sand -filters are less complete. At Mt. Vernon, N. Y., with reservoir-water, -the cost has averaged about two dollars per million gallons. At -Poughkeepsie, N. Y., with the Hudson River water, which is occasionally -moderately turbid, the cost for twenty years has averaged three dollars -per million gallons. This cost includes the cost of handling ice, and -as the average winter temperature is considerably below that suggested -for open filters, the expense of this work has been considerable, and -has increased considerably the total cost of operation. - -At Far Rockaway, L. I., and Red Bank N. J., for iron-removal plants, -the cost of operation has hardly been appreciable. The plants are both -close to the pumping-stations, and it has been possible to operate -them with the labor necessarily engaged at the pumping-station without -additional cost, except a very small amount of labor on the sand at Far -Rockaway. No computation has been made in these cases of the additional -coal required for pumping. - -At Lawrence, Mass., the cost of operation for 1895 was as follows: - - Cost of scraping and replacing sand $3,467 - Cost of care of ice 2,903 - ------ - Total cost of operation $6,370 - Water filtered, millions of gallons 1,097 - Cost per million gallons $5.80 - -The cost of care of ice has been excessive at Lawrence, and it has -been repeatedly recommended to cover the filter to avoid this expense. -The cost of handling sand has been very greatly increased, because the -filter is built in one bed, and all work upon it has to be done during -the comparatively short intervals when the filter is not in use, an -arrangement which is not at all economical in the use of labor. The -cost of operation is thus much higher than it would be had the plant -been constructed in several units, each of which could be disconnected -for the purpose of being cleaned in the ordinary manner. As against -this the first cost of construction was extremely low, and the saving -in interest charges should be credited against the increased cost of -labor in cleaning. - -The cost of operating filters at Ashland, Wis., has been estimated by -Mr. William Wheeler at $2.26 per million gallons. This estimate is -based upon the performance for the first year that they were in service. - -In the operation of mechanical filters one of the largest items of -expense is for the coagulant, and the amount of this depends entirely -upon the character of the raw water and the thoroughness of the -treatment required. The data regarding the other or general costs of -operation of mechanical filters are few and unsatisfactory. - -I recently made some estimates of cost of clarifying waters of various -degrees of turbidity by sand and mechanical filters. These estimates -were made for a special set of conditions, and I do not know that -they will fit others, but they have at least a suggestive value. The -results shown by Fig. 26 include only the cost of operation, and not -interest and depreciation charges. These figures, when used for plants -in connection with which preliminary treatments are used, should be -applied to the turbidity of the water as applied to the filters, and -not to the raw water, and the costs of the preliminary processes should -be added. - -With sand filters the frequency of scraping is nearly proportional -to the turbidity; and as scraping represents most of the expenses, -the costs of operation are proportional to the turbidity, except -the general costs, and the cost of the amount of scraping, which is -necessary with even the clearest waters. - -With mechanical filters the amount of sulphate of alumina required for -clarification increases with the turbidity, and most of the costs of -operation increase in the same ratio. The diagram shows the amount of -sulphate of alumina in grains per gallon necessary for clarification -with different degrees of turbidity. - -With the clearest waters the costs of operation on the two systems are -substantially equal. With muddy waters, the expense of operating sand -filters increases more rapidly than the expense of operating mechanical -filters. - -[Illustration: TURBIDITY -FIG. 26.—COST OF OPERATION OF FILTERS.] - -There is another element which often comes into the comparison, namely, -the question of purification from the effects of sewage-pollution. -Nearly all rivers used for public water-supplies receive more or less -sewage, and in filtering such waters it is regarded as necessary to -remove as completely as possible the bacteria. - -The quantities of sulphate of alumina required for the clarification -of the least turbid waters are not sufficient to give even tolerably -good bacterial efficiencies. To secure a reasonably complete removal of -bacteria with mechanical filters, the use of a considerable quantity -of sulphate of alumina is required. Let us assume that 98 per cent -bacterial efficiency is required, and that to produce this efficiency -it is necessary to use one grain of coagulant to the gallon. With water -requiring less than this quantity of coagulant for clarification this -quantity must nevertheless be used, and the costs will be controlled -by it, and not by the lower quantities which would suffice for -clarification, but would not give the required bacterial efficiency. - -I have added this line to the diagram, and this, combined with the -upper portion of the line showing cost of clarification, represents the -cost of treating waters with mechanical filters, where both bacterial -efficiency and clarification are required. - -This line, considered as a whole, increases much less rapidly with -increasing turbidity than does the corresponding line for sand filters, -and the two lines cross each other. With the clearest waters sand -filters are cheaper than mechanical filters, and for the muddiest -waters they are more expensive. It does not appear from the diagram, -but it is also true in each case, that the cheaper system is also the -more efficient. Sand filters are more efficient in removing bacteria -from clear waters than are mechanical filters, and mechanical filters -are more efficient in clarifying very muddy waters than are sand -filters. - - -WHAT WATERS REQUIRE FILTRATION? - -From the nature of the case a satisfactory general answer to this -question cannot be given, but a few suggestions may be useful. - -In the first place, ground-waters obviously do not require filtration: -they have already in most cases been thoroughly filtered in the ground -through which they have passed, and in the exceptional cases, as, for -instance, an artesian well drawing water through fissures in a ledge -from a polluted origin, a new supply will generally be chosen rather -than to attempt to improve so doubtful a raw material. - -River-waters should be filtered. It cannot be asserted that there -are no rivers in mountainous districts in which the water is at once -clear and free from pollution, and suitable in its natural state -for water-supply; but if so, they are not common, least of all in -the regions where water-supplies are usually required. The use of -river-waters in their natural state or after sedimentation only, -drawn from such rivers as the Merrimac, Hudson, Potomac, Delaware, -Schuylkill, Ohio, and Mississippi, is a filthy as well as an unhealthy -practice, which ought to be abandoned. - -The question is more difficult in the case of supplies drawn from -lakes or storage reservoirs. Many such supplies are grossly polluted -and should be either abandoned or filtered. Others are subject to algæ -growths, or are muddy, and would be much improved by filtration. Still -others are drawn either from unpolluted water-sheds, or the pollution -is so greatly diluted and reduced by storage that no known disadvantage -results from their use. - -In measuring the effects of the pollution of water-supplies, the -typhoid-fever death-rate is a most important aid. Not that typhoid -fever is the sole evil resulting from polluted water, but because it -is also a very useful index of other evils for which corresponding -statistics cannot be obtained, as, for instance, the causation of -diarrhœal diseases or the danger from invasion by cholera. - -I think we shall not go far wrong at the start to confine our attention -to those cities where there are over 25 deaths from typhoid fever per -100,000 of population. This will at once throw out of consideration -a large number of relatively good supplies, including those of New -York and Brooklyn. It is not my idea that none of these supplies -cause disease. Many of them, as for instance that of New York, are -known to receive sewage, and it is an interesting question worthy of -most careful study whether there are cases of sickness resulting from -this pollution. The point that I wish to make now is simply that in -those cases the death-rate itself is evidence that, with existing -conditions of dilution and storage, the resulting damage of which we -have knowledge is not great enough to justify the expense involved by -filtration. - -In this connection it should not be forgotten that, especially with -very small watersheds, there may be a danger as distinct from present -damage which requires consideration. Thus a single house or groups of -houses draining into a supply may not appreciably affect it for years, -until an outbreak of fever on the water-shed results in infecting the -water with the germs of disease and in an epidemic in the city below. -This danger decreases with increasing size of the water-shed and volume -of the water with which any such pollution would be mixed, and also -with the population draining into the water, as there is a probability -that the amount of infection continually added from a considerable town -will not be subject to as violent fluctuation as that from only a few -houses. - -Thus in Plymouth, Pa., in 1885, there were 1104 cases of typhoid -fever and 114 deaths among a population of 8000, as the result of the -discharge of the dejecta from a single typhoid patient into the water -of a relatively small impounding reservoir. The cost of this epidemic -was calculated with unusual care. The care of the sick cost in cash -$67,100.17, and the loss of wages for those who recovered amounted to -$30,020.08. The 114 persons who died were earning before their sickness -at the rate of $18,419.52 annually. - -Such an outbreak would hardly be possible with the Croton water-shed -of the New York water-supply, on account of the great dilution and -delay in the reservoirs, but it must be guarded against in small -supplies. - -Of the cities having more than 25 deaths per 100,000 from typhoid -fever, some will no doubt be found where milk epidemics or other -special circumstances were the cause; but I believe in a majority -of them, and in nearly all cases where the rate is year after year -considerably above that figure, the cause will be found in the -water-supply. Investigation should be made of this point; and if the -water is not at fault, the responsibility should be located. If the -water is guilty, it should be either purified or a new supply obtained. - - - - -CHAPTER XIV. - -WATER-SUPPLY AND DISEASE—CONCLUSIONS. - - -One of the most characteristic and uniform results of the direct -pollution of public water-supplies is the typhoid fever which results -among the users of the water. In the English and German cities with -almost uniformly good drinking-water, typhoid fever is already nearly -exterminated, and is decreasing from year to year. American cities -having unpolluted water-supplies have comparatively few deaths from -this cause, although the figures never go so low as in Europe, perhaps -on account of the fresh cases which are always coming in from less -healthy neighborhoods in ever-moving American communities. In other -American cities the death-rates from typhoid fever are many times what -they ought to be and what they actually are in other cities, and the -rates in various places, and in the same place at different times, -bear in general a close relation to the extent of the pollution of the -drinking-water. The power of suitable filtration to protect a city from -typhoid fever is amply shown by the very low death-rates from this -cause in London, Berlin, Breslau, and large numbers of other cities -drawing their raw water from sources more contaminated than those of -any but the very worst American supplies, and by the marked and great -reductions in the typhoid-fever death rates which have followed at once -the installation of filters at Zürich, Switzerland; Hamburg, Germany; -Lawrence, Mass., and other places. - -The following is a list of the cities of 50,000 inhabitants and upward -in the United States, with deaths from typhoid fever and the sources -of their water-supplies. The deaths and populations are from the -U. S. Census for 1890; the sources of the water-supplies, from the -_American Water-Works Manual_ for the same year. Four cities of this -size—Grand Rapids, Lincoln, St. Joseph, and Des Moines—are not included -in the census returns of mortality. Two cities with less than 50,000 -inhabitants with exceptionally high death-rates have been included, and -at the foot of the list are given corresponding data for some large -European cities for 1893. - - -TYPHOID FEVER DEATH-RATES AND WATER-SUPPLIES OF CITIES. - - -----------------+-----------+--------------+------------------------- - | | Deaths from | - | | Typhoid | - | | Fever. | - City. |Population.+------+-------+ Water-supply. - | | | Per | - | |Total.|100,000| - | | |living.| - -----------------+-----------+------+-------+------------------------- - Birmingham | 26,178 | 69 | 264 |Five Mile Creek - 1. Denver | 106,713 | 232 | 217 |North Platte River and - | | | | wells - 2. Allegheny | 105,287 | 192 | 182 |Allegheny River - 3. Camden | 58,313 | 77 | 132 |Delaware River - 4. Pittsburg | 238,617 | 304 | 127 |Allegheny and Monongahela - | | | | rivers - Lawrence | 44,654 | 54 | 121 |Merrimac River - 5. Newark | 181,830 | 181 | 100 |Passaic River - 6. Charleston | 54,955 | 54 | 98 |Artesian wells yielding - | | | | 1,600,000 gallons daily - 7. Washington | 230,392 | 200 | 87 |Potomac River - 8. Lowell | 77,696 | 64 | 82 |Merrimac River - 9. Jersey City | 163,003 | 134 | 82 |Passaic River - 10. Louisville | 161,129 | 122 | 76 |Ohio River - 11. Philadelphia | 1,046,964 | 770 | 74 |Delaware and Schuylkill - | | | | rivers - 12. Chicago | 1,099,850 | 794 | 72 |Lake Michigan - 13. Atlanta | 65,533 | 47 | 72 |South River - 14. Albany | 94,923 | 67 | 71 |Hudson River - 15. Wilmington | 61,431 | 43 | 70 |Brandywine Creek - 16. St. Paul | 133,156 | 92 | 69 |Lakes - 17. Troy | 60,956 | 42 | 69 |Hudson River and - | | | | impounding reservoirs - 18. Los Angeles | 50,395 | 34 | 67 |Los Angeles River and - | | | | springs - 19. Nashville | 76,168 | 49 | 64 |Cumberland River - 20. Cleveland | 261,353 | 164 | 63 |Lake Erie - 21. Richmond | 81,388 | 50 | 61 |James River - 22. Hartford | 53,230 | 32 | 60 |Connecticut River and - | | | | impounding reservoir - 23. Fall River | 74,398 | 44 | 59 |Watupa Lake - 24. Minneapolis | 164,738 | 94 | 57 |Mississippi River - 25. San Francisco| 298,997 | 166 | 56 |Lobus Creek, Lake Merced, - | | | | and mountain streams - 26. Indianapolis | 105,436 | 57 | 54 |White River - 27. Cincinnati | 296,908 | 151 | 51 |Ohio River - 28. Memphis | 64,495 | 33 | 51 |Artesian Wells - 29. Reading | 58,661 | 29 | 49 |Maiden Creek and Springs - 30. Baltimore | 434,439 | 202 | 47 |Impounding reservoir - 31. Omaha | 140,452 | 63 | 45 |Missouri River - 32. Columbus | 88,150 | 38 | 43 |Surface-water and wells - 33. Providence | 132,146 | 53 | 40 |Pawtuxet River - 34. Kansas City | 132,716 | 53 | 40 |Missouri River - 35. Rochester | 133,896 | 53 | 39 |Hemlock and Candice lakes - 36. Evansville | 50,756 | 20 | 39 |Ohio River - 37. Boston | 448,477 | 174 | 39 |Impounding reservoirs - 38. Toledo | 81,434 | 29 | 36 |Maumee River - 39. Cambridge | 70,028 | 24 | 34 |Impounding reservoir - 40. St. Louis | 451,770 | 145 | 32 |Mississippi River - 41. Scranton | 75,215 | 24 | 32 |Impounding reservoir - 42. Buffalo | 255,664 | 80 | 31 |Niagara River - 43. Milwaukee | 204,468 | 61 | 30 |Lake Michigan - 44. New Haven | 81,298 | 22 | 27 |Impounding reservoir - 45. Worcester | 84,655 | 22 | 26 |Impounding reservoir - 46. Paterson | 78,347 | 20 | 26 |Passaic River - | | | | (higher up) - 47. Dayton | 61,220 | 15 | 25 |Wells - 48. Brooklyn | 806,343 | 194 | 24 |Wells, ponds, and - | | | | impounding reservoirs - 49. New York | 1,515,301 | 348 | 23 |Impounding reservoir - 50. Syracuse | 88,143 | 18 | 20 |Impounding reservoir - | | | | and springs - 51. New Orleans | 242,039 | 45 | 19 |Mississippi River - 52. Detroit | 205,876 | 40 | 19 |Detroit River - 53. Lynn | 55,727 | 9 | 16 |Impounding reservoir - 54. Trenton | 57,458 | 9 | 16 |Delaware River - | | | | - London | 4,306,411 | 719 | 17 |Filtered Thames and Lea - | | | | rivers and 1/4 from - | | | | wells - Glasgow | 667,883 | 138 | 20 |Loch Katrine - Paris | 2,424,705 | 609 | 25 |Spring water - Amsterdam | 437,892 | 69 | 16 |Filtered dune-water - Rotterdam | 222,233 | 12 | 5 |Filtered Maas River - Hague | 169,828 | 3 | 2 |Filtered dune-water - Berlin | 1,714,938 | 161 | 9 |Filtered Havel and Spree - | | | | rivers - Hamburg | 634,878 | 115 | 18 |Filtered Elbe River - Breslau | 353,551 | 37 | 11 |Filtered Oder River - Dresden | 308,930 | 14 | 5 |Ground-water - Vienna | 1,435,931 | 104 | 7 |Spring-water - -----------------+-----------+------+-------+------------------------- - -Any full discussion of these data would require intimate acquaintances -with the various local conditions which it is impossible to take -up in detail here, but some of the leading facts cannot fail to be -instructive. - -Each of the places having over 100 deaths per 100,000 from typhoid -fever used unfiltered river-water. Lower in the list, but still very -high, Charleston, said to have been supplied only from artesian wells, -had an excessive rate; but the reported water-consumption is so low as -to suggest that private wells or other means of supply were in common -use. Chicago and Cleveland both drew their water from lakes where they -were contaminated by their own sewage. St. Paul’s supply came from -ponds, of which I do not know the character. With these exceptions all -of the 22 cities with over 50,000 inhabitants, at the head of the list, -had unfiltered river-water. - -The cities supplied from impounding reservoirs as a rule had lower -death rates and are at the lower end of the list, together with some -cities taking their water supplies from rivers or lakes at points where -they were subject to only smaller or more remote infection. Only three -of the American cities in the list were reported as being supplied -entirely with ground-water. - -It is not my purpose to make too close comparisons between the various -cities on the list; some of them may have been influenced by unusual -local conditions in 1890. Others have in one way or another improved -their water-supplies since that date, and there are several cities in -which I know the present typhoid-fever death-rates to be materially -lower than those of 1890 given in the table. On the other hand, it is -equally true that a number of cities, including some of the larger -ones, have since had severe epidemics of typhoid fever which have given -very much higher rates than those for 1890. - -These fluctuations would change the order of cities in the list from -year to year; they would not change the general facts, which are as -true to-day as they were in 1890. Nearly all of the great cities of the -United States are supplied with unfiltered surface-waters, and a great -majority of the waters are taken from rivers and lakes at points where -they are polluted by sewage. The death-rates from typhoid fever in -those cities, whether they are compared with better supplied cities of -this country, or with European cities, are enormously high. - -Such rates were formerly common in European cities, but they have -disappeared with better sanitary conditions. The introduction of -filters has often worked marvellous changes in Europe, and in Lawrence -the improvement in the city’s health with filtered water was prompt -and unquestionable. There is every reason to believe that the general -introduction of better water in American cities will work corresponding -revolutions; and looking at it from a merely money standpoint, the -value of the lives and the saving of the expenses of sickness will pay -handsomely when compared with the cost of good water. - -The reasons for believing that cholera is caused by polluted water -are entirely similar to those in the case of typhoid fever. It was no -accident that the epidemic of cholera which caused the death of 3400 -persons followed the temporary supply of unfiltered water by the East -London Water Company in 1866, while the rest of London remained nearly -free, or that the only serious outbreak of cholera in Western Europe -in 1892 was at Hamburg, which was also the only city in Germany which -used raw river-water. This latter caused the sickness of 20,000 and the -death of over 8000 people within a month, and an amount of suffering -and financial loss, with the panics which resulted, that cannot be -estimated, but that exceeded many times the cost of the filters which -have since been put in operation. Hamburg had several times before -suffered severely from cholera, and the removal of this danger was a -leading, although not the sole, motive for the construction of filters. - -How little cities supplied with pure water have to dread from -cholera is shown by the experience of Altona and other suburbs of -Hamburg with good water-supplies, which had but few cases of cholera -not directly brought from the latter place, and by the experience -of England, which maintained uninterrupted commercial intercourse -with the plague-stricken city, absolutely without quarantine, and, -notwithstanding a few cases which were directly imported, the disease -gained no foothold in England. - -I do not know of a single modern European instance where a city with a -good water-supply not directly infected by sewage has suffered severely -from cholera. I shall leave to others more familiar with the facts the -discussion of what happened before the introduction of modern sanitary -methods, as well as of the present conditions in Asia; although I -believe that in these cases also there is plenty of evidence as to the -part water plays in the spread of the disease. - -A considerable proportion of the water-supplies of the cities of the -United States are so polluted that in case cholera should gain a -foothold upon our shores we have no ground for hoping for the favorable -experience of the English cities rather than the plague of Hamburg in -1892. - -The fæces from a man contain on an average perhaps 1,000,000,000 -bacteria per gram,[47] most of them being the normal bacilli of -the intestines, _Bacillus coli communis_. Assuming that a man -discharges 200 grams or about 7 ounces of fæces daily, this would give -200,000,000,000 bacteria discharged daily per person. The number of -bacteria actually found in American sewage is usually higher, often -double this number per person; but there are other sources of bacteria -in sewage, and in addition growths or the reverse may take place in the -sewers, according to circumstances. - -This number of bacteria in sewage is so enormously large that the -addition of the sewage from a village or city to even a large river -is capable of affecting its entire bacterial composition. Thus taking -the population of Lowell in 1892 at 85,000, and the average daily -flow of the Merrimac at 6000 cubic feet per second, and assuming that -200,000,000,000 bacteria are discharged daily in the sewage from each -person, they would increase the number in the river by 1160 - -per cubic centimeter, or about 300,000 in an ordinary glass of water. -The average number found in the water eight miles below, at the intake -of the Lawrence water-works, was more than six times as great as this, -due in part to the sewage of other cities higher up. - -There is every reason to believe that the bulk of these bacteria were -harmless to the people of Lawrence, who drank them; but some of them -were not. Fæces of people suffering from typhoid fever contain the -germs of that disease. What proportion of the total number of bacteria -in such fæces are injurious is not known; but assuming that one fourth -only of the total number are typhoid germs, and supposing the fæces of -one man to be evenly mixed with the whole daily average flow of the -river, it would put one typhoid germ into every glass of water at the -Lawrence intake, and at low water several times as many proportionately -would be added. This gives some conception of the dilution required to -make a polluted water safe. - -One often hears of the growth of disease-germs in water, but as far -as the northern United States and Europe are concerned there is no -evidence whatever that this ever takes place. There are harmless forms -of bacteria which are capable of growing upon less food than the -disease-germs require and they often multiply in badly-polluted waters. -Typhoid-fever germs live for a longer or shorter period, and finally -die without growth. The few laboratory experiments which have seemed -to show an increase of typhoid germs in water have been made under -conditions so widely different from those of natural watercourses that -they have no value.[48] - -The proportionate number of cases of typhoid fever among the users -of a polluted water varies with the number of typhoid germs in the -water. Excessive pollution causes severe epidemics or continued high -death-rates according as the infection is continued or intermittent. -Slight infection causes relatively few cases of fever. Pittsburg and -Allegheny, taking their water-supplies from below the outlets of some -of their own sewers, have suffered severely (103.2 and 127.4 deaths -from typhoid fever annually per 100,000, respectively, from 1888 to -1892). Wheeling, W. Va., with similar conditions in 1890, was even -worse, a death rate of 345 per 100,000 from this cause being reported, -while Albany had only comparatively mild epidemics from the less -directly and grossly polluted Hudson. Lawrence and Lowell, taking their -water from the Merrimac, both had for many years continued excessive -rates, increasing gradually with increasing pollution; and the city -having the most polluted source had the higher rate. - -In Berlin and Altona, in winter, with open filters, epidemics of -typhoid fever followed decreased efficiency of filtration, but the -epidemics were often so mild that they would have entirely escaped -observation under present American conditions. Chicago has for years -suffered from typhoid fever, and the rate has fluctuated, as far as -reliable information can be obtained, with the fluctuations in the -pollution of the lake water. An unusual discharge of the Chicago River -results in a higher death-rate. Abandoning the shore inlet near the -mouth of the Chicago River in 1892, resulted in the following year in -a reduction of 60 per cent in the typhoid fever death-rate.[49] This -reduction shows, not that the present intakes are safe, but simply that -they are less polluted than the old ones to an extent measured by the -reduction in the death-rate. - -It is not supposed that in an epidemic of typhoid fever caused by -polluted water every single person contracts the disease directly by - -drinking the water. On the contrary, typhoid fever is often -communicated in other ways. If we have in the first place a thousand -cases in a city caused directly by the water, they will be followed -by a large number of other cases resulting directly from the presence -in the city of the first thousand cases. The conditions favoring this -spread may vary in different wards, resulting in considerable local -variations in the death-rates. Some persons also will suffer who did -not drink any tap-water. These facts, always noted in epidemics, afford -no ground for refusing to believe, in the presence of direct evidence, -that the water was the cause of the fever. These additional cases are -the indirect if not the direct result of the water. The broad fact that -cities with polluted water-supplies as a rule have high typhoid-fever -death-rates, and cities with good water-supplies do not (except in the -occasional cases of milk epidemics, or where they are overrun by cases -contracted in neighboring cities with bad water, as is the case with -some of Chicago’s suburbs), is at once the best evidence of the damage -from bad water and measure of its extent. - -The conditions which remove or destroy the sewage bacteria in a water -tend to make it safe. The most important of them are: (1) dilution; (2) -time, allowing the bacteria to die (sunlight may aid in this process, -although effective sunshine cannot reach the lower layer of turbid -waters or through ice); (3) sedimentation, allowing them to go to -the bottom, where they eventually die; and (4) natural or artificial -filtration. In rivers, distance is mainly useful in affording time, -and also, under some conditions, in allowing opportunities for -sedimentation. Thus a distance of 500 miles requires a week for water -travelling three miles an hour to pass, and will allow very important -changes to take place. The old theory that water purifies itself -in running a certain distance has no adequate foundation as far as -bacteria are concerned. Some purification takes place with the time -involved in the passage, but its extent has been greatly overestimated. - -The time required for the bacteria to die simply from natural causes -is considerable; certainly not less than three or four weeks can -be depended upon with any confidence. In storage reservoirs this -action is often considerable, and it is for this reason that American -water-supplies from large storage reservoirs are, as a rule, much more -healthy than those drawn from rivers or polluted lakes, even when the -sources of the former are somewhat polluted. The water-supplies of New -York and Boston may be cited as examples. In many other water-works -operations the entire time from the pollution to the consumption of -the water is but a few days or even less, and time does not materially -improve water in this period. - -Sedimentation removes bacteria only slowly, as might be expected from -their exceedingly small size; and in addition their specific gravity -probably is but slightly greater than that of water. The Lawrence -reservoir, holding from 10 to 14 days’ supply, effected, by the -combined effect of time and sedimentation, a reduction of 90 per cent -of the bacteria in the raw water. In spite of this the city suffered -severely and continuously from fever. It would probably have suffered -even more, however, had it not been for this reduction. Nothing is -known of the removal of bacteria by sedimentation from flowing rivers, -but, considering the slowness with which the process takes place in -standing water, it is evident that we cannot hope for very much in -streams, and especially rapid streams, where the opportunities for -sedimentation are still less favorable. - -Filtration as practiced in Europe removes promptly and certainly a very -large proportion of the bacteria—probably, under all proper conditions, -over 99 per cent, and is thus much more effective in purification -than even weeks of storage or long flows in rivers. The places using -filtered water have, in general, extremely low death-rates from typhoid -fever. The fever which has occurred at a few places drawing their -raw water from greatly polluted sources has resulted from improper -conditions which can be avoided, and affords no ground for doubt of the -efficiency of properly conducted filtration. - -Corresponding evidence has not yet been produced in connection with -the mechanical filters which have been largely used in the United -States; but the bacterial efficiencies secured with them, under proper -conditions, and with enough coagulant, have been such as to warrant the -belief that they also will serve to greatly diminish the danger from -such infection, although they have not shown themselves equal in this -respect to sand filters. - -The main point is that disease-germs shall not be present in our -drinking-water. If they can be kept out in the first place at -reasonable expense, that is the thing to do. Innocence is better -than repentance. If they cannot be kept out, we must take them out -afterwards; it does not matter much how this is done, so long as the -work is thorough. Sedimentation and storage may accomplish much, but -their action is too slow and often uncertain. Filtration properly -carried out removes bacteria promptly and thoroughly and at a -reasonable expense. - - - - -APPENDICES. - - - - -Appendix I. - - RULES OF THE GERMAN GOVERNMENT IN REGARD TO THE FILTRATION OF - SURFACE-WATERS USED FOR PUBLIC WATER-SUPPLIES. - - -Rules somewhat similar to those of which a translation is given -below were first issued by the Imperial Board of Health in 1892. -These rules were regarded as unnecessarily rigid, and a petition was -presented to the government signed by 37 water-works engineers and -directors requesting a revision.[50] As a result a conference was -organized consisting of 14 members.[51] Köhler presided, and Koch, -Gaffsky, Werner, Günther, and Reincke represented the Imperial Board -of Health. The bacteriologists were represented by Flügge, Wolffhügel, -and Fränkel, while Beer, Fischer, Lindley, Meyer, and Piefke were the -engineer members. - -This conference prepared the 17 articles given below in the first -days of January, 1894. A little later the first 16 articles were -issued to all German local authorities, signed by Bosse, minister of -the “Geistlichen,” and Haase, minister of the interior, and they are -considered as binding upon all water-works using surface-water. The -bacterial examinations were commenced April 1, 1894, by most of the -cities which had not previously had them. - -Although the articles do not deal with rate of filtration, or the -precautions against snow and ice, they have a very great interest both -because they are an official expression, and on account of the personal -standing of the men who prepared them. - - * * * * * - -§ 1. In judging of the quality of a filtered surface-water the -following points should be especially observed: - -_a_. The operation of a filter is to be regarded as satisfactory -when the filtrate contains the smallest possible number of bacteria, -not exceeding the number which practical experience has shown to be -attainable with good filtration at the works in question. In those -cases where there are no previous records showing the possibilities of -the works and the influence of the local conditions, especially the -character of the raw water, and until such information is obtained, -it is to be taken as the rule that a satisfactory filtration will -never yield an effluent with more than about 100 bacteria per cubic -centimeter. - -_b_. The filtrate must be as clear as possible, and, in regard to -color, taste, temperature, and chemical composition, must be no worse -than the raw water. - -§ 2. To allow a complete and constant control of the bacterial -efficiency of filtration, the filtrate from each single filter must be -examined daily. Any sudden increase in the number of bacteria should -cause a suspicion of some unusual disturbance in the filter, and should -make the superintendent more attentive to the possible causes of it. - -§ 3. Filters must be so constructed that samples of the effluent -from any one of them can be taken at any desired time for the -bacteriological examination mentioned in § 1. - -§ 4. In order to secure uniformity of method, the following is -recommended as the standard method for bacterial examination: - -The nutrient medium consists of 10 per cent meat extract gelatine with -peptone, 10 cc. of which is used for each experiment. Two samples of -the water under examination are to be taken, one of 1 cc. and one -of 1/2 cc. The gelatine is melted at a temperature of 30° to 35° C., -and mixed with the water as thoroughly as possible in the test-tube -by tipping back and forth, and is then poured upon a sterile glass -plate. The plates are put under a bell-jar which stands upon a piece -of blotting-paper saturated with water, and in a room in which the -temperature is about 20° C. - -The resulting colonies are counted after 48 hours, and with the aid of -a lens. - -If the temperature of the room in which the plates are kept is lower -than the above, the development of the colonies is slower, and the -counting must be correspondingly postponed. - -If the number of colonies in 1 cc. of the water is greater than about -100, the counting must be done with the help of the Wolffhügel’s -apparatus. - -§ 5. The person entrusted with the carrying-out of the bacterial -examinations must present a certificate that he possesses the necessary -qualifications, and wherever possible he shall be a regular employé of -the water-works. - -§ 6. When the effluent from a filter does not correspond to the -hygienic requirements it must not be used, unless the cause of the -unsatisfactory work has already been removed during the period covered -by the bacterial examinations. - -In case a filter for more than a very short time yields a poor -effluent, it is to be put out of service until the cause of the trouble -is found and corrected. - -It is, however, recognized from past experience that sometimes -unavoidable conditions (high water, etc.) make it impossible, from an -engineering standpoint, to secure an effluent of the quality stated -in § 1. In such cases it will be necessary to get along with a poorer -quality of water; but at the same time, if the conditions demand it -(outbreak of an epidemic, etc.), a suitable notice should be issued. - -§ 7. Every single filter must be so built that, when an inferior -effluent results, which does not conform to the requirements, it can be -disconnected from the pure-water pipes and the filtrate allowed to be -wasted, as mentioned in § 6. This wasting should in general take place, -so far as the arrangement of the works will permit it: - -(1) Immediately after scraping a filter; and - -(2) After replacing the sand to the original depth. - -The superintendent must himself judge, from previous experience with -the continual bacterial examinations, whether it is necessary to waste -the water after these operations, and, if so, how long a time will -probably elapse before the water reaches the standard purity. - -§ 8. The best sand-filtration requires a liberal area of -filter-surface, allowing plenty of reserve, to secure, under all local -conditions, a moderate rate of filtration adapted to the character of -the raw water. - -§ 9. Every single filter shall be independently regulated, and the -rate of filtration, loss of head, and character of the effluent shall -be known. Also each filter shall, by itself, be capable of being -completely emptied, and, after scraping, of having filtered water -introduced from below until the sand is filled to the surface. - -§ 10. The velocity of filtration in each single filter shall be capable -of being arranged to give the most favorable results, and shall be as -regular as possible, quite free from sudden changes or interruptions. -On this account reservoirs must be provided large enough to balance the -hourly fluctuation in the consumption of water. - -§ 11. The filters shall be so arranged that their working shall not be -influenced by the fluctuating level of the water in the filtered-water -reservoir or pump-well. - -§ 12. The loss of head shall not be allowed to become so great as -to cause a breaking through of the upper layer on the surface of -the filter. The limit to which the loss of head can be allowed to -go without damage is to be determined for each works by bacterial -examinations. - -§ 13. Filters shall be constructed throughout in such a way as to -insure the equal action of every part of their area. - -§ 14. The sides and bottoms of filters must be made water-tight, and -special pains must be taken to avoid the danger of passages or loose -places through which the unfiltered water on the filter might find its -way to the filtered-water channels. To this end special pains should be -taken to make and keep the ventilators for the filtered-water channels -absolutely tight. - -§ 15. The thickness of the sand-layer shall be so great that under no -circumstances shall it be reduced by scraping to less than 30 cm. (= -12 inches), and it is desirable, so far as local conditions allow, to -increase this minimum limit. - -Special attention must be given to the upper layer of sand, which must -be arranged and continually kept in the condition most favorable for -filtration. For this reason it is desirable that, after a filter has -been reduced in thickness by scraping and is about to be refilled, the -sand below the surface, as far as it is discolored, should be removed -before bringing on the new sand. - -§ 16. Every city in the German empire using sand-filtered water is -requested to make a quarterly report of its working results, especially -of the bacterial character of the water before and after filtration, -to the Imperial Board of Health (Kaiserlichen Gesundheitsamt), which -will keep itself in communication with the commission chosen by the -water-works engineers in regard to these questions; and it is believed -that after such statistical information is obtained for a period of -about two years some farther judgments can be reached. - -§ 17. The question as to the establishment of a permanent inspection -of public water-works, and, if so, under what conditions, can be best -answered after the receipt of the information indicated in § 16. - - - - -APPENDIX II. - -EXTRACTS FROM “BERICHT DES MEDICINAL-INSPECTORATS DES HAMBURGISCHEN -STAATES FÜR DAS JAHR 1892.” - - -The following are translations from Dr. Reincke’s most valuable report -upon the vital statistics of Hamburg for 1892. I much regret that I am -unable to reproduce in full the very complete and instructive tables -and diagrams which accompany the report. - -=Diarrhœa and Cholera Infantum= (page 10). “It is usually assumed that -the increase of diarrhœal diseases in summer is to be explained by -the high temperature, especially by the action of the heat upon the -principal food of infants—milk. Our observations, however, indicate -that a deeper cause must be sought.” (Tables and diagrams of deaths -from cholera infantum by months for Hamburg and for Altona with the -mean temperatures, 1871-1892.) - -“From these it appears that the highest monthly mortality of each year -in Hamburg occurred 7 times in July, 13 times in August, and 3 times -in September, and substantially the same in Altona. If one compares -the corresponding temperatures, it is found that in the three years -1886, 1891, and 1892, with high September mortalities, especially the -first two of them, had their maximum temperature much earlier, in fact -earlier than usual. Throughout, the correspondence between deaths and -temperatures is not well marked. Repeated high temperatures in May and -June have never been followed by a notable amount of cholera infantum, -although such periods have lasted for a considerable time. For example, -toward the end of May, 1892, for a long time the temperature was higher -than in the following August, when the cholera infantum appeared. - -“The following observations are still more interesting. As is seen -from the diagram, in addition to the annual rise in summer there is -also a smaller increase in the winter, which is especially marked -in Altona. In 1892 this winter outbreak was greater than the summer -one, and nearly as great in 1880 and in 1888. The few years when -this winter increase was not marked, 1876-7, 1877-8, 1881-2, 1883-4, -were warm winters in which the mean temperature did not go below the -freezing-point. It is also to be noted that the time of this winter -outbreak is much more variable than that of the summer one. In 1887 the -greatest mortality was in November; in 1889 in February; in other years -in December or January, and in Altona, in 1886 and 1888, in March, -which is sufficient evidence that it was not the result of Christmas -festivities. - -“Farther, the winter diarrhœa of Hamburg and of Altona are not parallel -as is the case in summer. In Hamburg the greatest mortality generally -comes before New Year’s; in Altona one to two months later. - -“In Bockendahl’s Generalbericht über das öffentliche Gesundheitswesen -der Provinz Schleswig-Holstein für das Jahr 1870, page 10, we read: -‘Yet more remarkable was an epidemic of cholera infantum in Altona -in February which proved fatal to 43 children. These cases were -distributed in every part of the city, and could not be explained -by the health officer until he ascertained that the water company -had supplied unfiltered water to the city. This occurred for a few -days only in January, and was the only time in the whole year that -unfiltered Elbe water was delivered. However little reason there may -be to believe that there was a connection between these circumstances, -future interruptions of the service of filtered water should be most -critically watched, as only in this way can reliable conclusions be -reached. Without attempting to draw any scientific conclusions from -the fact, I cannot do less than record that, prior to the outbreak -of cholera on August 20, 1871, unfiltered together with filtered -water had been supplied to the city August 11 to 18. The action of -the authorities was then justified when they forbade in future the -supply of unfiltered water except in cases of most urgent necessity, -as in case of general conflagration; and in such a case, or in case of -interruption due to broken pipes, that the public should be suitably -warned.’ - -“The author of this paragraph, Dr. Kraus, became later the health -officer of Hamburg, and in an opinion written by him in 1874, and now -before me, he most earnestly urged the adoption of sand-filtration in -Hamburg, and cites the above observations in support of his position. -In the annual report of vital statistics of Hamburg for 1875 he says -that it is quite possible that the addition of unfiltered Elbe water -to milk is the cause of the high mortality from cholera infantum, as -compared with London, and this idea was often afterward expressed by -him. Since then so much evidence has accumulated that his view may -fairly be considered proved. - -“For the information of readers not familiar with local conditions, -a mention of the sources of the water-supplies up to the present -time used by Hamburg and Altona will be useful. Both cities take -their entire water-supplies from the Elbe—Altona from a point about 7 -miles below the discharge of the sewage of both cities, Hamburg from -about 7 miles above. The raw water at Altona is thus polluted by the -sewage from the population of both cities, having now together over -700,000 inhabitants, and contains in general 20,000 to 40,000 or more -bacteria per cubic centimeter. The raw water of Hamburg has, however, -according to the time of year and tide, from 200 to 5000, but here also -occasionally much higher numbers are obtained when the ebb tide carries -sewage up to the intake. How often this takes place is not accurately -known, but most frequently in summer when the river is low, more rarely -in winter and in times of flood. Recent bacterial examinations show -that it occurs much more frequently than was formerly assumed from -float experiments. This water is pumped directly to the city raw, while -that for Altona is carefully filtered. - -“Years ago I expressed the opinion that the repeated typhoid epidemics -in Altona stood in direct connection with disturbances of the action -of the filters by frost, which result in the supply of insufficiently -purified water. Wallichs in Altona has also come to this conclusion -as a result of extended observation, and recently Robert Koch has -explained the little winter epidemic of cholera in Altona in the same -way, thus supporting our theory. When open filters are cleaned in cold, -frosty weather the bacteria in the water are not sufficiently held back -by the filters. Such disturbances of filtration not only preceded the -explosive epidemics of typhoid fever of 1886, 1887, 1888, 1891, and -1892, and the cholera outbreaks of 1871 and 1893, but also the winter -outbreaks of cholera infantum which have been so often repeated. It -cannot be doubted that these phenomena bear the relation to each other -of cause and effect. It is thus explained why in the warm winters no -such outbreaks have taken place, and also why the cholera infantum in -winter is not parallel in Hamburg and Altona. - - * * * * * - -“A farther support of this idea is furnished by Berlin, where in the -same way frost has repeatedly interfered with filtration. In the -following table are shown the deaths from diarrhœa and cholera infantum -for a few winter periods having unusual increases in mortality in -comparison with the bacteria in the water-supply.” (These tables show -that in March, 1886, March, 1888, February-March, 1889, and February, -1891, high numbers of bacteria resulted from frost disturbance at -the Stralau works, and in every case they were followed by greatly -increased death-rates from diarrhœal diseases.—A. H.) - -“No one who sees this exhibition can doubt that here also the supply -of inadequately purified water has every time cost the lives of many -children.” (100 to 400 or more each time.—A. H.) “Even more conclusive -is the evidence, published by the Berlin Health Office, that this -increase was confined to those parts of the city supplied from Stralau” -(with open filters.—A. H.), “and that the parts supplied from the -better Tegel works took no part in the outbreaks, which was exactly -the case with the well-known typhoid epidemic of February and March, -1889.... It was also found that those children nursed by their mothers -or by wet-nurses did not suffer, but only those fed on the milk of -animals or other substitutes, and which in any case were mixed with -more or less water.” - -Under =Cholera=, page 28, he says: “The revised statistics here given -differ slightly from preliminary figures previously issued and widely -published.” (The full tables, which cannot be here reproduced, show -16,956 cases and 8605 deaths. 8146 of the deaths occurred in the month -ending September 21. Of these, 1799 were under 5 years old; 776 were 5 -to 15; 744, 15 to 25; 3520, 25 to 50; 1369, 50 to 70; and 397 over 70 -or of unknown age. The bulk of the cases were thus among mature people, -children, except very young children, suffering the least severely of -any age class.) - -“The epidemic began on August 16, in the port where earlier outbreaks -have also had their origin. The original source of the infection -has not been ascertained with certainty, but was probably from one -of two sources. Either it came from certain Jews, just arrived from -cholera-stricken Russia, who were encamped in large numbers near the -American pier, or the infection came from Havre, where cholera had been -present from the middle of July. Perhaps the germs came in ships in -water-ballast which was discharged at Hamburg, which is so much more -probable, as the sewage of Havre is discharged directly into the docks. - -“It is remarkable that in Altona, compared to the total number of -cases, very few children had cholera, while in the epidemic of 1871 the -children suffered severely. This may be explained by supposing that the -cholera of 1892 in Altona was not introduced by water, but by other -means of infection.... - -“It is well known that the drinking-water (of Hamburg) is supposed to -have been from the first the carrier of the cholera-germs. In support -of this view the following points are especially to be noted: - -“1. The explosive rapidity of attack. The often-compared epidemic -in Munich in 1854, which could not have come from the water is -characteristically different in that its rise was much slower and was -followed by a gradual decline. In Hamburg, with six times as large a -population, the height of the epidemic was reached August 27, only 12 -days after the first cases of sickness, while in Munich 25 days were -required. In Hamburg also the bulk of the cases were confined to 12 -days, from August 25 to September 5, while in Munich the time was twice -as long. - -“2. The exact limit of the epidemic to the political boundary between -Hamburg and Altona and Wandsbeck, which also agrees with the boundary -between the respective water-supplies, while other differences were -entirely absent. Hamburg had for 1000 inhabitants 26.31 cases and 13.39 -deaths, but Altona only 3.81 cases and 2.13 deaths, and Wandsbeck 3.06 -cases and 2.09 deaths. - -“3. The old experience of cholera in fresh-water ports, and the analogy -of many earlier epidemics. In this connection the above-mentioned -epidemic of 1871 in Altona has a special interest, even though some -of the conclusions of Bockendahl’s in his report of 1871 are open to -objection. First there were 3 deaths August 3, which were not at once -followed by others. Then unfiltered Elbe water was supplied August 11 -to 18. On the 19th an outbreak of cholera extended to all parts of -the city, which reached its height August 25 and 26, and afterwards -gradually decreased. In all 105 persons died of cholera and 186 (179 of -them children) of diarrhœa. In Hamburg, four times as large, only 141 -persons died of cholera at this time, thus proportionately a smaller -number. The conditions were then the reverse of those of 1892, an -infection of the Altona water and a comparative immunity in Hamburg. - -“It is objected that the cholera-germs were not found in the water -in 1892. To my knowledge they were first looked for, and then -with imperfect methods, in the second half of September. In the -after-epidemics at Altona, they were found in the river-water by R. -Koch by the use of better methods. - -“It is quite evident that the germs were also distributed by other -methods than by the city water, especially by dock-laborers who became -infected while at their work and thus set up little secondary epidemics -where they went or lived.... These laborers and sailors, especially on -the smaller river-boats, had an enormously greater proportionate amount -of cholera than others.... These laborers do not live exclusively near -the water, but to a measure in all parts of the city.” (And in Altona -and Wandsbeck.—A. H.) - -“Altona had 5 deaths from cholera December 25 to January 4, and 19 -January 23 to February 11, and no more. As noted above, this is -attributed to the water-supply, and to defective filtration in presence -of frost.... - -“The cholera could never have reached the proportion which it did, had -the improvements in the drinking-water been earlier completed.” - -Further accounts of the water-supplies of Altona and of Hamburg and of -the new filtration works at the latter city are given in Appendices VII -and VIII. - - - - -APPENDIX III. - - -METHODS OF SAND-ANALYSIS. - -(From the Annual Report of the Massachusetts State Board of Health for -1892.) - -A knowledge of the sizes of the sand-grains forms the basis of many of -the computations. This information is obtained by means of mechanical -analyses. The sand sample is separated into portions having grains -of definite sizes, and from the weight of the several portions the -relative quantities of grains of any size can be computed. - -=Collection of Samples.=—In shipping and handling, samples of sand -are best kept in their natural moist condition, as there is then no -tendency to separation into portions of unequal-sized grains. Under no -circumstances should different materials be mixed in the same sample. -If the material under examination is not homogeneous, samples of each -grade should be taken in separate bottles, with proper notes in regard -to location, quantity, etc. Eight-ounce wide-necked bottles are most -convenient for sand samples, but with gravels a larger quantity is -often required. Duplicate samples for comparison after obtaining the -results of analyses are often useful. - -=Separation into Portions having Grains of Definite Sizes.=—Three -methods are employed for particles of different sizes—hand-picking -for the stones, sieves for the sands, and water elutriation for the -extremely fine particles. Ignition, or determination of albuminoid -ammonia, might be added for determining the quantity of organic matter, -which, as a matter of convenience, is assumed to consist of particles -less than 0.01 millimeter in diameter. - -The method of hand-picking is ordinarily applied only to particles -which remain on a sieve two meshes to an inch. The stones of this size -are spread out so that all are in sight, and a definite number of the -largest are selected and weighed. The diameter is calculated from the -average weight by the method to be described, while the percentage is -reckoned from the total weight. Another set of the largest remaining -stones is then picked out and weighed as before, and so on until the -sample is exhausted. With a little practice the eye enables one to pick -out the largest stones quite accurately. - -With smaller particles this process becomes too laborious, on account -of the large number of particles, and sieves are therefore used -instead. The sand for sifting must be entirely free from moisture, and -is ordinarily dried in an oven at a temperature somewhat above the -boiling-point. The quantity taken for analysis should rarely exceed -100-200 grams. The sieves are made from carefully-selected brass-wire -gauze, having, as nearly as possible, square and even-sized meshes. The -frames are of metal, fitting into each other so that several sieves can -be used at once without loss of material. It is a great convenience to -have a mechanical shaker, which will take a series of sieves and give -them a uniform and sufficient shaking in a short time; but without this -good results can be obtained by hand-shaking. A series which has proved -very satisfactory has sieves with approximately 2, 4, 6, 10, 20, 40, -70, 100, 140, and 200 meshes to an inch; but the exact numbers are of -no consequence, as the actual sizes of the particles are relied upon, -and not the number of meshes to an inch. - -It can be easily shown by experiment that when a mixed sand is shaken -upon a sieve the smaller particles pass first, and as the shaking -is continued larger and larger particles pass, until the limit is -reached when almost nothing will pass. The last and largest particles -passing are collected and measured, and they represent the separation -of that sieve. The size of separation of a sieve bears a tolerably -definite relation to the size of the mesh, but the relation is not to -be depended upon, owing to the irregularities in the meshes and also -to the fact that the finer sieves are woven on a different pattern -from the coarser ones, and the particles passing the finer sieves are -somewhat larger in proportion to the mesh than is the case with the -coarser sieves. For these reasons the sizes of the sand-grains are -determined by actual measurements, regardless of the size of the mesh -of the sieve. - -It has not been found practicable to extend the sieve-separations to -particles below 0.10 millimeter in diameter (corresponding to a sieve -with about 200 meshes to an inch), and for such particles elutriation -is used. The portion passing the finest sieve contains the greater -part of the organic matter of the sample, with the exception of roots -and other large undecomposed matters, and it is usually best to remove -this organic matter by ignition at the lowest possible heat before -proceeding to the water-separations. The loss in weight is regarded as -organic matter, and calculated as below 0.01 millimeter in diameter. -In case the mineral matter is decomposed by the necessary heat, the -ignition must be omitted, and an approximate equivalent can be obtained -by multiplying the albuminoid ammonia of the sample by 50.[52] In this -case it is necessary to deduct an equivalent amount from the other fine -portions, as otherwise the analyses when expressed in percentages would -add up to more than one hundred. - -Five grams of the ignited fine particles are put in a beaker 90 -millimeters high and holding about 230 cubic centimeters. The beaker -is then nearly filled with distilled water at a temperature of 20° C., -and thoroughly mixed by blowing into it air through a glass tube. A -larger quantity of sand than 5 grams will not settle uniformly in the -quantity of water given, but less can be used if desired. The rapidity -of settlement depends upon the temperature of the water, so that it is -quite important that no material variation in temperature should occur. -The mixed sand and water is allowed to stand for fifteen seconds, when -most of the supernatant liquid, carrying with it the greater part of -the particles less than 0.08 millimeter, is rapidly decanted into a -suitable vessel, and the remaining sand is again mixed with an equal -amount of fresh water, which is again poured off after fifteen seconds, -carrying with it most of the remaining fine particles. This process is -once more repeated, after which the remaining sand is allowed to drain, -and is then dried and weighed, and calculated as above 0.08 millimeter -in diameter. The finer decanted sand will have sufficiently settled -in a few minutes, and the coarser parts at the bottom are washed back -into the beaker and treated with water exactly as before, except that -one minute interval is now allowed for settling. The sand remaining -is calculated as above 0.04 millimeter, and the portion below 0.04 is -estimated by difference, as its direct determination is very tedious, -and no more accurate than the estimation by difference when sufficient -care is used. - -=Determination of the Sizes of the Sand-grains.=—The sizes of the -sand-grains can be determined in either of two ways—from the weight of -the particles or from micrometer measurements. For convenience the size -of each particle is considered to be the diameter of a sphere of equal -volume. When the weight and specific gravity of a particle are known, -the diameter can be readily calculated. The volume of a sphere is -1/6π_d_³, and is also equal to the weight divided by the specific -gravity. With the Lawrence materials the specific gravity is uniformly -2.65 within very narrow limits, and we have _w_/2.65 = 1/6π_d_³. -Solving for _d_ we obtain the formula _d_ =.9∛_w_, where _d_ -is the diameter of a particle in millimeters and _w_ its weight in -milligrams. As the average weight of particles, when not too small, -can be determined with precision, this method is very accurate, and -altogether the most satisfactory for particles above 0.10 millimeter; -that is, for all sieve separations. For the finer particles the method -is inapplicable, on account of the vast number of particles to be -counted in the smallest portion which can be accurately weighed, and -in these cases the sizes are determined by micrometer measurements. -As the sand-grains are not spherical or even regular in shape, -considerable care is required to ascertain the true mean diameter. The -most accurate method is to measure the long diameter and the middle -diameter at right angles to it, as seen by a microscope. The short -diameter is obtained by a micrometer screw, focussing first upon the -glass upon which the particle rests and then upon the highest point to -be found. The mean diameter is then the cube root of the product of the -three observed diameters. The middle diameter is usually about equal -to the mean diameter, and can generally be used for it, avoiding the -troublesome measurement of the short diameters. - -The sizes of the separations of the sieves are always determined from -the very last sand which passes through in the course of an analysis, -and the results so obtained are quite accurate. With the elutriations -average samples are inspected, and estimates made of the range in -size of particles in each portion. Some stray particles both above -and below the normal sizes are usually present, and even with the -greatest care the result is only an approximation to the truth; still, -a series of results made in strictly the same way should be thoroughly -satisfactory, notwithstanding possible moderate errors in the absolute -sizes. - -=Calculation of Results.=—When a material has been separated into -portions, each of which is accurately weighed, and the range in the -sizes of grains in each portion determined, the weight of the particles -finer than each size of separation can be calculated, and with enough -properly selected separations the results can be plotted in the form of -a diagram, and measurements of the curve taken for intermediate points -with a fair degree of accuracy. This curve of results may be drawn upon -a uniform scale, using the actual figures of sizes and of per cents by -weight, or the logarithms of the figures may be used in one or both -directions. The method of plotting is not of vital importance, and -the method for any set of materials which gives the most easily and -accurately drawn curves is to be preferred. In the diagram published -in the Report of the Mass. State Board of Health for 1891, page 430, -the logarithmic scale was used in one direction, but in many instances -the logarithmic scale can be used to advantage in both directions. With -this method it has been found that the curve is often almost a straight -line through the lower and most important section, and very accurate -results are obtained even with a smaller number of separations. - -=Examples of Calculation of Results.=—Following are examples of -representative analyses, showing the method of calculation used with -the different methods of separation employed with various materials. - - -I. ANALYSIS OF A GRAVEL BY HAND-PICKING, 11,870 GRAMS TAKEN FOR -ANALYSIS. - - --------+---------+-----------+-----------+-------------+-------+-------- - Number | Total | Average | Estimated |Corresponding| Total |Per Cent - of |Weight of| Weight of | Weight of | Size. | Weight| of - Stones | Portion.| Stones. | Smallest | Millimeters.| of |Total - in | Grams. |Milligrams.| Stones. | |Stones |Weight - Portion.| | |Milligrams.| |Smaller|Smaller - (Largest| | | | | than | than - Selected| | | | | this | this - Stones.)| | | | | Size. | Size. - --------+---------+-----------+-----------+-------------+-------+-------- - | .... | .... | .... | .... |11,870 |=100= - 10 | 3,320 | 332,000 | 250,000 | =56= | 8,550 | =72= - 10 | 1,930 | 193,000 | 165,000 | =49= | 6,620 | =56= - 10 | 1,380 | 138,000 | 124,000 | =45= | 5,240 | =44= - 20 | 2,200 | 110,000 | 93,000 | =41= | 3,040 | =26= - 20 | 1,520 | 76,000 | 64,000 | =36= | 1,520 | =13= - 20 | 1,000 | 50,000 | 36,000 | =30= | 520 | =4.4= - 20 | 460 | 23,000 | 10,000 | =20= | 60 | =.5= - 10 | 40 | 4,000 | 2,000 | =11= | 20 | =.2= - Dust | 20 | .... | .... | .... | .... | .... - --------+---------+-----------+-----------+-------------+-------+-------- - -The weight of the smallest stones in a portion given in the fourth -column is estimated in general as about half-way between the average -weight of all the stones in that portion and the average weight of the -stones in the next finer portion. - -The final results are shown by the figures in full-faced type in the -last and third from the last columns. By plotting these figures we -find that 10 per cent of the stones are less than 35 millimeters in -diameter, and 60 per cent are less than 51 millimeters. The “uniformity -coefficient,” as described below, is the ratios of these numbers, or -1.46, while the “effective size” is 35 millimeters. - - -II. ANALYSIS OF A SAND BY MEANS OF SIEVES. - -A portion of the sample was dried in a porcelain dish in an air-bath. -Weight dry, 110.9 grams. It was put into a series of sieves in a -mechanical shaker, and given one hundred turns (equal to about seven -hundred single shakes). The sieves were then taken apart, and the -portion passing the finest sieve weighed. After noting the weight, the -sand remaining on the finest sieve, but passing all the coarser sieves, -was added to the first and again weighed, this process being repeated -until all the sample was upon the scale, weighing 110.7 grams, showing -a loss by handling of only 0.2 gram. The figures were as follows: - - -------+------------+--------+--------- - | Size of | | - | Separation |Quantity|Per Cent - Sieve | of this | of Sand| of - Marked.| Sieve. |Passing.| Total - |Millimeters.|Grams. | Weight. - -------+------------+--------+--------- - 190 | =.105= | .5 | =.5= - 140 | =.135= | 1.3 | =1.2= - 100 | =.182= | 4.1 | =3.7= - 60 | =.320= | 23.2 | =21.0= - 40 | =.46= | 56.7 | =51.2= - 20 | =.93= | 89.1 | =80.5= - 10 | =2.04= | 104.6 | =94.3= - 6 | =3.90= | 110.7 | =100.0= - -------+------------+--------+-------- - -Plotting the figures in heavy-faced type, we find from the curve that -10 and 60 per cent respectively are finer than .25 and .62 millimeter, -and we have for effective size, as described above, .25, and for -uniformity coefficient 2.5. - - -III. ANALYSIS OF A FINE MATERIAL WITH ELUTRIATION. - -The entire sample, 74 grams, was taken for analysis. The sieves used -were not the same as those in the previous analysis, and instead of -mixing the various portions on the scale they were separately weighed. -The siftings were as follows: - - Remaining on sieve marked 10, above 2.2 millimeters 1.5 grams - Remaining on sieve marked 20, above .98 millimeters 7.0 grams - Remaining on sieve marked 40, above .46 millimeters 22.0 grams - Remaining on sieve marked 70, above .24 millimeters 20.2 grams - Remaining on sieve marked 140, above .13 millimeters 9.2 grams - Passing sieve 140, below .13 millimeters 14.1 grams - -The 14.1 grams passing the 140 sieve were thoroughly mixed, and one -third, 4.7 grams, taken for analysis. After ignition just below a red -heat in a radiator, the weight was diminished by 0.47 gram. The portion -above .08 millimeter and between .04 and .08 millimeter, separated as -described above, weighed respectively 1.27 and 1.71 grams, and the -portion below .04 millimeter was estimated by difference [4.7 - (0.47 -+ 1.27 + 1.71)] to be 1.25 grams. Multiplying these quantities by 3, -we obtain the corresponding quantities for the entire sample, and the -calculation of quantities finer than the various sizes can be made as -follows: - - -----------------------+-------+------------+-------------+----------- - | | Size of |Weight of all|Per Cent by - |Weight.| Largest | the Finer | Weight of - Size of Grain. | Grams.| Particles. | Particles. | all Finer - | |Millimeters.| Grams. | Particles. - -----------------------+-------+------------+-------------+----------- - Above 2.20 millimeters | 1.50 | .... | 74.00 | =100= - .98-2.20 millimeters | 7.00 | =2.20= | 72.50 | =98= - .46- .98 millimeters | 22.00 | =.98= | 65.50 | =89= - .24- .46 millimeters | 20.20 | =.46= | 43.50 | =60= - .13- .24 millimeters | 9.20 | =.24= | 23.30 | =32= - .08- .13 millimeters | 3.81 | =.13= | 14.10 | =19= - .04- .08 millimeters | 5.13 | =.08= | 10.29 | =14= - .01- .04 millimeters | 3.75 | =.04= | 5.16 | =7= - Loss on ignition | | | | - (assumed to be less | | | | - than .01 millimeter)| 1.41 | =.01= | 1.41 | =1.9= - -----------------------+-------+------------+-------------+----------- - -By plotting the heavy-faced figures we find that 10 and 60 per cent are -respectively finer than .055 and .46 millimeter, and we have effective -size .055 millimeter and uniformity coefficient 8. - - * * * * * - -The effective size and uniformity coefficient calculated in this way -have proved to be most useful in various calculations, particularly -in estimating the friction between the sands and gravels and water. -The remainder of the article in the Report of the Mass. State Board -of Health is devoted to a discussion of these relations which were -mentioned in Chapter III of this volume. - - - - -APPENDIX IV. - -FILTER STATISTICS. - - -STATISTICS OF OPERATION OF SAND FILTERS. - - ------------+----------+---------+-------+-------+---------+-------+---------- - | |Total | | Area | Average |Area of|Period, - | |Quantity | | of | Daily |Filter | - | |of Water | |Filters| Yield, |Surface|Million - | |filtered |Million|in use,| |cleaned|Gallons - Place. | Year | for |Gallons| | Million |in One |per Acre - | Ending. |One Year.| Daily.| Acres.| Gallons | Year, |filtered - | | Million | | |per Acre.| |between - | | Gallons.| | | |Acres. |Scrapings. - ------------+----------+---------+-------+-------+---------+-------+---------- - Altona |Mar., 1895| 1,620 | 4.44 | 3.08 | 1.45 | 31.0 | 52 - |Mar., 1896| 1,730 | 4.75 | 3.08 | 1.55 | 48.5 | 36 - |Mar., 1897| 1,960 | 5.40 | 3.08 | 1.75 | 44.0 | 45 - |Mar., 1898| 1,940 | 5.30 | 3.08 | 1.72 | 36.5 | 53 - Amsterdam, |Dec., 1894| 1,390 | 3.80 | 5.43 | 0.71 | 23 | 62 - River |Dec., 1896| 1,490 | 4.08 | 5.43 | 0.75 | 48 | 31 - |Dec., 1897| 1,600 | 4.40 | 5.43 | 0.81 | 30 | 53 - Amsterdam, |Dec., 1894| 2,330 | 6.40 | 4.94 | 1.29 |116 | 20 - Dunes |Dec., 1896| 2,360 | 6.50 | 4.75 | 1.37 | 90 | 26 - |Dec., 1897| 2,290 | 6.25 | 4.75 | 1.31 |109 | 21 - Ashland, |Feb., 1897| 398 | 1.09 | 0.50 | 2.18 | 4.83 | 83 - Wis. | | | | | | | - Berlin, |Mar., 1896| 13,000 | 35.60 | 25.10 | 1.42 | | - total |Mar., 1897| 12,900 | 35.40 | 25.10 | 1.40 | | - |Mar., 1898| 13,200 | 36.20 | 27.00 | 1.34 | | - Bremen |Mar., 1895| 1,190 | 3.27 | 2.51 | 1.31 | 50 | 24 - |Mar., 1896| 1,220 | 3.34 | 3.21 | 1.04 | 32.5 | 38 - |Mar., 1897| 1,280 | 3.50 | 3.21 | 1.09 | 25.2 | 50 - |Mar., 1898| 1,400 | 4.10 | 3.21 | 1.28 | 34.0 | 41 - Breslau |Mar., 1895| 2,840 | 7.80 | 5.12 | 1.52 | 45 | 64 - |Mar., 1896| 2,960 | 8.10 | 5.12 | 1.58 | 40.0 | 74 - |Mar., 1897| 2,990 | 8.20 | 5.12 | 1.60 | 37 | 81 - |Mar., 1898| 3,060 | 8.40 | 5.12 | 1.64 | 43 | 71 - Brunn |Dec., 1896| 1,110 | 3.04 | 1.62 | 1.87 | 8.6 | 128 - |Dec., 1897| 1,190 | 3.25 | 1.62 | 2.00 | 9.1 | 131 - Brunswick |Mar., 1895| 815 | 2.23 | 1.48 | 1.51 | 14.8 | 55 - |Mar., 1896| 840 | 2.30 | 1.48 | 1.56 | 13.3 | 63 - |Mar., 1897| 820 | 2.25 | 1.48 | 1.52 | 13.7 | 60 - |Mar., 1898| 870 | 2.38 | 1.48 | 1.61 | 11.9 | 73 - Budapest |Dec., 1892| 7,360 | 20.20 | 3.00 | 6.70 |254 | 29 - Copenhagen |Dec., 1895| 2,330 | 6.40 | 2.88 | 2.22 | 45 | 52 - |Dec., 1896| 2,490 | 6.80 | 2.88 | 2.35 | 52 | 48 - |Dec., 1897| 2,580 | 7.10 | 2.88 | 2.47 | 54 | 48 - Dordrecht |Dec., 1894| 365 | 1.00 | 0.56 | 1.79 | | - Frankfort |Dec., 1895| 310 | 0.85 | 0.37 | 2.28 | 2.9 | 107 - on Oder |Dec., 1896| 325 | 0.89 | 0.37 | 2.40 | 7.4 | 44 - |Dec., 1897| 356 | 0.98 | 0.37 | 2.65 | 8.8 | 41 - Hamburg |Dec., 1894| 11,450 | 31.40 | 34.0 | 0.92 |350 | 33 - |Dec., 1895| 11,700 | 32.10 | 34.0 | 0.94 |275 | 43 - |Dec., 1896| 11,500 | 31.70 | 34.0 | 0.93 |266 | 43 - |Dec., 1897| 12,000 | 32.70 | 34.0 | 0.96 |285 | 42 - |Dec., 1898| 11,900 | 32.60 | 43.0 | 0.76 |246 | 48 - Hudson, |Dec., 1892| 697 | 1.91 | 0.74 | 2.58 | | - N. Y. |Dec., 1893| 543 | 1.49 | 0.74 | 2.01 | | - |Dec., 1895| 535 | 1.46 | 0.74 | 1.98 | | - Ilion, N. Y.|Feb., 1899| 182 | 0.50 | 0.14 | 3.57 | 1.40 | 130 - Königsberg |Mar., 1895| 1,060 | 2.90 | 2.70 | 1.07 | 38.5 | 27 - |Mar., 1896| 1,085 | 2.97 | 2.70 | 1.10 | 35.0 | 31 - |Mar., 1897| 1,085 | 2.97 | 2.70 | 1.10 | 41.0 | 27 - |Mar., 1898| 1,140 | 3.12 | 2.70 | 1.16 | 44.0 | 26 - Lawrence |Dec., 1894| 1,050 | 2.88 | 2.50 | 1.15 | 10 | 105 - |Dec., 1895| 1,097 | 3.00 | 2.50 | 1.20 | 27 | 41 - |Dec., 1896| 1,101 | 3.02 | 2.50 | 1.20 | 30 | 37 - |Dec., 1897| 1,114 | 3.06 | 2.50 | 1.22 | 41 | 27 - Liverpool |Dec., 1896| 8,520 | 23.40 | 10.92 | 2.14 |158 | 54[53] - London, all |Dec., 1892| 65,783 |180 |109.75 | 1.64 | 90 | - filters |Dec., 1893| |195 |116.00 | 1.68 | | - but not |Dec., 1894| 68,700 |188 |117.00 | 1.60 | | - including |Dec., 1895| 76,900 |210 |123.75 | 1.70 | | - ground |Dec., 1896| 72,482 |198 |123.75 | 1.60 | | - water |Dec., 1897| 73,340 |201 |125.00 | 1.61 | | - London, |Dec., 1897| 5,370 | 14.70 | 8.00 | 1.85 | | - Chelsea | | | | | | | - E. London |Dec., 1897| 18,000 | 49.00 | 31.00 | 1.58 | | - Grand |Dec., 1897| 8,560 | 23.40 | 21.75 | 1.07 | | - Junction | | | | | | | - Lambeth |Dec., 1897| 10,370 | 28.40 | 12.25 | 2.30 | | - New River |Dec., 1897| 15,750 | 43.00 | 16.50 | 2.60 | | - Southwark & |Dec., 1897| 14,800 | 40.50 | 20.50 | 1.98 | | - Vauxhall | | | | | | | - West |Dec., 1897| 8,910 | 24.30 | 15.00 | 1.61 | | - Middlesex | | | | | | | - Lübeck |Mar., 1895| 1,520 | 4.15 | 1.40 | 2.95 | 16.2 | 94 - |Mar., 1896| 1,600 | 4.38 | 1.40 | 3.13 | 24.4 | 66 - |Mar., 1897| 1,650 | 4.50 | 1.40 | 3.22 | 27.0 | 61 - |Mar., 1898| 1,750 | 4.80 | 1.40 | 3.42 | 38.5 | 45 - Magdeburg |Mar., 1895| 1880 | 5.15 | 3.76 | 1.37 | 47.5 | 40 - |Mar., 1896| 1950 | 5.35 | 3.76 | 1.42 | 65.0 | 30 - |Mar., 1897| 1880 | 5.15 | 3.76 | 1.37 | 59.0 | 32 - |Mar., 1898| 2070 | 5.66 | 3.76 | 1.50 | 63.0 | 33 - Mt. Vernon, |Dec., 1895| 493 | 1.35 | 1.10 | 1.22 | 7.3 | 68 - N. Y |Dec., 1896| 608 | 1.66 | 1.10 | 1.51 | 9.2 | 66 - |Dec., 1897| 808 | 2.21 | 1.10 | 2.00 | 16.6 | 49 - |Dec., 1898| 933 | 2.56 | 1.10 | 2.34 | 18.4 | 51 - Posen |Mar., 1895| 305 | 0.84 | 0.70 | 1.20 | 10.3 | 30 - |Mar., 1896| 346 | 0.94 | 0.70 | 1.35 | 10.4 | 33 - |Mar., 1897| 325 | 0.89 | 0.70 | 1.27 | 10.1 | 32 - |Mar., 1898| 360 | 0.99 | 0.70 | 1.42 | 9.6 | 38 - Poughkeepsie|Dec., 1892| 696 | 1.91 | 0.68 | 2.81 | 14.0 | 50 - |Dec., 1893| 667 | 1.83 | 0.68 | 2.70 | 12.0 | 56 - |Dec., 1894| 633 | 1.73 | 0.68 | 2.55 | 14 | 45 - |Dec., 1895| 686 | 1.88 | 0.68 | 2.77 | 14 | 49 - |Dec., 1896| 664 | 1.82 | 0.68 | 2.68 | 9 | 73 - |Dec., 1897| 615 | 1.69 | 1.36 | 1.24 | | - |Dec., 1898| 611 | 1.67 | 1.36 | 1.23 | 10.88 | 57 - Rostock |June, 1897| 560 | 1.54 | 1.11 | 1.38 | 9.3 | 60 - |June, 1898| 625 | 1.71 | 1.11 | 1.55 | 9.0 | 70 - Rotterdam |Dec., 1893| 4850 | 13.30 | 6.30 | 2.11 | | - Stettin |Mar., 1895| 1130 | 3.10 | 2.26 | 1.37 | 26.5 | 43 - |Mar., 1896| 1030 | 2.83 | 2.26 | 1.25 | 15.5 | 66 - |Mar., 1897| 980 | 2.70 | 2.26 | 1.19 | 16.1 | 61 - |Mar., 1898| 1020 | 2.80 | 2.26 | 1.24 | 20.3 | 50 - Stockholm |Dec., 1895| 2375 | 6.50 | 2.78 | 2.33 | 70.0 | 34 - |Dec., 1896| 2500 | 6.85 | 2.78 | 2.45 | 68.0 | 37 - |Dec., 1897| 2750 | 7.50 | 3.60 | 2.08 | 76.0 | 36 - Stralsund |Mar., 1897| 215 | 0.59 | 1.11 | 0.53 | 16.0 | 13 - |Mar., 1898| 210 | 0.58 | 1.11 | 0.51 | 17.3 | 12 - Stuttgart |Mar., 1895| 1040 | 2.85 | 1.46 | 1.96 | 13.7 | 76 - |Mar., 1896| 1220 | 3.34 | 1.66 | 2.04 | 17.7 | 69 - |Mar., 1897| 1270 | 3.48 | 2.32 | 1.50 | 18.7 | 68 - |Mar., 1898| 1320 | 3.60 | 2.32 | 1.54 | 20.2 | 65 - Utrecht |Dec., 1896| 510 | 1.40 | 0.60 | 2.33 | 31 | 16 - Zürich |Dec., 1891| 2010 | 5.50 | 0.84 | 6.50 | 8 | 250 - |Dec., 1892| 2150 | 5.90 | 0.84 | 7.00 | 10 | 215 - |Dec., 1893| 2310 | 6.38 | 1.19 | 5.35 | 13 | 177 - |Dec., 1894| 2250 | 6.15 | 1.19 | 5.18 | 17 | 133 - |Dec., 1895| 2460 | 6.70 | 1.19 | 5.62 | 27 | 91 - |Dec., 1896| 2360 | 6.45 | 1.66 | 3.88 | 30 | 79 - |Dec., 1897| 2500 | 6.84 | 1.66 | 4.13 | 35 | 71 - |Dec., 1898| 2730 | 7.50 | 1.66 | 4.50 | 47 | 58 ---------------+----------+---------+-------+-------+---------+-------+---------- - - -PARTIAL LIST OF CITIES USING SAND FILTERS. - - -------------------+------------------+--------+--------+------------ - | When |Population.| Area | Number | Average - Place. |Built.| 1890. | of | of | Daily - | | |Filters.|Filters.|Consumption. - -------------------+------+-----------+--------+--------+------------ - UNITED STATES. - Poughkeepsie. N. Y.| 1872 | 24,000 | 1.36 | 3 | 1.67 - Hudson, N. Y. | 1874 | 9,970 | 0.74 | 2 | 1.50 - St. Johnsbury, Vt. |187(?)| 3,857 | 0.14 | 3 | 0.70 - Nantucket, Mass. | 1893 | 3,268 | 0.11 | 1 | 0.09 - Lawrence, Mass. | 1893 | 44,654 | 2.50 | 1 | 3.00 - Ilion, N. Y. | 1893 | 4,057 | 0.14 | 2 | 0.50 - Mount Vernon, N. Y.| 1894 | 10,830 | 1.10 | 3 | 1.66 - Grand Forks, N. D. | 1894 | 4,979 | 0.42 | 1 | .... - Milford, Mass. | 1895 | 9,956 | 0.25 | 1 | 0.70 - Ashland, Wis. | 1895 | 9,956 | 0.50 | 3 | 1.09 - Hamilton, N. Y. | 1895 | 1,744 | 0.12 | 1 | 0.03 - Lambertville, N. J.| 1896 | 4,142 | 0.28 | 2 | 0.25 - Far Rockaway, N. Y.| 1896 | 2,288 | 0.92 | 2 | 0.93 - Red Bank, N. J. | 1897 | 500 | 0.03 | 2 | 0.10 - Somersworth, N. H. | 1897 | 6,207 | 0.50 | 1 | .... - Little Falls, N. Y.| 1898 | 8,783 | 0.76 | 1 | .... - Berwyn, Penna. | 1898 | 826 | 0.52 | 3 | .... - Harrisburg, Penna. | 1899 | 1,200 | 0.12 | 2 | 0.15 - Albany, N. Y. | 1899 | 94,923 | 5.60 | 8 | 11.00[54] - Rock Island, | 1899 | 13,634 | 1.20 | 3 | 3.50 - Illinois | | | | | - +------+-----------+--------+--------+------------ - Total | | 259,774 | 17.31 | 45 | 26.87 - BRITISH COLUMBIA. - Victoria | | 16,841 | 0.82 | 3 | 1.80 - SOUTH AMERICA. - Buenos Ayres | | 500,000 | 4.15 | 3 | .... - Montevidio | | | Filters reported .... - HOLLAND. - Amsterdam | | 555,821 | 10.18 | 12 | 11.20 - Rotterdam | | 290,000 | 6.30 | 18 | 13.00 - The Hague | | 191,000 | 2.88 | 6 | 4.20 - Schiedam | | 25,300 | 1.33 | 5 | 0.68 - Utrecht | | 140,000 | 0.60 | .... | 1.40 - Groningen | | 57,900 | 0.59 | 2 | .... - Dordrecht | | 34,100 | 0.56 | 2 | 1.00 - Leeuwarden | | 30,700 | 0.31 | 2 | .... - Vlaardingen | | .... | .... | .... | .... - Sliedrecht | | .... | .... | .... | .... - Gorinchem | | 10,000 | .... | .... | .... - Zutphen | | 18,000 | .... | .... | .... - Leyden | | 44,200 | .... | .... | .... - Enschede | | .... | .... | .... | .... - Middelburg | | 17,000 | .... | .... | .... - +------+-----------+--------+--------+------------ - Total | | 1,414,021 | 22.75 | 47 | 31.48 - -------------------+------+-----------+--------+--------+------------ - - GREAT BRITAIN. - London | | 5,030,267 | 125.00 | 120 | 200.00 - Liverpool | | 790,000 | 10.92 | .... | 26.67 - Dublin | | 349,000 | 5.00 | 10 | 18.00 - Leeds | | 420,000 | 6.00 | 8 | 17.99 - Bradford | | 436,260 | 4.62 | 6 | 13.31 - Leicester | | 220,005 | 2.50 | .... | 4.75 - York | | 72,083 | 2.04 | 6 | 3.00 - Edinburgh | | 292,364 | 2.00 | 4 | 18.00 - Darlington | | 43,000 | 1.32 | 7 | .... - Wakefield | | 36,815 | 1.25 | .... | .... - Carlisle | | 40,000 | 0.90 | .... | .... - Dumfries | | 17,821 | 0.25 | .... | .... - Accrington | | 42,000 | .... | .... | .... - Birmingham | | 680,140 | .... | .... | 19.05 - Blackburn | | 130,000 | .... | .... | 4.10 - Bolton | | 250,000 | .... | .... | 6.60 - Chester | | 40,000 | .... | .... | .... - Halifax | | 217,000 | .... | .... | 5.18 - Hereford | | 20,000 | .... | .... | .... - Middlesborough | | 187,331 | .... | .... | 11.39 - Newcastle | | 320,000 | .... | .... | 14.00 - Oldham | | 145,800 | .... | .... | 5.30 - Oxford | | 53,000 | .... | .... | 1.59 - Preston | | 113,864 | .... | .... | 4.20 - Reading | | 71,558 | .... | .... | 3.00 - Southampton | | 76,430 | .... | .... | 3.45 - Wigan | | 60,000 | .... | .... | 1.22 - Worcester | | 45,000 | .... | .... | 1.93 - | +-----------+--------+--------+------------ - Total | |10,199,738 | 161.80 | 161 | 382.73 - GERMANY. - Hamburg | | 661,200 | 42.00 | 22 | 33.00 - Berlin | | 1,746,424 | 31.45 | 55 | 36.00 - Breslau | | 380,000 | 5.12 | 5 | 8.20 - Magdeburg | | 217,067 | 3.76 | 11 | 5.66 - Bremen | | 157,500 | 3.21 | 12 | 3.50 - Altona | | 162,427 | 3.08 | 13 | 5.40 - Königsberg | | 176,000 | 2.70 | 7 | 3.00 - Stuttgart | | 162,516 | 2.32 | .... | 4.00 - Stettin | | 145,000 | 2.26 | 9 | 3.00 - Lübeck | | 70,000 | 1.40 | 6 | 4.50 - Brunswick | | 100,883 | 1.48 | 4 | 2.30 - Stralsund | | 30,105 | 1.11 | 6 | 0.60 - Rostock | | 49,891 | 1.11 | 3 | 1.54 - Lignitz | | 46,852 | 0.96 | 6 | 1.40 - Posen | | 75,000 | 0.70 | 4 | 0.90 - Schwerin | | 36,000 | 0.65 | 4 | 0.50 - Chemnitz | | 164,743 | 0.59 | 3 | .... - Worms | | 30,000 | 0.50 | 3 | 0.64 - Ratibor | | 20,729 | 0.42 | 3 | - Frankfort on Oder | | 59,161 | 0.37 | 5 | 0.89 - Kiel | | 69,214 | 0.31 | | 1.50 - Tilsit | | 30,000 | 0.25 | | 0.20 - Brieg | | 20,154 | 0.20 | 4 | - Gluckstadt | | 6,214 | 0.14 | | 0.10 - Wandsbeck | | 22,000 | 0.13 | | 0.30 - | +-----------+--------+--------+------------ - Total | | 4,639,080 |106.22 | 185 | 117.13 - - OTHER EUROPEAN FILTERS. - Warsaw | | 500,000 | 6.20 | 12 | 6.00 - St. Petersburg | | 954,000 | 5.85 | 11 | 39.00 - Odessa | | 380,000 | 4.75 | 5 | 8.00 - Choisy le Roi and | | } 200,000 |{ 3.85 | 25 | 10.00 - Neuilly sur Marne | | } |{ 2.31 | 15 | - Copenhagen | | 340,000 | 2.88 | 9 | 6.80 - Stockholm | | 274,000 | 2.78 | | 7.00 - Antwerp | | 240,000 | 2.10 | 8 | 2.00 - Zürich | | 96,839 | 1.66 | | 7.00 - Brunn | | | 1.62 | | 3.04 - Constantinople, | | | 0.74 | 3 | - South side | | | | | - | +-----------+--------+--------+------------ - Total | | 2,984,839 | 34.74 | 88 | 88.84 - - ASIA. - Blandarwada, India | | | 1.97 | 6 | - Agra, India | | | 1.37 | | - Bombay, India | | 821,000 | 1.22 | 4 | - Shanghai, China | | | 0.88 | 4 | - Hong Kong | | | 0.67 | 6 | - Yokohama, Japan | | 110,000 | 0.58 | 3 | - Calcutta, India | | 466,000 | | | - Tokyo, Japan | | | | | - Baroda, India | | | | | - Allahabad, India | | | | | - | +-----------+--------+--------+------------ - Total | | 1,397,000 | 6.69 | 23 | - - SUMMARY. - United States | | 259,774 | 17.31 | 45 | 26.87 - British Columbia | | 16,841 | 0.82 | 3 | 1.80 - South America | | 500,000 | 4.15 | 3 | - Holland | | 1,414,021 | 22.75 | 47 | 31.48 - Great Britain | |10,199,738 |161.80 | 161 | 382.73 - Germany | | 4,639,080 |106.22 | 185 | 117.13 - Other European | | 2,984,839 | 34.74 | 88 | 88.84 - countries | | | | | - Asia | | 1,397,000 | 6.69 | 23 | - | +-----------+--------+--------+------------ - Total | |21,411,293 |354.48 | 555 | 648.85 - -------------------+------+-----------+--------+--------+------------ - - -LIST OF CITIES AND TOWNS USING MECHANICAL FILTERS. ARRANGED BY -POPULATIONS. - - Abbreviations.--P., Pressure filters; G., Gravity filters; J., Jewell - system; N. Y., New York system; W., Warren system; C., Continental - system; Am., American system. - - --------------------------+-----------+----------+-----------+ - | | | Nominal | - | | | Capacity | - Place. |Population,| Filters |of Filters,| - | 1890. | First | 1899. | - | |Installed.| Million | - | | | Gallons. | - --------------------------+-----------+----------+-----------+ - Denver, Col. | 108,204 | | | - Atlanta, Ga. | 65,533 | 1887 | 8 | - St. Joseph, Mo. | 52,324 | 1898 | 10.2 | - Oakland, Cal. | 48,682 | 1891 | 5 | - Kansas City, Kan. | 38,316 | 1898 | 6 | - Wilkesbarre, Pa.[55] | 37,718 | | 10 | - Norfolk, Va. | 34,871 | 1899 | 6 | - Augusta, Ga. | 33,300 | 1899 | 6 | - Quincy. Ill. | 30,494 | 1892 | 4 | - Dubuque, Iowa[56] | 30,311 | 1899 | 2 | - Terre Haute, Ind. | 30,217 | 1890 | 4 | - Elmira, N. Y. | 29,708 | 1897 | 6 | - Chattanooga, Tenn. | 29,100 | 1887 | 9 | - Davenport, Iowa | 26,872 | 1891 | 7.5 | - Little Rock, Ark. | 25,874 | 1891 | 5.5 | - Winnipeg, Mann. | 25,642 | 1887 | 1.5 | - Oshkosh, Wis. | 22,836 | 1891 | 2.4 | - Macon, Ga. | 22,746 | 1893 | 4 | - Burlington, Ia. | 22,565 | 1894 | 3.5 | - Knoxville, Tenn. | 22,535 | 1894 | 5 | - Lexington, Ky. | 21,567 | 1895 | 2 | - Kingston, N. Y. | 21,261 | 1897 | 4 | - York, Penna. | 20,793 | 1899 | 4 | - Biddeford, Maine | 20,500 | 1896 | 3 | - Newport, R. I. | 19,467 | | 4 | - Bangor, Maine | 19,103 | 1897 | 5 | - Cedar Rapids, Ia. | 18,020 | 1896 | 2.5 | - Elgin, Ill. | 17,823 | 1888 | 4.3 | - Decatur, Ill. | 16,841 | 1893 | 3 | - Belleville, Ill. | 15,361 | | 1 | - Columbia, S. C. | 15,353 | 1892 | 3 | - Keokuk, Ia. | 14,101 | 1893 | 3 | - Ottumwa, Ia. | 14,001 | 1895 | 2 | - Rock Island, Ill.[55] | 13,634 | | 2 | - Raleigh, N. C. | 12,678 | 1887 | 1 | - Shreveport, La. | 11,979 | 1889 | 1 | - New Castle, Penna | 11,600 | 1898 | 4 | - Charlotte, N. C. | 11,557 | 1896 | 1 | - Nebraska City, Neb. | 11,494 | 1891 | 0.4 | - Streator, Ill. | 11,414 | | 2 | - Hornelsville, N. Y.[58] | 10,966 | 1899 | 3 | - Augusta, Maine | 10,527 | 1887 | 0.6 | - St. Thomas, Ont. | 10,370 | 1891 | 2.5 | - Cairo, Ill. | 10,324 | 1889 | 0.8 | - Alton, Ill. | 10,294 | 1898 | 3 | - Asheville, N. C. | 10,235 | 1889 | 1 | - Greenwich, Conn. | 10,131 | 1887 | 2 | - Huntington, W. Va. | 10,108 | 1899 | 2 | - Beaver Falls, Pa. | 9,735 | | 2 | - Champaign, Ill.[57] | 9,719 | | | - Chatham, Ont. | 9,052 | 1895 | 1 | - Adrian, Mich. | 8,756 | 1899 | 1.75 | - Athens, Ga. | 8,639 | 1893 | 1 | - East Providence, R. I. | 8,422 | 1899 | 0.5 | - Winston, N. C. | 8,018 | 1895 | 0.5 | - Danville, Penna. | 7,998 | 1896 | 1 | - Clarksville, Tenn.[58] | 7,924 | 1899 | 1.5 | - Stevens Point, Wis. | 7,896 | 1889 | 0.5 | - Carlisle, Pa. | 7,620 | 1896 | 1.5 | - Calais, Me. | 7,290 | 1893 | 1.5 | - Long Branch, N. J. | 7,231 | 1888 | 3 | - Creston, Ia. | 7,200 | 1891 | 0.5 | - St. Hyacinthe, Que. | 7,016 | 1898 | 1 | - Rome, Ga.[58] | 6,957 | 1899 | 1.5 | - Westerly, R. I. | 6,813 | 1896 | 1.5 | - Merrill, Wis. | 6,809 | 1897 | 1 | - Dennison, Ohio[58] | 6,767 | 1899 | 1.25 | - Parsons, Kan. | 6,736 | 1894 | 2 | - Waterloo, Iowa | 6,674 | 1891 | 1.5 | - Somerville, N. J. | 6,417 | 1885 | 1.9 | - Athol, Mass. | 6,319 | 1888 | 1.5 | - Owego, N. Y. | 6,200 | 1887 | 1 | - Brunswick, Maine | 6,012 | 1887 | 0.6 | - Bucyrus, Ohio | 5,974 | 1887 | 0.5 | - Warren, Ohio | 5,973 | 1896 | 1.5 | - Hopkinsville, Ky. | 5,833 | 1895 | 0.5 | - Brainerd, Minn. | 5,703 | 1897 | 0.5 | - New Brighton, Pa. | 5,616 | 1889 | 0.5 | - Niagara Falls, N. Y. | 5,502 | 1896 | 4.5 | - Durham, N. C. | 5485 | 1893 | 0.9 | - Winfield, Kan. | 5184 | 1894 | 1 | - Louisiana, Mo. | 5090 | 1888 | 0.8 | - Trenton, Mo. | 5039 | 1889 | 0.4 | - Lorain, Ohio | 4863 | 1896 | 3 | - Sidney, Ohio[59] | 4850 | | | - Mexico, Mo. | 4789 | 1889 | 0.3 | - Mt. Clemens, Mich. | 4748 | 1888 | 1 | - Riverside, Cal. | 4683 | 1892 | 0.09 | - Columbus, Miss.[60] | 4559 | 1899 | 0.5 | - Winchester, Ky. | 4519 | 1894 | 0.75 | - Salisbury, N. C. | 4418 | 1889 | 0.5 | - Eufaula, Ala. | 4394 | 1897 | 0.5 | - Greenville, Tex. | 4330 | 1888 | 0.8 | - Exeter, N. H. | 4284 | 1887 | 0.114 | - Bordentown, N. J. | 4232 | 1890 | 0.5 | - Lake Forest, Ill. | 4203 | 1892 | 1 | - Henderson, N. C. | 4191 | 1899 | 0.25 | - Reading, Mass. | 4088 | 1896 | 1 | - Goldsboro, N. C. | 4017 | 1896 | 0.5 | - Rich Hill, Mo. | 4008 | 1893 | 0.5 | - Mt. Pleasant, Ia. | 3997 | 1888 | 0.5 | - Murphysboro, Ill. | 3880 | 1890 | 0.2 | - Brandon, Manitoba | 3778 | 1893 | 1 | - Danville, Ky. | 3766 | 1894 | 0.5 | - Royersford, Pa. | 3612 | 1893 | 1 | - Warsaw, Ind. | 3514 | 1896 | 0.5 | - Asbury Park, N. J. | 3500 | | 2 | - Keyport, N. J. | 3411 | 1895 | 0.5 | - Deseronto, Ont. | 3338 | 1896 | 0.5 | - Milledgeville, Ga. | 3322 | 1893 | 0.5 | - Carlinville, Ill. | 3293 | | 0.1 | - Gettysburg, Pa. | 3221 | 1894 | 0.3 | - Independence, Kan. | 3127 | 1891 | 0.75 | - LaGrange, Ga. | 3090 | 1893 | 0.25 | - Paola, Kan. | 2943 | 1887 | 0.25 | - Benwood, W. Va.[60] | 2934 | 1899 | 1 | - Gadsden, Ala. | 2901 | 1887 | 1.325 | - Lamar, Mo. | 2860 | 1891 | 0.25 | - Longueuil, Que. | 2757 | 1895 | 0.4 | - Washington, Mo. | 2725 | 1888 | 0.2 | - Renfrew, Ont. | 2611 | 1897 | 0.432 | - Oswego, Kan. | 2574 | 1893 | 0.5 | - Holden, Mo. | 2520 | 1893 | 0.2 | - Burlington, Kan. | 2239 | | 0.5 | - Council Grove, Kan. | 2211 | 1898 | 0.5 | - Wakefield, R. I.[61] | 2170 | | 0.15 | - Catonsville, Md. | 2115 | 1890 | 0.25 | - Attica, N. Y. | 1994 | 1896 | 0.4 | - Hightstown, N. J. | 1875 | 1899 | 0.25 | - No. Berwick, Me. | 1803 | 1896 | 0.3 | - Dunnville, Ont. | 1776 | 1899 | 0.5 | - Rogers Park, Ill. | 1708 | 1889 | 0.4 | - Eatonton, Ga. | 1682 | 1897 | 0.5 | - Caldwell, Kan. | 1642 | 1890 | 0.5 | - LaGrange, Tex. | 1626 | 1891 | 0.25 | - Richfield Springs, N. Y. | 1623 | 1889 | 0.35 | - Valatie, N. Y. | 1437 | 1894 | 0.15 | - Tunkhannock, Pa. | 1253 | | 0.1 | - Mechanics Falls, Me. | 1030 | 1898 | 0.72 | - New Bethlehem, Pa. | 1026 | 1899 | 0.1 | - Fairmount, W. Va. | 1023 | 1898 | 1 | - Atlantic Highlands, N. J. | 945 | | 0.3 | - Rumford Falls, Me. | 898 | 1897 | 0.5 | - Lakewood, N. J. | 730 | 1889 | 0.5 | - Veazie, Me. | 650 | 1889 | 1 | - Portersville, Cal. | 606 | 1890 | 0.151 | - Holmesburg, Pa. | | 1896 | 1 | - Pickering Creek, Pa. | | 1896 | 0.75 | - Overbrook, Penna. | | 1895 | 0.25 | - Vandergrift, Pa. | | 1897 | 0.5 | - Frazerville, P. Q.[62] | | 1899 | 0.2 | - Arnate, Pa. | | 1899 | 0.12 | - Chihuahua, Mex.[62] | | 1899 | 1 | - West Reading, Pa. | | | | - +-----------+ +-----------+ - Totals | 1,565,881 | | 252 | - --------------------------+-----------+----------+-----------+ - --------------------------+------------+--------+--------------------- - | Average | | - |Consumption,|Area of | - Place. | Million |Filters,| Filter - | Gallons: |Sq. Ft. | System. - |Water Works | 1899. | - | Manual. | | - --------------------------+------------+--------+--------------------- - Denver, Col. | | 2260 | Special. - Atlanta, Ga. | 4.54 | 2056 | N. Y. P. - St. Joseph, Mo. | | 3842 | J. G. - Oakland, Cal. | 10 | 1960 | N. Y. P. - Kansas City, Kan. | 2 | 2260 | J. G. - Wilkesbarre, Pa.[55] | | 3166 | J. G. - Norfolk, Va. | 3.5 | 2112 | J. G. - Augusta, Ga. | 3.8 | 2112 | N. Y. G. - Quincy. Ill. | 1.2 | 1582 | J. G. - Dubuque, Iowa[56] | | 880 | J. G. - Terre Haute, Ind. | 3 { | 1076 | N. Y. P. - | { | 226 | J. G. - Elmira, N. Y. | 3 | 2034 | J. G. - Chattanooga, Tenn. | | 2080 | J. & N. Y. P. - Davenport, Iowa | 3 | 2380 | Am. P. - Little Rock, Ark. | | 1544 | Am., J., & N. Y. P. - Winnipeg, Mann. | | 390 | N. Y. P. - Oshkosh, Wis. | 2.1 | 550 | W. G. - Macon, Ga. | 1.65 | 1437 | J., W., & N. Y. - Burlington, Ia. | | 1243 | J. G. - Knoxville, Tenn. | 1.93 | 1404 | W. G. - Lexington, Ky. | 1.2 | 678 | J. G. - Kingston, N. Y. | 1.5 | 1120 | N. Y. P. - York, Penna. | 2.37 | 1408 | J. G. - Biddeford, Maine | 2 | 780 | W. G. - Newport, R. I. | 2.1 | | Special. - Bangor, Maine | 3 | 1404 | W. G. - Cedar Rapids, Ia. | 2 | 905 | J. G. - Elgin, Ill. | 1 | 780 | Am. P. - Decatur, Ill. | 2 | 1008 | W. G. - Belleville, Ill. | 0.6 | 339 | J. G. - Columbia, S. C. | | 678 | J. G. - Keokuk, Ia. | | 980 | N. Y. P. - Ottumwa, Ia. | 1.2 | 678 | J. G. - Rock Island, Ill.[55] | 3.5 | 452 | J. G. - Raleigh, N. C. | 1 | 296 | N. Y. P. - Shreveport, La. | | 312 | N. Y. P. - New Castle, Penna | 2 | 1408 | N. Y. G. - Charlotte, N. C. | 0.5 | 530 | N. Y. G. - Nebraska City, Neb. | 0.7 | 116 | N. Y. P. - Streator, Ill. | 1.3 | 100 | Western & Am. P. - Hornelsville, N. Y.[58] | | 700 | N. Y. P. - Augusta, Maine | 1.6 | 100 | W. - St. Thomas, Ont. | 0.6 | 700 | N. Y. P. - Cairo, Ill. | 2.5 | 197 | N. Y. P. - Alton, Ill. | 1 | 1056 | N. Y. G. - Asheville, N. C. | 0.35 | 312 | N. Y. P. - Greenwich, Conn. | 0.4 | 592 | N. Y. P. - Huntington, W. Va. | | 704 | N. Y. G. - Beaver Falls, Pa. | 4.5 | | N. Y. - Champaign, Ill.[57] | 0.75 | | N. Y. - Chatham, Ont. | 0.4 | 280 | N. Y. P. - Adrian, Mich. | 0.45 | 565 | J. G. - Athens, Ga. | 0.45 | 420 | W. G. - East Providence, R. I. | | 176 | J. G. - Winston, N. C. | 0.3 | 156 | W. G. - Danville, Penna. | 1 | 226 | J. G. - Clarksville, Tenn.[58] | 0.5 | 704 | J. G. - Stevens Point, Wis. | 0.25 | 156 | N. Y. P. - Carlisle, Pa. | | 339 | J. G. - Calais, Me. | 0.85 | 275 | W. G. - Long Branch, N. J. | 1.3 | 904 | N. Y. P. - Creston, Ia. | 0.3 | 150 | J. - St. Hyacinthe, Que. | 0.84 | 294 | J. P. - Rome, Ga.[58] | 1.3 | 528 | J. G. - Westerly, R. I. | 0.375 | 396 | N. Y. G. - Merrill, Wis. | | 339 | J. G. - Dennison, Ohio[58] | 1 | 528 | J. G. - Parsons, Kan. | 0.6 | 452 | J. G. - Waterloo, Iowa | 0.7 | 565 | J. G. - Somerville, N. J. | 0.75 | 552 | N. Y. P. - Athol, Mass. | 0.5 | 350 | N. Y. P. - Owego, N. Y. | 0.75 | 234 | N. Y. P. - Brunswick, Maine | 0.33 | 100 | W. - Bucyrus, Ohio | 0.55 | 156 | N. Y. P. - Warren, Ohio | 1.5 | 462 | W. G. - Hopkinsville, Ky. | 0.15 | 140 | N. Y. P. - Brainerd, Minn. | | 156 | N. Y. P. - New Brighton, Pa. | | 156 | N. Y. P. - Niagara Falls, N. Y. | 2.62 | 1019 | J. G. - Durham, N. C. | 0.7 | 252 | W. G. - Winfield, Kan. | | 336 | W. G. - Louisiana, Mo. | | 242 | N. Y. P. & G. - Trenton, Mo. | | 128 | N. Y. P. - Lorain, Ohio | 1.5 | 1356 | J. G. - Sidney, Ohio[59] | 0.5 | | N. Y. - Mexico, Mo. | 0.4 | 66 | N. Y. P. - Mt. Clemens, Mich. | 0.6 | 251 | N. Y. P. - Riverside, Cal. | | 20 | N. Y. P. - Columbus, Miss.[60] | 0.175 | 176 | J. G. - Winchester, Ky. | 0.107 | 152 | J. P. - Salisbury, N. C. | 0.35 | 156 | N. Y. P. - Eufaula, Ala. | | 140 | N. Y. P. - Greenville, Tex. | 0.175 | 156 | N. Y. P. - Exeter, N. H. | 0.179 | 34 | N. Y. P. - Bordentown, N. J. | 0.5 | 156 | N. Y. P. - Lake Forest, Ill. | | 168 | J. P. - Henderson, N. C. | | 118 | W. G. - Reading, Mass. | 0.198 | 336 | W. G. - Goldsboro, N. C. | 0.1 | 156 | W. G. - Rich Hill, Mo. | 0.24 | 140 | N. Y. P. - Mt. Pleasant, Ia. | | 156 | N. Y. P. - Murphysboro, Ill. | | 60 | N. Y. P. - Brandon, Manitoba | 0.36 | 240 | N. Y. P. - Danville, Ky. | 0.1 | 140 | N. Y. P. - Royersford, Pa. | 0.08 | 226 | J. G. - Warsaw, Ind. | 0.5 | 156 | N. Y. P. - Asbury Park, N. J. | 0.5 | 670 | C. - Keyport, N. J. | 0.06 | 156 | W. G. - Deseronto, Ont. | 0.84 | 147 | J. P. - Milledgeville, Ga. | | 156 | N. Y. P. - Carlinville, Ill. | | 38 | Am. or Jackson. - Gettysburg, Pa. | 0.075 | 78 | W. G. - Independence, Kan. | 0.25 | 129 | Am. P. - LaGrange, Ga. | | 34 | N. Y. P. - Paola, Kan. | 0.45 | 66 | N. Y. P. - Benwood, W. Va.[60] | | 306 | J. G. - Gadsden, Ala. | | 430 | N. Y. P. & G. - Lamar, Mo. | | 78 | N. Y. P. - Longueuil, Que. | 0.3 | 100 | N. Y. P. - Washington, Mo. | 0.075 | 50 | N. Y. P. - Renfrew, Ont. | | 100 | N. Y. P. - Oswego, Kan. | 0.3 | 140 | N. Y. P. - Holden, Mo. | 0.05 | 100 | N. Y. P. - Burlington, Kan. | | 79 | J. - Council Grove, Kan. | 0.08 | 78 | N. Y. - Wakefield, R. I.[61] | 0.25 | | N. Y. - Catonsville, Md. | | 78 | N. Y. P. - Attica, N. Y. | | 100 | N. Y. P. - Hightstown, N. J. | 0.025 | 78 | N. Y. G. - No. Berwick, Me. | | 78 | W. G. - Dunnville, Ont. | | 140 | N. Y. P. - Rogers Park, Ill. | 0.35 | 100 | N. Y. P. - Eatonton, Ga. | | 132 | N. Y. G. - Caldwell, Kan. | | 156 | N. Y. P. - LaGrange, Tex. | | 34 | N. Y. P. - Richfield Springs, N. Y. | | 100 | N. Y. P. - Valatie, N. Y. | | 50 | N. Y. - Tunkhannock, Pa. | | | N. Y. - Mechanics Falls, Me. | | 176 | W. G. - New Bethlehem, Pa. | | 50 | J. G. - Fairmount, W. Va. | | 280 | N. Y. P. - Atlantic Highlands, N. J. | 0.109 | 130 | C. - Rumford Falls, Me. | | 113 | W. G. - Lakewood, N. J. | | 156 | N. Y. P. - Veazie, Me. | 0.1 | 176 | W. G. - Portersville, Cal. | 0.060 | 34 | N. Y. P. - Holmesburg, Pa. | 0.046 | 280 | N. Y. P. - Pickering Creek, Pa. | | 234 | W. G. - Overbrook, Penna. | | 78 | W. G. - Vandergrift, Pa. | | 156 | W. G. - Frazerville, P. Q.[62] | | 78 | N. Y. G. - Arnate, Pa. | | 50 | N. Y. G. - Chihuahua, Mex.[62] | | 612 | J. G. - West Reading, Pa. | 0.07 | | W. G. - +------------+--------+ - Totals | 108 |77,806 | - --------------------------+------------+--------+--------------------- - -Special filters, neither sand nor mechanical: Wilmington, Del.; Pop., -61,431; area, 10,000 sq. ft.; nominal capacity, 10 million gallons. See -Eng. News, Vol. 40, p. 146. - - -NOTES REGARDING SAND FILTERS IN THE UNITED STATES. - -POUGHKEEPSIE, N. Y. Designed by James P. Kirkwood, built in 1872, was -the earliest of its kind in the United States. It was enlarged by the -Superintendent, Charles E. Fowler, in 1896. The walls of the original -filters were of rubble, and in course of time developed cracks and -leaked badly. The walls of the new filter are of rubble, faced with -vitrified brick. The filters treat the water of the Hudson River, which -is sewage-polluted and more or less muddy. Description: Jour. N. E. -Water Works Assoc., Vol. 12, p. 209. - -HUDSON, N. Y. Designed by James P. Kirkwood, built in 1874. enlarged in -1888. The filters are open and are used for treating the Hudson River -water, which is sewage-polluted and more or less muddy. Description: -Eng. News, Vol. 31, p. 487. - -ST. JOHNSBURY, VT. (E. & T. Fairbanks & Co.) These filters were built -about 30 years ago, and have been recently enlarged. The filters were -originally open, but were afterwards covered with a roof. The single -roof proved inadequate to keep them from freezing, and a second roof -was added inside and under the main roof. They are used for filtering -pond water, which is quite clear and not subject to much pollution. The -water supply is one of two, the other is the town supply and is taken -from the Passumpsic River. No published description. - -NANTUCKET, MASS. Designed by J. B. Rider, built in 1892. This filter -is used to remove organisms from the reservoir water supply. It is -only used when the organisms are troublesome, and is satisfactory in -preventing the tastes and odors which formerly resulted from their -presence. Description: Jour. N. E. Water Works Assoc., Vol. 8, p. 171; -Eng. News, Vol. 31, p. 336. - -LAWRENCE, MASS. Designed by Hiram F. Mills, built in 1892-3, and put -in operation September, 1893. It is used for treating the water of the -Merrimac River, which contains a large amount of sewage. Description: -Report of the Mass. State Board of Health, 1893, p. 543; Jour. N. E. -Water Works Assoc., Vol. 9, p. 44; Eng. News, Vol. 30, p. 97. - -ILION, N. Y. Designed by the Stanwix Engineering Company and are used -for treating reservoir water, which is generally clear and not subject -to pollution. Description: Eng. News, Vol. 31, p. 466. - -MOUNT VERNON, N. Y. (New York Suburban Water Company.) Designed by -J. N. Chester, built in 1894. These filters are similar in general -construction to the Lawrence filter, although the dimensions both -vertical and horizontal are reduced, and the area is divided into three -parts. The filters are used for treating reservoir water, which is -generally quite clear, but which is polluted by a considerable amount -of sewage. Since the use of filters the reduction in the typhoid fever -death-rate has been very great. Description: Eng. News, Vol. 32, p. 155. - -MILFORD, MASS. Designed by F. L. Northrop. This filter is very simple -in construction, and is used for filtering Charles River water as an -auxiliary supply. Description: Jour. N. E. Water Works Assoc., Vol. 10, -p. 262. - -GRAND FORKS, N. D. Designed by W. S. Russell. These filters are covered -with roofs. They treat the water from the Red River, which is very -muddy, and also sewage-polluted, and which formerly caused typhoid -fever. Description: Eng. News, Vol. 33, p. 341. - -ASHLAND, WIS. Designed by William Wheeler, built in 1895. The Ashland -filters were the first vaulted masonry filters to be constructed in -the United States, and are used for treating the bay water, which -is polluted with sewage, and is at times muddy from the river water -discharging into the bay near the intake. The filters are below the bay -level, and receive water from it by gravity. Description: Jour. N. E. -Water Works Assoc., Vol. 11, p. 301; Eng. News, Vol. 38, p. 338. - -LAMBERTVILLE, N. J. Designed by Churchill Hungerford, and built in -1896. These are open filters with earth embankments, for filtration of -reservoir water. Description: Eng. News, Vol. 36, p. 4. - -FAR ROCKAWAY, L. I. (Queens County Water Company.) Designed by Charles -R. Bettes, Engineer in Charge; Charles B. Brush & Co., Chief Engineers; -and Allen Hazen, Consulting Engineer. Constructed in 1896. These -masonry filters were used for the removal of iron from well waters. -They are also designed to be suitable for the filtration of certain -brook waters which are available as auxiliary supplies, but the brook -water has been but rarely used. Description: Eng. Record, Vol. 40, p. -412. - -RED BANK, N. J. (Rumson Improvement Company.) Designed by Allen Hazen, -built in 1897. They are similar in construction to the Far Rockaway -filters, and are used for iron removal only. Description: Eng. Record, -Vol. 40, p. 412. - -HAMILTON, N. Y. Designed by the Stanwix Engineering Company, and were -built in 1895 to filter lake water. Description: Eng. News, Vol. 39, p. -254. - -LITTLE FALLS, N. Y. Designed by Stephen E. Babcock. These filters are -open, and were built in 1898, and are used for filtering river water. -Description: Eng. Record, Vol. 38, p. 7. - -SOMERSWORTH, N. H. Designed by William Wheeler. These were the second -vaulted filters to be built in the United States. The supply is from -the Salmon Falls River and flows to the filters by gravity, the filters -being below the river level. Description: Eng. News, Vol 40, p. 358; -Eng. Record, Vol. 38, p. 270. - -BERWYN, PENNA. Designed by J. W. Ledoux. These open filters are used -for filtering creek water. Description: Eng. News, Vol. 41, p. 150. - -HARRISBURG, PENNA. (State Lunatic Hospital.) Designed by Allen Hazen; -open masonry filters, used for treating the water from a small creek -which is often muddy and is subject to pollution. No published -description. - -ALBANY, N. Y. Designed by Allen Hazen. Constructed 1898-99. This -was the third and is the largest vaulted masonry filter plant yet -constructed in the United States. It is used for filtering the Hudson -River water, which is slightly muddy and much polluted by sewage. -Description: Eng. News, Vol. 39, p. 91; Vol. 40, p. 254. - -ROCK ISLAND, ILL. Designed by Jacob A. Harman. Open filters with -embankments, used for filtering the Mississippi River water, which is -very muddy and also polluted by sewage. No published description. - - * * * * * - -CAPACITY OF FILTERS. - -Estimating the total additional area of sand filters for which figures -are not available at 100 acres, and the maximum capacity of sand -filters at three million gallons per acre daily, and of mechanical -filters at three million gallons per thousand square feet of filtering -area, the total filtering capacity of all the filters in the world used -for public water supplies in 1899 is nearly 1600 million gallons daily, -of which 15 per cent is represented by mechanical filters and 85 per -cent by sand filters. In the United States, including Wilmington, the -total filtering capacity is nearly 300 million gallons daily, of which -18 per cent is represented by sand filters, 79 per cent by mechanical -filters, and 3 per cent by a special type of filters. - - - - -APPENDIX V. - -LONDON’S WATER-SUPPLY. - - -London alone among great capitals is supplied with water by private -companies. They are, however, under government supervision, and -the rates charged for water are regulated by law. There are eight -companies, each of which supplies its own separate district, so that -there is no competition whatever. One of the companies supplying -460,000 people uses only ground-water drawn from deep wells in the -chalk, but the other seven companies depend mainly upon the rivers -Thames and Lea for their water. All water so drawn is filtered, and -must be satisfactory to the water examiner, who is required to inspect -the water supplied by each company at frequent intervals, and the -results of the examinations are published each month. - -In 1893 the average daily supply was 235,000,000 gallons, of which -about 40,000,000 were drawn from the chalk, 125,000,000 from the -Thames, and 70,000,000 from the Lea. Formerly some of the water -companies drew water from the Thames within the city where it was -grossly polluted, and the plagues and cholera which formerly ravaged -London were in part due to this fact. These intakes were abandoned -many years ago, and all the companies now draw their water from points -outside of the city and its immediate suburbs. - -The area of the watershed of the Thames above the intakes of the water -companies is 3548 square miles, and the population living upon it in -1891 was 1,056,415. The Thames Conservancy Board has control of the -main river for its whole length, and of all tributaries within ten -miles in a straight line of the main river, but has no jurisdiction -over the more remote feeders. The area drained is essentially -agricultural, with but little manufacturing, and there are but few -large towns. In the area coming under the conservators there are but -six towns with populations above 10,000 and an aggregate population -of 170,000, and there are but two or three other large towns on the -remaining area more than ten miles from the river. These principal -towns are as follows: - - Town. Population 1891. Distance above - Water Intakes. - Reading 60,054 49 miles - Oxford 45,791 87 miles - New Swindon 27,295 116 miles - High Wycomb 13,435 33 miles - Windsor 12,327 18 miles - Maidenhead 10,607 25 miles - Guildford 14,319 20 miles - -Guildford is outside of the conservators’ area. All of the above towns -treat their sewage by irrigation. - -Among the places that are regarded as the most dangerous are Chertsey -and Staines, with populations of 9215 and 5060, only 8 and 11 miles -above the intakes respectively. These towns are only partially sewered -and still depend mainly on cesspools. An attempt is made to treat the -little sewage which they produce upon land, but the work has not as yet -been systematically carried out. There are also several small towns of -3000 inhabitants or less upon the upper river which do not treat their -sewage so far as they have any, but, owing to their great distance, -the danger from them is much less than from Chertsey and Staines. -Twenty-one of the principal towns upon the watershed have sewage farms, -and there are no chemical precipitation plants now in use. - -Boats upon the river are not allowed to drain into it, but are -compelled to provide receptacles for their sewage, and facilities -are provided for removing and disposing of it; and as an additional -precaution no boat is allowed to anchor within five miles of the -intakes. - -The conservators of the river Lea have control of its entire drainage -area, which is about 460 square miles, measured from the East London -water intakes, and has a population of 189,287. On this watershed there -is but a single town with more than 10,000 inhabitants, this being -Lutton near the headwaters of the river, with a population of 30,005. -The sewage from Lutton and from seventeen smaller places is treated -upon land. No crude sewage is known to be ordinarily discharged into -the river. At Hereford, eleven miles above the East London intakes, -there is a chemical precipitation plant. The conservators do not -regard this treatment as satisfactory, and have recently conducted -an expensive lawsuit against the local authorities to compel them to -further treat their effluent. The suit was lost, the court holding that -no actual injury to health had been shown. It is especially interesting -to note that of the thirty-nine places on the Thames and the Lea giving -their sewage systematic treatment there is but a single place using -chemical precipitation, and there it is not considered satisfactory. -Formerly quite a number of these towns used other processes than land -treatment, but in every case but Hereford land treatment has been -substituted. - -In regard to the efficiency of the sewage farms, it is believed that -in ordinary weather the whole of the sewage percolates through the -land, and the inspectors of the Conservancy Boards strongly object to -its being allowed to pass over the surface into the streams. The land, -however, is for the most part impervious, as compared to Massachusetts -and German sewage farms, and in times of heavy storms the land often -has all the water it can take without receiving even the ordinary flow -of sewage, and much less the increased storm-flow. At such times the -sewage either does go over the surface, or perhaps more frequently -is discharged directly into the rivers without even a pretence of -treatment. The conservators apparently regard this as an unavoidable -evil and do not vigorously oppose it. It is the theory that, owing -to the increased dilution with the storm-flows, the matter is -comparatively harmless, although it would seem that the reduced time -required for it to reach the water-works intakes might largely offset -the effect of increased dilution. - -The water companies have large storage and sedimentation basins with -an aggregate capacity equal to nine days’ supply, but the proportion -varies widely with the different companies. It is desired that the -water held in reserve shall be alone used while the river is in flood, -as, owing to its increased pollution, it is regarded as far more -dangerous than the water at other times; but as no record is kept of -the times when raw sewage is discharged, and no exact information is -available in regard to the times when the companies do not take in -raw water, it can safely be assumed that a considerable amount of raw -sewage does become mixed with the water which is drawn by the companies. - -The water drawn from the river is filtered through 113 filters having -an area of 116 acres. None of the filters are covered, and with an -average January temperature of 39° but little trouble with ice is -experienced. A few new filters are provided with appliances for -regulating the rate on each filter separately and securing regular and -determined rates of filtration, but nearly all of the filters are of -the simple type described on page 48, and the rates of filtration are -subject to more or less violent fluctuation, the extent of which cannot -be determined. - -The area of filters is being continually increased to meet increasing -consumption; the approximate areas of filters in use having been as -follows: - - 1839 First filters built - 1855 37 acres - 1866 47 acres - 1876 77 acres - 1886 104 acres - 1894 116 acres - -There has been a tendency to reduce somewhat the rate of filtration. In -1868, with 51 acres of filters, the average daily quantity of water -filtered was 111,000,000 gallons, or 2,180,000 gallons per acre. In -1884, with 97 acres of filter surface, the daily quantity filtered was -157,000,000 gallons, or 1,620,000 gallons per acre; and in 1893, with -116 acres of filter surface and 195,000,000 gallons daily, the yield -per acre was 1,680,000 gallons. - -Owing to the area of filter surface out of use while being cleaned, -the variations in consumption of water, and the imperfections of the -regulating apparatus, the actual rates of filtration are often very -much higher and at times may easily be double the figures given. - -Evidence regarding the healthfulness of the filtered river-water was -collected and examined in a most exhaustive manner in 1893 by a Royal -Commission appointed to consider the water-supply of the metropolis in -all its aspects with reference to future needs. This commission was -unable to obtain any evidence whatever that the water as then supplied -was unhealthy or likely to become so, and they report that the rivers -can safely be depended upon for many years to come. - -The numbers of deaths from all causes and from typhoid fever annually -per million of inhabitants for the years 1885-1891 in the populations -receiving their waters from different sources in London were as follows: - - Water used. Deaths from Deaths from - All Causes. Typhoid Fever. - Filtered Thames water only 19,501 125 - Filtered Lea water only 21,334 167 - Kent wells only 18,001 123 - Thames and Lea jointly 18,945 138 - Thames and Kent jointly 18,577 133 - -The population supplied exclusively from the Lea by the East London -Company is of a poorer class than that of the rest of London, and this -may account for the slightly higher death-rate in this section. Aside -from this the rate is remarkably uniform and shows no great difference -between the section drinking ground-water only and those drinking -filtered river-waters. The death-rate from typhoid fever is also very -uniform and, although higher than that of some Continental cities with -excellent water-supplies (Berlin, Vienna, Munich, Dresden), is very -low—lower than in any American city of which I have records. - -In this connection, it was shown by the Registrar-General that there -is only a very small amount of typhoid fever on the watersheds of -the Thames and Lea, so that the danger of infection of the water as -distinct from pollution is less than would otherwise be the case. Thus -for the seven years above mentioned the numbers of deaths from typhoid -fever per million of population were only 105 and 120 on the watersheds -of the Thames and the Lea respectively, as against 176 for the whole of -England and Wales. - - -LONDON FILTERS, 1896. - -Twenty-sixth Annual Report of the Local Government Board, pages 206-213. - - --------------+-------+---------+-----------------+-------------------------- - |Amount |Average | Average Rate | Bacterial Efficiency. - | of |Thickness| of Filtration. | - |Storage| of +--------+--------+--------+--------+-------- - | Raw | Sand, |Imperial|Millions|Maximum.|Minimum.|Average. - Company. |Water, | Feet. |Gallons | U. S. | | | - | Days. | | per |Gallons | | | - | | | Square |per Acre| | | - | | |Foot per| Daily. | | | - | | | Hour. | | | | - --------------+-------+---------+--------+--------+--------+--------+-------- - Chelsea | 12.0 | 4.0 | 1.75 | 2.19 | 99.92 | 99.62 | 99.86 - West Middlesex| 5.6 | 2.75 | 1.25 | 1.56 | 99.94 | 91.48 | 99.79 - Southwark & | | | | | | | - Vauxhall | 4.1 | 2.5 | 1.5 | 1.88 | 100.00 | 84.33 | 97.77 - Grand Junction| 3.3 | 2.25 | 1.63 | 2.05 | 99.98 | 84.03 | 99.31 - Lambeth | 6.0 | 2.8 | 2.08 | 2.60 | 99.97 | 96.45 | 99.81 - New River | 2.2 | 4.4 | 1.89 | 2.37 | 100.00 | 77.14 | 99.07 - East London | 15.0 | 2.0 | 1.33 | 1.67 | 99.93 | 97.03 | 99.56 - --------------+-------+---------+--------+--------+--------+--------+-------- - - - - -APPENDIX VI. - -THE BERLIN WATER-WORKS. - - -The original works were built by an English company in 1856, and were -sold to the city in 1873 for $7,200,000. - -The water was taken from the river Spree at the Stralau Gate, which -was then above, but is now surrounded by, the growing city. The water -was always filtered, and the original filters remained in use until -1893, when they were supplanted by the new works at Lake Müggel. Soon -after acquiring the works the city introduced water from wells by Lake -Tegel as a supplementary supply, but much trouble was experienced from -crenothrix, an organism growing in ground-waters containing iron, and -in 1883 this supply was replaced by filtered water from Lake Tegel. -With rapidly-increasing pollution of the Spree at Stralau the purity -of this source was questioned, and in 1893 it was abandoned (although -still held as a reserve in case of urgent necessity), the supply now -being taken from the river ten miles higher up, at Müggel. - -The watershed of the Spree above Stralau, as I found by map -measurement, is about 3800 square miles; the average rainfall is about -25 inches yearly. At extreme low water the river discharges 457 cubic -feet per second, or 295 million gallons daily, and when in flood 5700 -cubic feet per second may be discharged. The city is allowed by law to -take 46 million gallons daily for water-supply, and this quantity can -be drawn either at Stralau or at Müggel. - -Above Stralau the river is polluted by numerous manufactories and -washing establishments, and by the effluent from a considerable part -of the city’s extensive sewage farms. The shipping on this part of the -river also is heavy, and sewage from the boats is discharged directly -into the river. The average number of bacteria in the Spree at this -point is something over ten thousand per cubic centimeter, and 99.6 per -cent of them were removed by the filters in 1893. - -The watershed of the Spree above the new water-works at Müggel I found -by map measurement to be 2800 square miles, and the low water-discharge -is said to be 269 million gallons daily. The river at this point flows -through Lake Müggel, which forms a natural sedimentation-basin, and the -raw water is quite clear except in windy weather. - -There were 16 towns on the watershed with populations above 2000 each -in 1890, and an aggregate population of 132,000, which does not include -the population of the smaller places or country districts. None of -these places purify their sewage so far as they have any. Fürstenwalde -with a population of 12,935, and 22 miles above Müggel, has surface -sewers discharging directly into the river. Above Fürstenwalde the -river runs through numerous lakes which probably remove the effect -of the pollution from the more distant cities. There is considerable -shipping on the river for some miles above Fürstenwalde (which forms a -section of the Friedrich Wilhelm Canal), but hardly any between Müggel -and Fürstenwalde. The raw water at Müggel contains two or three hundred -bacteria per cubic centimeter, and is thus a comparatively pure water -before filtration. It is slightly peaty and the filtered water has a -light straw color. - -Lake Tegel, which supplies the other part of the city’s supply, is an -enlargement of the river Havel. The watershed above Tegel I find to be -about 1350 square miles, and the annual rainfall is about 22 inches. -The low water-discharge is said to be 182 million gallons daily, and -the city is allowed by law to take 23 million gallons for water-supply. - -There were ten towns upon the watershed with populations above 2000 -each in 1890, and with an aggregate population of 44,000. Of these -Tegel is directly upon the lake with a population of 3000, and -Oranienburg, 14 miles above, has a population of 6000 and is rapidly -increasing. The shipping on the lake and river is heavy. The lake water -ordinarily contains two or three hundred bacteria per cubic centimeter. -The lake is shallow and becomes turbid in windy weather. - -There are 21 filter-beds at Tegel with a combined area of 12.40 acres -to furnish a maximum of 23 million gallons of water daily, and 22 -filters at Müggel with a combined area of 12.7 acres to deliver the -same quantity. Twenty-two more filters will be built at Müggel within -a few years to purify the full quantity which can be taken from the -river. All of these filters are covered with brick arches supported by -pillars about 16 feet apart from centre to centre in each direction, -and the whole is covered by nearly 3 feet of earth, making them quite -frost-proof. The original filters at Stralau were open, but much -difficulty was experienced with them in winter. - -The bottom of the filters at Tegel consists of 8 inches of concrete -above 20 inches of packed clay and with 2 inches of cement above, and -slopes slightly from each side to the centre. The central drain goes -the whole length of the filters and has a uniform cross-section of -about 1/7300 of the area of the whole bed. There are no lateral drains, -but the water is brought to the central drain by a twelve-inch layer -of stones as large as a man’s fist; above this there is another foot -of gravel of graded sizes supporting two feet of fine sand, which is -reduced by scraping to half its thickness before the sand is replaced. -The average depth of water above the sand is nearly 5 feet. The filters -are not allowed to filter at a rate above 2.57 million gallons per -acre daily, and at this rate with 70 per cent of the area in service -the whole legal quantity of water can be filtered. The filters work -at precisely the same rate day and night, and the filtered water -is continuously pumped as filtered to ample storage reservoirs at -Charlottenburg. The pumps which lift the water from the lake to the -filters work against a head of 14 feet. The apparatus for regulating -the rate of filtration was described on page 51. - -As yet no full description of the Müggel works has been published, but -they resemble closely the Tegel works. Both were designed by or under -the direction of the late director of the water-works, Mr. Henry Gill. - -The average daily quantity of water supplied for the fiscal year ending -March 31, 1893, was 29,000,000 gallons daily, which estimate allows -10 percent for the slip of the pumps. Of this quantity 9,650,000 was -furnished by Stralau and 19,350,000 by Tegel. The greatest consumption -in a single day was 43,300,000 gallons, or 26.6 gallons per head, -while the average quantity for the year was 18.4 gallons per head. All -water without exception is sold by meter, the prices ranging from 27.2 -cents a thousand gallons for small consumers to 13.6 cents for large -consumers and manufacturers. The average receipts for all water pumped, -including that used for public purposes and not paid for, were 15.4 -cents a thousand gallons, against the cost of production, 9.8 cents, -which covers operating expenses, interest on capital, and provision for -sinking fund. This leaves a handsome net profit to the city. On account -of the comparatively high price of the city water and the ease with -which well-water is obtained, the latter is almost exclusively used -for running engines, manufacturing purposes, etc., and this in part -explains the very low per-capita consumption. - -The volume of sewage, however, for the same year, including rain-water, -except during heavy showers, was only 29 gallons per head, showing even -with the private water-supplies an extraordinarily low consumption. - -The friction of the water in the 4.75 miles of 3-foot pipe between -Tegel and the reservoir at Charlottenburg presents an interesting -point. When well-water with crenothrix was pumped, the friction rose -to 34.5 feet, when the velocity was 2.46 feet per second. According to -Herr Anklamm, who had charge of the works at the time, the friction was -reduced to 19.7 feet when filtered water was used and after the pipe -had been flushed, and this has not increased with continued use. He -calculated the friction for the velocity according to Darcy 15.0 feet, -Lampe 17.8 feet, Weisbach 18.7 feet, and Prony 21.5 feet. - - - - -APPENDIX VII. - -ALTONA WATER-WORKS. - - -The Altona water-works are specially interesting as an example of -a water drawn from a source polluted to a most unusual extent: the -sewage from cities with a population of 770,000, including its own, is -discharged into the river Elbe within ten miles above the intake and -upon the same side. - -The area of the watershed of the Elbe above Altona is about 52,000 -square miles, and the average rainfall is estimated to be about -28 inches, varying from 24 or less near its mouth to much higher -quantities in the mountains far to the south. On this watershed there -are 46 cities, which in 1890 had populations of over 20,000 each, -and in addition there is a permanent population upon the river-boats -estimated at 20,000, making in all 5,894,000 inhabitants, without -including either country districts or the numberless cities with less -than 20,000 inhabitants each. The sewage from about 1,700,000 of these -people is purified before being discharged; and assuming that as many -people living in cities smaller than 20,000 are connected with sewers -as live in larger places without being so connected, the sewage of -over four million people is discharged untreated into the Elbe and its -tributaries. - -The more important of these sources of pollution are the following: - - City Population On what Approximate - in 1890. River. Distance, Miles. - Shipping 20,000 - Altona 143,353 Elbe 6 - Hamburg 570,534 Elbe 7 - Wandsbeck 20,586 Elbe 8 - Harburg 35,101 Elbe 11 - Magdeburg 202,325 Elbe 185 - Dresden 276,085 Elbe 354 - Berlin and suburbs 1,787,859 Havel 243 - Halle 101,401 Saale 272 - Leipzig 355,485 Elster 305 - Chemnitz 138,955 Mulde 340 - Prague 310,483 Moldau 500 - -The sewage of Berlin and of most of its suburbs is treated before being -discharged, and in addition the Havel flows through a series of lakes -below the city, allowing better opportunities for natural purification -than in the case of any of the other cities. Halle treats less than a -tenth of its sewage. Magdeburg will treat its sewage in the course of -a few years. Leipzig, Chemnitz, and other places are thinking more or -less seriously of purification. - -The number of bacteria in the raw water at Altona fluctuates with the -tide and is extremely variable; numbers of 50,000 and 100,000 are not -infrequent, but 10,000 to 40,000 is perhaps about the usual range. - -The works were originally built by an English company in 1860, and have -since been greatly extended. They were bought by the city some years -ago. The water is pumped directly from the river to a settling-basin -upon a hill 280 feet above the river. From this it flows by gravity -through the filters to the slightly lower pure-water reservoir and -to the city without further pumping. The filters are open, with -nearly vertical masonry walls, as described in Kirkwood’s report. The -cross-section of the main underdrain is 1/2800 of the area of the beds. - -Considerable trouble has been experienced from frost. With continued -cold weather it is extremely difficult to satisfactorily scrape the -filters, and very irregular rates of filtration may result at such -times. In the last few years, with systematic bacterial investigation, -it has been found that greatly decreased efficiency frequently follows -continued cold weather, and the mild epidemics of typhoid fever -from which the city has long suffered have generally occurred after -these times. Thus a light epidemic of typhoid in 1886 came in March, -following a light epidemic in Hamburg. In 1887 a severe epidemic in -February followed a severe epidemic in Hamburg in December and January. -In 1888 a severe epidemic in March followed an epidemic in Hamburg -lasting from November to January. Hamburg’s epidemic of 1889, coming in -warm weather, September and October, was followed by only a very slight -increase in Altona. In 1891 Altona suffered again in February from a -severe epidemic, although very little typhoid had been in Hamburg. A -less severe outbreak also came in February, 1892, and a still slighter -one in February, 1893. In the ten years 1882-1892, of five well-marked -epidemics, three broke out in February and two in March, while two -smaller outbreaks came in December and January. No important outbreak -has ever occurred in summer or in the fall months, when typhoid -is usually most prevalent, thus showing clearly the bad effect of -frost upon open filters (see Appendix II). With steadily increasing -consumption the sedimentation-basin capacity of late years has become -insufficient as well as the filtering area, and it is not unlikely that -with better conditions a much better result could be obtained in winter -even with open filters.[63] - -The brilliant achievement of the Altona filters was in the summer of -1892, when they protected the city from the cholera which - -so ravaged Hamburg, although the raw water at Altona must have -contained a vastly greater quantity of infectious matter than that -which worked such havoc in Hamburg. - -From these records it appears that for about nine months of the year -the Altona filters protect the city from the impurities of the Elbe -water, but that during cold weather, with continued mean temperatures -below the freezing-point, such protection is not completely afforded, -and bad effects have occasionally resulted. Notwithstanding the recent -construction of open filters in Hamburg it appears to me that there -must always be more or less danger from open filters in such a climate. -Hamburg’s danger, however, will be much less than Altona’s on account -of its better intake above the outlets of the sewers of Hamburg and -Altona, which are the most important points of pollution at Altona. - - - - -APPENDIX VIII. - -HAMBURG WATER-WORKS. - - -The source and quality of the water previously supplied has been -sufficiently indicated in Appendix II. It was originally intended to -filter the water, but the construction of filters was postponed from -time to time until the fall of 1890, when the project was seriously -taken up, and work was commenced in the spring of 1891. Three years -were allowed for construction. In 1892, however, the epidemic of -cholera came, killing 8605 residents and doing incalculable damage to -the business interests of the city. The health authorities found that -the principal cause of this epidemic was the polluted water-supply. -To prevent a possible recurrence of cholera in 1893, the work of -construction of the filters was pressed forward much more rapidly than -had been intended. Electric lights were provided to allow the work to -proceed nights as well as days, and as a result the plant was put in -operation May 27, 1893, a full year before the intended time. Owing to -the forced construction the cost was materially increased. - -The new works take the raw water from a point one and a half miles -farther up-stream, where it is believed the tide can never carry the -city’s own sewage, as it did frequently to the old intake. The water -is pumped from the river to settling-basins against heads varying with -tide and the water-level in the basins from 8 to 22 feet. Each of the -four settling-basins has an area of about 10 acres, and, with the water -6.56 feet deep, holds 20,500,000 gallons, or 82,000,000 gallons in -all. The works are intended to supply a maximum of 48,000,000 gallons -daily, but the present average consumption is only about 35,000,000 -gallons (1892), or 59 gallons per head for 600,000 population. -This consumption is regarded as excessive, and it is hoped that it -will be reduced materially by the more general use of meters. The -sedimentation-basins are surrounded by earthen embankments with slopes -of 1:3, the inner sides being paved with brick above a clay layer. The -water flows by gravity from these basins to the filters, a distance -of 1-1/2 miles, through a conduit 8-1/2 feet in diameter. The flow of -the water out of the basins and from the lower end of the conduit is -regulated by automatic gates connected with floats, shown by Fig. 11, -page 60. - -The filters are 18 in number, and each has an effective area of 1.89, -or 34 acres in all. They are planned to filter at a rate of 1.60 -million gallons per acre daily, which with 16 filters in use gives a -daily quantity of 48,000,000 gallons as the present limit of the works. -The sides of the filters are embankments with 1:2 slopes. Both sides -and bottoms have 20 inches of packed clay, above which are 4 inches of -puddle, supporting a brick pavement laid in cement. The bricks are laid -flat on the bottom, but edge-wise on the sides where they will come in -contact with ice. - -The main effluent-drain has a cross-section for the whole length of -the filter of 4.73 square feet, or 1/17000 of the area of the filter; -and even at the low rate of filtration proposed, the velocity in the -drain will reach 0.97 foot. The drain has brick sides, 1.80 feet -high, covered with granite slabs. The lateral drains are all of brick -with numerous large openings for admission of water. They are not -ventilated, and I am unable to learn that any bad results follow this -omission. - -The filling of the filters consists of 2 feet of gravel, the top being -of course finer than the bottom layers, above which are 40 inches of -sand, which are to be reduced to 24 inches by scraping before being -refilled. The water over the sand, when the latter is of full depth, -is 43 inches deep, and will be increased to 59 inches with the minimum -sand-thickness. The apparatus for regulating the rate of filtration was -described page 52. The cost of the entire plant, including 34 acres -effective filter-surface, 40 acres of sedimentation-basins, over 2 -miles of 8-1/2-foot conduit, pumping-machinery, sand-washing apparatus, -laboratory, etc., was about 9,500,000 marks, or $2,280,000. This all -reckoned on the effective filter area is $67,000 per acre, or $3.80 per -head for a population of 600,000. - -The death-rate since the introduction of filtered water has been lower -than ever before in the history of the city, but as it is thought that -other conditions may help to this result, no conclusions are as yet -drawn. - - -DEATHS IN HAMBURG FROM ALL CAUSES, AND FROM TYPHOID FEVER, BEFORE AND -AFTER THE INTRODUCTION OF FILTERS. - - --------------------+-----------+-----------+-------------- - |Deaths from|Deaths from| - |all Causes | Typhoid | - Year. | per 1000 | Fever per | - | Living. | 100,000 | - | | Living. | - --------------------+-----------+-----------+-------------- - 1880 | 24.9 | 26 | - 1881 | 24.1 | 30 | - 1882 | 23.7 | 27 | - 1883 | 25.2 | 25 | - 1884 | 25.1 | 26 | - 1885 | 25.3 | 42 | - 1886 | 29.0 | 71 | - 1887 | 26.6 | 88 | - 1888 | 24.5 | 54 | - 1889 | 23.5 | 43 | - 1890 | 22.0 | 27 | - 1891 | 23.4 | 24 | - 1892 | 41.1 | 34 |Cholera year. - 1893 | 20.2 | 18 |Filtered water - | | | from May 28. - 1894 | 17.9 | 7 | - 1895 | 19.0 | 11 | - 1896 | 17.3 | 6 | - 1897 | 17.0 | 7 | - 1898 | 17.5 | 5 | - Average for 5 years,| | | - excluding cholera | | | - year, before | | | - filtration, | | | - 1887 to 1891 | 24.0 | 47.2 | - Average for 5 years | | | - with filtration, | | | - 1894 to 1898 | 17.7 | 7.2 | - --------------------+-----------+-----------+-------------- - - - - -APPENDIX IX. - -NOTES ON SOME OTHER EUROPEAN WATER-SUPPLIES. - - -=Amsterdam.=—The water is derived from open canals in the dunes. These -canals have an aggregate length of about 15 miles, and drain about 6200 -acres. The water, as it enters the canals from the fine dune-sand, -contains iron, but this is oxidized and deposited in the canals. The -water after collection is filtered. It has been suggested that by using -covered drains instead of open canals for collecting the water, the -filtration would be unnecessary; but, on the other hand, the cost of -building and maintaining covered drains in the very fine sand would be -much greater than that of the canals, and it is believed, also, that -the water so collected would contain iron, the removal of which might -prove as expensive as the present filtration. In 1887 filters were -built to take water from the river Vecht, but the city has refused to -allow the English company which owns the water-works to sell this water -for domestic purposes, and it is only used for public and manufacturing -purposes, only a fraction of the available supply being required. -Leyden, the Hague, and some other Dutch cities have supplies like the -dune supply of Amsterdam, and they are invariably filtered. - -=Antwerp= is also supplied by an English company. The raw water is -drawn from a small tidal river, which at times is polluted by the -sewage of Brussels. It is treated by metallic iron in Anderson revolver -purifiers, and is afterward filtered at a rather low average rate. The -hygienic results are closely watched by the city authorities, and are -said to be satisfactory. - -=Rotterdam.=—The raw water is drawn from the Maas, as the Dutch -call the main stream of the Rhine after it crosses their border. The -population upon the river and its tributaries in Switzerland, Germany, -Holland, France, and Belgium is very great; but the flow is also great, -and the low water flow is exceptionally large in proportion to the -average flow, on account of the melting snow in summer in Switzerland, -where it has its origin. - -The original filters had wooden under-drains, and there was constant -trouble with crenothrix until the filters were reconstructed without -wood, since which time there has been no farther trouble. The present -filters are large and well managed. There is ample preliminary -sedimentation. - -=Schiedam.=—The filters at Schiedam are comparatively small, but are -of unusual interest on account of the way in which they are operated. -The intake is from the Maas just below Rotterdam. The city was unable -to raise the money to seek a more distant source of supply, and the -engineer, H. P. N. Halbertsma, was unwilling to recommend a supply -from so doubtful a source without more thorough treatment than simple -sand-filtration was then thought to be. The plan adopted is to filter -the supply after preliminary sedimentation through two filters of 0.265 -acre each, and the resulting effluent is then passed through three -other filters of the same size. River sand is used for the first, and -the very fine dune sand for the second filtration. The cost both of -construction and operation was satisfactory to the city, and much below -that of any other available source; and the hygienic results have been -equally satisfactory, notwithstanding the unfavorable position of the -intake. - -=Magdeburg.=—The supply is drawn from the Elbe, and is filtered through -vaulted filters after preliminary sedimentation. The pollution of -the river is considerable, although less than at Altona or even at -Hamburg. The city has been troubled at times by enormous discharges of -salt solution from salt-works farther up, which at extreme low water -have sometimes rendered the whole river brackish and unpleasant to the -taste; but arrangements have now been made which, it is hoped, will -prevent the recurrence of this trouble. - -=Breslau= is supplied with filtered water from the river Oder, -which has a watershed of 8200 square miles above the intake, and is -polluted by the sewage from cities with an aggregate population of -about 200,000, some of which are in Galicia, where cholera is often -prevalent. In recent years the city has been free from cholera, and -from more than a very limited number of typhoid-fever cases; but the -pollution is so great as to cause some anxiety, notwithstanding the -favorable record of the filters, and there is talk of the desirability -of securing another supply. Until 1893 there were four filter-beds, -with areas of 1.03 acres each, and not covered. In 1893 a fifth bed was -added. This is covered by vaulting and is divided into four sections, -which are separately operated, so that it is really four beds of 0.25 -acre each. The vaulting is concrete arches, supported by steel I beams -in one direction. - -=Budapest.=—A great variety of temporary water-supplies have at -different times been used by this rapidly growing city. The filters -which for some years have supplied a portion of the supply have not -been altogether satisfactory; but perhaps this was due to lack of -preliminary sedimentation for the extremely turbid Danube water, and -also to inadequate filter-area. The city is rapidly building and -extending works for a supply of ground-water, and in 1894 the filters -were only used as was necessary to supplement this supply, and it was -hoped that enough well-water would be obtained to allow the filters to -be abandoned in the near future. The Danube above the intake receives -the sewage of Vienna and innumerable smaller cities, but the volume of -the river is very great compared to other European streams, so that the -relative pollution is not so great as in many other places. - -=Zürich.=—The raw water is drawn by the city from the Lake of Zürich -near its outlet, and but a few hundred feet from the heart of the city. -Although no public sewers discharge into the lake, there is some -pollution from boats and bathers and other sources, and, judging by -the number of bacteria in the raw water, this pollution is increasing. -The raw water is extremely free from sediment, and the filters only -become clogged very slowly. The rate of filtration is high, habitually -reaching 7,000,000 gallons per acre daily; but, with the clear lake -water and long periods between scrapings, the results are excellent -even at this rate. The filters are all covered with concrete groined -arches. - -Filtration was commenced in 1886, and was followed by a sharp decline -in the amount of typhoid fever, which, up to that time, had been rather -increasing; for the six years before the change there were sixty-nine -deaths from this cause annually per 100,000 living, and for the six -years after only ten, or one seventh as many; and this reduction is -attributed by the local authorities to the filtration.[64] - -=St. Petersburg.=—The supply is drawn from the Neva River by an English -company, and is filtered through vaulted filters at a very high rate. - -=Warsaw.=—The supply is drawn from the Weichsel River by the city, and -is filtered through vaulted filters after preliminary sedimentation at -a rate never exceeding 2,570,000 gallons per acre daily. - - -THE USE OF UNFILTERED SURFACE-WATERS. - -The use of surface-water without filtration in Europe is comparatively -limited. In Germany this use is now prohibited by the Imperial Board -of Health. In Great Britain, Glasgow draws its supply unfiltered from -Loch Katrine; and Manchester and some other towns use unfiltered -waters from lakes or impounding reservoirs the watersheds of which are -entirely free from population. The best English practice, however, as -in Germany, requires the filtration of such waters even if they are not -known to receive sewage, and the - -unpolluted supplies of Liverpool, Bradford, Dublin, and many other -cities are filtered before use. - - -THE USE OF GROUND-WATER.[65] - -Ground-waters are extensively used in Europe, and apparently in -some localities the geological formations are unusually favorable -to this kind of supply. Paris derives all the water it now uses for -domestic purposes from springs, but has a supplementary supply from -the river for other purposes. Vienna and Munich also obtain their -entire supplies from springs, while Budapest, Cologne, Leipzig, -Dresden, Frankfurt, many of the great French cities, Brussels, a part -of London, and many other English cities derive their supplies from -wells or filter-galleries, and among the smaller cities all over Europe -ground-water supplies are more numerous than other kinds. - - - - -APPENDIX X. - -LITERATURE OF FILTRATION. - - -The following is a list of a number of articles on filtration. The -list is not complete, but it is believed that it contains the greater -part of articles upon slow sand-filtration, and that it will prove -serviceable to those who wish to study the subject more in detail. - - ANKLAMM. Glasers Annalen, 1886, p. 48. - - A description of the Tegel filters at Berlin, with excellent plans. - -BAKER. Engineering News. - - Water purification in America: a series of descriptions of filters, as - follows: Aug. 3, 1893, Lawrence filter and description of apparatus of - screening sand and gravel; Apr. 26, 1894, filter at Nantucket, Mass.; - June 7, 1894, filters at Ilion, N. Y., plans; June 14, 1894, filters - at Hudson, N. Y.; July 12, 1894, filters at Zürich, Switzerland, - plans; Aug. 23, 1894, filters at Mt. Vernon, N. Y., plans. - -BERTSCHINGER. Journal für Gas- und Wasserversorgung, 1889, p. 1126. - - A record of experiments made at Zürich upon the effect of rate of - filtration, scraping, and the influence of vaulting. Rate and vaulting - were found to be without effect, but poorer results followed scraping. - The numbers of bacteria in the lake-water were too low to allow - conclusive results. - -—— Journal für Gas- und Wasserversorgung, 1891, p. 684. - - A farther account of the Zürich results, with full analyses and a - criticism of Fränkel and Piefke’s experiments. - -BOLTON. Pamphlet, 1884. - - Descriptions and statistics of London filters. - -BÖTTCHER and OHNESORGE. Zeitschrift für Bauwesen, 1876, p. 343. - - A description of the Bremen works, with full plans. - -BURTON. Water-supply of Towns. London, 1894. - - Pages 94-115 are upon filtration and mention a novel method of - regulating the rate. - -CODD. Engineering News, Apr. 26, 1894. - - A description of a filter at Nantucket, Mass. - -CRAMER. Centralblatt für Bauwesen, 1886, p. 42. - - A description of filters built at Brieg, Germany. - -CROOK. London Water-supply. London, 1883. - -DELBRUCK. Allgemeine Bauzeitung, 1853, p. 103. - - A general article on filtration; particularly valuable for notices of - early attempts at filtration and of the use of alum. - -Deutsche Verein von Gas- und Wasserfachmänner. - - Stenographic reports of the proceedings of this society are printed - regularly in the _Journal für Gas- und Wasserversorgung_, and the - discussions of papers are often most interesting. - -DROWN. Journal Association Eng. Societies, 1890, p. 356. - - Filtration of natural waters. - -FISCHER. Vierteljahresschrift für Gesundheitspflege, 1891, p. 82. - - Discussion of papers on water-filtration. - -FRÄNKEL. Vierteljahresschrift für Gesundheitspflege, 1891, p. 38. - - On filters for city water-works. - -FRÄNKEL and PIEFKE. Zeitschrift für Hygiene, 1891, p. 38, Leistungen -der Sandfiltern. - -E. FRANKLAND. Report in regard to the London filters for 1893 -in the Annual Summary of Births, Deaths, and Causes of Death in -London and Other Great Towns, 1893. Published by authority of the -Registrar-General. - -P. FRANKLAND. Proc. Royal Society, 1885, p. 379. - - The removal of micro-organisms from water. - -—— Proceedings Inst. Civil Engineers, 1886, lxxxv. p. 197. - - Water-purification; its biological and chemical basis. - -—— Trans. of Sanitary Institute of Great Britain, 1886. - - Filtration of water for town supply. - -FRÜHLING. Handbuch der Ingenieurwissenschaften, vol. ii. - - Chapter on water-filtration gives general account of filtration, with - details of Königsberg filters built by the author and not elsewhere - published. - - FULLER. Report Mass. State Board of Health, 1892, p. 449. - Report Mass. State Board of Health, 1893, p. 453. - - Accounts of the Lawrence experiments upon water-filtration for 1892 - and 1893. - -—— American Public Health Association, 1893, p. 152. - - On the removal of pathogenic bacteria from water by sand filtration. - -—— American Public Health Association, 1894, p. 64. - - Sand filtration of water with special reference to results obtained at - Lawrence, Mass. - -GILL. Deutsche Bauzeitung, 1881, p. 567. - - On American rapid filters. The author shows that they are not to be - thought of for Berlin, as they would be more expensive as well as - probably less efficient than the usual procedure. - -—— Journal für Gas- und Wasserversorgung, 1892, p. 596. - - A general account of the extension of the Berlin filters at Müggel. No - drawings. - -GRAHN. Journal für Gas- und Wasserversorgung, 1877, p. 543. - - On the filtration of river-waters. - -—— Journal für Gas- und Wasserversorgung, 1890, p. 511. - - Filters for city water-works. - -—— Vierteljahresschrift für Gesundsheitpflege, 1891, p. 76. - - Discussion of papers presented on filtration. - -—— Journal für Gas- und Wasserversorgung, 1894, p. 185. - - A history of the “Rules for Water-filtration” (Appendix I), with some - discussion of them. - -GRAHN and MEYER. Reiseberichte über künstliche central Sandfiltration. -Hamburg, 1876. - - An account of the observations of the authors in numerous cities, - especially in England. - -GRENZMER. Centralblatt der Bauverwaltung, 1888, p. 148. - - A description of new filters at Amsterdam, with plans. - -GRUBER. Centralblatt für Bakteriologie, 1893, p. 488. - - Salient points in judging of the work of sand-filters. - -HALBERTSMA. Journal für Gas- und Wasserversorgung, 1892, p. 43. - - Filter-works in Holland. Gives sand, gravel, and water thickness, with - diagrams. - -—— Journal für Gas- und Wasserversorgung, 1892, p. 686. - - Description of filters built by the author at Leeuwarden, Holland, - with plans. - -HART. Proceedings Inst. of Civil Engineers, 1890, c. p. 217. - - Description of filters at Shanghai. - -HAUSEN. Journal für Gas- und Wasserversorgung, 1892, p. 332. - - An account of experiments made for one year with three 16-inch filters - at Helsingfors, Finland, with weekly analyses of effluents. - -HAZEN. Report of Mass. State Board of Health, 1891, p. 601. - - Experiments upon the filtration of water. - -—— Report of Mass. State Board of Health, 1892, p. 539. - - Physical properties of sands and gravels with reference to their use - in filtration. (Appendix III.) - -HUNTER. Engineering, 1892, vol. 53, p. 621. - - Description of author’s sand-washing apparatus. - -KIRKWOOD. Filtration of River-waters. New York, 1869. - - A report upon European filters for the St. Louis Water Board in 1866. - Contains a full account of thirteen filtration-works visited by the - author, and of a number of filter-galleries, with a project for - filters for St. Louis. This project was never executed, but the report - is a wonderful work which appeared a generation before the American - public was able to appreciate it. It was translated into German, and - the German edition was widely circulated and known. - -KOCH. Zeitschrift für Hygiene, 1893. - - Water-filtration and Cholera: a discussion of the Hamburg epidemic of - 1892 in reference to the effect of filtration. - -KRÖHNKE. Journal für Gas- und Wasserversorgung, 1893, p. 513. - - An account of experiments made at Hamburg, as a result of which the - author recommends the addition of cuprous chloride to the water before - filtration to secure greater bacterial efficiency. - -KÜMMEL. Journal für Gas- und Wasserversorgung, 1877, p. 452. - - Operation of the Altona filters, with analyses. - -—— Vierteljahresschrift für Gesundheitspflege, 1881, p. 92. - - The water-works of the city of Altona. - -—— Journal für Gas- und Wasserversorgung, 1887, p. 522. - - An article opposing the use of rapid filters (David’s process). - -—— Journal für Gas- und Wasserversorgung, 1890, p. 531. - - A criticism of Fränkel and Piefke’s results, with some statistics of - German and English filters. (The English results are taken without - credit from Kirkwood.) - -—— Vierteljahresschrift für Gesundheitspflege, 1891, p. 87. - - Discussion of papers on filtration, with some statistics. - -—— Vierteljahresschrift für Gesundheitspflege, 1892, p. 385. - - The epidemic of typhoid-fever in Altona in 1891. - -—— Journal für Gas- und Wasserversorgung, 1893, p. 161. - - Results of experiments upon filtration made at Altona, and bacterial - results of the Altona filters in connection with typhoid death-rates. - -—— Trans. Am. Society of Civil Engineers, 1893, xxx. p. 330. - - Questions of water-filtration. - -LESLIE. Trans. Inst. Civil Engineers, 1883, lxxiv. p. 110. - - A short description of filters at Edinburgh. - -LINDLEY. A report for the commissioners of the Paris Exposition of -1889 upon the purification of river-waters, and published in French -or German in a number of journals, among them _Journal für Gas- und -Wasserversorgung_, 1890, p. 501. - - This is a most satisfactory discussion of the conditions which modern - experience has shown to be essential to successful filtration. - -MASON. Engineering News, Dec. 7, 1893. - - Filters at Stuttgart, Germany, with plans. - -MEYER and SAMUELSON. Deutsche Bauzeitung, 1881, p. 340. - - Project for filters for Hamburg, with diagrams. Except in detail, this - project is the same as that executed twelve years later. - -MEYER. Deutsche Bauzeitung, 1892, p. 519. - - Description of the proposed Hamburg filters, with diagrams. - -—— The Water-works of Hamburg. - - A paper presented to the International Health Congress at Rome, March - 1894, and published as a monograph. It contains a full description of - the filters as built, with drawings and views in greater detail than - the preceding paper. - -MILLS. Special Report Mass. State Board of Health on the Purification -of Sewage and Water, 1890, p. 601. - - An account of the Lawrence experiments, 1888-1890. - -—— Report Mass. State Board of Health, 1893, p. 543. - - The Filter of the Water-supply of the City of Lawrence and its Results. - -—— Trans. Am. Society of Civil Engineers, 1893, xxx. p. 350. - - Purification of Sewage and Water by Filtration. - -NEVILLE. Engineering, 1878, xxvi. p. 324. - - A description of the Dublin filters, with plans. - -NICHOLS. Report Mass. State Board of Health, 1878, p. 137. - - The filtration of potable water. - -OESTER. Gesundheits-Ingenieur, 1893, p. 505. - - What is the Rate of Filtration? A purely theoretical discussion. - -ORANGE. Trans. Inst. Civil Engineers, 1890, c. p. 268. - - Filters at Hong Kong. - -PFEFFER. Deutsche Bauzeitung, 1880, p. 399. - - A description of filters at Liegnitz, Germany. - -PIEFKE. Results of Natural and Artificial Filtration. Berlin, 1881. - - Pamphlet. - -—— Journal für Gas- und Wasserversorgung, 1887, p. 595. Die Principien -der Reinwassergewinnung vermittelst Filtration. - - A sketch of the theory and practical application of filtration. - -—— Zeitschrift für Hygiene, 1889, p. 128. Aphorismen über -Wasserversorgung. - - A discussion of the theory of filtration, with a number of experiments - on the thickness of sand-layers, etc. - -PIEFKE. Vierteljahresschrift für Gesundheitspflege, 1891, p. 59. - - On filters for city water-works. - -FRÄNKEL and PIEFKE. Zeitschrift für Hygiene, 1891, p. 38. - - Leistungen der Sandfiltern. An account of the partial obstruction of - the Stralau filters by ice, and a typhoid epidemic which followed. - Experiments were then made upon the passage of cholera and typhoid - germs through small filters. - -PIEFKE. Journal für Gas- und Wasserversorgung, 1891, p. 208. Neue -Ermittelungen über Sandfiltration. - - The above mentioned experiments being objected to on certain - grounds, they were repeated by Piefke alone, confirming the previous - observations on the passage of bacteria through filters, but under - other conditions. - -—— Zeitschrift für Hygiene, 1894, p. 151, Über Betriebsführung von -Sandfiltern. - - A full account of the operation of the Stralau filters in 1893, with - discussion of the efficiency of filtration, etc. - -PLAGGE AND PROSKAUER. Zeitschrift für Hygiene, 11. p. 403. - - Examination of water before and after filtration at Berlin, with - theory of filtration. - -REINCKE. Bericht über die Medicinische Statistik des Hamburgischen -Staates für 1892. - - Contains a most valuable discussion of the relations of filtration to - cholera, typhoid fever, and diarrhœa, with numerous tables and charts. - (Abstract in Appendix II.) - -REINSCH. Centralblatt für Bakteriologie, 1895, p. 881. - - An account of the operation of the Altona filters. High numbers of - bacteria in the effluents have often resulted from the discharge of - sludge from the sedimentation-basins onto the filters, due to the - interference of ice on the action of the floating outlet for the - basins, and this, rather than the direct effect of cold, is believed - to be the direct cause of the low winter efficiency. The author urges - the necessity of a deeper sand-layers in no case less than 18 inches - thick. - -RENK. Gesundheits-Ingenieur, 1886, p. 54. - -—— Über die Ziele der künstliche Wasserfiltration. - -RUHLMANN. Wochenblatt für Baukunde, 1887, p. 409. - - A description of filters at Zürich. - -SALBACH. Glaser’s Annalen, 1882. - - Filters at Groningen, Holland, built in 1880. Alum used. - -SAMUELSON. Translation of Kirkwood’s “Filtration of River-waters” into -German, with additional notes especially on the theory of filtration -and the sand to be employed. Hamburg, 1876. - -SAMUELSON. Filtration and constant water-supply. Pamphlet. Hamburg, -1882. - -—— Journal f. Gas- und Wasserversorgung, 1892, p. 660. - - A discussion of the best materials and arrangement for sand-filters. - -SCHMETZEN. Deutsche Bauzeitung, 1878, p. 314. - - Notice and extended criticism of Samuelson’s translation of Kirkwood. - -SEDDEN. Jour. Asso. Eng. Soc., 1889, p. 477. - - In regard to the sedimentation of river-waters. - -SEDGWICK. New England Water-works Association, 1892, p. 103. - - European methods of Filtration with Reference to American Needs. - -SOKAL. Wochenschrift der östreichen Ingenieur-Verein, 1890, p. 386. - - A short description of the filters at St. Petersburg, and a comparison - with those at Warsaw. - -STURMHÖFEL. Zeitschrift f. Bauwesen, 1880, p. 34. - - A description of the Magdeburg filters, with plans. - -TOMLINSON. American Water-works Association, 1888. - - A paper on filters at Bombay and elsewhere. - -TURNER. Proc. Inst. Civil Engineers, 1890, c. p. 285. - - Filters at Yokohama. - -VAN DER TAK. Tijdschrift van de Maatschapping van Bouwkunde, 1875(?). - - A description (in Dutch) of the Rotterdam water-works, including the - wooden drains which caused the trouble with crenothrix, and which have - since been removed. Diagrams. - -VAN IJSSELSTEYN. Tijdschrift van het Koninklijk Instituut van -Ingenieurs, 1892-5, p. 173. - - A description of the new Rotterdam filters, with full drawings. - -VEITMEYER. Verhandlungen d. polyt. Gesell. zu Berlin, April, 1880. - - Filtration and purification of water. - -WOLFFHÜGEL. Arbeiten aus dem Kaiserliche Gesundheitsamt, 1886, p. 1. - - Examinations of Berlin water for 1884-5, with remarks showing superior - bacterial efficiency with open filters. - -—— Journal für Gas- u. Wasserversorgung, 1890, p. 516. - - On the bacterial efficiency of the Berlin filters, with diagrams. - -ZOBEL. Zeitschrift des Vereins deutsche Ingenieure, 1884, p. 537. - - Description of filters at Stuttgart. - - -OTHER LITERATURE. - -Many scientific and engineering journals publish from time to time -short articles or notices on filtration which are not included in the -above list. Among such journals none gives more attention to filtration -than the _Journal für Gasbeleuchtung und Wasserversorgung_, which -publishes regularly reports upon the operation of many German filters, -and gives short notices of new construction. The first articles upon -filtration in this journal were a series of descriptions of German -water-works in 1870-73, including descriptions of filters at Altona, -Brunswick, Lübeck, etc. Stenographic reports of many scientific -meetings have been published, particularly since 1890, and since 1892 -there has been much discussion in regard to the “Rules for Filtration” -given in Appendix I. - -A Report of a Royal Commission to inquire into the water-supply of the -metropolis, with minutes of evidence, appendices, and maps (London, -1893-4), contains much valuable material in regard to filtration. - -The monthly reports of the water examiner, and other papers published -by the Local Government Board, London, are often of interest. - -The German “Verein von Gas- u. Wasserfachmänner” prints without -publishing a most useful annual summary of German water-works -statistics for distribution to members. Many of the statistics given in -this volume are from this source. - -Description of the filters at Worms was given in the _Deutsche -Bauzeitung_, 1892, p. 508; of the filters at Liverpool in -_Engineering_, 1889, p. 152, and 1892, p. 739. The latter journal also -has given a number of descriptions of filters built in various parts of -the world by English engineers, but, excepting the articles mentioned -in the above list, the descriptions are not given in detail. - - -MORE RECENT ARTICLES. - -The following are a few of the more important articles which have -appeared since the first edition of this book. In addition many -articles of current interest have appeared in the technical journals, -particularly in the journals mentioned above. - - CLARK. Reports of Mass. State Board of Health, 1894 to 1897, inclusive. - - Articles on the filtration of water, giving accounts of experiments at - the Lawrence Experiment Station, and records of the operation of the - Lawrence city filter. These experiments are directed principally to - the removal of bacteria from sewage-polluted waters. - -—— Jour. New England Water Works Assoc., XI., p. 277. - - Removal of Iron from Ground Waters. A description of certain - experiments. - -FOWLER. Jour. New England Water Works Assoc., XII., p. 209. - - The Operation of a Slow Sand Filter. A most helpful and thorough - description of the operation of sand filters at Poughkeepsie for a - long period of years. - -FULLER. Water Purification at Louisville. D. Van Nostrand Co., 1898. - - A report upon a series of most exhaustive experiments carried out at - Louisville, directed principally to the clarification of excessively - muddy waters. Contains a full account of methods of coagulation, and - of experiments with the electrical treatment of water. - -—— Report on Water Filtration at Cincinnati. City document, 1899. - - Account of experiments with sand filters, with and without coagulants, - and with other processes applied to the Ohio River water at Cincinnati. - -GILL. Filters at Muggel. Proc. Institute of Civil Engineers, 1894-5; -vol. 119, p. 236. - - A description of the new vaulted filter plant designed by the author - for Berlin, Germany. Plans and views. - -GOETZE. Journal für Gasbeleuchtung und Wasserversorgung, 1897, p. 169. - - Selbstthätige Wasseraustrittsregler besonders für Filter. A - description of the automatic regulating device for filters used at - Bremen. - -—— Zeitschrift des Vereines deutscher Ingenieure, XXX. - - Reinigung des Trinkwassers in Bremen durch mehrmalige Sandfiltration. - A description of the method of double filtration used at Bremen, - giving results obtained in full. No drawings. - -GRAHN. Journal für Gasbeleuchtung und Wasserversorgung, 1895. - - Water purification plant at the city of Magdeburg. A description of - the old plant, and the changes which have been made in it to increase - its capacity, and make it conform to the requirements of the German - official instructions regarding filtration. Many illustrations and - plans. - -HALBERTSMA. Journal für Gasbeleuchtung und Wasserversorgung, 1896. - - Die Resultate der doppelten Filtration zu Schiedam. A description of - double filtration at Schiedam, with the bacterial results for the two - years, 1894 and 1895, showing an average bacterial efficiency of 99.76 - per cent. - -HAZEN. Report to Filtration Commission, Pittsburgh. City document, 1899. - - A description of experiments upon the treatment of the Allegheny River - water by sand and mechanical filters. - -—— Ohio State Board of Health Report, 1897, p. 154. - - Report on the Mechanical Filtration of the Public Water Supply - of Lorain. Gives the results of a five-weeks test of the Jewell - mechanical filters at Lorain, treating Lake Erie water. - -KEMNA. The Biology of Sand Filtration. Read before the annual -convention of the British Association of Water Works Engineers. -Abstract in Engineering News, XLI., p. 419. - - Describing organisms which develop in open sand filters, both animal - and vegetable, and their effects upon the process. A quite full - account of the author’s extended experience, and the only paper - treating this subject. - -MAGAR. Journal für Gasbeleuchtung und Wasserversorgung, 1897, p. 4. - - Reinigungsbetrieb der offener Sandfilter des Hamburger Filterwerkes in - Frostzeiten. A new method of cleaning open filters in winter without - the removal of the ice. - -PANWITZ. Arbeiten aus dem Kaiserlichen Gesundheitsamte, XIV., p. 153. - - Die Filtration von Oberflächenwasser in den deutschen Wasserwerken - während der Jahre 1894 bis 1896. - - A description of the filtration works in Germany, and the results - obtained from them, particularly from the point of view of bacterial - efficiency. Results are graphically shown by a series of charts. - -REYNARD. Le Génie Civil, 1896, XXVIII., p. 321. - - Purification of water with the aid of metallic iron. Describing the - works of the Compagnie Général des Eaux for supplying the suburbs - of Paris with filtered water, the capacity of the works being over - 23,000,000 gallons daily. - -WESTON. Rhode Island State Board of Health, 1894. - - Report of the Results Obtained with Experimental Filters at the - Pattaconset Pumping Station of the Providence Water Works. Relates - particularly to the bacterial purification obtained with rapid - filtration aided by sulphate of alumina. These were the first - systematic experiments made with mechanical filters. - -WHEELER. Journal of the New England Water Works Assoc., XI., p. 301. -Covered Sand Filter at Ashland, Wis. - - A description of the covered filters built by the author at Ashland - Wis. for the purification of the bay water. Views and drawings. - - - - -APPENDIX XI. - -THE ALBANY WATER-FILTRATION PLANT. - -(Abridged from Proceedings American Society of Civil Engineers, Nov. -1899.) - - -Albany, N. Y., was originally supplied with water by gravity from -certain reservoirs on small streams west and north of the city. In -time, with increasing consumption, the supply obtained from these -sources became inadequate, and an additional supply from the Hudson -River was introduced. The water was obtained from the river through -a tunnel under the Erie Basin, and a pumping-station was erected in -Quackenbush Street to pump it to reservoirs, one of which served also -as the distributing point for one of the gravity supplies. The intake, -which was used first in 1873, drew water from the river opposite the -heart of the city. In recent years, the amount of water drawn from this -source has greatly exceeded that obtained from the gravity sources. - -The Hudson River, at the point of intake, has a drainage area of 8240 -square miles. Of this, 4541 square miles are tributary to the Hudson -above Troy, 3493 are tributary to the Mohawk, and 168 are tributary to -the Hudson below the Mohawk. - -The minimum flow may be estimated at 1657 cubic feet per second, or -1,060,000,000 gallons per 24 hours, or at least fifty times the maximum -consumption. - -The cities and larger towns upon the river above the intake, with -estimated populations and distances, are as follows: - - -MOST IMPORTANT CITIES, TOWNS, AND VILLAGES ON THE WATERSHED OF THE -HUDSON ABOVE ALBANY. - - ------------+-----------+-----------+----------------------------- - | |Approximate| Population in - Place. | County. | Distance +--------+-------+------------ - | | above | 1880. | 1890. | 1900. - | | Intake, | | | - | | Miles. | | |(Estimated.) - ------------+-----------+-----------+--------+-------+------------ - Troy |Rensselaer | 4 | 56,747 | 60,956| 65,470 - Watervliet |Albany | 4 | 8,820 | 12,967| 19,040 - Green Island|Rensselaer | 5 | 4,160 | 4,463| 4,788 - Cohoes |Albany | 8 | 19,416 | 22,509| 26,450 - Lansingburg |Rensselaer | 8 | 7,432 | 10,550| 14,980 - Waterford |Saratoga | 9 | (1,822)| 1,822| (1,822) - Schenectady |Schenectady| 28 | 13,655 | 19,002| 26,450 - Hoosic Falls|Rensselaer | 44 | 4,530 | 7,014| 10,860 - Amsterdam |Montgomery | 44 | 9,466 | 17,336| 31,730 - Glens Falls |Warren | 49 | 4,900 | 9,509| 18,450 - Saratoga |Saratoga | 51 | 8,421 | 11,975| 17,010 - Springs | | | | | - Johnstown |Fulton | 56 | 5,013 | 7,768| 12,040 - Gloversville|Fulton | 58 | 7,133 | 13,864| 26,930 - North Adams,| | | | | - Mass. |Berkshire | 68 | 10,191 | 16,074| 25,340 - Adams, Mass.|Berkshire | 75 | 5,591 | 9,213| 15,181 - Little Falls|Herkimer | 82 | 6,910 | 8,783| 11,160 - Utica |Oneida | 107 | 33,914 | 44,007| 57,090 - Rome |Oneida | 127 | 12,194 | 14,991| 18,430 - 32 villages | | | 52,523 | 61,869| 76,194 - ------------+-----------+-----------+--------+-------+------------ - Total, not including rural | | | - population |272,838 |354,672| 479,415 - Per square mile | 33 | 43| 59 - ------------------------------------+--------+-------+------------ - -Without entering into a detailed discussion, it may be said that the -amount of sewage, with reference to the size of the river and the -volume of flow, is a fraction less than that at Lawrence, Mass., -where a filter-plant has also been constructed, but the pollution is -much greater than that of most American rivers from which municipal -water-supplies are taken. - -The filtration-plant completed in 1899 takes the water from a point -about two miles above the old intake. Pumps lift the water to the -sedimentation-basin, from which it flows to the filters and thence -through a conduit to the pumping-station previously used. - - -DESCRIPTION OF PLANT. - -=Intake.=—The intake consists of a simple concrete structure in the -form of a box, having an open top covered with rails 6 inches apart, -and connected below, through a 36-inch pipe, with a well in the -pumping-station. Before going to the pumps the water passes through a -screen with bars 2 inches apart, so arranged as to be raked readily. -The rails over the intake and this screen are intended to stop matters -which might obstruct the passageways of the pumps, but no attempt is -made to stop fish, leaves, or other floating matters which may be -in the water. The arrangement, in this respect, is like that of the -filter at Lawrence, Mass., where the raw water is not subjected to -close screening. There is room, however, to place finer screens in the -pump-well, should they be found desirable. - -[Illustration: HUDSON RIVER - -NEAR INTAKE - -FIG. 1.] - -[Illustration: SEDIMENTATION-BASIN, PUMPING-STATION, AND OUTLETS.] - -[Illustration: SEDIMENTATION-BASIN, AN OUTLET, AND LABORATORY. - - [_To face page 290._] -] - -=Pumping-station.=—The centrifugal pumps have a guaranteed capacity -of 16,000,000 gallons per 24 hours against a lift of 18 feet, or -12,000,000 gallons per 24 hours against a lift of 24 feet. The ordinary -pumping at low water is against the higher lift, and under these -conditions either pump can supply the ordinary consumption, the other -pump being held in reserve. - -The pumping-station building, to a point above the highest flood-level, -is of massive concrete construction, without openings. Nearly all -the machinery is necessarily below this level, and in high water -the sluice-gates are closed, and the machinery is thus protected -from flooding. The superstructure is of pressed brick, with granite -trimmings. - -=Meter for Raw Water.=—Upon leaving the pumping-station the water -passes through a 36-inch Venturi meter having a throat diameter of 17 -inches, the throat area being two ninths of the area of the pipe. The -meter records the quantity of water pumped, and is also arranged to -show on gauges in the pumping-station the rate of pumping. - -=Aeration.=—After leaving the meter, the water passes to the -sedimentation-basin through eleven outlets. These outlets consist of -12-inch pipes on end, the tops of which are 4 feet above the nominal -flow-line of the sedimentation-basin. Each of these outlet-pipes is -pierced with 296 3/8-inch holes extending from 0.5 to 3.5 feet below -the top of the pipe. These holes are computed so that when 11,000,000 -gallons of water per day are pumped all the water will pass through the -holes, the water in the pipes standing flush with the tops. The water -is thus thrown out in 3256 small streams, and becomes aerated. When -more than the above amount is pumped, the excess flows over the tops of -the outlet-pipes in thin sheets, which are broken by the jets. - -[Illustration: - - GENERAL PLAN - -FIG. 2.] - -Regarding the necessity for aeration, no observations have been taken -upon the Hudson River, but, judging from experience with the Merrimac -at Lawrence, where the conditions are in many respects similar, the -water is at all times more or less aerated, and, for the greater -part of the year, it is nearly saturated with oxygen, and aeration -is not necessary. During low water in summer, however, there is much -less oxygen in the water, and at these times aeration is a distinct -advantage. Further, the river-water will often have a slight odor, and -aeration will tend to remove it. The outlets are arranged so that they -can be removed readily in winter if they are not found necessary at -that season. - -=Sedimentation-basin.=—The sedimentation-basin has an area of 5 acres -and is 9 feet deep. To the overflow it has a capacity of 14,600,000 -gallons, and to the flow-line of the filters 8,900,000 gallons. -There is thus a reserve capacity of 5,700,000 gallons between these -limits, and this amount can be drawn upon, without inconvenience, for -maintaining the filters in service while the pumps are shut down. This -allows a freedom in the operation of the pumps which would not exist -with the water supplied direct to the filters. - -The water enters the sedimentation-basin from eleven inlets along -one side, and is withdrawn from eleven outlets directly opposite. -The inlets and aerating devices described previously bring the water -into the basin without current and evenly distributed along one -side. Both inlets and outlets are controlled by gates, so that any -irregularities in distribution can be avoided. The concrete floor of -the sedimentation-basin is built with even slopes from the toe of each -embankment to a sump, the heights of these slopes being 1 foot, -whatever their lengths. The sump is connected with a 24-inch pipe -leading to a large manhole in which there is a gate through which water -can be drawn to empty the basin. There is an overflow from the basin -to this manhole which makes it impossible to fill the basin above the -intended level. - -[Illustration: LONGITUDINAL SECTION ON _a-b-c-d-e-f-g-h_ - -FILTER BEDS - -PLAN AND SECTION OF FILTER NO. 2 - -FIG. 3.] - -[Illustration: OUTSIDE WALL, READY FOR CONCRETE BACKING.] - -[Illustration: SEDIMENTATION-BASIN: SHOWING CONSTRUCTION OF FLOOR. - - [_To face page 294._] -] - -=Filters.=—The filters are of masonry, and are covered to protect them -against the winters, which are quite severe in Albany. The piers, -cross-walls, and linings of the outside walls, entrances, etc., are of -vitrified brick. All other masonry is concrete. The average depth of -excavation for the filters was 4 feet, and the material at the bottom -was usually blue or yellow clay. In some places shale was encountered. -In one place soft clay was found, and there the foundations were made -deeper. The floors consisted of inverted, groined, concrete arches, -arranged to distribute the weight of the walls and vaulting over the -whole area of the bottom. - -The groined arch-vaulting is of concrete with a clear span of 11 feet -11 inches, a rise of 2-1/2 feet, and a thickness of 6 inches at the -crown. It was put in in squares, the joints being on the crowns of the -arches parallel with the lines of the piers, and each pier being the -centre of one square. The manholes are in alternate sections, and are -of concrete, built in steel forms with castings at the tops, securely -jointed to the concrete. - -Above the vaulting there are 2 feet of earth and soil, grassed on -top. The tops of the manholes are 6 inches above the soil to prevent -rain-water from entering them. The drainage of the soil is effected -by a depression of the vaulting over each pier, partially filled with -gravel and sand, from which water is removed by a 2-inch tile-drain -going down the centre of the pier and discharging through its side just -above the top of the sand in the filter. - -In order to provide ready access to each filter, a part of the vaulting -near one side is elevated and made cylindrical in shape, making an -inclined runway from the sand-level to a door the threshold of which is -6 inches above the level of the overflow. - -[Illustration: - - FILTER BEDS - - SECTION OF FILTERS - -FIG. 4.] - -This sand-run is provided with permanent timber runways and with secure -doors. - -[Illustration: Section. - -Elevation. - -FIG. 5.—ENTRANCE TO A FILTER.] - -The manholes of the filters are provided with double covers of steel -plates to exclude the cold. The covers also exclude light. When -cleaning the filters, light can be admitted by removing the covers. -Supports for electric lights are placed in the vaulting, so that the -filters can be lighted by electricity and the work of cleaning can be -done at night, and in winter under heavy snow, without removing the -covers. The electric lights have not yet been installed. - -The regulator-houses, the entrances to the sand-runs, and all exposed -work are of pressed brick with Milford granite trimmings and slate -roofs. The regulator-houses have double walls and double windows and -a tight ceiling in the roof, to make them as warm as possible and to -avoid the necessity of artificial heat to prevent freezing. - -[Illustration: COMPUTED FRICTIONAL RESISTANCE OF DRAINAGE SYSTEM OF -ONE FILTER WHEN OPERATING AT A RATE OF 100 M.M. PER HOUR, EQUAL TO -2,570,000 GALS. PER ACRE DAILY. - -STANDARD GRAVEL SECTIONS. - -FIG. 6.] - -[Illustration: PLACING THE FLOOR OF A FILTER.] - -[Illustration: BUILDING THE BRICK PIERS. - - [_To face page 298._] -] - -The main underdrains for removing the filtered water are of -vitrified pipe surrounded by concrete and are entirely below the floors -of the filters. - -Connections with the main drain are made through thirty-eight 6-inch -outlets in each filter, passing through the floor and connected with -6-inch lateral drains running through the whole width of the filter. -These drains were made with pipes having one side of the bell cut off -so that they would lie flat on the floor and make concentric joints, -without support and without having to be wedged. They were laid with a -space of about 1 inch between the barrels, leaving a large opening for -the admission of water from the gravel. - -The underdrainage system is so designed that, when starting a filter -after cleaning, the friction of the sand is about 50 mm. at a rate of -3,000,000 gallons per acre daily, and the friction of the underdrainage -system is estimated at 10 mm. This very low friction, which is -necessary, is obtained by the use of ample sizes for the underdrains -and low velocities in them. In the outlet and measuring devices -moderate losses of head are not objectionable, and the sizes of the -pipes and connections are, therefore, smaller than the main underdrains. - -The gravel surrounding the underdrains is of three grades. The material -was obtained from the river-bed by dredging, and was of the same stock -as that used for preparing ballast for the concrete. It was separated -and cleaned by a special, cylindrical, revolving screen. The coarsest -grade of gravel was that which would not pass round holes 1 inch in -diameter, and free from stones more than about 2 inches in diameter. At -first it was required to pass a screen with holes 2 inches in diameter, -but this screen removed many stones which it was desired to retain, and -the screen was afterward changed to have holes 3 inches in diameter. -The intermediate grades of gravel passed the 1-inch holes, and were -retained by a screen with round holes 3/8 inch in diameter. The finest -gravel passed the above screens and was retained by a screen with -round holes 3/16 inch in diameter. The gravel was washed, until free -from sand and dirt, by water played upon it during the process of -screening, and it was afterward taken over screens in the chutes, where -it was separated from the dirty water, and, when necessary, further -quantities of water were played upon it at these points. - -[Illustration: - - INLET TO FILTER BED. SECTION ON M-N-O - - REGULATOR CHAMBER - LONGITUDINAL SECTION ON A-B-C-D - - REGULATOR CHAMBER - SECTION ON K-L - - FILTER BEDS - INLET VALVES AND REGULATOR CHAMBER - - INLET TO FILTER BED - SECTIONAL PLAN ON P-Q - - ORIFICE INDICATOR MARKER - DETAILS OF APPARATUS IN REGULATOR HOUSE - - REGULATOR CHAMBER - SECTIONAL PLAN ON E-F-G-H-J - -FIG. 7.] - -The average mechanical analyses of the three grades of gravel are shown -by Fig. 8. Their effective sizes were 23, 8, and 3 mm. respectively, -and for convenience they are designated by these numbers. The average -uniformity coefficient for each grade was about 1.8. - -The 23-mm. gravel entirely surrounded the 6-inch pipe-drains, and was -carried slightly above their tops. In some cases it was used to cover -nearly the whole of the floor, but this was not insisted upon. - -The 8-mm. gravel was obtained in larger quantity than the other sizes, -and was used to fill all spaces up to a plane 2-1/2 inches below the -finished surface of the gravel, this layer being about 2 inches thick -over the tops of the drains, and somewhat thicker elsewhere. - -The 3-mm. gravel was then applied in a layer 2-1/2 inches deep, and the -surface levelled. - -The preliminary estimates of cost were based upon the use of -filter-sand from a bank near the filter-site. Further examination -showed that this sand contained a considerable quantity of lime, and -it was found by experiment with a small filter constructed for that -purpose that the use of this sand would harden the water by about 2 -parts in 100,000, and the amount of lime contained in the sand, namely, -about 7 per cent, was sufficient to continue this hardening action -for a considerable number of years. This was regarded as a serious -objection to its use, and the specifications were drawn limiting the -amount of lime in the sand. This excluded all of the local bank sands. -The river-sands which were used were nearly free from lime, and in the -end the sand as secured was probably not only free from lime, but more -satisfactory in other ways, and also cheaper than the bank-sand would -have been. - -[Illustration: MECHANICAL COMPOSITION OF FILTER SAND AND GRAVELS. - -(ARROWS SHOW REQUIREMENT OF SPECIFICATION) - -_Diameters in Millimeters_ - -FIG. 8.] - -The specifications of the filter-sand require that “The filter-sand -shall be clean river-, beach-, or bank-sand, with either sharp or -rounded grains. It shall be entirely free from clay, dust, or organic -impurities, and shall, if necessary, be washed to remove such materials -from it. The grains shall, all of them, be of hard material which will -not disintegrate, and shall be of the following diameters: Not more -than 1 per cent, by weight, less than 0.13 mm., nor more than 10 per -cent less than 0.27 mm.; at least 10 per cent, by weight, shall be -less than 0.36 mm., and at least 70 per cent, by weight, shall be less -than 1 mm., and no particles shall be more than 5 mm. in diameter. -The diameters of the sand-grains will be computed as the diameters of -spheres of equal volume. The sand shall not contain more than 2 per -cent, by weight, of lime and magnesia taken together and calculated as -carbonates.” - -[Illustration: PLACING THE CONCRETE VAULTING.] - -[Illustration: GENERAL VIEW OF VAULTING, UNDER CONSTRUCTION. - - [_To face page 302._] -] - -[Illustration: FIG. 9.] - -The sand was obtained from the river at various places by dredging. -It was first taken up by dipper-dredges, and brought in scows to a -point in the back channel a little north of the filter-plant. It was -there dumped in a specially prepared place in the bottom of the river, -from which it was lifted by a hydraulic dredge and pumped through a -15-inch pipe an average distance of 525 feet to points selected, and -varied from time to time, on the flats north of the filters. The water -containing the sand was then put through screens having meshes which -excluded all stones 5 mm. in diameter and over, and was then taken into -basins where the sand was deposited and afterward carted to the filters. - -Two ejector sand-washing machines, shown in Fig. 9, are provided at -convenient places between the filters. In them the dirty sand is mixed -with water, and is thrown up by an ejector, after which it runs through -a chute into a receptacle, from which it is again lifted by another -ejector. It passes in all through five ejectors, part of the dirty -water being wasted each time. The sand is finally collected from the -last ejector, where it is allowed to deposit from the water. - -Water is admitted to each filter through a 20-inch pipe from a pipe -system connecting with the sedimentation-basin. Just inside of the -filter-wall is placed a standard gate, and beyond that a balanced -valve connected with an adjustable float to shut off the water when -it reaches the desired height on the filter. These valves and floats -were constructed from special designs, and are similar in principle to -valves used for the same purpose in the Berlin water-filters. - -Each filter is provided with an overflow, so arranged that it cannot be -closed, which prevents the water-level from exceeding a fixed limit in -case the balanced valve fails to act. An outlet is also provided near -the sand-run, so that unfiltered water can be removed quickly from the -surface of the filter, should it be necessary, to facilitate cleaning. - -The outlet of each filter is through a 20-inch gate controlled by a -standard graduated to show the exact distance the gate is open. The -water rises in a chamber and flows through an orifice in a brass plate -4 by 24 inches, the centre of which is 1 foot below the level of the -sand-line. At the nominal rate of filtration, 3,000,000 gallons per -acre daily, 1 foot of head is required to force the water through the -orifice. With other rates the head increases or decreases approximately -as the square of the rate and forms a measure of it. With water -standing in the lower chamber, so that the orifice is submerged, it is -assumed that the same rates will be obtained with a given difference -in level between the water on the two sides of the orifice as from an -equal head above the centre of the orifice when discharging into air. - -=Measurement of Effluent.=—In order to show the rate of filtration two -floats are connected with the water on the two sides of the orifice. -These floats are counterbalanced; one carries a graduated scale, and -the other a marker which moves in front of the scale and shows the rate -of filtration corresponding to the difference in level of the water -on the two sides. When the water in the lower chamber falls below the -centre of the orifice, the water in the float-chamber is nevertheless -maintained at this level. This is accomplished by making the lower part -of the tube water-tight, with openings just at the desired level, so -that when the water falls below this point in the outer chamber it does -not fall in the float-chamber. - -To prevent the loss of water in the float-chamber by evaporation or -from other causes, a lead pipe is brought from the other chamber and -supplies a driblet of water to it constantly; this overflows through -the openings, and maintains the water-level at precisely the desired -point. The floats thus indicate the difference in water-level on the -two sides of the orifice whenever the water in the lower chamber is -above the centre of the orifice; otherwise they indicate the height of -water in the upper chamber above the centre of the orifice, regardless -of the water-level in the lower chamber. The scale is graduated to show -the rates of filtration in millions of gallons per acre of filtering -area. In computing this scale the area of the filters is taken as 0.7 -acre, and the coefficient of discharge as 0.61. - -At the ordinary rates of filtration the errors introduced by the -different conditions under which the orifice operates will rarely -amount to as much as 100,000 gallons per acre daily, or one thirtieth -of the ordinary rate of filtration. Usually they are much less than -this. The apparatus thus shows directly, and with substantial accuracy, -the rate of filtration under all conditions. - -=Measurement of Loss of Head.=—Two other floats with similar -connections show the difference in level between the water standing on -the filter and the water in the main drain-pipe back of the gate, or, -in other words, the frictional resistance of the filter, including the -drains. This is commonly called the loss of head, and increases from -0.2 foot or less, with a perfectly clean filter, to 4 feet with the -filter ready for cleaning. When the loss of head exceeds 4 feet the -rate of filtration cannot be maintained at 3,000,000 gallons per acre -daily with the outlet devices provided, and, in order to maintain the -rate, the filter must be cleaned. - -=Adjustment of Gauges.=—The adjustment of the gauges showing the rate -of filtration and loss of head is extremely simple. When a filter is -put in service the gates from the lower chamber to the pure-water -reservoir and to the drain are closed, the outlet of the filter opened, -and both chambers allowed to fill to the level of the water on the -filter. The length of the wire carrying the gauge is then adjusted so -that the gauge will make the desired run without hitting at either end, -and then the marker is adjusted. As both the rate of filtration and -loss of head are zero under these conditions, it is only necessary to -set the markers to read zero on the gauges to adjust them. The gates -can then be opened for regular operation, and the readings on the -gauges will be correct. - -[Illustration: INTERIOR OF A FILTER: DRAIN, GRAVEL AND SAND LAYERS.] - -[Illustration: INTERIOR OF A FILTER, READY FOR USE. - - [_To face page 306._] -] - -It is necessary to use wires which are light, flexible, and which will -not stretch. At first piano-wire, No. 27 B. & S. gauge, was used, and -was well adapted to the purpose, except that it rusted rapidly. Because -of the rusting it was found necessary to substitute another wire, -and cold-drawn copper wire, No. 24 B. & S. gauge, was used with fair -results. Stretching is less serious than it would otherwise be, as the -correctness of the adjustment can be observed and corrected readily -every time a filter is out of service. - -From the lower chambers in the regulator-houses the water flows -through gates to the pipe system leading to the pure-water reservoir. -Drain-pipes are also provided which allow the water to be entirely -drawn out of each filter, should that be necessary for any reason, -and without interfering with the other filters or with the pure-water -reservoir. - -The outlets of the filters are connected in pairs, so that filtered -water can be used for filling the underdrains and sand of the filters -from below prior to starting, thus avoiding the disturbance which -results from bringing dirty water upon the sand of a filter not filled -with water. - -=Laboratory Building.=—The scientific control of filters is regarded -as one of the essentials to the best results, and to provide for this -there is a laboratory building at one end of the central court between -the filters and close to the sedimentation-basin, supplied with the -necessary equipment for full bacterial examinations, and also with -facilities for observing the colors and turbidities of raw and filtered -waters, and for making such chemical examinations as may be necessary. -This building also provides a comfortable office, dark room, and -storage room for tools, etc., used in the work. - -=Pure-water Reservoir.=—A small pure-water reservoir, 94 feet square -and holding about 600,000 gallons, is provided at the filter-plant. The -construction is similar to that of the filters, but the shapes of the -piers and vaulting were changed slightly, as there was no necessity for -the ledges about the bottoms of the piers and walls; while provision -is made for taking the rain-water, falling upon the vaulting above, to -the nearest filters instead of allowing it to enter the reservoir. The -floor and roof of the reservoir are at the same levels as those of the -filters. - - -CAPACITY OF PLANT AND MEANS OF REGULATION. - -The various filters have effective filtering areas of from 0.702 to -0.704 acre, depending upon slight differences in the thickness of the -walls in different places. For the purpose of computation, the area of -each filter is taken at 0.7 acre. The nominal rate of filtration is -taken as 3,000,000 gallons per acre daily, at which rate each filter -will yield 2,100,000 gallons daily, and, with one filter out of use -for the purpose of being cleaned, seven filters normally in use will -yield 14,700,000 gallons. The entrances and outlets are all made of -sufficient size, so that rates 50 per cent greater than the foregoing -are possible. The capacities of the intake, pumping-station, and piping -are such as to supply any quantity of water which the filters can -take, up to an extreme maximum of 25,000,000 gallons in 24 hours. The -pure-water conduit from the filters to Quackenbush Street is nominally -rated at 25,000,000 gallons per 24 hours, after it has become old and -somewhat tuberculated. In its present excellent condition it will carry -a larger quantity, - -At the pumping-station at Quackenbush Street there are three Allis -pumps, each capable of pumping 5,000,000 gallons per 24 hours. In -addition to the above there are the old reserve pumps with a nominal -capacity of 10,000,000 gallons per 24 hours, which can be used if -necessary, but which require so much coal that they are seldom used. -For practical purposes the 15,000,000 gallons represents the pumping -capacity of this station and also the capacity of the filters, but -the arrangements are such that in case of emergency the supply can be -increased to 20,000,000 or even 25,000,000 gallons for a short time. - -The water is pumped through rising mains to reservoirs holding -37,000,000 gallons, not including the Tivoli low-service reservoir, -which is usually supplied from gravity sources. The reservoir capacity -is such that the pumping can be suspended at Quackenbush Street -for considerable periods if necessary, and in practice it has been -suspended at certain times, especially on Sundays. The amount of water -required is also somewhat irregular. The drainage areas supplying the -gravity reservoirs are much larger, relatively, than the reservoirs, -and at flood periods the volume of the gravity supply is much greater -than that which can be drawn in dry weather. Thus it happens that, at -certain seasons of the year, the amount of water to be pumped is but a -fraction of the nominal capacity of the pumps, and at these times it is -possible to shut the pumps down for greater lengths of time. - -=Capacity of Pure-water Reservoir.=—The storage capacity provided -between the filters and the Quackenbush Street pumps is comparatively -small, namely, 600,000 gallons, or one hour’s supply at the full -nominal rate. A larger basin, holding as much as one third or one -half of a day’s supply, would be in many respects desirable in this -position, but the conditions were such as to make it practically -impossible. The bottom of the reservoir could not be put lower without -deepening and increasing greatly the expense of the conduit-line. On -the other hand, the flow-line of the reservoir could not be raised -without raising the level of the filters, which was hardly possible -upon the site selected. The available depth of the reservoir was thus -limited between very narrow bounds, and to secure a large capacity -would have necessitated a very large area, and consequently a great -expense. Under these circumstances, and especially in view of the -abundant storage capacity for filtered water in the distributing -reservoirs, it was not deemed necessary to provide a large storage, and -only so much was provided as would allow the pumps to be started at -the convenience of the engineer, and give a reasonable length of time -for the filters to be brought into operation. For this the pure-water -reservoir is ample, but it is not enough to balance any continued -fluctuations in the rate of pumping. - -=Method of Regulating and Changing the Rate of Filtration.=—With -all the Allis pumps running at their nominal capacity, the quantity -of water required will just about equal the nominal capacity of the -filters. When only one or two pumps are running, the rate of filtration -can be reduced. With the plant operating up to its full capacity, the -water-level in the pure-water reservoir will be below the level of -the standard orifices in the filter outlets. When the rate of pumping -is reduced, if no change is made in the gates controlling the filter -outlets, the water will gradually rise in the pure-water reservoir and -in the various regulator chambers, and will submerge the orifices and -gradually reduce the head on the filters, and consequently the rates -of filtration, until those rates equal the quantity pumped. In case -the pumping is stopped altogether, the filters will keep on delivering -at gradually reduced rates until the water-level in the pure-water -reservoir reaches that of the water on the filters. - -When the pumps are started up, after such stoppage or reduced rate -of pumping, the water-levels in the pure-water reservoir and in the -gate-chambers will be lowered gradually, and the filters will start -to operate it first with extremely low rates, which will increase -gradually until the water is depressed below the orifices, when they -will again reach the rates at which they were last set. The regulators -during all this time will show the rate of filtration on each filter, -and, if any inequalities occur which demand correction, the gates on -the various outlets can be adjusted accordingly. - -[Illustration: CENTRAL COURT, SHOWING SAND-WASHER, DIRTY SAND, ETC.] - -[Illustration: SEDIMENTATION BASIN, FILTERS, ETC. - - [_To face page 310._] -] - -The arrangement, in this respect, combines some of the features of -the English and German plants. In the English plants the filters are -usually connected directly with the clear-water basin, and that in turn -with the pumps, and the speed of filtration is required to respond -to the speed of the pumps, increasing and decreasing with it, being -regulated at all times by the height of water in the pure-water -reservoir. This arrangement has been subject to severe criticism, -because the rate of filtration fluctuates with the consumption, and -especially because the rates of filtration obtained simultaneously in -different filters may be different. There was no way to determine at -what rate any individual filter was working, and there was always a -tendency for a freshly scraped filter to operate much more rapidly than -those which had not been scraped for some time. - -This led to the procedure, first formulated by the Commission of German -Water-works Engineers in 1894, and provided for in most of the German -works built or remodelled since that time, of providing pure-water -storage sufficient in amount to make the rate of filtration entirely -independent of the operation of the pumps. Each filter was to be -controlled by itself, be independent of the others, and deliver its -water into a pure-water reservoir lower than itself, so that it could -never be affected by back-water, and so large that there would never be -a demand for sudden changes in the rate of filtration. - -This procedure has given excellent results in the German works; but -it leads oftentimes to expensive construction. It involves, in the -first place, a much greater loss of head in passing through the works, -because the pure-water reservoir must be lower than the filters, and -the cost of the pure-water reservoir is increased greatly because -of its large size. The regulation of the filters is put upon the -attendants entirely, or upon automatic devices, and regulation by what -is known as “responding to the pumps” is eliminated. - -More recently, the German authorities have shown less disposition to -insist rigidly upon the principles advanced in 1894. In a compilation -of the results of several years’ experience with German water-filters, -Dr. Pannwiz[66] makes a statement of particular interest, of which a -free translation is as follows: - -“Most of the German works have sufficient pure-water reservoir capacity -to balance the normal fluctuations in consumption, - -so that the rate of filtration is at least independent of the hourly -fluctuations in consumption. Of especial importance is the superficial -area of the pure-water reservoir. If it is sufficiently large, there is -no objection to allowing the water-level in it to rise to that of the -water upon the filters. With very low rates of consumption during the -night the filters may work slowly and even stop, without damage to the -sediment layers when the stopping and starting take place slowly and -regularly, because of the ample reservoir area.” - -“The very considerable fluctuations from day to day, especially those -arising from unusual and unforeseen occurrences, are not provided for -entirely by even very large and well-arranged reservoirs. To provide -for these without causing shock, the rate of filtration must be changed -carefully and gradually, and the first essential to success is a good -regulation apparatus.” - -“Responding to the pumps” has a great deal to recommend it. It allows -the pure-water reservoir to be put at the highest possible level, it -reduces to a minimum the loss of head in the plant, and yet provides -automatically, and without the slightest trouble on the part of the -attendants, for the delivery of the required quantity of water by the -filters at all times. If the filters are connected directly to the -pumps there is a tendency for the pulsations of the pumps to disturb -their operation, which is highly objectionable, even if the pumps are -far removed; and this exists where filters are connected directly to -the pumps, and a pure-water reservoir is attached to them indirectly. -By taking all the water through the pure-water reservoir and having no -connection except through it, this condition is absolutely avoided, and -the pull on the filters is at all times perfectly steady. - -Much has been said as to the effect of variation in the rate of -filtration upon the efficiency of filters. Experiments have been made -at Lawrence and elsewhere which have shown that, as long as the maximum -rate does not exceed a proper one, and under reasonable regulations, -and with the filter in all respects in good order, no marked decrease -in efficiency results from moderate fluctuations in rate. There is -probably a greater decrease in efficiency by stopping the filter -altogether, especially if it is done suddenly, than by simply reducing -the rate. The former sometimes results in loosening air-bubbles in the -sand, which rise to the surface and cause disturbances, but this is not -often caused by simple change in rate. - -On the whole, there is little evidence to show that, within reasonable -limits, fluctuations in rate are objectionable, or should be excluded -entirely, especially in such cases as at Albany, where arrangements to -prevent them would have resulted in very greatly increased first cost. -The inferior results sometimes obtained with the system of “responding -to the pumps” as it existed in earlier works, and still exists in many -important places, undoubtedly arises from the fact that there is no -means of knowing and controlling the simultaneous rate of filtration in -different filters, and that one filter may be filtering two or three -times as fast as another, with nothing to indicate it. - -This contingency is fully provided for in the Albany plant. The -orifices are of such size that even with a filter just scraped and -put in service, with the minimum loss of head, with the outlet-gate -wide open, and with the water-level in the pure-water reservoir clear -down—that is, with the most unfavorable conditions which could possibly -exist—the rate of filtration cannot exceed 5,000,000 or 6,000,000 -gallons per acre daily, or double the nominal rate. This rate, while -much too high for a filter which has just been cleaned, is not nearly -as high as was possible, and in fact actually occurred in the old -Stralau filters at Berlin, and in many English works; and, further, -such a condition could only occur through the gross negligence of -the attendants, because the rate of filtration is indicated clearly -at all times by the gauges. These regulating-devices have been -specially designed to show the rate with unmistakable clearness, so -that no attendant, however stupid, can make an error by an incorrect -computation from the gauge heights. It is believed that the advantage -of clearness by this procedure is much more important than any -increased accuracy which might be secured by refinements in the method -of computation, which should take into account variations in the value -of the coefficient of discharge, but which would render direct readings -impossible. - -In designing the Albany plant the object has been to combine the best -features of German regulation with the economical and convenient -features of the older English system, and filters are allowed to -respond to the pumps within certain limits, while guarding against the -dangers ordinarily incident thereto. - - -RESULTS OF OPERATION. - -The filters were designed to remove from the water the bacteria which -cause disease. They have already reached a bacterial efficiency of over -99 per cent, and it is expected that their use will result in a great -reduction in the death-rate from water-borne diseases in the city. They -also remove a part of the color and all of the suspended matters and -turbidity, so that the water is satisfactory in its physical properties. - -The filters have reached with perfect ease their rated capacity, and -on several occasions have been operated to deliver one third more than -this amount; that is to say, at a rate of 4,000,000 gallons per acre, -daily. - - -COST OF CONSTRUCTION. - -The approximate cost of the filtration-plant complete was as follows: - - Land $8,290 - Pumping-station and intake 49,745 - Filters and sedimentation-basin, with piping 323,960 - Pure-water conduit and connection with Quackenbush - Street pumping-station 86,638 - Engineering and minor expenses 28,000 - ———————— - Total $496,633 - -The filters, sedimentation-basin, and pure-water reservoir are -connected in such a way as to make an exact separation of their -costs impossible; but, approximately, the sedimentation-basin cost -$60,000, the pure-water reservoir $9,000, and the filters $255,000. -The sedimentation-basin thus cost $4,100 per million gallons capacity; -and the filters complete cost $45,600 per acre of net filtering area, -including all piping, office and laboratory building, but exclusive of -land and engineering. - - -ACKNOWLEDGMENT. - -The general plan and location of the plant were first conceived by the -Superintendent of Water-works, George I. Bailey, M. Am. Soc. C. E., and -the successful execution is largely due to his efforts. The members -of the Water Board, and especially the Construction Committee, have -followed the work in detail closely and personally, and their interest -and support have been essential factors in the results accomplished. In -the designs and specifications for the pure-water conduit the author -is greatly indebted to Emil Kuichling, M. Am. Soc. C. E., and also for -most valuable suggestions relative to the performance of this part of -the work. To William Wheeler, M. Am. Soc. C. E., of Boston, the author -is indebted for advice upon the vaulting and cross-sections of the -walls, and these matters were submitted to him before the plans were -put in final shape. All the architectural designs have been supplied -by Mr. A. W. Fuller, of Albany. W. B. Fuller, M. Am. Soc. C. E., as -Resident Engineer, has been in direct charge of the work, and its -success is largely due to his interest in it and the close attention -which he and the assistant engineers have given it. - - - - -FOOTNOTES: - -[1] The American gallon is 231 cubic inches or 0.8333 of the imperial -gallon. In this work American gallons are always used, and English -quantities are stated in American, not imperial, gallons. - -[2] Filtration of River Waters. Van Nostrand & Co., 1869. - -[3] Annual Report of Albert F. Noyes, City Engineer for 1891. - -[4] Rept. Mass. State Board of Health, 1892, p. 541. See Appendix III. - -[5] The method of calculating the size is given in Appendix III. - -[6] A full table of frictions with various velocities and gravels was -given in the Rept. of Mass. State Board of Health, 1892, p. 555. - -[7] Frühling, Handbuch der Ingenieurwissenschaften, II. Band, VI. -Kapitel. - -[8] The American gallon is used throughout this book; the English -gallon is one fifth larger. - -[9] Piefke, _Zeitschrift für Hygiene_, 1894, p. 177. - -[10] _Zeitschrift für Hygiene_, 1891, page 38. - -[11] _Journal für Gas- u. Wasserversorgung_, 1891, 208 and 228. - -[12] _Journal für Gas- u. Wasserversorgung_, 1893, 161. - -[13] Samuelson’s translation of Kirkwood’s “Filtration of -River-waters;” Lindley, Die Nutzbarmachung des Flusswassers, -_Journal für Gas- u. Wasserversorgung_, 1890, 501; Kaiserlichen -Gesundheitsamt, Grundsätze für die Reinigung von Oberflächenwasser -durch Sandfiltration; _Journal für Gas- u. Wasserversorgung_, 1894, -Appendix I. - -[14] Lindley, _Journal für Gas- u. Wasserversorgung_, 1890, 501; Grahn, -_Journal für Gas- u. Wasserversorgung_, 1890, 511; Halbertsma, _Journal -für Gas- u. Wasserversorgung_, 1892, 686; Piefke, _Zeitschrift für -Hygiene_, 1894, 151; and others. - -[15] Appendix I. - -[16] The Water Supply of Towns. London, 1894. - -[17] A special species of bacteria artificially added to secure more -precise information in regard to the passage of germs through the -filter. - -[18] _Zeitschrift für Hygiene_, 1894, p. 173. - -[19] Report Mass. State Board of Health for 1891, p. 438; 1892, page -409. - -[20] Appendix IV. - -[21] Piefke, _Zeitschrift für Hygiene_, 1894, p, 177. - -[22] _Journal für Gas- und Wasserversorgung_, 1887, p. 595. - -[23] _Zeitschrift für Hygiene_, 1894, p. 172. - -[24] Appendix IV. - -[25] Appendix I. - -[26] _Glaser’s Annalen_, 1886, p. 48; _Zeit. f. Hygiene_, 1889, p. 128. - -[27] _Vierteljahresschrift für öffentliche Gesundheitspflege_, 1891, p. -59. - -[28] _Journal für Gas- und Wasserversorgung_, 1891, 108. - -[29] _Zeitschrift für Hygiene_, 1894, 182. - -[30] I am informed that several other filters upon the same principle -have been more recently built. - -[31] Report on Water Purification at Cincinnati, page 378. - -[32] Translation in German in Dingler’s Polytechnical Journal, 1832, -386. - -[33] Water Purification at Louisville, page 378. - -[34] Special Report Mass. State Board of Health 1890, Purification of -Sewage and Water, page 747. - -[35] Water Purification at Cincinnati, p. 485. - -[36] Jour. of the New England Water Works Assoc., Vol. VIII, page 183. - -[37] Report of the Pittsburg Filtration Commission, 1899, page 55. - -[38] Rhode Island State Board of Health Report for 1894. - -[39] Report of the Rhode Island State Board of Health for 1894. - -[40] Report on the Investigations into the Purification of the Ohio -River Water at Louisville, Kentucky. D. Van Nostrand & Co., 1898. - -[41] Ohio State Board of Health Report, 1897, page 154. - -[42] Report of the Pittsburg Filtration Commission, City Document, 1899. - -[43] Fuller, Water Purification at Louisville, page 425. - -[44] Warren, Feb. 9; June 1; July 6. Jewell, July 1; Feb. 9, 16, 17. - -[45] “Removal of Iron from Ground Waters,” Journal of the New England -Water Works Association, Vol. xi, 1897, page 277. - -[46] Journal of the New England Water Works Association, Vol. ii, page -294. Description of plant by Supt. Lewis M. Bancroft. - -[47] This number was the result of numerous counts made from fæces from -persons suffering with typhoid fever in the Lawrence City Hospital -in 1891 and 1892. Mr. G. W. Fuller afterward made at the Lawrence -Experiment Station some further investigation of fæces from healthy -people in which the numbers were considerably lower, usually less than -200,000,000, per gram and sometimes as low as 10,000,000 per gram. - -[48] These experiments, so far as they have come to the notice of the -author, have been made with water sterilized by heating, usually in -small tubes stoppered with cotton-wool or other organic matter. In this -case the water, no matter how carefully purified in the first place, -becomes an infusion of organic matters capable of supporting bacterial -growths, and not at all to be compared to natural waters. - -In experiments often repeated under my direction, carefully distilled -water in bottles, _most scrupulously clean_, with glass stoppers, and -protected from dust, but _not sterilized_, has uniformly refused to -support bacterial growths even when cautiously seeded at the start, -and the same is usually true of pure natural waters. Some further -experiments showed hardly any bacterial growth even of the most hardy -water bacteria in a solution 1 part of peptone in 1,000,000,000 parts -of distilled water, and solutions ten times as strong only gave -moderate growths. - -[49] The Water-supply of Chicago: Its Source and Sanitary Aspects. By -Arthur R. Reynolds, M.D., Commissioner of Health of Chicago, and Allen -Hazen. _American Public Health Association_, 1893. Page 146. - -[50] _Journal für Gas- u. Wasserversorgung_, 1893, 694. - -[51] _Journal für Gas- u. Wasserversorgung_, 1894, 185. - -[52] The method of making this determination was given in the _American -Chemical Journal_, vol. 12, p. 427. - -[53] Some of the companies secure some ground water which they mix -with the filtered water, and this is included in the quantities for -the separate companies, but is excluded from the totals for all the -companies by years. - -[54] Exclusive of gravity supplies. - -[55] Not in use. - -[56] Under construction. - -[57] Not in use. - -[58] Under construction. - -[59] Not in use. - -[60] Under construction. - -[61] Not in use. - -[62] Under construction. - -[63] In the _Centralblatt für Bakteriologie_, 1895, page 881, Reinsch -discusses at length the cause of the inferior results at Altona in -winter, and has apparently discovered a new factor in producing -them. Owing to defective construction of the outlets for the -sedimentation-basins they have failed to act properly in presence of -excessive quantities of ice, and the sediment from the basins has been -discharged in large quantity upon the filters, and a small fraction of -the many millions of bacteria in it have passed through the filters. He -has experimented with this sediment applied to small filters, and has -become convinced that to secure good work under all conditions a much -deeper layer of sand than that generally considered necessary must be -used, and his work emphasizes the importance of the action of the sand -in distinction from the action of the sediment layer, which has often -been thought to be the sole, or at least the principal, requirement of -good filtration. - -[64] Licht- u. Wasserwerke, Zürich, 1892, page 32. - -[65] Descriptions of some of the leading European ground-water supplies -were given by the author in the Jour. Asso. Eng. Soc., Feb. 1895, p. -113. - -[66] “_Arbeiten aus dem Kaiserlichen Gesundheitsamte_,” vol. xiv. p. -260. - - - - -INDEX. - - - Albany, N. Y., filters at, 254, 288. - - Alkalinity, 155. - - Altona, double filtration at, 198. - filters at, 265. - - Alum, use of, in filtration, 92, 144. - - American cities, water-supplies of, and typhoid fever in, 211. - - Amsterdam, filters at, 272. - iron removal at, 192. - - Anderson process, 147. - - Antwerp, filters at, 272. - - Asbestos as filtering material, 181. - - Asbury Park, iron removal at, 192. - - Ashland, Wis., filters at, 252. - - Area of filters to be provided, 47. - - - Bacteria, apparent and actual removal of, by filters, 87. - from underdrains, 87. - in Elbe at Altona, 228. - in fæces, 215. - in water, 84. - number to be allowed in filtered water, 222. - of cholera in river water, 231. - of typhoid fever, life of, in water, 216. - of special kinds to test efficiency of filtration, 86. - to be determined daily, 222. - - Bacterial examination of water, 93. - - Berlin, regulation of depth of water, 59. - cholera infantum from water, 229. - friction in underdrains, 44. - regulation of rate, 53, 55. - water works, 261. - - Berwyn, Penn., filters at, 253. - - Boston, protection of purity of water-supply, 110. - experimental filters at, 73. - - Bremen, double filtration at, 198. - - Breslau, filters at, 274. - - Brussels, ground-water, supply of, 276. - - Budapest, filters at, 274. - - Burton, regulation of rate at Tokyo, Japan, 58. - - - Carpenter, Prof. L. G., 24. - - Chemnitz, intermittent filtration at, 107. - - Chicago, reduced death-rate with new intake, 217. - - Cholera infantum from impure water, 226. - - Cholera, in Hamburg from water, 230. - caused by water, 214. - - Clarification, definition of, 113. - - Clark, H. W., 24, 190. - - Clark’s process for softening water, 92, 145. - - Clay particles, size of, 123. - - Cleaning filters, 68. - - Coagulant, absorption of, by suspended matters, 154. - successive applications of, 154. - - Coagulants used in practice, 150. - - Coagulation of waters, 144. - - Cologne, water-supply of, from wells, 276. - - Color, 113. - amount of coagulant required to remove, 153. - amount of, in various waters, 115. - measurement of, 114. - - - Color, removal of, 117. - - Continuous filters, 5. - filtration, nature of, 83, 92. - - Cost of filters and filtration, 4, 48, 102, 200, 314. - - Covered filters, efficiency of, 17. - - Covers for filters, 12, 15. - at Albany, 295. - in the United States, 17. - omitted at Lawrence, 101. - - Crenothrix, 105, 186. - - - Diarrhœa from impure water, 226. - - Dibden, W. J., 129. - - Disease from water, 210. - - Double filtration at Schiedam, 273. - - Drainage areas of a number of rivers, 133. - - Dresden, water-supply of, from filter-gallery, 276. - - Drown, Dr. Thomas M., 150, 191. - - - Effective size of sand, 21, 238. - European sands, 25. - - Efficiency of filtration, 83, 88, 91. - effect of rate upon, 50. - effect of size of sand-grain upon, 30. - effect of thickness of sand layer upon, 34. - at Lawrence, 106. - European filters, 91, 260. - - Effluents, wasting after scraping, 74. - - - Fæces, number of bacteria in, 215. - - Far Rockaway, L. I., filters at, 193, 253. - - Filling sand with water from below, 68, 307. - - Filter beds, bottoms of, must be water-tight, 12. - covers for, 12. - form of, 11. - size of, 10. - - Filters, aggregate capacity of, 254. - depths of waters on, 45. - list of cities using, 244. - reserve area required, 47. - first constructed at London, 83. - for household use, 183. - general arrangement of, 6. - - Filters, statistics of, at various cities, 241. - - Filtration, cost of, 200. - degree of purification required, 5. - general nature of, 92. - - Fischer tile system, 181. - - FitzGerald, Desmond, 73, 111, 196. - - Flood flows not taken for supply, 10. - - Fränkel and Piefke, experiments on removal of disease germs, 86. - - Frankfort on Main, water supply of, from springs, 276. - - Frankland, Dr. Percy, 84. - - Friction of filtered water in pipes, 264. - water in gravel, 37. - water in sand, 22. - water in underdrains, 40. - - Frost, effect of, upon filters, 12, 229, 266. - - Frühling, on the heating of water by sunshine, 16. - underdraining at Königsberg, 39. - - Fuller, G. W., 118, 123, 131, 139, 140, 145, 152, 154, 161, 165. - - - German Imperial Board of Health, 34, 51, 54, 75, 95. - regulations in regard to filtration, 221. - - Gill, apparatus for regulation, 55. - - Glasgow, water-supply of, from Loch Katrine, 275. - - Gravel at Albany, 299. - layers, 35. - friction of water in, 37. - screening of, for filters, 37. - - Grand Forks, N. D., filters at, 252. - - Ground-water supplies, 3. - the use of, in Europe, 276. - - - Halbertsma, H. P. N., 54, 59. - - Hamburg, apparatus for regulating depth of water, 59. - health of, 226, 271. - regulation of rate of filtration, 56. - underdrains of filters at, 42. - water-supply of, 269. - - Hamilton, N. Y., filters at, 253. - - Hardness, removal of, 92, 145. - - Harrisburg, Penn., filters at, 253. - - Hermany, Charles, 161. - - High rates of filtration without coagulant, 182. - - Household filters, 183. - - Hudson, N. Y., filters at, 251. - - - Ice on filters, 13. - - Inlet regulators, 59. - - Impounding reservoirs, 2. - - Intermittent filtration, 97. - application of, 111, 197. - at Chemnitz, 107. - at Lawrence, 100. - of Pegan Brook, 110. - - Iron, compounds of, as coagulants, 146. - in ground-waters, 186. - in ground-water at Lawrence, 105. - metallic, the Anderson process, 147. - present as ferrous sulphate, 191. - removal plants in operation, 192. - - Iron waters, treatment of, 189. - - - Jewel filter, 151, 161, 162, 172, 173. - - - Kirkwood, James P., 8, 36, 47, 51, 55, 61, 63, 67. - - Kümmel, 50, 51, 86. - - - Lambertsville, N. J., filters at, 252. - - Lawrence City filter, description of, 100. - - Lawrence Experiment Station, 97. - air in water filtered in winter at, 46. - depth of sand removed at, 70. - depth of water on filters, 46. - effect of loss of head upon efficiency, 61. - effect of size of sand-grain upon efficiency, 32. - effect of size of sand-grain upon frequency of scraping, 32. - efficiency of filters at various rates, 50. - efficiency of filtration at, 86, 89. - experiments with continuous filtration, 110. - filters of fine sand, 31. - filters of various sand-grain sizes, 32. - gravel for filters at, 39. - growth of bacteria in sterilized sand at, 85. - intermittent filtration investigated, 97. - - Lawrence Experiment Station, method of sand analysis at, 20. - quantities of water filtered at various losses of head, 66. - wasting effluents not necessary, 75. - - Lawrence, typhoid fever at, 102. - - Leipzig, water-supply of, from wells, 276. - - Lime in sand, 29. - sterilizing effect of, 146. - as a coagulant, 145. - application of, to water, 157. - - Lindley, 43, 51, 54, 57, 81. - - Literature on filtration, 277, 285. - - Little Falls, N. Y., filters at, 253. - - Loam in filters, 35. - - London, cost of operating filters at, 202. - water-supply of, 255. - - Long, Prof., 131. - - Lorain, tests of mechanical filters, 161. - - Loss of head, 52. - limit to, 60, 67. - reasons for allowing high, 65. - - Louisville, mechanical filters at, 161. - - - Magdeburg, filters at, 273. - - Maignen system, 181. - - Manchester, water-supply of, 275. - - Manganese, compounds of, as coagulants, 148. - in ground-waters, 188. - - Massachusetts State Board of Health, see Lawrence Experiment - Station. - - Mechanical filters, 159. - application of, 199. - efficiency of, 179. - list of, 247. - pressure filters, 180. - rates of filtration used, 175. - types of, 172. - wasting effluent after washing, 163. - - Millford, Mass., filters at, 252. - - Mills, H. F., 97, 99, 102. - - Mount Vernon, N. Y., filters at, 252. - - Mud, see turbidity. - - Muddy waters, 113. - - Munich, water-supply of, from springs, 275. - - - Nichols, Prof., suspended matters in European streams, 131. - - Nitrification, effect of, upon bacteria, 98. - - - Odors, removal of, by filtration, 112. - - Organic matters in water, 83. - removed by intermittent filters, 98. - - - Paper manufacturing, filtration of water for, 5. - - Paris, ground-water supply of, 276. - - Palmer, Prof., 131. - - Passages through the sand in filters, 67. - - Pegan Brook, purification of, 110. - - Period, how computed and length of, 72. - length of, dependent upon turbidity, 137. - - Piefke, 48, 50, 54, 63, 69, 73, 74, 75, 80, 84, 85, 90. - - Pittsburgh, experiments with mechanical filters, 162. - - Plägge and Proskauer, 84. - - Plymouth, Penn., typhoid fever at, 208. - - Pollution of European water-supplies, 93. - - Polluted waters, utilization of excessively, 111. - - Porcelain filters for household use, 183. - - Poughkeepsie, N. Y., filters at, 251. - - Pressure filters, 180. - - Providence, mechanical filters at, 159. - - - Rate of filtration, 47, 224. - at various places, 241. - effect of, upon cost, 48. - effect of, upon efficiency, 50. - lower after scraping, 76. - regulation of, 52. - - Red Bank, N. J., filters at, 193, 253. - - Regulation of filters, 52. - old forms of regulators, 52. - modern forms of regulators, 54. - at Albany, 305, 308, 310. - of mechanical filters, 178. - - Reincke, Dr., report on health of Hamburg for 1892, 226. - - Reinsch on the cause of poor filtration at Altona, 267. - - Reserve area required in case of ice, 18. - - Reservoirs, purposes served by, 133. - - Rock Island, Ill., filters at, 254. - - Roofs for filters, 16. - - Rotterdam, filters at, 272. - - - St. Johnsbury, Vt., filters at, 251. - - St. Louis, regulators for proposed filters, 55. - - St. Petersburg, filters at, 275. - - Samuelson, 51. - - Sand, 20. - at Albany, 301. - analysis of European, 25. - analysis of, from leading works, 28. - appliances for moving, 68. - compactness of, in natural banks, 61. - depth of, in filters, 34. - depth to be removed from filters, 69. - dune, 26. - dune, washing of, impossible, 82. - effect of grain-size upon frequency of scraping, 32. - effect of grain-size upon the efficiency, 30. - effective size of, 21, 238. - extra scraping before replacing fresh, 71. - for filtration, 20, 33. - for mechanical filters, 175. - friction of water in, 22. - grain-size of, 20, 233. - in European filters, 24. - in Lawrence filters, two sizes of, 100. - lime in, 29. - method of analysis of, 233. - quantity to be removed by scraping, 74. - replacing, 71. - selection of, 33. - size of passages between grains of, 6. - sterilized, experiments with, 85. - thickness of layer, 34. - uniformity coefficient, 21, 238. - - Sand washing, 26, 76, 304. - cost of, 81. - water for, 80. - - Sandstone filters for household use, 183. - - Schiedam, double filtration at, 273. - - Scraping filters, 7, 68. - - Scraping filters, amount of labor required for, 81. - depth of sand removed, 33, 66, 69. - frequency of, 49, 72, 241. - - Sedgwick, Prof. W. T., 86. - - Sediment, removal of, 92, 133. - - Sediment layer, 6, 31. - influence of, upon bacterial purification, 84. - thickness of, 33, 66, 69. - - Sedimentation basins, 8, 133, 293. - effect of, 134. - - Sewage, number of bacteria in, 215. - - Simpson, James, 83. - - Soda-ash, application of, 157. - - Somersworth, N. H., filters at, 253. - - Storage for raw water, 136. - - Subsidence, limits to the use of, 142. - - Sulphate of alumina, action of, upon waters, 144. - - Surface-waters, use of, unfiltered, 275. - - Suspended matters, 113, 117. - in relation to turbidities, 122. - in various waters, 129. - - - The Hague, iron removal at, 192. - - Tokyo, regulation of rate at, 58. - - Trenched bottoms for filters, 36, 40, 100. - - Turbidity, 92, 113. - amount which is noticeable, 121. - amount in several streams, 124. - duration of, 128. - in relation to suspended matters, 122. - measurement of, 117. - power of sand filters to remove, 139. - preliminary processes to remove, 133. - source of, 123. - - Typhoid fever in Berlin and Altona, 12, 85, 267. - in American cities, 211. - - Typhoid fever in Hamburg, 271. - in Lawrence, 102. - in London, 259. - in Zürich, 275. - - Typhoid-fever germs, life of, in water, 216. - - - Underdrains, 35, 39. - bacteria from, 87. - friction of, at Albany, 299. - size of, 41. - ventilators for, 44. - - Uniformity coefficient of sand, 21, 238. - - - Ventilators for underdrains, 44. - - Vienna, water-supply of, from springs, 276. - - - Warren filter, 151, 161, 162, 172, 176, 177. - - Warsaw, filters at, 275. - friction in underdrains, 43. - regulation of rate at, 57. - - Wasting effluents, 74. - - Water, depth of, on filters, 45, 59. - heating of, in filters, 45. - organic matters in, 83. - - Water-supplies of American cities, 211. - - Water-supply and disease, 210. - - Waters, what require filtration, 207. - - Weston, E. B., 153, 154, 159. - - Weston, R. S., 153, 189. - - West Superior, iron in ground-water at, 189. - - Winter, effect of, upon filtration, 12. - temperatures of places having open and covered filters, 15. - - Worms tile system, 181. - - - Zürich, filters at, 274. - - - - - -SHORT-TITLE CATALOGUE - -OF THE - -PUBLICATIONS - -OF - -JOHN WILEY & SONS, - -NEW YORK. - -LONDON: CHAPMAN & HALL, LIMITED. - - -ARRANGED UNDER SUBJECTS. - -Descriptive circulars sent on application. Books marked with an -asterisk (*) are sold at _net_ prices only, a double asterisk (**) -books sold under the rules of the American Publishers’ Association at -_net_ prices subject to an extra charge for postage. All books are -bound in cloth unless otherwise stated. - - -AGRICULTURE. - - Armsby’s Manual of Cattle-feeding 12mo, $1 75 - Principles of Animal Nutrition 8vo, 4 00 - Budd and Hansen’s American Horticultural Manual: - Part I. Propagation, Culture, and Improvement 12mo, 1 50 - Part II. 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RATE OF FILTRATION AND LOSS OF HEAD 47 - Rate of Filtration 47 - Loss of Head and Apparatus for - regulating it 52 - Limit to the Loss of Head 60 - V. CLEANING FILTERS 68 - Scraping 68 - Frequency of Scraping 72 - Sand-washing 76 - VI. THEORY AND EFFICIENCY OF FILTRATION 83 - Bacterial Examination of Waters 93 - VII. INTERMITTENT FILTRATION 97 - The Lawrence Filter 100 - The Chemnitz Filter 107 - VIII. TURBIDITY AND COLOR, AND THE EFFECT OF MUD - UPON SAND FILTERS 113 - Color 114 - Turbidity 117 - Preliminary Processes to remove Mud 133 - Effect of Mud upon Sand Filters 137 - IX. COAGULATION OF WATERS 144 - Substances used for Coagulation 145 - Amount of Coagulant required to remove - Turbidity 150 - Amount of Coagulant required to remove - Color 153 - Successive Applications of Coagulant 154 - Amount of Coagulant which Waters will - receive 155 - X. MECHANICAL FILTERS 159 - Influence of Amount of Coagulant on - Bacterial Efficiency 165 - Types of Mechanical Filters 172 - XI. OTHER METHODS OF FILTRATION 181 - XII. REMOVAL OF IRON FROM GROUND-WATERS 186 - Cause of Iron in Ground-waters 187 - Treatment of Iron-containing Waters 189 - Iron-removal Plants in Operation 192 - XIII. TREATMENT OF WATERS 197 - Cost of Filtration 200 - XIV. WATER-SUPPLY AND DISEASE 210 - APPENDIX I. GERMAN OFFICIAL REGULATION IN - REGARD TO FILTRATION 221 - II. EXTRACTS FROM DR. REINCKE’S - REPORT UPON THE HEALTH OF - HAMBURG FOR 1892 226 - III. METHODS OF SAND-ANALYSIS 233 - IV. STATISTICS OF SOME FILTERS 241 - Results of Operation 241 - List of Sand Filters in Use 244 - List of Mechanical Filters in - Use 247 - Notes regarding Sand Filters - in America 251 - Extent of the Use of Filters 254 - V. WATER-SUPPLY OF LONDON 255 - VI. WATER-SUPPLY OF BERLIN 261 - VII. WATER-SUPPLY OF ALTONA 265 - VIII. WATER-SUPPLY OF HAMBURG 269 - IX. NOTES ON SOME OTHER EUROPEAN - SUPPLIES 272 - X. LITERATURE OF FILTRATION 277 - XI. THE ALBANY FILTRATION PLANT 288 - INDEX 317 - - -In the table of “ANALYSES OF SANDS USED IN WATER FILTRATION” the place -name “Owesty” has been corrested to read “Oswestry”. - -On page 270 the statement “the velocity in the drain will reach 0.97 -foot” should probably read “0.97 feet per second”. - - - -*** END OF THE PROJECT GUTENBERG EBOOK THE FILTRATION OF PUBLIC -WATER-SUPPLIES *** - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the -United States without permission and without paying copyright -royalties. Special rules, set forth in the General Terms of Use part -of this license, apply to copying and distributing Project -Gutenberg-tm electronic works to protect the PROJECT GUTENBERG-tm -concept and trademark. 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font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of The filtration of public water-supplies, by Allen Hazen</p> -<div style='display:block; margin:1em 0'> -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online -at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you -are not located in the United States, you will have to check the laws of the -country where you are located before using this eBook. -</div> - -<p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em'>Title: The filtration of public water-supplies</p> -<p style='display:block; margin-left:2em; text-indent:0; margin-top:0; margin-bottom:1em;'>Third edition, revised and enlarged.</p> -<p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em'>Author: Allen Hazen</p> -<p style='display:block; text-indent:0; margin:1em 0'>Release Date: September 21, 2022 [eBook #69025]</p> -<p style='display:block; text-indent:0; margin:1em 0'>Language: English</p> - <p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em; text-align:left'>Produced by: Charlene Taylor, Brian G. Wilcox and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.)</p> -<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK THE FILTRATION OF PUBLIC WATER-SUPPLIES ***</div> - -<div class="figcenter illowp100" id="frontis" style="max-width: 153.6875em;"> - <img class="w100" src="images/frontis.jpg" alt="" /> - <p class="caption"><span class="smcap">General View of Filters at Hamburg.</span></p> - -<p class="right">[<em>Frontispiece.</em>]</p> -</div> - -<h1><span class="larger">THE FILTRATION</span><br /> - -<br /><span class="smallest">OF</span><br /> - -<br /><span class="larger">PUBLIC WATER-SUPPLIES.</span></h1> - -<h2><span class="smallest">BY</span><br /> -ALLEN HAZEN,</h2> - -<p class="center noindent">MEMBER OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS, THE BOSTON SOCIETY OF CIVIL -ENGINEERS, THE AMERICAN WATER-WORKS ASSOCIATION, THE NEW ENGLAND -WATER-WORKS ASSOCIATION, THE AMERICAN CHEMICAL SOCIETY, -THE AMERICAN PUBLIC HEALTH ASSOCIATION, ETC.</p> - -<p class="center noindent padt2 padb2"><em>THIRD EDITION, REVISED AND ENLARGED.</em><br /> -SECOND THOUSAND.</p> - - -<p class="center">NEW YORK:<br /> -JOHN WILEY & SONS.<br /> -<span class="smcap">London</span>: CHAPMAN & HALL, <span class="smcap">Limited</span>.<br /> -1905. -</p> - -<hr class="chap x-ebookmaker-drop" /> - -<p class="center padt2 padb2"><span class="smaller">Copyright, 1900,<br /> -BY</span><br /> -ALLEN HAZEN.</p> - - -<p class="center">ROBERT DRUMMOND, ELECTROTYPER AND PRINTER, NEW YORK. -</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_iii">[Pg iii]</span></p> - -<h2 class="nobreak" id="PREFACE_TO_FIRST_EDITION">PREFACE TO FIRST EDITION.</h2> -</div> - -<p><span class="smcap">The</span> subject of water-filtration is commencing to receive a great deal -of attention in the United States. The more densely populated European -countries were forced to adopt filtration many years ago, to prevent -the evils arising from the unavoidable contaminations of the rivers -and lakes which were the only available sources for their public -water-supplies; and it has been found to answer its purpose so well -that at the present time cities in Europe nearly if not quite equal in -population to all the cities of the United States are supplied with -filtered water.</p> - -<p>Many years ago, when the whole subject of water-supply was still -comparatively new in this country, filtration was considered as a means -for rendering the waters of our rivers suitable for the purpose of -domestic water-supply. St. Louis investigated this subject in 1866, -and the engineer of the St. Louis Water Board, the late Mr. J. P. -Kirkwood, made an investigation and report upon European methods of -filtration which was published in 1869, and was such a model of full -and accurate statement combined with clearly-drawn conclusions that, up -to the present time, it has remained the only treatise upon the subject -in English, notwithstanding the great advances which have been made, -particularly in the last ten years, with the aid of knowledge of the -bacteria and the germs of certain diseases in water.</p> - -<p>Unfortunately the interest in the subject was not maintained in -America, but was allowed to lag for many years; it was cheaper to use -the water in its raw state than it was to purify it; the people became -indifferent to the danger of such use, and -<span class="pagenum" id="Page_iv">[Pg iv]</span> -the disastrous epidemics -of cholera and typhoid fever, as well as of minor diseases, which so -often resulted from the use of polluted water, were attributed to other -causes. With increasing study and diffusion of knowledge the relations -of water and disease are becoming better known, and the present state -of things will not be allowed to continue; indeed at present there is -inquiry at every hand as to the methods of improving waters.</p> - -<p>The one unfortunate feature is the question of cost. Not that the cost -of filtration is excessive or beyond the means of American communities; -in point of fact, exactly the reverse is the case; but we have been so -long accustomed to obtain drinking-water without expense other than -pumping that any cost tending to improved quality seems excessive, thus -affording a chance for the installation of inferior filters, which by -failing to produce the promised results tend to bring the whole process -into disrepute, since few people can distinguish between an adequate -filtration and a poor substitute for it. It is undoubtedly true that -improvements are made, and will continue to be made, in processes of -filtration; so it will often be possible to reduce the expense of the -process without decreasing the efficiency, but great care must be -exercised in such cases to maintain the conditions really essential to -success.</p> - -<p>In the present volume I have endeavored to explain briefly the nature -of filtration and the conditions which, in half a century of European -practice, have been found essential for successful practice, with a -view of stimulating interest in the subject, and of preventing the -unfortunate and disappointing results which so easily result from the -construction of inferior filters. The economies which may possibly -result by the use of an inferior filtration are comparatively small, -and it is believed that in those American cities where filtration is -necessary or desirable it will be found best in every case to furnish -filters of the best construction, fully able to do what is required of -them with ease and certainty.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_v">[Pg v]</span></p> - -<h2 class="nobreak" id="PREFACE_TO_THIRD_EDITION">PREFACE TO THIRD EDITION.</h2> -</div> - - -<p><span class="smcap">There</span> have been several distinct epochs in the development of water -purification in the United States. The first may be said to date -from Kirkwood’s report on the “Filtration of River Waters,” and the -second from the inauguration of the Lawrence Experiment Station by -the Massachusetts State Board of Health, and the construction of -the Lawrence city filter, with the demonstration of the wonderful -biological action of filters upon highly polluted waters.</p> - -<p>The third epoch is marked by the experiments at Louisville, Pittsburg -and Cincinnati, which have greatly increased our knowledge of the -treatment of waters containing enormous quantities of suspended matter, -and have reduced to something like order the previously existing -confused mass of data regarding coagulation and rapid filtration.</p> - -<p>The first edition of this book represented the earlier epochs -before the opening of the third. In the five years since it was -written, progress in the art of water purification has been rapid -and substantial. No apology is needed for the very complete revision -required to treat these newly investigated subjects as fully as were -other matters in the earlier editions.</p> - -<p>In the present edition the first seven chapters remain with but few -additions. Experience has strengthened the propositions contained -in them. New data might have been added, but in few cases would the -conclusions have been altered. The remaining<span class="pagenum" id="Page_vi">[Pg vi]</span> chapters of the book have -been entirely rewritten and enlarged to represent the added information -now available, so that the present edition is nearly twice as large as -the earlier ones. In the appendices, also, much matter has been added -relating to works in operation, particularly to those in America.</p> - -<p><span class="smcap">New York</span> January, 1900.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_vii">[Pg vii]</span></p> - -<h2 class="nobreak" id="CONTENTS">CONTENTS.</h2> -</div> - -<table class="autotable" summary="ToC"> -<tr> -<th class="tdr smaller normal" colspan="3">PAGE</th> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">Chapter</span> I.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Introduction.</span></p></td> -<td class="tdr vertb"><a href="#Page_1">1</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">II.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Continuous Filters and their Construction</span></p></td> -<td class="tdr vertb"><a href="#Page_5">5</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Sedimentation-basins</p></td> -<td class="tdr vertb"><a href="#Page_8">8</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Size of Filter-beds</p></td> -<td class="tdr vertb"><a href="#Page_10">10</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Form of Filter-beds</p></td> -<td class="tdr vertb"><a href="#Page_11">11</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Covers for Filters</p></td> -<td class="tdr vertb"><a href="#Page_12">12</a></td> -</tr> -<tr> -<td class="tdr vertt">III.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Filtering-materials</span></p></td> -<td class="tdr vertb"><a href="#Page_20">20</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Sand</p></td> -<td class="tdr vertb"><a href="#Page_20">20</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Sands Used in European Filters</p></td> -<td class="tdr vertb"><a href="#Page_24">24</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Effect of Size of Grain Upon Efficiency of Filtration</p></td> -<td class="tdr vertb"><a href="#Page_30">30</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Effect of Grain Size Upon Frequency of Scraping</p></td> -<td class="tdr vertb"><a href="#Page_32">32</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Selection of Sand</p></td> -<td class="tdr vertb"><a href="#Page_33">33</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Thickness of the Sand Layer</p></td> -<td class="tdr vertb"><a href="#Page_34">34</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Underdraining</p></td> -<td class="tdr vertb"><a href="#Page_35">35</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Gravel Layers</p></td> -<td class="tdr vertb"><a href="#Page_35">35</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Underdrains</p></td> -<td class="tdr vertb"><a href="#Page_39">39</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Depth of Water on Filters</p></td> -<td class="tdr vertb"><a href="#Page_45">45</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">IV.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Rate of Filtration and Loss of Head</span></p></td> -<td class="tdr vertb"><a href="#Page_47">47</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Effect of Rate Upon Cost of Filtration</p></td> -<td class="tdr vertb"><a href="#Page_48">48</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Effect of Rate Upon Efficiency of Filtration</p></td> -<td class="tdr vertb"><a href="#Page_50">50</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Loss of Head</p></td> -<td class="tdr vertb"><a href="#Page_52">52</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Regulation of the Rate and Loss of Head in the Older Filters</p></td> -<td class="tdr vertb"><a href="#Page_52">52</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Apparatus For Regulating the Rate and Loss of Head</p></td> -<td class="tdr vertb"><a href="#Page_55">55</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Apparatus For Regulating the Rate Directly</p></td> -<td class="tdr vertb"><a href="#Page_57">57</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Apparatus For Regulating the Height of Water Upon Filters</p></td> -<td class="tdr vertb"><a href="#Page_59">59</a></td> -</tr> -<tr><td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Limit to the Loss of Head</p></td> -<td class="tdr vertb"><a href="#Page_60">60</a></td> -</tr> -<tr> -<td class="tdr vertt">V.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Cleaning Filters</span></p></td> -<td class="tdr vertb"><a href="#Page_68">68</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Frequency of Scraping</p></td> -<td class="tdr vertb"><a href="#Page_72">72</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Quantity of Sand to Be Removed</p></td> -<td class="tdr vertb"><a href="#Page_74">74</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Wasting the Effluents After Scraping</p></td> -<td class="tdr vertb"><a href="#Page_74">74</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Sand-washing</p></td> -<td class="tdr vertb"><a href="#Page_76">76</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">VI.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Theory and Efficiency of Filtration</span></p></td> -<td class="tdr vertb"><a href="#Page_83">83</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Bacterial Examination of Waters</p></td> -<td class="tdr vertb"><a href="#Page_93">93</a></td> -</tr> -<tr> -<td class="tdr vertt">VII.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Intermittent Filtration</span></p></td> -<td class="tdr vertb"><a href="#Page_97">97</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Lawrence Filter</p></td> -<td class="tdr vertb"><a href="#Page_100">100</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Chemnitz Water-Works</p></td> -<td class="tdr vertb"><a href="#Page_107">107</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Application of Intermittent Filtration</p></td> -<td class="tdr vertb"><a href="#Page_111">111</a></td> -</tr> -<tr> -<td class="tdr vertt">VIII.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Turbidity and Color, and the Effect of Mud upon Sand Filters</span></p></td> -<td class="tdr vertb"><a href="#Page_113">113</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Measurement of Color</p></td> -<td class="tdr vertb"><a href="#Page_114">114</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Amount of Color in American Waters</p></td> -<td class="tdr vertb"><a href="#Page_115">115</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Removal of Color</p></td> -<td class="tdr vertb"><a href="#Page_117">117</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Measurement of Turbidity</p></td> -<td class="tdr vertb"><a href="#Page_117">117</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Relation of Platinum-wire Turbidities to Suspended Matters</p></td> -<td class="tdr vertb"><a href="#Page_122">122</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Source of Turbidity</p></td> -<td class="tdr vertb"><a href="#Page_123">123</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Amounts of Suspended Matters in Water</p></td> -<td class="tdr vertb"><a href="#Page_129">129</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Preliminary Processes to remove Mud</p></td> -<td class="tdr vertb"><a href="#Page_133">133</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Effect of Mud upon Sand Filters</p></td> -<td class="tdr vertb"><a href="#Page_137">137</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Effect of Turbidity Upon the Length of Period</p></td> -<td class="tdr vertb"><a href="#Page_137">137</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Power of Sand Filters to Produce Clear Effluents from Muddy Water</p></td> -<td class="tdr vertb"><a href="#Page_139">139</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Effect of Mud Upon Bacterial Efficiency of Filters</p></td> -<td class="tdr vertb"><a href="#Page_141">141</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Limits to the Use of Subsidence for the Preliminary Treatment of Muddy -Waters</p></td> -<td class="tdr vertb"><a href="#Page_142">142</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">IX.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Coagulation of Waters</span></p></td> -<td class="tdr vertb"><a href="#Page_144">144</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Substances used for Coagulation</p></td> -<td class="tdr vertb"><a href="#Page_145">145</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Coagulants Which Have Been Used</p></td> -<td class="tdr vertb"><a href="#Page_150">150</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Amount of Coagulant required to remove Turbidity</p></td> -<td class="tdr vertb"><a href="#Page_150">150</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Amount of Coagulant required to remove Color</p></td> -<td class="tdr vertb"><a href="#Page_153">153</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Successive Applications of Coagulant</p></td> -<td class="tdr vertb"><a href="#Page_154">154</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Amount of Coagulant which Various Waters will receive</p></td> -<td class="tdr vertb"><a href="#Page_155">155</a></td> -</tr> -<tr> -<td class="tdr vertb"><span class="pagenum" id="Page_viii">[Pg viii]</span></td> -</tr> -<tr> -<td class="tdr vertt">X.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Mechanical Filters</span></p></td> -<td class="tdr vertb"><a href="#Page_159">159</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Providence Experiments</p></td> -<td class="tdr vertb"><a href="#Page_159">159</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Louisville_Experiments</p></td> -<td class="tdr vertb"><a href="#Page_161">161</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Lorain Tests</p></td> -<td class="tdr vertb"><a href="#Page_161">161</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Pittsburg Experiments</p></td> -<td class="tdr vertb"><a href="#Page_162">162</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Wasting Effluent After Washing Filters</p></td> -<td class="tdr vertb"><a href="#Page_163">163</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Influence of Amount of Sulphate of Alumina on Bacterial Efficiency of -Mechanical Filters</p></td> -<td class="tdr vertb"><a href="#Page_165">165</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Influence of Degree of Turbidity upon Bacterial Efficiency of Mechanical Filters</p></td> -<td class="tdr vertb"><a href="#Page_167">167</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Average Results Obtained with Various Quantities of Sulphate of Alumina</p></td> -<td class="tdr vertb"><a href="#Page_171">171</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Types of Mechanical Filters</p></td> -<td class="tdr vertb"><a href="#Page_172">172</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Efficiency of Mechanical Filters</p></td> -<td class="tdr vertb"><a href="#Page_179">179</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Pressure Filters</p></td> -<td class="tdr vertb"><a href="#Page_180">180</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">XI.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Other Methods of Filtration</span></p></td> -<td class="tdr vertb"><a href="#Page_181">181</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Worms Tile System</p></td> -<td class="tdr vertb"><a href="#Page_181">181</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Use of Asbestos</p></td> -<td class="tdr vertb"><a href="#Page_181">181</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Filters Using High Rates of Filtration Without Coagulants</p></td> -<td class="tdr vertb"><a href="#Page_182">182</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Household Filters</p></td> -<td class="tdr vertb"><a href="#Page_183">183</a></td> -</tr> -<tr> -<td class="tdr vertt">XII.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Removal of Iron from Ground-waters</span></p></td> -<td class="tdr vertb"><a href="#Page_186">186</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Amount of Iron Required to Render Water Objectionable</p></td> -<td class="tdr vertb"><a href="#Page_186">186</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Cause of Iron in Ground-waters</p></td> -<td class="tdr vertb"><a href="#Page_187">187</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Treatment of Iron-containing Waters</p></td> -<td class="tdr vertb"><a href="#Page_189">189</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Iron-removal Plants in Operation</p></td> -<td class="tdr vertb"><a href="#Page_192">192</a></td> -</tr> -<tr> -<td class="tdr vertt">XIII.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Treatment of Waters</span></p></td> -<td class="tdr vertb"><a href="#Page_197">197</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Cost of Filtration</p></td> -<td class="tdr vertb"><a href="#Page_200">200</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">What Waters Require Filtration</p></td> -<td class="tdr vertb"><a href="#Page_207">207</a></td> -</tr> -<tr> -<td class="tdr vertt">XIV.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Water-supply and Disease—Conclusions</span></p></td> -<td class="tdr vertb"><a href="#Page_210">210</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">Appendix I.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Rules of the German Government in Regard to the Filtration of -Surface-waters Used For Public Water-supplies</span></p></td> -<td class="tdr vertb"><a href="#Page_221">221</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">II.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Extracts from “Bericht Des Medicinal-inspectorats Des Hamburgischen -Staates Für Das Jahr 1892”</span></p></td> -<td class="tdr vertb"><a href="#Page_226">226</a></td> -</tr> -<tr> -<td class="tdr vertt">III.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Methods of Sand-analysis</span></p></td> -<td class="tdr vertb"><a href="#Page_233">233</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">IV.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Filter Statistics</span></p></td> -<td class="tdr vertb"><a href="#Page_241">241</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Statistics of Operation of Sand Filters</p></td> -<td class="tdr vertb"><a href="#Page_241">241</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Partial List of Cities Using Sand Filters</p></td> -<td class="tdr vertb"><a href="#Page_244">244</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">List of Cities and Towns Using Mechanical Filters</p></td> -<td class="tdr vertb"><a href="#Page_247">247</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Notes Regarding Sand Filters in the United States</p></td> -<td class="tdr vertb"><a href="#Page_251">251</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Capacity of Filters</p></td> -<td class="tdr vertb"><a href="#Page_254">254</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">V.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">London’s Water-supply</span></p></td> -<td class="tdr vertb"><a href="#Page_255">255</a></td> -</tr> -<tr> -<td class="tdr vertt">VI.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">The Berlin Water-works</span></p></td> -<td class="tdr vertb"><a href="#Page_261">261</a></td> -</tr> -<tr> -<td class="tdr vertt">VII.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Altona Water-works</span></p></td> -<td class="tdr vertb"><a href="#Page_265">265</a></td> -</tr> -<tr> -<td class="tdr vertt">VIII.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Hamburg Water-works</span></p></td> -<td class="tdr vertb"><a href="#Page_269">269</a></td> -</tr> -<tr> -<td class="tdr vertt">IX.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Notes on Some Other European Water-supplies</span></p></td> -<td class="tdr vertb"><a href="#Page_272">272</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Use of Unfiltered Surface-waters.</p></td> -<td class="tdr vertb"><a href="#Page_275">275</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">The Use of Ground-water.</p></td> -<td class="tdr vertb"><a href="#Page_276">276</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">X.</span></td> -<td class="tdr vertb"><p class="indent"><span class="smcap">Literature of Filtration</span></p></td> -<td class="tdr vertb"><a href="#Page_277">277</a></td> -</tr> -<tr> -<td class="tdr vertt">XI.</td> -<td class="tdr vertb"><p class="indent"><span class="smcap">The Albany Water-filtration Plant</span></p></td> -<td class="tdr vertb"><a href="#Page_288">288</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Description of Plant.</p></td> -<td class="tdr vertb"><a href="#Page_289">289</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Capacity of Plant and Means of Regulation.</p></td> -<td class="tdr vertb"><a href="#Page_308">308</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Results of Operation.</p></td> -<td class="tdr vertb"><a href="#Page_314">314</a></td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl padl2"><p class="indent">Cost of Construction.</p></td> -<td class="tdr vertb"><a href="#Page_314">314</a></td> -</tr> -<tr> -<td class="tdr vertt"><span class="smcap">Index</span></td> -<td> </td> -<td class="tdr vertb"><a href="#Page_317">317</a></td> -</tr> -</table> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_ix">[Pg ix]</span></p> - -<h2 class="nobreak" id="UNITS_EMPLOYED">UNITS EMPLOYED.</h2> -</div> - -<p class="padb1">The units used in this work are uniformly those in common use in -America, with the single exception of data in regard to sand-grain -sizes, which are given in millimeters. The American units were not -selected because the author prefers them or considers them particularly -well suited to filtration, but because he feared that the use of the -more convenient metric units in which the very comprehensive records -of Continental filter plants are kept would add to the difficulty of -a clear comprehension of the subject by those not familiar with those -units, and so in a measure defeat the object of the book.</p> - -<table class="autotable" summary="table of equivalents"> -<tr> -<th class="tdc large normal" colspan="4">TABLE OF EQUIVALENTS.</th> -</tr> -<tr> -<th class="tdc normal">Unit.</th> -<th class="tdc normal" colspan="2">Metric Equivalent.</th> -<th class="tdl normal">Reciprocal.</th> -</tr> -<tr> -<td class="tdl vertt">Foot</td> -<td class="tdl vertt"><span class="add1p5em">0.3048</span></td> -<td class="tdl vertt">meter</td> -<td class="tdl vertt">3.2808</td> -</tr> -<tr> -<td class="tdl vertb">Mile</td> -<td class="tdr vertb">1609.34</td> -<td class="tdl vertb">meters</td> -<td class="tdr vertb">0.0006214</td> -</tr> -<tr> -<td class="tdl vertb">Acre</td> -<td class="tdr vertb">4047</td> -<td class="tdl vertb">square meters</td> -<td class="tdr vertb">0.0002471</td> -</tr> -<tr> -<td class="tdl vertb">Gallon<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">[1]</a></td> -<td class="tdr vertb"> 3.785</td> -<td class="tdl vertb">liters</td> -<td class="tdr vertb">0.26417</td> -</tr> -<tr> -<td class="tdl vertb">1 million gallons</td> -<td class="tdr vertb">3785</td> -<td class="tdr vertb">cubic meters</td> -<td class="tdr vertb">0.00026417</td> -</tr> -<tr> -<td class="tdl vertb">Cubic yard</td> -<td class="tdr vertb"><span class="add1p5em">0.7645</span></td> -<td class="tdl vertb">cubic meters</td> -<td class="tdr vertb">1.308</td> -</tr> -<tr> -<td class="tdl vertb"><p class="indent">1 million gallons per acre daily</p></td> -<td class="tdr vertb"><span class="add1p5em">0.9354</span></td> -<td class="tdl vertb"><p class="indent">meter in depth of water daily</p></td> -<td class="tdr vertb">1.070</td> -</tr> -</table> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<h2 class="nobreak" id="ACKNOWLEDGMENT">ACKNOWLEDGMENT.</h2> -</div> - -<p><span class="smcap">I wish</span> to acknowledge my deep obligation to the large number of -European engineers, directors, and superintendents of water-works, and -to the health officers, chemists, bacteriologists, and other officials -who have kindly aided me in studying the filtration-works in their -respective cities, and who have repeatedly furnished me with valuable -information, statistics, plans, and reports.</p> - -<p>To mention all of them would be impossible, but I wish particularly to -mention Major-General Scott, Water-examiner of London; Mr. Mansergh, -Member of the Royal Commission on the Water-supply of the Metropolis; -Mr. Bryan, Engineer of the East London Water Company; and Mr. Wilson, -Manager of the Middlesborough Water-works, who have favored me with -much valuable information.</p> - -<p>In Holland and Belgium I am under special obligations to Messrs. Van -Hasselt and Kemna, Directors of the water companies at Amsterdam and -Antwerp respectively; to Director Stang of the Hague Water-works; to -Dr. Van’t Hoff, Superintendent of the Rotterdam filters; and to my -friend H. P. N. Halbertsma, who, as consulting engineer, has built many -of the Dutch water-works.</p> - -<p>In Germany I must mention Profs. Frühling, at Dresden, and Flügge, at -Breslau; Andreas Meyer, City Engineer of Hamburg; and the Directors of -water-works, Beer at Berlin, Dieckmann at Magdeburg, Nau at Chemnitz, -and Jockmann at Liegnitz, as well as the Superintendent Engineers -Schroeder at Hamburg, Debusmann at Breslau, and Anklamm and Piefke at -Berlin, the latter the distinguished head of the Stralau works, the -first and most widely known upon the Continent of Europe.</p> - -<p>I have to acknowledge my obligation to City Engineer Sechner at -Budapest, and to the Assistant Engineer in charge of water-works, -Kajlinger; to City Engineer Peters and City Chemist Bertschinger<span class="pagenum" id="Page_xii">[Pg xii]</span> at -Zürich; and to Assistant Engineer Regnard of the Compagnie Générale des -Eaux at Paris.</p> - -<p>On this side of the Atlantic also I am indebted to Hiram F. Mills, -C.E., under whose direction I had the privilege of conducting -for nearly five years the Lawrence experiments on filtration; to -Profs. Sedgwick and Drown for the numerous suggestions and friendly -criticisms, and to the latter for kindly reading the proof of this -volume; to Mr. G. W. Fuller for full information in regard to the -more recent Lawrence results; to Mr. H. W. Clark for the laborious -examination of the large number of samples of sands used in actual -filters and mentioned in this volume; and to Mr. Desmond FitzGerald -for unpublished information in regard to the results of his valuable -experiments on filtration at the Chestnut Hill Reservoir, Boston.</p> - -<p class="right"><span class="smcap">Allen Hazen.</span><span class="add2em"> </span></p> - -<p><span class="smcap">Boston</span>, April, 1895.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_1">[Pg 1]</span></p> - -<p class="center"><span class="largest">FILTRATION OF PUBLIC WATER-SUPPLIES.</span></p> -</div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<h2 class="nobreak" id="CHAPTER_I">CHAPTER I.<br /> -<br /> - -<span class="smaller">INTRODUCTION.</span></h2></div> - -<p><span class="smcap">The</span> rapid and enormous development and extension of water-works in -every civilized country during the past forty years is a matter which -deserves our most careful consideration, as there is hardly a subject -which more directly affects the health and happiness of almost every -single inhabitant of all cities and large towns.</p> - -<p>Considering the modern methods of communication, and the free exchange -of ideas between nations, it is really marvellous how each country has -met its problems of water-supply from its own resources, and often -without much regard to the methods which had been found most useful -elsewhere. England has secured a whole series of magnificent supplies -by impounding the waters of small streams in reservoirs holding enough -water to last through dry periods, while on Continental Europe such -supplies are hardly known. Germany has spent millions upon millions in -purifying turbid and polluted river-waters, while France and Austria -have striven for mountain-spring waters and have built hundreds of -miles of costly aqueducts to secure them. In the United States an -abundant supply of some liquid has too often been the objective point, -and the efforts have been most<span class="pagenum" id="Page_2">[Pg 2]</span> successful, the American works being -entirely unrivalled in the volumes of their supplies. I do not wish -to imply that quality has been entirely neglected in our country, for -many cities and towns have seriously and successfully studied their -problems, with the result that there are hundreds of water-supplies -in the United States which will compare favorably upon any basis with -supplies in any part of the world; but on the other hand it is equally -true that there are hundreds of other cities, including some among -the largest in the country, which supply their citizens with turbid -and unhealthy waters which cannot be regarded as anything else than a -national disgrace and a menace to our prosperity.</p> - -<p>One can travel through England, Belgium, Holland, Germany, and large -portions of other European countries and drink the water at every city -visited without anxiety as to its effect upon his health. It has not -always been so. Formerly European capitals drank water no better than -that so often dispensed now in America. As recently as 1892 Germany’s -great commercial centre, Hamburg, having a water-supply essentially -like those of Philadelphia, Pittsburg, Cincinnati, St. Louis, New -Orleans, and a hundred other American cities, paid a penalty in one -month of eight thousand lives for its carelessness. The lesson was a -dear one, but it was not wasted. Hamburg now has a new and wholesome -supply, and other German cities the qualities of whose waters were open -to question have been forced to take active measures to better their -conditions. We also can learn something from their experience.</p> - -<p>There are three principal methods of securing a good water-supply for a -large city. The first consists of damming a stream from an uninhabited -or but sparsely inhabited watershed, thus forming an impounding -reservoir. This method is extensively used in England and in the United -States. In the latter most of the really good and large supplies are so -obtained. It is only applicable to places having suitable watersheds -within a reasonable<span class="pagenum" id="Page_3">[Pg 3]</span> distance, and there are large regions where, owing -to geological and other conditions, it cannot be applied. It is most -useful in hilly and poor farming countries, as in parts of England and -Wales, in the Atlantic States, and in California. It cannot be used to -any considerable extent in level and fertile countries which are sure -to be or to become densely populated, as is the case with large parts -of France and Germany and in the Middle States.</p> - -<p>The second method is to secure ground-water, that is, spring or well -water, which by its passage through the ground has become thoroughly -purified from any impurities which it may have contained. This was the -earliest and is the most widely used method of securing good water. -It is specially adapted to small supplies. Under favorable geological -conditions very large supplies have been obtained in this manner. In -Europe Paris, Vienna, Budapest, Munich, Cologne, Leipzig, Dresden, a -part of London, and very many smaller places are so supplied. This -method is also extensively used in the United States for small and -medium-sized places, and deserves to be most carefully studied, and -used whenever possible, but is unfortunately limited by geological -conditions and cannot be used except in a fraction of the cases where -supplies are required. No ground-water supplies yet developed in the -United States are comparable in size to those used in Europe.</p> - -<p>The third process of securing a good water-supply is by means of -filtration of surface waters which would otherwise be unsuitable for -domestic purposes. The methods of filtration, which it is the purpose -of this volume to explain, are beyond the experimental stage; they -are now applied to the purification of the water-supplies of European -cities with an aggregate population of at least 20,000,000 people. In -the United States the use of filters is much less common, and most of -the filters in use are of comparatively recent installation.</p> - -<p>Great interest has been shown in the subject during the last<span class="pagenum" id="Page_4">[Pg 4]</span> few -years, and the peculiar character of some American waters, which differ -widely in their properties from those of many European streams, has -received careful and exhaustive consideration. In Europe filtration has -been practised with continually improving methods since 1829, and the -process has steadily received wider and wider application. It has been -most searchingly investigated in its hygienic relations, and has been -repeatedly found to be a most valuable aid in reducing mortality. The -conditions under which satisfactory results can be obtained are now -tolerably well known, so that filters can be built in the United States -with the utmost confidence that the result will not be disappointing.</p> - -<p>The cost of filtration, although considerable, is not so great as to -put it beyond the reach of American cities. It may be roughly estimated -that the cost of filtration, with all necessary interest and sinking -funds, will add 10 per cent to the average cost of water as at present -supplied.</p> - -<p>It may be confidently expected that when the facts are better -understood and realized by the American public, we shall abandon the -present filthy and unhealthy habit of drinking polluted river and -lake waters, and shall put the quality as well as the quantity of our -supplies upon a level not exceeded by those of any country.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_5">[Pg 5]</span></p> - -<h2 class="nobreak" id="CHAPTER_II">CHAPTER II.<br /> -<br /> - -<span class="smaller">CONTINUOUS FILTERS AND THEIR CONSTRUCTION.</span></h2></div> - -<p><span class="smcap">Filtration</span> of water consists in passing it through some substance -which retains or removes some of its impurities. In its simplest form -filtration is a straining process, and the results obtained depend upon -the fineness of the strainer, and this in turn is regulated by the -character of the water and the uses to which it is to be put. Thus in -the manufacture of paper an enormous volume of water is required free -from particles which, if they should become imbedded in the paper, -would injure its appearance or texture. Obviously for this purpose the -removal of the smaller particles separately invisible to the unaided -eye, and thus not affecting the appearance of the paper, and the -removal of which would require the use of a finer filter at increased -expense, would be a simple waste of money. When, however, a water is -to be used for a domestic water supply and transparency is an object, -the still finer particles which would not show themselves in paper, but -which are still able, in bulk, to render a water turbid, should be as -far as possible removed, thus necessitating a finer filter; and, when -there is reason to think that the water contains the germs of disease, -the filter must be fine enough to remove with certainty those organisms -so extraordinarily small that millions of them may exist in a glass of -water without imparting a visible turbidity.</p> - -<p>It is now something over half a century since the first successful -attempts were made to filter public water-supplies, and there are -now hundreds of cities supplied with clear, healthy, filtered water. -(Appendix IV.) While the details of the filters<span class="pagenum" id="Page_6">[Pg 6]</span> used in different -places present considerable variations, the general form is, in -Europe at least, everywhere the same. The most important parts of a -filter are shown by the accompanying sketch, in which the dimensions -are much exaggerated. The raw water is taken from the river into a -settling-basin, where the heaviest mud is allowed to settle. In the -case of lake and pond waters the settling-tank is dispensed with, but -it is essential for turbid river-water, as otherwise the mud clogs -the filter too rapidly. The partially clarified water then passes to -the filter, which consists of a horizontal layer of rather fine sand -supported by gravel and underdrained, the whole being enclosed in a -suitable basin or tank. The water in passing through the sand leaves -behind upon the sand grains the extremely small particles which were -too fine to settle out in the settling-basin, and is quite clear as it -goes from the gravel to the drains and the pumps, which forward it to -the reservoir or city.</p> - -<div class="figcenter illowp100" id="image006" style="max-width: 101.5em;"> - <img class="w100" src="images/image006.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 1.—Sketch Showing General Arrangement of Filter -Plants.</span></p></div> - -<p class="padt1">The passages between the grains of sand through which the water must -pass are extremely small. If the sand grains were spherical and <sup>1</sup>⁄<sub>50</sub> of -an inch in diameter, the openings would only allow the passage of other -spheres <sup>1</sup>⁄<sub>320</sub> of an inch in diameter, and with actual irregular sands -much finer particles are held back. As a result the coarser matters -in the water are retained on the surface of the sand, where they -quickly form a layer of sediment, which itself becomes a filter much -finer than the sand alone, and which is capable of holding back under -suitable conditions even the bacteria of the passing water. The water -which passes before this takes place may be less perfectly<span class="pagenum" id="Page_7">[Pg 7]</span> filtered, -but even then, the filter may be so operated that nearly all of the -bacteria will be deposited in the sand and not allowed to pass through -into the effluent.</p> - -<p>As the sediment layer increases in thickness with continued filtration, -increased pressure is required to drive the desired volume of water -through its pores, which are ever becoming smaller and reduced in -number. When the required quantity of water will no longer pass with -the maximum pressure allowed, it is necessary to remove, by scraping, -the sediment layer, which should not be more than an inch deep. This -layer contains most of the sediment, and the remaining sand will then -act almost as new sand would do. The sand removed may be washed for use -again, and eventually replaced when the sand layer becomes too thin -by repeated scrapings. These operations require that the filter shall -be temporarily out of use, and as water must in general be supplied -without intermission, a number of filters are built together, so that -any of them can be shut out without interfering with the action of the -others.</p> - -<p>The arrangement of filters in relation to the pumps varies with local -conditions. With gravity supplies the filters are usually located below -the storage reservoir, and, properly placed, involve only a few feet -loss of head.</p> - -<p>In the case of tidal rivers, as at Antwerp and Rotterdam, the quality -of the raw water varies with the tide, and there is a great advantage -in having the settling-basins low enough so that a whole day’s supply -can be rapidly let in when the water is at its best, without pumping. -At Antwerp the filters are higher, and the water is pumped from the -settling basins to them, and again from the reservoir receiving the -effluents from the filters to the city. In several of the London -works (East London, Grand Junction, Southwark and Vauxhall, etc.) the -settling-basins are lower than the river, and the filters are still -lower, so that a single pumping suffices, that coming between the -filter and the city, or elevated distributing reservoir.</p> - -<p><span class="pagenum" id="Page_8">[Pg 8]</span></p> - -<p>In many other English filters and in most German works the -settling-basins and filters are placed together a little higher than -the river, thus avoiding at once trouble from floods and cost for -excavation. The water requires to be pumped twice, once before and once -after filtration. At Altona the settling-basins and filters are placed -upon a hill, to which the raw Elbe water is pumped, and from which it -is supplied to the city after filtration by gravity without further -pumping. The location of the works in this case is said to have been -determined by the location of a bed of sand suitable for filtration on -the spot where the filters were built.</p> - -<p>When two pumpings are required they are frequently done, especially in -the smaller places, in the same pumping-station, with but one set of -boilers and engines, the two pumps being connected to the same engine. -The cost is said to be only slightly greater than that of a single -lift of the same total height. In very large works, as at Berlin and -Hamburg and some of the London companies, two separate sets of pumping -machinery involve less extra cost relatively than would be the case -with smaller works.</p> - -<div class="section"> -<h3 class="nobreak" id="SEDIMENTATION_BASINS">SEDIMENTATION-BASINS.</h3></div> - -<p>Kirkwood<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">[2]</a> found in 1866 that sedimentation-basins were essential -to the successful treatment of turbid river-waters, and subsequent -experience has not in any way shaken his conclusion. The German works -visited by him, Berlin (Stralau) and Altona, were both built by English -engineers, and their settling-basins did not differ materially from -those of corresponding works in England. Since that time, however, -there has been a well-marked tendency on the part of the German -engineers to use smaller, while the English engineers have used much -larger sedimentation-basins, so that the practices of the two countries -are <span class="pagenum" id="Page_9">[Pg 9]</span>now widely separated, the difference no doubt being in part at -least due to local causes.</p> - -<p class="padb1">Kirkwood found sedimentation-basins at Altona with a capacity of -2<sup>1</sup>⁄<sub>4</sub> times the daily supply. In 1894 the same basins were in use, -although the filtering area had been increased from 0.82 acre to 2.20 -acres, and still more filters were in course of construction, and -the average daily quantity of water had increased from 600,000 to -4,150,000 gallons in 1891-2, or more than three times the capacity of -the sedimentation-basins. In 1890 the depth of mud deposited in these -basins was reported to be two feet deep in three months. At Stralau in -Berlin, also, in the same time the filtering area was nearly doubled -without increasing the size of the sedimentation-basins, but the Spree -at this point has such a slow current that it forms itself a natural -sedimentation-basin. At Magdeburg on the Elbe works were built in 1876 -with a filtering area of 1.92 acres, and a sedimentation-basin capacity -of 11,300,000 gallons, but in 1894 half of the latter had been built -over into filters, which with two other filters gave a total filtering -surface of 3.90 acres, with a sedimentation-basin capacity of only -5,650,000 gallons. The daily quantity of water pumped for 1891-2 was -5,000,000 gallons, so that the present sedimentation-basin capacity is -about equal to one day’s supply, or relatively less than a third of the -original provision. The idea followed is that most of the particles -which will settle at all will do so within twenty-four hours, and that -a greater storage capacity may allow the growth of algæ, and that the -water may deteriorate rather than improve in larger tanks.</p> - -<div class="figcenter illowp77" id="facing010_1" style="max-width: 59.9375em;"> - <img class="w100" src="images/facing010_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Paved Embankment between Two Filters, East -London.</span></p></div> - -<div class="figcenter illowp93 padt1" id="facing010_2" style="max-width: 62.3125em;"> - <img class="w100" src="images/facing010_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Filters and Channels for Raw Water, Antwerp.</span></p> - -<p class="right">[<em>To face page 10.</em>]</p></div> - -<p class="padt1">At London, on the other hand, the authorities consider a large storage -capacity for unfiltered water as one of the most important conditions -of successful filtration, the object however, being perhaps as much to -secure storage as to allow sedimentation. In 1893 thirty-nine places -were reported upon the Thames and the Lea which were giving their -sewage systematic treatment before discharging it into the streams -from which London’s<span class="pagenum" id="Page_10">[Pg 10]</span> water is drawn. These sewage treatments are, with -hardly an exception, dry-weather treatments, and as soon as there is -a considerable storm crude sewage is discharged into the rivers at -every point. The rivers are both short, and are quickly flooded, and -afterwards are soon back in their usual condition. At these times of -flood, the raw water is both very turbid and more polluted by sewage -than at other times, and it is the aim of the authorities to have the -water companies provide reservoir capacity enough to carry them through -times of flood without drawing any water whatever from the rivers. This -obviously involves much more extensive reservoirs than those used in -Germany, and the companies actually have large basins and are still -adding to them. The storage capacities of the various companies vary -from 3 to 18 times the respective average daily supplies, and together -equal 9 times the total supply.</p> - -<p>In case the raw water is taken from a lake or a river at a point where -there is but little current, as in a natural or artificial pond, -sedimentation-basins are unnecessary. This is the case at Zürich (lake -water), at Berlin when the rivers Havel and Spree spread into lakes, at -Tegel and Müggel, and at numerous other works.</p> - -<div class="section"> -<h3 class="nobreak" id="SIZE_OF_FILTER_BEDS">SIZE OF FILTER-BEDS.</h3></div> - -<p>The total area of filters required in any case is calculated from the -quantity of water required, the rate of filtration, and an allowance -for filters out of use while being cleaned. To prevent interruptions -of the supply at times of cleaning, the filtering area is divided into -beds which are operated separately, the number and size of the beds -depending upon local conditions. The cost per acre is decreased with -large beds on account of there being less wall or embankment required, -while, on the other hand, the convenience of operation may suffer, -especially in small works. It is also frequently urged that with large -filters it is difficult or impossible to get an even rate of filtration -over the entire area owing<span class="pagenum" id="Page_11">[Pg 11]</span> to the frictional resistance of the -underdrains for the more distant parts of the filter. A discussion of -this point is given in Chapter III, page 41. At Hamburg, where the size -of the single beds, 1.88 acres each, is larger than at any other place, -it is shown that there is no serious cause for anxiety; and even if -there were, the objectionable resistance could be still farther reduced -by a few changes in the under-drains. The sizes of filter-beds used at -a large number of places are given in Appendix IV.</p> - -<p>At a number of places having severe winters, filters are vaulted over -as a protection from cold, and in the most important of these, Berlin, -Warsaw, and St. Petersburg, the areas of the single beds are nearly -the same, namely, from 0.52 to 0.59 acre. The works with open filters -at London (seven companies), Amsterdam, and Breslau have filter-beds -from 0.82 to 1.50 acres each. Liverpool and Hamburg alone use filters -with somewhat larger areas. Large numbers of works with both covered -and open filters have much smaller beds than these sizes, but generally -this is to avoid too small a number of divisions in a small total area, -although such works have sometimes been extended with the growth of the -cities until they now have a considerable number of very small basins.</p> - -<div class="section"> -<h3 class="nobreak" id="FORM_OF_FILTER_BEDS">FORM OF FILTER-BEDS.</h3></div> - -<p>The form and construction of the filter-beds depend upon local -conditions, the foundations, and building materials available, the -principles governing these points being in general the same as for the -construction of ordinary reservoirs. The bottoms require to be made -water-tight, either by a thin layer of concrete or by a pavement upon -a puddle layer. For the sides either masonry walls or embankments are -used, the former saving space, but being in general more expensive in -construction. Embankments must, of course, be substantially paved near -the<span class="pagenum" id="Page_12">[Pg 12]</span> water-line to withstand the action of ice, and must not be injured -by rapid fluctuations in the water-levels in the filters.</p> - -<p>Failure to make the bottoms water-tight has perhaps caused more -annoyance than any other single point. With a leaky bottom there -is either a loss of water when the water in the filters is higher -than the ground-water, or under reverse conditions, the ground-water -comes in and mixes with the filtered water, and the latter is rarely -improved and may be seriously damaged by the admixture. And with very -bad conditions water may pass from one filter to another, with the -differences in pressure always existing in neighboring filters, with -most unsatisfactory results.</p> - -<div class="section"> -<h3 class="nobreak" id="COVERS_FOR_FILTERS">COVERS FOR FILTERS.</h3></div> - -<p>The filters in England and Holland are built open, without protection -from the weather. In Germany the filters first built were also open, -but in the colder climates more or less difficulty was experienced -in keeping the filters in operation in cold weather. An addition to -the Berlin filters, built in 1874, was covered with masonry vaulting, -over which several feet of earth were placed, affording a complete -protection against frost. The filters at Magdeburg built two years -later were covered in the same way, and since that time covered filters -have been built at perhaps a dozen different places.</p> - -<div class="figcenter padt1 padb1 illowp96" id="facing012_1" style="max-width: 96.5em;"> - <img class="w100" src="images/facing012_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Interior View of Covered Filter, Ashland, Wis.</span><br /> - -When in use the water rises nearly to the springing line of the arches.</p></div> - -<div class="figcenter illowp94" id="facing012_2" style="max-width: 96.5em;"> - <img class="w100" src="images/facing012_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Covered Filter in Course of Construction, showing -Wooden Centers for Masonry Vaulting, Somersworth, N. H.</span></p> -<p class="right">[<em>To face page 12.</em>]</p> -</div> - -<p>It was found at Berlin that, owing to the difficulty of properly -cleaning the open filters in winter, it was impossible to keep the -usual proportion of the area in effective service, and as a result -portions of the filters were greatly overtaxed during prolonged -periods of cold weather. This resulted in greatly decreased bacterial -efficiency, the bacteria in March, 1889, reaching 3000 to 4000 per -cc. (with 100,000 in the raw water), although ordinarily the effluent -contained less than 100. An epidemic of typhoid fever followed, and -was confined to that part of the city supplied -<span class="pagenum" id="Page_13">[Pg 13]</span> -from the Stralau works, the wards supplied from the covered Tegel -filters remaining free from fever. Open filters have since been -abandoned in Berlin.</p> - -<p>At Altona also, where the water is taken from an excessively polluted -source, decreased bacterial efficiency has repeatedly resulted in -winter, and the occasional epidemics of typhoid fever in that city, -which have invariably come in winter, appear to have been directly due -to the effect of cold upon the open filters. The city has just extended -the open filters, and hopes with an increased reserve area to avoid -the difficulty in future without resource to covered filters. (See -Appendices II and VII.)</p> - -<p>Brunswick, Lübeck, and Frankfort on Oder with cold winters have open -filters, but draw their water-supplies from less polluted sources, and -have thus far escaped the fate of Berlin and Altona. The new filters -at Hamburg also are open. At Zürich, where open and covered filters -were long used side by side, the covered filters were much more -satisfactory, and the old open filters have recently been vaulted over.</p> - -<p>Königsberg originally built open filters, but was afterward obliged to -cover them, on account of the severe winters; and at Breslau, where -open filters have long been used, the recent additions are vaulted over.</p> - -<p>The fact that inferior efficiency of filtration results with open -filters during prolonged and severe winter weather is generally -admitted, although there is some doubt as to the exact way in which -the disturbance is caused. In some works I am informed that in cutting -the ice around the edges of the filter and repeatedly piling the -loose pieces upon the floating cake, the latter eventually becomes so -thickened at the sides that the projecting lower corners actually touch -the sand, with the fluctuating levels which often prevail in these -works, and that in this way the sediment layer upon the top of the sand -is broken and the water rapidly passes without adequate purification at -the points of disturbance.</p> - -<p><span class="pagenum" id="Page_14">[Pg 14]</span></p> - -<p>This theory is, however, inadequate to account for many cases where -such an accumulation of ice is not allowed. In these cases the poor -work is not obtained until after the filters have been scraped. The -sand apparently freezes slightly while the water is off, and when water -is brought back and filtration resumed, normal results are for some -reason not again obtained for a time.</p> - -<p>In addition to the poorer work from open filters in cold weather, the -cost of removing the ice adds materially to the operating expenses, and -in very cold climates would in itself make covers advisable.</p> - -<p>I have arranged the European filter plants, in regard to which I have -sufficient information, in the table on page 15, in the order of the -normal mean January temperatures of the respective places. This may not -be an ideal criterion of the necessity of covering filters, but it is -at least approximate, and in the absence of more detailed comparisons -it will serve to give a good general idea of the case. I have not -found a single case where covered filters are used where the January -temperature is 32° F. or above. In some of these places some trouble is -experienced in unusually cold weather, but I have not heard of any very -serious difficulty or of any talk of covering filters at these places -except at Rotterdam, where a project for covering was being discussed.</p> - -<p>Those places having January temperatures below 30° experience a great -deal of difficulty with open filters; so much so, that covered filters -may be regarded as necessary for them, although it is possible to keep -open filters running with decreased efficiency and increased expense by -freely removing the ice, with January temperatures some degrees lower.</p> - -<p class="padb1">Where the mean January temperature is 30° to 32° F. there is room for -doubt as to the necessity of covering filters, but, judging from the -experience of Berlin and Altona, the covered filters are much safer at -this temperature.</p> - -<p><span class="pagenum" id="Page_15">[Pg 15]</span></p> - -<table class="autotable" summary="places having open and covered filters"> -<tr> -<th class="tdc normal padt1" colspan="3">TABLE OF PLACES HAVING OPEN AND COVERED FILTERS.</th> -</tr> -<tr> -<th class="tdc normal small padb1" colspan="3">ARRANGED ACCORDING TO THE MEAN JANUARY TEMPERATURES.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Normal Mean January Temperature.<br />Degrees F.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Place.</th> -<th class="tdc normal small bord_top bord_bot">Kind of Filters and Results.</th> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">37-40°</td> -<td class="tdl vertt bord_right vertb">All English cities</td> -<td class="tdl vertt"><p class="indent">Open filters only are used, and no great -difficulty with ice is experienced.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">33-35°</td> -<td class="tdl vertt bord_right vertb">Cities in Holland</td> -<td class="tdl vertt"><p class="indent">All filters are open, and there is little serious -trouble with ice; but at Amsterdam -and Rotterdam the bacteria in -effluents are said to be higher in winter -than at other times.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">32°</td> -<td class="tdl vertt bord_right vertb">Bremen</td> -<td class="tdl vertt"><p class="indent">Open filters.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">31°</td> -<td class="tdl vertt bord_right vertb">Altona</td> -<td class="tdl vertt"><p class="indent">Much difficulty with ice in open filters -(see Appendices II and VII).</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">31°</td> -<td class="tdl vertt bord_right vertb">Brunswick</td> -<td class="tdl vertt"><p class="indent">Open filters.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">31°</td> -<td class="tdl vertt bord_right vertb">Hamburg</td> -<td class="tdl vertt"><p class="indent">Open filters.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">31°</td> -<td class="tdl vertt bord_right vertb">Lübeck</td> -<td class="tdl vertt"><p class="indent">Open filters.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">31°</td> -<td class="tdl vertt bord_right vertb">Berlin</td> -<td class="tdl vertt"><p class="indent">Open filters were formerly used, but owing -to decreased efficiency in cold weather -they have been abandoned for covered ones.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">31°</td> -<td class="tdl vertt bord_right vertb">Magdeburg</td> -<td class="tdl vertt"><p class="indent">Covered filters, but a recent addition is -not covered.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">30°</td> -<td class="tdl vertt bord_right vertb">Frankfort on Oder</td> -<td class="tdl vertt"><p class="indent">Open filters.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">30°</td> -<td class="tdl vertt bord_right vertb">Stuttgart</td> -<td class="tdl vertt"><p class="indent">Part of the filters are covered.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">30°</td> -<td class="tdl vertt bord_right vertb">Stettin</td> -<td class="tdl vertt"><p class="indent">Part of the filters are covered.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">29°</td> -<td class="tdl vertt bord_right vertb">Zürich</td> -<td class="tdl vertt"><p class="indent">Covered filters were much the most satisfactory, -and the open ones were covered -in 1894. The raw water has a -temperature of 35°.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">29°</td> -<td class="tdl vertt bord_right vertb">Liegnitz</td> -<td class="tdl vertt"><p class="indent">Open filters.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">29°</td> -<td class="tdl vertt bord_right vertb">Breslau</td> -<td class="tdl vertt"><p class="indent">Open filters have been used, but recent -additions are covered.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">29°</td> -<td class="tdl vertt bord_right vertb">Budapest</td> -<td class="tdl vertt"><p class="indent">Covered filters only.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">29°</td> -<td class="tdl vertt bord_right vertb">Posen</td> -<td class="tdl vertt"><p class="indent">Covered filters only.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">26°</td> -<td class="tdl vertt bord_right vertb">Königsberg</td> -<td class="tdl vertt"><p class="indent">The original filters were open, but it was -found necessary to cover them.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right vertb">24°</td> -<td class="tdl vertt bord_right vertb">Warsaw</td> -<td class="tdl vertt"><p class="indent">Covered filters only.</p></td> -</tr> -<tr> -<td class="tdc vertt bord_right bord_bot">16°</td> -<td class="tdl vertt bord_right bord_bot">St. Petersburg</td> -<td class="tdl vertt bord_bot"><p class="indent">Covered filters only.</p></td> -</tr> -</table> - -<p class="padt1">In case the raw water was drawn from a lake at a depth where its -minimum temperature was above 32°, which is the temperature which must -ordinarily be expected in surface-waters in winter, open filters might -be successfully used in slightly colder places.</p> - -<p>The covers are usually of brick or concrete vaulting supported<span class="pagenum" id="Page_16">[Pg 16]</span> by -pillars at distances of 11 to 15 feet in each direction, the whole -being covered by 2 or 3 feet of earth; and the top can be laid out as -a garden if desired. Small holes for the admission of air and light -are usually left at intervals. The thickness of the masonry and the -sizes of the pillars used in some of the earlier German vaultings are -unnecessarily great, and some of the newer works are much lighter. For -American use, vaulting like that used for the Newton, Mass., covered -reservoir<a id="FNanchor_3" href="#Footnote_3" class="fnanchor">[3]</a> should be amply strong.</p> - -<p>Roofs have been used at Königsberg, Posen, and Budapest instead of -the masonry vaulting. They are cheaper, but do not afford as good -protection against frost, and even with great care some ice will form -under them.</p> - -<p>Provision must be made for entering the filters freely to introduce and -remove sand. This is usually accomplished by raising one section of -vaulting and building a permanent incline under it from the sand line -to a door above the high-water line in the filter.</p> - -<p>The cost of building covered filters is said to average fully one half -more than open filters.</p> - -<p>Among the incidental advantages of covered filters is that with the -comparative darkness there is no tendency to algæ growths on the -filters in summer, and the frequency of scraping is therefore somewhat -reduced. At Zürich, in 1892, where both covered and open filters were -in use side by side, the periods between scrapings averaged a third -longer in the covered than in the open filters.</p> - -<p>It has been supposed that covered filters kept the water cool in summer -and warm in winter, but owing to the large volume of water passing, the -change in temperature in any case is very slight; Frühling found that -even in extreme cases a change of over 3° F. in either direction is -rarely observed.</p> - -<div class="figcenter padt1 padb1 illowp100" id="facing016" style="max-width: 125em;"> - <img class="w100" src="images/facing016.jpg" alt="" /> - <p class="caption"><span class="smcap">Removing Ice from a Filter, East London.</span><br /> - -This represents the greatest accumulation of ice in the history of the -works.</p> -<p class="right">[<em>To face page 16.</em>]</p> -</div> - -<p><span class="pagenum" id="Page_17">[Pg 17]</span></p> - -<p>At Berlin, where open and covered filters were used side by side at -Stralau for twenty years, it was found that, bacterially, the open -filters were, except in severe winter weather, more efficient. It was -long supposed that this was caused by the sterilizing action of the -sunlight upon the water in the open filters. This result, however, was -not confirmed elsewhere, and it was finally discovered, in 1893, that -the higher numbers were due to the existence of passages in corners -on the columns of the vaulted roof and around the ventilators for the -underdrains, through which, practically, unfiltered water found its -way into the effluent. This at once removes the evidence in favor of -the superior bacterial efficiency of open filters and suggests the -necessity of preventing such passages. The construction of a ledge all -around the walls and pillars four inches wide and a little above the -gravel, as shown in the sketch, might be useful in this way, and the -slight lateral movement of the water in the sand above would be of no -consequence. The sand would evidently make a closer joint with the -horizontal ledge than with the vertical wall.</p> - -<div class="figcenter padt1 padb1 illowp67" id="image017" style="max-width: 51.9375em;"> - <img class="w100" src="images/image017.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 2.</span></p></div> - -<p>In regard to the probable requirement or advisability of covers for -filters in the United States, I judge, from the European experience, -that places having January temperatures below the freezing-point will -have considerable trouble from open filters, and would best have -covered filters. Places having higher winter temperatures will be -able to get along with the ice which may form on open filters, and -the construction of covers would hardly be advisable except under -exceptional local conditions, as, for instance, with a water with an -unusual tendency to algæ growths.</p> - -<p><span class="pagenum" id="Page_18">[Pg 18]</span></p> - -<p>I have drawn a line across a map of the United States on this basis -(shown by the accompanying plate) and it would appear that places far -north of the line would require covered filters, and that those south -of it would not, while for the places in the immediate vicinity of the -line (comparable to Hamburg and Altona) there is room for discussion.</p> - -<p>In the United States covered filters have been constructed at St. -Johnsbury, Vt., Somersworth, N. H., Albany, N. Y., Ashland, Wis., and -Grand Forks, N. Dak., all of these places being considerably north of -the above-mentioned line.</p> - -<p>The filter at Lawrence, Mass., with a mean January temperature of -about 25°, is not covered, but serious difficulty and expense have -been experienced at times from the ice, so much so that it has been -repeatedly recommended to cover it. Open filters have also been in use -for many years at Hudson and Poughkeepsie, N. Y., with mean January -temperatures about 24°; and although considerable difficulty has been -experienced from ice at times, these filters, particularly the ones -at Poughkeepsie, have been kept in very serviceable condition at all -times, notwithstanding the ice.</p> - -<p>At Mount Vernon, N. Y., with a mean January temperature of about -31°, and with a reservoir water, no serious difficulty has been -experienced with ice; and at Far Rockaway, L. I., with a slightly -higher temperature and well-water, no difficulty whatever has been -experienced with open filters. Filters at Ilion, N. Y., with a mean -January temperature of about 23°, are not covered, and are fed from a -reservoir. No serious difficulty has been experienced with ice, which -is probably due to the fact that the water applied to them is taken -from near the bottom of the reservoir, and ordinarily has a temperature -somewhat above the freezing-point throughout the winter.</p> - -<div class="figcenter padt1 padb1 illowp100" id="facing019" style="max-width: 125em;"> - <img class="w100" src="images/facing019.jpg" alt="" /> - <p class="caption">Map showing<br /> - -<span class="sans large">Normal Mean January Temperatures</span><br /> - -<span class="smcap sans">in the United States</span><br /> - -<span class="sans">and the Area in which Filters should be covered</span></p></div> - -<p>The cost of removing ice from filters depends, among other things, -upon the amount of reserve filter area. When this reserve is small -the filters must be kept constantly at work nearly up to their rated -capacity; the ice must be removed promptly whenever<span class="pagenum" id="Page_19">[Pg 19]</span> the filters -require cleaning, and under some conditions the expense of doing this -may be considerable. If, on the other hand, there is a considerable -reserve area, so that when a filter becomes clogged in severe weather, -the work can be turned upon other filters and the clogged filter -allowed to remain until more moderate weather, or until a thaw, the -expense of ice removal may be kept at a materially lower figure.</p> - -<p>In case open filters are built near or north of this line, I would -suggest that plenty of space between and around the filters for piling -up ice in case of necessity may be found advantageous, and that a -greater reserve of filtering area for use in emergencies should be -provided than would be considered necessary with vaulted filters or -with open filters in a warmer climate.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_20">[Pg 20]</span></p> - -<h2 class="nobreak" id="CHAPTER_III">CHAPTER III.<br /> -<br /> - -<span class="smaller">FILTERING MATERIALS.</span></h2></div> - -<div class="section"> -<h3 class="nobreak" id="SAND">SAND.</h3></div> - -<p><span class="smcap">The</span> sand used for filtration may be obtained from the sea-shore, from -river-beds or from sand-banks. It consists mainly of sharp quartz -grains, but may also contain hard silicates. As it occurs in nature it -is frequently mixed with clayey or other fine particles, which must be -removed from it by washing before it is used. Some of the New England -sands, however, as that used for the Lawrence City filter, are so clean -that washing would be superfluous.</p> - -<p>The grain size of the sand best adapted to filtration has been -variously stated at from <sup>1</sup>⁄<sub>8</sub> to 1 mm., or from 0.013 to 0.040 inch. -The variations in the figures, however, are due more to the way that -the same sand appears to different observers than to actual variations -in the size of sands used, which are but a small fraction of those -indicated by these figures.</p> - -<p>As a result of experiments made at the Lawrence Experiment Station<a id="FNanchor_4" href="#Footnote_4" class="fnanchor">[4]</a> -we have a standard by which we can definitely compare various sands. -The size of a sand-grain is uniformly taken as the diameter of a sphere -of equal volume, regardless of its shape. As a result of numerous -measurements of grains of Lawrence sands, it is found that when the -diameter, as given above, is 1, the three axes of the grain, selecting -the longest possible and taking the other two at right angles to it, -are, on an average, 1.38, 1.05, and 0.69, respectively and the mean -diameter is equal to the cube root of their product.</p> - -<p><span class="pagenum" id="Page_21">[Pg 21]</span></p> - -<p>It was also found that in mixed materials containing particles of -various sizes the water is forced to go around the larger particles and -through the finer portions which occupy the intervening spaces, so that -it is the finest portion which mainly determines the character of the -sand for filtration. As a provisional basis which best accounts for the -known facts, the size of grain such that 10 per cent by weight of the -particles are smaller and 90 per cent larger than itself, is considered -to be the <em>effective size</em>. The size so calculated is uniformly -referred to in speaking of the size of grain in this work.</p> - -<div class="figcenter padb1 illowp66" id="image021" style="max-width: 25em;"> - <img class="w100" src="images/image021.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 3.—Apparatus Used for Measuring the Friction of -Water in Sands.</span></p></div> - -<p>Another important point in regard to a material is its degree of -uniformity—whether the particles are mainly of the same size or whether -there is a great range in their diameters. This is shown by the -<em>uniformity coefficient</em>, a term used to designate the ratio of -the size of the grain which has 60 per cent of the sample finer than -itself to the size which has 10 per cent finer than itself.</p> - -<p><span class="pagenum" id="Page_22">[Pg 22]</span></p> - -<p>The frictional resistance of sand to water when closely packed, with -the pores completely filled with water and in the entire absence of -clogging, was found to be expressed by the formula</p> - -<p class="center padt1 padb1"> -<em>v</em> = <em>cd</em><sup>2</sup>(<em>h</em>/<em>l</em>)(<em>t</em> Fah. + 10°)/60, -</p> - -<p class="indent6">where <em>v</em> is the velocity of the water in meters daily in a solid column -of the same area as that of the sand, or approximately in -million gallons per acre daily;</p> -<p><span class="add2em"><em>c</em> is an approximately constant factor;</span><br /> -<span class="add3em"><em>d</em> is the effective size of sand grain in millimeters;</span><br /> -<span class="add3em"><em>h</em> is the loss of head (Fig. 3);</span><br /> -<span class="add3em"><em>l</em> is the thickness of sand through which the water passes;</span><br /> -<span class="add3em"><em>t</em> is the temperature (Fahr.).</span></p> - -<table class="autotable" summary=""> -<tr> -<th class="tdc normal" colspan="9">TABLE SHOWING RATE AT WHICH WATER WILL PASS THROUGH EVEN-GRAINED AND -CLEAN SANDS OF THE STATED GRAIN SIZES AND WITH VARIOUS HEADS AT A -TEMPERATURE OF 50°.</th> -</tr> -<tr> -<th class="tdc normal bord_top bord_right bord_bot" rowspan="2"><span class="u"><em>h</em></span><br /><em>l</em></th> -<td class="tdc normal bord_top bord_bot" colspan="8">Effective Size in Millimeters 10 per cent finer than:</td> -</tr> -<tr> -<td class="tdc bord_right bord_bot">0.10</td> -<td class="tdc bord_right bord_bot">0.20</td> -<td class="tdc bord_right bord_bot">0.30</td> -<td class="tdc bord_right bord_bot">0.35</td> -<td class="tdc bord_right bord_bot">0.40</td> -<td class="tdc bord_right bord_bot">0.50</td> -<td class="tdc bord_right bord_bot">1.00</td> -<td class="tdc bord_bot">3.00</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb"> </td> -<td class="tdc" colspan="8">Million Gallons per Acre daily.</td> -</tr> -<tr> -<td class="tdr vertt bord_right vertb">.001</td> -<td class="tdr vertt bord_right vertb">.01</td> -<td class="tdr vertt bord_right vertb">.04</td> -<td class="tdr vertt bord_right vertb">.10</td> -<td class="tdr vertt bord_right vertb">.13</td> -<td class="tdr vertt bord_right vertb">.17</td> -<td class="tdr vertt bord_right vertb">.27</td> -<td class="tdr vertt bord_right vertb">1.07</td> -<td class="tdr vertt">9.63</td> -</tr> -<tr> -<td class="tdr vertt bord_right vertb">.005</td> -<td class="tdr vertt bord_right vertb">.05</td> -<td class="tdr vertt bord_right vertb">.21</td> -<td class="tdr vertt bord_right vertb">.48</td> -<td class="tdr vertt bord_right vertb">.65</td> -<td class="tdr vertt bord_right vertb">.85</td> -<td class="tdr vertt bord_right vertb">1.34</td> -<td class="tdr vertt bord_right vertb">5.35</td> -<td class="tdr vertt">48.15</td> -</tr> -<tr> -<td class="tdr vertt bord_right vertb">.010</td> -<td class="tdr vertt bord_right vertb">.11</td> -<td class="tdr vertt bord_right vertb">.43</td> -<td class="tdr vertt bord_right vertb">.96</td> -<td class="tdr vertt bord_right vertb">1.31</td> -<td class="tdr vertt bord_right vertb">1.71</td> -<td class="tdr vertt bord_right vertb">2.67</td> -<td class="tdr vertt bord_right vertb">10.70</td> -<td class="tdr vertt">96.30</td> -</tr> -<tr> -<td class="tdr vertt bord_right vertb">.050</td> -<td class="tdr vertt bord_right vertb">.54</td> -<td class="tdr vertt bord_right vertb">2.14</td> -<td class="tdr vertt bord_right vertb">4.82</td> -<td class="tdr vertt bord_right vertb">6.55</td> -<td class="tdr vertt bord_right vertb">8.55</td> -<td class="tdr vertt bord_right vertb">13.40</td> -<td class="tdr vertt bord_right vertb">53.50</td> -<td class="tdr vertt"> </td> -</tr> -<tr> -<td class="tdr vertt bord_right vertb">.100</td> -<td class="tdr vertt bord_right vertb">1.07</td> -<td class="tdr vertt bord_right vertb">4.28</td> -<td class="tdr vertt bord_right vertb">9.63</td> -<td class="tdr vertt bord_right vertb">13.10</td> -<td class="tdr vertt bord_right vertb">17.10</td> -<td class="tdr vertt bord_right vertb">26.70</td> -<td class="tdr vertt bord_right vertb">107.00</td> -<td class="tdr vertt"> </td> -</tr> -<tr> -<td class="tdr bord_right bord_bot">1.000</td> -<td class="tdr bord_right bord_bot">10.70</td> -<td class="tdr bord_right bord_bot">42.80</td> -<td class="tdr bord_right bord_bot">96.30</td> -<td class="tdr bord_right bord_bot">131.00</td> -<td class="tdr bord_right bord_bot">171.00</td> -<td class="tdr bord_right bord_bot">267.00</td> -<td class="tdr bord_right bord_bot"> </td> -<td class="tdr bord_bot"> </td> -</tr> -</table> - -<p class="padt1">The above table is computed with the value <em>c</em> taken as 1000, this -being approximately the values deduced from the earliest experiments. -More recent and extended data have shown that the value of <em>c</em> is -not entirely constant, but depends upon the uniformity coefficient, -upon the shape of the sand grains, upon their chemical composition, and -upon the cleanliness and closeness of packing of the sand. The value -may be as high as 1200 for very uniform, and perfectly clean sand, and -maybe as low as 400<span class="pagenum" id="Page_23">[Pg 23]</span> for very closely packed sands containing a good -deal of alumina or iron, and especially if they are not quite clean. -The friction is usually less in new sand than in sand which has been in -use for some years. In making computations of the frictional resistance -of filters, the average value of <em>c</em> may be taken at from 700 to -1000 for new sand, and from 500 to 700 for sand which has been in use -for a number of years.</p> - -<p>The value of <em>c</em> decreases as the uniformity coefficient -increases. With ordinary filter sands with uniformity coefficients -of 3 or less the differences are not great. With mixed sands having -much higher uniformity coefficients, lower and less constant values of -<em>c</em> are obtained, and the arrangement of the particles becomes a -controlling factor in the increase in friction.</p> - -<p>The friction of the surface layer of a filter is often greater than -that of all the sand below the surface. It must be separately computed -and added to the resistances computed by the formula, as it depends -largely upon other conditions than those controlling the resistance of -the sand.</p> - -<p>While the value of <em>c</em> is thus not entirely constant, it can be -estimated with approximate accuracy for various conditions, from a -knowledge of the composition, condition, and cleanliness of the sand, -and closeness of packing.</p> - -<p>The following table shows the quantity of water passing sands at -different temperatures. This table was computed with temperature -factors as given above, which were based upon experiments upon the -flow of water through sands, checked by the coefficients obtained from -experiments with long capillary tubes entirely submerged in water of -the required temperature.</p> - -<table class="autotable" summary=""> -<tr> -<th class="tdc normal" colspan="2">RELATIVE QUANTITIES OF WATER PASSING AT DIFFERENT TEMPERATURES.</th> -</tr> -<tr> -<td class="tdr vertb">32°</td> -<td class="tdl vertb">0.70</td> -</tr> -<tr> -<td class="tdr vertb">35°</td> -<td class="tdl vertb">0.75</td> -</tr> -<tr> -<td class="tdr vertb">38°</td> -<td class="tdl vertb">0.80</td> -</tr> -<tr> -<td class="tdr vertb">41°</td> -<td class="tdl vertb">0.85</td> -</tr> -<tr> -<td class="tdr vertb">44°</td> -<td class="tdl vertb">0.90</td> -</tr> -<tr> -<td class="tdr vertb">47°</td> -<td class="tdl vertb">0.95</td> -</tr> -<tr> -<td class="tdr vertb">50°</td> -<td class="tdl vertb">1.00</td> -</tr> -<tr> -<td class="tdr vertb">53°</td> -<td class="tdl vertb">1.05</td> -</tr> -<tr> -<td class="tdr vertb">56°</td> -<td class="tdl vertb">1.10</td> -</tr> -<tr> -<td class="tdr vertb">59°</td> -<td class="tdl vertb">1.15</td> -</tr> -<tr> -<td class="tdr vertb">62°</td> -<td class="tdl vertb">1.20</td> -</tr> -<tr> -<td class="tdr vertb">65°</td> -<td class="tdl vertb">1.25</td> -</tr> -<tr> -<td class="tdr vertb">68°</td> -<td class="tdl vertb">1.30</td> -</tr> -<tr> -<td class="tdr vertb">71°</td> -<td class="tdl vertb">1.35</td> -</tr> -<tr> -<td class="tdr vertb">74°</td> -<td class="tdl vertb">1.40</td> -</tr> -<tr> -<td class="tdr vertb">77°</td> -<td class="tdl vertb">1.45</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_24">[Pg 24]</span></p> - -<p>The effect of temperature upon the passage of water through sands -and soils has been further discussed by Prof. L. G. Carpenter, -<cite>Engineering News</cite>, Vol. <span class="allsmcap">XXXIX</span>, p. 422. This article -reviews briefly the literature of the subject, and refers at length to -the formula of Poiseuille, published in the <cite>Memoires des Savants -Etrangers</cite>, Vol. <span class="allsmcap">XI</span>, p. 433 (1846). This formula, in which -the quantity of water passing at 0.0° Cent., is taken as unity, is as -follows:</p> - -<p class="center padt1 padb1"> -Temperature factor = 1 + 0.033679<em>t</em> + 0.000221<em>t</em><sup>2</sup>. -</p> - -<p>The results obtained by this formula agree very closely with those -given in the above table throughout the temperature range for -which computations are most frequently required. At the higher and -lower temperatures the divergencies are greater, as is shown in a -communication in the <cite>Engineering News</cite>, Vol. <span class="allsmcap">XL</span>, p. 26.</p> - -<p>The quantity of water passing at a temperature of 50° Fahr. is in many -respects more convenient as a standard than the quantity passing at the -freezing-point. Near the freezing-point, owing to molecular changes in -the water, the changes in its action are rapid, and the results are -less certain, and also 50° Fahr. is a much more convenient temperature -for precise experiments than is the freezing point.</p> - - -<div class="section"> -<h3 class="nobreak" id="SANDS_USED_IN_EUROPEAN_FILTERS">SANDS USED IN EUROPEAN FILTERS.</h3></div> - -<p>To secure definite information in regard to the qualities of the sands -actually used in filtration, a large number of European works were -visited in 1894, and samples of sand were collected for analysis. These -samples were examined at the Lawrence Experiment Station by Mr. H. W. -Clark, the author’s method of analysis described in Appendix III being -used. In the following table, for the sake of compactness, only the -leading points of the analyses, namely, effective size, uniformity -coefficient, and albuminoid ammonia, are given. On page 28 full -analyses of some samples from a few of the leading works are given.</p> - -<p><span class="pagenum" id="Page_25">[Pg 25]</span></p> - -<table class="autotable" summary="analyses of sands used in water filtration"> -<tr> -<th class="tdc normal" colspan="5">ANALYSES OF SANDS USED IN WATER FILTRATION.</th> -</tr> -<tr> -<th class="tdc normal bord_top bord_right bord_bot">Source.</th> -<th class="tdc normal bord_top bord_right bord_bot">Effective<br />Size; 10% Finer<br />than<br />(Milli-<br />meters).</th> -<th class="tdc normal bord_top bord_right bord_bot">Uni-<br />formity<br />Coeffi-cient.</th> -<th class="tdc normal bord_top bord_right bord_bot">Albu-<br />minoid<br />Ammo-<br />ia.<br />Parts in<br />100,000.</th> -<th class="tdc normal bord_top bord_bot">Remarks.</th> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, E. London Co.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.44</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.8</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.45</span></td> -<td class="tdl vertt"><p class="indent">New sand, never used or washed.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, E. London Co.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.39</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">26.20</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand, very old.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, E. London Co.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.37</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">8.60</span></td> -<td class="tdl vertt"><p class="indent">Same, washed by hand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Grand Junc.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.26</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.9</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.90</span></td> -<td class="tdl vertt"><p class="indent">Sand from rough filter.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Grand Junc.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.40</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">10.00</span></td> -<td class="tdl vertt"><p class="indent">Old sand in final filter.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Grand Junc.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.41</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.70</span></td> -<td class="tdl vertt"><p class="indent">Freshly washed old sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Southw’k & V.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.38</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">5.00</span></td> -<td class="tdl vertt"><p class="indent">Freshly washed old sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Southw’k & V.</td> -<td class="tdr bord_right vertt"><span class="padr1">0.30</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.8</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.80</span></td> -<td class="tdl vertt"><p class="indent">Freshly washed new sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Lambeth</td> -<td class="tdr bord_right vertt"><span class="padr1">0.36</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.3</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.60</span></td> -<td class="tdl vertt"><p class="indent">Freshly washed old sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Lambeth</td> -<td class="tdr bord_right vertt"><span class="padr1">0.36</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.4</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.35</span></td> -<td class="tdl vertt"><p class="indent">New unused sand, washed.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Lambeth</td> -<td class="tdr bord_right vertt"><span class="padr1">0.25</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.70</span></td> -<td class="tdl vertt"><p class="indent">New extremely fine sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">London, Chelsea</td> -<td class="tdr bord_right vertt"><span class="padr1">0.36</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.4</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.10</span></td> -<td class="tdl vertt"><p class="indent">Freshly washed old sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Middlesborough</td> -<td class="tdr bord_right vertt"><span class="padr1">0.42</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">17.60</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand, ordinary scraping.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Middlesborough</td> -<td class="tdr bord_right vertt"><span class="padr1">0.43</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">7.30</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Birmingham</td> -<td class="tdr bord_right vertt"><span class="padr1">0.29</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.9</span></td> -<td class="tdr bord_right vertt"><span class="padr1">33.20</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Birmingham</td> -<td class="tdr bord_right vertt"><span class="padr1">0.29</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.9</span></td> -<td class="tdr bord_right vertt"><span class="padr1">7.20</span></td> -<td class="tdl vertt"><p class="indent">Sand below surface of filter.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Reading</td> -<td class="tdr bord_right vertt"><span class="padr1">0.30</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">4.00</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Reading</td> -<td class="tdr bord_right vertt"><span class="padr1">0.22</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.50</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Antwerp</td> -<td class="tdr bord_right vertt"><span class="padr1">0.38</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">7.80</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Antwerp</td> -<td class="tdr bord_right vertt"><span class="padr1">0.39</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.40</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Hamburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.28</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">8.50</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Hamburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.31</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.3</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.80</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Hamburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.34</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">7.90</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand, another sample.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Hamburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.30</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.90</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing drums.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Hamburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.34</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.3</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.50</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing ejectors.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Altona</td> -<td class="tdr bord_right vertt"><span class="padr1">0.32</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">9.00</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand, old filters.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Altona</td> -<td class="tdr bord_right vertt"><span class="padr1">0.37</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.50</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Altona</td> -<td class="tdr bord_right vertt"><span class="padr1">0.33</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.8</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.50</span></td> -<td class="tdl vertt"><p class="indent">Washed sand for new filters.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Stralau</td> -<td class="tdr bord_right vertt"><span class="padr1">0.33</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.9</span></td> -<td class="tdr bord_right vertt"><span class="padr1">12.20</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand-pile.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Stralau</td> -<td class="tdr bord_right vertt"><span class="padr1">0.35</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">4.50</span></td> -<td class="tdl vertt"><p class="indent">Filter No. 6, 3″ below surface.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Stralau</td> -<td class="tdr bord_right vertt"><span class="padr1">0.34</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">6.30</span></td> -<td class="tdl vertt"><p class="indent">Filter No. 7 3″ below surface.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Stralau</td> -<td class="tdr bord_right vertt"><span class="padr1">0.35</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">4.00</span></td> -<td class="tdl vertt"><p class="indent">Filter No. 10 3″ below surface.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Tegel</td> -<td class="tdr bord_right vertt"><span class="padr1">0.38</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">11.00</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand, old filters.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Tegel</td> -<td class="tdr bord_right vertt"><span class="padr1">0.38</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.80</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing, old filters.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Tegel</td> -<td class="tdr bord_right vertt"><span class="padr1">0.35</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.20</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing, new filters.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Müggel</td> -<td class="tdr bord_right vertt"><span class="padr1">0.35</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.8</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.80</span></td> -<td class="tdl vertt"><p class="indent">Sand from filters below surface.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Müggel</td> -<td class="tdr bord_right vertt"><span class="padr1">0.33</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">6.30</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand, ordinary scraping.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Berlin, Müggel</td> -<td class="tdr bord_right vertt"><span class="padr1">0.34</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">15.30</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand, another sample.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Charlottenburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.40</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.3</span></td> -<td class="tdr bord_right vertt"><span class="padr1">7.20</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Chemnitz</td> -<td class="tdr bord_right vertt"><span class="padr1">0.35</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.20</span></td> -<td class="tdl vertt"><p class="indent">New sand not yet used.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Magdeburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.39</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">9.50</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Magdeburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.40</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.80</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Breslau</td> -<td class="tdr bord_right vertt"><span class="padr1">0.39</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.8</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.40</span></td> -<td class="tdl vertt"><p class="indent">Normal new sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Budapest</td> -<td class="tdr bord_right vertt"><span class="padr1">0.20</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.80</span></td> -<td class="tdl vertt"><p class="indent">New washed Danube sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Zürich</td> -<td class="tdr bord_right vertt"><span class="padr1">0.28</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">6.20</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Zürich</td> -<td class="tdr bord_right vertt"><span class="padr1">0.30</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.50</span></td> -<td class="tdl vertt"><p class="indent">Same, after washing.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Hague</td> -<td class="tdr bord_right vertt"><span class="padr1">0.19</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.70</span></td> -<td class="tdl vertt"><p class="indent">Dune-sand used for filtration.</p><span class="pagenum" id="Page_26">[Pg 26]</span></td> -</tr> -<tr> -<td class="tdl bord_right vertt">Schiedam</td> -<td class="tdr bord_right vertt"><span class="padr1">0.18</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">5.60</span></td> -<td class="tdl vertt"><p class="indent">Dune-sand used for filtration; dirty.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Schiedam</td> -<td class="tdr bord_right vertt"><span class="padr1">0.31</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">13.50</span></td> -<td class="tdl vertt"><p class="indent">River-sand; dirty.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Amsterdam</td> -<td class="tdr bord_right vertt"><span class="padr1">0.17</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.40</span></td> -<td class="tdl vertt"><p class="indent">Dune-sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Rotterdam</td> -<td class="tdr bord_right vertt"><span class="padr1">0.34</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.30</span></td> -<td class="tdl vertt"><p class="indent">River-sand; new.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Liverpool, Rivington</td> -<td class="tdr bord_right vertt"><span class="padr1">0.43</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.76</span></td> -<td class="tdl vertt"><p class="indent">Sand from bottom of filter.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Liverpool, Rivington</td> -<td class="tdr bord_right vertt"><span class="padr1">0.32</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.00</span></td> -<td class="tdl vertt"><p class="indent">New sand unwashed and unscreened.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Liverpool, Rivington</td> -<td class="tdr bord_right vertt"><span class="padr1">0.43</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">4.10</span></td> -<td class="tdl vertt"><p class="indent">Washed sand which has been in use 30 to 40 years.</p></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Liverpool, Oswestry</td> -<td class="tdr bord_right vertt"><span class="padr1">0.30</span></td> -<td class="tdr bord_right vertt"><span class="padr1">2.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">9.40</span></td> -<td class="tdl vertt"><p class="indent">Dirty sand.</p></td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot vertt">Liverpool, Oswestry</td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">0.31</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">4.7</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">2.20</span></td> -<td class="tdl vertt bord_bot"><p class="indent">Same, after washing.</p></td> -</tr> -</table> - -<div class="blockquot"> - -<p><span class="smcap">Note.</span>—It is obvious that in case the sands used at any place -are not always of the same character, as is shown to be the case by -different samples from some of the works, the examination of such a -limited number of samples as the above from each place is entirely -inadequate to establish accurately the sizes of sand used at that -particular place, or to allow close comparisons between the different -works, and for this reason no such comparisons will be made. The -object of these investigations was to determine the sizes of the sands -commonly used in Europe, and, considering the number and character of -the different works represented, it is believed that the results are -ample for this purpose.</p> -</div> - -<p class="padt1">The English and most of the German sands are washed, even when entirely -new, before being used, to remove fine particles. At Breslau, however, -sand dredged from the river Oder is used in its natural state, and -new sand is used for replacing that removed by scraping. At Budapest, -Danube sand is used in the same way, but with a very crude washing, and -it is said that only new unwashed sand is used at Warsaw.</p> - -<p>In Holland, so far as I learned, no sand is washed, but new sand is -always used for refilling. At most of the works visited dune-sand -with an effective size of only 0.17 to 0.19 mm. is used, and this is -the finest sand which I have ever found used for water filtration on -a large scale. It should be said, however, that the waters filtered -through these fine sands are fairly clear before<span class="pagenum" id="Page_27">[Pg 27]</span> filtration, and are -not comparable to the turbid river-waters often filtered elsewhere, -and their tendency to choke the filters is consequently much less. At -Rotterdam and Schiedam, where the raw water is drawn from the Maas, as -the principal stream of the Rhine is called in Holland, river-sand of -much larger grain size is employed. It is obtained by dredging in the -river and is never washed, new sand always being employed for refilling.</p> - -<p>The average results of the complete analyses of sands from ten leading -works are shown in the table on page 28. These figures are the average -of all the analyses for the respective places, except that one sample -from the Lambeth Co., which was not a representative one, was omitted.</p> - -<p>The London companies were selected for this comparison both on -account of their long and favorable records in filtering the polluted -waters of the Thames and Lea, and because they are subject to close -inspection; and there is ample evidence that the filtration obtained is -good—evidence which is often lacking in the smaller and less closely -watched works. For the German works Altona was selected because of -its escape from cholera in 1892, due to the efficient action of its -filters, and Stralau because of its long and favorable record when -filtering the much-polluted Spree water. These two works also have -perhaps contributed more to the modern theories of filtration than all -the other works in existence. The remaining works are included because -they are comparatively new, and have been constructed with the greatest -care and attention to details throughout, and the results obtained are -most carefully recorded.</p> - -<p class="padb1">Some of the most interesting of these results are shown graphically on -page 29. The method of plotting is that described in Appendix III.</p> - -<p><span class="pagenum" id="Page_28">[Pg 28]</span></p> - -<table class="autotable" summary="average per cent of grains finer than various sizes in sands from leading works"> -<tr> -<th class="tdc normal" colspan="9">TABLE SHOWING THE AVERAGE PER CENT OF THE GRAINS FINER THAN VARIOUS SIZES IN SANDS FROM LEADING WORKS.</th> -</tr> -<tr> -<th class="tdc normal bord_top bord_right bord_bot" rowspan="2"> </th> -<th class="tdc normal smaller bord_top bord_bot" colspan="8">Per Cent by Weight Finer than</th> -</tr> -<tr> -<th class="tdc normal smaller bord_top bord_right bord_bot">0.106<br />mm.</th> -<th class="tdc normal smaller bord_top bord_right bord_bot">0.186<br />mm.</th> -<th class="tdc normal smaller bord_top bord_right bord_bot">0.316<br />mm.</th> -<th class="tdc normal smaller bord_top bord_right bord_bot">0.46<br />mm.</th> -<th class="tdc normal smaller bord_top bord_right bord_bot">0.93<br />mm.</th> -<th class="tdc normal smaller bord_top bord_right bord_bot">2.04<br />mm.</th> -<th class="tdc normal smaller bord_top bord_right bord_bot">3.89<br />mm.</th> -<th class="tdc normal smaller bord_top bord_bot">5.89<br />mm.</th> -</tr> -<tr> -<td class="tdl bord_right vertt">East London</td> -<td class="tdr bord_right vertt"><span class="padr1">0.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">22.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">69.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">89.8</span></td> -<td class="tdr bord_right vertt"><span class="padr1">95.0</span></td> -<td class="tdr vertt"><span class="padr1">99.0</span></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Grand Junction</td> -<td class="tdr bord_right vertt"><span class="padr1">0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">3.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">17.4</span></td> -<td class="tdr bord_right vertt"><span class="padr1">47.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">68.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">84.7</span></td> -<td class="tdr vertt"><span class="padr1">93.6</span></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Southwark and Vauxhall</td> -<td class="tdr bord_right vertt"><span class="padr1"> </span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">8.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">34.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">69.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">83.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">90.0</span></td> -<td class="tdr vertt"><span class="padr1">94.0</span></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Lambeth</td> -<td class="tdr bord_right vertt"><span class="padr1">0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">5.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">26.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">63.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">79.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">88.0</span></td> -<td class="tdr vertt"><span class="padr1">94.3</span></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Chelsea</td> -<td class="tdr bord_right vertt"><span class="padr1">0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">5.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">28.6</span></td> -<td class="tdr bord_right vertt"><span class="padr1">63.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">76.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">86.0</span></td> -<td class="tdr vertt"><span class="padr1">93.6</span></td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Hamburg</td> -<td class="tdr bord_right vertt"><span class="padr1">0.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">10.9</span></td> -<td class="tdr bord_right vertt"><span class="padr1">33.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">74.4</span></td> -<td class="tdr bord_right vertt"><span class="padr1">95.7</span></td> -<td class="tdr vertt bord_right vertb"><span class="padr1">99.5</span></td> -<td class="tdr vertt"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Altona</td> -<td class="tdr bord_right vertt"><span class="padr1">0.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">1.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">7.8</span></td> -<td class="tdr bord_right vertt"><span class="padr1">28.7</span></td> -<td class="tdr bord_right vertt"><span class="padr1">72.1</span></td> -<td class="tdr bord_right vertt"><span class="padr1">92.1</span></td> -<td class="tdr vertt bord_right vertb"><span class="padr1">95.8</span></td> -<td class="tdr vertt"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Stralau</td> -<td class="tdr bord_right vertt"><span class="padr1"> </span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.3</span></td> -<td class="tdr bord_right vertt"><span class="padr1">7.0</span></td> -<td class="tdr bord_right vertt"><span class="padr1">37.3</span></td> -<td class="tdr bord_right vertt"><span class="padr1">86.9</span></td> -<td class="tdr bord_right vertt"><span class="padr1">95.4</span></td> -<td class="tdr vertt bord_right vertb"><span class="padr1">97.6</span></td> -<td class="tdr vertt"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Tegel</td> -<td class="tdr bord_right vertt"><span class="padr1"> </span></td> -<td class="tdr bord_right vertt"><span class="padr1">0.2</span></td> -<td class="tdr bord_right vertt"><span class="padr1">4.5</span></td> -<td class="tdr bord_right vertt"><span class="padr1">35.4</span></td> -<td class="tdr bord_right vertt"><span class="padr1">94.3</span></td> -<td class="tdr bord_right vertt"><span class="padr1">98.5</span></td> -<td class="tdr vertt tdr bord_right vertb"><span class="padr1">99.1</span></td> -<td class="tdr vertt"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Müggel</td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">0.1</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">0.5</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">7.9</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">33.6</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">79.7</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">94.3</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">98.5</span></td> -<td class="tdr bord_bot"> </td> -</tr> -<tr> -<td class="tdl bord_right bord_bot vertt"><p class="indent"><span class="add1em">Average of all</span></p></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">0.06</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">0.56</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">6.33</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">29.71</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">71.99</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">87.34</span></td> -<td class="tdr bord_right bord_bot vertt"><span class="padr1">93.42</span></td> -<td class="tdr bord_bot vertt"><span class="padr1">(97.45)</span></td> -</tr> -</table> - -<table class="autotable" summary="properties of sands from ten leading works"> -<tr> -<th class="tdc normal large" colspan="5"> <br />AVERAGE EFFECTIVE SIZE, UNIFORMITY COEFFICIENT, -AND ALBUMINOID AMMONIA IN SANDS FROM TEN LEADING WORKS.</th> -</tr> -<tr> -<th class="tdc normal" colspan="5">I. LONDON FILTERS.</th> -</tr> -<tr> -<th class="tdc normal bord_top bord_right bord_bot" rowspan="2"> </th> -<th class="tdc normal smallest bord_top bord_right bord_bot" rowspan="2">Effective<br />Size; 10%<br />Finer than<br />(Millimeters).</th> -<th class="tdc normal smallest bord_top bord_right bord_bot" rowspan="2">Uniformity<br />Coefficient.</th> -<th class="tdc normal smallest bord_top bord_bot" colspan="2">Albuminoid Ammonia.</th> -</tr> -<tr> -<th class="tdc normal smallest bord_top bord_right bord_bot">Dirty Sand.</th> -<th class="tdc normal smallest bord_top bord_bot">Washed Sand.</th> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">East London</td> -<td class="tdc bord_right vertb">0.40</td> -<td class="tdc bord_right vertb">2.0</td> -<td class="tdc bord_right vertb">26.00</td> -<td class="tdc">8.60</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Grand Junction</td> -<td class="tdc bord_right vertb">0.40</td> -<td class="tdc bord_right vertb">3.6</td> -<td class="tdc bord_right vertb">10.00</td> -<td class="tdc">2.70</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Southwark and Vauxhall</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">2.5</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc">3.90</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Lambeth</td> -<td class="tdc bord_right vertb">0.36</td> -<td class="tdc bord_right vertb">2.4</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc">2.60</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Chelsea</td> -<td class="tdc bord_right vertb">0.36</td> -<td class="tdc bord_right vertb">2.4</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc">2.10</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb"> Average</td> -<td class="tdc bord_right bord_top">0.37</td> -<td class="tdc bord_right bord_top">2.6</td> -<td class="tdc bord_right bord_top">18.00</td> -<td class="tdc bord_top">3.98</td> -</tr> -<tr> -<th class="tdc normal bord_top bord_bot" colspan="5"> <br />II. GERMAN WORKS.</th> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Stralau</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">1.7</td> -<td class="tdc bord_right vertb">12.20</td> -<td class="tdc">4.00</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Tegel</td> -<td class="tdc bord_right vertb">0.37</td> -<td class="tdc bord_right vertb">1.6</td> -<td class="tdc bord_right vertb">11.00</td> -<td class="tdc">3.00</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Müggel</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">2.0</td> -<td class="tdc bord_right vertb">10.80</td> -<td class="tdc">0.80</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Altona</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">2.3</td> -<td class="tdc bord_right vertb">9.00</td> -<td class="tdc">1.50</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Hamburg</td> -<td class="tdc bord_right vertb">0.31</td> -<td class="tdc bord_right vertb">2.3</td> -<td class="tdc bord_right vertb">8.20</td> -<td class="tdc">1.07</td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot"> Average</td> -<td class="tdc bord_right bord_bot bord_top">0.34</td> -<td class="tdc bord_right bord_bot bord_top">2.0</td> -<td class="tdc bord_right bord_bot bord_top">10.25</td> -<td class="tdc bord_bot bord_top">2.07</td> -</tr> -</table> - -<div class="figcenter padt1 padb1 illowp100" id="facing028" style="max-width: 125em;"> - <img class="w100" src="images/facing028.jpg" alt="" /> - <p class="caption"><span class="smcap">Placing Sand in a Filter, Hamburg.</span></p> - -<p class="right">[<em>To face page 28.</em></p></div> - -<p><span class="pagenum" id="Page_29">[Pg 29]</span></p> - -<p>The averages show the effective size of the English sands to be -slightly greater than that of the German sands—0.37 instead of 0.34 -mm.—but the difference is very small. The entire range for the ten -works is only from 0.31 to 0.40 mm., and these may be taken as the -ordinary limits of effective size of the sands employed in the best -European works. The average for the other sixteen works given above, -including dune-sands, is 0.31 mm., or, omitting the dune-sands, 0.34 mm.</p> - -<div class="figcenter padt1 padb1 illowp93" id="image029" style="max-width: 93.75em;"> - <img class="w100" src="images/image029.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig.</span> 3<em>a</em>.—<span class="smcap">Sand Analysis Sheet, with -Analyses of Several European Filter Sands.</span></p></div> - -<p>It is important that filter sands should be free from lime. When water -is filtered through such sands, no increase in hardness results. When, -however, water is filtered through sand containing<span class="pagenum" id="Page_30">[Pg 30]</span> lime, some of it -is usually dissolved and the water is made harder. The amount of lime -taken up in this way depends both upon the character of the sand, and -upon the solvent power of the water; and it does not necessarily follow -that a sand containing lime cannot be used for filtration, but a sand -nearly free from lime is to be preferred.</p> - -<p>The presence of lime in sand can usually be detected by moistening it -with hydrochloric acid. The evolution of gas shows the presence of -lime. Some idea of the amount of lime can be obtained from the amount -of gas given off, and the appearance of the sample after the treatment, -but chemical analysis is necessary to determine correctly the amount.</p> - -<p>Experiments with filters at Pittsburg were made with sand containing -1.3 per cent of lime, the result being that the hardness of the water -was increased about one part in 100,000; but the amount of lime in the -sand was so small that it would be washed out after a time, and then -the hardening effect would cease. Larger amounts of lime would continue -their action for a number of years and would be more objectionable.</p> - -<p>Turning to the circumstances which influence the selection of the -sand size, we find that both the quality of the effluent obtained by -filtration and the cost of filtration depend upon the size of the -sand-grains.</p> - -<p>With a fine sand the sediment layer forms more quickly and the removal -of bacteria is more complete, but, on the other hand, the filter clogs -quicker and the dirty sand is more difficult to wash, so that the -expense is increased.</p> - -<div class="section"> -<h3 class="nobreak" id="EFFECT_OF_GRAIN_SIZE_UPON_EFFICIENCY_OF_FILTRATION">EFFECT OF SIZE OF GRAIN UPON EFFICIENCY OF FILTRATION.</h3></div> - -<p>It is frequently stated that it is only the sediment layer which -performs the work of filtration, and that the sand which supports -it plays hardly a larger part than does the gravel which<span class="pagenum" id="Page_31">[Pg 31]</span> carries -the sand, and under some circumstances this is undoubtedly the case. -Nevertheless sand in itself, without any sediment layer, especially -when not too coarse and not in too thin layers, has very great -purifying powers, and, in addition, acts as a safeguard by positively -preventing excessive rates of filtration on account of its frictional -resistance. As an illustration take the case of a filter of sand with -an effective size of 0.35 mm. and the minimum thickness of sand allowed -by the German Board of Health, namely, one foot, and let us suppose -that with clogging the loss of head has reached two feet to produce -the desired velocity of 2.57 million gallons per acre daily. Suppose -now that by some accident the sediment layer is suddenly broken or -removed from a small area, the water will rush through this area, -until a new sediment layer is formed, at a rate corresponding to the -size, pressure, and depth of the sand, or 260 million gallons per -acre daily—a hundred times the standard rate. Under these conditions -the passing water will not be purified, but will pollute the entire -effluent from the filter. Under corresponding conditions, with a deep -filter of fine sand, say with an effective size of 0.20 mm. and 5 feet -deep, the resulting rate would be only 17 million gallons per acre -daily, or less than seven times the normal, and with the water passing -through the full depth of fine sand, the resulting deterioration in the -effluent before the sand again became so clogged as to reduce the rate -to nearly the normal, would be hardly appreciable.</p> - -<p>The results at Lawrence have shown that with very fine sands 0.09 and -0.14 mm., and 4 to 5 feet deep, with the quantity of water which can -practically be made to pass through them, it is almost impossible to -drive more than an insignificant fraction of the bacteria into the -effluent. Even when the sands are entirely new, or have been scraped or -disturbed in the most violent way, the first effluent passing, before -the sediment layer could have been formed, is of good quality. Still -finer materials, 0.04 to 0.06 mm., as far as could be determined, -secured the absolute<span class="pagenum" id="Page_32">[Pg 32]</span> removal of all bacteria, but the rates of -filtration which were possible were so low as to preclude their -practical application.</p> - -<p>With coarser sands, as long as the filter is kept at a steady rate of -filtration, without interruptions of any kind, entirely satisfactory -results are often obtained, although never quite so good as with the -finer sands. Thus at Lawrence the percentages of bacteria (<em>B. -prodigiosus</em>) appearing in the effluents under comparable conditions -were as follows:</p> - -<table class="autotable" summary="percentages of bacteria in the effluents"> -<tr> -<th class="tdl"> </th> -<th class="tdc normal">1892</th> -<th class="tdc normal">1893</th> -</tr> -<tr> -<td class="tdl vertb">With effective grain size 0.38 mm</td> -<td class="tdc">0.16</td> -<td class="tdc">....</td> -</tr> -<tr> - -<td class="tdl vertb">With effective grain size 0.29 mm</td> -<td class="tdc">0.16</td> -<td class="tdc">....</td> -</tr> -<tr> - -<td class="tdl vertb">With effective grain size 0.26 mm</td> -<td class="tdc">0.10</td> -<td class="tdc">....</td> -</tr> -<tr> - -<td class="tdl vertb">With effective grain size 0.20 mm</td> -<td class="tdc">0.13</td> -<td class="tdc">0.01</td> -</tr> -<tr> - -<td class="tdl vertb">With effective grain size 0.14 mm</td> -<td class="tdc">0.04</td> -<td class="tdc">0.03</td> -</tr> -<tr> - -<td class="tdl vertb">With effective grain size 0.09 mm</td> -<td class="tdc">0.02</td> -<td class="tdc">0.02</td> -</tr> -</table> - -<p>We may thus conclude that fine sands give normally somewhat better -effluents than coarser ones, and that they are much more likely to -give at least a tolerably good purification under unusual or improper -conditions.</p> - -<div class="section"> -<h3 class="nobreak" id="EFFECT_OF_GRAIN_SIZE_UPON_FREQUENCY_OF_SCRAPING">EFFECT OF GRAIN SIZE UPON FREQUENCY OF SCRAPING.</h3></div> - -<p>The practical objection to the use of fine sand is that it becomes -rapidly clogged, so that filters require to be scraped at shorter -intervals, and the sand washing is much more difficult and expensive. -The quantities of water filtered between successive scrapings at -Lawrence in millions of gallons per acre under comparable conditions -have been as follows:</p> - - -<table class="autotable" summary="water filtered between successive scrapings"> -<tr> -<th class="tdl"> </th> -<th class="tdc normal">1892</th> -<th class="tdc normal">1893</th> -</tr> -<tr> -<td class="tdl vertb">Effective size of sand grain 0.38 mm</td> -<td class="tdc">....</td> -<td class="tdc">79</td> -</tr> -<tr> - -<td class="tdl vertb">Effective size of sand grain 0.29 mm</td> -<td class="tdc">....</td> -<td class="tdc">70</td> -</tr> -<tr> - -<td class="tdl vertb">Effective size of sand grain 0.26 mm</td> -<td class="tdc">....</td> -<td class="tdc">57</td> -</tr> -<tr> - -<td class="tdl vertb">Effective size of sand grain 0.20 mm</td> -<td class="tdc">58</td> -<td class="tdc">....</td> -</tr> -<tr> - -<td class="tdl vertb">Effective size of sand grain 0.14 mm</td> -<td class="tdc">45</td> -<td class="tdc">49</td> -</tr> -<tr> - -<td class="tdl vertb">Effective size of sand grain 0.09 mm</td> -<td class="tdc">24</td> -<td class="tdc">14</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_33">[Pg 33]</span></p> - -<p class="padt1">The increase in the quantities passed between scrapings with increasing -grain size is very marked.</p> - -<p>With the fine sands, the depth to which the sand becomes dirty is much -less than with the coarse sands, but as it is not generally practicable -to remove a layer of sand less than about 0.6 inch thick, even when the -actual clogged layer is thinner than this, the full quantity of sand -has to be removed; and the quantities of sand to be removed and washed -are inversely proportional to the quantities of water filtered between -scrapings. On the other hand, with very coarse sands the sediment -penetrates the sand to a greater depth than the 0.6 inch necessarily -removed, so that a thicker layer of sand has to be removed, which -may more than offset the longer interval. This happens occasionally -in water-works, and a sand coarse enough to allow it occur is always -disliked by superintendents, and is replaced with finer sand as soon as -possible. It is obvious that the minimum expense for cleaning will be -secured with a sand which just does not allow this deep penetration, -and I am inclined to think that the sizes of the sands in use have -actually been determined more often than otherwise in this way, and -that the coarsest samples found, having effective sizes of about 0.40 -mm., represent the practical limit to the coarseness of the sand, -and that any increase above this size would be followed by increased -expense for cleaning as well as by decreased efficiency.</p> - -<div class="section"> -<h3 class="nobreak" id="SELECTION_OF_SAND">SELECTION OF SAND.</h3></div> - -<p>In selecting a sand for filtration, when it is considered that repeated -washings will remove some of the finest particles, and so increase -slightly the effective size, a new sand coarser than 0.35 mm. would -hardly be selected. Perhaps 0.20 might be given as a suitable lower -limit. For comparatively clear lake- or reservoir-waters a finer -sand could probably be used than would be the case with a turbid -river-water. A mixed sand having a<span class="pagenum" id="Page_34">[Pg 34]</span> uniformity coefficient above 3.0 -would be difficult to wash without separating it into portions of -different sizes, and, in general, the lower the coefficient, that is, -the more uniform the grain sizes, the better. Great pains should be -taken to have the sand of the same quality throughout, especially in -the same filter, as any variations in the grain sizes would lead to -important variations in the velocity of filtration, the coarser sands -passing more than their share of water (in proportion to the square of -the effective sizes) and with reduced efficiency.</p> - -<p>At Lawrence a sufficient quantity of natural sand was found of the -grade required; but where suitable material cannot be so obtained it -is necessary to use other methods. A mixed material can be screened -from particles which are too large, and can be washed to free it from -its finer portions, and in this way a good sand can be prepared, if -necessary, from what might seem to be quite unpromising material. The -methods of sand-washing will be described in Chapter V.</p> - -<div class="section"> -<h3 class="nobreak" id="THICKNESS_OF_THE_SAND_LAYER">THICKNESS OF THE SAND LAYER.</h3></div> - -<p>The thickness of the sand layer is made so great that when it is -repeatedly scraped in cleaning the sand will not become too thin for -good filtration for a considerable time. When this occurs the removed -sand must be replaced with clean sand. The original thickness of the -sand in European filters is usually from 24 to 48 inches, thicknesses -between 30 and 40 inches being extremely common, and this is reduced -before refilling to from 12 to 24 inches. The Imperial Board of Health -of Germany has fixed 12 inches as a limit below which the sand should -never be scraped, and a higher limit is recommended wherever possible.</p> - -<p>A thick sand layer has the same steadying action as a fine sand, and -tends to prevent irregularities in the rate of filtration in proportion -to its frictional resistance, and that without increasing the frequency -of cleaning; but, on the other hand, it increases<span class="pagenum" id="Page_35">[Pg 35]</span> the necessary height -of the filter, throughout, and consequently the cost of construction.</p> - -<p>In addition to the steadying effect of a deep sand layer, some -purification takes place in the lower part of the sand even with a good -sediment layer on the surface, and the efficiency of deep filters is -greater than that of shallow ones.</p> - -<p>Layers of finer materials, as fine sand or loam, in the lower part -of a filter, which would otherwise give increased efficiency without -increasing the operating expenses, cannot be used. Their presence -invariably gives rise sooner or later to sub-surface clogging at the -point of junction with the coarser sand, as has been found by repeated -tests at Lawrence as well as in some of the Dutch filters where such -layers were tried; and as there is no object in putting a coarser sand -under a finer, the filter sand is best all of the same size and quality -from top to bottom.</p> - -<div class="section"> -<h3 class="nobreak" id="UNDERDRAINING">UNDERDRAINING.</h3></div> - -<p>The underdrains of a filter are simply useful for collecting the -filtered water; they play no part in the purification. One of the first -requirements of successful filtration is that the rate of filtration -shall be practically the same in all parts of the filter. This is most -difficult to secure when the filter has just been cleaned and the -friction of the sand layer is at a minimum. If the friction of the -water in entering and passing through the underdrains is considerable, -the more remote parts of the filters will work under less pressure, -and will thus do less than their share of the work, while the parts -near the outlet will be overtaxed, and filtering at too high rates will -yield poor effluents.</p> - -<p>To avoid this condition the underdrains must have such a capacity -that their frictional resistance will be only a small fraction of the -friction in the sand itself just after cleaning.</p> - -<div class="section"> -<h3 class="nobreak" id="GRAVEL_LAYERS">GRAVEL LAYERS.</h3></div> - -<p>The early filters contained an enormous quantity of gravel, but the -quantity has been steadily reduced in successive plants.<span class="pagenum" id="Page_36">[Pg 36]</span> Thus in 1866 -Kirkwood, as a result of his observations, recommended the use of a -layer four feet thick, and in addition a foot of coarse sand, while -at the present time new filters rarely have more than two feet of -gravel. Even this quantity seems quite superfluous, when calculations -of its frictional resistance are made. Thus a layer of gravel with an -effective size of 20 mm.<a id="FNanchor_5" href="#Footnote_5" class="fnanchor">[5]</a> (which is much finer than that generally -employed) only 6 inches thick will carry the effluent from a filter -working at a rate of 2.57 million gallons per acre daily for a distance -of 8 feet (that is, with underdrains 16 feet apart), with a loss of -head of only 0.001 foot, and for longer distances tile drains are -cheaper than gravel. To prevent the sand from sinking into the coarse -gravel, intermediate sizes of gravel must be placed between, each grade -being coarse enough so that there is no possibility of its sinking into -the layer below. The necessary thickness of these intermediate layers -is very small, the principal point being to have a layer of each grade -at every point. Thus on the 6 inches of 20 mm. gravel mentioned above, -three layers of two inches each, of 8 and 3 mm. gravel and coarse -sand, with a total height of six inches, or other corresponding and -convenient depths and sizes, would, if carefully placed, as effectually -prevent the sinking of the filter sand into the coarse gravel as the -much thicker layers used in the older plants.</p> - -<p>The gravel around the drains should receive special attention. Larger -stones can be here used with advantage, taking care that adequate -spaces are left for the entrance of the water into the drains at a low -velocity, and to make everything so solid in this neighborhood that -there will be no chance for the stones to settle which might allow the -sand to reach the drains.</p> - -<div class="figcenter padt1 padb1 illowp76" id="facing036_1" style="max-width: 60.8125em;"> - <img class="w100" src="images/facing036_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Reconstructing the Underdrainage System of a Filter -after 25 Years of Use, Bremen.</span></p></div> - -<div class="figcenter padb1 illowp95" id="facing036_2" style="max-width: 60.8125em;"> - <img class="w100" src="images/facing036_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Placing Sand in a Filter, Choisy le Roi (Paris).</span></p> - -<p class="right">[<em>To face page 36.</em>]</p></div> - -<p>At the Lawrence filter, at Königsberg in Prussia, at Amsterdam and -other places, the quantity of gravel is reduced by putting the drains -in trenches, so that the gravel is reduced from<span class="pagenum" id="Page_37">[Pg 37]</span> a maximum thickness -at the drain to nothing half way between drains. The economy of the -arrangement, however, as far as friction is concerned is not so great -as would appear at first sight, and the cost of the bottom may be -increased; but on the other hand it gives a greater depth of gravel for -covering the drains with a small total amount of gravel.</p> - -<p>As even a very small percentage of fine material is capable of -getting in the narrow places and reducing the carrying power of the -gravel, it is important that all such matters should be carefully -removed by washing before putting the gravel in place. In England and -Germany gravel is commonly screened for use in revolving cylinders of -wire-cloth of the desired sizes, on which water is freely played from -numerous jets, thus securing perfectly clean gravel. In getting gravel -for the Lawrence filter, an apparatus was used, in which advantage was -taken of the natural slope of the gravel bank to do the work, and the -use of power was avoided. The respective grades of gravel obtained were -even in size, and reasonably free from fine material, but it was deemed -best to wash them with a hose before putting them in the filter.</p> - -<p>To calculate the frictional resistance of water in passing gravel, we -may assume that for the very low velocities which are actually found in -filters the quantity of water passing varies directly with the head, -which for these velocities is substantially correct, although it would -not be true for higher rates, especially with the coarser gravels.<a id="FNanchor_6" href="#Footnote_6" class="fnanchor">[6]</a> -In the case of parallel underdrains the friction from the middle point -between drains to the drains may be calculated by the formula:</p> - -<p>Total head = (<sup>1</sup>⁄<sub>2</sub>)[(Rate of filtration × (<sup>1</sup>⁄<sub>2</sub> distance between -drains)<sup>2</sup>)/(Average depth of gravel × discharge coefficient)].</p> - -<p>The discharge coefficient for any gravel is 1000 times the quantity -<span class="pagenum" id="Page_38">[Pg 38]</span> -of water which will pass when <sup><em>h</em></sup>⁄<sub><em>l</em></sub> is <sup>1</sup>⁄<sub>1000</sub> expressed -in million gallons per acre daily. The approximate values of this -coefficient for different-sized gravels are as follows:</p> - -<table class="autotable" summary="discharge coefficient for gravel"> -<tr> -<th class="tdc normal" colspan="4">VALUES OF DISCHARGE COEFFICIENT.</th> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc"> 5 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc"> 23,000</td> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc">10 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc"> 65,000</td> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc">15 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc">110,000</td> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc">20 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc">160,000</td> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc">25 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc">230,000</td> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc">30 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc">300,000</td> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc">35 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc">390,000</td> -</tr> -<tr> - -<td class="tdl vertb">For gravel with effective size</td> -<td class="tdc">40 mm</td> -<td class="tdc"><em>c</em> =</td> -<td class="tdc">480,000</td> -</tr> -</table> - - -<p>Example: What is the loss of head in the gravel at a rate of filtration -of 2 million gallons per acre daily, with underdrains 20 feet apart, -where the supporting gravel has an effective size of 35 millimeters, -and is uniformly 1 ft. deep?</p> - -<p>Total head = (<sup>1</sup>⁄<sub>2</sub>)[(2 × 10<sup>2</sup>)/(1 × 390,000)] = .000256 ft.</p> - -<p>The total friction would be the same with the same average depth of -gravel whether it was uniformly 1 foot deep, or decreasing from 1.5 at -the drains to 0.5 in the middle, or from 2.0 to 0. The reverse case -with the gravel layer thicker in the middle than at the drains does not -occur and need not be discussed.</p> - -<p>The depth of gravel likely to be adopted as a result of this -calculation, when the drains are not too far apart, will be much less -than that actually used in most European works, but as the two feet or -more there employed are, I believe, simply the result of speculation, -there is no reason for following the precedent where calculations show -that a smaller quantity is adequate.</p> - -<p>The reason for recommending a thin lower layer of coarse gravel, which -alone is assumed to provide for the lateral movement<span class="pagenum" id="Page_39">[Pg 39]</span> of the water, -is that if more than about six inches of gravel is required to give a -satisfactory resistance, it will almost always be cheaper to use more -drains instead of more gravel; and the reason for recommending thinner -upper layers for preventing the sand from settling into the coarse -gravel is that no failures of this portion of filters are on record, -and in the few instances where really thin layers have been used the -results have been entirely satisfactory. In Königsberg filters were -built by Frühling,<a id="FNanchor_7" href="#Footnote_7" class="fnanchor">[7]</a> in which the sand was supported by five layers -of gravel of increasing sizes, respectively 1.2, 1.2, 1.6, 2.0, 3.2, -or, together, 9.2 inches thick, below which there were an average of -five inches of coarse gravel. These were examined after eight years of -operation and found to be in perfect order.</p> - -<p>At the Lawrence Experiment Station filters have been repeatedly -constructed with a total depth of supporting gravel layers not -exceeding six inches, and among the scores of such filters there has -not been a single failure, and so far as they have been dug up there -has never been found to have been any movement whatever of the sand -into the gravel. The Lawrence city filter, built with corresponding -layers, has shown no signs of being inadequately supported. In -arranging the Lawrence gravel layers care has always been taken that no -material should rest on another material more than three or four times -as coarse as itself, and that each layer should be complete at every -point, so that by no possibility could two layers of greater difference -in size come together. And it is believed that if this is carefully -attended to, no trouble need be anticipated, however thin the single -layers may be.</p> - -<div class="section"> -<h3 class="nobreak" id="UNDERDRAINS">UNDERDRAINS.</h3></div> - -<p>The most common arrangement, in other than very small filters, is to -have a main drain through the middle of the filter,<span class="pagenum" id="Page_40">[Pg 40]</span> with lateral -drains at regular intervals from it to the sides. The sides of the main -drain are of brick, laid with open joints to admit water freely, and -the top is usually covered with stone slabs. The lateral drains may be -built in the same way, but tile drains are also used and are cheaper. -Care must be taken with the latter that ample openings are left for the -admission of water at very low velocities. It is considered desirable -to have these drains go no higher than the top of the coarsest gravel; -and this will often control the depth of gravel used. If they go -higher, the top must be made tight to prevent the entrance of the fine -gravels or sand. Sometimes they are sunk in part or wholly (especially -the main drain) below the floor of the filter. With gravel placed in -waves, that is, thicker over the drains than elsewhere, as mentioned -above, the drains are covered more easily than with an entirely -horizontal arrangement. When this is done, the floor of the filter is -trenched to meet the varying thickness of gravel, so that the top of -the latter is level, and the sand has a uniform thickness.</p> - -<p>Many filters (Lambeth, Brunswick, etc.) are built with a double bottom -of brick, the upper layer of which, with open joints, supports the -gravel and sand, and is itself supported by numerous small arches or -other arrangements of brick, which serve to carry the water to the -outlet without other drains. This arrangement allows the use of a -minimum quantity of gravel, but is undoubtedly more expensive than the -usual form, with only the necessary quantity of gravel; and I am unable -to find that it has any corresponding advantages.</p> - -<p>The frictional resistance of underdrains requires to be carefully -calculated; and in doing this quite different standards must be -followed from those usually employed in determining the sizes -of water-pipes, as a total frictional resistance of only a few -hundredths of a foot, including the velocity head, may cause serious -irregularities in the rate of filtration in different parts of the -filter.</p> - -<p><span class="pagenum" id="Page_41">[Pg 41]</span></p> - -<p>The sizes of the underdrains differ very widely in proportion to the -sizes of the filters in European works, some of them being excessively -large, while in other cases they are so small as to suggest a doubt as -to their allowing uniform rates of filtration, especially just after -cleaning.</p> - -<p>I would suggest the following rules as reasonably sure to lead to -satisfactory results without making an altogether too lavish provision: -In the absence of a definite determination to run filters at some -other rate, calculate the drains for the German standard rate of a -daily column of 2.40 meters, equal to 2.57 million gallons per acre -daily. This will insure satisfactory work at all lower rates, and -no difficulty on account of the capacity of the underdrains need be -then anticipated if the rate is somewhat exceeded. The area for a -certain distance from the main drain depending upon the gravel may be -calculated as draining directly into it, provided there are suitable -openings, and the rest of the area is supposed to drain to the nearest -lateral drain.</p> - -<p>In case the laterals are round-tile drains I would suggest the -following limits to the areas which they should be allowed to drain:</p> - -<table class="autotable" summary="limits to areas drained"> -<tr> -<th class="tdc normal smaller">Diameter of Drain.</th> -<th class="tdc normal smaller">To Drain an Area not<br />Exceeding</th> -<th class="tdc normal smaller">Corresponding Velocity of<br />Water in Drain.</th> -</tr> -<tr> -<td class="tdl vertb"> 4 inches</td> -<td class="tdc"> 290 square feet.</td> -<td class="tdc">0.30 foot.</td> -</tr> -<tr> -<td class="tdl vertb"> 6 inches</td> -<td class="tdc"> 750 square feet.</td> -<td class="tdc">0.35 foot.</td> -</tr> -<tr> -<td class="tdl vertb"> 8 inches</td> -<td class="tdc">1530 square feet.</td> -<td class="tdc">0.40 foot.</td> -</tr> -<tr> -<td class="tdl vertb">10 inches</td> -<td class="tdc">2780 square feet.</td> -<td class="tdc">0.46 foot.</td> -</tr> -<tr> -<td class="tdl vertb">12 inches</td> -<td class="tdc">4400 square feet.</td> -<td class="tdc">0.51 foot.</td> -</tr> -</table> - -<p>And for larger drains, including the main drains, their cross-sections -at any point should be at least <sup>1</sup>⁄<sub>6000</sub> of the area drained, giving a -velocity of 0.55 foot per second with the rate of filtration mentioned -above.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image042" style="max-width: 75em;"> - <img class="w100" src="images/image042.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 4.—Plan of one of the Hamburg Filters, Showing -Frictional Resistance of the Underdrains.</span></p></div> - -<p>The total friction of the underdrains from the most remote points -to the outlet will be friction in the gravel, plus friction in<span class="pagenum" id="Page_42">[Pg 42]</span> -the lateral drains, plus the friction in main drain, plus the velocity head.</p> - -<div class="figcenter padt1 padb1 illowp100" id="facing042" style="max-width: 125em;"> - <img class="w100" src="images/facing042.jpg" alt="" /> - <p class="caption"><span class="smcap">Constructing the Underdrainage System of a Filter, -Hamburg.</span></p> - -<p class="right">[<em>To face page 42.</em>]</p></div> - -<p>I have calculated in this way the friction of one of the Hamburg -filters for the rate of 1,600,000 gallons per acre daily at which it -is used. The friction was calculated for each section of the drains -separately, so that the friction from intermediate points was also -known. Kutter’s formula was used throughout with <em>n</em> = 0.013. On -the accompanying plan of the filter I have drawn the lines of equal -frictional resistance from the junction of the main drain with the last -laterals. My information was incomplete in regard to one or two points, -so that the calculation may not be strictly accurate, but it is nearly -so and will illustrate the principles involved.</p> - -<p>The extreme friction of the underdrains is 11 millimeters = 0.036 foot.</p> - -<p>The frictional resistance of the sand 39 inches thick, effective size -0.32 mm. and rate 1.60 million gallons per acre daily, when absolutely -free from clogging, is by the formula, page 21, 15mm., or .0490 -<span class="pagenum" id="Page_43">[Pg 43]</span> -foot, when the temperature is 50°. Practically there is some matter -deposited upon the surface of the sand before filtration starts, and -further, after the first scraping, there is some slight clogging in the -sand below the layer removed by scraping. We can thus safely take the -minimum frictional resistance of the sand including the surface layer -at .07 foot. The average friction of the underdrains for all points -is about .023 foot and the friction at starting will be .07 + .023 = -.093 foot (including the friction in the last section to the effluent -well where the head is measured, .100 foot, but the friction beyond the -last lateral does not affect the uniformity of filtration). The actual -head on the sand close to the outlet will be .093 and the rate of -filtration <sup>.093</sup>⁄<sub>.070</sub> · 1.60 = 2.12. The actual head at the most remote -point will be .093 - .036 = .057, and the rate of filtration will there -be <sup>.057</sup>⁄<sub>.070</sub> · 160 = 1.30 million gallons per acre daily. The extreme -rates of filtration are thus 2.12 and 1.30, instead of the average rate -of 1.60. As can be seen from the diagram, only very small areas work -at these extreme rates, the great bulk of the area working at rates -much nearer the average. Actually the filter is started at a rate below -1.60, and the nearest portion never filters so rapidly as 2.12, for -when the rate is increased to the standard, the sand has become so far -clogged that the loss of head is more than the .07 foot assumed, and -the differences in the rates are correspondingly reduced. Taking this -into account, it would not seem that the irregularities in the rate of -filtration are sufficient to affect seriously the action of the filter. -They could evidently have been largely reduced by moderately increasing -the sizes of the lower ends of the underdrains, where most of the -friction occurs with the high velocities (up to .97 foot) which there -result.</p> - -<p>The underdrains of the Warsaw filters were designed by Lindley to have -a maximum loss of head of only .0164 foot when<span class="pagenum" id="Page_44">[Pg 44]</span> filtering at a rate of -2.57, which gives a variation of only 10 per cent in the rates with the -minimum loss of head of .169 foot in the entire filter assumed by him. -The underdrains of the Berlin filters, according to my calculations, -have .020 to .030 foot friction, of which an unusually large proportion -is in the gravel, owing to the excessive distances, in some cases over -80 feet, which the gravel is required to carry the water. In this case, -using less or finer gravel would obviously have been fatal, but the -friction as well as the expense of construction would be much reduced -by using more drains and less gravel.</p> - -<p>The underdrains might appropriately be made slightly smaller, with a -deep layer of fine sand, than under opposite conditions, as in this -case the increased friction in the drains would be no greater in -proportion to the increased friction in the sand itself.</p> - -<p>The underdrains of a majority of European filters have water-tight -pipes connecting with them at intervals, and going up through the sand -and above the water, where they are open to the air. These pipes were -intended to ventilate the underdrains and allow the escape of air when -the filter is filled with water introduced from below. It may be said, -however, that in case the drains are surrounded by gravel and there is -an opportunity for the air to pass from the top of the drain into the -gravel, it will so escape without special provision being made for it, -and go up through the sand with the much larger quantity of air in the -upper part of the gravel which is incapable of being removed by pipes -connecting with the drains.</p> - -<p>These ventilator pipes where they are used are a source of much -trouble, as unfiltered water is apt to run down through cracks in the -sand beside them, and, under bad management, unfiltered water may even -go down through the pipes themselves. I am unable to find that they -are necessary, except with underdrains so constructed that there is -no other chance for the escape of air from the tops of them, or that -they serve any useful<span class="pagenum" id="Page_45">[Pg 45]</span> purpose, while there are positive objections to -their use. In some of the newer filters they have been omitted with -satisfactory results.</p> - -<div class="section"> -<h3 class="nobreak" id="DEPTH_OF_WATER_ON_THE_FILTERS">DEPTH OF WATER ON THE FILTERS.</h3></div> - -<p>In the older works with but crude appliances for regulating the rate of -filtration and admission of raw water, a considerable depth of water -was necessary upon the filter to balance irregularities in the rates -of filtration; the filter was made to be, to a certain extent, its own -storage reservoir. When, however, appliances of the character to be -described in Chapter IV are used for the regulation of the incoming -water, and with a steady rate of filtration, this provision becomes -quite superfluous.</p> - -<p>With open filters a depth of water in excess of the thickness of any -ice likely to be formed is required to prevent disturbance or freezing -of the sand in winter. It is also frequently urged that with a deep -water layer on the filter the water does not become so much heated in -summer, but this point is not believed to be well taken, for in any -given case the total amount of heat coming from the sun to a given area -is constant, and the quantity of water heated in the whole day—that -is, the amount filtered—is constant, and variations in the quantity -exposed at one time will not affect the average resulting increase in -temperature. If the same water remained upon the filter without change -it would of course be true that a thin layer would be heated more than -a deep one, but this is not the case.</p> - -<p>It is also sometimes recommended that the depth of water should be -sufficient to form a sediment layer before filtration starts, but this -point would seem to be of doubtful value, especially where the filter -is not allowed to stand a considerable time with the raw water upon it -before starting filtration.</p> - -<p>It is also customary to have a depth of water on the filter in excess -of the maximum loss of head, so that there can never be a<span class="pagenum" id="Page_46">[Pg 46]</span> suction in -the sand just below the sediment layer. It may be said in regard to -this, however, that a suction below is just as effective in making the -water pass the sand as an equal head above. At the Lawrence Experiment -Station filters have been repeatedly used with a water depth of only -from 6 to 12 inches, with losses of head reaching 6 feet, without the -slightest inconvenience. The suction only commences to exist as the -increasing head becomes greater than the depth of water, and there is -no way in which air from outside can get in to relieve it. In these -experimental filters in winter, when the water is completely saturated -with air, a small part of the air comes out of the water just as it -passes the sediment layer and gets into reduced pressure, and this -air prevents the satisfactory operation of the filters. But this is -believed to be due more to the warming and consequent supersaturation -of the water in the comparatively warm places in which the filters -stand than to the lack of pressure, and as not the slightest trouble -is experienced at other seasons of the year, it may be questioned -whether there would be any disadvantage at any time in a corresponding -arrangement on a large scale where warming could not occur.</p> - -<p>The depths of water actually used in European filters with the full -depth of sand are usually from 36 to 52 inches. In only a very few -unimportant cases is less than the above used, and only a few of the -older works use a greater depth, which is not followed in any of the -modern plants. As the sand becomes reduced in thickness by scraping, -the depth of water is correspondingly increased above the figures given -until the sand is replaced. The depth of water on the German covered -filters is quite as great as upon corresponding open filters. Thus the -Berlin covered filters have 51, while the new open filters at Hamburg -have only 43 inches.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_47">[Pg 47]</span></p> - -<h2 class="nobreak" id="CHAPTER_IV">CHAPTER IV.<br /> -<br /> - -<span class="smaller">RATE OF FILTRATION AND LOSS OF HEAD.</span></h2></div> - - -<p><span class="smcap">The</span> rate of filtration recommended and used has been gradually reduced -during the past thirty years. In 1866 Kirkwood found that 12 vertical -feet per day, or 3.90 million gallons per acre daily, was recommended -by the best engineers, and was commonly followed as an average rate. -In 1868 the London filters averaged a yield of 2.18 million gallons<a id="FNanchor_8" href="#Footnote_8" class="fnanchor">[8]</a> -per acre daily, including areas temporarily out of use, while in 1885 -the quantity had been reduced to 1.61. Since that time the rate has -apparently been slightly increased.</p> - -<p>The Berlin filters at Stralau constructed in 1874 were built to filter -at a rate of 3.21 million gallons per acre daily. The first filters at -Tegel were built for a corresponding rate, but have been used only at -a rate of 2.57, while the more recent filters were calculated for this -rate. The new Hamburg filters, 1892-3, were only intended to filter -at a rate of 1.60 million gallons per acre daily. These in each case -(except the London figures) are the standard rates for the filter-beds -actually in service.</p> - -<p>In practice the area of filters is larger than is calculated from -these figures, as filters must be built to meet maximum instead of -average daily consumptions, and a portion of the filtering area usually -estimated at from 5 to 15 per cent, but in extreme cases reaching 50 -per cent, is usually being cleaned, and so is for the time out of -service. In some works also the rate of filtration on starting a filter -is kept lower than the standard rate for a day or two, or the first -portion of the effluent, supposed to be of inferior quality, is</p> - -<p><span class="pagenum" id="Page_48">[Pg 48]</span></p> - -<p>wasted, the amount so lost reaching in an extreme case 9 to 14 per -cent of the total quantity of water filtered.<a id="FNanchor_9" href="#Footnote_9" class="fnanchor">[9]</a> In many of the older -works also, there is not storage capacity enough for filtered water to -balance the hourly fluctuations in consumption, and the filters must be -large enough to meet the maximum hourly as well as the maximum daily -requirements. For these reasons the actual quantity of water filtered -in a year is only from 50 to 75 per cent of what would be the case if -the entire area of the filters worked constantly at the full rate. A -statement of the actual yields of a number of filter plants is given in -Appendix IV. The figures for the average annual yields can be taken as -quite reliable. The figures given for rate, in many cases, have little -value, owing to the different ways in which they are calculated at -different places. In addition most of the old works have no adequate -means of determining what the rate at any particular time and for a -single filter really is, and statements of average rates have only -limited value. The filters at Hamburg are not allowed to filter faster -than 1.60 or those at Berlin faster than 2.57 million gallons per acre -daily, and adequate means are provided to secure this condition. Other -German works aim to keep within the latter limit. Beyond this, unless -detailed information in regard to methods is presented, statements of -rate must be taken with some allowance.</p> - -<div class="section"> -<h3 class="nobreak" id="EFFECT_OF_RATE_UPON_COST_OF_FILTRATION">EFFECT OF RATE UPON COST OF FILTRATION.</h3></div> - -<p>The size of the filters required, and consequently the first cost, -depends upon the rate of filtration, but with increasing rates the cost -is not reduced in the same proportion as the increase in rate, since -the allowance for area out of use is sensibly the same for high and low -rates, and in addition the operating expenses depend upon the quantity -filtered and not upon the filtering area. Thus, to supply 10 million -gallons at a maximum rate of 2 million gallons per acre daily we should -require 10 ÷ 2 = 5 acres + 1 acre reserve for cleaning = 6 acres, while -with a rate twice<span class="pagenum" id="Page_49">[Pg 49]</span> -as great, and with the same reserve (since the same amount of cleaning -must be done, as will be shown below), we should require 10 ÷ 4 + 1 -= 3.5 acres, or 58 per cent of the area required for the lower rate. -Thus beyond a certain point increasing the rate does not effect a -corresponding reduction in the first cost.</p> - -<p>The operating cost for the same quantity of water filtered does not -appear to be appreciably affected by the rate. It is obvious that -at high rates filters will became clogged more rapidly, and will -so require to be scraped oftener than at low rates, and it might -naturally be supposed that the clogging would increase more rapidly -than the rates, but this does not seem to be the case. At the Lawrence -Experiment Station, under strictly parallel conditions and with -identically the same water, filters running at various rates became -clogged with a rapidity directly proportional to the rates, so that -the quantities of water filtered between scrapings under any given -conditions are the same whether the rate is high or low.</p> - -<p>The statistics bearing upon this point are interesting, if not entirely -conclusive. There were eleven places in Germany filtering river waters, -from which statistics were available for the year 1891-92. Of these -there were four places with high rates, Lübeck, Stettin, Stuttgart, and -Magdeburg, yielding 3.70 million gallons per acre daily, which filtered -on an average 59 million gallons per acre between scrapings. Three -other places, Breslau, Altona, and Frankfurt, yielding 1.85, passed -on an average 55 million gallons per acre between scrapings, and four -other places, Bremen, Königsberg, Brunswick and Posen, yielding 1.34 -million gallons per acre daily, passed only 40 million gallons per -acre between scrapings. The works filtering at the highest rates thus -filtered more water in proportion to the sand clogged than did those -filtering more slowly, but I cannot think that this was the result of -the rate. It is more likely that some of the places have clearer waters -than others, and that this both allows the higher rate and causes less -clogging than the more turbid waters.</p> - -<p><span class="pagenum" id="Page_50">[Pg 50]</span></p> - -<div class="section"> -<h3 class="nobreak" id="EFFECT_OF_RATE_UPON_EFFICIENCY_OF_FILTRATION">EFFECT OF RATE UPON EFFICIENCY OF FILTRATION.</h3></div> - -<p>The effect of the rate of filtration upon the quality of the effluent -has been repeatedly investigated. The efficiency almost uniformly -decreases rapidly with increasing rate. Fränkel and Piefke<a id="FNanchor_10" href="#Footnote_10" class="fnanchor">[10]</a> first -found that with the high rates the number of bacteria passing some -experimental filters was greatly increased. Piefke<a id="FNanchor_11" href="#Footnote_11" class="fnanchor">[11]</a> afterward -repeated these experiments, eliminating some of the features of the -first series to which objection was made, and confirmed the first -results. The results were so marked that Piefke was led to recommend -the extremely low limit of 1.28 million gallons per acre daily as the -safe maximum rate of filtration, but he has since repeatedly used 2.57 -million gallons.</p> - -<p>Kümmel,<a id="FNanchor_12" href="#Footnote_12" class="fnanchor">[12]</a> on the other hand, in a somewhat limited series of -experiments, was unable to find any marked connection between the rate -and the efficiency, a rate of 2.57 giving slightly better results than -rates of either 1.28 or 5.14.</p> - -<p>The admirably executed experiments made at Zürich in 1886-8 upon this -point, which gave throughout negative results, have but little value in -this connection, owing to the extremely low number of bacteria in the -original water.</p> - -<p class="padb1">At Lawrence in 1892 the following percentages of bacteria (<em>B. -prodigiosus</em>) passed at the respective rates:</p> - -<table class="autotable" summary="Lawrence 1892 percentages of bacteria passed"> -<tr> -<th class="tdc smaller normal bord_top bord_bot bord_right" rowspan="2">No. of<br />Filter.</th> -<th class="tdc smaller normal bord_top bord_bot bord_right" rowspan="2">Depth.</th> -<th class="tdc smaller normal bord_top bord_bot bord_right" rowspan="2">Effective<br />Size of<br />Sand.</th> -<th class="tdc smaller normal bord_top bord_bot" colspan="5">Rate. Millions gallons per acre daily.</th> -</tr> -<tr> -<td class="tdc smaller normal bord_top bord_bot bord_right vertb">0.5</td> -<td class="tdc smaller normal bord_top bord_bot bord_right vertb">1.0</td> -<td class="tdc smaller normal bord_top bord_bot bord_right vertb">1.5</td> -<td class="tdc smaller normal bord_top bord_bot bord_right vertb">2.0</td> -<td class="tdc smaller normal bord_top bord_bot">3.0</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">33A</td> -<td class="tdc bord_right vertb">60</td> -<td class="tdc bord_right vertb">0.14</td> -<td class="tdc bord_right vertb">0.002</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.040</td> -<td class="tdc">.....</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">34A</td> -<td class="tdc bord_right vertb">60</td> -<td class="tdc bord_right vertb">0.09</td> -<td class="tdc bord_right vertb">0.001</td> -<td class="tdc bord_right vertb">0.005</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.020</td> -<td class="tdc">.....</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">36A</td> -<td class="tdc bord_right vertb">60</td> -<td class="tdc bord_right vertb">0.20</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.050</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc">0.050</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">37 </td> -<td class="tdc bord_right vertb">60</td> -<td class="tdc bord_right vertb">0.20</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.010</td> -<td class="tdc bord_right vertb">0.130</td> -<td class="tdc">.....</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">38 </td> -<td class="tdc bord_right vertb">24</td> -<td class="tdc bord_right vertb">0.20</td> -<td class="tdc bord_right vertb">0.018</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.140</td> -<td class="tdc bord_right vertb">0.110</td> -<td class="tdc">0.310</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">39 </td> -<td class="tdc bord_right vertb">12</td> -<td class="tdc bord_right vertb">0.20</td> -<td class="tdc bord_right vertb">0.014</td> -<td class="tdc bord_right vertb">0.070</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.080</td> -<td class="tdc">0.520</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">40 </td> -<td class="tdc bord_right vertb">12</td> -<td class="tdc bord_right vertb">0.20</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.070</td> -<td class="tdc bord_right vertb">.....</td> -<td class="tdc bord_right vertb">0.090</td> -<td class="tdc">.....</td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot">42 </td> -<td class="tdc bord_bot bord_right vertb">12</td> -<td class="tdc bord_bot bord_right vertb">0.20</td> -<td class="tdc bord_bot bord_right vertb">0.016</td> -<td class="tdc bord_bot bord_right vertb">.....</td> -<td class="tdc bord_bot bord_right vertb">.....</td> -<td class="tdc bord_bot bord_right vertb">0.150</td> -<td class="tdc bord_bot">0.550</td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot" colspan="3"> Average</td> -<td class="tdc bord_right bord_bot">0.010</td> -<td class="tdc bord_right bord_bot">0.048</td> -<td class="tdc bord_right bord_bot">0.067</td> -<td class="tdc bord_right bord_bot">0.088</td> -<td class="tdc bord_bot">0.356</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_51">[Pg 51]</span></p> - -<p class="padt1">These results show a very marked decrease in efficiency with -increasing rates, the number of bacteria passing increasing in general -as rapidly as the square of the rate. The 1893 results also showed -decreased efficiency with high rates, but the range in the rates -under comparable conditions was less than in 1892, and the bacterial -differences were less sharply marked.</p> - -<p>While the average results at Lawrence, as well as most of the European -experiments, show greatly decreased efficiency with high rates, there -are many single cases, particularly with deep layers of not too coarse -sand, where, as in Kümmel’s experiments, there seems to be little -connection between the rate and efficiency. An explanation of these -apparently abnormal results will be given in Chapter VI.</p> - -<p>It is commonly stated<a id="FNanchor_13" href="#Footnote_13" class="fnanchor">[13]</a> that every water has its own special rate of -filtration, which must be determined by local experiments, and that -this rate may vary widely in different cases. Thus it is possible that -the rate of 1.60 adopted at Hamburg for the turbid Elbe water, the rate -of 2.57 used at Berlin, and about the same at London for much clearer -river-waters, and the rate of 7.50 used at Zürich for the almost -perfectly clear lake-water are in each case the most suitable for the -respective waters. In other cases however, where rates much above 2.57 -are used for river-waters, as at Lübeck and Stettin, there is a decided -opinion that these rates are excessive, and in these instances steps -are now being taken to so increase the filtering areas as to bring the -rates within the limit of 2.57 million gallons per acre daily.</p> - -<p>From the trend of European practice it would seem that for American -river-waters the rate of filtration should not exceed 2.57 in place of -the 3.90 million gallons per acre daily recommended by Kirkwood, or -even that a somewhat lower rate might be desirable in some cases. Of -course, in addition to the area -<span class="pagenum" id="Page_52">[Pg 52]</span> -necessary to give this rate, a reserve for fluctuating rates and for -cleaning should be provided, reducing the average yield to 2.00, 1.50, -or even less. In the case of water from clear lakes, ponds, or storage -reservoirs, especially when they are not subject to excessive sewage -pollution or to strong algæ growths, it would seem that rates somewhat -and perhaps in some cases very much higher (as at Zürich) could be -satisfactorily used.</p> - -<div class="section"> -<h3 class="nobreak" id="THE_LOSS_OF_HEAD">THE LOSS OF HEAD.</h3></div> - -<p>The loss of head is the difference between the heads of the waters -above and below the sand layer, and represents the frictional -resistance of that layer. When a filter is quite free from clogging -this frictional resistance is small, but gradually increases with the -deposit of a sediment layer from the water filtered until it becomes so -great that the clogging must be removed by scraping before the process -can be continued. After scraping the loss of head is reduced to, or -nearly to, its original amount. With any given amount of clogging the -loss of head is directly proportional to the rate of filtration; that -is, if a filter partially clogged, filtering at a rate of 1.0, has a -frictional resistance of 0.5 ft., the resistance will be doubled by -increasing the rate to 2.00 million gallons per acre daily, provided -no disturbance of the sediment layer is allowed. This law for the -frictional resistance of water in sand alone also applies to the -sediment layer, as I have found by repeated tests, although in so -violent a change as that mentioned above, the utmost care is required -to make the change gradually and prevent compression or breaking of the -sediment layer. From this relation between the rate of filtration and -the loss of head it is seen that the regulation of either involves the -regulation of the other, and it is a matter of indifference which is -directly and which indirectly controlled.</p> - -<div class="section"> -<h3 class="nobreak" id="REGULATION_OF_THE_RATE_AND_LOSS_OF_HEAD_IN_THE_OLDER_FILTERS">REGULATION OF THE RATE AND LOSS OF HEAD IN THE OLDER FILTERS.</h3></div> - -<p>In the older works, and in fact in all but a few of the newest<span class="pagenum" id="Page_53">[Pg 53]</span> works, -the underdrains of the filters connect directly through a pipe with a -single gate with the pure-water reservoir or pump-well, which is so -built that the water in it may rise nearly or quite as high as that -standing upon the filter.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image053" style="max-width: 50em;"> - <img class="w100" src="images/image053.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 5.—Simplest Form of Regulation: Stralau Filters -at Berlin.</span></p></div> - -<p>A typical arrangement of this sort was used at the Stralau works at -Berlin (now discontinued), Fig. 5. With this arrangement the rate of -filtration is dependent upon the height of water in the reservoir or -pump-well, and so upon the varying consumption. When the water in the -receptacle falls with increasing consumption the head is increased, -and with it the rate of filtration, while, on the other hand, with -decreasing draft and rising water in the reservoir, the rate of -filtration decreases and would eventually be stopped if no water were -used. This very simple arrangement thus automatically, within limits, -adjusts the rate of filtration to the consumption, and at the same time -always gives the highest possible level of water in the pump-well, thus -also economizing the coal required for pumping.</p> - -<p>In plants of this type the loss of head may be measured by floats -on little reservoirs built for that purpose, connected with the -underdrains; but more often there is no means of determining it, -although the maximum loss of head at any time is the difference between -the levels of the water on the filter and in the reservoir, or the -outlet of the drain-pipe, in case the latter is above<span class="pagenum" id="Page_54">[Pg 54]</span> the water-line -in the reservoir. The rate of filtration can only be measured with this -arrangement by shutting off the incoming water for a definite interval, -and observing the distance that the water on the filter sinks. The -incoming water is regulated simply by a gate, which a workman opens or -closes from time to time to hold the required height of water on the -filter.</p> - -<p>The only possible regulation of the rate and loss of head is effected -by a partial closing of the gate on the outlet-pipe, by which the -freshly-cleaned filters with nearly-closed gates are kept from -filtering more rapidly than the clogged filters, the gates of which -are opened wide. Often, however, this is not done, and then the fresh -filters filter many times as rapidly as those which are partially -clogged.</p> - -<p>A majority of the filters now in use are built more or less upon this -plan, including most of those in London and also the Altona works, -which had such a favorable record with cholera in 1892.</p> - -<p>The invention and application of methods of bacterial examination in -the last years have led to different ideas of filtration from those -which influenced the construction of the earlier plants. As a result -it is now regarded as essential by most German engineers<a id="FNanchor_14" href="#Footnote_14" class="fnanchor">[14]</a> that -each filter shall be provided with devices for measuring accurately -and at any time both the rate of filtration and the loss of head, and -for controlling them, and also for making the rate independent of -consumption by reservoirs for filtered water large enough to balance -hourly variations (capacity <sup>1</sup>⁄<sub>4</sub> to <sup>1</sup>⁄<sub>3</sub> maximum daily quantity) and low -enough so that they can never limit the rate of filtration by causing -back-water on the filters. These points are now insisted upon by the -German Imperial Board of Health,<a id="FNanchor_15" href="#Footnote_15" class="fnanchor">[15]</a> and all new filters are built in -accordance with them, while most of the old works are being built over -to conform to the requirements.</p> - -<p><span class="pagenum" id="Page_55">[Pg 55]</span></p> -<div class="section"> -<h3 class="nobreak" id="APPARATUS_FOR_REGULATING_THE_RATE_AND_LOSS_OF_HEAD"> -APPARATUS FOR REGULATING THE RATE AND LOSS of HEAD.</h3></div> - -<p>Many appliances have been invented for the regulation of the rate and -loss of head. In the apparatus designed by Gill and used at both Tegel -and Müggel at Berlin the regulation is effected by partially closing -a gate through which the effluent passes into a chamber in which the -water-level is practically constant (Fig. 6). The rate is measured -by the height of water on the weir which serves as the outlet for -this second chamber into a third connecting with the main reservoir, -while the loss of head is shown by the difference in height of floats -upon water in the first chamber, representing the pressure in the -underdrains, and upon water in connection with the raw water on the -filter. From the respective heights of the three floats the attendant -can at any time see the rate of filtration and the loss of head, and -when a change is required it is effected by moving the gate.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image055" style="max-width: 50em;"> - <img class="w100" src="images/image055.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 6.—Regulation Apparatus at Berlin (Tegel).</span></p></div> - -<p>In the apparatus designed in 1866 by Kirkwood for St. Louis and never -built (Fig. 7) the loss of head was directly, and the rate indirectly, -regulated by a movable weir, which was to have been lowered from time -to time by the attendant to secure the required results. This plan is -especially remarkable as it meets<span class="pagenum" id="Page_56">[Pg 56]</span> the modern requirements of a regular -rate independent of rate of consumption and of the water-level in the -reservoir, and also allows continual measurements of both rate (height -of water on the weir) and head (difference in water-levels on filter -and in effluent chamber) to be made, and control of the same by the -position of the weir. Mr. Kirkwood found no filters in Europe with such -appliances, and it was many years after his report was published before -similar devices were used, but they are now regarded as essential.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image056a" style="max-width: 50em;"> - <img class="w100" src="images/image056a.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 7.—Regulation Apparatus and Section of Filter -recommended for St. Louis by Kirkwood in 1866.</span></p></div> - -<div class="figcenter padb1 illowp100" id="image056b" style="max-width: 37.5em;"> - <img class="w100" src="images/image056b.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 8.—Regulation Apparatus used at Hamburg.</span></p></div> - -<p>The regulators for new filters at Hamburg (Fig. 8) are built upon the -principle of Kirkwood’s device, but provision is made for a second -measurement of the water if desired by the loss of<span class="pagenum" id="Page_57">[Pg 57]</span> head in passing a -submerged orifice. Both the rate and loss of head are indicated by a -float on the first chamber connecting directly with the underdrain, -which at the same time indicates the head on a fixed scale, the zero of -which corresponds to the height of the water above the filter, and the -rate upon a scale moving with the weir, the zero of which corresponds -with the edge of the weir. The water on the filter is held at a -perfectly constant level.</p> - -<p>The regulators in use at Worms and those recently introduced at -Magdeburg act upon the same principle, but the levels of the water on -the filters are allowed to fluctuate, and the weirs and in fact, the -whole regulating appliances are mounted on big floats in surrounding -chambers of water connecting with the unfiltered water on the filters. -I am unable to find any advantages in these appliances, and they are -much more complicated than the forms shown by the cuts.</p> - -<div class="section"> -<h3 class="nobreak" id="APPARATUS_FOR_REGULATING_THE_RATE_DIRECTLY">APPARATUS FOR REGULATING THE RATE DIRECTLY.</h3></div> - -<div class="figcenter padt1 padb1 illowp100" id="image057" style="max-width: 50em;"> - <img class="w100" src="images/image057.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 9.—Lindley’s Regulation Apparatus at Warsaw, -Russia.</span></p></div> - -<p>The above-mentioned regulators control directly the loss of head, -and only indirectly the rate of filtration. The regulators at Warsaw -were designed by Lindley to regulate the rate directly and make it -independent of the loss of head. The quantity of water flowing away -is regulated by a float upon the water<span class="pagenum" id="Page_58">[Pg 58]</span> in the effluent chamber, -which holds the top of the telescope outlet-pipe a constant distance -below the surface and so secures a constant rate. As the friction of -the filter increases the float sinks with the water until it reaches -bottom, when the filter must be scraped. A counter-weight reduces the -weight on the float, and at the same time allows a change in the rate -when desired. This apparatus is automatic. All of the other forms -described require to be occasionally adjusted by the attendant, but -the attention they require is very slight, and watchmen are always on -duty at large plants, who can easily watch the regulators. The Warsaw -apparatus is reported to work very satisfactorily, no trouble being -experienced either by leaking or sticking of the telescope-joint, -which is obviously the weakest point of the device, but fortunately a -perfectly tight joint is not essential to the success of the apparatus. -Regulators acting upon the same principle have recently been installed -at Zürich, where they are operating successfully.</p> - -<p>Burton<a id="FNanchor_16" href="#Footnote_16" class="fnanchor">[16]</a> has described an ingenious device designed by him for the -filters at Tokyo, Japan. It consists of a double acting valve of gun -metal (similar to that shown by Fig. 11), through which the effluent -must pass. This valve is opened and closed by a rod connecting with -a piston in a cylinder, the opposite sides of which connect with the -effluent pipe above and below a point where the latter is partially -closed, so that the valve is opened and closed according as the loss -of head in passing this obstruction is below or above the amount -corresponding to the desired rate of filtration.</p> - -<p>The use of the Venturi meter in connection with the regulation of -filters would make an interesting study, and has, I believe, never been -considered.</p> - -<div class="figcenter padt1 padb1 illowp82" id="facing058_1" style="max-width: 56.25em;"> - <img class="w100" src="images/facing058_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Regulator-house, showing Rate of Filtration and Loss -of Head on the Outside, Bremen.</span></p></div> - -<div class="figcenter padb1 illowp76" id="facing058_2" style="max-width: 56.25em;"> - <img class="w100" src="images/facing058_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Inlet for Admission of Raw Water to a Filter, East -London.</span></p> - -<p class="right">[<em>To face page 58.</em>]</p></div> - -<p><span class="pagenum" id="Page_59">[Pg 59]</span></p> - -<div class="section"> -<h3 class="nobreak" id="APPARATUS_FOR_REGULATING_THE_HEIGHT_OF_WATER_UPON_FILTERS"> -APPARATUS FOR REGULATING THE HEIGHT OF WATER UPON FILTERS.</h3></div> - -<p>It will be seen by reference to the diagrams of the Berlin and Hamburg -effluent regulators (Figs. 6 and 8) that their perfect operation -is dependent upon the maintenance of a constant water-level upon -the filters. The old-fashioned adjustment of the inlet-gate by the -attendant is hardly accurate enough.</p> - -<p>The first apparatus for accurately and automatically regulating the -level of the water upon the filters was constructed at Leeuwarden, -Holland, by the engineer, Mr. Halbertsma, who has since used a similar -device at other places, and improved forms of which are now used at -Berlin and at Hamburg.</p> - -<p>At Berlin (Müggel) the water-level is regulated by a float upon the -water in the filter which opens or shuts a balanced double valve on -the inlet-pipe directly beneath, as shown in Fig. 10. It is not at all -necessary that this valve should shut water-tight; it is only necessary -that it should prevent the continuous inflow from becoming so great as -to raise the water-level, and for this reason loose, easily-working -joints are employed. The apparatus is placed in a little pit next to -the side of the filter, and the overflowing water is prevented from -washing the sand by paving the sand around it for a few feet.</p> - -<div class="figcenter padt1 padb1 illowp82" id="image059" style="max-width: 41.625em;"> - <img class="w100" src="images/image059.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 10.—Regulation of Inflow used at Müggel, -Berlin.</span></p></div> - -<p>At Hamburg the same result is obtained by putting the valve<span class="pagenum" id="Page_60">[Pg 60]</span> in a -special chamber outside of the filter and connected with the float by a -walking-beam (Fig. 11).</p> - -<div class="figcenter padt1 padb1 illowp100" id="image060" style="max-width: 50em;"> - <img class="w100" src="images/image060.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 11.—Regulation of Inflow used at Hamburg.</span></p></div> - -<p>The various regulators require to be protected from cold and ice by -special houses, except in the case of covered filters, where they can -usually be arranged with advantage in the filter itself. In regard to -the choice of the form of regulator for both the inlets and outlets of -filters, so far as I have been able to ascertain, each of the modern -forms described as in use performs its functions satisfactorily, and in -special cases any of them could properly be selected which would in the -local conditions be the simplest in construction and operation.</p> - -<div class="section"> -<h3 class="nobreak" id="LIMIT_TO_THE_LOSS_OF_HEAD">LIMIT TO THE LOSS OF HEAD.</h3></div> - -<p>The extent to which the loss of head is allowed to go before filters -are cleaned differs widely in the different works, some of the newer -works limiting it sharply because it is believed that low bacterial -efficiency results when the pressure is too great, although the -frequency of cleaning and consequently the cost of operation are -thereby increased.</p> - -<p>At Darlington, England, I believe as a result of the German theories, -the loss of head is limited to about 18 inches by a masonry weir built -within the last few years. At Berlin, both at<span class="pagenum" id="Page_61">[Pg 61]</span> Tegel and Müggel, the -limit is 24 inches, while at the new Hamburg works 28 inches are -allowed. At Stralau in 1893 an effort was made to not exceed a limit -of 40 inches, but previously heads up to 60 inches were used, which -corresponds with the 56 inches used at Altona; and, in the other old -works, while exact information is not easily obtained because of -imperfect records, I am convinced that heads of 60 or even 80 inches -are not uncommon. At the Lawrence Experiment Station heads of 70 inches -have generally been used, although some filters have been limited to 36 -and 24 inches.</p> - -<p>In 1866 Kirkwood became convinced that the loss of head should not go -much above 30 inches, first, because high heads would, by bringing -extra weight upon the sand, make it too compact, and, second, because -when the pressure became too great the sediment layer on the surface of -the sand, in which most of the loss of head occurs, would no longer be -able to support the weight and, becoming broken, would allow the water -to pour through the comparatively large resulting openings at greatly -increased rates and with reduced efficiency.</p> - -<p>In regard to the first point, a straight, even pressure many times -that of the water on the filter is incapable of compressing the sand. -It is much more the effect of the boots of the workmen when scraping -that makes the sand compact. I have found sand in natural banks at -Lawrence 70 or 80 feet below the surface, where it had been subjected -to corresponding pressure for thousands of years, to be quite as porous -as when packed in water in experimental filters in the usual way.</p> - -<p>The second reason mentioned, or, as I may call it, the breaking-through -theory, is very generally if not universally accepted by German -engineers, and this is the reason for the low limit commonly adopted by -them.</p> - -<p>A careful study of the results at Lawrence fails to show the slightest -deterioration of the effluents up to the limit used, 72 inches. Thus -in 1892, taking only the results of the continuous<span class="pagenum" id="Page_62">[Pg 62]</span> filters of full -height (Nos. 33A, 34A, 36A, and 37), we find that for the three days -before scraping, when the head was nearly 72 inches, the average -number of bacteria in the effluents was 31 per cc., while for the -three days after scraping, with very low heads, the number was 47. -The corresponding numbers of <em>B. prodigiosus</em><a id="FNanchor_17" href="#Footnote_17" class="fnanchor">[17]</a> were 1.1 and -2.7. This shows better work with the highest heads, but is open to the -objection that the period just after scraping, owing to the disturbance -of the surface, is commonly supposed to be a period of low efficiency.</p> - -<p>To avoid this criticism in calculating the corresponding results for -1893, the numbers of the bacteria for the intermediate days which could -not have been influenced either by scraping or by excessive head are -put side by side with the others. Taking these results as before for -continuous filters 72 inches high, and excluding those with extremely -fine sands and a filter which was only in operation a short time toward -the end of the year, we obtain the following results:</p> - -<table class="autotable" summary="bacteria counts following scraping"> -<tr> -<th class="tdl"> </th> -<th class="tdc small normal">Water<br />Bacteria<br />per cc.</th> -<th class="tdc small normal">B.<br />Prodigiosus<br />per cc.</th> -</tr> -<tr> - -<td class="tdl vertb">Average 1st day after scraping, low heads</td> -<td class="tdc">79</td> -<td class="tdc">6.1</td> -</tr> -<tr> - -<td class="tdl vertb">Average 2d day after scraping, low heads</td> -<td class="tdc">44</td> -<td class="tdc">4.1</td> -</tr> -<tr> - -<td class="tdl vertb">Average 3d day after scraping, low heads</td> -<td class="tdc">45</td> -<td class="tdc">3.6</td> -</tr> -<tr> - -<td class="tdl vertb">Intermediate days, medium heads</td> -<td class="tdc">59</td> -<td class="tdc">4.5</td> -</tr> -<tr> - -<td class="tdl vertb">Second from last day, heads of nearly 72 inches</td> -<td class="tdc">66</td> -<td class="tdc">2.7</td> -</tr> -<tr> - -<td class="tdl vertb">Next to the last day, heads of nearly 72 inches</td> -<td class="tdc">56</td> -<td class="tdc">3.2</td> -</tr> -<tr> - -<td class="tdl vertb">Last day, heads of nearly 72 inches</td> -<td class="tdc">83</td> -<td class="tdc">2.5</td> -</tr> -</table> - -<p class="padt1">These figures show a very slight increase of the water bacteria in -the effluent as the head approaches the limit, but no such increase -as might be expected from a breaking through of the sediment layer, -and the <em>B. prodigiosus</em> which is believed to better indicate -the removal of the bacteria of the original water,<span class="pagenum" id="Page_63">[Pg 63]</span> actually shows a -decrease, the last day being the best day of the whole period.</p> - -<p>The Lawrence results, then, uniformly and clearly point to a conclusion -directly opposite to the commonly accepted view, and I have thus -been led to examine somewhat closely the grounds upon which the -breaking-through theory rests.</p> - -<p>The two works which have perhaps contributed most to the theories -of filtration are the Stralau and Altona works. After examining the -available records of these works, I am quite convinced that at these -places there has been, at times at least, decreased efficiency with -high heads. For the Stralau works this is well shown by Piefke’s plates -in the <cite>Zeitschrift für Hygiene</cite>, 1894, after page 188. In both -of these works, however, the apparatus (or lack of apparatus) for -regulating the rate is that shown by Fig. 5, page 49, and the rate -of filtration is thus dependent upon the rate of consumption and the -height of water in the reservoir. At the Stralau works, at the time -covered by the above-mentioned diagrams, the daily quantity of water -filtered was 27 times the capacity of the reservoir, and the rate -of filtration must consequently have adapted itself to the hourly -consumptions. The data which formed the basis of Kirkwood’s conclusions -are not given in detail, but it is quite safe to assume that they were -obtained from filters regulated as those at Altona and Stralau are -regulated, and what is said in regard to the latter will apply equally -to his results.</p> - -<p>Piefke<a id="FNanchor_18" href="#Footnote_18" class="fnanchor">[18]</a> shows that among the separate filters at Stralau, all -connected with the same pure-water reservoir, those connected through -the shorter pipes gave poorer effluents than the more remote filters, -and he attributes the difference to the frictional resistance of the -connecting pipes, which helped to prevent excessive rates in the -filters farthest away when the water in the reservoir became low, and -thus the fluctuations in the rates in these filters were less than in -those close to the reservoir. He -<span class="pagenum" id="Page_64">[Pg 64]</span> -does not, however, notice, in speaking of the filters in which the -decreased efficiencies with high heads were specially marked, that they -follow in nearly the same order, and that of the four open filters -mentioned three were near the reservoir and only one was separated by -a comparatively long pipe, indicating that the deterioration with high -heads was only noticeable, or at least was much more conspicuous, in -those filters where the rates fluctuated most violently.</p> - -<p>It requires no elaborate calculation to show that of two filters -connected with the same pure-water reservoir, as shown by Fig. 5, -with only simple gates on the connecting pipes, one of them clean and -throttled by a nearly closed gate, so that the normal pressure behind -the gate is above the highest level of water in the reservoir, and the -other clogged so that the normal pressure of the water in the drain is -considerably below the highest level of the water in the reservoir, -the latter will suffer much the more severe shocks with fluctuating -water-levels; and the fact being admitted that fluctuating levels are -unfavorable, we must go farther and conclude that the detrimental -action will increase with increasing loss of head. I am inclined to -think that this theory is adequate to explain the Stralau and Altona -results without resource to the breaking-through theory.</p> - -<p>While the above does not at all prove the breaking-through theory to be -false, it explains the results upon which it rests in another way, and -can hardly fail to throw so much doubt upon it as to make us refuse to -allow its application to those works where a regular rate of filtration -is maintained regardless of variations in the consumption, until proof -is furnished that it is applicable to them.</p> - -<p>I have been totally unable to find satisfactory European results in -regard to this point. The English works can furnish nothing, both on -account of the lack of regulating appliances and because the monthly -bacterial examinations are inadequate for a discussion of hourly or -daily changes. The results from<span class="pagenum" id="Page_65">[Pg 65]</span> the older Continental works are also -excluded for one or the other, or more often for both, of the above -reasons. The Hamburg, Tegel, and Müggel results, so far as they go, -show no deterioration with increased heads, but the heads are limited -to 24 or 28 inches by the construction of the filters, and the results -thus entirely fail to show what would be obtained with heads more than -twice as high.</p> - -<p>I am thus forced to conclude that there is no adequate evidence of -inferior efficiency with high heads in filters where the rates are -independent of the water-level in the pure-water reservoir, the -only results directly to the point—the Lawrence results mentioned -above—indicating that the full efficiency is maintained with heads -reaching at least 72 inches.</p> - -<p>The principal reason for desiring to allow a considerable loss of head -is an economical one; the period will then be lengthened, while the -frequency of scraping and the volume of sand to be washed and replaced -will be correspondingly reduced. There may be other advantages in long -periods, such as less trouble with scraping and better work in cold -winter weather, but the cost is the most important consideration.</p> - -<p>It is the prevalent idea among the German engineers that the loss of -head after reaching 24 to 30 inches would increase very rapidly, so -that the quantity of water filtered, in case a much higher head was -allowed, would not be materially increased. No careful investigations, -however, have been made, and indeed they are hardly possible with -existing arrangements, as in the older filters the loss of head -fluctuates with varying rates of filtration in such a way that only -results of very doubtful value can be obtained, and in the newer works -the loss of head is too closely limited, and the curves which can be -drawn by extrapolation are evidently no safe indications of what would -actually happen if the process was carried farther.</p> - -<p>On the other hand, I was told by the attendant at Darlington, England, -that since the building of the weir a few years ago,<span class="pagenum" id="Page_66">[Pg 66]</span> which now limits -the loss of head to about 18 inches instead of the 5 feet or more -formerly used, the quantity of sand to be removed has been three times -as great as formerly. No records are kept, and this can only be given -as the general impression of the man who superintends the work.</p> - -<p>At Lawrence the average quantities of water filtered between scrapings -with sand of an effective size of 0.20 mm. have been as follows:</p> - - -<table class="autotable" summary="At Lawrence the average quantities of water filtered between scrapings"> -<tr> -<th class="tdc normal smaller">Maximum Loss of<br />Head.</th> -<th class="tdc normal smaller" colspan="3">Million Gallons per Acre filtered<br />between Scrapings.</th> -</tr> -<tr> -<th> </th> -<th class="tdc normal smaller">1892.</th> -<th class="tdc normal smaller">1893.</th> -<th class="tdc normal smaller">Average.</th> -</tr> -<tr> -<td class="tdl vertb">70 inches</td> -<td class="tdc">58</td> -<td class="tdc">88</td> -<td class="tdc">73</td> -</tr> -<tr> -<td class="tdl vertb">34 inches</td> -<td class="tdc">32</td> -<td class="tdc">22</td> -<td class="tdc">27</td> -</tr> -<tr> -<td class="tdl vertb">22 inches</td> -<td class="tdc">17</td> -<td class="tdc">16</td> -<td class="tdc">16</td> -</tr> -<tr> -<td class="tdc" colspan="4">With sand of an effective size of 0.29 mm. the results were:</td> -</tr> -<tr> -<th> </th> -<th> </th> -<th class="tdc normal smaller">1893.</th> -<th> </th> -</tr> -<tr> -<td class="tdl vertb">70 inches</td> -<td> </td> -<td class="tdc">70</td> -<td> </td> -</tr> -<tr> -<td class="tdl vertb">22 inches</td> -<td> </td> -<td class="tdc">29</td> -<td> </td> -</tr> -</table> - -<p>These results indicate a great increase in the quantity of water -filtered between scrapings with increasing heads, the figures being -nearly proportional to the maximum heads used in the respective -cases. It is, of course, quite possible that the results would differ -in different places with the character of the raw water and of the -filtering material.</p> - -<p>The depth of sand to be removed by scraping at one time is, within -limits, practically independent of the quantity of dirt which it has -accumulated, and any lengthening of the period means a corresponding -reduction in the quantity of sand to be removed, washed and replaced -and consequently an important reduction in the operating cost, as well -as a reduction in the area of filters out of use while being cleaned, -and so, in the capital cost.</p> - -<p>Among the minor objections to an increased loss of head are the -greater head against which the water must be pumped, and<span class="pagenum" id="Page_67">[Pg 67]</span> the possible -increased difficulty of filling filters with filtered water from below -after scraping, but these would hardly have much weight against the -economy indicated by the Lawrence experiments for the higher heads.</p> - -<p>High heads will also drive an increased quantity of water through any -cracks or passages in the filter. Such leaks have at last been found to -be the cause of the inferior work of the covered filters at Stralau, -the water going down unfiltered in certain corners, especially at high -heads; but with careful construction there should be no cracks, and -with the aid of bacteriology to find the possible leaks this ought not -to be a valid objection.</p> - -<p>In conclusion: the trend of opinion is strongly in favor of limiting -the loss of head to about 24 to 30 inches as was suggested by Kirkwood, -but I am forced to conclude that there is reason to believe that -equally good results can be obtained with lower operating expenses by -allowing higher heads to be used, at least in the case of filters with -modern regulating appliances, and, I would suggest that filters should -be built so as not to exclude the use of moderately high heads, and -that the limit to be permanently used should be determined by actual -tests of efficiency and length of period with various losses of head -after starting the works.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_68">[Pg 68]</span></p> - -<h2 class="nobreak" id="CHAPTER_V">CHAPTER V.<br /> -<br /> - -<span class="smaller">CLEANING FILTERS.</span></h2></div> - -<p><span class="smcap">When</span> a filter has become so far clogged that it will no longer pass -a satisfactory quantity of water with the allowable head it must be -cleaned by scraping off and removing the upper layer of dirty sand.</p> - -<p>To do this without unnecessary loss of time the unfiltered water -standing upon the filter is removed by a drain above the sand provided -for that purpose. The water in the sand must then be lowered below the -surface of the sand by drawing water from the underdrains until the -sand is firm enough to bear the weight of the workmen. By the time -that this is accomplished the last water on the surface should have -soaked away, and the filter is ready to be scraped. This is done by -workmen with wide, sharp shovels, and the sand removed is taken to -the sand-washing apparatus to be washed and used again. Special pains -are given to securing rapid and cheap transportation of the sand. In -some cases it is wheeled out of the filter on an inclined plane to the -washer. In other cases a movable crane is provided which lifts the sand -in special receptacles and allows it to fall into cars on a tram-line -on which the crane also moves. The cars as filled are run to the washer -and also serve to bring back the washed sand. When the dirty sand has -been removed, the surface of the sand is carefully smoothed and raked. -This is especially necessary to remove the effects of the workmen’s -boots.</p> - -<p>It is customary in the most carefully managed works to fill the sand -with filtered water from below, introduced through the underdrains. In -case the ordinary level of the water in the<span class="pagenum" id="Page_69">[Pg 69]</span> pure-water canal is higher -than the surface of the sand in the filters, this is accomplished -by simply opening a gate provided for the purpose, which allows the -water to pass around the regulating apparatus. Otherwise filters can -be filled from a special pipe taking its water from any filter which -at that time can deliver its effluent high enough for that purpose. -The quantity of water required for filling the sand from below is -ordinarily but a fraction of one per cent of the quantity filtered.</p> - -<p>Formerly, instead of filling from below, after cleaning, the raw water -was brought directly onto the surface of the filter. This was said to -only imperfectly fill the sand-pores, which still contained much air. -If, however, the water is not brought on too rapidly it will sink into -the sand near the point where it is applied, pass laterally through the -sand or underlying gravel to other parts of the filter, and then rise, -so that even in this case all but a little of the filter will be really -filled from below. This is, however, open to the objection that however -slowly the water is introduced, the sand which absorbs it around the -inlet filters it at a very high rate and presumably imperfectly, so -that the water in the underdrains at the start will be poor quality -and the sand around the inlet will be unduly clogged. The practice of -filling from below is therefore well founded.</p> - -<p>As soon as the surface of the sand is covered with the water from -below, raw water is introduced from above, filling the filter to -the standard height, care being taken at first that no currents -are produced which might wash the surface of the sand. It has been -recommended by Piefke and others that this water should be allowed -to stand for a time up to twenty-four hours before starting the -filtration, to allow the formation of a sediment layer, and in some -places, especially at Berlin and the works of some of the London -companies, this is done; but varying importance is attached to the -procedure, and it is invariably omitted, so far as I can learn, when -the demand for water is heavy.</p> - -<p>The depth of sand removed by scraping must at least equal<span class="pagenum" id="Page_70">[Pg 70]</span> the -depth of the discolored layer, but there is no sharp dividing line, -the impurities gradually decreasing from the surface downward. -Fig. 12 shows the relative number of bacteria found in the sand at -various depths in one of the Lawrence experimental filters, and is a -representative result, although the actual numbers vary at different -times. In general it may be said that the bulk of the sediment is -retained in the upper quarter inch, but it is desirable to remove also -the less dirty sand below and, in fact, it is apparently impossible -with the method of scraping in use to remove so thin a layer as one -fourth inch. Practically the depth to which sand is removed is stated -to be from 0.40 to 1.20 inch. Exact statistics are not easily obtained, -but I think that 2 centimeters or 0.79 inch may be safely taken as -about the average depth usually removed in European filters, and it is -this depth which is indicated on Fig. 12.</p> - -<div class="figcenter padt1 padb1 illowp90" id="image070" style="max-width: 37.5em;"> - <img class="w100" src="images/image070.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 12.—Diagram Showing Accumulation of Bacteria -near the Surface of the Sand.</span></p></div> - -<p>At the Lawrence Experiment Station, the depth removed is often much -less than this, and depends upon the size of grain of the sand -employed, the coarser sands requiring to be more deeply scraped than -the finer ones. The method of scraping, however, which allows the -removal of very thin sand layers, is<span class="pagenum" id="Page_71">[Pg 71]</span> only possible because of the -small size of the filters, and as it is incapable of application on a -large scale, the depths thus removed are only interesting as showing -the results which might be obtained in practice with a more perfect -method of scraping.</p> - -<p>The replacing of the washed sand is usually delayed until the filter -has been scraped quite a number of times—commonly for a year. The last -scraping before refilling is much deeper than usual, because the sand -below the depth of the ordinary scraping is somewhat dirty, and might -cause trouble if left below the clean sand.</p> - -<p>In England it is the usual if not the universal practice to replace the -washed sand at the bottom between the old sand and the gravel. This is -done by digging up the entire filter in sections about six feet wide. -The old sand in the first section is removed clear down to the gravel, -and the depth of washed sand which is to be replaced is put in its -place. The old sand from the next six-foot section is then shovelled -upon the first section of clean sand, and its place is in turn filled -with fresh sand. With this practice the workmen’s boots are likely to -disturb the gravel each year, necessitating a thicker layer of the -upper and finest grade than would otherwise be required.</p> - -<p>In Germany this is also sometimes done, but more frequently the upper -layer of slightly clogged sand below the regular scraping is removed -as far as the slightest discoloration can be seen, perhaps 6 inches -deep. The sand below is loosened for another 6 inches and allowed to -stand dry, if possible, for some days; afterwards the washed sand is -brought on and placed above. The washed sand is never replaced without -some such treatment, because the slightly clogged sand below the layer -removed would act as if finer than the freshly washed sand,<a id="FNanchor_19" href="#Footnote_19" class="fnanchor">[19]</a> and -there would be a tendency to sub-surface clogging.</p> - -<p><span class="pagenum" id="Page_72">[Pg 72]</span></p> - -<div class="section"> -<h3 class="nobreak" id="FREQUENCY_OF_SCRAPING">FREQUENCY OF SCRAPING.</h3></div> - -<p>The frequency of scraping depends upon the character of the raw water, -the thoroughness of the preliminary sedimentation, the grain-size of -the filter sand, the rate of filtration, and the maximum loss of head -allowed. With suitable conditions the period between scrapings should -never be less than one week, and will but rarely exceed two months. -Under exceptional conditions, however, periods have been recorded as -low as one day and as high as one hundred and ten days. Periods of less -than a week’s duration are almost conclusive evidence that something -is radically wrong, and the periods of one day mentioned were actually -accompanied by very inadequate filtration. In 1892 the average periods -at the German works varied from 9.5 days at Stettin (with an excessive -rate) to 40 days at Brunswick, the average of all being 25 days.<a id="FNanchor_20" href="#Footnote_20" class="fnanchor">[20]</a></p> - -<p>The quantity of water per acre filtered between scrapings forms the -most convenient basis for calculation. The effect of rate (page -49), loss of head (page 65), and size of sand grain (page 32) have -already been discussed, and it will suffice to say here that the total -quantity filtered between scrapings is apparently independent of the -rate of filtration, but varies with the maximum loss of head and with -the grain-size of the sand, and apparently nearly in proportion to -them. Eleven German filter-works in 1892, drawing their waters from -rivers, filtered on an average 51 million gallons of water per acre -between scrapings, the single results ranging from 28 at Bremen to 71 -at Stuttgart, while Zürich, drawing its water from a lake which is -but very rarely turbid, filtered 260 million gallons per acre between -scrapings. Unfortunately, the quantities at Berlin, where (in 1892 two -thirds and now all) the water is drawn from comparatively large ponds -on the rivers, are not available for comparison.</p> - -<p>At London, in 1884, the average quantities of water filtered -<span class="pagenum" id="Page_73">[Pg 73]</span> -between scrapings varied from 43 to 136 million gallons per acre with -the different companies, averaging 85, and in 1892 the quantities -ranged from 73 to 157, averaging 90 million gallons per acre. The -greater quantity filtered at London may be due to the greater sizes of -the sedimentation-basins, which for all the companies together hold a -nine days’ supply at London against probably less than one day’s supply -for the German works.</p> - -<p>There is little information available in regard to the frequency -of scraping with water drawn from impounding reservoirs. In some -experiments made by Mr. FitzGerald at the Chestnut Hill reservoir, -Boston, the results of which are as yet unpublished, a filter with -sand of an effective size of only .09 mm. averaged 58 million gallons -per acre between scrapings for nine periods, the rate of filtration -being 1.50 million gallons per acre daily, while another filter, with -sand of an effective size of .18 mm., passed an average of 93 million -gallons per acre for ten periods at the same rate. These experiments -extended through all seasons of the year, and taking into account the -comparative fineness of the sands they show rather high quantities of -water filtered between scrapings.</p> - -<p>The quantity of water filtered between scrapings is usually greatest -in winter, owing to the smaller quantity of sediment in the raw water -at this season, and is lowest in times of flood, regardless of season. -In summer the quantity is often reduced to a very low figure in waters -supporting algæ growths, especially when the filters are not covered. -Thus at Stralau in 1893 during the algæ period the quantity was reduced -to 14 million gallons per acre for open filters,<a id="FNanchor_21" href="#Footnote_21" class="fnanchor">[21]</a> but this was quite -exceptional, the much-polluted, though comparatively clear, Spree water -furnishing unusually favorable conditions for the algæ.</p> - -<p><span class="pagenum" id="Page_74">[Pg 74]</span></p> - -<div class="section"> -<h3 class="nobreak" id="QUANTITY_OF_SAND_TO_BE_REMOVED">QUANTITY OF SAND TO BE REMOVED.</h3></div> - -<p>In regard to the quantity of sand to be removed and washed, if we -take the average result given above for the German works filtering -river-waters of 51,000,000 gallons per acre filtered between scrapings, -and the depth of sand removed at two centimeters or 0.79 inch, we -find that one volume of sand is required for every 2375 volumes of -water filtered, or 2.10 cubic yards per million gallons. At Bremen, -the highest average result, the quantity would be 3.80 yards, and at -Stralau during the algæ season 7.70 yards. At Zürich, on the other -hand, the quantity is only 0.41 yard, and at London, with 87,000,000 -gallons per acre filtered between scrapings, the quantity of sand -washed would be 1.24 yards per million gallons; assuming always that -the layer removed is 0.79 inch thick.</p> - -<p>These estimates are for the regular scrapings only, and do not include -the annual deeper scraping before replacing the sand, which would -increase them by about one third.</p> - -<div class="section"> -<h3 class="nobreak" id="WASTING_THE_EFFLUENTS_AFTER_SCRAPING">WASTING THE EFFLUENTS AFTER SCRAPING.</h3></div> - -<p>It has already been stated that an important part of the filtration -takes place in the sediment layer deposited on top of the sand from -the water. When this layer is removed by scraping its influence is -temporarily removed, and reduced efficiency of filtration may result. -The significance of this reduced efficiency became apparent when the -bacteria in the water were studied in their relations to disease, and -Piefke suggested<a id="FNanchor_22" href="#Footnote_22" class="fnanchor">[22]</a> that the first effluent after scraping should -be rejected for one day after ordinary scrapings and for one week -after replacing the sand. In a more recent paper<a id="FNanchor_23" href="#Footnote_23" class="fnanchor">[23]</a> he reduces these -estimates to the first million gallons of water per acre filtered after -scraping</p> - -<p><span class="pagenum" id="Page_75">[Pg 75]</span></p> - -<p>for open and twice as great a quantity for covered filters, and to six -days after replacing the sand, which last he estimates will occur only -once a year. Taking the quantity of water filtered between scrapings at -13.9 million gallons per acre, the quantity observed at Stralau in the -summer of 1893, he finds that it is necessary to waste 9 per cent of -the total quantity of effluent from open and 13.8 per cent of that from -covered filters.</p> - -<p>The eleven German water-works<a id="FNanchor_24" href="#Footnote_24" class="fnanchor">[24]</a> filtering river-waters, however, -filtered on an average 51.0 instead of 13.9 million gallons per acre -between scrapings, and applying Piefke’s figures to them the quantities -of water to be wasted would be only about one fourth of his estimates -for Stralau.</p> - -<p>The rules of the Imperial Board of Health<a id="FNanchor_25" href="#Footnote_25" class="fnanchor">[25]</a> require that every German -filter shall be so constructed “that when an inferior effluent results -it can be disconnected from the pure-water pipes and the filtrate -allowed to be wasted.” The drain-pipe for removing the rejected water -should be connected below the apparatus for regulating the rate and -loss of head, so that the filter can be operated exactly as usual, -and the effluent can be turned back to the pure-water pipes without -stopping or changing the rate. The works at Berlin and at Hamburg -conform to this requirement, and most of the older German works have -been or are being built over to make them do so.</p> - -<p>In regard to the extent of deterioration after scraping, Piefke’s -experiments have always shown much larger numbers of bacteria both of -the ordinary forms and of special applied forms on the first day after -scraping, the numbers frequently being many times as high as at other -times.</p> - -<p>At the Lawrence Experiment Station it was found in 1892 that on an -average the number of water bacteria was increased by 70 per cent -(continuous filters only) for the three days following scraping, while -<em>B. prodigiosus</em> when applied was increased 140 per -<span class="pagenum" id="Page_76">[Pg 76]</span> -cent, the increase being most marked where the depth of sand was -least, and with the highest rate of filtration.</p> - -<p>The same tendency was found in 1893, when the increase in the water -bacteria on the first day after scraping was only 19 per cent and -<em>B. prodigiosus</em> 64 per cent, but for a portion of the year the -difference was greater, averaging 132 and 262 per cent, respectively. -These differences are much less than those recorded by Piefke, and with -the high efficiencies regularly obtained at Lawrence they would hardly -justify the expensive practice of wasting the effluent.</p> - -<p>The reduction in efficiency following scraping is much less at low -rates, and if a filter is started at much less than its normal rate -after scraping, and then gradually increased to the standard after -the sediment layer is formed, the poor work will be largely avoided. -Practically this is done at Berlin and at Hamburg. The filters are -started at a fourth or less of the usual rates and are gradually -increased, as past experience with bacterial results has shown it can -be safely done, and the effluent is then even at first so well purified -that it need not be wasted.</p> - -<p>Practically in building new filters the provision of a suitable -connection for wasting the effluents into the drain which is necessary -for emptying them involves no serious expense and should be provided, -but it may be questioned how often it should be used for wasting the -effluents. If the raw water is so bad that a good effluent cannot be -obtained by careful manipulation even just after scraping, the course -of the Berlin authorities in closing the Stralau works and seeking a -less polluted supply would seem to be the only really safe procedure.</p> - -<div class="section"> -<h3 class="nobreak" id="SAND_WASHING">SAND-WASHING.</h3></div> - -<div class="figcenter padt1 padb1 illowp76" id="facing076_1" style="max-width: 59.375em;"> - <img class="w100" src="images/facing076_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Cleaning a Filter, East London.</span></p></div> - -<div class="figcenter padb1 illowp78" id="facing076_2" style="max-width: 59.375em;"> - <img class="w100" src="images/facing076_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Washing Dirty Sand with Hose, Antwerp.</span></p> - -<p class="right">[<em>To face page 76.</em>]</p></div> - -<p>The sand-washing apparatus is an important part of most European -filtering plants. It seldom happens that a natural sand can be found -clean enough and sufficiently free from fine particles although such -a sand was found and used for the Lawrence filter. Most of the sand in -use for filtration in Europe was originally washed. In the operation of -the filters also, sand-washing is used for the dirty sand, which can -then be used over and over at a much lower cost than would be the case -if fresh sand was used for refilling. The methods used for washing sand -at the different works present a great variety both in their details -and in the underlying principles. Formerly boxes with double perforated -bottoms in which the sand was placed and stirred by a man as water from -below rose through them, and other similar arrangements were commonly -used, but they are at present only retained, so far as I know, in some -of the smaller English works. The cleansing obtained is apparently -considerably less thorough than with some of the modern devices.</p> - -<div class="figcenter padt1 padb1 illowp82" id="image077" style="max-width: 50em;"> - <img class="w100" src="images/image077.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 13.—Hose-washing for Dirty Sand.</span></p></div> - -<p>Hose-washing is used in London by the Southwark and Vauxhall, Lambeth -and Chelsea companies, and also at Antwerp. For this a platform is -constructed about 15 feet long by 8 feet wide, with a pitch lengthwise -of 6 to 8 inches (Fig. 13). The<span class="pagenum" id="Page_78">[Pg 78]</span> platform is surrounded by a wall -rising from one foot at the bottom to three feet high at the top, -except the lower end, which is closed by a removable plank weir 5 or 6 -inches high. From two to four cubic yards of the sand are placed upon -this platform and a stream of water from a hose with a <sup>3</sup>⁄<sub>4</sub> or <sup>7</sup>⁄<sub>8</sub>-inch -nozzle is played upon it, moving it about from place to place. The sand -itself is always kept toward the upper end of the platform, while the -water with the dirt removed flows down into the pond made by the weir, -where the sand settles out and the dirt overflows with the water. When -the water comes off clear, which is usually after an hour or a little -less, the weir is removed, and, after draining, the sand is removed. -These arrangements are built in pairs so that the hose can be used in -one while the sand is being changed in the other. They are usually -built of brick laid in cement, but plank and iron are also used. The -corners are sometimes carried out square as in the figure, but are more -often rounded. The washing is apparently fairly well done.</p> - -<p>In Germany the so-called “drum” washing-machine, drawings of which have -been several times published,<a id="FNanchor_26" href="#Footnote_26" class="fnanchor">[26]</a> has come to be almost universally -used. It consists of a large revolving cylinder, on the bottom of the -inside of which the sand is slowly pushed up toward the higher end by -endless screw-blades attached to the cylinder, while water is freely -played upon it all the way. The machine requires a special house for -its accommodation and from 2 to 4 horse-power for its operation. It -washes from 2.5 to 4 yards of sand per hour most thoroughly, with a -consumption of from 11 to 14 times as large a volume of water. The -apparatus is not patented or made for sale, but full plans can be -easily secured.</p> - -<p>A machine made by Samuel Pegg & Sons, Leicester, Eng., pushes the -sand up a slight incline down which water flows. It is very heavy and -requires power to operate it. The patent has -<span class="pagenum" id="Page_79">[Pg 79]</span> -expired. A machine much like it but lighter and more convenient and -moved by water-power derived from the water used for washing instead of -steam-power is used at Zürich with good results.</p> - -<p>In Greenway’s machine the sand is forced by a screw through a long -narrow cylinder in which there is a current of water in the opposite -direction. The power required is furnished by a water-motor, as with -the machine at Zürich. The apparatus is mounted on wheels and is -portable; it has an appliance for piling up the washed sand or loading -it onto cars. It is patented and is manufactured by James Gibb & Co., -London.</p> - -<p>Several of the London water companies are now using ejector washers, -and such an apparatus has been placed by the side of the “drum” washers -at Hamburg. This apparatus was made by Körting Brothers in Hannover, -and combines the ejectors long made by that firm with hoppers from -designs by Mr. Bryan, engineer of the East London Water Company. An -apparatus differing from this only in the shape of the ejectors and -some minor details has been patented in England, and is for sale by -Messrs. Hunter, Frazer & Goodman, Bow, London.</p> - -<p>Both of these forms consist of a series of conical hoppers, from the -bottom of each of which the sand and water are forced into the top of -the next by means of ejectors, the excess of dirty water overflowing -from the top of each hopper. The apparatus is compact and not likely -to get out of order, but is not portable. It can be easily arranged to -take the sand at the level of the ground, or even lower if desired, and -deliver it washed at some little elevation, thus minimizing hand-labor. -The washing is regular and thorough. The objection most frequently -raised against its use is the quantity of water required, but at -Hamburg I was informed that the volume of water required was only about -15 times that of the sand, while almost as much (13-14 volumes) were -required for the “drum” washers, and<span class="pagenum" id="Page_80">[Pg 80]</span> the saving in power much more -than offset the extra cost for water.</p> - -<p>In addition to the above processes of sand-washing, Piefke’s method -of cleaning without scraping<a id="FNanchor_27" href="#Footnote_27" class="fnanchor">[27]</a> might be mentioned, although as -yet it has hardly passed the experimental stage, and has only been -used on extremely small filters. The process consists of stirring -the surface sand of the filter with “waltzers” while a thin sheet of -water rapidly flows over the surface. This arrangement necessitates a -special construction of the filters, providing for rapidly removing -the unfiltered water from the surface, and for producing a regular and -rapid movement of a thin sheet of water over the surface. In the little -filters now in use, one of which I saw in a brewery in Berlin, the -cleaning is rapidly, cheaply, and apparently well done.</p> - -<p>In washing dirty sand it is obvious that any small sand-grains will -be removed with the dirt, and in washing new sand the main object is -to remove the grains below a certain size. It is also apparent that -the sizes of grains which will and those which will not be removed -are dependent upon the mechanical arrangements of the washer, as, for -example, with the ejectors, upon the sizes of the hoppers, and the -quantity of water passing through them, and care should be taken to -make them correspond with the size of grain selected for the filter -sand. This can only be done by experiment, as no results are available -on this point.</p> - -<p>In some places filtered water is used for sand-washing, although this -seems quite unnecessary, as ordinary river-water answers very well. -It is, however, often cheaper, especially in small works, to use the -filtered water from the mains rather than provide a separate supply for -the washers.</p> - -<p>The quantity of water required for washing may be estimated at 15 times -the volume of the sand and the sand as 0.04 per cent of the volume of -the water filtered (page 74), so that<span class="pagenum" id="Page_81">[Pg 81]</span> -0.6 per cent of the total quantity of water filtered will be required -for sand-washing.</p> - -<p class="padb1">The cost of sand-washing in Germany with the “drum” washers is said -to be from 14 to 20 cents per cubic yard, including labor, power, and -water. In America the water would cost no more, but the labor would be -perhaps twice as dear. With an ejector apparatus I should estimate the -cost of washing dirty sand as follows: The sand would be brought and -dumped near to the washer, and one man could easily feed it in, as no -lifting is required. Two men would probably be required to shovel the -washed sand into barrows or carts with the present arrangements, but I -think with a little ingenuity this handling could be made easier.</p> - -<table class="autotable" summary="estimated cost of operating ejector washers"> -<tr> -<th class="tdc normal" colspan="2">ESTIMATED COST OF OPERATING EJECTOR WASHERS 9 HOURS.</th> -</tr> -<tr> -<td class="tdl vertb"><p class="indent">Wages of 3 men at $2.00</p></td> -<td class="tdr vertt">$6.00</td> -</tr> -<tr> -<td class="tdl vertb"><p class="indent">110,000 gals, water (15 times the volume of sand) at 0.05 a thousand gals.</p></td> -<td class="tdr bord_bot vertb">5.50</td> -</tr> -<tr> -<td class="tdl vertb"><p class="indent">Total cost of washing 36 cubic yards<br />or 32 cents a cubic yard.</p></td> -<td class="tdr vertt">$11.50</td> -</tr> -</table> - -<p class="padt1">The cost of washing new sand might be somewhat less. The other costs of -cleaning filters, scraping, transporting, and replacing the sand are -much greater than the washing itself. Lindley states that at Warsaw 29 -days’ labor of 10 hours for one man are required to scrape an acre of -filter surface, and four times as much for the annual deep scraping, -digging up, and replacing the sand. The first expense occurs in general -monthly, and the second only once a year. At other places where I have -secured corresponding data the figures range from 19 to 40 days’ labor -to scrape one acre, and average about the same as Lindley estimates.</p> - -<p>Under some conditions sand-washing does not pay, and in<span class="pagenum" id="Page_82">[Pg 82]</span> still others -it is almost impossible. No apparatus has yet been devised which will -wash the dirt out of the fine dune-sands used in Holland without -washing a large part of the sand itself away, and in these works fresh -sand, which is available in unlimited quantities and close to the -works, is always used. At Breslau the dirty sand is sold for building -purposes for one third of the price paid for new sand dredged from the -river, delivered at the works, and no sand is ever washed. Budapest, -Warsaw, and Rotterdam also use fresh river-sand without washing, except -a very crude washing to remove clay at Budapest.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_83">[Pg 83]</span></p> - -<h2 class="nobreak" id="CHAPTER_VI">CHAPTER VI.<br /> -<br /> - -<span class="smaller">THEORY AND EFFICIENCY OF CONTINUOUS FILTRATION.</span></h2></div> - -<p><span class="smcap">The</span> first filters for a public water-supply were built by James -Simpson, engineer of the Chelsea Water Company at London in 1829. They -were apparently intended to remove dirt from the water in imitation -of natural processes, and without any very clear conception of either -the exact extent of purification or the way in which it was to be -accomplished. The removal of turbidity was the most obvious result, and -a clear effluent was the single test of the efficiency of filtration, -as it remains the legal criterion of the work of the London filters -even to-day, notwithstanding the discovery and use of other and more -delicate tests.</p> - -<p>The invention and use of methods for determining the organic matters -in water by Wanklyn and Frankland, about 1870, led to the discovery -that the proportion of organic matters removed by filtration was -disappointingly low, and as, at the time, and for many years afterward, -an exaggerated importance was given to the mere quantities of organic -matters in water, it was concluded that filtration had only a limited -influence upon the healthfulness of the filtered water, and that -practically as much care must be given to securing an unpolluted water -as would be the case if it were delivered direct without filtration. -This theory, although not confirmed by more recent investigation, -undoubtedly has had a good influence upon the English works by causing -the selection of raw waters free from excessive pollutions, and, in -cases like the London supplies, drawn from the Thames and the Lea, in -stimulating a most jealous care of the watersheds and the purification -of sewage by the towns upon them.</p> - -<p><span class="pagenum" id="Page_84">[Pg 84]</span></p> - -<p>It was only after the discovery of the bacteria in water and their -relations to health that the hygenic significance of filtration -commenced to be really understood. Investigations of the bacteria in -the waters before and after filtration were carried out at Berlin -by Plagge and Proskauer, at London by Dr. Percy Frankland, and also -at Zürich, Altona, and on a smaller scale at other places. These -investigations showed that the bacteria were mainly removed by -filtration, the numbers in the effluents rarely exceeding two or three -per cent of those in the raw water. This gave a new aspect to the -problem.</p> - -<p>It was further observed, especially at Berlin and Zürich, that the -numbers of bacteria in effluents were apparently quite independent -of the numbers in the raw water, and the theory was formed that all -of the bacteria were stopped by the filters, and that those found in -the effluents were the result of contamination from the air and of -growths in the underdrains. The logical conclusion from this theory was -that filtered water was quite suitable for drinking regardless of the -pollution of its source.</p> - -<p>It was, however, found that the numbers of bacteria in the effluents -were higher immediately after scraping than at other times, and it was -concluded that before the formation of the sediment layer some bacteria -were able to pass the sand, and it was therefore recommended that the -first water filtered after scraping should be rejected.</p> - -<p>Piefke at Berlin gave the subject careful study, and came to the -conclusion that it was almost entirely the sediment layer which -stopped the bacteria, and that the bacteria themselves in the sediment -layer formed a slimy mass which completely intercepted those in the -passing water. When this layer was removed by scraping, the action -was stopped until a new crop of bacteria had accumulated. In support -of this idea he stated that he had taken ordinary good filter-sand -and killed the bacteria in it by heating it, and that on passing -water through, no purification was effected—in fact, the effluent -contained more<span class="pagenum" id="Page_85">[Pg 85]</span> bacteria than the raw water. After a little, bacteria -established themselves in the sand, and then the usual purification -was obtained. Piefke concluded that the action of the filter was a -biological one; that simple straining was quite inadequate to produce -the results obtained; that the action of the filter was mainly confined -to the sediment layer, and that the depth of sand beyond the slight -depth necessary for the support of this layer had no appreciable -influence upon the results. The effect of this theory is still seen in -the shallow sand layers used at Berlin and some other German works, -although at London the tendency is rather toward thicker sand layers.</p> - -<p>Piefke’s deductions, however, are not entirely supported by his data -as we understand them in the light of more recent investigation. -The experiment with sterilized sand has been repeatedly tried at -the Lawrence Experiment Station with results which quite agree with -Piefke’s, but it has also been found that the high numbers, often many -times as high as in the raw water, do not represent bacteria which pass -in the ordinary course of filtration, but instead enormous growths of -bacteria throughout the sand supported by the cooked organic matter in -it. It has been repeatedly found that ordinary sand quite incapable of -supporting bacterial growths, after heating to a temperature capable -of killing the bacteria will afterwards furnish the food for most -extraordinary numbers. A filter of such sand may stop the bacteria of -the passing water quite as effectually as any other filter, but if so, -the fact cannot be determined without recourse to special methods, on -account of the enormous numbers of bacteria in the sand, a small part -of which are carried forward by the passing water, and completely mask -the normal action of the filter.</p> - -<p>The theory that all or practically all of the bacteria are intercepted -by the sediment layer, and that those in the effluent are the result -of growths in the sand or underdrains, received two hard blows in 1889 -and 1891, when mild epidemics of typhoid fever<span class="pagenum" id="Page_86">[Pg 86]</span> followed unusually -high numbers of bacteria in the effluents at Altona and at Stralau in -Berlin, with good evidence in each case that the fever was directly due -to the water. Both of these cases came during, and as the result of, -severe winter weather with open filters and under conditions which are -now recognized as extremely unfavorable for good filtration.</p> - -<p>As a result of the first of these epidemics a series of experiments -were made at Stralau by Fränkel and Piefke in 1890. Small filters were -constructed, and water passed exactly as in the ordinary filters. -Bacteria of special kinds not existing in the raw water or effluents -were then applied, and the presence of a very small fraction of them -in the effluents demonstrated beyond a doubt that they had passed -through the filters under the ordinary conditions of filtration. These -experiments were afterwards repeated by Piefke alone under somewhat -different conditions with similar results. The numbers of bacteria -passing, although large enough to establish the point that some do -pass, were nevertheless in general but a small fraction of one per cent -of the many thousands applied.</p> - -<p>This method of testing the efficiency of filters had already been -used quite independently by Prof. Sedgwick at the Lawrence Experiment -Station in connection with the purification of sewage, and has since -been extensively used there for experiments with water-filtration.</p> - -<p>Kümmel also found at Altona that while in the regular samples for -bacterial examination, all taken at the same time in the day, there -was no apparent connection between the numbers of bacteria in the raw -water and effluents, by taking samples at frequent intervals throughout -the twenty-four hours, as has been done in a more recent series of -experiments, and allowing for the time required for the water to pass -the filters, a well-marked connection was found to exist between the -numbers of bacteria in the raw water and in the effluents.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image087" style="max-width: 37.5em;"> - <img class="w100" src="images/image087.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 14.—Showing Bacteria supposed to come through -Filters and from the Underdrains.</span></p></div> - -<p>The subject has more recently been studied in much detail at<span class="pagenum" id="Page_87">[Pg 87]</span> the -Lawrence Experiment Station, and it now appears that the bacteria -in the effluent from a filter are from two sources: directly from -the filtered water, and from the lower layers of the filter and -underdrains. Thus we may say:</p> - -<p class="noindent">Bacteria in effluent = Bacteria from underdrains + <sup><em>a</em></sup>⁄<sub>100</sub> × bacteria in raw water,</p> - -<p class="noindent">where <em>a</em> is the per cent of bacteria actually passing the filter.</p> - -<p>Both of these terms depend upon a whole series of complex and but -imperfectly understood conditions. In general the bacteria from the -underdrains are low in cold winter weather, often almost <em>nil</em>, -while at Lawrence with water temperatures of 70 to 75 degrees, and -over, in July and August, the numbers from this source may reach 200 or -300, but for the other ten months of the year rarely exceed 50 under -normal conditions. In summer especially it seems to be greater at low -than at high rates of filtration (although a high rate for a short time -only increases it), and so varies in the opposite way from the numbers -actually passing the filters. This subject is by no means clearly -understood; it is difficult, almost impossible, to separate the numbers -of bacteria into the two parts—those which come directly through and -may be dangerous, and those which have other origins and are harmless. -The sketch, Fig. 14, is drawn to represent my idea of the way they may -be divided. It has no statistical basis whatever. The light unshaded -section shows the percentage number of bacteria<span class="pagenum" id="Page_88">[Pg 88]</span> which I conceive to -be coming through a filter under given conditions at various rates of -filtration, while the shaded section above represents the bacteria from -other sources, and the upper line represents the sum of the two, or -the total number of bacteria in the effluent. The relative importance -of the two parts would probably vary widely with various conditions. -With the conditions indicated by the sketch the number of bacteria in -the effluent is almost constant: for a variation of only from 1.4 to -2.5 per cent of the number applied for the whole range is not a wide -fluctuation for bacterial results, but the number in the lower and -dangerous section is always rapidly increasing with increasing rate.</p> - -<p>This theory of filtration accounts for many otherwise perplexing facts. -The conclusion reached at Zürich and elsewhere that the efficiency of -filtration is independent of rate may be explained in this way. This is -especially probable at Zürich, where the number of bacteria in the raw -water was only about 200, and an extremely large proportion relatively -would have to pass to make a well-marked impression upon the total -number in the effluent.</p> - -<p>These underdrain bacteria are, so far as we know, entirely harmless; -we are only interested in them to determine how far they are capable -of decreasing the apparent efficiency of filtration below the actual -efficiency, or the per cent of bacteria really removed by the filter.</p> - -<p>This efficiency is dependent upon a large number of conditions many -of which have already been discussed in connection with grain-size -of filter sand, underdrains, rate of filtration, loss of head, etc., -and a mere reference to them here will suffice. Perhaps the most -important single condition is the rate, the numbers of bacteria passing -increase rapidly with it. Next, fine sand and in moderately deep -layers tends to give high efficiency. The influence of the loss of -head, often mentioned, is not shown to be important by the Lawrence -results, nor can I find<span class="pagenum" id="Page_89">[Pg 89]</span> satisfactory European results in support of -it. Uniformity in the rate of filtration on all parts of the filtering -area and a constant rate throughout the twenty-four hours are regarded -as essential conditions for the best results. Severe winter weather -has indirectly, by disturbing the regular action of open filters, an -injurious influence, and has been the cause of most of the cases where -filtered waters have been known to injure the health of those who have -drunk them. This action is excluded in filters covered with masonry -arches and soil, and such construction is apparently necessary for the -best results in places subject to cold winters.</p> - -<p>The efficiency of filtration under various conditions has been studied -by a most elaborate series of experiments at Lawrence with small -filters to which water has been applied containing a bacterium (<em>B. -prodigiosus</em>) which does not occur naturally in this country and -is not capable of growing in the filter, so that the results should -represent only the bacteria coming through the filter and not include -any additions from the underdrains. These results, which have been -published in full in the reports of the Massachusetts State Board of -Health, especially for the years 1892 and 1893, show that the number -of bacteria passing increases rapidly with increasing rate, and slowly -with decreasing sand thickness and increased size of sand-grain.</p> - -<p>Assuming that the number of bacteria passing is expressed by the formula</p> - -<p class="noindent"><span class="add11p5em">1</span> [(rate)<sup>2</sup> × effective size of sand]<br /> -Per cent bacteria passing = — —————————————<br /> -<span class="add11p5em">2</span> √<span class="o">thickness of the sand in inches</span></p> - -<p class="noindent">where the rate is expressed in million gallons per acre daily, and -calculating by it the numbers of bacteria for the seventy-three months -for which satisfactory data are available from 11 filters in 1892 and -1893, we find that</p> - -<p class="noindent">In 14 cases the numbers observed were 4 to 9 times as great as the -calculated numbers;</p> - -<p class="noindent">In 6 cases they were 2 to 3 times as great;</p> - -<p><span class="pagenum" id="Page_90">[Pg 90]</span></p> - -<p class="noindent">In 35 cases they were between <sup>1</sup>⁄<sub>2</sub> and 2 times the calculated numbers.</p> - -<p class="noindent">In 17 cases they were <sup>1</sup>⁄<sub>2</sub> to <sup>1</sup>⁄<sub>3</sub> of them.</p> - -<p class="noindent">In 11 cases they were less than <sup>1</sup>⁄<sub>3</sub> the calculated numbers.</p> - -<p>The agreement is only moderately good, and in fact no such formula -could be expected to give more than very rough approximations, because -it does not take into consideration the numerous other elements, such -as uniformity and regularity of filtration, the influence of scraping, -the character of the sediment in the raw water, etc., which are known -to affect the results. Perhaps the most marked general difference is -the tendency of new or freshly-filled filters to give higher, and -of old and well-compacted filters to give lower, results than those -indicated by the formula.</p> - -<p>Comparing this formula with Piefke’s results given in his “Neue -Ermittelungen”<a id="FNanchor_28" href="#Footnote_28" class="fnanchor">[28]</a> the formula gives in the first series (0.34 mm. -sand, 0.50 m. thick, and rate 100 mm. per hour), 0.25 per cent passing, -while the average number of <em>B. violacious</em> reported, excluding -the first day of decreased efficiency after scraping, was 0.26 per -cent. In the second series, with half as high a rate the numbers -checked exactly the calculated 0.06 per cent.</p> - -<p>In other experiments,<a id="FNanchor_29" href="#Footnote_29" class="fnanchor">[29]</a> however, in 1893, when the calculated per -cent was also 0.25, only 0.03, 0.04, and 0.07 per cent were observed in -the effluents.</p> - -<p class="padb1">Comparing the results from the actual filters, (which numbers also -include the bacteria from the underdrains and should therefore be -somewhat higher) with the numbers calculated as passing through, -I find that for the 46 days, Aug. 20 to Oct. 4, 1893, for which -detailed results of the Stralau works are given by Piefke, the average -calculated number passing is 0.20 per -<span class="pagenum" id="Page_91">[Pg 91]</span> -cent, while twice as many were observed in the effluents; although -three of the filters gave better effluents than the other eight, and -the numbers from them approximated closely the calculated numbers. If -we calculate the percentages of bacteria passing a number of filters, -using the maximum rate of filtration allowed for the German filters -where this is accurately determined, and for the English filters -taking the maximum rate at one and one-half times the rate obtained by -dividing the daily quantity by the area of filters actually in use, we -obtain:</p> - -<table class="autotable" summary="percentage bacteria passing filters at various locations"> -<tr> -<th class="tdl bord_top bord_bot bord_right vertb"> </th> -<th class="tdc normal smaller bord_top bord_bot bord_right vertb">Average<br />Depth of<br />Sand,<br />Inches.</th> -<th class="tdc normal smaller bord_top bord_bot bord_right vertb">Effective<br />Size of<br />Sand-<br />grain.</th> -<th class="tdc normal smaller bord_top bord_bot bord_right vertb">Maximum<br />Rate of<br />Filtration.</th> -<th class="tdl normal smaller bord_top bord_bot"> Per cent<br /> Bacteria<br /> passing<br /> - 1 <em>r</em><sup>2</sup><em>d</em><br /> -= — ———<br /> - 2 √<span class="o">sand</span></th> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Hamburg</td> -<td class="tdc bord_right vertb">32</td> -<td class="tdc bord_right vertb">0.31</td> -<td class="tdc bord_right vertb">1.60</td> -<td class="tdc">0.07</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Altona</td> -<td class="tdc bord_right vertb">28</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">2.57</td> -<td class="tdc">0.21</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Berlin, Stralau</td> -<td class="tdc bord_right vertb">20</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">2.57</td> -<td class="tdc">0.25</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Berlin, Müggel</td> -<td class="tdc bord_right vertb">20</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">2.57</td> -<td class="tdc">0.25</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Berlin, Tegel</td> -<td class="tdc bord_right vertb">20</td> -<td class="tdc bord_right vertb">0.37</td> -<td class="tdc bord_right vertb">2.57</td> -<td class="tdc">0.27</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">London, Southwark & Vauxhall</td> -<td class="tdc bord_right vertb">36</td> -<td class="tdc bord_right vertb">0.34</td> -<td class="tdc bord_right vertb">2.81</td> -<td class="tdc">0.22</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">London, West Middlesex</td> -<td class="tdc bord_right vertb">39</td> -<td class="tdc bord_right vertb">0.37</td> -<td class="tdc bord_right vertb">2.81</td> -<td class="tdc">0.23</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">London, Chelsea</td> -<td class="tdc bord_right vertb">54</td> -<td class="tdc bord_right vertb">0.36</td> -<td class="tdc bord_right vertb">3.27</td> -<td class="tdc">0.26</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">London, Grand Junction</td> -<td class="tdc bord_right vertb">30</td> -<td class="tdc bord_right vertb">0.40</td> -<td class="tdc bord_right vertb">3.27</td> -<td class="tdc">0.39</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">London, Lambeth</td> -<td class="tdc bord_right vertb">36</td> -<td class="tdc bord_right vertb">0.36</td> -<td class="tdc bord_right vertb">3.75</td> -<td class="tdc">0.42</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Middlesborough</td> -<td class="tdc bord_right vertb">20</td> -<td class="tdc bord_right vertb">0.42</td> -<td class="tdc bord_right vertb">5.85</td> -<td class="tdc">1.58</td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot">Zürich</td> -<td class="tdc bord_right bord_bot">26</td> -<td class="tdc bord_right bord_bot">0.35</td> -<td class="tdc bord_right bord_bot">7.50</td> -<td class="tdc bord_bot">1.90</td> -</tr> -</table> - -<p class="padt1">The numbers actually observed are in every case higher than the -calculated per cents passing, as indeed they should be on account of -those coming from the underdrains, accidental contamination of the -samples, etc.</p> - -<p>It may be said that filtration now practised in European works under -ordinary conditions never allows over 1 or 2 per cent bacteria of the -raw water to pass, and ordinarily not over one fourth to one half -of one per cent, although exact data cannot be obtained owing to -masking effect of the bacteria which come from below and which bear -no relation to those of the raw water. By increasing the size of the -filters, fineness and<span class="pagenum" id="Page_92">[Pg 92]</span> depth of sand (as at Hamburg), the efficiency -can be materially increased above these figures. At the same time -it must be borne in mind that the effectiveness of a filter may be -greatly impaired by inadequate underdraining, by fluctuating rates of -filtration where these are allowed, by freezing in winter in the case -of open filters in cold climates, and by other irregularities, all of -which can be prevented by careful attention to the respective points.</p> - -<p>The action of a continuous filter throughout is mainly that of an -exceedingly fine strainer, and like a strainer is mainly confined to -the suspended or insoluble matters in the raw water. The turbidity, -sediment, and bacteria of the raw water are largely or entirely -removed, while hardness, organic matter, and color, so far as they are -in solution, are removed to only a slight extent, if at all. Hardness -can be removed by the addition of lime in carefully determined quantity -before filtration (Clark’s process), by means of which the excess of -carbonic acid in the water is absorbed and the lime added, together -with that previously in the water, is precipitated.</p> - -<p>Ordinary filtration will remove from one fourth to one third of the -yellow-brown color of peaty water. A larger proportion can be removed -by the addition of alum, which by decomposing forms an insoluble -compound of alumina with the coloring matter, while the acid of the -alum goes into the effluent either as free acid, or in combination with -the lime or other base in the water, according to their respective -quantities. Freshly precipitated alumina can be substituted for the -alum at increased expense and trouble, and tends to remove the color -without adding acid to the water. These will be discussed more in -detail in connection with mechanical filters. Alum is but rarely used -in slow sand filtration, the most important works where it is used -being in Holland with peaty waters.</p> - -<p>After all, the most conclusive test of the efficiency of filtration is -the healthfulness of the people who drink the filtered water;<span class="pagenum" id="Page_93">[Pg 93]</span> and the -fact that many European cities take water-supplies from sources which -would not be considered fit for use in the United States and, after -filtering them, deliver them to populations having death-rates from -water-carried diseases which are so low as to be the objects of our -admiration, is the best proof of the efficiency of carefully conducted -filtration.</p> - -<p>It is only necessary to refer to London, drawing its water from the -two small and polluted rivers, the Thames and the Lea; to Altona, -drawing its water from the Elbe, polluted by the sewage of 6,000,000 -people, 700,000 of them within ten miles above the intakes; to Berlin, -using the waters of the Havel and the Spree; to Breslau, taking its -water from the Oder charged with the sewage of mining districts in -Silicia and Galicia, where cholera is so common; to Lawrence, with its -greatly decreased death-rate since it has had filtered water, and to -the hundred other places which protect themselves from the infectious -matters in their raw waters by means of filtration. A few of these -cases are described more in detail in Appendices V to IX, and many -others in the literature mentioned in Appendix X.</p> - -<p>An adequate presentation of even those data which have been already -worked up and published would occupy too much space. I think every one -who has carefully studied the recent history of water filtration in -its relation to disease has been convinced that filtration carefully -executed under suitable and normal conditions, even if not an absolute, -is at least a very substantial protection against water-carried -diseases, and the few apparent failures to remove objectionable -qualities have been without exception due to abnormal conditions which -are now understood and in future can be prevented.</p> - -<div class="section"> -<h3 class="nobreak" id="BACTERIAL_EXAMINATION_OF_WATERS">BACTERIAL EXAMINATION OF WATERS.</h3></div> - -<p>Every large filter-plant should have arrangements for the systematic -bacterial examination of the water before and after<span class="pagenum" id="Page_94">[Pg 94]</span> filtration, -especially where the raw water is subject to serious pollution. Such -examinations need not be excessively expensive, and they will not -only show the efficiency of the plant as a whole, but may be made to -show the relative efficiencies of the separate filters, the relative -efficiencies at different parts of the periods of operation, the effect -of cold weather, etc., and will then be a substantial aid to the -superintendent in always securing good effluents at the minimum cost.</p> - -<p>In addition a complete record of the bacteria in the water at different -times may aid in determining definitely whether the water was connected -with outbreaks of disease. Thus if an outbreak of disease of any -kind were preceded at a certain interval by a great increase in the -number of bacteria,—as has been the case, for example, with the -typhoid epidemics at Altona and Berlin (see Appendices II and VII),—a -presumption would arise that they might have been connected with -each other, and each time it was repeated the presumption would be -strengthened, while, on the other hand, outbreaks occurring while the -bacteria remained constantly low would tend to discredit such a theory.</p> - -<p>Bacterial investigations inaugurated after an epidemic is recognized, -as has frequently been done, seldom lead to results of value, both -because the local normal bacterial conditions are generally unknown at -the commencement of the investigation, and because the most important -time, the time of infection, is already long past before the first -samples are taken. The fact that such sporadic activities have led -to few definite results should throw no discredit upon continued -observations, which have repeatedly proved of inestimable value.</p> - -<p>Considerable misconception of the use of bacterial examinations -exists. The simple bacterial count ordinarily used, and of which I -am now speaking, does not and cannot show whether a water contains -disease-germs or not. I object to the Chicago water, not so much -because a glass of it contains a hundred thousand bacteria more -or less, as because I am convinced, by a study<span class="pagenum" id="Page_95">[Pg 95]</span> of its source in -connection with the city’s death-rate, that it actually carries -disease-germs which prove injurious to thousands of those who drink -it. Now the fact being admitted that the water is injurious to health, -variations in the numbers of bacteria in the water drawn from different -intakes and at different times probably correspond roughly with varying -proportions of fresh sewage, and indicate roughly the relative dangers -from the use of the respective waters. If filters should be introduced, -the numbers of bacteria in the effluents under various conditions would -be an index of the respective efficiencies of filtration, and would -serve to detect poor work, and would probably suggest the measures -necessary for better results.</p> - -<p>I would suggest the desirability of such investigations where -mechanical filters are used, quite as much as in connection with -slow filtration; and it would also be most desirable in the case of -many water-supplies which are not filtered at all. Such continued -observations have been made at Berlin since 1884; at London since 1886; -at Boston and Lawrence since 1888; and recently at a large number -of places, including Chicago, where observations by the city were -commenced in 1894. They are now required by the German Government in -the case of all filtered public water-supplies in Germany, without -regard to the source of the raw water. The German standard requires -that the effluent from each single filter, as well as the mixed -effluent and raw water, shall be examined daily, making at some works -10 to 30 samples daily. This amount of work, however, can usually be -done by a single man; and when a laboratory is once started, the cost -of examining 20 samples a day will not be much greater than if only -20 a week are taken. In England and at some of the Continental works -drawing their waters from but slightly polluted sources, much smaller -numbers of samples are examined.</p> - -<p>The question whether the examinations should be made under the -direction of the water-works company or department, or by an -independent body—as, for instance, by the Board of Health—will<span class="pagenum" id="Page_96">[Pg 96]</span> depend -upon local conditions. The former arrangement gives the superintendent -of the filters the best chance to study their action, as he can himself -control the collection of samples in connection with the operation -of the filters, and arrange them to throw light upon the points he -wishes to investigate; while examination by a separate authority -affords perhaps greater protection against the possible carelessness or -dishonesty of water-works officials. An arrangement being adopted in -many cases in Germany is to have a bacterial laboratory at the works -which is under the control of the superintendent, and in which the very -numerous compulsory observations are made, while the Board of Health -causes to be examined from time to time by its own representatives, -who have no connection with the water-works, samples taken to check -the water-works figures, as well as to show the character of the water -delivered.</p> - -<p>It seems quite desirable to have a man whose principal business is to -make these examinations; as in case he also has numerous other duties, -the examinations may be found to have been neglected at some time when -they are most wanted. Such a man should have had thorough training in -the principles of bacterial manipulation, but it is quite unnecessary -that he should be an expert bacteriologist, especially if a competent -bacteriologist is retained for consultation in cases of doubt or -difficulty.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_97">[Pg 97]</span></p> - -<h2 class="nobreak" id="CHAPTER_VII">CHAPTER VII.<br /> -<br /> - -<span class="smaller">INTERMITTENT FILTRATION.</span></h2></div> - -<p><span class="smcap">By</span> intermittent nitration is understood that filtration in which the -filtering material is systematically and adequately ventilated, and -where the water during the course of filtration is brought in contact -with air in the pores of the sand. In continuous filtration, which -alone has been previously considered, the air is driven out of the sand -as completely as possible before the commencement of filtration, and -the sand is kept continuously covered with water until the sand becomes -clogged and a draining, with an incidental aeration, is necessary to -allow the filter to be scraped and again put in service.</p> - -<p>In intermittent filtration, on the other hand, water is taken over the -top of the drained sand and settles into it, coming in contact with -the air in the pores of the sand, and passes freely through to the -bottom when the water-level is kept well down. After a limited time the -application of water is stopped, and the filter is allowed to again -drain and become thoroughly aerated preparatory to receiving another -dose of water.</p> - -<p>This system of treating water was suggested by the unequalled -purification of sewage effected by a similar treatment. It has been -investigated at the Lawrence Experiment Station, and applied to the -construction of a filter for the city of Lawrence, both of which are -due to the indefatigable energy of Hiram F. Mills, C.E.</p> - -<p>In its operation intermittent differs from continuous filtration in -that the straining action is less perfect, because the filters yield -no water while being aerated, and must therefore filter at a greater -velocity when in use to yield the same quantity of water in a given -time, and also on account of the mechanical disturbance<span class="pagenum" id="Page_98">[Pg 98]</span> which is -almost invariably caused by the application of the water; but, on the -other hand, the oxidizing powers of the filter, or the tendency to -nitrify and destroy the organic matters, are stronger, and in addition, -if the rate is not too high, the bacteria die more rapidly in the -thoroughly aerated sand than is the case with ordinary filters.</p> - -<p>It was found at Lawrence in connection with sewage filters that when -nitrification was actively taking place the numbers of bacteria were -much lower than under opposite conditions, and it was thought that -nitrification in itself might cause the death of the bacteria. Later -experiments, however, with pure cultures of bacteria of various kinds -applied to intermittent filters with water to which ammonia and salts -suitable for nitrification were added, showed that bacteria of all -the species tried were able to pass the filter in the presence of -nitrification, producing at least one thousand times as much nitrates -as could result in any case of water-filtration, as freely as was -the case when the ammonia was not added and there was but little -nitrification. These results showed conclusively that nitrification -in itself is not an important factor in bacterial removal, although -nitrification and bacterial purification do to some extent go together; -perhaps in part because the nitrification destroys the food of the -bacteria and so starves them out, but probably much more because the -conditions of aeration, temperature, etc., which favor nitrification -also favor equally, and even in its absence, the death of the bacteria.</p> - -<p>The rate at which water must pass through an intermittent filter -is, on account of the intervals of rest, considerably greater than -that required to give a corresponding total yield from a continuous -filter, and its straining effect is reduced to an extent comparable to -this increase in rate; and if other conditions did not come in, the -bacterial efficiency of an intermittent filter would remain below that -of a continuous one.</p> - -<p>As a matter of fact the bacterial efficiency has usually been<span class="pagenum" id="Page_99">[Pg 99]</span> found -to be less with intermittent filters at the Lawrence Experiment -Station, when they have been run at rates such as are commonly used for -continuous filters in Europe, say from one and one half to two million -gallons and upwards per acre daily. With lower rates, and especially -with rather fine materials, the bacterial efficiency is much greater; -but it may be doubted whether it would ever be greater than that of a -continuous filter with the same filtering material and the same total -yield per acre. The number of bacteria coming from the underdrains is -apparently generally less, and with very high summer temperatures much -less, than in continuous filters, and this often gives an apparent -bacterial superiority to the intermittent filters.</p> - -<p>The effluents from intermittent often contain less slightly organic -matter than those from continuous filters; but, on the other hand, -hardly any water proposed for a public water-supply has organic matter -enough to be of any sanitary significance whatever, apart from the -living bodies which often accompany it; and if the latter are removed -by straining or otherwise, we can safely disregard the organic matters. -In addition, the water filtered will in a great majority of cases have -enough air dissolved in itself to produce whatever oxidation there is -time for in the few hours required for it to pass the filter, and it is -only at very low rates of filtration that intermittent filters produce -effluents of greater chemical purity than by the ordinary process. The -yellow-brown coloring matter present in so many waters appears to be -quite incapable of rapid nitrification; and where it is to some extent -removed by filtration, the action is dependent upon other and but -imperfectly understood causes which seem to act equally in continuous -and intermittent filters.</p> - -<p>The peculiarities of construction involved by this method of filtration -will be best illustrated by a discussion of the Lawrence city filter -designed by Hiram F. Mills, C.E., which is the only filter in existence -upon this plan.<a id="FNanchor_30" href="#Footnote_30" class="fnanchor">[30]</a></p> - -<p><span class="pagenum" id="Page_100">[Pg 100]</span></p> - -<div class="section"> -<h3 class="nobreak" id="THE_LAWRENCE_FILTER">THE LAWRENCE FILTER.</h3></div> - -<p>The filter consists of a single bed 2<sup>1</sup>⁄<sub>2</sub> acres in area, the bottom of -which is 7 feet below low water in the river, and filled with gravel -and sand to an average depth of 4<sup>1</sup>⁄<sub>2</sub> feet. The filter is all in a -single bed instead of being divided into the three or four sections -which would probably have been used for a continuous filter of this -size. The water-tight bottom also was dispensed with, and the gravel -was prevented from sinking into the silt by thin intermediate layers -of graded materials. The saving in cost was considerable; but, on the -other hand, a considerable quantity of ground-water comes up through -the bottom and increases the hardness of the water from 1.5 to 2.6 -parts of calcium carbonate in 100,000; and while the water when -compared with many other waters is still extremely soft, the addition -cannot be regarded as desirable. The ground-water also contains iron, -which increases the color of the water above what it would otherwise be.</p> - -<p>The underdrains have a frictional resistance ten times as great as -would be desirable for a continuous filter, the idea being to check -extreme rates of filtration in case of unequal flooding, and also to -limit the quantity of water which could be gotten through the filter to -that corresponding to a moderate rate of filtration.</p> - -<p>The sand, instead of being all of the same-sized grain, is of two -grades, with effective sizes respectively 0.25 and 0.30 mm., the -coarser sand being placed farthest away from the underdrains, where -its greater distance is intended to balance its reduced frictional -resistance and make all parts filter at an equal rate.</p> - -<p>The surface instead of being level is waved, that is, there are ridges -thirty feet apart, sloping evenly to the valleys one foot deep half -way between them, to allow water to be brought on<span class="pagenum" id="Page_101">[Pg 101]</span> rapidly without -disturbing the sand surface. For the same reason, as well as to secure -equality of distribution, a system of concrete carriers for the raw -water goes to all parts of the filter, reducing the effective filtering -area by 4 or 5 per cent. The filter is scraped as necessary in -sections, the work being performed when the filter is having its daily -rest and aeration. Owing to the difference in frictional resistance -before and after scraping, and to the fact that it is impossible to -scrape the entire area in one day, considerable variations in the rate -of filtration in different parts of the filter must occur. The heavy -frictional resistance of the underdrains when more than the proper -quantity of water passes them tends to correct this tendency especially -for the more remote parts of the filter, but perhaps at the expense of -those near to the main drain.</p> - -<p>The filter is not covered as the suggestions in Chapter II would -require, but this is hardly on account of its being an intermittent -filter.</p> - -<p>The annual report of the Massachusetts State Board of Health for 1893 -states that during the first half of December, 1893, the surface -remained covered, that is, it was used continuously, and after December -16th it was so used when the temperature was below 24°, and was drained -only when the temperature was 24° or above. The days on which the -filter was drained during the remainder of December are not given, but -during January and February, 1894, the filter remained covered 29 days -and was drained 30 days. Bacterial samples were taken on 44 of these -days, 22 days when it was drained and 22 when it was not. The average -number of bacteria on the days when it was not drained was 137 and on -those days when it was drained 252 per cubic centimeter.</p> - -<p>From February 24th to March 12th the number of bacteria were unusually -high, averaging 492 per cubic centimeter, or 5.28 per cent of the 9308 -applied. During this period the filter was used intermittently; there -was ice upon it, and parts of the surface<span class="pagenum" id="Page_102">[Pg 102]</span> were scraped under the ice, -and high rates of filtration undoubtedly resulted on the scraped areas. -After March 12th the ice had disappeared and very much better results -were obtained.</p> - -<p>While there may be some question as to the direct cause of this -decreased efficiency with continued cold weather and ice, the results -certainly are not such as to show the advisability of building open -filters in the Lawrence climate.</p> - -<p>The cost of building the filter in comparison with European filters -was extraordinarily low—only $67,000, or $27,000 per acre of filter -surface. To have constructed open continuous filters of the same area -with water-tight bottoms, divided into sections with separate drains -and regulating apparatus, with the necessary piping, would have cost at -least half as much more, and with the masonry cover which I regard as -most desirable in the Lawrence climate the cost would have been two or -three times the expenditure actually required.</p> - -<p>It was no easy matter to secure the consent of the city government to -the expenditure of even the sum used; there was much skepticism as to -the process of filtration in general, and it was said that mechanical -filters could be put in for about the same cost. Insisting upon the -more complete and expensive form might have resulted either in an -indefinite postponement of action, or in the adoption of an inferior -and entirely inadequate process. Still I feel strongly that in the -end the greater expense would have proved an excellent investment in -securing softer water and in the greater facility and security of -operating the filter in winter.</p> - -<p>In regard to the effect of the Lawrence filter upon the health of -the city, I can best quote from Mr. Mills’ paper in the Report of -the Massachusetts State Board of Health for 1893, and also published -in the Journal of the New England Water-works Association. Mr. Mills -says: “In the following diagram [Fig. 15] the average number of deaths -from typhoid fever at Lawrence<span class="pagenum" id="Page_103">[Pg 103]</span> for each month from October to May, in -the preceding five years, are given by the heavy dotted line; and the -number during the past eight months are given by the heavy full line.</p> - -<p>“The total number for eight months in past years has been forty-three, -and in the present year seventeen, making a saving of twenty-six. Of -the seventeen who died nine were operatives in the mills, each of whom -was known to have drunk unfiltered canal water, which is used in the -factories at the sinks for washing.</p> - -<div class="figcenter padt1 padb1 illowp97" id="image103" style="max-width: 37.5em;"> - <img class="w100" src="images/image103.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 15.—Typhoid Fever in Lawrence.</span></p></div> - -<p>“The finer full line shows the number of those who died month after -month who are not known to have used the poisoned canal water. The -whole number in the eight months is eight.</p> - -<p>“It is evident from the previous diagram [not reproduced] that the -numbers above the fine full line, here, follow after those at Lowell in -the usual time, and were undoubtedly caused by the sickness at Lowell; -but we have satisfactory reason to conclude that the disease was not -propagated through the filter but that the germs were conveyed directly -into the canals and to those who drank of the unfiltered canal water. -Among the operatives<span class="pagenum" id="Page_104">[Pg 104]</span> of one of the large corporations not using the -canal water there was not a case of typhoid fever during this period. -Warnings have been placed in the mills where canal water is used to -prevent the operatives from drinking it.</p> - -<p>“We find, then, that the mortality from typhoid fever has, during the -use of the filter, been reduced to 40 per cent of the former mortality, -and that the cases forming nearly one half of this 40 per cent were -undoubtedly due to the continued use of unfiltered river water drawn -from the canals.”</p> - -<p class="padb1">The records of typhoid fever in Lawrence before and after the -introduction of filters are as follows:</p> - -<table class="autotable" summary="typhoid fever in Lawrence"> -<tr> -<th class="tdc normal" colspan="5">DEATHS FROM TYPHOID FEVER IN LAWRENCE, 1888-98.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Years.</th> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Total Number<br />of Deaths.</th> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Deaths per 10,000<br />of Population.</th> -<th class="tdc normal small bord_top bord_bot" colspan="2">Persons who are known to have been<br />exposed to infection.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">By drinking Canal<br />Water.</th> -<th class="tdc normal small bord_bot">While living out<br />of town just before<br />falling sick in<br />Lawrence.</th> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1888</td> -<td class="tdc bord_right vertb">48</td> -<td class="tdc bord_right vertb">11.36</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1889</td> -<td class="tdc bord_right vertb">55</td> -<td class="tdc bord_right vertb">12.66</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1890</td> -<td class="tdc bord_right vertb">60</td> -<td class="tdc bord_right vertb">13.44</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1891</td> -<td class="tdc bord_right vertb">55</td> -<td class="tdc bord_right vertb">11.94</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1892</td> -<td class="tdc bord_right vertb">50</td> -<td class="tdc bord_right vertb">10.52</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1893</td> -<td class="tdc bord_right vertb">39</td> -<td class="tdc bord_right vertb">7.96</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1894</td> -<td class="tdc bord_right vertb">24</td> -<td class="tdc bord_right vertb">4.75</td> -<td class="tdc bord_right vertb">12</td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1895</td> -<td class="tdc bord_right vertb">16</td> -<td class="tdc bord_right vertb">3.07</td> -<td class="tdc bord_right vertb">9</td> -<td class="tdc">2</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1896</td> -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">1.86</td> -<td class="tdc bord_right vertb">2</td> -<td class="tdc">4</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">1897</td> -<td class="tdc bord_right vertb">9</td> -<td class="tdc bord_right vertb">1.62</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot">1898</td> -<td class="tdc bord_right bord_bot">8</td> -<td class="tdc bord_right bord_bot">1.39</td> -<td class="tdc bord_right bord_bot">1</td> -<td class="tdc bord_bot"> </td> -</tr> -<tr> -<td class="tdl" colspan="4"><p class="indent">Filter put in operation September, 1893.</p></td> -<td> </td> -</tr> -<tr> -<td class="tdl" colspan="4"><p class="indent">Average rate before the introduction of filtered water (1888-92)</p></td> -<td class="tdr vertb">11.31</td> -</tr> -<tr> -<td class="tdl" colspan="4"><p class="indent">Average rate afterward (1894-98)</p></td> -<td class="tdr vertb">2.54</td> -</tr> -</table> - -<p class="padt1">These results show a striking reduction in the deaths from typhoid -fever with the introduction of filtered water, which has been most -gratifying in every way.</p> - -<p>The more recent history of the underdrains of the Lawrence filter -is particularly instructive. Owing to the absence of a water-tight -bottom to the filter, and its low position, a certain amount of water -constantly entered the filter from the ground below.<span class="pagenum" id="Page_105">[Pg 105]</span> This water -contained iron in solution as ferrous carbonate. When this water came -in contact with the filtered water in the gravel and underdrains, the -iron was oxidized by the dissolved oxygen carried in the filtered water -and precipitated. This was accompanied by a growth of crenothrix in -the gravel and underdrains, which gradually reduced their carrying -capacity. This reduction in carrying capacity first became apparent -in cold weather when the yield from the filter was less free than -formerly. There was difficulty in maintaining the supply during the -winter of 1896-7 and more difficulty in the following winter.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image105" style="max-width: 50em;"> - <img class="w100" src="images/image105.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 16.—Typhoid Fever in Lawrence, 1888 to -1898.</span></p></div> - -<p>The sand of the filter was as capable of filtering the full supply -of water as it ever had been, and the efficiency was as good; but -the underdrains were no longer able to collect the filtered water -and deliver it. As the filtering area was ample for the supply, it -was desired to avoid construction of additional filtering area. The -underdrains were dug up and cleaned during the periods when the filter -was drained. As the filter is all in one bed, the times when the filter -could be allowed to remain drained, and when the work could proceed, -were limited. Great care was taken to leave the work in good condition, -and free from passages, at the end of each day’s work, but the numbers -of bacteria in the<span class="pagenum" id="Page_106">[Pg 106]</span> effluent nevertheless increased somewhat. Some -weeks afterward the number of cases of typhoid fever in the city -increased. The numbers did not become as high as they had been prior to -the introduction of filtered water, but they were much higher than they -had been since that time, and they pointed strongly to the disturbance -of the underdrains as the cause of the increase.</p> - -<p class="padb1">The numbers of bacteria in the applied water and in the effluent from -the Lawrence filter by months, from the time the filter was put in -operation, compiled from the reports of the State Board of Health, as -far as available, are as follows:</p> - -<table class="autotable" summary="bacteria in lawrence water"> -<tr> -<th class="tdc normal" colspan="7">BACTERIA IN WATER APPLIED TO AND EFFLUENT FROM LAWRENCE FILTER.</th> -</tr> -<tr> -<th class="tdc normal small" colspan="7">RAW WATER.</th> -</tr> -<tr> -<th class="tdc bord_top bord_right bord_bot"> </th> -<th class="tdc normal small bord_top bord_right bord_bot">1893.</th> -<th class="tdc normal small bord_top bord_right bord_bot">1894.</th> -<th class="tdc normal small bord_top bord_right bord_bot">1895.</th> -<th class="tdc normal small bord_top bord_right bord_bot">1896.</th> -<th class="tdc normal small bord_top bord_right bord_bot">1897.</th> -<th class="tdc normal small bord_top bord_bot">1898.</th> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">January</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">7,700</td> -<td class="tdc bord_right vertb">18,700</td> -<td class="tdc bord_right vertb">7,500</td> -<td class="tdc bord_right vertb">13,314</td> -<td class="tdc">6,519</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">February</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">7,600</td> -<td class="tdc bord_right vertb">15,040</td> -<td class="tdc bord_right vertb">12,600</td> -<td class="tdc bord_right vertb">13,113</td> -<td class="tdc">4,653</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">March</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">6,500</td> -<td class="tdc bord_right vertb">20,770</td> -<td class="tdc bord_right vertb">5,900</td> -<td class="tdc bord_right vertb">12,055</td> -<td class="tdc">3,748</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">April</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">11,200</td> -<td class="tdc bord_right vertb">8,420</td> -<td class="tdc bord_right vertb">3,800</td> -<td class="tdc bord_right vertb">6,904</td> -<td class="tdc">2,320</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">May</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">6,000</td> -<td class="tdc bord_right vertb">7,000</td> -<td class="tdc bord_right vertb">9,600</td> -<td class="tdc bord_right vertb">4,625</td> -<td class="tdc">2,050</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">June</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">8,300</td> -<td class="tdc bord_right vertb">9,000</td> -<td class="tdc bord_right vertb">6,400</td> -<td class="tdc bord_right vertb">4,650</td> -<td class="tdc">6,775</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">July</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">2,400</td> -<td class="tdc bord_right vertb">10,000</td> -<td class="tdc bord_right vertb">3,900</td> -<td class="tdc bord_right vertb">6,240</td> -<td class="tdc">2,840</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">August</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">3,100</td> -<td class="tdc bord_right vertb">5,000</td> -<td class="tdc bord_right vertb">2,700</td> -<td class="tdc bord_right vertb">10,700</td> -<td class="tdc">8,575</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">September</td> -<td class="tdc bord_right vertb">57,500</td> -<td class="tdc bord_right vertb">6,500</td> -<td class="tdc bord_right vertb">5,000</td> -<td class="tdc bord_right vertb">12,300</td> -<td class="tdc bord_right vertb">27,300</td> -<td class="tdc">6,100</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">October</td> -<td class="tdc bord_right vertb">22,200</td> -<td class="tdc bord_right vertb">25,300</td> -<td class="tdc bord_right vertb">19,000</td> -<td class="tdc bord_right vertb">5,300</td> -<td class="tdc bord_right vertb">13,200</td> -<td class="tdc">5,120</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">November</td> -<td class="tdc bord_right vertb">10,800</td> -<td class="tdc bord_right vertb">16,600</td> -<td class="tdc bord_right vertb">8,700</td> -<td class="tdc bord_right vertb">5,600</td> -<td class="tdc bord_right vertb">6,644</td> -<td class="tdc">4,310</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">December</td> -<td class="tdc bord_right bord_bot">8,100</td> -<td class="tdc bord_right bord_bot">23,800</td> -<td class="tdc bord_right bord_bot">6,700</td> -<td class="tdc bord_right bord_bot">9,695</td> -<td class="tdc bord_right bord_bot">5,581</td> -<td class="tdc bord_bot">5,200</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb"> Average</td> -<td class="tdc bord_right vertb">24,650</td> -<td class="tdc bord_right vertb">10,417</td> -<td class="tdc bord_right vertb">11,111</td> -<td class="tdc bord_right vertb">7,108</td> -<td class="tdc bord_right vertb">10,360</td> -<td class="tdc">4,850</td> -</tr> -<tr> -<th class="tdc normal small" colspan="7">EFFLUENT.</th> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">January</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">129</td> -<td class="tdc bord_right vertb">206</td> -<td class="tdc bord_right vertb">166</td> -<td class="tdc bord_right vertb">91</td> -<td class="tdc">39</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">February</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">244</td> -<td class="tdc bord_right vertb">283</td> -<td class="tdc bord_right vertb">315</td> -<td class="tdc bord_right vertb">79</td> -<td class="tdc">45</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">March</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">455</td> -<td class="tdc bord_right vertb">405</td> -<td class="tdc bord_right vertb">133</td> -<td class="tdc bord_right vertb">67</td> -<td class="tdc">34</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">April</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">281</td> -<td class="tdc bord_right vertb">84</td> -<td class="tdc bord_right vertb">40</td> -<td class="tdc bord_right vertb">47</td> -<td class="tdc">21</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">May</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">134</td> -<td class="tdc bord_right vertb">68</td> -<td class="tdc bord_right vertb">56</td> -<td class="tdc bord_right vertb">35</td> -<td class="tdc">48</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">June</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">110</td> -<td class="tdc bord_right vertb">68</td> -<td class="tdc bord_right vertb">22</td> -<td class="tdc bord_right vertb">56</td> -<td class="tdc">50</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">July</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">25</td> -<td class="tdc bord_right vertb">50</td> -<td class="tdc bord_right vertb">39</td> -<td class="tdc bord_right vertb">106</td> -<td class="tdc">22</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">August</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">36</td> -<td class="tdc bord_right vertb">38</td> -<td class="tdc bord_right vertb">146</td> -<td class="tdc bord_right vertb">72</td> -<td class="tdc">28</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">September</td> -<td class="tdc bord_right vertb">6,850</td> -<td class="tdc bord_right vertb">42</td> -<td class="tdc bord_right vertb">40</td> -<td class="tdc bord_right vertb">37</td> -<td class="tdc bord_right vertb">98</td> -<td class="tdc">67</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">October</td> -<td class="tdc bord_right vertb">1,216</td> -<td class="tdc bord_right vertb">116</td> -<td class="tdc bord_right vertb">60</td> -<td class="tdc bord_right vertb">30</td> -<td class="tdc bord_right vertb">33</td> -<td class="tdc">28</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">November</td> -<td class="tdc bord_right vertb">161</td> -<td class="tdc bord_right vertb">175</td> -<td class="tdc bord_right vertb">64</td> -<td class="tdc bord_right vertb">37</td> -<td class="tdc bord_right vertb">27</td> -<td class="tdc">122</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">December</td> -<td class="tdc bord_right bord_bot">111</td> -<td class="tdc bord_right bord_bot">364</td> -<td class="tdc bord_right bord_bot">84</td> -<td class="tdc bord_right bord_bot">67</td> -<td class="tdc bord_right bord_bot">24</td> -<td class="tdc bord_bot"> </td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb"> Average</td> -<td class="tdc bord_right vertb">2,084</td> -<td class="tdc bord_right vertb">176</td> -<td class="tdc bord_right vertb">121</td> -<td class="tdc bord_right vertb">91</td> -<td class="tdc bord_right vertb">61</td> -<td class="tdc">46</td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot"> Average efficiency</td> -<td class="tdc bord_right bord_bot">91.55</td> -<td class="tdc bord_right bord_bot">98.31</td> -<td class="tdc bord_right bord_bot">98.91</td> -<td class="tdc bord_right bord_bot">98.72</td> -<td class="tdc bord_right bord_bot">99.41</td> -<td class="tdc bord_bot">98.95</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_107">[Pg 107]</span></p> - -<div class="section"> -<h3 class="nobreak" id="CHEMNITZ_WATER_WORKS">CHEMNITZ WATER-WORKS.</h3></div> - -<p>The only other place which I have found where anything approaching -intermittent filtration of water is systematically employed is -Chemnitz, Germany. The method there used bears the same relation to -intermittent filtration as does broad irrigation of sewage to the -corresponding method of sewage treatment; that is, the principles -involved are mainly the same, but a much larger filtering area is used, -and the processes take place at a lower rate and under less close -control.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image107" style="max-width: 75em;"> - <img class="w100" src="images/image107.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 17.—Plan of Area used for Intermittent -Filtration at Chemnitz.</span></p></div> - -<p>The water-works were built about twenty years ago by placing -thirty-nine wells along the Zwönitz River, connected by siphon pipes, -with a pumping-station which forced the water to an elevated reservoir -near the city (Fig. 17). The wells are built of masonry, 5 or 6 feet in -diameter and 10 or 12 feet deep, and are on the rather low bank of the -river. The material, with the exception of the surface soil, and loam -about 3 feet deep, is a somewhat mixed gravel with an effective size of -probably from 0.25 to 0.50 mm., so that water is able to pass through -it freely. The wells are, on an average, about 120 feet apart, and the -line is seven eighths of a mile long.</p> - -<p>It was found that in dry times the ground-water level in the<span class="pagenum" id="Page_108">[Pg 108]</span> entire -neighborhood was lowered some feet below the level of the river without -either furnishing water enough or stopping the flow of the river below. -The channel of the river was so silted that, notwithstanding the porous -material, the water could not penetrate it to go toward the wells.</p> - -<p>A dam was now built across the river near the pumping-station, and -a canal was dug from above the dam, crossing the line of wells and -running parallel to it on the back side for about half a mile. Later a -similar canal was dug back of the remaining upper wells. Owing to the -difference in level in the river above and below, the canals can be -emptied and filled at pleasure. They are built with carefully prepared -sand bottoms, and the sand sides are protected by an open paving, to -allow the percolation of as much water as possible, and the sand is -cleaned by scraping, as is usual with ordinary sand filters, once a -year or oftener.</p> - -<p>The yield from the wells was much increased by these canals, but the -water of the river is polluted to an extent which would ordinarily -quite prevent even the thought of its being used for water-supply, and -it was found that the water going into the ground from the canals, -and passing through the always saturated gravel to the wells, without -coming in contact with air at any point, after a time contained iron -and had an objectionable odor.</p> - -<p>To avoid this disagreeable result the meadow below the pumping-station -was laid out as an irrigation field (Fig. 16). The water from above the -dam was taken by a canal on the opposite side of the river through a -sedimentation pond (which, however, is not now believed to be necessary -and is not always used), and then under the river by a siphon to a -slightly elevated point on the meadow, from which it is distributed -by a system of open ditches, exactly as in sewage irrigation. The -area irrigated is not exactly defined and varies somewhat from time -to time; the rate of filtration may be roughly estimated<span class="pagenum" id="Page_109">[Pg 109]</span> at from -100,000 to 150,000 gallons per acre daily, although limited portions -may occasionally get five times these quantities for a single day. The -water passes through the three feet of soil and loam, and afterward -through an average of six feet of drained coarse sand or gravel in -which it meets air, and afterward filters laterally through the -saturated gravel to the wells. The water so obtained is invariably of -good quality in every way, colorless, free from odor and from bacteria. -The surface of the irrigated land is covered with grass and has -fruit-trees (mostly apple) at intervals over its entire area.</p> - -<p>This first system of irrigation is entirely by gravity. On account -of natural limits to the land it could not be conveniently extended -at this point, and to secure more area, the higher land above the -pumping-station was being made into an irrigation field in 1894. This -is too high to be flooded by gravity, and will be used only for short -periods in extremely dry weather. The water is elevated the few feet -necessary by a gas-engine on the river-bank. In times of wet weather -enough water is obtained from the wells without irrigation, and the -land is only irrigated when the ground-water level is too low.</p> - -<p>During December, January, and February irrigation is usually impossible -on account of temperature, and the canals are then used, keeping them -filled with water so that freezing to the bottom is impossible; but -trouble with bad odors in the filtered water drawn from the wells is -experienced at these times.</p> - -<p>The drainage area of the Zwönitz River is only about 44 square miles, -and upon it are a large number of villages and factories, so that the -water is excessively polluted. The water in the wells, however, whether -coming from natural sources, or from irrigation, or from the canals, -has never had as many as 100 bacteria per cubic centimeter, and is -regarded as entirely wholesome.</p> - -<p>In extremely dry weather the river, even when it is all used for -irrigation so that hardly any flows away below, cannot be<span class="pagenum" id="Page_110">[Pg 110]</span> made to -supply the necessary daily quantity of 2,650,000 gallons, and to supply -the deficiency at such times, as well as to avoid the use of the canals -in winter, a storage reservoir holding 95,000,000 gallons has recently -been built on a feeder of the river. This water, which is from an -uninhabited drainage area, is filtered through ordinary continuous -filters and flows to the city by gravity. Owing to the small area of -the watershed it is incapable of supplying more than a fraction of the -water for the city, and will be used to supplement the older works.</p> - -<p>This Chemnitz plant is of especial interest as showing the successful -utilization of a river-water so grossly polluted as to be incapable of -treatment by the ordinary methods. Results obtained at the Lawrence -Experiment Station have shown that sewage is incapable of being -purified by continuous filtration, the action of air being essential -for a satisfactory result. With ordinary waters only moderately -polluted this is not so; for they carry enough dissolved air to effect -their own purification. In Chemnitz, however, as shown by the results -with the canals, the pollution is so great that continuous filtration -is inadequate to purify the water, and the intermittent filtration -adopted is the only method likely to yield satisfactory results in such -cases.</p> - -<p>Intermittent filtration is now being adopted for purifying brooks -draining certain villages and discharging into the ponds or reservoirs -from which Boston draws its water-supply. The water of Pegan Brook -below Natick has been so filtered since 1893 with most satisfactory -results, and affords almost absolute protection to Boston from any -infection which might otherwise enter the water from that town. A -similar treatment is soon to be given to a brook draining the city of -Marlborough. The sewage from these places is not discharged into the -brooks, but is otherwise provided for, but nevertheless they receive -many polluting matters from the houses and streets upon their banks.</p> - -<p>The filtration used resembles in a measure that at Chemnitz,<span class="pagenum" id="Page_111">[Pg 111]</span> and I am -informed by the engineer, Mr. Desmond FitzGerald, that it was adopted -on account of its convenience for this particular problem, and not -because he attaches any special virtue to the intermittent feature.</p> - -<div class="section"> -<h3 class="nobreak" id="APPLICATION_OF_INTERMITTENT_FILTRATION">APPLICATION OF INTERMITTENT FILTRATION.</h3></div> - -<p>In regard to the use of waters as grossly polluted as the Zwönitz, -the tendency is strongly to avoid their use, no matter how complete -the process of purification may be; but in case it should be deemed -necessary to use so impure a water for a public supply, intermittent -filtration is the only process known which would adequately purify -it. And it should be used at comparatively low rates of filtration. -I believe that an attempt to filter the Zwönitz at the rate used for -the Merrimac water at Lawrence, which is by comparison but slightly -polluted, would result disastrously.</p> - -<p>The operation in winter must also be considered. Intermittent -filtration of sewage on open fields in Massachusetts winters is only -possible because of the comparatively high temperature of the sewage -(usually 40° to 50°), and would be a dismal failure with sewage at -the freezing-point, the temperature to be expected in river-waters in -winter.</p> - -<p>It is impossible to draw a sharp line between those waters which are -so badly polluted as to require intermittent filtration for their -treatment and those which are susceptible to the ordinary continuous -filtration. Examples of river-waters polluted probably beyond the -limits reached in any American waters used for drinking purposes and -successfully filtered with continuous filters are furnished by Altona, -Breslau, and London.</p> - -<p>Intermittent filtration may be considered in those cases where it -is proposed to use a water polluted entirely beyond the ordinary -limits, and for waters containing large quantities of decomposable -organic matters and microscopical organisms; but in those cases where -a certain and expeditious removal of mud is<span class="pagenum" id="Page_112">[Pg 112]</span> desired, and where -waters are only moderately polluted by sewage, but still in their raw -state are unhealthy, it is not apparent that intermittent filtration -has any advantages commensurate with the disadvantages of increased -rate to produce the same total yield and of the increased difficulty -of operation, particularly in winter; and in such cases continuous -filtration is to be preferred.</p> - -<p>In the removal of tastes and odors from pond or reservoir waters which -are not muddy, but which are subject to the growths of low forms of -plants, which either by their growth or decomposition impart to the -water disagreeable tastes and odors, intermittent filtration may have a -distinct advantage. In such cases there is often an excess of organic -matter to be disposed of by oxidation, and the additional aeration -secured by intermittent filtration is of substantial assistance in -disposing of these matters.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_113">[Pg 113]</span></p> - -<h2 class="nobreak" id="CHAPTER_VIII">CHAPTER VIII.<br /> -<br /> - -<span class="smaller">TURBIDITY AND COLOR, AND THE EFFECT OF MUD UPON SAND-FILTERS.</span></h2></div> - -<p><span class="smcap">The</span> ideal water in appearance is distilled water, which is perfectly -clear and limpid, and has a slight blue color. When other waters are -compared with it, the divergences in color from the color of distilled -water are measured, and not the absolute colors of the waters. Many -spring waters and filtered waters are indistinguishable in appearance -from distilled water.</p> - -<p>Public water-supplies from surface sources contain two substances or -classes of substances which injure their appearance, namely, peaty -coloring matters, and mud. Waters discolored by peaty matters are most -common in New England and in certain parts of the Northwest, while -muddy waters are found almost everywhere, but of different degrees of -muddiness, according to the physical conditions of the water-sheds from -which they are obtained.</p> - -<p>Muddy waters are often spoken of as colored waters, and in a sense this -is correct where the mud consists of clays or other materials having -distinct colors; but it is more convenient to classify impurities of -this kind as turbidities only, and to limit the term colored waters to -those waters containing in solution vegetable matters which color them.</p> - -<p>The removal of either color or turbidity may be called clarification.</p> - -<p>Colored waters are usually drawn from water-sheds where the underlying -rock is hard and does not rapidly disintegrate, and where the soils are -firm and sandy, and especially from swamps. The water here comes in -contact with peat or muck, which colors<span class="pagenum" id="Page_114">[Pg 114]</span> it, but is so firm as not to -be washed by flood flows, and so does not cause turbidity.</p> - -<p>Large parts of the United States have for rock foundations shales or -other soft materials which readily disintegrate when exposed, and -which form clayey soils readily washed by hard rains. Waters from -such watersheds are generally turbid and very rarely colored. In fact -a water carrying much clay in suspension is usually found colorless -when the clay is removed, even if it were originally colored. It thus -happens that waters which are colored and turbid at the same time -hardly exist in nature.</p> - -<p>Color-producing matters and turbidity-producing matters are different -in their natures, and the methods which must be used to remove them are -different.</p> - -<div class="section"> -<h3 class="nobreak" id="THE_MEASUREMENT_OF_COLOR">THE MEASUREMENT OF COLOR.</h3></div> - -<p>The colors of waters are measured and recorded by comparing them with -colors of solutions or substances which are permanent, or which can be -reproduced at will. One of the earliest methods of measuring colors of -waters was to compare them with the colors of the Nessler standards -used for the estimation of ammonia in water analysis. The Nessler -standards were similar in appearance to yellow waters, and their colors -depended upon the amounts of ammonia which had been used in preparing -them, and a record was made of the standard which most closely -resembled the water under examination.</p> - -<p>The method was open to the serious objections that the hues of the -standards did not match closely the hues of the waters; that the colors -produced with different lots of Nessler reagent differed considerably, -and therefore the exact values of results were more or less uncertain; -and further, that the numbers obtained for color were not even -approximately proportional to the amounts of coloring matter present. -Because of this peculiarity, in filtration the percentage of color -removal, as determined by the use of these<span class="pagenum" id="Page_115">[Pg 115]</span> standards, is not even -approximately correct, but is much above the truth.</p> - -<p>In the Lovibond tintometer, which has been extensively used in England, -the standards of color are based upon the colors of certain glass -slips, which are in turn compared with standard originals kept for -that purpose. This process answers quite well, but is open to some -objections because of possible uncertainties in the standardization of -the units.</p> - -<p>Another method of measuring colors is to compare them with dilute -solutions of platinum and cobalt. The ratio of cobalt to platinum can -be varied to make the hue correspond very closely with the hues of -natural waters, and the amount of platinum required to match a water -affords a measure of its color, one part of metallic platinum in 10,000 -parts of water forming the unit of color.</p> - -<p>This standard has the advantages that it can be readily prepared with -absolute accuracy in any laboratory, and that by varying the ratio of -platinum to cobalt the hues of various waters can be most perfectly -matched. It is important that the observations should not be made in -too great a depth, as the discrepancy in hues increases much more -rapidly than the depth of color.</p> - -<p>For further information regarding colors the reader is referred to -articles in the American Chemical Journal, 1892, vol. xiv, page 300; -Journal of the American Chemical Society, vol. ii, page 8; vol. xviii, -1896, pp. 68, 264, and 484; Journal of the Franklin Institute, Dec. -1894, p. 402; Journal of the New England Water Works Association, vol. -xiii, 1898, p. 94.</p> - -<div class="section"> -<h3 class="nobreak" id="AMOUNT_OF_COLOR_IN_AMERICAN_WATERS">AMOUNT OF COLOR IN AMERICAN WATERS.</h3></div> - -<p>New England surface-waters have colors ranging from almost nothing -up to 2.00. The colors of the public water-supplies of Massachusetts -cities have been recorded in the reports of the State Board of Health -for some ten years. The figures given were<span class="pagenum" id="Page_117">[Pg 117]</span> recorded first upon the -Nessler standard, and afterwards upon a modification of the same, known -as the natural water standard. The figures given are approximately -equal to those for the platinum color standard, the relations between -the two having been frequently determined by various observers and -published in the above-mentioned papers. The accompanying diagram shows -the colors in several Massachusetts supplies, as plotted from the -figures given in the published reports.</p> - -<div class="figcenter padt1 padb1 illowp51" id="image116" style="max-width: 50em;"> - <img class="w100" src="images/image116.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 18.—Colors of Waters.</span><br /> - -<span class="small">(Analyses of the Mass. State Board of Health.)</span></p></div> - -<p>In Connecticut also the colors of many public water-supplies have been -recorded in the reports of the State Board of Health on the platinum -color-standard.</p> - -<p>The waters of the Middle States, with rare exceptions, are almost free -from color. In the Northwest waters are obtained often with very high -colors, even considerably higher than the New England waters, and some -of the Southern swamps also yield highly colored waters.</p> - -<div class="section"> -<h3 class="nobreak" id="REMOVAL_OF_COLOR">REMOVAL OF COLOR.</h3></div> - -<p>Peaty coloring-matter is almost perfectly in solution, and only a -portion of it is capable of being removed by any form of simple -filtration. In order to remove the coloring-matter it is necessary to -change it chemically, or to bring it into contact with some substance -capable of absorbing it. For this reason sand filtration with ordinary -sands, having no absorptive power for color, commonly removes only from -one fourth to one third of the color of the raw water.</p> - -<div class="section"> -<h3 class="nobreak" id="MEASUREMENT_OF_TURBIDITY">MEASUREMENT OF TURBIDITY.</h3></div> - -<p>The amount of mud or turbidity in a water is often expressed as the -weight of the suspended matters in a given weight of the water. Most -of the data relating to turbidities of waters are stated in this -way, because this was the only method recognized by the earlier -investigators.</p> - -<p><span class="pagenum" id="Page_118">[Pg 118]</span></p> - -<p>This method of statement has some disadvantages: it fails to take -into account the different sizes of particles which are carried in -suspension by different waters, and at different times. Thus the -Merrimac River in a great flood may carry 100 parts in 100,000 of -fine sand in suspension, and still it could hardly be called muddy; -while another stream carrying only a fraction of this amount of fine -clay would be extremely muddy. Further, an accurate determination of -suspended matters is a very troublesome and tedious operation, and -cannot be undertaken as frequently as is necessary for an adequate -study of the mud question.</p> - -<p>Turbidity is principally important as it affects the appearance of -water, and it would seem that optical rather than gravimetric methods -should be used for its determination. Various optical methods of -measuring turbidity have been proposed. The general method employed -is to measure the thickness of the layer of water through which some -object can be seen under definite conditions of lighting. The most -accurate results can probably be obtained in closed receptacles and -with artificial light. Such a method has been used by Mr. G. W. Fuller -at Louisville and Cincinnati in connection with his experiments, and is -described by Parmelee and Ellms in the Technology Quarterly for June, -1899. This apparatus is called by Mr. Fuller a diaphanometer.</p> - -<p>At the Lawrence Experiment Station of the Massachusetts State Board of -Health as early as 1889 it became necessary to express the turbidities -of various waters approximately, and the very simple device of -sticking a pin into a stick, and pushing it down into the water under -examination as far as it could be seen, was adopted. Afterwards a -platinum wire 0.04 of an inch in diameter was substituted for the pin, -and the stick was graduated so that the turbidities could be read from -it directly. The figures on the stick were inversely proportional to -their distances from the wire. When the wire could be seen one inch -below the surface, the turbidity was reported as 1.00; when the wire -could be seen two inches, the turbidity was 0.50, and when it could -be seen ten<span class="pagenum" id="Page_119">[Pg 119]</span> inches the turbidity was 0.10, etc. This scale is much -more convenient than a scale showing the depth at which the wire can -be seen; and within certain limits the figures obtained with it are -directly proportional to the amount of the elements which obstruct -light in the water. Thus, if a water having a turbidity of 1.00 is -mixed with an equal volume of clear water, the mixture will have a -turbidity of 0.50. Advantage is taken of this fact for the measurement -of turbidities so great that they cannot be accurately determined -by direct observation. For turbidities much above 1.00 it is very -difficult to read the depth of wire with sufficient accuracy, and such -waters are diluted with one, two, or more times their volume of clear -water in a pail or other receptacle, the turbidity of the diluted water -is taken, and multiplied by the appropriate factor.</p> - -<p>For the greatest accuracy it is necessary that the observations should -be taken in the open air and not under a roof. They should preferably -be made in the middle of the day when the light is strongest, and in -case the sun is shining, the wire must be kept in shadow and not in -direct sunlight.</p> - -<p>The turbidities of effluents are usually so slight that they cannot -be taken in this manner; in fact, turbidities of less than 0.02, with -the wire visible 50 inches below the surface, cannot be conveniently -read in this way. For the estimation of lower turbidities a water is -taken having a turbidity of 0.03 or 0.04 and as free as possible from -large suspended particles. The turbidity of this water is measured by -a platinum wire in the usual way, and the water is then diluted with -clear water to make standards for the lower turbidities.</p> - -<p>The comparisons between standards and waters are best made in bottles -of perfectly clear glass, holding at least a gallon, and the comparison -is facilitated by surrounding the bottles with black cloth except at -the point of observation, and lighting the water by electric lights so -arranged that the light passes through the water but is hidden from -the observer. In case the water under<span class="pagenum" id="Page_120">[Pg 120]</span> examination is colored, the -comparison is rendered difficult, and it is often advisable to add a -small amount of methyl orange to the standards to make the colors equal.</p> - -<p>Instead of diluting a water of known turbidity for the standards, a -standard can be made by precipitating a known amount of silver chloride -in the water. For this purpose about one per cent of common salt is -dissolved in clear water and small measured amounts of silver nitrate -added, until the turbidity produced is equal to that of the water under -examination. The relation of the amount of silver nitrate used to the -turbidity is entirely arbitrary, and is established by comparisons of -standards made in this way with waters having turbidities from 0.02 to -0.04, the turbidities of which are measured with the platinum wire, and -which afterwards serve to rate the standards. The silver chloride has a -slight color, which is an objection to its use, and perhaps some other -substance could be substituted for it with advantage. The standards -have to be made freshly each day.</p> - -<p>One disadvantage of the platinum-wire method of observing turbidities -in the open air, as compared with the diaphanometric method using -artificial light, is that observations cannot be made in the night. To -get the general character of the water in a stream, daily observations -taken about noon will generally be sufficient; but for some purposes it -is important to know the turbidity at different hours of the day, and -in such cases the platinum-wire method is at a distinct disadvantage. -Variations in the amount of light, within reasonable limits, do not -affect the results materially, although extreme variations are to be -avoided. The size of the wire also influences the results somewhat. The -wire commonly used is 0.04 of an inch or one millimeter in diameter. -A wire only four tenths of this size in some experiments at Pittsburg -gave results 25 per cent higher; with a wire twice as large the -results were lower, but the differences were much less. Wire 0.04 of -an inch in diameter was adopted as being very well adapted to rather -turbid river-waters. For very<span class="pagenum" id="Page_121">[Pg 121]</span> clear lake or reservoir waters, usually -transparent to a great depth, a much larger object is preferable. -Within certain limits the results obtained with an object of any size -can be converted into corresponding figures for another object, or -another light, by the use of a constant factor. Thus the turbidities -obtained with a platinum wire always have approximately the same ratio -to the turbidities of the same waters determined by the diaphanometer.</p> - -<p>The platinum-wire method has been used in many cases with most -satisfactory results. If it lacks something in theoretical accuracy -as compared with more elaborate methods, it more than makes up for it -by its simplicity; and reliable observations can be taken with it by -people who would be entirely incompetent to operate more elaborate -apparatus; and it can thus be used in many cases where other methods -would be impossible.</p> - -<p>Upon this scale the most turbid waters which have come under the -observation of the author have turbidities of about 2.50, although -waters much more turbid than this undoubtedly exist. A water with -a turbidity of 1.00 is extremely muddy, and only one tenth of this -turbidity would cause remark and complaint among those who use it for -domestic purposes. In an ordinary pressed-glass tumbler a turbidity of -0.02 is just visible to an ordinary observer who looks at the water -closely, but it is not conspicuous, nor would it be likely to cause -general complaint; and this amount may be taken as approximately the -allowable limit of turbidity in a good public water-supply. In a -carefully polished, and perfectly transparent glass a turbidity of 0.01 -will be visible, and in larger receptacles still lower turbidities may -be seen if the water is examined carefully. In gallon bottles of very -clear glass, under electric light and surrounded by black cloth, a -turbidity of 0.001 can be distinguished, but a turbidity even several -times as large as this could hardly be detected except by the use of -special appliances, or where water is seen in a depth of several feet.</p> - -<p><span class="pagenum" id="Page_122">[Pg 122]</span></p> - -<div class="section"> -<h3 class="nobreak" id="RELATION_OF_PLATINUM_WIRE_TURBIDITIES_TO_SUSPENDED_MATTERS">RELATION OF PLATINUM-WIRE TURBIDITIES TO SUSPENDED MATTERS.</h3></div> - -<p>The relation of turbidity to the weight of suspended matters is -approximately constant for waters from which the coarser matters have -been entirely removed by sedimentation. For these waters the suspended -matters in parts per 100,000 are about 16 times the turbidity. For -river-waters the ratios are always larger. With very sluggish rivers -the ratio is only a little larger than for settled waters. For average -river-waters the ratio is considerably higher, and increases with the -turbidity, and for very rapid rivers and torrents the ratio is much -wider, as the suspended matters consist largely of particles which are -heavy but do not increase very much the turbidity.</p> - -<p class="padb1">The following table gives the amounts of suspended matters for various -classes of waters corresponding to the turbidities stated, which have -been deduced from the experience of the author. It is very likely that -ratios different from the above would be obtained with waters in which -the sediment was of different character.</p> - -<table class="autotable" summary="suspended matters for various -classes of waters"> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Turbidity,<br />Platinum-wire<br />Standard.</th> -<th class="tdc normal small bord_top bord_bot" colspan="4">Suspended Matters: Parts in 100,000.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Settled<br />Waters.</th> -<th class="tdc normal small bord_right bord_bot">River Waters,<br />Finest Sediment.</th> -<th class="tdc normal small bord_right bord_bot">River Waters,<br />Average Sediment.</th> -<th class="tdc normal small bord_bot">River Waters,<br />Coarsest Sediment.</th> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 0.01</td> -<td class="tdc bord_right vertb"> 0.16</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdc bord_right vertb">0.05</td> -<td class="tdc bord_right vertb"> 0.80</td> -<td class="tdc bord_right vertb"> 0.85</td> -<td class="tdc bord_right vertb"> 1.30</td> -<td class="tdc"> 2.40</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">0.10</td> -<td class="tdc bord_right vertb"> 1.60</td> -<td class="tdc bord_right vertb"> 1.75</td> -<td class="tdc bord_right vertb"> 2.60</td> -<td class="tdc"> 4.90</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">0.20</td> -<td class="tdc bord_right vertb"> 3.20</td> -<td class="tdc bord_right vertb"> 3.60</td> -<td class="tdc bord_right vertb"> 5.50</td> -<td class="tdc"> 10.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">0.30</td> -<td class="tdc bord_right vertb"> 4.80</td> -<td class="tdc bord_right vertb"> 5.70</td> -<td class="tdc bord_right vertb"> 8.50</td> -<td class="tdc"> 15.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">0.40</td> -<td class="tdc bord_right vertb"> 6.40</td> -<td class="tdc bord_right vertb"> 7.80</td> -<td class="tdc bord_right vertb"> 11.60</td> -<td class="tdc"> 21.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">0.50</td> -<td class="tdc bord_right vertb"> 8.00</td> -<td class="tdc bord_right vertb"> 10.00</td> -<td class="tdc bord_right vertb"> 15.00</td> -<td class="tdc"> 26.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">1.00</td> -<td class="tdc bord_right vertb">16.00</td> -<td class="tdc bord_right vertb"> 23.00</td> -<td class="tdc bord_right vertb"> 36.00</td> -<td class="tdc"> 59.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">1.50</td> -<td class="tdc bord_right vertb">24.00</td> -<td class="tdc bord_right vertb"> 40.00</td> -<td class="tdc bord_right vertb"> 62.00</td> -<td class="tdc"> 97.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">2.00</td> -<td class="tdc bord_right vertb">32.00</td> -<td class="tdc bord_right vertb"> 61.00</td> -<td class="tdc bord_right vertb"> 94.00</td> -<td class="tdc">140.00</td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot">3.00</td> -<td class="tdc bord_right bord_bot">48.00</td> -<td class="tdc bord_right bord_bot">110.00</td> -<td class="tdc bord_right bord_bot">175.00</td> -<td class="tdc bord_bot">250.00</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_123">[Pg 123]</span></p> - -<div class="section"> -<h3 class="nobreak" id="SOURCE_OF_TURBIDITY">SOURCE OF TURBIDITY.</h3></div> - -<p>Much turbidity originates in plowed fields of clayey soil, or in -fields upon which crops are growing. If it has not rained for some -days, and the surface-soil is comparatively dry, the first rain that -falls upon such land is absorbed by the pores of the soil until they -are filled. If the rain is not heavy, but little runs off over the -surface. If, however, the rain continues rapidly after the surface-soil -is saturated, the excess runs off over the surface to the nearest -watercourse. The impact of the rain-drops upon the soil loosens -the particles, and the water flowing off carries some of them in -suspension, and the water is said to be muddy.</p> - -<p>The particles carried off in this way are extremely small. Mr. George -W. Fuller, in his report upon water purification at Louisville, -estimates that many of them are not more than a hundred thousandth of -an inch in diameter, and not more than a tenth as large as common water -bacteria.</p> - -<p>The turbidity of the water flowing from a field of loose soil may be -2.00 or more; that is to say, the wire is hidden by a depth of half an -inch of water or less. When the water reaches the nearest watercourse -it meets with water from other kinds of land, such as woodlands and -grassed fields, and these waters are less turbid. The water in the -first little watercourse is thus a mixture and has a turbidity of -perhaps 1.00.</p> - -<p>The conditions which control the turbidity of any brook are numerous -and complicated. The turbidity of a stream receiving various brooks -depends upon the turbidities of all the waters coming into it. -Generally speaking, the turbidity of a river depends directly upon the -turbidities of its feeders, and is not affected materially by erosion -of its bed or by sedimentation in it. There are, of course, some -streams which in times of great floods cut their banks, and all streams -pick up and move about from place to place more or less of the sand and -other coarse<span class="pagenum" id="Page_124">[Pg 124]</span> materials upon their bottoms. The materials thus moved, -however, have but little influence upon the turbidity.</p> - -<p>After the rain is over some of the water held by the soil will find -its way to the watercourses by underground channels, and will prevent -the stream from drying up between rains, but the average volume of the -stream-flows between rains will be much less than the volumes during -the rains when the water is most turbid.</p> - -<div class="figcenter illowp100" id="image124" style="max-width: 50em;"> - <img class="w100" src="images/image124.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 19.—Fluctuations in Turbidity of the Water of -the Allegheny River at Pittsburg during 1898.</span></p></div> - -<p>These conditions are well illustrated by a few data upon the turbidity -of three Pennsylvania streams, recently collected by the author. One -of these streams is a small brook having a drainage area of less than -three square miles. The observations extended over a period of 47 days. -During this time there were five floods, or an average of one flood in -ten days. The duration of floods was less than twenty-four hours in -each case. Selecting the days when the turbidity was the highest, to -the number of one tenth<span class="pagenum" id="Page_125">[Pg 125]</span> of the whole number of days, the sum of the -turbidities for these days was 67 per cent of the aggregate turbidities -for the whole period. That is to say, 67 per cent of the whole amount -of mud was in the water of only a tenth of the days; the water of the -other nine tenths of the days contained only 33 per cent of the whole -amount of turbidity. The average turbidity of the water for the flood -days was eighteen times as great as the average turbidity for the -remaining days.</p> - -<p>The next stream is a considerable creek having a drainage area of -350 square miles. The observations extended over 117 days, during -which time there were seven floods, or an average of one flood in 19 -days. The floods lasted in each case one or two days, and the sum of -the turbidities for the one tenth of the whole number of days when -the water was muddiest was 55 per cent of the aggregate of all the -turbidities for the period.</p> - -<p>The last case is that of a large river, with a drainage area of over -11,000 square miles. The observations extended over a full year. In -this period there were sixteen floods, each lasting from one to six -days, and the sum of the turbidities for the one tenth of the whole -number of days when the water was muddiest is 45 per cent of the -aggregate turbidities for the year. The floods occurred on an average -of once in 22 days, and the average duration was two and one half days.</p> - -<p>The results are very striking as showing that a very large proportion -of the mud is carried by the water in flood flows of comparatively -short duration. They also show that in small streams the proportion of -mud in the flood-flows is greater, and the average duration of floods -is shorter, than in larger streams. In other words, the differences -between flood- and low-water flows are greatest in small streams, and -gradually become less as the size of the stream increases.</p> - -<p>When a stream is used for water-works purposes in the usual way, a -certain quantity of water is taken from the stream each day, which -quantity is nearly constant, and is not dependent upon<span class="pagenum" id="Page_126">[Pg 126]</span> the condition -of the stream, or the volume of its flow. The proportions of the -total flows taken at high- and low-water stages are very different, -and it thus happens that the average quality of the water taken for -water-works purposes is different from the average quality of all the -water flowing in the stream.</p> - -<p>Let us assume, for example, a stream having a watershed of such a -size that in times of moderate floods water from the most distant -points reaches the water-works intake in twenty-four hours. Let us -assume further that rainfalls of sufficient intensity to cause floods -and muddy water occur, on an average, once in ten days, and that the -turbidity of the water at these times reaches 1.00, and that for the -rest of the time the turbidity averages 0.10. Let us assume further -that at times of storms the average flow of the stream is 100 units -of volume, and for the nine days between storms the average flow is -10 units of volume. We shall then have in a ten days’ period, for one -day, 100 volumes of water with a turbidity of 1.00, and nine days with -10 volumes each, or a total of 90 volumes of water with a turbidity -of 0.10. The total discharge of the stream will then be 190 volumes, -and the average turbidity 0.57. The turbidity of 0.57 represents the -average turbidity all the water flowing in the stream, or, in other -words, the turbidity which would be found in a lake if all the water -for ten days should flow into it and become thoroughly mixed without -other change.</p> - -<p>Now let us compute the average turbidity of the water taken from the -stream for water-works purposes. The water-works require, let us -say, one volume each day, and we have for the first day water with a -turbidity of 1.00, and then for nine days water with a turbidity of -0.10. The average turbidity of the water taken by the water-works for -the period is thus only 0.19 in place of 0.57, the average turbidity of -the whole run-off.</p> - -<p>The average turbidity of all the water flowing in the stream is thus -three times as great as that of the water taken from the stream for -water-works purposes.</p> - -<p><span class="pagenum" id="Page_127">[Pg 127]</span></p> - -<p>It is often noted that with long streams the water becomes muddier -farther down, and it may naturally be thought that it is because of the -added erosion of the stream upon its bed in its longer course. This, of -course, may be a cause, or the lower tributaries may be muddier than -the upper ones, but the fact that the water taken at the lower point is -more muddy than farther up is not an indication of this.</p> - -<p>Let us take, for example, a watershed of twice the size of that assumed -above, that is, so long that 48 hours will be required for the water -from the most remote feeders to reach the water-works intake. Let us -divide this shed into two parts, which we will assume to be equal, one -of which furnishes water reaching the intake within 24 hours, and the -other water reaching the intake between 24 and 48 hours. Now suppose -a storm upon the watershed producing turbidities equal to those just -assumed for the smaller stream. On the first day the water from the -lower half of the shed, namely, 100 volumes having a turbidity of 1.00, -passes the intake, but this is mixed with 10 volumes of water from -the upper half of the watershed, having a turbidity of 0.10, and the -total flow is thus 110 volumes of water having a turbidity of 0.92. -On the second day the water from the lower half of the watershed has -returned to its normal condition, and the flood-flow of the upper half -of the watershed, 100 volumes with a turbidity of 1.00, is passing, -and mingles with the 10 volumes from the lower half with a turbidity -of 0.10, and the total flow is again 110 volumes having a turbidity of -0.92. The following eight days, until the next rain, will have flows -of 20 volumes each, with turbidities of 0.10. The average turbidity of -all of the water flowing off is 0.57 as before, but the water taken -for water-works purposes will consist of 2 volumes of water with -turbidities of 0.92, and 8 volumes with turbidities of 0.10 making 10 -volumes with an average turbidity of 0.26.</p> - -<p>By doubling the length of the watershed we have thus doubled the length -of time during which the water is turbid, and have<span class="pagenum" id="Page_128">[Pg 128]</span> increased the -average turbidity of the water taken for water-works purposes from 0.19 -to 0.26, although the average turbidity of all the water running off -remains exactly the same.</p> - -<p>If now we assume a watershed so long that three days are required -for the water from the most remote points to reach the intake, with -computations as above, water taken for water-works purposes will have -an average turbidity of 0.32; and with still longer watersheds this -amount will increase, until with a watershed so long that ten days, -or the interval between rains, are required for the water from the -upper portions to reach the intake, the average turbidity of the water -taken for water-works purposes will reach the average turbidity of the -run-off, namely, 0.57.</p> - -<p>In the above computations the numbers taken are round ones, and of -course do not represent closely actual conditions. They do serve, -however, to illustrate clearly the principle that the larger the -watershed, other things being equal, the more muddy will be the water -obtained from it for water-works purposes, and the longer will be the -periods of muddy water, and the shorter the periods of clear water -between them.</p> - -<p>It cannot be too strongly emphasized that the period of duration of -muddy water is, in general, dependent upon the length of time necessary -for the muddy water to run out of the stream system after it is once in -it, and be replaced by clear water; and that the settling out of the -mud in the river has very little to do with it.</p> - -<p>Muddy waters result principally from the action of rains upon the -surface of ground capable of being washed, and the turbidities of the -stream at any point below will occur at the times when the muddy waters -reach it in the natural course of flow, and will disappear again when -the muddy waters present in the stream system at the end of the rain -have run out, and have been replaced with clear water from underground -sources, or from clearer surface sources.</p> - -<p><span class="pagenum" id="Page_129">[Pg 129]</span></p> - -<div class="section"> -<h3 class="nobreak" id="THE_AMOUNTS_OF_SUSPENDED_MATTERS_IN_WATER">THE AMOUNTS OF SUSPENDED MATTERS IN WATER.</h3></div> - -<p>There is a large class of waters, including most lake and reservoir -waters, and surface-waters from certain geological formations, which -are almost free from suspended matters and turbidities. That is to say, -the average turbidities are less than 0.10, and the average suspended -matters are less than 2 parts in 100,000, and are often only small -fractions of these figures. This class includes the raw waters of the -supplies of many English cities drawn from impounding reservoirs, and -also the waters of the rivers Thames and Lea at London, and the raw -waters used by both of the Berlin water-works, and in the United States -the waters of the great lakes except at special points near the mouths -of rivers, nearly all New England waters, and many other waters along -the Atlantic coast and elsewhere where the geological formations are -favorable.</p> - -<p>Data regarding the suspended matters in these waters are extremely -meagre. The official examinations of the London waters contain no -records of suspended matters, although the clearness of filtered -waters is daily reported. Dibden, in his analytical investigations of -the London water-supply, mentioned in his book upon “The Purification -of Sewage and Water,” reports the average suspended matters in the -water of the Thames near the water-works intakes as 0.77 part in -100,000. No figures are available for the raw waters used by the Berlin -water-works, but both are taken from lakes, and are generally quite -clear. Even in times of floods of the rivers feeding the lakes, the -turbidities are not very high, because the gathering grounds for the -waters are almost entirely of a sandy nature, yielding waters with low -turbidities, and further, the streams flow through successions of lakes -before finally reaching the lakes from which the waters are taken. It -is safe to assume that the suspended matters and turbidities do not -exceed those of the London waters. Even at times when somewhat turbid -water is obtained, due to agitation by heavy winds, the suspended -matter is mainly of a<span class="pagenum" id="Page_130">[Pg 130]</span> sandy nature, readily removed by settling, and -it does not seriously interfere with filtration.</p> - -<p>The examinations of the Massachusetts State Board of Health, with a -very few exceptions, contain no statements of suspended matters. This -is due to the fact that the suspended matters, in most of the waters, -are so small in amount as to make them hardly capable of determination -by the ordinary gravimetric processes, and the determinations if made -would have but little value. The Merrimac River at Lawrence, at the -time of the greatest flood in fifty years, carried silt to the amount -of about 111 parts in 100,000. This was for a very short time, and the -suspended matter consisted almost entirely of sand, which deposited -in banks, the deposited sand having an effective size of 0.04 or 0.05 -millimeter. No clayey matter is ever carried in quantity by the river.</p> - -<p>The reports of the Connecticut State Board of Health also contain no -records of suspended matters for the same reason. It may be safely said -that the average suspended matters of New England waters are almost -always less than 1 part in 100,000.</p> - -<p>Lake waters are generally almost entirely free from sediment. At -Chicago the city water drawn from Lake Michigan has slightly more than -1 part in 100,000 of suspended matters, as determined by Professor Long -in 1888-9, and by Professor Palmer in 1896. The suspended matter in -this case is probably due to the nearness of the intake to the mouth of -the Chicago River, and to mud brought up from the bottom in times of -storms. The lake-water further away from the shore would probably give -much lower results.</p> - -<p>Turning now to waters having considerable turbidities, at Pittsburg the -average suspended matters in the Allegheny River water, as shown by -the weekly or semi-weekly analyses of the Filtration Commission during -1897-8, were 4 parts in 100,000. During a large part of the time the -suspended matters were so small that it was not deemed worth while -to determine them, and the results are returned as zero. This is not -quite correct, and a recomputation of the amount of suspended matters, -based on the<span class="pagenum" id="Page_131">[Pg 131]</span> observed amounts, and the amounts calculated from the -turbidities when they were very low, leads to an average of a little -less than 5 parts in 100,000, which is probably more accurate than the -direct average. The average turbidity on the platinum-wire scale was -0.16.</p> - -<p>At Cincinnati the suspended matters are about 23 parts in 100,000, -and at Louisville about 35 parts, both of these figures being from -Mr. Fuller’s reports. In all these cases the enormous and rapid -fluctuations in the turbidity of the water is a most striking feature -of the results.</p> - -<p>Observations on the Mississippi River above the Ohio have been -made by Professor Long in 1888-9, and by Professor Palmer in 1896. -These results are not as full and systematic as could be desired, -but indicate averages of 20 to 30 parts in 100,000 at the different -points. Professor William Ripley Nichols, in his work on water-supply, -states the amount of suspended matter in the water of the Mississippi, -probably referring to the lower river, as 66.66 parts.</p> - -<p>Investigations of Professor Long and Professor Palmer for numerous -interior Illinois streams extending over considerable periods give -average results ranging from 1 to 8 parts in 100,000. The very much -lower results for the interior streams as compared with the Mississippi -and Ohio rivers may be due to the relative sizes and lengths of the -streams, or in part to other causes.</p> - -<p>Regarding muddy European rivers there are but few data. The Maas, used -for the water-supply of Rotterdam, is reported by Professor Nichols as -having from 1.40 to 47.61 and averaging 10 parts of suspended matters -in 100,000. More recent information is to the effect that the raw water -has at most 30 parts of suspended matters, and that that quantity is -very seldom reached.</p> - -<p>At Bremen the Weser often becomes quite turbid. The turbidity of the -water is noted every day by taking the depth at which a black line on a -white surface can be seen. Assuming that this procedure is equivalent -to the platinum-wire procedure, the<span class="pagenum" id="Page_132">[Pg 132]</span> depths at which the wire can be -seen, namely, from 15 to 600 millimeters, correspond to turbidities of -from 0.04 to 1.70, a result not very different from the conditions at -Pittsburg.</p> - -<p>At Hamburg and Altona the water is generally tolerably clear, but at -times of flood the Elbe becomes very turbid, and the amount of mud -deposited in the sedimentation-basins is considerable. At Dresden, -several hundred miles up the river, I have repeatedly seen the -river-water extremely turbid with clayey matter, the color of the clay -varying from day to day, corresponding to the color of the earth from -which it had been washed.</p> - -<p>At Budapest, where filters were used temporarily, the Danube water -was excessively muddy with clayey material. At first very high rates -of filtration were employed and the results were not satisfactory. -Afterward the rate of filtration was limited to 1.07 million gallons -per acre daily, and good results were secured. There was no preliminary -sedimentation. Professor Nichols reports the average suspended matters -in the Danube at 32.68 parts in 100,000, but does not state at what -place.</p> - -<p>Many of the French and German rivers drain prairie country not -different in its general aspect from the Mississippi basin, and the -soil is probably in many places similar. There is no reason to suppose -that the turbidities of these streams in general are materially -different from those of corresponding streams in the United States, -although it is true that, other things being equal, the average -turbidity of water taken for water-works purposes will increase with -the size of the stream; and it may be that some American streams, -especially the Ohio, Missouri, and Mississippi rivers, are of larger -size than European streams, and consequently that the turbidity of the -water taken from them for water-works purposes may be greater.</p> - -<p>The following are the drainage areas of a number of European and -American streams yielding more or less muddy waters at points where -they are used for public water-supplies after filtration, with a few -other American points for comparison. The<span class="pagenum" id="Page_133">[Pg 133]</span> results are obtained in most -cases from measurements of the best available maps.</p> - -<table class="autotable" summary="drainage areas of European and American streams"> - -<tr> -<th class="tdc smaller normal bord_top bord_right bord_bot">Place.</th> -<th class="tdc smaller normal bord_top bord_right bord_bot">River.</th> -<th class="tdc smaller normal bord_top bord_bot">Drainage Area,<br />Square Miles.</th> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">New Orleans, La.</td> -<td class="tdl vertt bord_right vertb">Mississippi</td> -<td class="tdr vertt">1,261,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">St. Louis, Mo.</td> -<td class="tdl vertt bord_right vertb">Mississippi</td> -<td class="tdr vertt">700,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">St. Petersburg</td> -<td class="tdl vertt bord_right vertb">Neva</td> -<td class="tdr vertt">108,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Louisville, Ky.</td> -<td class="tdl vertt bord_right vertb">Ohio</td> -<td class="tdr vertt">90,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Rock Island, Ill.</td> -<td class="tdl vertt bord_right vertb">Mississippi</td> -<td class="tdr vertt">88,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Budapest</td> -<td class="tdl vertt bord_right vertb">Danube</td> -<td class="tdr vertt">79,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Cincinnati, O.</td> -<td class="tdl vertt bord_right vertb">Ohio</td> -<td class="tdr vertt">75,700</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Dordrecht</td> -<td class="tdl vertt bord_right vertb">Maas</td> -<td class="tdr vertt">68,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Rotterdam</td> -<td class="tdl vertt bord_right vertb">Maas</td> -<td class="tdr vertt">68,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Schiedam</td> -<td class="tdl vertt bord_right vertb">Maas</td> -<td class="tdr vertt">68,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Altona</td> -<td class="tdl vertt bord_right vertb">Elbe</td> -<td class="tdr vertt">52,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Hamburg</td> -<td class="tdl vertt bord_right vertb">Elbe</td> -<td class="tdr vertt">52,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Stettin</td> -<td class="tdl vertt bord_right vertb">Oder</td> -<td class="tdr vertt">40,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Magdeburg</td> -<td class="tdl vertt bord_right vertb">Elbe</td> -<td class="tdr vertt">36,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Warsaw</td> -<td class="tdl vertt bord_right vertb">Weichsel</td> -<td class="tdr vertt">34,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Odessa</td> -<td class="tdl vertt bord_right vertb">Dneister</td> -<td class="tdr vertt">26,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Worms</td> -<td class="tdl vertt bord_right vertb">Rhine</td> -<td class="tdr vertt">25,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Grand Forks, N. Dak.</td> -<td class="tdl vertt bord_right vertb">Red River of the North</td> -<td class="tdr vertt">22,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Frankfort on Oder</td> -<td class="tdl vertt bord_right vertb">Oder</td> -<td class="tdr vertt">21,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Bremen</td> -<td class="tdl vertt bord_right vertb">Weser</td> -<td class="tdr vertt">15,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Suburbs of Paris</td> -<td class="tdl vertt bord_right vertb">Seine</td> -<td class="tdr vertt">12,000</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Poughkeepsie, N. Y.</td> -<td class="tdl vertt bord_right vertb">Hudson</td> -<td class="tdr vertt">11,600</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Pittsburg, Penn.</td> -<td class="tdl vertt bord_right vertb">Allegheny</td> -<td class="tdr vertt">11,400</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Posen</td> -<td class="tdl vertt bord_right vertb">Wartha</td> -<td class="tdr vertt">9,400</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Hudson, N. Y.</td> -<td class="tdl vertt bord_right vertb">Hudson</td> -<td class="tdr vertt">9,200</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Albany, N. Y.</td> -<td class="tdl vertt bord_right vertb">Hudson</td> -<td class="tdr vertt">8,200</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Breslau</td> -<td class="tdl vertt bord_right vertb">Oder</td> -<td class="tdr vertt">8,200</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Brieg</td> -<td class="tdl vertt bord_right vertb">Oder</td> -<td class="tdr vertt">7,500</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Lawrence, Mass.</td> -<td class="tdl vertt bord_right vertb">Merrimac</td> -<td class="tdr vertt">4,634</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Stuttgart</td> -<td class="tdl vertt bord_right vertb">Neckar</td> -<td class="tdr vertt">1,660</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">Brunswick</td> -<td class="tdl vertt bord_right vertb">Ocker</td> -<td class="tdr vertt">650</td> -</tr> -<tr> -<td class="tdl bord_right bord_bot">Somersworth, N. H.</td> -<td class="tdl bord_right bord_bot">Salmon</td> -<td class="tdr bord_bot">171</td> -</tr> -</table> - -<div class="section"> -<h3 class="nobreak" id="PRELIMINARY_PROCESSES_TO_REMOVE_MUD">PRELIMINARY PROCESSES TO REMOVE MUD.</h3></div> - -<p>With both sand and mechanical filtration the difficulty and expense -of treatment of a water increase nearly in direct proportion to the -turbidity of the water as applied to the filter; and it is thus highly -important to secure a water for filtration with as little turbidity -as possible, and thus to develop to their economical limits the -preliminary processes for the removal of mud. One of the most important -of these processes is the use of reservoirs.</p> - -<p>Reservoirs serve two purposes in connection with waters drawn<span class="pagenum" id="Page_134">[Pg 134]</span> -from streams: they allow sedimentation, and they afford storage. -If a water having a turbidity of 1.00 is allowed to remain in a -sedimentation-basin for 24 hours, its turbidity may be reduced by -as much as 40 per cent, or to 0.60. If it is held a second day the -additional reduction is much less.</p> - -<p>If samples are taken of the water in the reservoir before and after -settling and sent to the chemist for analysis, he will probably report -that from 70 to 80 per cent of the suspended matters have been removed -by the process. The suspended matters are removed in much larger ratio -than the turbidity. This arises from the fact that there is a certain -proportion of comparatively coarse material in the water as it is -taken from the river. This coarse material increases the weight of the -suspended matters without increasing the turbidity in a corresponding -degree. In 24 hours the coarser materials are removed completely, and -at the end of that time only the clayey or finer particles remain in -suspension. It is these clayey particles, however, that constitute the -turbidity, which are most objectionable in appearance, and which are -most difficult of removal by filtration or otherwise.</p> - -<p>Sedimentation thus removes the heavier matters from the water, -but it does not remove the finer matters which principally affect -the appearance of the water and are otherwise most troublesome. A -sedimentation of 24 hours removes practically all of the coarser -matters, and the clayey material remaining at the end of that time -can hardly be removed by further sedimentation. The economic limit of -sedimentation is about 24 hours.</p> - -<p>Sedimentation has practically no effect upon the clearer waters between -flood periods.</p> - -<p>Let us consider the effect of a sedimentation-basin, or reservoir -holding a 24-hours’ supply of water, into which water is constantly -pumped at one end, and from which an equal quantity is constantly -withdrawn from the other, upon the water of a stream of such size -that the time of passage of water from the feeders to the intake is -less than 24 hours. During the period between storms<span class="pagenum" id="Page_135">[Pg 135]</span> the water is -comparatively clear and passes through the sedimentation basin without -change. When a storm comes the water in the stream promptly becomes -muddy, and muddy water is supplied to the reservoir; but owing to -the time required for water to pass through it, the outflowing water -remains clear for some hours. There is a gradual mixing, however, and -long before the expiration of 24 hours somewhat muddy water appears -at the outlet. The turbid-water period rarely lasts in streams of -this size more than 24 hours, and at the expiration of that time the -water in the sedimentation-basin is as muddy or muddier than the water -flowing in the stream. After the height of the flood the stream clears -itself by the flowing away of the turbid water much more rapidly than -the water clears itself by sedimentation in the reservoir. That is to -say, if at the time of maximum turbidity we take a certain quantity of -water from the stream and put it aside to settle, at no time will the -improvement by settling equal the improvement which has taken place in -the stream from natural causes. Generally the improvement in the stream -is several times as rapid as in the sedimentation-basin, and the water -from it will at times have only a fraction of the turbidity of the -water in the basin.</p> - -<p>Let us now consider what the sedimentation has done to improve the -water. During the period of clear water, that is for most of the -time, it has done nothing. For the first day of each flood period -very much clearer water has been obtained from it than was flowing -in the stream. For the first days following floods the water in the -sedimentation-basin has been more muddy than the water in the stream. -The only time when the sedimentation-basin has been of use is during -the first part of floods, that is, when the turbidity of the water in -the stream is increasing. During this period it has been of service -principally because of its storage capacity, yielding up water received -from the stream previously, when it was less muddy. Such sedimentation -as has been secured is merely incidental and generally not important in -amount.</p> - -<p><span class="pagenum" id="Page_136">[Pg 136]</span></p> - -<p>It will be obvious from the above that for these conditions storage -is much more important than sedimentation. This brings us back to -the old English idea of having storage-reservoirs large enough to -carry water-works over flood periods without the use of flood-waters. -Reservoirs of this kind were, and still are, considered necessary for -the successful utilization of waters of many English rivers, although -these waters do not approach in turbidity the waters of some American -streams. This idea of storage has been but little used in the United -States.</p> - -<p>In the above case, if we use our reservoir for storage instead of as a -sedimentation-basin, the average quality of the water can be greatly -improved. The reservoir should ordinarily be kept full, and pumping to -it should be stopped whenever the turbidity exceeds a certain limit, -to be determined by experience; and the reservoir is then to be drawn -upon for the supply until the turbidity again falls to the normal. In -the case assumed above, with a stream in which all of the water reaches -the intake in 24 hours, a reservoir holding a 24-hours’ supply, or in -practice, to be safe, a somewhat larger one, would yield a water having -a very much lower average turbidity than would be obtained with water -pumped constantly from the stream without a reservoir.</p> - -<p>With a river having a watershed so long that 48 hours are required to -bring the water down from the most remote feeders, a reservoir twice as -large would be required, and would result in a still greater reduction -in the average turbidity.</p> - -<p>As the stream becomes larger, and the turbid periods longer, the size -of a reservoir necessary to utilize this action rapidly becomes larger, -and the times during which it can be filled are shortened, and thus the -engineering difficulties of the problem are increased. For moderately -short streams, cost for cost, storage is far more effective than -sedimentation, and we must come back to the old English practice of -stopping our pumps during periods of maximum turbidity.</p> - -<p><span class="pagenum" id="Page_137">[Pg 137]</span></p> - -<div class="section"> -<h3 class="nobreak" id="EFFECT_OF_MUD_UPON_SAND_FILTERS">EFFECT OF MUD UPON SAND FILTERS.</h3></div> - -<p>There are two aspects of the effect of mud upon the operation of sand -filters which require particular consideration. The first relates to -the rapidity of clogging, and consequently the frequency of scraping -and the cost of operation; while the second relates to the ability of -the filters to yield well-clarified effluents.</p> - -<div class="section"> -<h3 class="nobreak" id="EFFECT_OF_TURBIDITY_UPON_THE_LENGTH_OF_PERIOD"> -EFFECT OF TURBIDITY UPON THE LENGTH OF PERIOD.</h3></div> - -<p>The amount of water which can be filtered between scrapings is directly -dependent upon the turbidity of the raw water. The greater the -turbidity, the more frequently will filters require to be scraped. In -the experiments of the Pittsburg Filtration Commission, with 4 feet of -sand of an effective size of about 0.30 millimeter, and with rates of -filtration of about three million gallons per acre daily, and with the -loss of head limited to 4 feet, sand filters were operated as follows: -For five periods the turbidities of the raw water ranged from 0.035 to -0.062, and averaged 0.051, and the corresponding periods ranged from -102 to 136, and averaged 113 million gallons per acre filtered between -scrapings. For ten periods the turbidities of the raw water ranged from -0.079 to 0.128, and averaged 0.102, and the periods averaged 78 million -gallons per acre between scrapings. For fifteen other periods the -turbidities of the raw water ranged from 0.134 to 0.269, and averaged -0.195, and the periods averaged 52 million gallons per acre between -scrapings. In two other periods the turbidities of the raw water -averaged 0.67, and the periods between scrapings averaged 16 million -gallons. In all cases the turbidity is taken as that of the water -applied to the filter. Usually this was the turbidity of the settled -water, but in some cases raw water was applied, and in these case the -turbidity of the raw water is taken. These results are approximately -represented by the formula</p> - -<table class="autotable" summary="turbidity calculation"> -<tr> -<td class="tdr vertb"><p class="indent">Period between scrapings,<br /> -million gallons per acre</p></td> -<td class="tdc"><span class="double">}</span></td> -<td class="tdc">=</td> -<td class="tdc">12<br /><span class="o">turbidity + 0.05</span></td> -</tr> -</table> - -<p><span class="pagenum" id="Page_138">[Pg 138]</span></p> - -<p>Except for very clear waters the amount of water passed between -scrapings is nearly inversely proportional to the turbidity. With twice -as great an amount of turbidity, filters will have to be cleaned twice -as often, the reserve area for cleaning will require to be twice as -great, and the cost of scraping filters and of washing and replacing -sand, which is the most important element in the cost of operation, -will be doubled.</p> - -<p>With waters having turbidities of 0.20 upon this basis, the average -period will be about 51 million gallons per acre between scrapings. -This is about the average result obtained at the German works filtering -river waters, and there is no serious difficulty in operating filters -which require to be scraped with this frequency. With more turbid -waters the period is decreased. With an average turbidity of 0.50 the -average period is only 24 million gallons per acre between scrapings, a -condition which means very difficult operation and a very high cost of -cleaning. With much more turbid waters the difficulties are increased, -and if the duration of turbid water should be long-continued, the -operation of sand filters would clearly be impracticable, and the -expense, also, would be prohibitive.</p> - -<p>In applying these figures to actual cases it must be borne in mind -that the turbidity is only one of the several factors which control -the length of period; and that the turbidity of a water of a given -stream is never constant, but fluctuates within wide limits; and that -raw water can be applied to filters for a short time without injurious -results, even though it is so turbid that its continued application -would be fatal.</p> - -<p>It is very likely also that the suspended matters in different streams -differ in their natures to such an extent that equal turbidities would -give quite different periods, although the Pittsburg results were so -regular as to give confidence in their application to other conditions -within reasonable limits, and when so applied they afford a most -convenient method of computing the approximate cost of operation of -filters for waters of known or estimated turbidities.</p> - -<p><span class="pagenum" id="Page_139">[Pg 139]</span></p> - -<div class="section"> -<h3 class="nobreak" id="POWER_OF_SAND_FILTERS_TO_PRODUCE_CLEAR_EFFLUENTS_FROM_MUDDY_WATER"> -POWER OF SAND FILTERS TO PRODUCE CLEAR EFFLUENTS FROM MUDDY WATER.</h3></div> - -<p>When the turbidity of the applied water is not too great it is entirely -removed in the course of filtration. With extremely muddy raw waters, -however, turbid effluents are often produced with sand filters. -The conditions which control the passage of the finest suspended -matters through filters have been studied by Mr. Fuller at Cincinnati -at considerable length. They are similar in a general way to the -conditions which control the removal of bacteria. That is to say, the -removal is more complete with fine filter sand than with coarse sand; -with a deep sand layer than with a shallow sand layer; and with low -rates of filtration than with high rates. The practicable limits to -the size of sand grain, depth of sand layer, and rate of filtration -are established by other conditions, and the question remains whether -within these limits a clear effluent can be produced.</p> - -<p>At Pittsburg the turbidity of the effluent from a sand filter operated -as mentioned above, which received water which had passed through a -sedimentation-basin holding about a 24-hours’ supply, but without -taking any advantage of storage to avoid the use of muddy water, was -nearly always less than 0.02, which may be taken as the admissible -limit of turbidity in a public water-supply. This limit was exceeded on -less than 20 days out of 365, these days being during the winter and -spring freshets, and on these days the excess was not such as would be -likely to be particularly objectionable. For the water of the Allegheny -River, then, sand filtration with one day’s sedimentation is capable -of yielding a water not absolutely clear, but sufficiently clear to be -quite satisfactory for the purpose of municipal water-supply.</p> - -<p>At Cincinnati, on the other hand, where the amount of suspended matters -was five times as great as at Pittsburg, the effluents which could be -obtained by sand filtration without recourse to the use of alum, even -under most favorable conditions,<span class="pagenum" id="Page_140">[Pg 140]</span> were very much more turbid than those -obtained at Pittsburg, and were, in fact, so turbid as to be seriously -objectionable for the purpose of public water-supply.</p> - -<p>With rivers no more turbid than the Allegheny River at Pittsburg, and -rivers having floods of such short duration that the use of flood-flows -can be avoided by the use of reservoirs, sand filters are adequate for -clarification. For waters which are much muddier than the Allegheny, -as, for instance, the Ohio at Cincinnati and at Louisville, sand -filtration alone is inadequate. Mr. Fuller,<a id="FNanchor_31" href="#Footnote_31" class="fnanchor">[31]</a> as a result of his -Cincinnati experiments, has stated the case as follows:</p> - -<p>“For the sake of explicitness it is desired to show, with the data -of the fairly normal year of 1898, the proportion of the time when -English filters (that is, sand filters) would be inapplicable in the -purification of the unsubsided Ohio River water at Cincinnati. This -necessitates fixing an average limit of permissible suspended matter in -this river water, and is a difficult matter from present evidence.</p> - -<p>“In part this is due to variations in the character and in the relative -amounts of the suspended silt, clay, and organic matter; and in part -it is due to different amounts of clay stored in the sand layer, which -affects materially the capacity of the filter to retain the clay of the -applied water. During these investigations the unsubsided river-water -was not regularly applied to filters; and, with the exception of -the results of tests for a few days only, it is necessary to depend -upon general information obtained with reference to this point. So -far as the information goes, it appears that an average of 125 parts -per million is a conservative estimate of the amount of suspended -matters in the unsubsided river-water, which could be regularly and -satisfactorily handled by English filters. But at times this estimated -average would be too low, and at other times too high....</p> - -<p>“While English filters are able to remove satisfactorily on an -<span class="pagenum" id="Page_141">[Pg 141]</span> -average about 125 parts of silt and clay of the unsubsided water, -actual experience shows that they can regularly handle suspended -clay in subsided water in amounts ranging only as high as from 30 to -70 parts (depending upon the amount of the clay stored in the sand -layer), and averaging about 50 parts per million. But it is true that -for two or three days on short rises in the river, or at the beginning -of long freshets, the retentive capacity of the sand layer allows of -satisfactory results with the clay in the applied water considerably in -excess of 70 parts. If this capacity is greatly overtaxed, however, the -advantage is merely temporary, as the stored clay is washed out later, -producing markedly turbid effluents.”</p> - -<p>Translating Mr. Fuller’s results into terms of turbidity, the 125 -parts per million of suspended matters in the raw water represent a -turbidity of about 0.40, and the 30 to 70 parts of suspended matters in -the settled water represent turbidities from 0.20 to 0.40, the average -of 50 parts of suspended matters corresponding to a turbidity of about -0.30.</p> - -<p>Upon this basis, then, sand filters are capable of treating raw waters -with average turbidities up to 0.40, or settled waters with average -turbidities up to 0.30, but waters more turbid than this are incapable -of being successfully treated without the use of coagulants or other -aids to the process. These results are in general accordance with -the results of the experiments at Pittsburg, and demonstrate that -while sand filters as generally used in Europe are adequate for the -clarification of many, if not most, river waters in the United States, -there are other waters carrying mud in such quantities as to make the -process inapplicable to them.</p> - -<div class="section"> -<h3 class="nobreak" id="EFFECT_OF_MUD_UPON_BACTERIAL_EFFICIENCY_OF_FILTERS"> -EFFECT OF MUD UPON BACTERIAL EFFICIENCY OF FILTERS.</h3></div> - -<p>The question is naturally raised as to whether or not the presence of -large quantities of mud in the raw water will not seriously<span class="pagenum" id="Page_142">[Pg 142]</span> interfere -with the bacterial efficiency of filters. Experiments at Cincinnati -and Pittsburg have given most conclusive and satisfactory information -upon this point. Up to the point where the effluents become quite -turbid, the mud in the raw water has no influence upon the bacterial -efficiency; and even somewhat beyond this point, with effluents so -turbid that they would hardly be suitable for the purpose of a public -water-supply, the bacterial efficiency remains substantially equal to -that obtained with the clearest waters. Only in the case of excessive -quantities of mud, where, for other reasons, sand filters can hardly -be considered applicable, is there a moderate reduction in bacterial -efficiency. As mentioned above, particles constituting turbidity are -often much smaller than the bacteria, and in addition, the bacteria -probably have an adhesive power far in excess of that of the clay -particles. For these reasons clay particles are able to pass filters -under conditions which almost entirely prevent the passage of bacteria.</p> - -<p>On the other hand, it does not necessarily follow that the removal -of turbidity is accompanied by high bacterial efficiency. Although -this is often the case, there are marked exceptions, particularly in -connection with the use of coagulants, where very good clarification is -obtained, and notwithstanding this, effluents are produced containing -comparatively large numbers of bacteria.</p> - -<div class="section"> -<h3 class="nobreak" id="LIMITS_TO_THE_USE_OF_SUBSIDENCE_FOR_THE_PRELIMINARY_TREATMENT_OF_MUDDY_WATERS"> -LIMITS TO THE USE OF SUBSIDENCE FOR THE PRELIMINARY TREATMENT OF MUDDY -WATERS.</h3></div> - -<p>When water is too muddy to be applied directly to filters, the most -obvious treatment is to remove as much of the sediment as possible by -sedimentation. Sedimentation-basins are considered as essential parts -of filtration plants for the treatment of muddy waters. The effect of -sedimentation, as noted above, is to remove principally the larger -particles in the raw water. By doing this the deposit upon the surface -of the filters and the cost of operation are greatly reduced.</p> - -<p>These larger particles are mainly removed by a comparatively<span class="pagenum" id="Page_143">[Pg 143]</span> short -period of sedimentation, and the improvement effected after the first -24 hours is comparatively slight. The particles remaining in suspension -at the end of this time consist almost entirely of very fine clay, and -the rate of their settlement through the water is extremely slow; and -currents in the basin, due to temperature changes, winds, etc., almost -entirely offset the natural tendency of the sediment to fall to the -bottom.</p> - -<p>There is thus a practical limit to the effect of sedimentation which is -soon reached, and it has not been found feasible to extend the process -so as to allow much more turbid waters to be brought within the range -which can be economically treated by sand filtration.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_144">[Pg 144]</span></p> - -<h2 class="nobreak" id="CHAPTER_IX">CHAPTER IX.<br /> -<br /> - -<span class="smaller">THE COAGULATION OF WATERS.</span></h2></div> - -<p><span class="smcap">The</span> coagulation of water consists in the addition to it of some -substance which forms an inorganic precipitate in the water, the -presence of which has a physical action upon the suspended matters, and -allows them to be more readily removed by subsidence or filtration.</p> - -<p>The most common coagulant is sulphate of alumina. When this substance -is added to water it is decomposed into its component parts, sulphuric -acid and alumina, the former of which combines with the lime or other -base present in the water, or in case enough of this is lacking, it -remains partly as free acid and partly undecomposed in its original -condition; while the alumina forms a gelatinous precipitate which draws -together and surrounds the suspended matters present in the water, -including the bacteria, and allows them to be much more easily removed -by filtration than would otherwise be the case. In addition, the -alumina has a chemical attraction for dissolved organic matters, and -the chemical purification may be more complete at very high rates than -would be possible with sand filtration without coagulant at any rate, -however low.</p> - -<p>Coagulants have been employed in connection with filtration from -very early times. As early as 1831 D’Arcet published in the “Annales -d’hygiène publique,”<a id="FNanchor_32" href="#Footnote_32" class="fnanchor">[32]</a> an account of the purification of Nile water -in Egypt by adding alum to the water, and afterwards filtering it -through small household filters. More recently alum has been repeatedly -used in connection with sand filters, particularly</p> - -<p><span class="pagenum" id="Page_145">[Pg 145]</span></p> - -<p>at Leeuwarden, Groningen, and Schiedam in Holland, where the river -waters used for public supplies are colored by peaty matter which -cannot be removed by simple filtration.</p> - -<div class="section"> -<h3 class="nobreak" id="SUBSTANCES_USED_FOR_COAGULATION">SUBSTANCES USED FOR COAGULATION.</h3></div> - -<p>Mr. Fuller<a id="FNanchor_33" href="#Footnote_33" class="fnanchor">[33]</a> has given a very full account of the substances which -can be used for the clarification of waters. Without taking up all of -the unusual substances which have been suggested, the most important of -the coagulants will be briefly described below.</p> - -<p><em>Lime.</em>—Lime has been extensively used in connection with the -purification of sewage, and also for softening water. Lime is first -slaked and converted into calcium hydrate, which is afterwards -dissolved in water, and applied to the water under treatment. The -amount of lime to be used is fixed by the amount of carbonic acid in -the water. So much lime is always used as will exactly convert the -whole of the carbonic acid of the water into normal carbonate of lime. -This substance is but slightly soluble in water and it precipitates. -The precipitate is crystalline rather than flocculent, and is not as -well adapted to aid in the removal of clayey matters as some other -substances, although its action in this respect is considerable. The -precipitate is quite heavy, and is largely removed by sedimentation, -although filtration must be used to complete the process. Water which -has been treated with lime is slightly caustic; that is to say, there -is a deficiency of carbonic acid in it, and it deposits lime in the -pipes, in pumps, etc.; and although the precipitated calcium carbonate -is much softer than steel, it rapidly destroys pumps used for lifting -it.</p> - -<p>Principally for these reasons it is necessary to supply carbonic acid -to water which has been treated in this way, and this is done by -bringing it in contact with flue-gases, or by the direct addition of -carbonic acid.</p> - -<p>The use of lime for softening waters is known as Clark’s process. It -was patented in England many years ago, and the<span class="pagenum" id="Page_146">[Pg 146]</span> -patent has now expired. Various ingenious devices have been constructed -for facilitating various parts of the operation. The process has hardly -been used in the United States, but there is a large field for it in -connection with the softening of very hard waters, and where such -waters also contain iron or clay, these substances will be incidentally -removed by the process.</p> - -<p>Larger quantities of lime have an action upon the suspended matters -which is entirely different from that secured in Clark’s process, and -the action upon bacteria is particularly noteworthy. This action was -noted in experiments at Lawrence,<a id="FNanchor_34" href="#Footnote_34" class="fnanchor">[34]</a> where it was found that sewage -was almost completely sterilized by the application of considerable -quantities of lime. An extremely interesting series of experiments upon -the application of large quantities of lime to water was made by Mr. -Fuller in 1899.<a id="FNanchor_35" href="#Footnote_35" class="fnanchor">[35]</a> The bacterial results were extremely favorable, -although the necessity for removing the excess of lime afterward is a -somewhat serious matter, and in these experiments it was not entirely -accomplished.</p> - -<p><em>Aluminum Compounds.</em>—Sulphate of alumina is most commonly -employed. It can be obtained in a state of considerable purity at a -very moderate price, and important improvements in the methods used for -its manufacture have been recently introduced. Potash and soda alums -have no advantage over sulphate of alumina, and, in fact, are less -efficient per pound, while their costs are greater. Chloride of alumina -is practically equivalent to the sulphate in purifying power, but is -more expensive.</p> - -<p><em>Sodium Aluminate</em> has been examined by Mr. Fuller, who states -that experience has shown that its use is impracticable in the case of -the Ohio River water.</p> - -<p><em>Compounds of Iron.</em>—Iron forms two classes of compounds, namely, -ferrous and ferric salts. When the ferrous salts are applied to water, -under certain conditions, ferrous hydrate is precipitated, <span class="pagenum" id="Page_147">[Pg 147]</span>but this -substance is not entirely insoluble in water containing carbonic acid. -Under some conditions the precipitated ferrous hydrate is oxidized -by oxygen present in the water to ferric hydrate, and so far as this -is the case, good results can be obtained. Ferrous sulphate is not -as readily oxidized when applied to water as is the ferric carbonate -present in many natural waters, and for this reason ferrous sulphate -has not been successfully used in water purification. In the treatment -of sewage, where the requirements are somewhat different, it has been -one of the most satisfactory coagulants.</p> - -<p>Ferric sulphate acts in much the same way as sulphate of alumina, -and is entirely suitable for use where sulphate of alumina could be -employed, but it has not been used in practice, due probably to its -increased cost as compared with its effect, and to the practical -difficulties of applying it in the desired quantities due to its -physical condition.</p> - -<p><em>Metallic Iron: The Anderson Process.</em>—The use of metallic iron -for water purification in connection with a moderately slow filtration -through filters of the usual form is known as Anderson’s process -(patented), and has been used at Antwerp and elsewhere on a large -scale, and has been experimentally examined at a number of other places.</p> - -<p>The process consists in agitating the water in contact with metallic -iron, a portion of which is taken into solution as ferrous carbonate. -Upon subsequent aeration this is supposed to become oxidized and -precipitate out as ferric hydrate, with all the good and none of the -bad effects which follow the use of alum. The precipitate is partially -removed by sedimentation, while filtration completes the process. -The process is admirable theoretically, and in an experimental way -upon a very small scale often gives most satisfactory results, muddy -waters very difficult of filtration, and colored peaty waters yielding -promptly clear and colorless effluents.</p> - -<p>In applying the process on a larger scale, however, with peaty -<span class="pagenum" id="Page_148">[Pg 148]</span> waters -at least, it seems impossible to get enough iron to go into solution -in the time which can be allowed, and the small quantity which is -taken up either remains in solution or else slowly and incompletely -precipitates out, without the good effects which follow the sudden and -complete precipitation of a larger quantity, and in this case the color -is seldom reduced, and may even be increased above the color of the raw -water by the iron remaining in solution.</p> - -<p>The ingenuity of those who have studied the process has not yet found -any adequate means of avoiding these important practical objections; -and even at Antwerp a great extension of the filtering area, as well -as the use of alum at times of unusual pollution, is good evidence -that simple filtration, in distinction from the effect of the iron, is -relied upon much more than formerly.</p> - -<p>At Dordrecht also, where the process has been long in use, the rate of -filtration does not exceed the ordinary limits; nor is the result, so -far as I could ascertain, in any way superior to that obtained a few -miles away at Rotterdam, by ordinary filtration, with substantially the -same raw water.</p> - -<p>The results obtained at Boulogne-sur-Seine, near Paris, have been -closely watched by the public chemist and bacteriologist of Paris, -and have been very favorable, and a number of new plants of very -considerable capacity have been built, to supply some of the suburbs of -Paris, but even in these cases only moderate rates of filtration are -employed which would yield excellent effluents without the iron.</p> - -<p><em>Compounds of Manganese.</em>—Manganese forms compounds similar to -those of iron, that is to say manganous and manganic salts, but their -use in connection with water filtration has not been found possible. In -addition, manganese forms a series of compounds, known as manganates -and permanganates, quite different in their structure and action from -the others. These compounds contain an excess of oxygen which they -give up very readily to organic matters capable of absorbing oxygen, -and because of this<span class="pagenum" id="Page_149">[Pg 149]</span> power, they have been extensively used in the -treatment of sewage. Applied to the treatment of waters their action is -very slight, and the compounds are so expensive that they have not been -employed for this purpose. Theoretically the action is very attractive, -as the oxygen liberated by their decomposition oxidizes some of the -organic matter of the water, thereby purifying it in part, while the -manganese is precipitated as a flocculent precipitate having all of -the advantages pertaining to a precipitate of hydrate of alumina, and -without the disadvantage of adding acid to the water, as is the case -with the compounds of alumina and iron. These chemicals, when used in -comparatively concentrated condition, have powerful germicidal actions, -but in water purification the amounts which can be used are so small -that no action of this kind results. The amount which can be applied to -a water is limited to the amount which can be decomposed by the organic -matters present in the water, and is not large.</p> - -<p><em>The Use of Metallic Iron and Aluminum, with the Aid of -Electricity.</em>—Elaborate experiments were made at Louisville with -metallic iron and aluminum oxidized and made available by the aid of -electric currents. The use of iron with electric currents was tried -in sewage purification some years ago, under the name of the Webster -process, but was never put to practical use. The theory is to oxidize -the iron or aluminum in contact with the water, with the formation -of flocculent hydrates, by the aid of an electric current, thereby -securing the advantages of the application of salts of these metals to -the water without the disadvantage of the addition of acid.</p> - -<p><em>Other Chemicals Employed.</em>—A solution containing chlorine -produced by electrical action has been suggested. Chlorine is a -powerful disinfectant, and when used in large quantities kills -bacteria. It is not possible to use enough chlorine to kill the -bacteria in the water without rendering it unfit for human use. -The nature of this treatment has been concisely described by<span class="pagenum" id="Page_150">[Pg 150]</span> Dr. -Drown,<a id="FNanchor_36" href="#Footnote_36" class="fnanchor">[36]</a> who shows that the electrically prepared fluids do not -differ in their action in any way from well-known chemicals, the use of -which would be hardly considered.</p> - -<p>The use of ozone and peroxide of hydrogen have also been suggested, but -I do not know that they have been successfully used on a large scale. -The same is true of many other chemicals, the consideration of which is -hardly necessary in this connection.</p> - -<div class="section"> -<h3 class="nobreak" id="COAGULANTS_WHICH_HAVE_BEEN_USED">COAGULANTS WHICH HAVE BEEN USED.</h3></div> - -<p>In actual work sulphate of alumina is practically the only coagulant -which has been employed, excepting the alums, which are practically its -equivalent in action, differing only in strength. Nearly all important -experiments upon the coagulation of water have been made with sulphate -of alumina, and in the further discussion of this subject only this -coagulant will be considered.</p> - -<div class="section"> -<h3 class="nobreak" id="AMOUNT_OF_COAGULANT_REQUIRED_TO_REMOVE_TURBIDITY"> -AMOUNT OF COAGULANT REQUIRED TO REMOVE TURBIDITY.</h3></div> - -<p>In the coagulation of turbid waters a certain definite amount of -coagulant must be employed. If less than this amount is used either no -precipitate will be formed, or it will not be formed in sufficient bulk -to effect the desired results. It is necessary that the precipitate -should be sufficient, and that it should be formed practically all at -one time. The amount of coagulant necessary to accomplish this purpose -is dependent upon the turbidity of the raw water. With practically -clear waters sulphate of alumina of the ordinary commercial strength, -that is to say, with about 17 per cent soluble oxide of aluminum, -used in quantities as small as 0.3 or 0.4 of a grain per gallon, will -produce coagulation. As the turbidity increases larger amounts must be -employed.</p> - -<p>A special study was made of this point in connection with the Pittsburg -experiments.<a id="FNanchor_37" href="#Footnote_37" class="fnanchor">[37]</a> As an average of these results it was found that two -grains per gallon of sulphate of alumina were<span class="pagenum" id="Page_151">[Pg 151]</span> -required to properly coagulate waters having turbidities of 1.00, so -that they could be filtered by the Jewell filter, and 2.75 grains were -required for the Warren filter.</p> - -<div class="figcenter padt1 padb1 illowp88" id="image151" style="max-width: 75em;"> - <img class="w100" src="images/image151.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 20.—Amount of Coagulant Required to Remove -Turbidity.</span></p></div> - -<p>Aside from the amount required to produce a precipitate in the clearest -waters, the amount of coagulant required was proportional to the -turbidity. As an average for the two filters the required quantity was -approximately 0.30 of a grain, and in addition 0.02 of a grain for each -0.01 of turbidity. Thus a water having a turbidity of 0.20 requires -0.70 of a grain per gallon; a water having a turbidity of 0.50 requires -1.30 grains; of 1.00, 2.30 grains; of 2.00, 4.30 grains, etc. These are -average minimum results. Occasionally clear effluents were produced -with smaller quantities of coagulant, while at other times larger -quantities were necessary for satisfactory results.</p> - -<p><span class="pagenum" id="Page_152">[Pg 152]</span></p> - -<p>The amount of coagulant required for clarification at Cincinnati has -been stated by Mr. Fuller in his report. A number of his results are -brought together in the following table, to which has also been added a -column showing approximately the corresponding results at Pittsburg.</p> - -<table class="autotable" summary="amount of chemical for different grades of water"> -<tr> -<th class="tdc normal" colspan="5">ESTIMATED AVERAGE AMOUNTS OF REQUIRED CHEMICAL FOR DIFFERENT GRADES OF WATER.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Suspended Matter,<br />Parts in 100,000.</th> -<th class="tdc normal small bord_top bord_bot" colspan="4">Chemical Required, Grains per Gallon.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Raw Water for<br />Sand Filters.<br />Cincinnati<br />Report, Page 290.</th> -<th class="tdc normal small bord_right bord_bot">Subsided Water for<br />Cincinnati<br />Report, Page 290.</th> -<th class="tdc normal small bord_right bord_bot">Subsided Water for<br />Mechanical Filters.<br />Cincinnati<br />Report, Page 341.</th> -<th class="tdc normal small bord_bot">Minimum for<br />Raw Water for<br />Mechanical Filters.<br />Pittsburg.</th> -</tr> -<tr> -<td class="tdc bord_right vertb"> 1.0</td> -<td class="tdc bord_right vertb">0</td> -<td class="tdc bord_right vertb">0</td> -<td class="tdc bord_right vertb">0.75</td> -<td class="tdc">0.40</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 2.5</td> -<td class="tdc bord_right vertb">0</td> -<td class="tdc bord_right vertb">0</td> -<td class="tdc bord_right vertb">1.25</td> -<td class="tdc">0.50</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 5.0</td> -<td class="tdc bord_right vertb">0</td> -<td class="tdc bord_right vertb">0</td> -<td class="tdc bord_right vertb">1.50</td> -<td class="tdc">0.70</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 7.5</td> -<td class="tdc bord_right vertb">0</td> -<td class="tdc bord_right vertb">1.30</td> -<td class="tdc bord_right vertb">1.95</td> -<td class="tdc">0.90</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 10.0</td> -<td class="tdc bord_right vertb">1.50</td> -<td class="tdc bord_right vertb">1.60</td> -<td class="tdc bord_right vertb">2.20</td> -<td class="tdc">1.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 12.5</td> -<td class="tdc bord_right vertb">1.60</td> -<td class="tdc bord_right vertb">1.80</td> -<td class="tdc bord_right vertb">2.45</td> -<td class="tdc">1.15</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 15.0</td> -<td class="tdc bord_right vertb">1.70</td> -<td class="tdc bord_right vertb">2.00</td> -<td class="tdc bord_right vertb">2.65</td> -<td class="tdc">1.30</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 17.5</td> -<td class="tdc bord_right vertb">1.80</td> -<td class="tdc bord_right vertb">2.10</td> -<td class="tdc bord_right vertb">2.85</td> -<td class="tdc">1.40</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 20.0</td> -<td class="tdc bord_right vertb">1.95</td> -<td class="tdc bord_right vertb">2.20</td> -<td class="tdc bord_right vertb">3.00</td> -<td class="tdc">1.60</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 30.0</td> -<td class="tdc bord_right vertb">2.25</td> -<td class="tdc bord_right vertb">2.45</td> -<td class="tdc bord_right vertb">3.80</td> -<td class="tdc">2.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 40.0</td> -<td class="tdc bord_right vertb">2.50</td> -<td class="tdc bord_right vertb">2.75</td> -<td class="tdc bord_right vertb">4.40</td> -<td class="tdc">2.50</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 50.0</td> -<td class="tdc bord_right vertb">2.80</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 60.0</td> -<td class="tdc bord_right vertb">3.05</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 75.0</td> -<td class="tdc bord_right vertb">3.40</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdc bord_right vertb">100.0</td> -<td class="tdc bord_right vertb">4.00</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot">120.0</td> -<td class="tdc bord_right bord_bot">4.75</td> -<td class="tdc bord_right bord_bot"> </td> -<td class="tdc bord_right bord_bot"> </td> -<td class="tdc bord_bot"> </td> -</tr> -</table> - -<p class="padt1">Mr. Fuller’s results seem to show that a greater amount of coagulant -is required for the preparation of water for mechanical filters than -is necessary in connection with sand filters. The results with sand -filters indicate that settled waters and raw waters containing equal -amounts of suspended matters are about equally difficult to treat. The -results at Pittsburg indicate that the raw waters required much smaller -quantities of coagulant for given amounts of suspended matters than was -the case with subsided waters at Cincinnati, the results agreeing more -closely with the amounts required to prepare raw water for sand filters -at Cincinnati.</p> - -<p><span class="pagenum" id="Page_153">[Pg 153]</span></p> - -<div class="section"> -<h3 class="nobreak" id="AMOUNT_OF_COAGULANT_REQUIRED_TO_REMOVE_COLOR"> -AMOUNT OF COAGULANT REQUIRED TO REMOVE COLOR.</h3></div> - -<p>The information upon this point is, unfortunately, very inadequate. In -some experiments made by Mr. E. B. Weston at Providence in 1893 with a -mechanical filter,<a id="FNanchor_38" href="#Footnote_38" class="fnanchor">[38]</a> with quantities of sulphate of alumina averaging -0.6 or 0.7 of a grain per gallon, the removal of color was usually -from 70 to 90 per cent. The standard used for the measurement of color -is not stated, and there is no statement of the basis of the scale, -consequently no means of determining the absolute color of the raw -water upon standards commonly used.</p> - -<p>At Westerly, R. I., with a New York filter, the actual quantity of -potash alum employed from Oct. 10, 1896, to March 1, 1897, was 1.94 -grains per gallon, the amount being regulated to as low a figure as it -was possible to use to secure satisfactory decolorization. There is no -record of the color of the raw water. A very rough estimate would place -it at 0.50 upon the platinum scale. The chemical employed in this case -was alum, and two thirds as large a quantity of sulphate of alumina -would probably have done corresponding work, had suitable apparatus for -applying it been at hand.</p> - -<p>At Superior, Wisconsin, the water in the bay coming from the St. -Louis River, having a color of 2.40 platinum scale, was treated -experimentally with quantities of sulphate of alumina up to 4 grains -per gallon, by Mr. R. S. Weston in January, 1899, but even this -quantity of coagulant utterly failed to coagulate and decolorize it.</p> - -<p>At Greenwich, Conn., during 1898 the average amount of sulphate of -alumina employed, as computed from quantities stated in the annual -report of the Connecticut State Board of Health for 1898, was about -0.44 of a grain per gallon, and this quantity sufficed to reduce the -color of the raw water from 0.40 to 0.30, platinum standard. This -reduction is very slight, and it is -<span class="pagenum" id="Page_154">[Pg 154]</span> -obvious that this quantity of coagulant was not enough for -decolorization.</p> - -<p>Some experiments bearing on color removal were made at East Providence, -R. I., by Mr. E. B. Weston, and are described in the Proceedings of the -American Society of Civil Engineers for September, 1899. In this case -the color is reported to have been reduced from 0.58 to 0.10 platinum -standard by the use of one grain of sulphate of alumina, containing 22 -per cent of effective alumina, equivalent to about 1.30 grains of the -ordinary article per gallon.</p> - -<p>The various experiments seem to indicate that a removal from 80 to -90 per cent of the color can be effected by the use of a quantity of -sulphate of alumina equal to rather more than two grains per gallon -for waters having colors of 1.00, platinum standard, and proportionate -quantities for more and less deeply colored waters. With much less -sulphate of alumina decolorization is not effected, and even larger -quantities do not remove all of the color.</p> - -<p>The data are much less complete than could be desired, and it is to be -hoped that experiments will be undertaken to throw more light upon this -important subject.</p> - -<div class="section"> -<h3 class="nobreak" id="SUCCESSIVE_APPLICATION_OF_COAGULANT"> -SUCCESSIVE APPLICATION OF COAGULANT.</h3></div> - -<p>Mr. Fuller, in his experiments at Louisville, has ascertained that when -sulphate of alumina is added to extremely muddy water the sediment -absorbs some of the chemical before it has time to decompose, and -carries it to the bottom, and so far as this is the case, no benefit -is derived from that part of the coagulant which is absorbed. In other -words, it is necessary to add more coagulant than would otherwise be -necessary because of this action. The data showed that different kinds -of suspended matters took up very different amounts of coagulant in -this way. With only moderately turbid waters the loss of chemical -from this source is unimportant. Hardly any trace of it was found at -Pittsburg with<span class="pagenum" id="Page_155">[Pg 155]</span> the Allegheny River water. At Louisville, however, it -was an important factor, as shown by Mr. Fuller’s results.</p> - -<p>To avoid this loss of chemical Mr. Fuller has suggested the removal of -the greater part of the suspended matters by sedimentation, without -chemicals, or with the aid of a small quantity of chemical, followed by -the application of the final coagulant prior to filtration. With the -worst waters encountered at Louisville the saving in coagulant to be -effected in this way is very great.</p> - -<p>Mr. Fuller states in “Water Purification at Louisville,” p. 417: “The -practical conclusions to be drawn from this experience are that with -preliminary coagulation, followed by subsidence for a period of about -three hours, the application of coagulants may be divided to advantage, -and a considerable portion of the suspended matter kept off the filter, -when the total amount of required coagulant ranges from 2 to 2.5 -grains or more of ordinary sulphate of alumina per gallon. In the case -of a water requiring more than this amount of coagulating treatment, -a proper division of the application would increase the saving of -coagulants and would diminish the frequency of washing the filter.”</p> - -<p>In his final summary and conclusions, page 441, Mr. Fuller estimates -the amount of sulphate of alumina required for the clarification of the -Ohio River at Louisville at 3.00 grains per gallon of water filtered -if all applied at one point, or at 1.75 grains by taking advantage of -subsidence to its economical limit prior to the final coagulation. The -saving to be effected in this way is sufficient to justify the works -necessary to allow it to be carried out. With less turbid waters, or -waters highly turbid for only short intervals, the advantages of double -coagulation would be less apparent.</p> - -<div class="section"> -<h3 class="nobreak" id="THE_AMOUNT_OF_COAGULANT_WHICH_VARIOUS_WATERS_WILL_RECEIVE"> -THE AMOUNT OF COAGULANT WHICH VARIOUS WATERS WILL RECEIVE.</h3></div> - -<p>The amount of coagulant which can be safely used is dependent upon -the alkalinity of the raw water. When sulphate of alumina<span class="pagenum" id="Page_156">[Pg 156]</span> is added -to water it is decomposed, as explained above, with the formation -of alumina, which is alone useful in the work of purification, and -sulphuric acid, which combines with the calcium carbonate or lime -present in the water. There should always be an excess of alkalinity or -lime in the raw water. If for any reason there is not, there is nothing -to combine with the liberated sulphuric acid, and the decomposition of -the coagulant is not complete, and a portion of it goes undecomposed -into the effluent. The effluent then has an acid reaction, and is unfit -for domestic supply. When distributed through iron pipes, it attacks -the iron, rusting the pipes, and giving rise to all the disagreeable -consequences of an iron containing water.</p> - -<p>The amount of lime in a water available to combine with the sulphuric -acid can be determined by a very simple chemical operation, namely, -by titration with standard acid with a suitable indicator. The amount -of coagulant corresponding to a given quantity of lime can be readily -and accurately calculated, but it is not regarded safe to use as -much sulphate of alumina as corresponds to the lime. The quantity of -coagulant used is not susceptible to exact control, but fluctuates -somewhat, and if the exact theoretical quantity should be employed -during 24 hours, there would surely be an excess during some portion of -that time from which bad results would be experienced. It is therefore -considered only prudent to use three quarters as much sulphate of -alumina as corresponds to the lime in the water. With sulphate of -alumina containing 17 per cent of soluble aluminum oxide and the -corresponding amount of sulphuric acid, the amount which can be applied -to a water in grains per gallon is slightly less than the alkalinity -expressed in terms of parts in 100,000 of calcium carbonate.</p> - -<p>Many waters contain sufficient lime to combine with the acid of all -the coagulant which is necessary for their coagulation. Others will -not, and it thus becomes an important matter to determine whether a -given water is capable of decomposing sufficient<span class="pagenum" id="Page_157">[Pg 157]</span> coagulant for its -treatment. It is usually the flood-flows of rivers which control in -this respect. The water at such times requires much larger quantities -of coagulant for its clarification, and it also usually contains much -less lime than the low-water flows. The reason for this is obviously -that the water of the flood-flows is largely rain-water which has come -over the surface without coming into very intimate contact with the -soil, and consequently without having taken from it much lime, while -the low-water flows contain a considerable proportion of water which -has percolated through the soil and has thus become charged with lime.</p> - -<p>In some parts of the country, as, for instance, in New England, the -soil and underlying rock are almost entirely free from lime, and -rivers from such watersheds are capable of receiving only very small -quantities of coagulant without injurious results.</p> - -<p>The deficiency of alkalinity in raw water can be corrected by the -addition to it of lime or of soda-ash. Lime has been used for this -purpose in many cases. When used only in moderate amounts it hardens -the water, and is thus seriously objectionable. The use of so large a -quantity as would precipitate out, as in Clark’s process, has not been -employed in practice. If it should be attempted, the amount of lime -would require to be very accurately controlled, and the effluent would -have to be treated with carbonic acid to make it suitable for supply.</p> - -<p>Waters so hard as to require the use of the Clark process almost always -have sufficient alkalinity, and do not require to be treated with lime -in connection with the use of sulphate of alumina.</p> - -<p>The use of soda-ash is free from the objections to the use of lime, -but is more expensive, and would require to be used with caution. Its -use has often been suggested, but I do not know that it has ever been -employed in practice. In small works the use of a filtering material -containing marble-dust, or other calcareous matter, would seem to have -some advantages in case of deficiency of alkalinity, although it would -harden the water so treated.</p> - -<p><span class="pagenum" id="Page_158">[Pg 158]</span></p> - -<p class="padb1">The alkalinities of a number of waters computed as parts in 100,000 of -calcium carbonate (approximately equal to the safe doses of sulphate to -alumina in grains per gallon) are as follows:</p> - -<table class="autotable" summary="alkalinities"> -<tr> -<th class="tdc bord_top bord_right bord_bot"> </th> -<th class="tdc normal small bord_top bord_right bord_bot">Maximum.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Minimum.</th> -<th class="tdc normal small bord_top bord_bot">Average.</th> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Boston water, 1898</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">2.87</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">0.33</span></td> -<td class="tdr vertt"><span class="padr1">1.08</span></td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Conestoga Creek, Lancaster, Penn.</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">12.20</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">3.70</span></td> -<td class="tdr vertt"><span class="padr1">6.80</span></td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Allegheny River, Pittsburg</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">8.00</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">1.02</span></td> -<td class="tdr vertt"><span class="padr1">2.90</span></td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Mahoning River and tributaries, 1897</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">20.00</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">2.20</span></td> -<td class="tdr vertt"><span class="padr1">10.00</span></td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Scioto River and tributaries, 1897</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">35.00</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">10.00</span></td> -<td class="tdr vertt"><span class="padr1">20.00</span></td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Ohio River, Cincinnati, 1898</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">7.00</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">2.00</span></td> -<td class="tdr vertt"><span class="padr1">4.50</span></td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Ohio River, Louisville</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">10.87</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">2.12</span></td> -<td class="tdr vertt"><span class="padr1">6.70</span></td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">Lake Erie, Lorain, Ohio</td> -<td class="tdl vertt bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdr vertt"><span class="padr1">9.50</span></td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot">Lake Michigan, Chicago</td> -<td class="tdc bord_right bord_bot"> </td> -<td class="tdc bord_right bord_bot"> </td> -<td class="tdr bord_bot"><span class="padr1">11.50</span></td> -</tr> -</table> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_159">[Pg 159]</span></p> - -<h2 class="nobreak" id="CHAPTER_X">CHAPTER X.<br /> -<br /> - -<span class="smaller">MECHANICAL FILTERS.</span></h2></div> - -<p><span class="smcap">The</span> term mechanical filters is used to designate a general class of -filters differing in many respects quite radically from the sand -filters previously described. They had their origin in the United -States, and consisted originally of iron or wooden cylinders filled -with sand through which the water was forced at rates of one to two -hundred million gallons per acre daily, or from fifty to one hundred -times the rates usually employed with sand filters. These filters were -first used in paper-mills to remove from the large volumes of water -required the comparatively large particles, which would otherwise -affect the appearance and texture of the paper; and in their earlier -forms they were entirely inadequate to remove the finer particles, -such as the bacteria, and the clay particles which constitute the -turbidity of river waters. Various improvements in construction have -since been made, and, in connection with the use of coagulants, much -more satisfactory results can now be obtained with filters of this -class; and their use has been extended from manufacturing operations to -municipal supplies, in many cases with most satisfactory results.</p> - -<p>The information gathered in regard to the conditions essential to the -successful design and operation of these filters in the last few years -is very great, and may be briefly reviewed.</p> - -<div class="section"> -<h3 class="nobreak" id="PROVIDENCE_EXPERIMENTS">PROVIDENCE EXPERIMENTS.<a id="FNanchor_39" href="#Footnote_39" class="fnanchor">[39]</a></h3></div> - -<p>The first data of importance were secured from a series of experiments -conducted by Mr. Edmund B. Weston of Providence, R. I., in 1893 and -1894, upon the Pawtuxet river water used by<span class="pagenum" id="Page_160">[Pg 160]</span> -that city. The experimental filter was 30 inches in diameter, and had -a layer of sand 2 feet 10 inches deep. The sand was washed by the use -of a reverse current, the sand being stirred by a revolving rake at the -same time. The amount of coagulant employed was about 0.7 of a grain -per gallon. The raw water was practically free from turbidity, and the -filter was operated to remove color and bacteria.</p> - -<p>The removal of color, as stated in Mr. Weston’s report, amounted to -from 70 to 90 per cent. The experiments extended over a period of -ten months. The rate of filtration employed was about 128 million -gallons per acre daily. The bacterial results of the first six months’ -operations were rejected by Mr. Weston on account of defective methods -of manipulation.</p> - -<p>During the period from November 17, 1893, to January 30, 1894, the -average bacterial efficiency of filtration was about 95 per cent, and -the manipulation was considered to be in every respect satisfactory. -The efficiency was occasionally below 90 per cent, but for four -selected weeks was as high as 98.6 per cent. The average amount of -sulphate of alumina used, as calculated from Mr. Weston’s tables, was -two thirds of a grain per gallon. The highest efficiency followed the -application of a solution of caustic soda to the filtering material. -The first day following this treatment the bacterial efficiency was -above 99 per cent. Afterwards it decreased until January 30, when the -experiments were stopped. The high bacterial efficiency following the -use of caustic soda was of such short duration as to suggest very -grave doubts as to its practical value. It is extremely unfortunate -that the experiments stopped only a week after this experiment, and -the results were never repeated. I consider that the average bacterial -efficiency of about 95 per cent obtained for the period of October 17 -to January 30, when the manipulation was considered to be in every way -satisfactory, more nearly represents what can be obtained under these -conditions than the results for certain periods, particularly after the -use of the caustic soda.</p> - -<p><span class="pagenum" id="Page_161">[Pg 161]</span></p> - -<div class="section"> -<h3 class="nobreak" id="LOUISVILLE_EXPERIMENTS">LOUISVILLE EXPERIMENTS.<a id="FNanchor_40" href="#Footnote_40" class="fnanchor">[40]</a></h3></div> - -<p>These experiments were inaugurated by the Louisville Water Company -in connection with the manufacturers of certain patented filters. -Mr. Charles Hermany, Chief Engineer of the Company, had general -charge of the experiments. Mr. George W. Fuller was Chief Chemist and -Bacteriologist and had direct charge of the work and has made a most -elaborate report upon the same. In these examinations many devices were -investigated; but the two which particularly deserve our attention are -the filters known as the Warren Filter and the Jewell Filter.</p> - -<p>These filters were operated for two periods, namely, from October -18, 1895, to July 30, 1896, and from April 5 to July 24, 1897. The -investigations were directed toward the clarification of the river -water from the mud, and to the removal of bacteria. The water was -substantially free from color. The character of the water at this -point was such that in its best condition at least three fourths of -a grain of sulphate of alumina were necessary for its coagulation, -and with this and with larger quantities of coagulant fair bacterial -purification was nearly always obtained. The problem studied -therefore was principally that of clarification from mud. The average -efficiencies, as shown by the total averages, (page 248,) were as -follows: Warren filter, bacterial efficiency, 96.7 per cent; Jewell -filter, 96.0 per cent.</p> - -<div class="section"> -<h3 class="nobreak" id="LORAIN_TESTS">LORAIN TESTS.<a id="FNanchor_41" href="#Footnote_41" class="fnanchor">[41]</a></h3></div> - -<p>These tests were made by the author of a set of Jewell filters at -Lorain, Ohio. The filters were six in number, each 17 feet in diameter, -having an effective filtering area of 226 square feet each, or 1356 -square feet in all. The construction of the filters was in all respects -similar to the Jewell filter used at Louisville. The raw water was from -Lake Erie, and during the examination was -<span class="pagenum" id="Page_162">[Pg 162]</span> -always comparatively clear, but contained considerable numbers of -bacteria. The problem was thus entirely one of bacterial efficiency. -The question of clarification hardly presented itself. Although -the water became turbid at times it did not approach in muddiness -the condition of the Ohio River water, and an amount of coagulant -sufficient for a tolerable bacterial efficiency in all cases was more -than sufficient for clarification.</p> - -<p class="padb1">A summary of the results obtained is as follows:</p> - -<table class="autotable" summary="tests of jewell filters at lorain ohio"> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Week Ending<br />6:00 P.M.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Average Rate<br />of Filtration,<br />Gallons per<br />Sq. Ft. Min.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Sulphate of<br />Alumina,<br />Grains per<br />Gallon.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Bacteria in<br />Lake Water.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Bacteria in<br />Effluent.</th> -<th class="tdc normal small bord_top bord_bot">Bacterial<br />Efficiency<br />per cent.</th> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">June 19</td> -<td class="tdc bord_right vertb">1.06</td> -<td class="tdc bord_right vertb">2.58</td> -<td class="tdc bord_right vertb">1441</td> -<td class="tdc bord_right vertb">16</td> -<td class="tdc">98.9</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb"><span class="add2em">26</span></td> -<td class="tdc bord_right vertb">1.10</td> -<td class="tdc bord_right vertb">2.50</td> -<td class="tdc bord_right vertb">385</td> -<td class="tdc bord_right vertb">6</td> -<td class="tdc">98.4</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb">July 3</td> -<td class="tdc bord_right vertb">1.11</td> -<td class="tdc bord_right vertb">2.27</td> -<td class="tdc bord_right vertb">367</td> -<td class="tdc bord_right vertb">9</td> -<td class="tdc">97.5</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb"><span class="add2em">10</span></td> -<td class="tdc bord_right vertb">1.28</td> -<td class="tdc bord_right vertb">1.07</td> -<td class="tdc bord_right vertb">154</td> -<td class="tdc bord_right vertb">14</td> -<td class="tdc">90.9</td> -</tr> -<tr> - -<td class="tdl vertt bord_right vertb"><span class="add2em">17</span></td> -<td class="tdc bord_right vertb">1.14</td> -<td class="tdc bord_right vertb">0.94</td> -<td class="tdc bord_right vertb">189</td> -<td class="tdc bord_right vertb">26</td> -<td class="tdc">86.3</td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot"><span class="add1em">Average</span></td> -<td class="tdc bord_right bord_bot">1.14</td> -<td class="tdc bord_right bord_bot">1.83</td> -<td class="tdc bord_right bord_bot">507</td> -<td class="tdc bord_right bord_bot">14</td> -<td class="tdc bord_bot">96.4</td> -</tr> -<tr> -<td class="tdl" colspan="6">The average bacterial efficiency was 96.4 per cent with 1.83 grains of -sulphate of alumina per gallon.</td> -</tr> -</table> - -<div class="section"> -<h3 class="nobreak" id="PITTSBURG_EXPERIMENTS">PITTSBURG EXPERIMENTS.<a id="FNanchor_42" href="#Footnote_42" class="fnanchor">[42]</a></h3></div> - -<p>The Pittsburg experiments were inaugurated by the Pittsburg Filtration -Commission. The operation of the filters extended from January to -August, 1898. A Jewell and a Warren filter were used similar in design -to those used at Louisville. The raw water contained large numbers of -bacteria, and was also often very turbid, although less turbid than at -Louisville. At times more coagulant was necessary for clarification -than was required for bacterial efficiency; while as a rule more was -required for satisfactory bacterial purification than was necessary for -clarification. The opportunities were therefore favorable for the study -of both of these conditions. The amount of coagulant necessary for -clarification has been mentioned in connection with coagulation.</p> - -<p>The results secured upon the relation of the quantity of -<span class="pagenum" id="Page_163">[Pg 163]</span> -coagulant to the number of bacteria in the effluent were more complete -than any other experiments available, and are therefore here reproduced -from the Pittsburg report nearly in full.</p> - -<p>It was found that the amount of sulphate of alumina employed was -more important than any other factor in determining the bacterial -efficiency, and special experiments were made to establish the effect -of more and of less coagulant than used in the ordinary work. These -experiments were made upon the Warren filter during May, and with -the Jewell filter during June. The monthly averages for these months -are thus abnormal and are not to be considered. The remaining six -months for each filter may be taken as normal and as representing -approximately the work of these filters under ordinary careful working -conditions.</p> - -<p>During the six months when the Warren filter was in normal order the -raw water contained 11,531 bacteria and the effluent 201, the average -bacterial efficiency being 98.26 per cent. The bacterial efficiency was -very constant, ranging only, by months, from 97.48 to 98.96 per cent. -During the same period a sand filter receiving the same water yielded -an effluent having an average of 105 bacteria per cubic centimeter.</p> - -<p>The Jewell filter, for the six months in which it was in normal order, -received raw water containing an average of 11,481 bacteria and yielded -an effluent containing an average of 293, the bacterial efficiency -being 97.45 per cent, and ranging, in different months, from 93.23 to -98.61 per cent.</p> - -<div class="section"> -<h3 class="nobreak" id="WASTING_EFFLUENT_AFTER_WASHING_FILTERS">WASTING EFFLUENT AFTER WASHING FILTERS.</h3></div> - -<p>After washing a mechanical filter the effluent for the first few -minutes is often inferior in quality to that obtained at other times, -and if samples are taken at these times and averaged with other samples -taken during the run, an apparent efficiency may be obtained inferior -to the true efficiency. To guard against this source of error, whenever -samples have been taken at such times, the average work for the day -has been taken, not as the numerical<span class="pagenum" id="Page_164">[Pg 164]</span> average of the results, but each -sample has been given weight in proportion to the amount of time which -it could be taken as representing; so that the results represent as -nearly as possible the average number of bacteria in the effluent for -the whole run. As a matter of fact, however, comparatively few samples -were taken during these periods of reduced efficiency, and thus most of -the results represent the normal efficiency exclusive of this period. A -study has been made, however, of the results of examinations of samples -taken directly after washing, somewhat in detail. The following is a -tabular statement of the average results obtained from each filter by -months, including only the results obtained on those days when samples -were taken within twenty minutes after washing, the results of other -days being excluded.</p> - -<table class="autotable" summary="samples taken directly after washing"> -<tr> -<th class="tdc normal" colspan="5">AVERAGE NUMBER OF BACTERIA IN EFFLUENT.</th> -</tr> -<tr> -<th class="tdc bord_top bord_right bord_top"> </th> -<th class="tdc normal small bord_top bord_right bord_top">Shown by<br />Record Sheets.</th> -<th class="tdc normal small bord_top bord_right bord_top">Within Ten<br />Minutes after<br />Washing.</th> -<th class="tdc normal small bord_top bord_right bord_top">11 to 20<br />Minutes after<br />Washing.</th> -<th class="tdc normal small bord_top bord_top">More than<br />Twenty<br />Minutes after<br />Washing.</th> -</tr> -<tr> -<td class="tdc bord_top bord_right bord_top">WARREN FILTER.</td> -<td class="tdc bord_top bord_right bord_top"> </td> -<td class="tdc bord_top bord_right bord_top"> </td> -<td class="tdc bord_top bord_right bord_top"> </td> -<td class="tdc bord_top bord_top"> </td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">February</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">115</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1"> </span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">118</span></td> -<td class="tdr vertt"><span class="padr1">114</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">March</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">316</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">50</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">515</span></td> -<td class="tdr vertt"><span class="padr1">301</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">April</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">79</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">417</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">207</span></td> -<td class="tdr vertt"><span class="padr1">75</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">May</td> -<td class="tdc bord_right" colspan="3">(Special experiments, omitted.)</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">June</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">197</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">493</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">272</span></td> -<td class="tdr vertt"><span class="padr1">170</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">July</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">300</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1"> </span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">546</span></td> -<td class="tdr vertt"><span class="padr1">207</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">August</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">174</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">356</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">601</span></td> -<td class="tdr vertt"><span class="padr1">223</span></td> -</tr> -<tr> -<td class="tdc bord_right vertb">JEWELL FILTER.</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">February</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">2453</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">2425</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1"> </span></td> -<td class="tdr vertt"><span class="padr1">2099</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">March</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">455</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">657</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">958</span></td> -<td class="tdr vertt"><span class="padr1">354</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">April</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">99</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">665</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">462</span></td> -<td class="tdr vertt"><span class="padr1">165</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">May</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">144</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">998</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">346</span></td> -<td class="tdr vertt"><span class="padr1">127</span></td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">June</td> -<td class="tdc bord_right" colspan="3">(Special experiments, omitted.)</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">July</td> -<td class="tdl vertt bord_right vertb"><span class="padr1">279</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">1330</span></td> -<td class="tdl vertt bord_right vertb"><span class="padr1">272</span></td> -<td class="tdr vertt"><span class="padr1">274</span></td> -</tr> -<tr> -<td class="tdl bord_right bord_bot">August</td> -<td class="tdr bord_right bord_bot"><span class="padr1">344</span></td> -<td class="tdr bord_right bord_bot"><span class="padr1">612</span></td> -<td class="tdr bord_right bord_bot"><span class="padr1">323</span></td> -<td class="tdr bord_bot"><span class="padr1">376</span></td> -</tr> -</table> - -<p class="padt1">The time of inferior work very rarely exceeded twenty minutes. It -will be seen from the tables that the results as shown by the record -sheets are never very much higher, and are occasionally lower than the -results of samples taken on corresponding days more than twenty minutes -after washing; and thus while a decrease in bacterial efficiency was -noted after washing, no<span class="pagenum" id="Page_165">[Pg 165]</span> material increase in the average bacterial -efficiency of the mechanical filters would have been obtained if these -results had been excluded. The results for the whole time would be -affected much less than is indicated by the table, because the table -includes only results of those days when samples were taken just after -washing, while the much larger number of days when no such samples were -taken would show no change whatever.</p> - -<p>It has been suggested that these inferior effluents after washing -should be wasted. Such a procedure would mean wasting probably on -an average two per cent of the water filtered, and a corresponding -increase in the cost of filtering. Mr. Fuller<a id="FNanchor_43" href="#Footnote_43" class="fnanchor">[43]</a> in his Louisville -report comes to the conclusion that with adequate washing and -coagulation it is unnecessary to waste any effluent, and that inferior -results after washing usually indicate incomplete washing. While our -experiments certainly indicate a reduction in efficiency after washing -so regular and persistent as to make it doubtful whether incomplete -washing can be the cause of it, it may be questioned whether or -not wasting the effluent would be necessary or desirable in actual -operation. At any rate the results as given in this report are not -materially influenced by this factor.</p> - -<div class="section"> -<h3 class="nobreak" id="INFLUENCE_OF_AMOUNT_OF_SULPHATE_OF_ALUMINA_ON_BACTERIAL_EFFICIENCY_OF_MECHANICAL_FILTERS"> -INFLUENCE OF AMOUNT OF SULPHATE OF ALUMINA ON BACTERIAL EFFICIENCY OF -MECHANICAL FILTERS.</h3></div> - -<p class="padb1">The number of bacteria passing a mechanical filter is dependent -principally upon the amount of sulphate of alumina used; and by using -a larger quantity of sulphate of alumina than was actually used in the -experiments the bacterial efficiency could be considerably increased. -To investigate this point, the results obtained each day with each -of the mechanical filters were arranged in the order of the sulphate -of alumina quantities used, and averaged by classes. In this and the -following tables a few abnormal results were omitted.<a id="FNanchor_44" href="#Footnote_44" class="fnanchor">[44]</a> A summary of -the results is as follows:</p> - -<p><span class="pagenum" id="Page_166">[Pg 166]</span></p> - -<table class="autotable" summary="the number of bacteria passing a mechanical filter"> -<tr> -<th class="tdc normal" colspan="7">SUMMARY OF RESULTS WITH WARREN MECHANICAL FILTER, ARRANGED ACCORDING TO -SULPHATE OF ALUMINA QUANTITIES.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Number<br />of Days<br />Represented.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Turbidity.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" colspan="2">Bacteria.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />remaining.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />removed.</th> -<th class="tdc normal small bord_top bord_top bord_bot" rowspan="2">Sulphate of<br />Alumina<br />used Grains<br />per Gallon.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Raw Water.</th> -<th class="tdc normal small bord_right bord_bot">Effluent.</th> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 7</td> -<td class="tdc bord_right vertb">0.05</td> -<td class="tdc bord_right vertb"> 4,773</td> -<td class="tdc bord_right vertb">1713</td> -<td class="tdc bord_right vertb">35.89</td> -<td class="tdc bord_right vertb">64.11</td> -<td class="tdc">0.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 2</td> -<td class="tdc bord_right vertb">0.08</td> -<td class="tdc bord_right vertb"> 2,785</td> -<td class="tdc bord_right vertb"> 850</td> -<td class="tdc bord_right vertb">30.52</td> -<td class="tdc bord_right vertb">69.48</td> -<td class="tdc">0.12</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 4</td> -<td class="tdc bord_right vertb">0.10</td> -<td class="tdc bord_right vertb"> 5,109</td> -<td class="tdc bord_right vertb"> 726</td> -<td class="tdc bord_right vertb">14.21</td> -<td class="tdc bord_right vertb">85.79</td> -<td class="tdc">0.26</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 2</td> -<td class="tdc bord_right vertb">0.20</td> -<td class="tdc bord_right vertb"> 8,713</td> -<td class="tdc bord_right vertb"> 214</td> -<td class="tdc bord_right vertb"> 2.45</td> -<td class="tdc bord_right vertb">97.55</td> -<td class="tdc">0.36</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 8</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb"> 3,224</td> -<td class="tdc bord_right vertb"> 112</td> -<td class="tdc bord_right vertb"> 3.47</td> -<td class="tdc bord_right vertb">96.53</td> -<td class="tdc">0.44</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">19</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb"> 3,488</td> -<td class="tdc bord_right vertb"> 123</td> -<td class="tdc bord_right vertb"> 3.53</td> -<td class="tdc bord_right vertb">96.47</td> -<td class="tdc">0.55</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">11</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb"> 5,673</td> -<td class="tdc bord_right vertb"> 154</td> -<td class="tdc bord_right vertb"> 2.71</td> -<td class="tdc bord_right vertb">97.29</td> -<td class="tdc">0.64</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.10</td> -<td class="tdc bord_right vertb"> 6,100</td> -<td class="tdc bord_right vertb"> 112</td> -<td class="tdc bord_right vertb"> 1.84</td> -<td class="tdc bord_right vertb">98.16</td> -<td class="tdc">0.74</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 8</td> -<td class="tdc bord_right vertb">0.09</td> -<td class="tdc bord_right vertb"> 8,647</td> -<td class="tdc bord_right vertb"> 148</td> -<td class="tdc bord_right vertb"> 1.71</td> -<td class="tdc bord_right vertb">98.29</td> -<td class="tdc">0.85</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 5</td> -<td class="tdc bord_right vertb">0.16</td> -<td class="tdc bord_right vertb"> 5,645</td> -<td class="tdc bord_right vertb"> 142</td> -<td class="tdc bord_right vertb"> 2.52</td> -<td class="tdc bord_right vertb">97.48</td> -<td class="tdc">0.93</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">13</td> -<td class="tdc bord_right vertb">0.12</td> -<td class="tdc bord_right vertb">10,397</td> -<td class="tdc bord_right vertb"> 200</td> -<td class="tdc bord_right vertb"> 1.92</td> -<td class="tdc bord_right vertb">98.08</td> -<td class="tdc">1.07</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.08</td> -<td class="tdc bord_right vertb">12,778</td> -<td class="tdc bord_right vertb"> 121</td> -<td class="tdc bord_right vertb"> 0.95</td> -<td class="tdc bord_right vertb">99.05</td> -<td class="tdc">1.13</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">13</td> -<td class="tdc bord_right vertb">0.14</td> -<td class="tdc bord_right vertb">13,397</td> -<td class="tdc bord_right vertb"> 164</td> -<td class="tdc bord_right vertb"> 1.22</td> -<td class="tdc bord_right vertb">98.78</td> -<td class="tdc">1.25</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">19</td> -<td class="tdc bord_right vertb">0.13</td> -<td class="tdc bord_right vertb">10,462</td> -<td class="tdc bord_right vertb"> 160</td> -<td class="tdc bord_right vertb"> 1.53</td> -<td class="tdc bord_right vertb">98.47</td> -<td class="tdc">1.34</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.12</td> -<td class="tdc bord_right vertb">12,851</td> -<td class="tdc bord_right vertb"> 107</td> -<td class="tdc bord_right vertb"> 0.83</td> -<td class="tdc bord_right vertb">99.17</td> -<td class="tdc">1.46</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 4</td> -<td class="tdc bord_right vertb">0.27</td> -<td class="tdc bord_right vertb">16,015</td> -<td class="tdc bord_right vertb"> 77</td> -<td class="tdc bord_right vertb"> 0.48</td> -<td class="tdc bord_right vertb">99.52</td> -<td class="tdc">1.57</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 7</td> -<td class="tdc bord_right vertb">0.53</td> -<td class="tdc bord_right vertb">12,262</td> -<td class="tdc bord_right vertb"> 191</td> -<td class="tdc bord_right vertb"> 1.18</td> -<td class="tdc bord_right vertb">98.82</td> -<td class="tdc">1.64</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 4</td> -<td class="tdc bord_right vertb">0.58</td> -<td class="tdc bord_right vertb">26,950</td> -<td class="tdc bord_right vertb"> 347</td> -<td class="tdc bord_right vertb"> 1.29</td> -<td class="tdc bord_right vertb">98.71</td> -<td class="tdc">1.74</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 5</td> -<td class="tdc bord_right vertb">0.29</td> -<td class="tdc bord_right vertb">14,570</td> -<td class="tdc bord_right vertb"> 86</td> -<td class="tdc bord_right vertb"> 0.59</td> -<td class="tdc bord_right vertb">99.41</td> -<td class="tdc">1.84</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 3</td> -<td class="tdc bord_right vertb">0.23</td> -<td class="tdc bord_right vertb">13,833</td> -<td class="tdc bord_right vertb"> 153</td> -<td class="tdc bord_right vertb"> 1.11</td> -<td class="tdc bord_right vertb">98.89</td> -<td class="tdc">1.92</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">19</td> -<td class="tdc bord_right vertb">0.40</td> -<td class="tdc bord_right vertb">18,222</td> -<td class="tdc bord_right vertb"> 92</td> -<td class="tdc bord_right vertb"> 0.50</td> -<td class="tdc bord_right vertb">99.50</td> -<td class="tdc">2.48</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 5</td> -<td class="tdc bord_right vertb">0.45</td> -<td class="tdc bord_right vertb">29,300</td> -<td class="tdc bord_right vertb">1119</td> -<td class="tdc bord_right vertb"> 3.82</td> -<td class="tdc bord_right vertb">96.18</td> -<td class="tdc">3.37</td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot"> 5</td> -<td class="tdc bord_right bord_bot">1.06</td> -<td class="tdc bord_right bord_bot">33,030</td> -<td class="tdc bord_right bord_bot"> 535</td> -<td class="tdc bord_right bord_bot"> 1.62</td> -<td class="tdc bord_right bord_bot">98.38</td> -<td class="tdc bord_bot">8.06</td> -</tr> -<tr> -<th class="tdc normal" colspan="7">SUMMARY OF RESULTS WITH JEWELL MECHANICAL FILTER, ARRANGED ACCORDING TO SULPHATE OF ALUMINA QUANTITIES.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Number<br />of Days<br />Represented.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Turbidity.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" colspan="2">Bacteria.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />remaining.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />removed.</th> -<th class="tdc normal small bord_top bord_top bord_bot" rowspan="2">Sulphate of<br />Alumina<br />used Grains<br />per Gallon.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Raw Water.</th> -<th class="tdc normal small bord_right bord_bot">Effluent.</th> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 6</td> -<td class="tdc bord_right vertb">0.03</td> -<td class="tdc bord_right vertb">14,037</td> -<td class="tdc bord_right vertb">6217</td> -<td class="tdc bord_right vertb">44.29</td> -<td class="tdc bord_right vertb">55.71</td> -<td class="tdc">0.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 5</td> -<td class="tdc bord_right vertb">0.07</td> -<td class="tdc bord_right vertb"> 4,267</td> -<td class="tdc bord_right vertb"> 680</td> -<td class="tdc bord_right vertb">15.93</td> -<td class="tdc bord_right vertb">84.07</td> -<td class="tdc">0.24</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">14</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb"> 2,613</td> -<td class="tdc bord_right vertb"> 170</td> -<td class="tdc bord_right vertb"> 6.50</td> -<td class="tdc bord_right vertb">93.50</td> -<td class="tdc">0.35</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb"> 2,446</td> -<td class="tdc bord_right vertb"> 113</td> -<td class="tdc bord_right vertb"> 4.62</td> -<td class="tdc bord_right vertb">95.38</td> -<td class="tdc">0.44</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 9</td> -<td class="tdc bord_right vertb">0.11</td> -<td class="tdc bord_right vertb"> 7,303</td> -<td class="tdc bord_right vertb">234</td> -<td class="tdc bord_right vertb"> 3.20</td> -<td class="tdc bord_right vertb">96.80</td> -<td class="tdc">0.55</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">20</td> -<td class="tdc bord_right vertb">0.09</td> -<td class="tdc bord_right vertb"> 6,979</td> -<td class="tdc bord_right vertb"> 220</td> -<td class="tdc bord_right vertb"> 3.15</td> -<td class="tdc bord_right vertb">96.85</td> -<td class="tdc">0.65</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 9</td> -<td class="tdc bord_right vertb">0.08</td> -<td class="tdc bord_right vertb"> 5,191</td> -<td class="tdc bord_right vertb"> 130</td> -<td class="tdc bord_right vertb"> 2.50</td> -<td class="tdc bord_right vertb">97.50</td> -<td class="tdc">0.75</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">16</td> -<td class="tdc bord_right vertb">0.12</td> -<td class="tdc bord_right vertb"> 8,504</td> -<td class="tdc bord_right vertb"> 242</td> -<td class="tdc bord_right vertb"> 2.84</td> -<td class="tdc bord_right vertb">97.16</td> -<td class="tdc">0.83</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">22</td> -<td class="tdc bord_right vertb">0.16</td> -<td class="tdc bord_right vertb"> 8,506</td> -<td class="tdc bord_right vertb"> 99</td> -<td class="tdc bord_right vertb"> 1.16</td> -<td class="tdc bord_right vertb">98.84</td> -<td class="tdc">0.96</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">12</td> -<td class="tdc bord_right vertb">0.11</td> -<td class="tdc bord_right vertb">11,998</td> -<td class="tdc bord_right vertb"> 246</td> -<td class="tdc bord_right vertb"> 2.05</td> -<td class="tdc bord_right vertb">97.95</td> -<td class="tdc">1.05</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">14</td> -<td class="tdc bord_right vertb">0.18</td> -<td class="tdc bord_right vertb">18,982</td> -<td class="tdc bord_right vertb"> 423</td> -<td class="tdc bord_right vertb"> 2.23</td> -<td class="tdc bord_right vertb">97.77</td> -<td class="tdc">1.16</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 5</td> -<td class="tdc bord_right vertb">0.14</td> -<td class="tdc bord_right vertb">13,981</td> -<td class="tdc bord_right vertb"> 224</td> -<td class="tdc bord_right vertb"> 1.60</td> -<td class="tdc bord_right vertb">98.40</td> -<td class="tdc">1.23</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 9</td> -<td class="tdc bord_right vertb">0.27</td> -<td class="tdc bord_right vertb">19,806</td> -<td class="tdc bord_right vertb"> 325</td> -<td class="tdc bord_right vertb"> 1.64</td> -<td class="tdc bord_right vertb">98.36</td> -<td class="tdc">1.34</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">14</td> -<td class="tdc bord_right vertb">0.27</td> -<td class="tdc bord_right vertb">16,549</td> -<td class="tdc bord_right vertb"> 324</td> -<td class="tdc bord_right vertb"> 1.96</td> -<td class="tdc bord_right vertb">98.04</td> -<td class="tdc">1.45</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 9</td> -<td class="tdc bord_right vertb">0.29</td> -<td class="tdc bord_right vertb">12,194</td> -<td class="tdc bord_right vertb"> 96</td> -<td class="tdc bord_right vertb"> 0.79</td> -<td class="tdc bord_right vertb">99.21</td> -<td class="tdc">1.54</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 6</td> -<td class="tdc bord_right vertb">0.25</td> -<td class="tdc bord_right vertb">13,483</td> -<td class="tdc bord_right vertb"> 51</td> -<td class="tdc bord_right vertb"> 0.38</td> -<td class="tdc bord_right vertb">99.62</td> -<td class="tdc">1.65</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 7</td> -<td class="tdc bord_right vertb">0.53</td> -<td class="tdc bord_right vertb">24,243</td> -<td class="tdc bord_right vertb"> 220</td> -<td class="tdc bord_right vertb"> 0.91</td> -<td class="tdc bord_right vertb">99.09</td> -<td class="tdc">1.72</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 3</td> -<td class="tdc bord_right vertb">0.90</td> -<td class="tdc bord_right vertb">20,953</td> -<td class="tdc bord_right vertb"> 602</td> -<td class="tdc bord_right vertb"> 2.88</td> -<td class="tdc bord_right vertb">97.12</td> -<td class="tdc">1.90</td> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 5</td> -<td class="tdc bord_right vertb">0.43</td> -<td class="tdc bord_right vertb">25,958</td> -<td class="tdc bord_right vertb"> 307</td> -<td class="tdc bord_right vertb"> 1.19</td> -<td class="tdc bord_right vertb">98.81</td> -<td class="tdc">2.19</td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot"> 4</td> -<td class="tdc bord_right bord_bot">0.84</td> -<td class="tdc bord_right bord_bot">21,017</td> -<td class="tdc bord_right bord_bot"> 228</td> -<td class="tdc bord_right bord_bot"> 1.09</td> -<td class="tdc bord_right bord_bot">98.91</td> -<td class="tdc bord_bot">3.71</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_167">[Pg 167]</span></p> - -<p>These results are shown graphically by Fig. 21.</p> - -<div class="figcenter padt1 padb1 illowp82" id="image167" style="max-width: 62.5em;"> - <img class="w100" src="images/image167.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 21.—Bacterial Efficiencies of Mechanical -Filters.</span></p></div> - -<div class="section"> -<h3 class="nobreak" id="INFLUENCE_OF_DEGREE_OF_TURBIDITY_UPON_BACTERIAL_EFFICIENCY_OF_MECHANICAL_FILTERS"> -INFLUENCE OF DEGREE OF TURBIDITY UPON BACTERIAL EFFICIENCY OF -MECHANICAL FILTERS.</h3></div> - -<p>It will be noticed by referring to the tables that as the sulphate of -alumina quantities increased the turbidities increased and the numbers -of bacteria increased, as well as the bacterial efficiencies. That -is to say, with the less turbid waters, small sulphate of alumina -quantities have been used, the numbers of bacteria in the raw water -have been low, and the bacterial efficiencies have also been low. With -turbid waters much larger quantities of sulphate of alumina have been -used, the raw water has contained more bacteria, and the bacterial -efficiencies have been higher. It may<span class="pagenum" id="Page_168">[Pg 168]</span> be then that the increased -efficiencies with increased quantities of sulphate of alumina are not -due alone to the increased sulphate of alumina, but in part also to -other conditions. Thus it may be easier to remove a large percentage of -bacteria from a water containing many than from a water containing only -a few.</p> - -<p>To investigate this matter and eliminate the influence of turbidity and -numbers of bacteria in the raw water, the results were first classified -with reference to turbidity. The results with waters having turbidities -of 0.10 or less, and called for convenience turbid waters, are arranged -by alum quantities as before. Afterwards the results obtained with -turbidities from 0.11 to 0.50, and called for convenience muddy -waters, are grouped; and finally the results with turbid water having -turbidities of 0.51 and over, and called for convenience thick waters. -The results thus arranged are as follows:</p> - -<table class="autotable" summary="bacteria passing a mechanical filter with reference to turbidity"> -<tr> -<th class="tdc normal" colspan="7">SUMMARY OF RESULTS WITH WARREN MECHANICAL FILTER, ARRANGED ACCORDING TO TURBIDITIES AND SULPHATE OF ALUMINA QUANTITIES.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Number<br />of Days<br />Represented.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Turbidity.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" colspan="2">Bacteria.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />remaining.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />removed.</th> -<th class="tdc normal small bord_top bord_top bord_bot" rowspan="2">Sulphate of<br />Alumina<br />used Grains<br />per Gallon.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Raw Water.</th> -<th class="tdc normal small bord_right bord_bot">Effluent.</th> -</tr> -<tr> - -<td class="tdc bord_right vertb"> 7</td> -<td class="tdc bord_right vertb">0.05</td> -<td class="tdc bord_right vertb"> 4,773</td> -<td class="tdc bord_right vertb">1713</td> -<td class="tdc bord_right vertb">35.89</td> -<td class="tdc bord_right vertb">64.11</td> -<td class="tdc">0.00</td> -</tr> -<tr> - - -<td class="tdc bord_right vertb"> 2</td> -<td class="tdc bord_right vertb">0.07</td> -<td class="tdc bord_right vertb"> 2,785</td> -<td class="tdc bord_right vertb"> 850</td> -<td class="tdc bord_right vertb">30.52</td> -<td class="tdc bord_right vertb">69.48</td> -<td class="tdc">0.12</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">12</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">3,209</td> -<td class="tdc bord_right vertb">224</td> -<td class="tdc bord_right vertb">7.00</td> -<td class="tdc bord_right vertb">93.00</td> -<td class="tdc">0.42</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">31</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">4,238</td> -<td class="tdc bord_right vertb">119</td> -<td class="tdc bord_right vertb">2.81</td> -<td class="tdc bord_right vertb">97.19</td> -<td class="tdc">0.60</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">9</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">7,953</td> -<td class="tdc bord_right vertb">130</td> -<td class="tdc bord_right vertb">1.64</td> -<td class="tdc bord_right vertb">98.36</td> -<td class="tdc">0.84</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">16</td> -<td class="tdc bord_right vertb">0.04</td> -<td class="tdc bord_right vertb">11,265</td> -<td class="tdc bord_right vertb">137</td> -<td class="tdc bord_right vertb">1.22</td> -<td class="tdc bord_right vertb">98.78</td> -<td class="tdc">1.11</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">29</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">11,500</td> -<td class="tdc bord_right vertb">158</td> -<td class="tdc bord_right vertb">1.37</td> -<td class="tdc bord_right vertb">98.63</td> -<td class="tdc">1.58</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">5</td> -<td class="tdc bord_right vertb">0.17</td> -<td class="tdc bord_right vertb">8,783</td> -<td class="tdc bord_right vertb">416</td> -<td class="tdc bord_right vertb">4.73</td> -<td class="tdc bord_right vertb">95.27</td> -<td class="tdc">0.36</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.16</td> -<td class="tdc bord_right vertb">6,535</td> -<td class="tdc bord_right vertb">165</td> -<td class="tdc bord_right vertb">2.54</td> -<td class="tdc bord_right vertb">97.46</td> -<td class="tdc">0.85</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">13</td> -<td class="tdc bord_right vertb">0.19</td> -<td class="tdc bord_right vertb">13,253</td> -<td class="tdc bord_right vertb">186</td> -<td class="tdc bord_right vertb">1.40</td> -<td class="tdc bord_right vertb">98.60</td> -<td class="tdc">1.13</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">15</td> -<td class="tdc bord_right vertb">0.22</td> -<td class="tdc bord_right vertb">10,944</td> -<td class="tdc bord_right vertb">93</td> -<td class="tdc bord_right vertb">0.85</td> -<td class="tdc bord_right vertb">99.15</td> -<td class="tdc">1.36</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">13</td> -<td class="tdc bord_right vertb">0.29</td> -<td class="tdc bord_right vertb">14,089</td> -<td class="tdc bord_right vertb">112</td> -<td class="tdc bord_right vertb">0.80</td> -<td class="tdc bord_right vertb">99.20</td> -<td class="tdc">1.73</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.35</td> -<td class="tdc bord_right vertb">18,088</td> -<td class="tdc bord_right vertb">102</td> -<td class="tdc bord_right vertb">0.57</td> -<td class="tdc bord_right vertb">99.43</td> -<td class="tdc">2.38</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">5</td> -<td class="tdc bord_right vertb">0.29</td> -<td class="tdc bord_right vertb">25,580</td> -<td class="tdc bord_right vertb">540</td> -<td class="tdc bord_right vertb">2.11</td> -<td class="tdc bord_right vertb">97.89</td> -<td class="tdc">4.30</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">6</td> -<td class="tdc bord_right vertb">0.87</td> -<td class="tdc bord_right vertb">25,433</td> -<td class="tdc bord_right vertb">369</td> -<td class="tdc bord_right vertb">1.45</td> -<td class="tdc bord_right vertb">98.55</td> -<td class="tdc">1.74</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">6</td> -<td class="tdc bord_right vertb">0.73</td> -<td class="tdc bord_right vertb">26,566</td> -<td class="tdc bord_right vertb">79</td> -<td class="tdc bord_right vertb">0.30</td> -<td class="tdc bord_right vertb">99.70</td> -<td class="tdc">2.64</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">4</td> -<td class="tdc bord_right vertb">1.35</td> -<td class="tdc bord_right vertb">42,037</td> -<td class="tdc bord_right vertb">1388</td> -<td class="tdc bord_right vertb">3.30</td> -<td class="tdc bord_right vertb">96.70</td> -<td class="tdc">8.16</td> -</tr> -<tr> -<th class="tdc normal bord_top" colspan="7"><span class="pagenum" id="Page_169">[Pg 169]</span> -SUMMARY OF RESULTS WITH JEWELL MECHANICAL FILTER, ARRANGED ACCORDING TO TURBIDITIES AND SULPHATE OF ALUMINA QUANTITIES.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Number<br />of Days<br />Represented.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Turbidity.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" colspan="2">Bacteria.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />remaining.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />removed.</th> -<th class="tdc normal small bord_top bord_top bord_bot" rowspan="2">Sulphate of<br />Alumina<br />used Grains<br />per Gallon.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Raw Water.</th> -<th class="tdc normal small bord_right bord_bot">Effluent.</th> -</tr> -<tr> -<td class="tdc bord_right vertb">6</td> -<td class="tdc bord_right vertb">0.03</td> -<td class="tdc bord_right vertb">14,037</td> -<td class="tdc bord_right vertb">6217</td> -<td class="tdc bord_right vertb">44.29</td> -<td class="tdc bord_right vertb">55.71</td> -<td class="tdc">0.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">3</td> -<td class="tdc bord_right vertb">0.07</td> -<td class="tdc bord_right vertb">5,170</td> -<td class="tdc bord_right vertb">991</td> -<td class="tdc bord_right vertb">19.15</td> -<td class="tdc bord_right vertb">80.85</td> -<td class="tdc">0.21</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">25</td> -<td class="tdc bord_right vertb">0.05</td> -<td class="tdc bord_right vertb">2,403</td> -<td class="tdc bord_right vertb">143</td> -<td class="tdc bord_right vertb">5.95</td> -<td class="tdc bord_right vertb">94.05</td> -<td class="tdc">0.38</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">20</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">6,531</td> -<td class="tdc bord_right vertb">185</td> -<td class="tdc bord_right vertb">2.84</td> -<td class="tdc bord_right vertb">97.16</td> -<td class="tdc">0.64</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">27</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">5,811</td> -<td class="tdc bord_right vertb">122</td> -<td class="tdc bord_right vertb">2.10</td> -<td class="tdc bord_right vertb">97.90</td> -<td class="tdc">0.88</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">14</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">14,978</td> -<td class="tdc bord_right vertb">412</td> -<td class="tdc bord_right vertb">2.75</td> -<td class="tdc bord_right vertb">97.25</td> -<td class="tdc">1.11</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">15,787</td> -<td class="tdc bord_right vertb">390</td> -<td class="tdc bord_right vertb">2.47</td> -<td class="tdc bord_right vertb">97.53</td> -<td class="tdc">1.37</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.05</td> -<td class="tdc bord_right vertb">10,847</td> -<td class="tdc bord_right vertb">47</td> -<td class="tdc bord_right vertb">0.43</td> -<td class="tdc bord_right vertb">99.57</td> -<td class="tdc">2.17</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">14</td> -<td class="tdc bord_right vertb">0.16</td> -<td class="tdc bord_right vertb">7,525</td> -<td class="tdc bord_right vertb">256</td> -<td class="tdc bord_right vertb">3.40</td> -<td class="tdc bord_right vertb">96.60</td> -<td class="tdc">0.60</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">17</td> -<td class="tdc bord_right vertb">0.24</td> -<td class="tdc bord_right vertb">11,310</td> -<td class="tdc bord_right vertb">208</td> -<td class="tdc bord_right vertb">1.84</td> -<td class="tdc bord_right vertb">98.16</td> -<td class="tdc">0.91</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">15</td> -<td class="tdc bord_right vertb">0.24</td> -<td class="tdc bord_right vertb">15,441</td> -<td class="tdc bord_right vertb">262</td> -<td class="tdc bord_right vertb">1.70</td> -<td class="tdc bord_right vertb">98.30</td> -<td class="tdc">1.13</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">10</td> -<td class="tdc bord_right vertb">0.28</td> -<td class="tdc bord_right vertb">17,842</td> -<td class="tdc bord_right vertb">232</td> -<td class="tdc bord_right vertb">1.30</td> -<td class="tdc bord_right vertb">98.70</td> -<td class="tdc">1.43</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">8</td> -<td class="tdc bord_right vertb">0.29</td> -<td class="tdc bord_right vertb">9,556</td> -<td class="tdc bord_right vertb">59</td> -<td class="tdc bord_right vertb">0.62</td> -<td class="tdc bord_right vertb">99.38</td> -<td class="tdc">1.59</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">4</td> -<td class="tdc bord_right vertb">0.29</td> -<td class="tdc bord_right vertb">20,212</td> -<td class="tdc bord_right vertb">135</td> -<td class="tdc bord_right vertb">0.67</td> -<td class="tdc bord_right vertb">99.33</td> -<td class="tdc">2.00</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">5</td> -<td class="tdc bord_right vertb">0.66</td> -<td class="tdc bord_right vertb">23,680</td> -<td class="tdc bord_right vertb">336</td> -<td class="tdc bord_right vertb">1.42</td> -<td class="tdc bord_right vertb">98.58</td> -<td class="tdc">1.42</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">7</td> -<td class="tdc bord_right vertb">0.96</td> -<td class="tdc bord_right vertb">30,200</td> -<td class="tdc bord_right vertb">475</td> -<td class="tdc bord_right vertb">1.57</td> -<td class="tdc bord_right vertb">98.43</td> -<td class="tdc">1.74</td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot">4</td> -<td class="tdc bord_right bord_bot">1.25</td> -<td class="tdc bord_right bord_bot">37,587</td> -<td class="tdc bord_right bord_bot">496</td> -<td class="tdc bord_right bord_bot">1.32</td> -<td class="tdc bord_right bord_bot">98.68</td> -<td class="tdc bord_bot">2.81</td> -</tr> -</table> - -<p class="padt1 padb1">The following table shows the bacterial efficiencies with turbid, -muddy, and thick waters, with substantially equal quantities of -sulphate of alumina:</p> - -<table class="autotable" summary=""> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot" colspan="3">Grains of Sulphate of Alumina.</th> -<th class="tdc normal small bord_top bord_bot" colspan="3">Corresponding Bacterial Efficiencies.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Turbid.</th> -<th class="tdc normal small bord_right bord_bot">Muddy.</th> -<th class="tdc normal small bord_right bord_bot">Thick.</th> -<th class="tdc normal small bord_right bord_bot">Turbid.</th> -<th class="tdc normal small bord_right bord_bot">Muddy.</th> -<th class="tdc normal small bord_bot">Thick.</th> -</tr> -<tr> -<td class="tdc" colspan="6">WARREN FILTER.</td> -</tr> -<tr> -<td class="tdc bord_right vertb">0.42</td> -<td class="tdc bord_right vertb">0.36</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">93.00</td> -<td class="tdc bord_right vertb">95.27</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdc bord_right vertb">0.84</td> -<td class="tdc bord_right vertb">0.85</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">98.36</td> -<td class="tdc bord_right vertb">97.46</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdc bord_right vertb">1.11</td> -<td class="tdc bord_right vertb">1.13</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">98.78</td> -<td class="tdc bord_right vertb">98.60</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdc bord_right vertb">1.58</td> -<td class="tdc bord_right vertb">1.73</td> -<td class="tdc bord_right vertb">1.74</td> -<td class="tdc bord_right vertb">98.63</td> -<td class="tdc bord_right vertb">99.20</td> -<td class="tdc">98.55</td> -</tr> -<tr> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">2.38</td> -<td class="tdc bord_right vertb">2.64</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">99.43</td> -<td class="tdc">99.70</td> -</tr> -<tr> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">4.30</td> -<td class="tdc bord_right vertb">8.16</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">97.89</td> -<td class="tdc">96.70</td> -</tr> -<tr> -<td class="tdc" colspan="6">JEWELL FILTER.</td> -</tr> -<tr> -<td class="tdc bord_right vertb">0.64</td> -<td class="tdc bord_right vertb">0.60</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">97.16</td> -<td class="tdc bord_right vertb">96.60</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdc bord_right vertb">0.88</td> -<td class="tdc bord_right vertb">0.91</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">97.90</td> -<td class="tdc bord_right vertb">98.16</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdc bord_right vertb">1.11</td> -<td class="tdc bord_right vertb">1.13</td> -<td class="tdc bord_right vertb"> </td> -<td class="tdc bord_right vertb">97.25</td> -<td class="tdc bord_right vertb">98.30</td> -<td class="tdc"> </td> -</tr> -<tr> -<td class="tdc bord_right vertb">1.37</td> -<td class="tdc bord_right vertb">1.43</td> -<td class="tdc bord_right vertb">1.42</td> -<td class="tdc bord_right vertb">97.53</td> -<td class="tdc bord_right vertb">98.70</td> -<td class="tdc">98.58</td> -</tr> -<tr> -<td class="tdc bord_right vertb">2.17</td> -<td class="tdc bord_right vertb">1.59</td> -<td class="tdc bord_right vertb">1.74</td> -<td class="tdc bord_right vertb">99.57</td> -<td class="tdc bord_right vertb">99.38</td> -<td class="tdc">98.43</td> -</tr> -<tr> -<td class="tdc bord_right bord_bot"> </td> -<td class="tdc bord_right bord_bot">2.00</td> -<td class="tdc bord_right bord_bot">2.81</td> -<td class="tdc bord_right bord_bot"> </td> -<td class="tdc bord_right bord_bot">99.33</td> -<td class="tdc bord_bot">98.68</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_170">[Pg 170]</span></p> - -<p class="padt1">It appears from this table that waters of various degrees of turbidity -give substantially equal bacterial efficiencies with equal quantities -of sulphate of alumina, the results varying as often in one direction -as the other. Within certain limits it may thus be said that turbidity -is without influence upon the bacterial efficiency obtained in -mechanical filtration.</p> - -<p>It must be borne in mind, however, that the quantities of sulphate -of alumina, with very few exceptions, were sufficient to produce -full coagulation. Mr. Fuller has shown in his Louisville report that -considerable quantities of sulphate of alumina may be added to turbid -waters without producing appreciable coagulation; and therefore if -a quantity of sulphate of alumina sufficient to produce a certain -bacterial efficiency in a clear water should be added to a water so -turbid that it was unable to coagulate it, scarcely any effect would -be produced. The above statement therefore only applies in those cases -where sufficient sulphate of alumina is used to adequately coagulate -the water.</p> - -<p>As the numbers of bacteria often vary with the turbidity, the variation -in the numbers of bacteria in the different classes is much less than -in the first tables; but to further investigate the question of whether -the numbers of bacteria in the raw water have an important influence -upon the bacterial efficiencies, each of the two largest classes in the -foregoing tables was divided into two parts, according to the bacterial -numbers in the raw water, namely, the results from the Jewell filter -with turbid waters and with sulphate of alumina quantities ranging from -0.75 to 1.00 grain per gallon, and the results from the Warren filter -with turbid waters and with sulphate of alumina quantities of 1.25 -grains per gallon and upward. The results are as follows:</p> - -<p><span class="pagenum" id="Page_171">[Pg 171]</span></p> - -<table class="autotable" summary="influence of numbers of bacteria in the raw water"> -<tr> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Number<br />of Days<br />Represented.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Turbidity.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" colspan="2">Bacteria.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />remaining.</th> -<th class="tdc normal small bord_top bord_right bord_top bord_bot" rowspan="2">Per cent<br />removed.</th> -<th class="tdc normal small bord_top bord_top bord_bot" rowspan="2">Sulphate of<br />Alumina<br />used Grains<br />per Gallon.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Raw Water.</th> -<th class="tdc normal small bord_right bord_bot">Effluent.</th> -</tr> -<tr> -<td class="tdc" colspan="7">JEWELL FILTER.</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">14</td> -<td class="tdc bord_right vertb">0.05</td> -<td class="tdc bord_right vertb">3,938</td> -<td class="tdc bord_right vertb">81</td> -<td class="tdc bord_right vertb">2.06</td> -<td class="tdc bord_right vertb">97.94</td> -<td class="tdc">0.88</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">13</td> -<td class="tdc bord_right vertb">0.07</td> -<td class="tdc bord_right vertb">7,827</td> -<td class="tdc bord_right vertb">167</td> -<td class="tdc bord_right vertb">2.13</td> -<td class="tdc bord_right vertb">97.87</td> -<td class="tdc">0.87</td> -</tr> -<tr> - -<td class="tdc" colspan="7">WARREN FILTER.</td> -</tr> -<tr> - -<td class="tdc bord_right vertb">15</td> -<td class="tdc bord_right vertb">0.06</td> -<td class="tdc bord_right vertb">3,545</td> -<td class="tdc bord_right vertb">59</td> -<td class="tdc bord_right vertb">1.66</td> -<td class="tdc bord_right vertb">98.34</td> -<td class="tdc">1.67</td> -</tr> -<tr> - -<td class="tdc bord_right bord_bot">14</td> -<td class="tdc bord_right bord_bot">0.06</td> -<td class="tdc bord_right bord_bot">20,022</td> -<td class="tdc bord_right bord_bot">265</td> -<td class="tdc bord_right bord_bot">1.32</td> -<td class="tdc bord_right bord_bot">98.68</td> -<td class="tdc bord_bot">1.48</td> -</tr> -</table> - -<p class="padt1">It will be observed that the bacterial efficiencies are substantially -the same, with the lower and with the higher numbers of bacteria in -the raw water. That is to say, other things being equal, as the number -of bacteria increase in the raw water the number of bacteria in the -effluent increase in the same ratio. A further analysis of other groups -of results would perhaps show variations in one direction or the other, -but on the whole it is believed that the comparison is a fair one, and -that there is no well-marked tendency for bacterial efficiencies of -mechanical filters to increase or decrease with increasing numbers of -bacteria.</p> - -<div class="section"> -<h3 class="nobreak" id="AVERAGE_RESULTS_OBTAINED_WITH_VARIOUS_QUANTITIES_OF_SULPHATE_OF_ALUMINA"> -AVERAGE RESULTS OBTAINED WITH VARIOUS QUANTITIES OF SULPHATE OF ALUMINA.</h3></div> - -<p>As it appears that neither the turbidity nor the number of bacteria in -the raw water has a material influence upon the percentage bacterial -efficiency obtained, we can take the results given above, which -include all the results obtained (except a very few abnormal ones) for -computing the various efficiencies obtained with various quantities of -sulphate of alumina. These results are graphically shown by Fig. 21, p. -167, on which lines have been drawn indicating the normal efficiencies -from various quantities of sulphate of alumina as deduced from our -experiments.</p> - -<p>In computing the amount of sulphate of alumina which it would be -necessary to use in operating a plant at a given place to<span class="pagenum" id="Page_172">[Pg 172]</span> give these -efficiencies, the quantities of sulphate of alumina shown by the -diagram can be taken as those which it would be necessary to use during -those days in the year when the raw water was clear, or sufficiently -clear, so that the amounts of sulphate of alumina mentioned would -suffice to properly coagulate it.</p> - -<div class="section"> -<h3 class="nobreak" id="TYPES_OF_MECHANICAL_FILTERS">TYPES OF MECHANICAL FILTERS.</h3></div> - -<p>Sections of the Warren and Jewell filters used at Pittsburg are -presented herewith. The filters here shown are practically identical -with those used at Lorain and Louisville, and nearly all the exact -information regarding mechanical filters relates to filters of these -types. These sections show clearly the constructions used at Pittsburg -and Louisville, but there are some points in connection with the -designs of these filters which require to be considered more in detail.</p> - -<p>The simplest idea of a mechanical filter is a tub, with sand in the -bottom and some form of drainage system. Water is run over the sand, -passes through it, and is collected by the drainage system. When the -sand becomes clogged it is washed by the use of a reverse current of -water. This reverse current of water is so rapid as to preclude the use -of a drainage system consisting of gravel, tile-drains, etc., such as -are used in sand filters operated at lower rates, and instead metallic -strainers in some form are used. The sand comes directly against these -strainers, which are made as coarse as it is possible to have them, -without allowing the sand to pass.</p> - -<p>The rate of washing is usually from five to seven gallons per square -foot per minute. In the Warren filter the openings in the strainers at -the bottom are 6 to 8 per cent of the total area, and during washing -the water has an average velocity of 0.20 foot per second upward -through them. This velocity is so slow that the friction of the water -in passing through the openings in the screen is practically nothing. -A result of this is that if there is any<span class="pagenum" id="Page_173">[Pg 173]</span> unequal resistance of the -sand to the water, the bulk of the water goes up at the points of least -resistance in the sand.</p> - -<div class="figcenter padt1 padb1 illowp71" id="image173" style="max-width: 75em;"> - <img class="w100" src="images/image173.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 22.—Section of Jewell Mechanical Filter used in -Pittsburg Experiments.</span></p></div> - -<p>This tendency would be fatal were it not for the revolving rake which -loosens and mixes the sand and largely corrects it. The correction, -however, is imperfect, and some parts of the filter are washed more -than others.</p> - -<p>The rake is also necessary to prevent the separation of sand into -coarser and finer particles. It is practically impossible to get<span class="pagenum" id="Page_174">[Pg 174]</span> -filter sand the grains of which are all of the same size. When a filter -is washed the tendency is for the wash water to go up in limited areas. -The larger sand grains tend to collect at these points while the -finer grains collect in places where there is no upward current, or -where it is less rapid. In many filters this tendency is very strong. -The revolving rake is necessary to correct it, and to keep the sand -thoroughly mixed, otherwise when a filter is put in operation after -washing, the frictional resistance through the coarse sand being less, -the bulk of the water goes through it, with the result that a part of -the area, and the part which is least efficient as a filter, passes -nearly all of the water, and with inferior results.</p> - -<p>In the Jewell filter provision is made for the distribution of the wash -water over the whole area in another way. The strainers have areas at -the surface amounting to 1.2 to 1.4 per cent of the whole area, but -the water before reaching them passes through throats much smaller in -size than the strainer outlets, and amounting in the aggregate to only -about 0.07 per cent of the filter area. When washing at a rate of seven -gallons per square foot per minute, water passes through these necks -at a velocity of 22 feet per second. The friction and velocity head in -passing these necks is estimated to be about 30 vertical feet, and is -so much greater than the friction of the outlets proper, and of the -sand, that the water passes through each strainer with approximately -the same velocity, and the wash water is equally distributed over the -whole area of the bottom of the filter.</p> - -<p>This result is accomplished, however, at a great loss of head in the -wash water. When a filter is washed from the pressure-mains without -separate pumping, the pressure is usually sufficient and there is no -disadvantage in the arrangement. When, however, the water is specially -pumped for washing, the required head is much greater than would -otherwise be necessary.</p> - -<div class="figcenter padt1 padb1 illowp94" id="facing174" style="max-width: 93.75em;"> - <img class="w100" src="images/facing174.jpg" alt="" /> - <p class="caption"><span class="smcap">Mechanical Filters at Elmira, N. Y. Outlet to -Filters with Controller and Pure-water Flume.</span></p> - -<p class="right">[<em>To face page 174.</em>]</p></div> - -<p>It would not be possible to increase the size of the necks, thereby -decreasing the friction, without increasing very largely the -<span class="pagenum" id="Page_175">[Pg 175]</span> -size of the pipes in the underdrainage system into which the strainers are -fastened. These pipes are so small that during washing the velocity in -them is about 13 feet per second, and if the throats of the necks were -increased without also enlarging these pipes, the friction would be so -reduced that most of the water would go through the necks nearest the -supply, thus failing to reach the object to be attained.</p> - -<p>A more rational system would be to increase the sizes of all the -waterways in the outlet and wash-water system. The Jewell filter is -also provided with a rake to keep the sand mixed during washing, as -this is necessary even with the complete distribution of wash-water -over the area of the filter.</p> - -<p>Both the Warren and the Jewell filters are provided with receptacles -through which the water passes after receiving the coagulant, and -before entering the filter. In the Jewell filter the receptacle, called -a sedimentation-basin, is of such size as to hold as much water as is -filtered in 15 minutes. In the Warren filter the receptacle is entirely -independent and larger, holding about an hour’s supply.</p> - -<p>The rates of filtration used in the experiments have ranged from less -than 100 to about 130 million gallons per acre daily. To employ a rate -much higher than this involves the use of a much coarser sand, or an -increase in the height of water upon the filter to an impracticable -extent. There would seem to be no material advantage in the use of -lower rates within certain limits, while the cost of filters would be -greatly increased.</p> - -<p>The sand used in the Warren filters has been crushed quartz. In the -Jewell filters a silicious sand from Red Wing, Minn., with rounded -grains has been used. These sands are somewhat coarser than are -commonly used in sand filters, and the uniformity coefficients are -very low. It is necessary to use sand with the very lowest uniformity -coefficients to avoid the separation of sand particles according to -sizes as mentioned above, and for this reason<span class="pagenum" id="Page_178">[Pg 178]</span> the sand must be -selected with much greater care than is required for sand filters.</p> - -<div class="figcenter padt1 illowp100" id="image176_1" style="max-width: 107.8125em;"> - <img class="w100" src="images/image176_1.jpg" alt="" /> - <p class="caption"><span class="sans large">PLAN JUST ABOVE COPPER.</span></p></div> - -<div class="figcenter padb1 illowp94" id="image176_2" style="max-width: 117.375em;"> - <img class="w100" src="images/image176_2.jpg" alt="" /> - <p class="caption"><span class="sans large">SECTION SHOWING FILTER DURING ORDINARY OPERATION.</span><br /> -<span class="smcap small">Fig. 23.—Warren Filter: Pittsburg Experiments. Section No. 1.</span></p></div> - -<div class="figcenter padt1 illowp89" id="image177_1" style="max-width: 83em;"> - <img class="w100" src="images/image177_1.jpg" alt="" /> - <p class="caption sans large">PLAN OF AGITATOR, GUTTER CASTINGS, ETC.</p></div> - -<div class="figcenter padb1 illowp93" id="image177_2" style="max-width: 112.625em;"> - <img class="w100" src="images/image177_2.jpg" alt="" /> - <p class="caption"><span class="sans large">SECTION SHOWING FILTER DURING OPERATION OF WASHING.</span><br /> -<span class="smcap">Fig. 24.—Warren Filter: Pittsburg Experiments. Section No. 2.</span></p></div> - -<p>The round-grained sand is more readily and completely washed than the -angular crushed quartz. It has been claimed that the crushed quartz is -more efficient as a filtering material, but the evidence of this is not -very clear.</p> - -<p>The amount of water filtered by a filter between washings is, in a -general way, about the same as that filtered by a sand filter between -scrapings, in relation to its area. The amount of water required for -washing is, on an average, about equal to a vertical column 5 or 6 -feet high equal in area to the area of the filter, exclusive of water -on the top of the filter wasted before the current is reversed. With -clear waters, as for instance, the Allegheny at low water, the amount -of washing is almost directly proportional to the amount of sulphate -of alumina used. With muddy waters the sulphate of alumina required is -proportional to the mud, and the frequency of washing and the amount of -wash-water are proportional to both. The amount of wash-water required -averages about five per cent; with very muddy waters more is required. -At Louisville, with the worst waters, the per cents of wash-water rose -at times to 30 per cent of the total quantity of water filtered.</p> - -<p>The rate of filtration with mechanical filters should be kept as -constant as possible, and can be regulated by devices similar to -those described in connection with sand filters. Owing to the smaller -areas and capacities, the amounts of water to be handled in the units -are smaller, and the regulating devices are thus smaller, and have -always been made of metal, either cast iron or copper. None of the -devices employed in the above-mentioned experiments has been entirely -satisfactory in this respect. The devices employed have been too small, -and the water has gone through at too high velocities to allow close -adjustment.</p> - -<div class="figcenter padt1 padb1 illowp97" id="facing178" style="max-width: 112.5em;"> - <img class="w100" src="images/facing178.jpg" alt="" /> - <p class="caption"><span class="smcap">Mechanical Filters at Elmira, N. Y. Upper Platform -and General Arrangement of Filters.</span></p> - -<p class="right">[<em>To face page 178.</em>]</p></div> - -<p>As between the two types of filters, the Jewell filter requires a large -loss of head. The water has to be pumped at a sufficient elevation -to reach the top of a tank about 18 feet high, while the -<span class="pagenum" id="Page_179">[Pg 179]</span> effluent -must be drawn off at the extreme bottom. The Warren filter is much -more economical in head, the plants at Pittsburg and Louisville only -requiring about 9 feet from the inlet to the outlet.</p> - -<p>The earlier mechanical filters were usually constructed of wrought -iron or steel plates. More recently wooden tanks have been commonly -employed, although steel is regarded as preferable. Concrete or masonry -tanks have been suggested, but they have not as yet been employed.</p> - -<div class="section"> -<h3 class="nobreak" id="EFFICIENCY_OF_MECHANICAL_FILTERS">EFFICIENCY OF MECHANICAL FILTERS.</h3></div> - -<p>The efficiency of mechanical filters depends entirely upon the use of -coagulants. Without coagulants they can only be used to remove very -large particles. The efficiency of the filtration depends much more -upon the kind, and amount, and method of application of coagulant than -upon the arrangement of the filter. In fact, the arrangements of the -filter are more directed to the convenience and economy of operation -and washing than towards the efficiency of the results.</p> - -<p>The conditions which control the efficiency of mechanical filters -have been discussed in connection with coagulation. With sufficient -coagulant the removal of turbidity or mud is complete. Color also can -be removed with these filters. The bacterial efficiencies secured with -them have been discussed at length in connection with the Pittsburg -experiments.</p> - -<p>With careful coagulation and manipulation it is possible to get 98 per -cent bacterial efficiency without difficulty. The results are somewhat -irregular, for reasons not as yet fully understood. On some occasions -higher bacterial efficiencies are secured with smaller quantities of -coagulant, while at other times the efficiencies are less without -apparent reason. There seems to be a limit to the bacterial efficiency -which can be secured with any amount of sulphate of alumina and -rapid filtration, and it is doubtful if a plant could be operated to -regularly secure as high a bacterial efficiency as 99 per cent with any -amount of sulphate of alumina.</p> - -<p><span class="pagenum" id="Page_180">[Pg 180]</span></p> - -<div class="section"> -<h3 class="nobreak" id="PRESSURE_FILTERS">PRESSURE FILTERS.</h3></div> - -<p>Pressure mechanical filters are constructed in entirely closed -receptacles, through which the water is forced under pressure and not -by gravity. Many of the earlier mechanical filters were of this type. -In small plants this system has the distinct advantage that the water -can be pumped from a river or other source of supply through a filter -direct to the reservoir or into the mains, while any other system would -involve a second pumping. Pressure filters are extensively used for -hotel supplies, etc., where, from the conditions, gravity filters are -impossible. The practical objections to this system have been found -to be so great that it is rarely used under other conditions. Some -experiments were made at Louisville with a filter of this type, but -they were not long continued, and aside from them there is no precise -information as to what can be accomplished with filters of this type.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_181">[Pg 181]</span></p> - -<h2 class="nobreak" id="CHAPTER_XI">CHAPTER XI.<br /> -<br /> - -<span class="smaller">OTHER METHODS OF FILTRATION.</span></h2></div> - -<div class="section"> -<h3 class="nobreak" id="WORMS_TILE_SYSTEM">WORMS TILE SYSTEM.</h3></div> - -<p><span class="smcap">This</span> system, invented and patented by Director Fischer of the Worms -water-works, consists of the filtration of water through artificial -hollow sandstone tiles, made by heating a mixture of broken glass -and sand, sifted to determined sizes, to a point just below the -melting-point of the glass, in suitable moulds or forms. The glass -softens and adheres to the sand, forming a strong porous substance -through which water can be passed. These tiles are made hollow and -are immersed in the water to be treated, the effluent being removed -from the centre of each tile. They are connected together in groups -corresponding in size to the units of a sand-filtration plant. They -are washed by a reverse current of filtered water. These tiles have -been used for some years at Worms, Germany, and at a number of smaller -places, and were investigated experimentally at Pittsburg. Some -difficulty has been experienced in getting tiles with pores small -enough to yield an effluent of the desired purity, and at the same time -large enough to allow a reasonable quantity of water to pass. In fact, -with other than quite clear waters, it has not been found feasible to -accomplish both objects at the same time, and it has been necessary -to treat the water with coagulants and preliminary sedimentation or -filtration before applying it to the tiles. The problem of making the -joints between the tiles and the collection-pipes water-tight when -surrounded by the raw water also is a matter of some difficulty.</p> - -<div class="section"> -<h3 class="nobreak" id="THE_USE_OF_ASBESTOS">THE USE OF ASBESTOS.</h3></div> - -<p>It has been suggested by Mr. P. A. Maignen that the surface of sand -filters should be covered with a thin layer of asbestos,<span class="pagenum" id="Page_182">[Pg 182]</span> applied in -the form of a pulp, with the first water put onto the filter after -scraping. The asbestos forms a sort of a paper on the sand which -intercepts the sediment of the passing water. The advantage of the -process is in the cleaning. When dried to the right consistency this -asbestos can be rolled up like a carpet, and taken from the filter -without removing any of the sand.</p> - -<p>This procedure is almost identical with that which has occurred -naturally in iron-removal plants, where algæ grow in the water upon the -filters, and form a fibrous substance with the ferric oxide removed -from the water, which can be rolled up and removed in the same way -as the asbestos. The advantages of the process, from an economical -standpoint, are less clear.</p> - -<div class="section"> -<h3 class="nobreak" id="FILTERS_USING_HIGH_RATES_OF_FILTRATION_WITHOUT_COAGULANTS"> -FILTERS USING HIGH RATES OF FILTRATION WITHOUT COAGULANTS.</h3></div> - -<p>Numerous filters have been suggested, and a few have been constructed -for the use of much higher rates of filtration than are usually -employed with sand filters, but without the use of coagulants. The -results obtained depend upon the requirements and upon the character -of the raw water. If a reservoir water contains an algæ growth, it can -often be removed by a coarse and rapid filter. The organisms in this -case are many times larger than the bacteria, and many times larger -than the clay particles which constitute turbidity. The requirements in -this case are rather in the nature of straining than of filtration.</p> - -<p>The conditions necessary for the removal of bacteria and turbidity are -very well understood, and it can be stated with the utmost confidence -that no system of filtration through sand at rates many times as -high as are used in ordinary sand filtration, and without the use of -coagulants, will be satisfactory where either bacterial efficiency -or clarification is required. The application of such systems of -filtration would therefore seem to be somewhat limited.</p> - -<div class="figcenter padt1 padb1 illowp100" id="facing182" style="max-width: 125em;"> - <img class="w100" src="images/facing182.jpg" alt="" /> - <p class="caption"><span class="smcap">Removing Dirty Asbestos Covering from an -Experimental Filter. Maignen System.</span></p> -<p class="right">[<em>To face page 182.</em>]</p></div> - -<p><span class="pagenum" id="Page_183">[Pg 183]</span></p> - -<div class="section"> -<h3 class="nobreak" id="HOUSEHOLD_FILTERS">HOUSEHOLD FILTERS.</h3></div> - -<p>The subject of household filters is a somewhat broad one, as the -variety in these filters is even greater than in the larger filters, -and the range in the results to be expected from them is at least as -great. I shall only attempt to indicate here some of the leading points -in regard to them.</p> - -<p>Household filters may be used to remove mud or iron rust from the tap -water, or to remove the bacteria in case the latter is sewage-polluted, -or to do both at once. Perhaps oftener they are used simply because -it is believed to be the proper thing, and without any clear -conception either of the desired result or the way in which it can -be accomplished. I shall consider them only in their relations to -the removal of bacteria, as I credit the people who employ them with -being sufficiently good judges of their efficiency in removing visible -sediment.</p> - -<p>In the first place, as a general rule, which has very few if any -exceptions, we may say that all small filters which allow a good stream -of water to pass do not remove the bacteria. The reason for this is -simply that a material open enough to allow water to pass through it -rapidly is not fine enough to stop such small bodies as the bacteria. -The filters which are so often sold as “germ-proof,” consisting of -sand, animal charcoal, wire-cloth, filter-paper, etc., do not afford -protection against any unhealthy qualities which there may be in the -raw water. Animal charcoal removes color without retaining the far more -objectionable bacteria.</p> - -<p>The other household filters have filtering materials of much finer -grain, unglazed porcelain and natural sandstone being the most -prominent materials, while infusorial earth is also used. The smaller -sizes of these filters allow water to pass only drop by drop, and when -a fair stream passes them the filters have considerable filtering -area (as a series of filter-tubes connected together). On account of -their slow action, filters of this class are, as a rule, provided with -storage reservoirs so that filtered water to the<span class="pagenum" id="Page_184">[Pg 184]</span> capacity of the -reservoir can be drawn rapidly (provided the calls do not come too -often). Some of these filters are nearly germ-proof, and are comparable -in their efficiency to large sand-filters. There is no sharp line -between the filters which stop and which do not stop the bacteria; but -in general the rule that a filter which works rapidly in proportion to -its size does not do so, and <em>vice versa</em>, will be found correct.</p> - -<p>In thinking of the efficiency of household filters we must distinguish -between the filter carefully prepared for an award at an exhibition -and the filter of the same kind doing its average daily work in the -kitchen. If we could be sure in the latter case that an unbroken layer -of fine sandstone or porcelain was always between ourselves and the raw -tap-water we could feel comparatively safe. The manufacturers of the -filters claim that leaky joints, cracked tubes, etc., are impossible; -but I would urge upon the people using water filtered in this way that -they personally assure themselves that this is actually the case with -their own filters, for in case any such accident should happen the -consequences might be most unpleasant. The increased yield of a filter -due to a leaky joint is sure not to decrease it in favor with the cook, -who is probably quite out of patience with it because it works so -slowly, that is, in case it is good for anything.</p> - -<p>The operation of household filters is necessarily, with rare -exceptions, left to the kitchen-girl and luck. Scientific supervision -is practically impossible. With a large filter, on the other hand, -concentrating all the filters for the city at a single point, a -competent man can be employed to run them in the best-known way; and -if desired, and as is actually done in very many places, an entirely -independent bacteriologist can be employed to determine the efficiency -of filtration. With the methods of examination now available, and -a little care in selecting the times and places of collecting the -samples, it is quite impossible for a filter-superintendent to -deliver a poor effluent very often or for any considerable length of -time without being caught. The safety of properly-conducted central -filtration is thus infinitely greater<span class="pagenum" id="Page_185">[Pg 185]</span> than that from even the best -household filters. Further, it may be doubted whether an infected water -can be sent into every house in the city to be used for washing and all -the purposes to which water is put except drinking, without causing -disease, although less than it would if it were also used for drinking.</p> - -<p>The use of household filters must be regarded as a somewhat desperate -method of avoiding some of the bad consequences of a polluted -water-supply, and they are adopted for the most part by citizens who -in some measure realize the dangers from bad water, but who cannot -persuade their fellow-citizens to a more thorough and adequate solution -of the problem. Such citizens, by the use of the best filters, and by -carefully watching their action, or by having their drinking-water -boiled, can avoid the principal dangers from bad water, but their -vigilance does not protect their more careless neighbors.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_186">[Pg 186]</span></p> - -<h2 class="nobreak" id="CHAPTER_XII">CHAPTER XII.<br /> -<br /> - -<span class="smaller">REMOVAL OF IRON FROM GROUND-WATERS.</span></h2></div> - -<p><span class="smcap">The</span> filtration of ground-waters is a comparatively recent development. -Ground-waters are filtered by their passage through soil generally -much more perfectly than it is possible to filter other waters, and -any further filtration of them is useless. Such waters, however, -occasionally contain iron in solution as ferrous carbonate.</p> - -<p>Waters containing iron have been used as mineral waters for a very long -time. Such waters have an astringent taste, and have been esteemed -for some purposes. As ordinary water-supplies, however, they are -objectionable. The iron deposits in the pipes when the current is -slow, and is flushed out when it is rapid, and makes the water turbid -and disagreeable; and still worse, the iron often gets through the -pipe-system in solution, and deposits in the wash-tub, coloring the -linen a rusty brown and quite spoiling it.</p> - -<p>An organism called crenothrix grows in pipes carrying waters containing -iron, and after a while this organism dies, and decomposes, and -gives rise to very disagreeable tastes and odors. It thus happens -that ground-waters containing iron are unsatisfactory as public -water-supplies, and are sources of serious complaint.</p> - -<div class="section"> -<h3 class="nobreak" id="AMOUNT_OF_IRON_REQUIRED_TO_RENDER_WATER_OBJECTIONABLE"> -AMOUNT OF IRON REQUIRED TO RENDER WATER OBJECTIONABLE. -</h3></div> - -<p>Three hundredths of a part in 100,000 of metallic iron very rarely -precipitate or cause any trouble. Five hundredths occasionally -precipitate, and this amount may be taken as about the allowable -limit of iron in a satisfactory water. One tenth of a part is quite -sure to precipitate and give rise to serious complaint. Two or three -tenths make the water entirely unsuitable for<span class="pagenum" id="Page_187">[Pg 187]</span> laundry purposes, and -are otherwise seriously objectionable, and will hardly be tolerated -by a community. Under some conditions ground-waters carry as much -as 1 part in 100,000 of iron, and such waters are hardly usable. In -iron-removal plants an effluent containing less than 0.05 is regarded -as satisfactory. One containing less than 0.02, as is the case with -many plants, is all that can be desired. The percentage of removal is -of no significance, but only the amount left in the effluent.</p> - -<div class="section"> -<h3 class="nobreak" id="CAUSE_OF_IRON_IN_GROUND_WATERS"> -CAUSE OF IRON IN GROUND-WATERS.</h3></div> - -<p>Natural sands, gravels, and rocks almost always contain iron, often in -considerable amount. The iron is usually combined with oxygen as ferric -oxide, and in this condition it is insoluble in water. Water passing -through iron containing materials will not ordinarily take up iron. -When, however, the water contains a large amount of organic matter in -solution, this organic matter takes part of the oxygen away from the -iron, and reduces the ferric oxide to ferrous oxide. The ferrous oxide -combines with carbonic acid, always present under these conditions, -forming ferrous carbonate, which is soluble and which goes into -solution.</p> - -<p>Surface-waters nearly always carry free oxygen, and when such waters -enter the ground they carry oxygen with them, and the organic matters -in the water use up the free oxygen before they commence to take oxygen -away from the iron of the ground. It is thus only in the presence of -organic matters, and in the absence of free oxygen, that the solution -of iron is possible. It sometimes happens that the organic matters -which reduce the iron are contained in the soil itself, in which -case iron may be taken up even by water originally very pure, as for -instance, by rain-water.</p> - -<p>Generally speaking, iron is everywhere present in sufficient quantity -in the strata from which ground-waters are obtained, and wherever the -conditions of the organic matters and oxygen necessary for solution -occur, iron-containing waters are secured, and the iron is usually -present in the earth in such quantity that the water<span class="pagenum" id="Page_188">[Pg 188]</span> can dissolve as -much as it will take up for a long series of years, or for centuries, -without exhausting the supply. There is thus little prospect of -improvement of such waters from exhaustion of the supply of iron.</p> - -<p>The circumstances which control the solution of iron are very -complicated and difficult to determine. Wells near a river, and drawing -their water largely from it by seepage, are apt to yield a water -containing iron sooner or later, especially where the river-water -carries a large amount of organic matter in solution. Waters drawn from -extensive gravel deposits, in which the water is renewed principally by -the rainfall upon the surface of the deposits themselves, often remain -entirely free from iron indefinitely. The rain-water is almost free -from organic matter, and the air is able to take care of decomposing -organic matters in the surface soil, and below this there are no -accumulations of organic matter sufficient to cause the solution of -iron. Under other conditions there are subterranean sources of organic -matter which result in the solution of iron under conditions which, on -the surface, appear most favorable for securing good water. Wells are -often used for many years without developing iron, when suddenly iron -will appear. This appearance of iron is often connected with increasing -consumption of water. In some cases it may result from drawing water -from areas not previously drawn upon.</p> - -<p>When iron once makes its appearance in a water, it seldom disappears -completely afterward, although it often fluctuates widely at different -seasons of the year and under different conditions of pumping. In some -cases a decrease in the quantity of iron is noted after a number of -years, but in other cases this does not happen.</p> - -<p>In a few cases manganese has been found in ground-waters. Manganese in -water behaves much like iron, but there are some points of difference, -so that the possibility of the presence of this substance should be -borne in mind.</p> - -<p>Iron-containing waters are generally entirely free from oxygen,<span class="pagenum" id="Page_189">[Pg 189]</span> and -when first drawn from the ground they are bright and clear and do not -differ in appearance from other ground-waters. On exposure to the air -they quickly become turbid from the oxidation of the iron, and its -precipitation as ferric hydrate. At West Superior, Wisconsin, a water -was found containing both iron and dissolved oxygen. It was turbid -as pumped from the well. This condition of affairs seemed abnormal, -but was repeatedly checked, and the theory was advanced by Mr. R. S. -Weston, who made the observations, that it resulted from a mixture in -the wells of two entirely different waters, namely, a water resulting -from the rainfall on sand deposits back of the wells, containing -dissolved oxygen and no iron, and water from the lake which had seeped -through the sand, and which contained a considerable amount of iron -in solution but no dissolved oxygen. The wells thus drew water from -opposite directions, and the two waters were entirely different in -character, and the mixture thus had a composition which would not have -been possible in a water all of which came from a single source.</p> - -<div class="section"> -<h3 class="nobreak" id="TREATMENT_OF_IRON_CONTAINING_WATERS"> -TREATMENT OF IRON-CONTAINING WATERS.</h3></div> - -<p>The removal of iron from ground-water is ordinarily a very simple -procedure. It is simply necessary to aerate the water, by which process -the ferrous carbonate is decomposed, and oxidized with the formation -of ferric hydrate, which forms a flocculent precipitate and is readily -removed by filtration. The aeration required varies in different cases. -The quantity of oxygen required to oxidize the iron is only a small -fraction of the amount which water will dissolve, and allowing water to -simply fall through the air for a few feet in fine streams will usually -supply several times as much oxygen as is necessary for this purpose.</p> - -<p>Aerating devices of this kind have proved sufficient in a number of -cases, as at Far Rockaway, L. I., and at Red Bank, N. J. In some cases, -however, a further aeration is necessary, not for the purpose of -getting more oxygen into the water,<span class="pagenum" id="Page_190">[Pg 190]</span> but to get the excess of carbonic -acid out of it. Carbonic acid seems to retard in some way the oxidation -of the iron, and it is occasionally present in ground-waters in -considerable quantity, and quite seriously interferes with the process. -It can be removed sufficiently by aeration, but the necessary amount of -exposure to air is much greater than that required to simply introduce -oxygen.</p> - -<p>Coke-towers have sometimes been used for this purpose. The towers are -filled with coarse coke and have open sides, and water is sprinkled -over the tops of them and allowed to drip through to the bottoms. In -general the simple exposure of water to the air for a sufficient length -of time, in any form of apparatus or simply in open channels, will -accomplish the desired results.</p> - -<p>Mr. H. W. Clark<a id="FNanchor_45" href="#Footnote_45" class="fnanchor">[45]</a> has called attention to the fact that in some cases -coke seems to have a direct chemical action upon the water which is -entirely independent of its aerating effect. In his experiments there -seemed to be some property in the coke which caused the iron to oxidize -and flocculate in many cases when it refused to do so with simple -aeration and filtration.</p> - -<p>When the right conditions are reached the oxidation of the iron is -very rapid, and it separates out in flakes of such size that they can -be removed by filtration at almost any practicable rate. Mechanical -filters have been used for this purpose, with rates of filtration -of 100 million gallons per acre daily. In Germany, where plants for -the removal of iron are quite common, modified forms of sand filters -have usually been employed which have been operated at rates up to 25 -million gallons per acre daily.</p> - -<p>In experiments made by the Massachusetts State Board of Health rates -from 10 to 25 million gallons per acre daily have been employed.</p> - -<p>The sand used for filtration may appropriately be somewhat coarser than -would be used for treating surface-waters, and the thickness of the -sand layer may be reduced. Owing to the higher<span class="pagenum" id="Page_191">[Pg 191]</span> -rates the underdrainage system must be more ample than is otherwise -necessary.</p> - -<p>The rate of filtration employed is usually not a matter of vital -importance, but by selecting a rate that is not too high it is possible -to use a moderate loss of head. It is thus not necessary to clean the -filters too often, and the expenses of operation are not as high as -with an extreme rate. In some cases it is desired to accomplish other -results than the removal of iron by filtration, and this may lead to -the selection of a rate lower than would otherwise be used.</p> - -<p>Under normal conditions of operation all of the iron separates on the -top of the sand. No appreciable amount of it penetrates the sand at -all. With open filters at Far Rockaway and at Red Bank there is an algæ -growth in the water upon the filters which, with the iron, forms a -mat upon the surface of the filter; and when the filter is put out of -service and allowed to partially dry, this mat can be rolled up like a -carpet and thrown off without removing any sand, and the filters have -been in use for several years without renewing any sand and without any -important decrease in the thickness of the sand layer.</p> - -<p>Some waters contain iron in such a form that it cannot be successfully -removed in this manner. Thus at Reading, Mass., it was reported by -Dr. Thomas M. Drown that the iron was present in the form of ferrous -sulphate instead of ferrous carbonate, and that it was not capable of -being separated by simple aeration and filtration. A Warren mechanical -filter was installed, and the water is treated by aeration and with -the addition of lime and alum. The cost of the process is thereby much -increased, and the hardness of the water is increased threefold.</p> - -<p>Several other cases have been reported where it was believed that -simple aeration and filtration were inadequate; but the advantages of -the simple procedure are so great as to make it worth a very careful -study to determine if more complete aeration, or the use of coke-towers -and perhaps slower filtration, would not serve<span class="pagenum" id="Page_192">[Pg 192]</span> in these cases without -resorting to the use of chemicals and their attendant disadvantages.</p> - -<div class="section"> -<h3 class="nobreak" id="IRON_REMOVAL_PLANTS_IN_OPERATION"> -IRON-REMOVAL PLANTS IN OPERATION.</h3></div> - -<p>Iron-removal plants are now in use at Amsterdam and The Hague in -Holland, at Copenhagen in Denmark, at Kiel, Charlottenburg, Leipzig, -Halle, and many other places in Germany; at Reading, Mass.; Far -Rockaway, L. I.; Red Bank, Asbury Park, Atlantic Highlands, and -Keyport, N. J.</p> - -<p>Among the earliest plants for the removal of iron were the filters -constructed at Amsterdam and The Hague in Holland. At Amsterdam the -water is derived from open canals in the dunes draining a large area. -The water has its origin in the rain-water falling upon the sand. The -sand is very fine and contains organic matter in sufficient amount -so that the ground-water is impregnated with iron. In flowing to a -central point in the open canals the water becomes aerated and the iron -oxidized. There are also algæ growths in the water which perhaps aid -the process. Sand filters of ordinary construction are used, and remove -both the iron and the algæ, and the rate of filtration is not higher -than is usually used in the treatment of river-waters, although it -could probably be largely increased without detriment to the supply.</p> - -<p>The works at The Hague are very similar to those at Amsterdam, but -covered collectors are used to supplement the open canals. Both -of these plants were built before much was known about iron in -ground-waters and the means for its removal, but they have performed -their work with uniformly satisfactory results. In the more recent -German works various aerating devices are employed, and filters similar -in general construction to ordinary sand filters, but with larger -connections suited to very high rates of filtration, are employed.</p> - -<p>The plant at Asbury Park was the first of importance constructed in -America. The water is raised from wells from 400 to 1100 feet deep -by compressed air by a Pohle lift. It is delivered<span class="pagenum" id="Page_193">[Pg 193]</span> into a square -masonry receiving-basin holding some hours’ supply. The aeration of -the water by this means is very complete. It is afterwards pumped -through Continental pressure filters direct into the service-pipes. The -reservoir for the aerated water was not a part of the original plant, -but was added afterwards to facilitate operation, and to give more -complete aeration before filtration.</p> - -<p>At Far Rockaway, L. I., the water is lifted from wells by a Worthington -Pump, and is discharged over the bell of a vertical 16-inch pipe, -from which it falls through the air to the water in a receiving -chamber around it. The simple fall through the air aerates the water -sufficiently. From the receiving-chamber the water is taken to either -or both of two filters, each with an area of 20,000 square feet. These -filters are open, with brick walls and concrete bottoms, three feet -of sand and one foot of gravel, and the underdrains are of the usual -type. The water flows through regulator-chambers to a well 25 feet in -diameter and 12 feet deep, from which it is pumped to a stand-pipe in -the town. The plant was built to treat easily three million gallons -per day, and has occasionally treated a larger quantity. Either filter -yields the whole supply while the other is being cleaned. The rate of -filtration in this case was made lower than would have otherwise been -necessary, as there was an alternate supply, namely, the water from -two brooks, which could be used on occasions, and to purify which a -lower rate of filtration was regarded necessary, than would have been -required for the well-water. The removal of iron is complete.</p> - -<div class="figcenter padt1 padb1 illowp72" id="image194" style="max-width: 87.5em;"> - <img class="w100" src="images/image194.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 25.</span></p></div> - -<p>The plant of the Rumson Improvement Company at Red Bank, N. J., is -quite similar to that at Far Rockaway, but is much smaller. The outlet -is a 6-inch pipe perforated with <sup>1</sup>⁄<sub>4</sub>-inch holes which throws the water -out in a pine-tree shape to the receiving-tank, thoroughly aerating -it. Each of the two filters has 770 square feet of area. The filtering -material is three feet of beach sand. From the regulator-chamber the -water flows to a circular well 18 feet in diameter, covered by a brick -dome and holding<span class="pagenum" id="Page_194">[Pg 194]</span> 17,000 gallons, from which it is pumped to the -stand-pipe. Either of the filters will treat ten thousand gallons of -water per hour, which is equal to the capacity of the pumps; and as -the consumption<span class="pagenum" id="Page_195">[Pg 195]</span> is considerably less than this figure, they are only -in use for a part of each day, the number of hours depending upon the -consumption. These filters are shown by the accompanying plan. The cost -of the work was as follows:</p> - -<table class="autotable" summary="Red Bank NJ costs"> -<tr> -<td class="tdr bord_right vertb"><p class="indent">Filters and pure-water reservoir, with piping and drains complete</p></td> -<td class="tdr vertb">$3,799.47</td> -</tr> -<tr> -<td class="tdr bord_right vertb"><p class="indent">New pump and connections</p></td> -<td class="tdr vertb">492.68</td> -</tr> -<tr> -<td class="tdr bord_right vertb"><p class="indent">Engineering and superintendence</p></td> -<td class="tdr vertb bord_bot">992.91</td> -</tr> -<tr> -<td class="tdr bord_right vertb"> Total cost of plant</td> -<td class="tdr vertt">$5,285.06</td> -</tr> -</table> - - -<p>The engineer who operates the pumps takes care of the filters, and no -additional labor has been required. The entire cost of operation is -thus represented by the additional coal required for the preliminary -lift from the wells to the filters. The effluent is always free from -iron.</p> - -<p>The plant at Reading,<a id="FNanchor_46" href="#Footnote_46" class="fnanchor">[46]</a> Mass., was installed by the Cumberland -Manufacturing Company, and combines aeration, treatment with lime and -sulphate of alumina and rapid filtration. The aeration is effected -by pumping air through the water, after the water has received the -lime. It afterwards receives sulphate of alumina and passes to a -settling-tank holding 40,000 gallons, in which the water remains for -about an hour. There are six filters of the Warren type, each with an -effective filtering area of 54 square feet.</p> - -<p>The cost of coagulant is considerable. The chief disadvantage of the -process is that it hardens the water, which is naturally soft. From -the completion of the plant in July, 1896, to the end of the year the -hardness of the water was increased, according to analyses of the State -Board of Health, from 4.1 to 11.3 parts in 100,000, and for the year -1897 the increase was from 4.0 to 12.7. The iron, which is present in -the raw water to the extent of about 0.26 part in 100,000, is removed -sufficiently at all times.</p> - -<p><span class="pagenum" id="Page_196">[Pg 196]</span></p> - -<p>Prior to the erection of this plant Mr. Desmond FitzGerald advised -aeration followed by sedimentation in two reservoirs holding half a -million gallons each, and by rapid filtration. Mr. Bancroft states that -in his opinion, if the reservoir recommended by Mr. FitzGerald had been -built, the filters could be run with very little or no coagulation, and -consequently without increase in hardness, which is the most obvious -disadvantage to the procedure. The nominal capacity of the plant is -one million gallons, and the average consumption about 200,000 gallons -daily.</p> - -<p>The plant at Keyport, N. J., is similar, but smaller.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_197">[Pg 197]</span></p> - -<h2 class="nobreak" id="CHAPTER_XIII">CHAPTER XIII.<br /> -<br /> - -<span class="smaller">TREATMENT OF WATERS.</span></h2></div> - -<p><span class="smcap">Having</span> now reviewed the most important methods in use for the treatment -of waters, we may take a general view of their application to various -classes of waters. Different raw waters vary so much, and the -requirements of filtration are so different, that it is not possible -to outline any general procedure or combination of procedures, but -each problem must be taken up by itself. Nevertheless, some general -suggestions may be of service.</p> - -<p>In the first place, we may consider the case of waters containing very -large quantities of oxidizable organic matter. Such waters are obtained -from some reservoirs containing very active vegetable and animal -growths, or from rivers receiving large amounts of sewage. Waters -of both of these classes are, if possible, to be avoided for public -water-supplies. When circumstances require their use, they can best be -treated by intermittent filtration, this process being best adapted to -the destruction by oxygen of excessive quantities of organic matter.</p> - -<p>Where the pollution is less, so that the dissolved oxygen contained -in the raw water is sufficient for the oxidation of the organic -matters, continuous filtration will give substantially as good results -as intermittent filtration, and in other respects it has important -advantages. The application of intermittent filtration for the -treatment of public water-supplies is thus somewhat limited, and, as a -matter of fact, it has been used in only a few cases.</p> - -<p>For the treatment of very highly polluted waters double filtration has -been used in a number of cases, notably by the Grand Junction Company -at London, at Schiedam in Holland, and at Bremen and Altona in Germany. -At the two first-mentioned<span class="pagenum" id="Page_198">[Pg 198]</span> places two separate systems of filters are -provided differing somewhat in construction, the first filters being at -a higher level than the after filters. The first filters supply water -of comparative purity, and very constant composition, to the after -filters, which are able to treat it with great efficiency and at very -low operating cost.</p> - -<p>This procedure is probably the most perfect which has been used for the -removal of disease-producing qualities from highly polluted waters; and -the cost of the process may not be as much greater than that of simple -filtration as would at first appear, because the cost of cleaning the -after filters is merely nominal, and the attendance, pumping, etc., -are practically common to both sets of filters, and are not materially -greater than they would be for a single set.</p> - -<p>For very bad waters the first filters might appropriately be -intermittent, while the after filters should be continuous. This was -the procedure originally intended for Lawrence, but the intermittent -filter first constructed yielded such very good results that it has not -been considered necessary to complete the plant as originally projected.</p> - -<p>At Bremen and at Altona a different procedure has been adopted. The -filters are all upon the same level, and of the same construction. -When a filter is put in service the effluent from it, instead of being -taken to the pure-water reservoir, is taken to another filter which -has already been some time in service. After the first filter has been -in operation for some time its effluent is taken to the pure-water -reservoir, and in turn it is supplied with the effluent from a filter -more recently cleaned. The loss of head of water passing a freshly -cleaned filter is comparatively slight, and the water of the second -filter is allowed to fall a few inches below the high-water mark, -at which level it will take the effluent from the other filter. The -connections between the filters are made by siphons of large pipe, the -summits of which are considerably above the high-water line. These -siphons are filled by exhausting the<span class="pagenum" id="Page_199">[Pg 199]</span> air, and when opened to the air -there is no possibility of a flow of water through them. The process -has given extremely good results in practice, yielding effluents of the -very greatest purity and at a quite moderate cost of operation.</p> - -<p>An objection to the method is the possible filling of a siphon some -time when the water standing upon the after-filter is higher than that -in the pure-water well of the fore-filter, and while the fore-filter is -connected with the pure-water reservoir. Such a connection would send -unfiltered water into the pure-water reservoir direct. I do not know -that any trouble of this kind has ever been experienced at Bremen or at -Altona; and the objection to this system is perhaps not well founded -where the management is careful and conscientious. The fact that an -unscrupulous attendant can make the connection at any time to help out -a deficiency of supply, or simply through carelessness, is certainly -objectionable.</p> - -<p>For the treatment of river-waters and lake-waters containing only -a small quantity of sediment, and where the removal of bacteria or -disease-producing qualities is the most important object of filtration, -sand filters can be used. Where the rivers are subject to floods and -moderate amounts of muddy water, sedimentation-basins or storage -reservoirs for raw water will often be found advantageous.</p> - -<p>For the treatment of extremely muddy waters, and waters which are -continuously muddy for long periods of time, and for the removal -of color from very highly colored waters, resource must be had to -coagulants. The coagulants which are necessary in each special case and -which can be used without injury to the water must be determined by -most careful investigation of the raw water.</p> - -<p>For the filtration of these waters after coagulation either sand or -mechanical filters can be employed. As the principal work in this -case is done by the coagulant, the kind of filtration employed is -of less consequence than where filtration alone is relied upon,<span class="pagenum" id="Page_200">[Pg 200]</span> -and the cheapest form of filter will naturally be employed. Under -present conditions mechanical filters will usually be cheaper than -sand filters for use in this way; but where waters, in addition to the -mud, carry bacteria in such large numbers as to make high bacterial -efficiency a matter of importance, sand filters may be selected, as the -bacterial efficiency obtained with them is not dependent upon the use -of coagulant; and is therefore less subject to interruptions from the -failure to apply coagulant in the right proportion.</p> - -<p>Mechanical filters have also been used for the treatment of -comparatively clear waters where bacterial efficiency was the principal -object of filtration. For this purpose the efficiencies obtained with -them are usually inferior to those obtained with sand filters, while -the cost of coagulants is so great as to make their use often more -expensive than that of sand filters.</p> - -<p>In the case of many streams which are comparatively clear for a part of -the year, but occasionally are quite turbid, the use of sand filters -has this advantage, that the use of coagulants can be stopped and the -cost of operation reduced whenever the water is clear enough to allow -of satisfactory treatment by them; and that coagulant can be employed -on those days when otherwise insufficient clarification would be -obtained.</p> - -<p>In this case the high bacterial efficiency is secured at all times, -while the cost of coagulant is saved during the greater part of the -time. In such cases, also, the preliminary process of sedimentation and -storage should be developed as far as possible.</p> - -<p>The application of other processes of filtration to special problems -are not sufficiently well understood to allow general discussion, and -must be taken up separately with reference to the requirements of each -special situation.</p> - -<div class="section"> -<h3 class="nobreak" id="COST_OF_FILTRATION">COST OF FILTRATION.</h3></div> - -<p>The cost of filtration of water depends upon the character of the raw -water, upon the nature of the plant employed, upon its<span class="pagenum" id="Page_201">[Pg 201]</span> size, and -upon the skill and economy of manipulation. These conditions affect -the cost to such an extent as to make any accurate general estimate -quite impossible. Nevertheless a little consideration of the subject, -although not leading to exact results, may be helpful as furnishing a -rough idea of the probable cost before estimates for local conditions -are made.</p> - -<p>Open sand filters, with masonry walls, with reasonably favorable -conditions of construction, and not too small in area, have averaged -to cost in the United States within the last few years perhaps about -thirty thousand dollars per acre. The relative cost of small plants is -somewhat greater, and with embankments instead of masonry walls, the -cost is somewhat reduced. The cost is less where natural deposits of -sand can be made use of practically in their original condition, and is -increased where the filtering materials have to be transported by rail -for long distances, or where the sites are difficult to build upon. -Covered filters cost about a half more than open filters. Mechanical -filters at current prices cost about $20 per square foot of filtering -area, to which must be added the cost of foundations and buildings, -which perhaps average to cost half as much more, but are dependent upon -local conditions and the character of the buildings.</p> - -<p>To these figures must be added the costs of pumps, reservoirs, -sedimentation-basins, and pipe-connections, which are often greater -than the costs of the filters, but which differ so widely in different -cases as to make any general estimate impossible.</p> - -<p>Filters must be provided sufficient to meet the maximum and not the -average consumption. The excess of maximum over average requirements -varies greatly in different cities, and depends largely upon reservoir -capacities and arrangements.</p> - -<p>As a result of a considerable number of estimates made by the author -for average American conditions, the cost of installing filters may -be taken very roughly as five dollars per inhabitant, but the amounts -differ widely in various cases.</p> - -<p>The cost of operation of sand filters in England probably<span class="pagenum" id="Page_202">[Pg 202]</span> averages -about one dollar per million gallons of water filtered. The following -table shows the costs of operation of the filters of the seven London -companies for fifteen years, compiled in the office of Mr. W. B. Bryan, -Chief Engineer of the East London Water Company. The results have been -computed to dollars per million U. S. gallons, and include the cost of -all labor, sand, and supplies for the filters, but do not include any -pumping or interest costs.</p> - -<table class="autotable" summary="costs of operation of the seven London -companies"> -<tr> -<th class="tdc normal" colspan="9">COST OF FILTRATION, LONDON WATER COMPANIES.</th> -</tr> -<tr> -<th class="tdc normal" colspan="9">(Computed from data furnished Wm. B. Bryan, C.E., East London Water Works.)</th> -</tr> -<tr> -<th class="tdc normal small" colspan="9">Dollars per Million U. S. Gallons.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot"> </th> -<th class="tdc normal small bord_top bord_right bord_bot">Chelsea<br />Co.</th> -<th class="tdc normal small bord_top bord_right bord_bot">East<br />London<br />Co.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Grand<br />Junction<br />Co.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Lambeth<br />Co.</th> -<th class="tdc normal small bord_top bord_right bord_bot">New<br />River<br />Co.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Southwark<br />&<br />Vauxhall<br />Co.</th> -<th class="tdc normal small bord_top bord_right bord_bot">West<br />Middlesex<br />Co.</th> -<th class="tdc normal small bord_top bord_bot">Average.</th> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1880-1</td> -<td class="tdc bord_right vertb">1.16</td> -<td class="tdc bord_right vertb">1.16</td> -<td class="tdc bord_right vertb">1.00</td> -<td class="tdc bord_right vertb">0.83</td> -<td class="tdc bord_right vertb">1.34</td> -<td class="tdc bord_right vertb">1.16</td> -<td class="tdc bord_right vertb">1.67</td> -<td class="tdc">1.19</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1881-2</td> -<td class="tdc bord_right vertb">1.19</td> -<td class="tdc bord_right vertb">1.39</td> -<td class="tdc bord_right vertb">0.95</td> -<td class="tdc bord_right vertb">0.82</td> -<td class="tdc bord_right vertb">1.15</td> -<td class="tdc bord_right vertb">1.37</td> -<td class="tdc bord_right vertb">1.54</td> -<td class="tdc">1.20</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1882-3</td> -<td class="tdc bord_right vertb">1.10</td> -<td class="tdc bord_right vertb">1.23</td> -<td class="tdc bord_right vertb">1.39</td> -<td class="tdc bord_right vertb">0.96</td> -<td class="tdc bord_right vertb">1.40</td> -<td class="tdc bord_right vertb">1.47</td> -<td class="tdc bord_right vertb">1.74</td> -<td class="tdc">1.33</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1883-4</td> -<td class="tdc bord_right vertb">1.00</td> -<td class="tdc bord_right vertb">1.06</td> -<td class="tdc bord_right vertb">1.73</td> -<td class="tdc bord_right vertb">0.92</td> -<td class="tdc bord_right vertb">1.11</td> -<td class="tdc bord_right vertb">1.62</td> -<td class="tdc bord_right vertb">1.67</td> -<td class="tdc">1.30</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1884-5</td> -<td class="tdc bord_right vertb">1.06</td> -<td class="tdc bord_right vertb">1.06</td> -<td class="tdc bord_right vertb">1.82</td> -<td class="tdc bord_right vertb">0.90</td> -<td class="tdc bord_right vertb">1.02</td> -<td class="tdc bord_right vertb">1.40</td> -<td class="tdc bord_right vertb">1.30</td> -<td class="tdc">1.22</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1885-6</td> -<td class="tdc bord_right vertb">1.15</td> -<td class="tdc bord_right vertb">1.16</td> -<td class="tdc bord_right vertb">1.35</td> -<td class="tdc bord_right vertb">0.90</td> -<td class="tdc bord_right vertb">1.00</td> -<td class="tdc bord_right vertb">1.15</td> -<td class="tdc bord_right vertb">1.07</td> -<td class="tdc">1.11</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1886-7</td> -<td class="tdc bord_right vertb">0.80</td> -<td class="tdc bord_right vertb">0.96</td> -<td class="tdc bord_right vertb">1.39</td> -<td class="tdc bord_right vertb">0.87</td> -<td class="tdc bord_right vertb">0.98</td> -<td class="tdc bord_right vertb">1.43</td> -<td class="tdc bord_right vertb">1.70</td> -<td class="tdc">1.16</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1887-8</td> -<td class="tdc bord_right vertb">1.07</td> -<td class="tdc bord_right vertb">1.22</td> -<td class="tdc bord_right vertb">1.74</td> -<td class="tdc bord_right vertb">0.90</td> -<td class="tdc bord_right vertb">0.92</td> -<td class="tdc bord_right vertb">1.28</td> -<td class="tdc bord_right vertb">1.00</td> -<td class="tdc">1.16</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1888-9</td> -<td class="tdc bord_right vertb">0.83</td> -<td class="tdc bord_right vertb">1.28</td> -<td class="tdc bord_right vertb">1.55</td> -<td class="tdc bord_right vertb">0.95</td> -<td class="tdc bord_right vertb">0.98</td> -<td class="tdc bord_right vertb">1.52</td> -<td class="tdc bord_right vertb">0.83</td> -<td class="tdc">1.13</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1889-90</td> -<td class="tdc bord_right vertb">0.66</td> -<td class="tdc bord_right vertb">1.50</td> -<td class="tdc bord_right vertb">1.22</td> -<td class="tdc bord_right vertb">0.88</td> -<td class="tdc bord_right vertb">0.90</td> -<td class="tdc bord_right vertb">1.70</td> -<td class="tdc bord_right vertb">3.56</td> -<td class="tdc">1.49</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1890-1</td> -<td class="tdc bord_right vertb">0.72</td> -<td class="tdc bord_right vertb">1.42</td> -<td class="tdc bord_right vertb">1.32</td> -<td class="tdc bord_right vertb">0.85</td> -<td class="tdc bord_right vertb">1.02</td> -<td class="tdc bord_right vertb">1.16</td> -<td class="tdc bord_right vertb">1.00</td> -<td class="tdc">1.07</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1891-2</td> -<td class="tdc bord_right vertb">0.75</td> -<td class="tdc bord_right vertb">1.54</td> -<td class="tdc bord_right vertb">1.23</td> -<td class="tdc bord_right vertb">1.00</td> -<td class="tdc bord_right vertb">0.92</td> -<td class="tdc bord_right vertb">1.15</td> -<td class="tdc bord_right vertb">0.96</td> -<td class="tdc">1.08</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1892-3</td> -<td class="tdc bord_right vertb">0.67</td> -<td class="tdc bord_right vertb">1.42</td> -<td class="tdc bord_right vertb">1.30</td> -<td class="tdc bord_right vertb">1.19</td> -<td class="tdc bord_right vertb">1.16</td> -<td class="tdc bord_right vertb">1.26</td> -<td class="tdc bord_right vertb">1.42</td> -<td class="tdc">1.20</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1893-4</td> -<td class="tdc bord_right vertb">1.15</td> -<td class="tdc bord_right vertb">2.63</td> -<td class="tdc bord_right vertb">2.00</td> -<td class="tdc bord_right vertb">1.46</td> -<td class="tdc bord_right vertb">1.43</td> -<td class="tdc bord_right vertb">1.52</td> -<td class="tdc bord_right vertb">0.95</td> -<td class="tdc">1.59</td> -</tr> -<tr> -<td class="tdl vertt bord_right vertb">1894-5</td> -<td class="tdc bord_right vertb">0.60</td> -<td class="tdc bord_right vertb">1.68</td> -<td class="tdc bord_right vertb">1.67</td> -<td class="tdc bord_right vertb">2.53</td> -<td class="tdc bord_right vertb">1.03</td> -<td class="tdc bord_right vertb">1.34</td> -<td class="tdc bord_right vertb">0.96</td> -<td class="tdc">1.40</td> -</tr> -<tr> -<td class="tdl bord_right bord_bot">Average</td> -<td class="tdc bord_right bord_bot">0.93</td> -<td class="tdc bord_right bord_bot">1.38</td> -<td class="tdc bord_right bord_bot">1.44</td> -<td class="tdc bord_right bord_bot">1.06</td> -<td class="tdc bord_right bord_bot">1.09</td> -<td class="tdc bord_right bord_bot">1.37</td> -<td class="tdc bord_right bord_bot">1.43</td> -<td class="tdc bord_bot">1.24</td> -</tr> -<tr> -<td class="tdl small" colspan="9"><p>Average of seven companies for 15 years, $1.24 per million gallons.</p></td> -</tr> -<tr> -<td class="tdl small" colspan="9"><p>Variations from year to year are caused by differences in the amounts of ice, -and in the quantities of new sand purchased. Wages average about $1.00 per -day. At Liverpool for 1896 the cost was $1.08 per million U. S. gallons.</p></td> -</tr> -</table> - -<p>In Germany, with more turbid river-waters, the costs of operation are -somewhat higher than the London figures, while at Zürich, where the -water is very clear, they are lower.</p> - -<p>In the United States the data regarding the cost of operation of sand -filters are less complete. At Mt. Vernon, N. Y., with<span class="pagenum" id="Page_203">[Pg 203]</span> reservoir-water, -the cost has averaged about two dollars per million gallons. At -Poughkeepsie, N. Y., with the Hudson River water, which is occasionally -moderately turbid, the cost for twenty years has averaged three dollars -per million gallons. This cost includes the cost of handling ice, and -as the average winter temperature is considerably below that suggested -for open filters, the expense of this work has been considerable, and -has increased considerably the total cost of operation.</p> - -<p>At Far Rockaway, L. I., and Red Bank N. J., for iron-removal plants, -the cost of operation has hardly been appreciable. The plants are both -close to the pumping-stations, and it has been possible to operate -them with the labor necessarily engaged at the pumping-station without -additional cost, except a very small amount of labor on the sand at Far -Rockaway. No computation has been made in these cases of the additional -coal required for pumping.</p> - -<p>At Lawrence, Mass., the cost of operation for 1895 was as follows:</p> - -<table class="autotable" summary="Lawrence, Mass. costs"> -<tr> -<td class="tdr bord_right vertb"><p class="indent">Cost of scraping and replacing sand</p></td> -<td class="tdr vertb"> </td> -<td class="tdr vertb">$3,467</td> -</tr> -<tr> -<td class="tdr bord_right vertb"><p class="indent">Cost of care of ice</p></td> -<td class="tdr vertb"> </td> -<td class="tdr vertb">2,903</td> -</tr> -<tr> -<td class="tdr bord_right vertb"><p class="indent"> Total cost of operation</p></td> -<td class="tdr vertb"> </td> -<td class="tdr vertb bord_top">$6,370</td> -</tr> -<tr> -<td class="tdr bord_right vertb"><p class="indent"> Water filtered, millions of gallons</p></td> -<td class="tdr vertb">1,097</td> -<td class="tdr vertb"> </td> -</tr> -<tr> -<td class="tdr bord_right vertb"><p class="indent"> Cost per million gallons</p></td> -<td class="tdr vertb">$5.80</td> -<td class="tdr vertb"> </td> -</tr> -</table> - -<p>The cost of care of ice has been excessive at Lawrence, and it has -been repeatedly recommended to cover the filter to avoid this expense. -The cost of handling sand has been very greatly increased, because the -filter is built in one bed, and all work upon it has to be done during -the comparatively short intervals when the filter is not in use, an -arrangement which is not at all economical in the use of labor. The -cost of operation is thus much higher than it would be had the plant -been constructed in several units, each of which could be disconnected -for the purpose of being cleaned in the ordinary manner. As against -this the first cost<span class="pagenum" id="Page_204">[Pg 204]</span> of construction was extremely low, and the saving -in interest charges should be credited against the increased cost of -labor in cleaning.</p> - -<p>The cost of operating filters at Ashland, Wis., has been estimated by -Mr. William Wheeler at $2.26 per million gallons. This estimate is -based upon the performance for the first year that they were in service.</p> - -<p>In the operation of mechanical filters one of the largest items of -expense is for the coagulant, and the amount of this depends entirely -upon the character of the raw water and the thoroughness of the -treatment required. The data regarding the other or general costs of -operation of mechanical filters are few and unsatisfactory.</p> - -<p>I recently made some estimates of cost of clarifying waters of various -degrees of turbidity by sand and mechanical filters. These estimates -were made for a special set of conditions, and I do not know that -they will fit others, but they have at least a suggestive value. The -results shown by Fig. 26 include only the cost of operation, and not -interest and depreciation charges. These figures, when used for plants -in connection with which preliminary treatments are used, should be -applied to the turbidity of the water as applied to the filters, and -not to the raw water, and the costs of the preliminary processes should -be added.</p> - -<p>With sand filters the frequency of scraping is nearly proportional -to the turbidity; and as scraping represents most of the expenses, -the costs of operation are proportional to the turbidity, except -the general costs, and the cost of the amount of scraping, which is -necessary with even the clearest waters.</p> - -<p>With mechanical filters the amount of sulphate of alumina required for -clarification increases with the turbidity, and most of the costs of -operation increase in the same ratio. The diagram shows the amount of -sulphate of alumina in grains per gallon necessary for clarification -with different degrees of turbidity.</p> - -<p><span class="pagenum" id="Page_205">[Pg 205]</span></p> - -<p>With the clearest waters the costs of operation on the two systems are -substantially equal. With muddy waters, the expense of operating sand -filters increases more rapidly than the expense of operating mechanical -filters.</p> - -<div class="figcenter padt1 padb1 illowp70" id="image205" style="max-width: 93.75em;"> - <img class="w100" src="images/image205.jpg" alt="" /> - <p class="caption"><span class="sans large">TURBIDITY</span><br /> -<span class="smcap">Fig. 26.—Cost of Operation of Filters.</span></p></div> - -<p>There is another element which often comes into the comparison, namely, -the question of purification from the effects of sewage-pollution. -Nearly all rivers used for public water-supplies<span class="pagenum" id="Page_206">[Pg 206]</span> receive more or less -sewage, and in filtering such waters it is regarded as necessary to -remove as completely as possible the bacteria.</p> - -<p>The quantities of sulphate of alumina required for the clarification -of the least turbid waters are not sufficient to give even tolerably -good bacterial efficiencies. To secure a reasonably complete removal of -bacteria with mechanical filters, the use of a considerable quantity -of sulphate of alumina is required. Let us assume that 98 per cent -bacterial efficiency is required, and that to produce this efficiency -it is necessary to use one grain of coagulant to the gallon. With water -requiring less than this quantity of coagulant for clarification this -quantity must nevertheless be used, and the costs will be controlled -by it, and not by the lower quantities which would suffice for -clarification, but would not give the required bacterial efficiency.</p> - -<p>I have added this line to the diagram, and this, combined with the -upper portion of the line showing cost of clarification, represents the -cost of treating waters with mechanical filters, where both bacterial -efficiency and clarification are required.</p> - -<p>This line, considered as a whole, increases much less rapidly with -increasing turbidity than does the corresponding line for sand filters, -and the two lines cross each other. With the clearest waters sand -filters are cheaper than mechanical filters, and for the muddiest -waters they are more expensive. It does not appear from the diagram, -but it is also true in each case, that the cheaper system is also the -more efficient. Sand filters are more efficient in removing bacteria -from clear waters than are mechanical filters, and mechanical filters -are more efficient in clarifying very muddy waters than are sand -filters.</p> - -<p><span class="pagenum" id="Page_207">[Pg 207]</span></p> - -<div class="section"> -<h3 class="nobreak" id="WHAT_WATERS_REQUIRE_FILTRATION">WHAT WATERS REQUIRE FILTRATION?</h3></div> - -<p>From the nature of the case a satisfactory general answer to this -question cannot be given, but a few suggestions may be useful.</p> - -<p>In the first place, ground-waters obviously do not require filtration: -they have already in most cases been thoroughly filtered in the ground -through which they have passed, and in the exceptional cases, as, for -instance, an artesian well drawing water through fissures in a ledge -from a polluted origin, a new supply will generally be chosen rather -than to attempt to improve so doubtful a raw material.</p> - -<p>River-waters should be filtered. It cannot be asserted that there -are no rivers in mountainous districts in which the water is at once -clear and free from pollution, and suitable in its natural state -for water-supply; but if so, they are not common, least of all in -the regions where water-supplies are usually required. The use of -river-waters in their natural state or after sedimentation only, -drawn from such rivers as the Merrimac, Hudson, Potomac, Delaware, -Schuylkill, Ohio, and Mississippi, is a filthy as well as an unhealthy -practice, which ought to be abandoned.</p> - -<p>The question is more difficult in the case of supplies drawn from -lakes or storage reservoirs. Many such supplies are grossly polluted -and should be either abandoned or filtered. Others are subject to algæ -growths, or are muddy, and would be much improved by filtration. Still -others are drawn either from unpolluted water-sheds, or the pollution -is so greatly diluted and reduced by storage that no known disadvantage -results from their use.</p> - -<p>In measuring the effects of the pollution of water-supplies, the -typhoid-fever death-rate is a most important aid. Not that typhoid -fever is the sole evil resulting from polluted water, but because it -is also a very useful index of other evils for which corresponding -statistics cannot be obtained, as, for instance, the causation of -diarrhœal diseases or the danger from invasion by cholera.</p> - -<p><span class="pagenum" id="Page_208">[Pg 208]</span></p> - -<p>I think we shall not go far wrong at the start to confine our attention -to those cities where there are over 25 deaths from typhoid fever per -100,000 of population. This will at once throw out of consideration -a large number of relatively good supplies, including those of New -York and Brooklyn. It is not my idea that none of these supplies -cause disease. Many of them, as for instance that of New York, are -known to receive sewage, and it is an interesting question worthy of -most careful study whether there are cases of sickness resulting from -this pollution. The point that I wish to make now is simply that in -those cases the death-rate itself is evidence that, with existing -conditions of dilution and storage, the resulting damage of which we -have knowledge is not great enough to justify the expense involved by -filtration.</p> - -<p>In this connection it should not be forgotten that, especially with -very small watersheds, there may be a danger as distinct from present -damage which requires consideration. Thus a single house or groups of -houses draining into a supply may not appreciably affect it for years, -until an outbreak of fever on the water-shed results in infecting the -water with the germs of disease and in an epidemic in the city below. -This danger decreases with increasing size of the water-shed and volume -of the water with which any such pollution would be mixed, and also -with the population draining into the water, as there is a probability -that the amount of infection continually added from a considerable town -will not be subject to as violent fluctuation as that from only a few -houses.</p> - -<p>Thus in Plymouth, Pa., in 1885, there were 1104 cases of typhoid -fever and 114 deaths among a population of 8000, as the result of the -discharge of the dejecta from a single typhoid patient into the water -of a relatively small impounding reservoir. The cost of this epidemic -was calculated with unusual care. The care of the sick cost in cash -$67,100.17, and the loss of wages for those who recovered amounted to -$30,020.08. The 114 persons who died were earning before their sickness -at the rate of $18,419.52 annually.</p> - -<p>Such an outbreak would hardly be possible with the Croton<span class="pagenum" id="Page_209">[Pg 209]</span> water-shed -of the New York water-supply, on account of the great dilution and -delay in the reservoirs, but it must be guarded against in small -supplies.</p> - -<p>Of the cities having more than 25 deaths per 100,000 from typhoid -fever, some will no doubt be found where milk epidemics or other -special circumstances were the cause; but I believe in a majority -of them, and in nearly all cases where the rate is year after year -considerably above that figure, the cause will be found in the -water-supply. Investigation should be made of this point; and if the -water is not at fault, the responsibility should be located. If the -water is guilty, it should be either purified or a new supply obtained.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_210">[Pg 210]</span></p> - -<h2 class="nobreak" id="CHAPTER_XIV">CHAPTER XIV.<br /> -<br /> - -<span class="smaller">WATER-SUPPLY AND DISEASE—CONCLUSIONS.</span></h2></div> - -<p><span class="smcap">One</span> of the most characteristic and uniform results of the direct -pollution of public water-supplies is the typhoid fever which results -among the users of the water. In the English and German cities with -almost uniformly good drinking-water, typhoid fever is already nearly -exterminated, and is decreasing from year to year. American cities -having unpolluted water-supplies have comparatively few deaths from -this cause, although the figures never go so low as in Europe, perhaps -on account of the fresh cases which are always coming in from less -healthy neighborhoods in ever-moving American communities. In other -American cities the death-rates from typhoid fever are many times what -they ought to be and what they actually are in other cities, and the -rates in various places, and in the same place at different times, -bear in general a close relation to the extent of the pollution of the -drinking-water. The power of suitable filtration to protect a city from -typhoid fever is amply shown by the very low death-rates from this -cause in London, Berlin, Breslau, and large numbers of other cities -drawing their raw water from sources more contaminated than those of -any but the very worst American supplies, and by the marked and great -reductions in the typhoid-fever death rates which have followed at once -the installation of filters at Zürich, Switzerland; Hamburg, Germany; -Lawrence, Mass., and other places.</p> - -<p>The following is a list of the cities of 50,000 inhabitants and -upward<span class="pagenum" id="Page_211">[Pg 211]</span> in the United States, with deaths from typhoid fever and the -sources of their water-supplies. The deaths and populations are from -the U. S. Census for 1890; the sources of the water-supplies, from -the <cite>American Water-Works Manual</cite> for the same year. Four cities -of this size—Grand Rapids, Lincoln, St. Joseph, and Des Moines—are -not included in the census returns of mortality. Two cities with less -than 50,000 inhabitants with exceptionally high death-rates have been -included, and at the foot of the list are given corresponding data for -some large European cities for 1893.</p> - -<table class="autotable" summary="typhoid fever death rates"> -<tr> -<th class="tdc normal" colspan="6">TYPHOID FEVER DEATH-RATES AND WATER-SUPPLIES OF CITIES.</th> -</tr> -<tr> -<th class="tdc normal normal small bord_top bord_right bord_bot" rowspan="2" colspan="2">City.</th> -<th class="tdc normal normal small bord_top bord_right bord_bot" rowspan="2">Population.</th> -<th class="tdc normal normal small bord_top bord_right bord_bot" colspan="2">Deaths from<br />Typhoid<br />Fever.</th> -<th class="tdc normal normal small bord_top bord_bot" rowspan="2">Water-supply.</th> -</tr> -<tr> -<th class="tdc normal normal small bord_right bord_bot">Total.</th> -<th class="tdc normal normal small bord_right bord_bot">Per<br />100,000<br />living.</th> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Birmingham</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">26,178</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">69</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">264</span></td> -<td class="tdr vertb">Five Mile Creek</td> -</tr> -<tr> -<td class="tdr vertt">1.</td> -<td class="tdl vertt bord_right vertb">Denver</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">106,713</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">232</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">217</span></td> -<td class="tdr vertb">North Platte River and wells</td> -</tr> -<tr> -<td class="tdr vertt">2.</td> -<td class="tdl vertt bord_right vertb">Allegheny</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">105,287</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">192</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">182</span></td> -<td class="tdr vertb">Allegheny River</td> -</tr> -<tr> -<td class="tdr vertt">3.</td> -<td class="tdl vertt bord_right vertb">Camden</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">58,313</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">77</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">132</span></td> -<td class="tdr vertb">Delaware River</td> -</tr> -<tr> -<td class="tdr vertt">4.</td> -<td class="tdl vertt bord_right vertb">Pittsburg</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">238,617</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">304</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">127</span></td> -<td class="tdr vertb">Allegheny and Monongahela rivers</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Lawrence</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">44,654</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">54</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">121</span></td> -<td class="tdr vertb">Merrimac River</td> -</tr> -<tr> -<td class="tdr vertt">5.</td> -<td class="tdl vertt bord_right vertb">Newark</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">181,830</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">181</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">100</span></td> -<td class="tdr vertb">Passaic River</td> -</tr> -<tr> -<td class="tdr vertt">6.</td> -<td class="tdl vertt bord_right vertb">Charleston</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">54,955</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">54</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">98</span></td> -<td class="tdr vertb">Artesian wells yielding 1,600,000 gallons daily</td> -</tr> -<tr> -<td class="tdr vertt">7.</td> -<td class="tdl vertt bord_right vertb">Washington</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">230,392</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">200</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">87</span></td> -<td class="tdr vertb">Potomac River</td> -</tr> -<tr> -<td class="tdr vertt">8.</td> -<td class="tdl vertt bord_right vertb">Lowell</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">77,696</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">64</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">82</span></td> -<td class="tdr vertb">Merrimac River</td> -</tr> -<tr> -<td class="tdr vertt">9.</td> -<td class="tdl vertt bord_right vertb">Jersey City</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">163,003</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">134</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">82</span></td> -<td class="tdr vertb">Passaic River</td> -</tr> -<tr> -<td class="tdr vertt">10.</td> -<td class="tdl vertt bord_right vertb">Louisville</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">161,129</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">122</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">76</span></td> -<td class="tdr vertb">Ohio River</td> -</tr> -<tr> -<td class="tdr vertt">11.</td> -<td class="tdl vertt bord_right vertb">Philadelphia</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">1,046,964</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">770</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">74</span></td> -<td class="tdr vertb">Delaware and Schuylkill rivers</td> -</tr> -<tr> -<td class="tdr vertt">12.</td> -<td class="tdl vertt bord_right vertb">Chicago</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">1,099,850</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">794</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">72</span></td> -<td class="tdr vertb">Lake Michigan</td> -</tr> -<tr> -<td class="tdr vertt">13.</td> -<td class="tdl vertt bord_right vertb">Atlanta</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">65,533</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">47</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">72</span></td> -<td class="tdr vertb">South River</td> -</tr> -<tr> -<td class="tdr vertt">14.</td> -<td class="tdl vertt bord_right vertb">Albany</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">94,923</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">67</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">71</span></td> -<td class="tdr vertb">Hudson River</td> -</tr> -<tr> -<td class="tdr vertt">15.</td> -<td class="tdl vertt bord_right vertb">Wilmington</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">61,431</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">43</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">70</span></td> -<td class="tdr vertb">Brandywine Creek</td> -</tr> -<tr> -<td class="tdr vertt">16.</td> -<td class="tdl vertt bord_right vertb">St. Paul</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">133,156</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">92</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">69</span></td> -<td class="tdr vertb">Lakes</td> -</tr> -<tr> -<td class="tdr vertt">17.</td> -<td class="tdl vertt bord_right vertb">Troy</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">60,956</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">42</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">69</span></td> -<td class="tdr vertb">Hudson River and impounding reservoirs</td> -</tr> -<tr> -<td class="tdr vertt">18.</td> -<td class="tdl vertt bord_right vertb">Los Angeles</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">50,395</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">34</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">67</span></td> -<td class="tdr vertb">Los Angeles River and springs</td> -</tr> -<tr> -<td class="tdr vertt">19.</td> -<td class="tdl vertt bord_right vertb">Nashville</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">76,168</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">49</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">64</span></td> -<td class="tdr vertb">Cumberland River</td> -</tr> -<tr> -<td class="tdr vertt">20.</td> -<td class="tdl vertt bord_right vertb">Cleveland</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">261,353</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">164</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">63</span></td> -<td class="tdr vertb">Lake Erie</td> -</tr> -<tr> -<td class="tdr vertt">21.</td> -<td class="tdl vertt bord_right vertb">Richmond</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">81,388</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">50</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">61</span></td> -<td class="tdr vertb">James River</td> -</tr> -<tr> -<td class="tdr vertt">22.</td> -<td class="tdl vertt bord_right vertb">Hartford</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">53,230</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">32</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">60</span></td> -<td class="tdr vertb">Connecticut River and impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">23.</td> -<td class="tdl vertt bord_right vertb">Fall River</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">74,398</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">44</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">59</span></td> -<td class="tdr vertb">Watupa Lake</td> -</tr> -<tr> -<td class="tdr vertt">24.</td> -<td class="tdl vertt bord_right vertb">Minneapolis</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">164,738</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">94</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">57</span></td> -<td class="tdr vertb">Mississippi River</td> -</tr> -<tr> -<td class="tdr vertt">25.</td> -<td class="tdl vertt bord_right vertb">San Francisco</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">298,997</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">166</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">56</span></td> -<td class="tdr vertb">Lobus Creek, Lake Merced, and mountain streams</td> -</tr> -<tr> -<td class="tdr vertt">26.</td> -<td class="tdl vertt bord_right vertb">Indianapolis</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">105,436</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">57</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">54</span></td> -<td class="tdr vertb">White River</td> -</tr> -<tr> -<td class="tdr vertt">27.</td> -<td class="tdl vertt bord_right vertb">Cincinnati</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">296,908</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">151</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">51</span></td> -<td class="tdr vertb">Ohio River</td> -</tr> -<tr> -<td class="tdr vertt">28.</td> -<td class="tdl vertt bord_right vertb">Memphis</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">64,495</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">33</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">51</span></td> -<td class="tdr vertb">Artesian Wells</td> -</tr> -<tr> -<td class="tdr vertt">29.</td> -<td class="tdl vertt bord_right vertb">Reading</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">58,661</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">29</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">49</span></td> -<td class="tdr vertb">Maiden Creek and Springs</td> -</tr> -<tr> -<td class="tdr vertt">30.</td> -<td class="tdl vertt bord_right vertb">Baltimore</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">434,439</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">202</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">47</span></td> -<td class="tdr vertb">Impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">31.</td> -<td class="tdl vertt bord_right vertb">Omaha</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">140,452</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">63</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">45</span></td> -<td class="tdr vertb">Missouri River</td> -</tr> -<tr> -<td class="tdr vertt">32.</td> -<td class="tdl vertt bord_right vertb">Columbus</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">88,150</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">38</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">43</span></td> -<td class="tdr vertb">Surface-water and wells</td> -</tr> -<tr> -<td class="tdr vertt">33.</td> -<td class="tdl vertt bord_right vertb">Providence</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">132,146</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">53</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">40</span></td> -<td class="tdr vertb">Pawtuxet River</td> -</tr> -<tr> -<td class="tdr vertt">34.</td> -<td class="tdl vertt bord_right vertb">Kansas City</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">132,716</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">53</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">40</span></td> -<td class="tdr vertb">Missouri River</td> -</tr> -<tr> -<td class="tdr vertt">35.</td> -<td class="tdl vertt bord_right vertb">Rochester</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">133,896</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">53</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">39</span></td> -<td class="tdr vertb">Hemlock and Candice lakes</td> -</tr> -<tr> -<td class="tdr vertt">36.</td> -<td class="tdl vertt bord_right vertb">Evansville</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">50,756</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">20</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">39</span></td> -<td class="tdr vertb">Ohio River</td> -</tr> -<tr> -<td class="tdr vertt">37.</td> -<td class="tdl vertt bord_right vertb">Boston</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">448,477</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">174</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">39</span></td> -<td class="tdr vertb">Impounding reservoirs</td> -</tr> -<tr> -<td class="tdr vertt">38.</td> -<td class="tdl vertt bord_right vertb">Toledo</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">81,434</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">29</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">36</span></td> -<td class="tdr vertb">Maumee River</td> -</tr> -<tr> -<td class="tdr vertt">39.</td> -<td class="tdl vertt bord_right vertb">Cambridge</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">70,028</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">24</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">34</span></td> -<td class="tdr vertb">Impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">40.</td> -<td class="tdl vertt bord_right vertb">St. Louis</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">451,770</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">145</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">32</span></td> -<td class="tdr vertb">Mississippi River</td> -</tr> -<tr> -<td class="tdr vertt">41.</td> -<td class="tdl vertt bord_right vertb">Scranton</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">75,215</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">24</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">32</span></td> -<td class="tdr vertb">Impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">42.</td> -<td class="tdl vertt bord_right vertb">Buffalo</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">255,664</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">80</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">31</span></td> -<td class="tdr vertb">Niagara River</td> -</tr> -<tr> -<td class="tdr vertt">43.</td> -<td class="tdl vertt bord_right vertb">Milwaukee</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">204,468</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">61</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">30</span></td> -<td class="tdr vertb">Lake Michigan</td> -</tr> -<tr> -<td class="tdr vertt">44.</td> -<td class="tdl vertt bord_right vertb">New Haven</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">81,298</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">22</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">27</span></td> -<td class="tdr vertb">Impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">45.</td> -<td class="tdl vertt bord_right vertb">Worcester</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">84,655</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">22</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">26</span></td> -<td class="tdr vertb">Impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">46.</td> -<td class="tdl vertt bord_right vertb">Paterson</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">78,347</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">20</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">26</span></td> -<td class="tdr vertb">Passaic River (higher up)</td> -</tr> -<tr> -<td class="tdr vertt">47.</td> -<td class="tdl vertt bord_right vertb">Dayton</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">61,220</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">15</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">25</span></td> -<td class="tdr vertb">Wells</td> -</tr> -<tr> -<td class="tdr vertt">48.</td> -<td class="tdl vertt bord_right vertb">Brooklyn</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">806,343</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">194</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">24</span></td> -<td class="tdr vertb">Wells, ponds, and impounding reservoirs</td> -</tr> -<tr> -<td class="tdr vertt">49.</td> -<td class="tdl vertt bord_right vertb">New York</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">1,515,301</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">348</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">23</span></td> -<td class="tdr vertb">Impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">50.</td> -<td class="tdl vertt bord_right vertb">Syracuse</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">88,143</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">18</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">20</span></td> -<td class="tdr vertb">Impounding reservoir and springs</td> -</tr> -<tr> -<td class="tdr vertt">51.</td> -<td class="tdl vertt bord_right vertb">New Orleans</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">242,039</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">45</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">19</span></td> -<td class="tdr vertb">Mississippi River</td> -</tr> -<tr> -<td class="tdr vertt">52.</td> -<td class="tdl vertt bord_right vertb">Detroit</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">205,876</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">40</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">19</span></td> -<td class="tdr vertb">Detroit River</td> -</tr> -<tr> -<td class="tdr vertt">53.</td> -<td class="tdl vertt bord_right vertb">Lynn</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">55,727</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">9</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">16</span></td> -<td class="tdr vertb">Impounding reservoir</td> -</tr> -<tr> -<td class="tdr vertt">54.</td> -<td class="tdl vertt bord_right vertb">Trenton</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">57,458</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">9</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">16</span></td> -<td class="tdr vertb">Delaware River</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">London</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">4,306,411</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">719</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">17</span></td> -<td class="tdr vertb">Filtered Thames and Lea rivers and <sup>1</sup>⁄<sub>4</sub> from wells</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Glasgow</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">667,883</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">138</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">20</span></td> -<td class="tdr vertb">Loch Katrine</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Paris</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">2,424,705</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">609</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">25</span></td> -<td class="tdr vertb">Spring water</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Amsterdam</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">437,892</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">69</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">16</span></td> -<td class="tdr vertb">Filtered dune-water</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Rotterdam</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">222,233</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">12</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">5</span></td> -<td class="tdr vertb">Filtered Maas River</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Hague</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">169,828</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">3</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">2</span></td> -<td class="tdr vertb">Filtered dune-water</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Berlin</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">1,714,938</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">161</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">9</span></td> -<td class="tdr vertb">Filtered Havel and Spree rivers</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Hamburg</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">634,878</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">115</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">18</span></td> -<td class="tdr vertb">Filtered Elbe River</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Breslau</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">353,551</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">37</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">11</span></td> -<td class="tdr vertb">Filtered Oder River</td> -</tr> -<tr> -<td class="tdr vertt"> </td> -<td class="tdl vertt bord_right vertb">Dresden</td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">308,930</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">14</span></td> -<td class="tdl vertt bord_right vertb"><span class="padrp5">5</span></td> -<td class="tdr vertb">Ground-water</td> -</tr> -<tr> -<td class="tdr vertt bord_bot"> </td> -<td class="tdl vertt bord_bot">Vienna</td> -<td class="tdr vertt bord_right bord_bot"><span class="padrp5">1,435,931</span></td> -<td class="tdr vertt bord_right bord_bot"><span class="padrp5">104</span></td> -<td class="tdl vertt bord_right bord_bot"><span class="padrp5">7</span></td> -<td class="tdr bord_bot">Spring-water</td> -</tr> -</table> - -<p class="padt1">Any full discussion of these data would require intimate acquaintances -with the various local conditions which it is impossible to take -up in detail here, but some of the leading facts cannot fail to be -instructive.</p> - -<p>Each of the places having over 100 deaths per 100,000 from typhoid -fever used unfiltered river-water. Lower in the list, but<span class="pagenum" id="Page_213">[Pg 213]</span> still very -high, Charleston, said to have been supplied only from artesian wells, -had an excessive rate; but the reported water-consumption is so low as -to suggest that private wells or other means of supply were in common -use. Chicago and Cleveland both drew their water from lakes where they -were contaminated by their own sewage. St. Paul’s supply came from -ponds, of which I do not know the character. With these exceptions all -of the 22 cities with over 50,000 inhabitants, at the head of the list, -had unfiltered river-water.</p> - -<p>The cities supplied from impounding reservoirs as a rule had lower -death rates and are at the lower end of the list, together with some -cities taking their water supplies from rivers or lakes at points where -they were subject to only smaller or more remote infection. Only three -of the American cities in the list were reported as being supplied -entirely with ground-water.</p> - -<p>It is not my purpose to make too close comparisons between the various -cities on the list; some of them may have been influenced by unusual -local conditions in 1890. Others have in one way or another improved -their water-supplies since that date, and there are several cities in -which I know the present typhoid-fever death-rates to be materially -lower than those of 1890 given in the table. On the other hand, it is -equally true that a number of cities, including some of the larger -ones, have since had severe epidemics of typhoid fever which have given -very much higher rates than those for 1890.</p> - -<p>These fluctuations would change the order of cities in the list from -year to year; they would not change the general facts, which are as -true to-day as they were in 1890. Nearly all of the great cities of the -United States are supplied with unfiltered surface-waters, and a great -majority of the waters are taken from rivers and lakes at points where -they are polluted by sewage. The death-rates from typhoid fever in -those cities, whether they are compared with better supplied cities of -this country, or with European cities, are enormously high.</p> - -<p><span class="pagenum" id="Page_214">[Pg 214]</span></p> - -<p>Such rates were formerly common in European cities, but they have -disappeared with better sanitary conditions. The introduction of -filters has often worked marvellous changes in Europe, and in Lawrence -the improvement in the city’s health with filtered water was prompt -and unquestionable. There is every reason to believe that the general -introduction of better water in American cities will work corresponding -revolutions; and looking at it from a merely money standpoint, the -value of the lives and the saving of the expenses of sickness will pay -handsomely when compared with the cost of good water.</p> - -<p>The reasons for believing that cholera is caused by polluted water -are entirely similar to those in the case of typhoid fever. It was no -accident that the epidemic of cholera which caused the death of 3400 -persons followed the temporary supply of unfiltered water by the East -London Water Company in 1866, while the rest of London remained nearly -free, or that the only serious outbreak of cholera in Western Europe -in 1892 was at Hamburg, which was also the only city in Germany which -used raw river-water. This latter caused the sickness of 20,000 and the -death of over 8000 people within a month, and an amount of suffering -and financial loss, with the panics which resulted, that cannot be -estimated, but that exceeded many times the cost of the filters which -have since been put in operation. Hamburg had several times before -suffered severely from cholera, and the removal of this danger was a -leading, although not the sole, motive for the construction of filters.</p> - -<p>How little cities supplied with pure water have to dread from -cholera is shown by the experience of Altona and other suburbs of -Hamburg with good water-supplies, which had but few cases of cholera -not directly brought from the latter place, and by the experience -of England, which maintained uninterrupted commercial intercourse -with the plague-stricken city, absolutely without quarantine, and, -notwithstanding a few cases which were directly imported, the disease -gained no foothold in England.</p> - -<p><span class="pagenum" id="Page_215">[Pg 215]</span></p> - -<p>I do not know of a single modern European instance where a city with a -good water-supply not directly infected by sewage has suffered severely -from cholera. I shall leave to others more familiar with the facts the -discussion of what happened before the introduction of modern sanitary -methods, as well as of the present conditions in Asia; although I -believe that in these cases also there is plenty of evidence as to the -part water plays in the spread of the disease.</p> - -<p>A considerable proportion of the water-supplies of the cities of the -United States are so polluted that in case cholera should gain a -foothold upon our shores we have no ground for hoping for the favorable -experience of the English cities rather than the plague of Hamburg in -1892.</p> - -<p>The fæces from a man contain on an average perhaps 1,000,000,000 -bacteria per gram,<a id="FNanchor_47" href="#Footnote_47" class="fnanchor">[47]</a> most of them being the normal bacilli of -the intestines, <em>Bacillus coli communis</em>. Assuming that a man -discharges 200 grams or about 7 ounces of fæces daily, this would give -200,000,000,000 bacteria discharged daily per person. The number of -bacteria actually found in American sewage is usually higher, often -double this number per person; but there are other sources of bacteria -in sewage, and in addition growths or the reverse may take place in the -sewers, according to circumstances.</p> - -<p>This number of bacteria in sewage is so enormously large that the -addition of the sewage from a village or city to even a large river -is capable of affecting its entire bacterial composition. Thus taking -the population of Lowell in 1892 at 85,000, and the average daily -flow of the Merrimac at 6000 cubic feet per second, and assuming that -200,000,000,000 bacteria are discharged daily in the sewage from each -person, they would increase the number in the river by 1160<span class="pagenum" id="Page_216">[Pg 216]</span> -per cubic centimeter, or about 300,000 in an ordinary glass of water. -The average number found in the water eight miles below, at the intake -of the Lawrence water-works, was more than six times as great as this, -due in part to the sewage of other cities higher up.</p> - -<p>There is every reason to believe that the bulk of these bacteria were -harmless to the people of Lawrence, who drank them; but some of them -were not. Fæces of people suffering from typhoid fever contain the -germs of that disease. What proportion of the total number of bacteria -in such fæces are injurious is not known; but assuming that one fourth -only of the total number are typhoid germs, and supposing the fæces of -one man to be evenly mixed with the whole daily average flow of the -river, it would put one typhoid germ into every glass of water at the -Lawrence intake, and at low water several times as many proportionately -would be added. This gives some conception of the dilution required to -make a polluted water safe.</p> - -<p>One often hears of the growth of disease-germs in water, but as far -as the northern United States and Europe are concerned there is no -evidence whatever that this ever takes place. There are harmless forms -of bacteria which are capable of growing upon less food than the -disease-germs require and they often multiply in badly-polluted waters. -Typhoid-fever germs live for a longer or shorter period, and finally -die without growth. The few laboratory experiments which have seemed -to show an increase of typhoid germs in water have been made under -conditions so widely different from those of natural watercourses that -they have no value.<a id="FNanchor_48" href="#Footnote_48" class="fnanchor">[48]</a></p> - -<p><span class="pagenum" id="Page_217">[Pg 217]</span></p> - -<p>The proportionate number of cases of typhoid fever among the users -of a polluted water varies with the number of typhoid germs in the -water. Excessive pollution causes severe epidemics or continued high -death-rates according as the infection is continued or intermittent. -Slight infection causes relatively few cases of fever. Pittsburg and -Allegheny, taking their water-supplies from below the outlets of some -of their own sewers, have suffered severely (103.2 and 127.4 deaths -from typhoid fever annually per 100,000, respectively, from 1888 to -1892). Wheeling, W. Va., with similar conditions in 1890, was even -worse, a death rate of 345 per 100,000 from this cause being reported, -while Albany had only comparatively mild epidemics from the less -directly and grossly polluted Hudson. Lawrence and Lowell, taking their -water from the Merrimac, both had for many years continued excessive -rates, increasing gradually with increasing pollution; and the city -having the most polluted source had the higher rate.</p> - -<p>In Berlin and Altona, in winter, with open filters, epidemics of -typhoid fever followed decreased efficiency of filtration, but the -epidemics were often so mild that they would have entirely escaped -observation under present American conditions. Chicago has for years -suffered from typhoid fever, and the rate has fluctuated, as far as -reliable information can be obtained, with the fluctuations in the -pollution of the lake water. An unusual discharge of the Chicago River -results in a higher death-rate. Abandoning the shore inlet near the -mouth of the Chicago River in 1892, resulted in the following year in -a reduction of 60 per cent in the typhoid fever death-rate.<a id="FNanchor_49" href="#Footnote_49" class="fnanchor">[49]</a> This -reduction shows, not that the present intakes are safe, but simply that -they are less polluted than the old ones to an extent measured by the -reduction in the death-rate.</p> - -<p>It is not supposed that in an epidemic of typhoid fever caused by -polluted water every single person contracts the disease directly by<span class="pagenum" id="Page_218">[Pg 218]</span> -drinking the water. On the contrary, typhoid fever is often -communicated in other ways. If we have in the first place a thousand -cases in a city caused directly by the water, they will be followed -by a large number of other cases resulting directly from the presence -in the city of the first thousand cases. The conditions favoring this -spread may vary in different wards, resulting in considerable local -variations in the death-rates. Some persons also will suffer who did -not drink any tap-water. These facts, always noted in epidemics, afford -no ground for refusing to believe, in the presence of direct evidence, -that the water was the cause of the fever. These additional cases are -the indirect if not the direct result of the water. The broad fact that -cities with polluted water-supplies as a rule have high typhoid-fever -death-rates, and cities with good water-supplies do not (except in the -occasional cases of milk epidemics, or where they are overrun by cases -contracted in neighboring cities with bad water, as is the case with -some of Chicago’s suburbs), is at once the best evidence of the damage -from bad water and measure of its extent.</p> - -<p>The conditions which remove or destroy the sewage bacteria in a water -tend to make it safe. The most important of them are: (1) dilution; (2) -time, allowing the bacteria to die (sunlight may aid in this process, -although effective sunshine cannot reach the lower layer of turbid -waters or through ice); (3) sedimentation, allowing them to go to -the bottom, where they eventually die; and (4) natural or artificial -filtration. In rivers, distance is mainly useful in affording time, -and also, under some conditions, in allowing opportunities for -sedimentation. Thus a distance of 500 miles requires a week for water -travelling three miles an hour to pass, and will allow very important -changes to take place. The old theory that water purifies itself -in running a certain distance has no adequate foundation as far as -bacteria are concerned. Some purification takes place with the time -involved in the passage, but its extent has been greatly overestimated.</p> - -<p>The time required for the bacteria to die simply from natural<span class="pagenum" id="Page_219">[Pg 219]</span> causes -is considerable; certainly not less than three or four weeks can -be depended upon with any confidence. In storage reservoirs this -action is often considerable, and it is for this reason that American -water-supplies from large storage reservoirs are, as a rule, much more -healthy than those drawn from rivers or polluted lakes, even when the -sources of the former are somewhat polluted. The water-supplies of New -York and Boston may be cited as examples. In many other water-works -operations the entire time from the pollution to the consumption of -the water is but a few days or even less, and time does not materially -improve water in this period.</p> - -<p>Sedimentation removes bacteria only slowly, as might be expected from -their exceedingly small size; and in addition their specific gravity -probably is but slightly greater than that of water. The Lawrence -reservoir, holding from 10 to 14 days’ supply, effected, by the -combined effect of time and sedimentation, a reduction of 90 per cent -of the bacteria in the raw water. In spite of this the city suffered -severely and continuously from fever. It would probably have suffered -even more, however, had it not been for this reduction. Nothing is -known of the removal of bacteria by sedimentation from flowing rivers, -but, considering the slowness with which the process takes place in -standing water, it is evident that we cannot hope for very much in -streams, and especially rapid streams, where the opportunities for -sedimentation are still less favorable.</p> - -<p>Filtration as practiced in Europe removes promptly and certainly a very -large proportion of the bacteria—probably, under all proper conditions, -over 99 per cent, and is thus much more effective in purification -than even weeks of storage or long flows in rivers. The places using -filtered water have, in general, extremely low death-rates from typhoid -fever. The fever which has occurred at a few places drawing their -raw water from greatly polluted sources has resulted from improper -conditions which can be avoided, and affords no ground for doubt of the -efficiency of properly conducted filtration.</p> - -<p><span class="pagenum" id="Page_220">[Pg 220]</span></p> - -<p>Corresponding evidence has not yet been produced in connection with -the mechanical filters which have been largely used in the United -States; but the bacterial efficiencies secured with them, under proper -conditions, and with enough coagulant, have been such as to warrant the -belief that they also will serve to greatly diminish the danger from -such infection, although they have not shown themselves equal in this -respect to sand filters.</p> - -<p>The main point is that disease-germs shall not be present in our -drinking-water. If they can be kept out in the first place at -reasonable expense, that is the thing to do. Innocence is better -than repentance. If they cannot be kept out, we must take them out -afterwards; it does not matter much how this is done, so long as the -work is thorough. Sedimentation and storage may accomplish much, but -their action is too slow and often uncertain. Filtration properly -carried out removes bacteria promptly and thoroughly and at a -reasonable expense.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_221">[Pg 221]</span></p> - -<p class="center"><span class="largest">APPENDICES.</span></p> -</div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<h2 class="nobreak" id="APPENDIX_I">APPENDIX I.<br /> -<br /> - -<span class="small">RULES OF THE GERMAN GOVERNMENT IN REGARD TO THE FILTRATION OF -SURFACE-WATERS USED FOR PUBLIC WATER-SUPPLIES.</span></h2></div> - -<p><span class="smcap">Rules</span> somewhat similar to those of which a translation is given -below were first issued by the Imperial Board of Health in 1892. -These rules were regarded as unnecessarily rigid, and a petition was -presented to the government signed by 37 water-works engineers and -directors requesting a revision.<a id="FNanchor_50" href="#Footnote_50" class="fnanchor">[50]</a> As a result a conference was -organized consisting of 14 members.<a id="FNanchor_51" href="#Footnote_51" class="fnanchor">[51]</a> Köhler presided, and Koch, -Gaffsky, Werner, Günther, and Reincke represented the Imperial Board -of Health. The bacteriologists were represented by Flügge, Wolffhügel, -and Fränkel, while Beer, Fischer, Lindley, Meyer, and Piefke were the -engineer members.</p> - -<p>This conference prepared the 17 articles given below in the first -days of January, 1894. A little later the first 16 articles were -issued to all German local authorities, signed by Bosse, minister of -the “Geistlichen,” and Haase, minister of the interior, and they are -considered as binding upon all water-works using surface-water. The -bacterial examinations were commenced April 1, 1894, by most of the -cities which had not previously had them.</p> - -<p><span class="pagenum" id="Page_222">[Pg 222]</span></p> - -<p>Although the articles do not deal with rate of filtration, or the -precautions against snow and ice, they have a very great interest both -because they are an official expression, and on account of the personal -standing of the men who prepared them.</p> - -<p class="padt1">§ 1. In judging of the quality of a filtered surface-water the -following points should be especially observed:</p> - -<p><em>a</em>. The operation of a filter is to be regarded as satisfactory -when the filtrate contains the smallest possible number of bacteria, -not exceeding the number which practical experience has shown to be -attainable with good filtration at the works in question. In those -cases where there are no previous records showing the possibilities of -the works and the influence of the local conditions, especially the -character of the raw water, and until such information is obtained, -it is to be taken as the rule that a satisfactory filtration will -never yield an effluent with more than about 100 bacteria per cubic -centimeter.</p> - -<p><em>b</em>. The filtrate must be as clear as possible, and, in regard to -color, taste, temperature, and chemical composition, must be no worse -than the raw water.</p> - -<p>§ 2. To allow a complete and constant control of the bacterial -efficiency of filtration, the filtrate from each single filter must be -examined daily. Any sudden increase in the number of bacteria should -cause a suspicion of some unusual disturbance in the filter, and should -make the superintendent more attentive to the possible causes of it.</p> - -<p>§ 3. Filters must be so constructed that samples of the effluent -from any one of them can be taken at any desired time for the -bacteriological examination mentioned in § 1.</p> - -<p>§ 4. In order to secure uniformity of method, the following is -recommended as the standard method for bacterial examination:</p> - -<p>The nutrient medium consists of 10 per cent meat extract gelatine with -peptone, 10 cc. of which is used for each experiment. Two samples of -the water under examination are to be taken, one<span class="pagenum" id="Page_223">[Pg 223]</span> of 1 cc. and one -of <sup>1</sup>⁄<sub>2</sub> cc. The gelatine is melted at a temperature of 30° to 35° C., -and mixed with the water as thoroughly as possible in the test-tube -by tipping back and forth, and is then poured upon a sterile glass -plate. The plates are put under a bell-jar which stands upon a piece -of blotting-paper saturated with water, and in a room in which the -temperature is about 20° C.</p> - -<p>The resulting colonies are counted after 48 hours, and with the aid of -a lens.</p> - -<p>If the temperature of the room in which the plates are kept is lower -than the above, the development of the colonies is slower, and the -counting must be correspondingly postponed.</p> - -<p>If the number of colonies in 1 cc. of the water is greater than about -100, the counting must be done with the help of the Wolffhügel’s -apparatus.</p> - -<p>§ 5. The person entrusted with the carrying-out of the bacterial -examinations must present a certificate that he possesses the necessary -qualifications, and wherever possible he shall be a regular employé of -the water-works.</p> - -<p>§ 6. When the effluent from a filter does not correspond to the -hygienic requirements it must not be used, unless the cause of the -unsatisfactory work has already been removed during the period covered -by the bacterial examinations.</p> - -<p>In case a filter for more than a very short time yields a poor -effluent, it is to be put out of service until the cause of the trouble -is found and corrected.</p> - -<p>It is, however, recognized from past experience that sometimes -unavoidable conditions (high water, etc.) make it impossible, from an -engineering standpoint, to secure an effluent of the quality stated -in § 1. In such cases it will be necessary to get along with a poorer -quality of water; but at the same time, if the conditions demand it -(outbreak of an epidemic, etc.), a suitable notice should be issued.</p> - -<p>§ 7. Every single filter must be so built that, when an inferior -effluent results, which does not conform to the requirements, it can be -disconnected from the pure-water pipes and the filtrate allowed<span class="pagenum" id="Page_224">[Pg 224]</span> to be -wasted, as mentioned in § 6. This wasting should in general take place, -so far as the arrangement of the works will permit it:</p> - -<p>(1) Immediately after scraping a filter; and</p> - -<p>(2) After replacing the sand to the original depth.</p> - -<p>The superintendent must himself judge, from previous experience with -the continual bacterial examinations, whether it is necessary to waste -the water after these operations, and, if so, how long a time will -probably elapse before the water reaches the standard purity.</p> - -<p>§ 8. The best sand-filtration requires a liberal area of -filter-surface, allowing plenty of reserve, to secure, under all local -conditions, a moderate rate of filtration adapted to the character of -the raw water.</p> - -<p>§ 9. Every single filter shall be independently regulated, and the -rate of filtration, loss of head, and character of the effluent shall -be known. Also each filter shall, by itself, be capable of being -completely emptied, and, after scraping, of having filtered water -introduced from below until the sand is filled to the surface.</p> - -<p>§ 10. The velocity of filtration in each single filter shall be capable -of being arranged to give the most favorable results, and shall be as -regular as possible, quite free from sudden changes or interruptions. -On this account reservoirs must be provided large enough to balance the -hourly fluctuation in the consumption of water.</p> - -<p>§ 11. The filters shall be so arranged that their working shall not be -influenced by the fluctuating level of the water in the filtered-water -reservoir or pump-well.</p> - -<p>§ 12. The loss of head shall not be allowed to become so great as -to cause a breaking through of the upper layer on the surface of -the filter. The limit to which the loss of head can be allowed to -go without damage is to be determined for each works by bacterial -examinations.</p> - -<p>§ 13. Filters shall be constructed throughout in such a way as to -insure the equal action of every part of their area.</p> - -<p><span class="pagenum" id="Page_225">[Pg 225]</span></p> - -<p>§ 14. The sides and bottoms of filters must be made water-tight, and -special pains must be taken to avoid the danger of passages or loose -places through which the unfiltered water on the filter might find its -way to the filtered-water channels. To this end special pains should be -taken to make and keep the ventilators for the filtered-water channels -absolutely tight.</p> - -<p>§ 15. The thickness of the sand-layer shall be so great that under no -circumstances shall it be reduced by scraping to less than 30 cm. (= -12 inches), and it is desirable, so far as local conditions allow, to -increase this minimum limit.</p> - -<p>Special attention must be given to the upper layer of sand, which must -be arranged and continually kept in the condition most favorable for -filtration. For this reason it is desirable that, after a filter has -been reduced in thickness by scraping and is about to be refilled, the -sand below the surface, as far as it is discolored, should be removed -before bringing on the new sand.</p> - -<p>§ 16. Every city in the German empire using sand-filtered water is -requested to make a quarterly report of its working results, especially -of the bacterial character of the water before and after filtration, -to the Imperial Board of Health (Kaiserlichen Gesundheitsamt), which -will keep itself in communication with the commission chosen by the -water-works engineers in regard to these questions; and it is believed -that after such statistical information is obtained for a period of -about two years some farther judgments can be reached.</p> - -<p>§ 17. The question as to the establishment of a permanent inspection -of public water-works, and, if so, under what conditions, can be best -answered after the receipt of the information indicated in § 16.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_226">[Pg 226]</span></p> - -<h2 class="nobreak" id="APPENDIX_II">APPENDIX II.<br /> -<br /> - -<span class="small">EXTRACTS FROM “BERICHT DES MEDICINAL-INSPECTORATS DES HAMBURGISCHEN -STAATES FÜR DAS JAHR 1892.”</span></h2></div> - -<p><span class="smcap">The</span> following are translations from Dr. Reincke’s most valuable report -upon the vital statistics of Hamburg for 1892. I much regret that I am -unable to reproduce in full the very complete and instructive tables -and diagrams which accompany the report.</p> - -<p><b>Diarrhœa and Cholera Infantum</b> (page 10). “It is usually assumed -that the increase of diarrhœal diseases in summer is to be explained -by the high temperature, especially by the action of the heat upon the -principal food of infants—milk. Our observations, however, indicate -that a deeper cause must be sought.” (Tables and diagrams of deaths -from cholera infantum by months for Hamburg and for Altona with the -mean temperatures, 1871-1892.)</p> - -<p>“From these it appears that the highest monthly mortality of each year -in Hamburg occurred 7 times in July, 13 times in August, and 3 times -in September, and substantially the same in Altona. If one compares -the corresponding temperatures, it is found that in the three years -1886, 1891, and 1892, with high September mortalities, especially the -first two of them, had their maximum temperature much earlier, in fact -earlier than usual. Throughout, the correspondence between deaths and -temperatures is not well marked. Repeated high temperatures in May and -June have never been followed by a notable amount of cholera infantum, -although such periods have lasted for a considerable time. For example, -toward the end of May, 1892, for a long time the temperature was higher -than in the following August, when the cholera infantum appeared.</p> - -<p><span class="pagenum" id="Page_227">[Pg 227]</span></p> - -<p>“The following observations are still more interesting. As is seen -from the diagram, in addition to the annual rise in summer there is -also a smaller increase in the winter, which is especially marked -in Altona. In 1892 this winter outbreak was greater than the summer -one, and nearly as great in 1880 and in 1888. The few years when -this winter increase was not marked, 1876-7, 1877-8, 1881-2, 1883-4, -were warm winters in which the mean temperature did not go below the -freezing-point. It is also to be noted that the time of this winter -outbreak is much more variable than that of the summer one. In 1887 the -greatest mortality was in November; in 1889 in February; in other years -in December or January, and in Altona, in 1886 and 1888, in March, -which is sufficient evidence that it was not the result of Christmas -festivities.</p> - -<p>“Farther, the winter diarrhœa of Hamburg and of Altona are not parallel -as is the case in summer. In Hamburg the greatest mortality generally -comes before New Year’s; in Altona one to two months later.</p> - -<p>“In Bockendahl’s Generalbericht über das öffentliche Gesundheitswesen -der Provinz Schleswig-Holstein für das Jahr 1870, page 10, we read: -‘Yet more remarkable was an epidemic of cholera infantum in Altona -in February which proved fatal to 43 children. These cases were -distributed in every part of the city, and could not be explained -by the health officer until he ascertained that the water company -had supplied unfiltered water to the city. This occurred for a few -days only in January, and was the only time in the whole year that -unfiltered Elbe water was delivered. However little reason there may -be to believe that there was a connection between these circumstances, -future interruptions of the service of filtered water should be most -critically watched, as only in this way can reliable conclusions be -reached. Without attempting to draw any scientific conclusions from -the fact, I cannot do less than record that, prior to the outbreak -of cholera on August 20, 1871, unfiltered together with filtered -water had been supplied to the city August 11 to 18. The action of -the authorities was then justified when<span class="pagenum" id="Page_228">[Pg 228]</span> they forbade in future the -supply of unfiltered water except in cases of most urgent necessity, -as in case of general conflagration; and in such a case, or in case of -interruption due to broken pipes, that the public should be suitably -warned.’</p> - -<p>“The author of this paragraph, Dr. Kraus, became later the health -officer of Hamburg, and in an opinion written by him in 1874, and now -before me, he most earnestly urged the adoption of sand-filtration in -Hamburg, and cites the above observations in support of his position. -In the annual report of vital statistics of Hamburg for 1875 he says -that it is quite possible that the addition of unfiltered Elbe water -to milk is the cause of the high mortality from cholera infantum, as -compared with London, and this idea was often afterward expressed by -him. Since then so much evidence has accumulated that his view may -fairly be considered proved.</p> - -<p>“For the information of readers not familiar with local conditions, -a mention of the sources of the water-supplies up to the present -time used by Hamburg and Altona will be useful. Both cities take -their entire water-supplies from the Elbe—Altona from a point about 7 -miles below the discharge of the sewage of both cities, Hamburg from -about 7 miles above. The raw water at Altona is thus polluted by the -sewage from the population of both cities, having now together over -700,000 inhabitants, and contains in general 20,000 to 40,000 or more -bacteria per cubic centimeter. The raw water of Hamburg has, however, -according to the time of year and tide, from 200 to 5000, but here also -occasionally much higher numbers are obtained when the ebb tide carries -sewage up to the intake. How often this takes place is not accurately -known, but most frequently in summer when the river is low, more rarely -in winter and in times of flood. Recent bacterial examinations show -that it occurs much more frequently than was formerly assumed from -float experiments. This water is pumped directly to the city raw, while -that for Altona is carefully filtered.</p> - -<p>“Years ago I expressed the opinion that the repeated typhoid<span class="pagenum" id="Page_229">[Pg 229]</span> epidemics -in Altona stood in direct connection with disturbances of the action -of the filters by frost, which result in the supply of insufficiently -purified water. Wallichs in Altona has also come to this conclusion -as a result of extended observation, and recently Robert Koch has -explained the little winter epidemic of cholera in Altona in the same -way, thus supporting our theory. When open filters are cleaned in cold, -frosty weather the bacteria in the water are not sufficiently held back -by the filters. Such disturbances of filtration not only preceded the -explosive epidemics of typhoid fever of 1886, 1887, 1888, 1891, and -1892, and the cholera outbreaks of 1871 and 1893, but also the winter -outbreaks of cholera infantum which have been so often repeated. It -cannot be doubted that these phenomena bear the relation to each other -of cause and effect. It is thus explained why in the warm winters no -such outbreaks have taken place, and also why the cholera infantum in -winter is not parallel in Hamburg and Altona.</p> - -<hr class="tb" /> - -<p>“A farther support of this idea is furnished by Berlin, where in the -same way frost has repeatedly interfered with filtration. In the -following table are shown the deaths from diarrhœa and cholera infantum -for a few winter periods having unusual increases in mortality in -comparison with the bacteria in the water-supply.” (These tables show -that in March, 1886, March, 1888, February-March, 1889, and February, -1891, high numbers of bacteria resulted from frost disturbance at -the Stralau works, and in every case they were followed by greatly -increased death-rates from diarrhœal diseases.—A. H.)</p> - -<p>“No one who sees this exhibition can doubt that here also the supply -of inadequately purified water has every time cost the lives of many -children.” (100 to 400 or more each time.—A. H.) “Even more conclusive -is the evidence, published by the Berlin Health Office, that this -increase was confined to those parts of the city supplied from Stralau” -(with open filters.—A. H.), “and that the parts supplied from the -better Tegel works took no part in the outbreaks,<span class="pagenum" id="Page_230">[Pg 230]</span> which was exactly -the case with the well-known typhoid epidemic of February and March, -1889.... It was also found that those children nursed by their mothers -or by wet-nurses did not suffer, but only those fed on the milk of -animals or other substitutes, and which in any case were mixed with -more or less water.”</p> - -<p>Under <b>Cholera</b>, page 28, he says: “The revised statistics here -given differ slightly from preliminary figures previously issued and -widely published.” (The full tables, which cannot be here reproduced, -show 16,956 cases and 8605 deaths. 8146 of the deaths occurred in the -month ending September 21. Of these, 1799 were under 5 years old; 776 -were 5 to 15; 744, 15 to 25; 3520, 25 to 50; 1369, 50 to 70; and 397 -over 70 or of unknown age. The bulk of the cases were thus among mature -people, children, except very young children, suffering the least -severely of any age class.)</p> - -<p>“The epidemic began on August 16, in the port where earlier outbreaks -have also had their origin. The original source of the infection -has not been ascertained with certainty, but was probably from one -of two sources. Either it came from certain Jews, just arrived from -cholera-stricken Russia, who were encamped in large numbers near the -American pier, or the infection came from Havre, where cholera had been -present from the middle of July. Perhaps the germs came in ships in -water-ballast which was discharged at Hamburg, which is so much more -probable, as the sewage of Havre is discharged directly into the docks.</p> - -<p>“It is remarkable that in Altona, compared to the total number of -cases, very few children had cholera, while in the epidemic of 1871 the -children suffered severely. This may be explained by supposing that the -cholera of 1892 in Altona was not introduced by water, but by other -means of infection....</p> - -<p>“It is well known that the drinking-water (of Hamburg) is supposed to -have been from the first the carrier of the cholera-germs. In support -of this view the following points are especially to be noted:</p> - -<p>“1. The explosive rapidity of attack. The often-compared epidemic<span class="pagenum" id="Page_231">[Pg 231]</span> -in Munich in 1854, which could not have come from the water is -characteristically different in that its rise was much slower and was -followed by a gradual decline. In Hamburg, with six times as large a -population, the height of the epidemic was reached August 27, only 12 -days after the first cases of sickness, while in Munich 25 days were -required. In Hamburg also the bulk of the cases were confined to 12 -days, from August 25 to September 5, while in Munich the time was twice -as long.</p> - -<p>“2. The exact limit of the epidemic to the political boundary between -Hamburg and Altona and Wandsbeck, which also agrees with the boundary -between the respective water-supplies, while other differences were -entirely absent. Hamburg had for 1000 inhabitants 26.31 cases and 13.39 -deaths, but Altona only 3.81 cases and 2.13 deaths, and Wandsbeck 3.06 -cases and 2.09 deaths.</p> - -<p>“3. The old experience of cholera in fresh-water ports, and the analogy -of many earlier epidemics. In this connection the above-mentioned -epidemic of 1871 in Altona has a special interest, even though some -of the conclusions of Bockendahl’s in his report of 1871 are open to -objection. First there were 3 deaths August 3, which were not at once -followed by others. Then unfiltered Elbe water was supplied August 11 -to 18. On the 19th an outbreak of cholera extended to all parts of -the city, which reached its height August 25 and 26, and afterwards -gradually decreased. In all 105 persons died of cholera and 186 (179 of -them children) of diarrhœa. In Hamburg, four times as large, only 141 -persons died of cholera at this time, thus proportionately a smaller -number. The conditions were then the reverse of those of 1892, an -infection of the Altona water and a comparative immunity in Hamburg.</p> - -<p>“It is objected that the cholera-germs were not found in the water -in 1892. To my knowledge they were first looked for, and then -with imperfect methods, in the second half of September. In the -after-epidemics at Altona, they were found in the river-water by R. -Koch by the use of better methods.</p> - -<p>“It is quite evident that the germs were also distributed by other<span class="pagenum" id="Page_232">[Pg 232]</span> -methods than by the city water, especially by dock-laborers who became -infected while at their work and thus set up little secondary epidemics -where they went or lived.... These laborers and sailors, especially on -the smaller river-boats, had an enormously greater proportionate amount -of cholera than others.... These laborers do not live exclusively near -the water, but to a measure in all parts of the city.” (And in Altona -and Wandsbeck.—A. H.)</p> - -<p>“Altona had 5 deaths from cholera December 25 to January 4, and 19 -January 23 to February 11, and no more. As noted above, this is -attributed to the water-supply, and to defective filtration in presence -of frost....</p> - -<p>“The cholera could never have reached the proportion which it did, had -the improvements in the drinking-water been earlier completed.”</p> - -<p>Further accounts of the water-supplies of Altona and of Hamburg and of -the new filtration works at the latter city are given in Appendices VII -and VIII.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_233">[Pg 233]</span></p> - -<h2 class="nobreak" id="APPENDIX_III">APPENDIX III.<br /> -<br /> - -<span class="small">METHODS OF SAND ANALYSIS</span><br /> -<br /> -<span class="smallest">(From the Annual Report of the Massachusetts State Board of Health for -1892.)</span></h2></div> - -<p><span class="smcap">A knowledge</span> of the sizes of the sand-grains forms the basis of many of -the computations. This information is obtained by means of mechanical -analyses. The sand sample is separated into portions having grains -of definite sizes, and from the weight of the several portions the -relative quantities of grains of any size can be computed.</p> - -<p><b>Collection of Samples.</b>—In shipping and handling, samples of sand -are best kept in their natural moist condition, as there is then no -tendency to separation into portions of unequal-sized grains. Under no -circumstances should different materials be mixed in the same sample. -If the material under examination is not homogeneous, samples of each -grade should be taken in separate bottles, with proper notes in regard -to location, quantity, etc. Eight-ounce wide-necked bottles are most -convenient for sand samples, but with gravels a larger quantity is -often required. Duplicate samples for comparison after obtaining the -results of analyses are often useful.</p> - -<p><b>Separation into Portions having Grains of Definite Sizes.</b>—Three -methods are employed for particles of different sizes—hand-picking -for the stones, sieves for the sands, and water elutriation for the -extremely fine particles. Ignition, or determination of albuminoid -ammonia, might be added for determining the quantity of organic matter, -which, as a matter of convenience, is assumed to consist of particles -less than 0.01 millimeter in diameter.</p> - -<p><span class="pagenum" id="Page_234">[Pg 234]</span></p> - -<p>The method of hand-picking is ordinarily applied only to particles -which remain on a sieve two meshes to an inch. The stones of this size -are spread out so that all are in sight, and a definite number of the -largest are selected and weighed. The diameter is calculated from the -average weight by the method to be described, while the percentage is -reckoned from the total weight. Another set of the largest remaining -stones is then picked out and weighed as before, and so on until the -sample is exhausted. With a little practice the eye enables one to pick -out the largest stones quite accurately.</p> - -<p>With smaller particles this process becomes too laborious, on account -of the large number of particles, and sieves are therefore used -instead. The sand for sifting must be entirely free from moisture, and -is ordinarily dried in an oven at a temperature somewhat above the -boiling-point. The quantity taken for analysis should rarely exceed -100-200 grams. The sieves are made from carefully-selected brass-wire -gauze, having, as nearly as possible, square and even-sized meshes. The -frames are of metal, fitting into each other so that several sieves can -be used at once without loss of material. It is a great convenience to -have a mechanical shaker, which will take a series of sieves and give -them a uniform and sufficient shaking in a short time; but without this -good results can be obtained by hand-shaking. A series which has proved -very satisfactory has sieves with approximately 2, 4, 6, 10, 20, 40, -70, 100, 140, and 200 meshes to an inch; but the exact numbers are of -no consequence, as the actual sizes of the particles are relied upon, -and not the number of meshes to an inch.</p> - -<p>It can be easily shown by experiment that when a mixed sand is shaken -upon a sieve the smaller particles pass first, and as the shaking -is continued larger and larger particles pass, until the limit is -reached when almost nothing will pass. The last and largest particles -passing are collected and measured, and they represent the separation -of that sieve. The size of separation of a sieve bears a tolerably -definite relation to the size of the mesh, but the relation<span class="pagenum" id="Page_235">[Pg 235]</span> is not to -be depended upon, owing to the irregularities in the meshes and also -to the fact that the finer sieves are woven on a different pattern -from the coarser ones, and the particles passing the finer sieves are -somewhat larger in proportion to the mesh than is the case with the -coarser sieves. For these reasons the sizes of the sand-grains are -determined by actual measurements, regardless of the size of the mesh -of the sieve.</p> - -<p>It has not been found practicable to extend the sieve-separations to -particles below 0.10 millimeter in diameter (corresponding to a sieve -with about 200 meshes to an inch), and for such particles elutriation -is used. The portion passing the finest sieve contains the greater -part of the organic matter of the sample, with the exception of roots -and other large undecomposed matters, and it is usually best to remove -this organic matter by ignition at the lowest possible heat before -proceeding to the water-separations. The loss in weight is regarded as -organic matter, and calculated as below 0.01 millimeter in diameter. -In case the mineral matter is decomposed by the necessary heat, the -ignition must be omitted, and an approximate equivalent can be obtained -by multiplying the albuminoid ammonia of the sample by 50.<a id="FNanchor_52" href="#Footnote_52" class="fnanchor">[52]</a> In this -case it is necessary to deduct an equivalent amount from the other fine -portions, as otherwise the analyses when expressed in percentages would -add up to more than one hundred.</p> - -<p>Five grams of the ignited fine particles are put in a beaker 90 -millimeters high and holding about 230 cubic centimeters. The beaker -is then nearly filled with distilled water at a temperature of 20° C., -and thoroughly mixed by blowing into it air through a glass tube. A -larger quantity of sand than 5 grams will not settle uniformly in the -quantity of water given, but less can be used if desired. The rapidity -of settlement depends upon the temperature of the water, so that it is -quite important that no material variation in temperature should occur. -The mixed sand and water is allowed<span class="pagenum" id="Page_236">[Pg 236]</span> to stand for fifteen seconds, when -most of the supernatant liquid, carrying with it the greater part of -the particles less than 0.08 millimeter, is rapidly decanted into a -suitable vessel, and the remaining sand is again mixed with an equal -amount of fresh water, which is again poured off after fifteen seconds, -carrying with it most of the remaining fine particles. This process is -once more repeated, after which the remaining sand is allowed to drain, -and is then dried and weighed, and calculated as above 0.08 millimeter -in diameter. The finer decanted sand will have sufficiently settled -in a few minutes, and the coarser parts at the bottom are washed back -into the beaker and treated with water exactly as before, except that -one minute interval is now allowed for settling. The sand remaining -is calculated as above 0.04 millimeter, and the portion below 0.04 is -estimated by difference, as its direct determination is very tedious, -and no more accurate than the estimation by difference when sufficient -care is used.</p> - -<p><b>Determination of the Sizes of the Sand-grains.</b>—The sizes of the -sand-grains can be determined in either of two ways—from the weight -of the particles or from micrometer measurements. For convenience the -size of each particle is considered to be the diameter of a sphere -of equal volume. When the weight and specific gravity of a particle -are known, the diameter can be readily calculated. The volume of a -sphere is <sup>1</sup>⁄<sub>6</sub>π<em>d</em><sup>3</sup>, and is also equal to the weight divided -by the specific gravity. With the Lawrence materials the specific -gravity is uniformly 2.65 within very narrow limits, and we have -<sup><em>w</em></sup>⁄<sub>2.65</sub> = <sup>1</sup>⁄<sub>6</sub>π<em>d</em><sup>3</sup>. Solving for <em>d</em> we obtain the -formula <em>d</em> = .9∛<span class="o"><em>w</em></span>, where <em>d</em> is the diameter of -a particle in millimeters and <em>w</em> its weight in milligrams. As -the average weight of particles, when not too small, can be determinedd -with precision, this method is very accurate, and altogether the most -satisfactory for particles above 0.10 millimeter; that is, for all -sieve separations. For the finer particles the method is inapplicable, -on account of the vast number of particles to be counted in the -smallest portion<span class="pagenum" id="Page_237">[Pg 237]</span> which can be accurately weighed, and in these cases -the sizes are determined by micrometer measurements. As the sand-grains -are not spherical or even regular in shape, considerable care is -required to ascertain the true mean diameter. The most accurate method -is to measure the long diameter and the middle diameter at right -angles to it, as seen by a microscope. The short diameter is obtained -by a micrometer screw, focussing first upon the glass upon which the -particle rests and then upon the highest point to be found. The mean -diameter is then the cube root of the product of the three observed -diameters. The middle diameter is usually about equal to the mean -diameter, and can generally be used for it, avoiding the troublesome -measurement of the short diameters.</p> - -<p>The sizes of the separations of the sieves are always determined from -the very last sand which passes through in the course of an analysis, -and the results so obtained are quite accurate. With the elutriations -average samples are inspected, and estimates made of the range in -size of particles in each portion. Some stray particles both above -and below the normal sizes are usually present, and even with the -greatest care the result is only an approximation to the truth; still, -a series of results made in strictly the same way should be thoroughly -satisfactory, notwithstanding possible moderate errors in the absolute -sizes.</p> - -<p><b>Calculation of Results.</b>—When a material has been separated into -portions, each of which is accurately weighed, and the range in the -sizes of grains in each portion determined, the weight of the particles -finer than each size of separation can be calculated, and with enough -properly selected separations the results can be plotted in the form of -a diagram, and measurements of the curve taken for intermediate points -with a fair degree of accuracy. This curve of results may be drawn upon -a uniform scale, using the actual figures of sizes and of per cents by -weight, or the logarithms of the figures may be used in one or both -directions. The method of plotting is not of vital importance, and -the method for any set of materials which gives the most easily and -accurately drawn curves<span class="pagenum" id="Page_238">[Pg 238]</span> is to be preferred. In the diagram published -in the Report of the Mass. State Board of Health for 1891, page 430, -the logarithmic scale was used in one direction, but in many instances -the logarithmic scale can be used to advantage in both directions. With -this method it has been found that the curve is often almost a straight -line through the lower and most important section, and very accurate -results are obtained even with a smaller number of separations.</p> - -<p><b>Examples of Calculation of Results.</b>—Following are examples of -representative analyses, showing the method of calculation used with -the different methods of separation employed with various materials.</p> - -<p class="center padt1 padb1">I. ANALYSIS OF A GRAVEL BY HAND-PICKING, 11,870 GRAMS TAKEN FOR ANALYSIS.</p> - -<table class="autotable" summary="analysis by hand picking"> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Number of Stones<br />in Portion.<br />(Largest<br />Selected<br />Stones.)</th> -<th class="tdc normal small bord_top bord_right bord_bot">Total<br />Weight of<br />Portion.<br />Grams.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Average<br />Weight of<br />Stones.<br />Milligrams.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Estimated<br />Weight of<br />Smallest<br />Stones<br />Milligrams.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Corresponding<br />Size.<br />Millimeters.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Total<br />Weight of<br />Stones<br />Smaller than<br />this Size.</th> -<th class="tdc normal small bord_top bord_bot">Per Cent of<br />Total<br />Weight<br />Smaller than<br />this Size.</th> -</tr> -<tr> -<td class="tdl bord_right vertb"> </td> -<td class="tdc bord_right vertb">....</td> -<td class="tdc bord_right vertb">....</td> -<td class="tdc bord_right vertb">....</td> -<td class="tdc bord_right vertb">....</td> -<td class="tdr bord_right vertb"><span class="padrp5">11,870</span></td> -<td class="tdr vertb"><b>100 </b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">10</td> -<td class="tdr bord_right vertb"><span class="padrp5">3,320</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">332,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">250,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>56</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">8,550</span></td> -<td class="tdr vertb"><b>72 </b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">10</td> -<td class="tdr bord_right vertb"><span class="padrp5">1,930</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">193,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">165,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>49</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">6,620</span></td> -<td class="tdr vertb"><b>56 </b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">10</td> -<td class="tdr bord_right vertb"><span class="padrp5">1,380</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">138,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">124,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>45</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">5,240</span></td> -<td class="tdr vertb"><b>44 </b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">20</td> -<td class="tdr bord_right vertb"><span class="padrp5">2,200</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">110,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">93,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>41</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">3,040</span></td> -<td class="tdr vertb"><b>26 </b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">20</td> -<td class="tdr bord_right vertb"><span class="padrp5">1,520</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">76,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">64,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>36</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">1,520</span></td> -<td class="tdr vertb"><b>13 </b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">20</td> -<td class="tdr bord_right vertb"><span class="padrp5">1,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">50,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">36,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>30</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">520</span></td> -<td class="tdr vertb"><b>4.4</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">20</td> -<td class="tdr bord_right vertb"><span class="padrp5">460</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">23,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">10,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>20</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">60</span></td> -<td class="tdr vertb"><b>.5</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">10</td> -<td class="tdr bord_right vertb"><span class="padrp5">40</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">4,000</span></td> -<td class="tdr bord_right vertb"><span class="padrp5">2,000</span></td> -<td class="tdc bord_right vertb"><span class="padrp5"><b>11</b></span></td> -<td class="tdr bord_right vertb"><span class="padrp5">20</span></td> -<td class="tdr vertb"><b>.2</b></td> -</tr> -<tr> -<td class="tdl bord_right bord_bot">Dust</td> -<td class="tdr bord_right bord_bot"><span class="padrp5">20</span></td> -<td class="tdc bord_right bord_bot"><span class="padrp5">....</span></td> -<td class="tdc bord_right bord_bot"><span class="padrp5">....</span></td> -<td class="tdc bord_right bord_bot"><span class="padrp5">....</span></td> -<td class="tdc bord_right bord_bot"><span class="padrp5">....</span></td> -<td class="tdc bord_bot"><span class="padrp5">....</span></td> -</tr> -</table> - -<p class="padt1">The weight of the smallest stones in a portion given in the fourth -column is estimated in general as about half-way between the average -weight of all the stones in that portion and the average weight of the -stones in the next finer portion.</p> - -<p>The final results are shown by the figures in full-faced type in the -last and third from the last columns. By plotting these figures we -find that 10 per cent of the stones are less than 35 millimeters in -diameter, and 60 per cent are less than 51 millimeters. The “uniformity -coefficient,” as described below, is the ratios of these numbers, or -1.46, while the “effective size” is 35 millimeters.</p> - -<p><span class="pagenum" id="Page_239">[Pg 239]</span></p> - -<p class="center padt1 padb1">II. ANALYSIS OF A SAND BY MEANS OF SIEVES.</p> - -<p class="padb1">A portion of the sample was dried in a porcelain dish in an air-bath. -Weight dry, 110.9 grams. It was put into a series of sieves in a -mechanical shaker, and given one hundred turns (equal to about seven -hundred single shakes). The sieves were then taken apart, and the -portion passing the finest sieve weighed. After noting the weight, the -sand remaining on the finest sieve, but passing all the coarser sieves, -was added to the first and again weighed, this process being repeated -until all the sample was upon the scale, weighing 110.7 grams, showing -a loss by handling of only 0.2 gram. The figures were as follows:</p> - -<table class="autotable" summary="analysis by sieve"> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Sieve<br />Marked.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Size of<br />Separation<br />of this<br />Sieve.<br />Millimeters.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Quantity<br />of Sand<br />Passing.<br />Grams.</th> -<th class="tdc normal small bord_top bord_bot">Per Cent<br />of<br />Total<br />Weight.</th> -</tr> -<tr> -<td class="tdl bord_right vertb">190</td> -<td class="tdc bord_right vertb"><b>.105</b></td> -<td class="tdc bord_right vertb">.5</td> -<td class="tdc"><b> .5</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">140</td> -<td class="tdc bord_right vertb"><b>.135</b></td> -<td class="tdc bord_right vertb">1.3</td> -<td class="tdc"><b> 1.2</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb">100</td> -<td class="tdc bord_right vertb"><b>.182</b></td> -<td class="tdc bord_right vertb">4.1</td> -<td class="tdc"><b> 3.7</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb"> 60</td> -<td class="tdc bord_right vertb"><b>.320</b></td> -<td class="tdc bord_right vertb">23.2</td> -<td class="tdc"><b> 21.0</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb"> 40</td> -<td class="tdc bord_right vertb"><b>.46 </b></td> -<td class="tdc bord_right vertb">56.7</td> -<td class="tdc"><b> 51.2</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb"> 20</td> -<td class="tdc bord_right vertb"><b>.93 </b></td> -<td class="tdc bord_right vertb">89.1</td> -<td class="tdc"><b> 80.5</b></td> -</tr> -<tr> -<td class="tdl bord_right vertb"> 10</td> -<td class="tdc bord_right vertb"><b>2.04 </b></td> -<td class="tdc bord_right vertb">104.6</td> -<td class="tdc"><b> 94.3</b></td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot"> 6</td> -<td class="tdc bord_right bord_bot"><b>3.90 </b></td> -<td class="tdc bord_right bord_bot">110.7</td> -<td class="tdc bord_bot"><b>100.0</b></td> -</tr> -</table> - -<p class="padt1">Plotting the figures in heavy-faced type, we find from the curve that -10 and 60 per cent respectively are finer than .25 and .62 millimeter, -and we have for effective size, as described above, .25, and for -uniformity coefficient 2.5.</p> - -<p class="center padt1 padb1">III. ANALYSIS OF A FINE MATERIAL WITH ELUTRIATION.</p> - -<p class="padb1">The entire sample, 74 grams, was taken for analysis. The sieves used -were not the same as those in the previous analysis, and instead of -mixing the various portions on the scale they were separately weighed. -The siftings were as follows:</p> - -<p>Remaining on sieve marked 10, above 2.2 millimeters 1.5 grams<br /> -<span class="add1em">Remaining</span> on sieve marked 20, above .98 millimeters 7.0 grams<br /> -<span class="add1em">Remaining</span> on sieve marked 40, above .46 millimeters 22.0 grams<br /> -<span class="add1em">Remaining</span> on sieve marked 70, above .24 millimeters 20.2 grams<br /> -<span class="add1em">Remaining</span> on sieve marked 140, above .13 millimeters 9.2 grams<br /> -<span class="add1em">Passing</span> sieve<span class="add6em">140,</span> below .13 millimeters 14.1 grams -</p> - -<p><span class="pagenum" id="Page_240">[Pg 240]</span></p> - -<p class="padt1 padb1">The 14.1 grams passing the 140 sieve were thoroughly mixed, and one -third, 4.7 grams, taken for analysis. After ignition just below a red -heat in a radiator, the weight was diminished by 0.47 gram. The portion -above .08 millimeter and between .04 and .08 millimeter, separated as -described above, weighed respectively 1.27 and 1.71 grams, and the -portion below .04 millimeter was estimated by difference [4.7 - (0.47 -+ 1.27 + 1.71)] to be 1.25 grams. Multiplying these quantities by 3, -we obtain the corresponding quantities for the entire sample, and the -calculation of quantities finer than the various sizes can be made as -follows:</p> - -<table class="autotable" summary="quantities finer than the various sizes"> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Size of Grain.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Weight.<br />Grams.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Size of<br />Largest<br />Particles.<br />Millimeters.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Weight of all<br />the Finer<br />Particles.<br />Grams.</th> -<th class="tdc normal small bord_top bord_bot">Per Cent by<br />Weight of<br />all Finer<br />Particles.</th> -</tr> -<tr> - -<td class="tdc bord_right vertb">Above 2.20 millimeters </td> -<td class="tdc bord_right vertb"> 1.50</td> -<td class="tdc bord_right vertb">....</td> -<td class="tdc bord_right vertb">74.00</td> -<td class="tdc"><b>100</b></td> -</tr> -<tr> - -<td class="tdc bord_right vertb">.98-2.20 millimeters</td> -<td class="tdc bord_right vertb"> 7.00</td> -<td class="tdc bord_right vertb"><b>2.20</b></td> -<td class="tdc bord_right vertb">72.50</td> -<td class="tdc"> <b>98</b></td> -</tr> -<tr> - -<td class="tdc bord_right vertb">.46- .98 millimeters</td> -<td class="tdc bord_right vertb">22.00</td> -<td class="tdc bord_right vertb"> <b>.98</b></td> -<td class="tdc bord_right vertb">65.50</td> -<td class="tdc"> <b>89</b></td> -</tr> -<tr> - -<td class="tdc bord_right vertb">.24- .46 millimeters</td> -<td class="tdc bord_right vertb">20.20</td> -<td class="tdc bord_right vertb"> <b>.46</b></td> -<td class="tdc bord_right vertb">43.50</td> -<td class="tdc"> <b>60</b></td> -</tr> -<tr> - -<td class="tdc bord_right vertb">.13- .24 millimeters</td> -<td class="tdc bord_right vertb"> 9.20</td> -<td class="tdc bord_right vertb"> <b>.24</b></td> -<td class="tdc bord_right vertb">23.30</td> -<td class="tdc"> <b>32</b></td> -</tr> -<tr> - -<td class="tdc bord_right vertb">.08- .13 millimeters</td> -<td class="tdc bord_right vertb"> 3.81</td> -<td class="tdc bord_right vertb"> <b>.13</b></td> -<td class="tdc bord_right vertb">14.10</td> -<td class="tdc"> <b>19</b></td> -</tr> -<tr> - -<td class="tdc bord_right vertb">.04- .08 millimeters</td> -<td class="tdc bord_right vertb"> 5.13</td> -<td class="tdc bord_right vertb"> <b>.08</b></td> -<td class="tdc bord_right vertb">10.29</td> -<td class="tdc"> <b>14</b></td> -</tr> -<tr> - -<td class="tdc bord_right vertb">.01- .04 millimeters</td> -<td class="tdc bord_right vertb"> 3.75</td> -<td class="tdc bord_right vertb"> <b>.04</b></td> -<td class="tdc bord_right vertb"> 5.16</td> -<td class="tdc"> <b>7</b></td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot"><p class="indent">Loss on ignition (assumed to be less than .01 millimeter)</p></td> -<td class="tdc bord_right bord_bot"> 1.41</td> -<td class="tdc bord_right bord_bot"> <b>.01</b></td> -<td class="tdc bord_right bord_bot"> 1.41</td> -<td class="tdc bord_bot"> <b>1.9</b></td> -</tr> -</table> - -<p class="padt1 padb1">By plotting the heavy-faced figures we find that 10 and 60 per cent are -respectively finer than .055 and .46 millimeter, and we have effective -size .055 millimeter and uniformity coefficient 8.</p> - -<p>The effective size and uniformity coefficient calculated in this way -have proved to be most useful in various calculations, particularly -in estimating the friction between the sands and gravels and water. -The remainder of the article in the Report of the Mass. State Board -of Health is devoted to a discussion of these relations which were -mentioned in Chapter III of this volume.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_241">[Pg 241]</span></p> - -<h2 class="nobreak" id="APPENDIX_IV">APPENDIX IV.<br /> -<br /> - -<span class="small">FILTER STATISTICS.</span></h2></div> - -<table class="autotable" summary="statistics_of_operation_of_sand_filters"> -<tr> -<th class="tdc normal" colspan="8" id="STATISTICS_OF_OPERATION_OF_SAND_FILTERS">STATISTICS OF OPERATION OF SAND FILTERS.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Place.</th> -<th class="tdc normal small bord_top bord_right bord_bot" colspan="2">Year Ending.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Total<br />Quantity<br />of Water<br />filtered<br />for<br />One Year.<br />Million<br />Gallons.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Million<br />Gallons<br />Daily.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Area<br />of<br />Filters<br />in use,<br /> <br />Acres.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Average<br />Daily<br />Yield,<br /> <br />Million<br />Gallons<br />per Acre.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Area of<br />Filter<br />Surface<br />cleaned<br />in One<br />Year,<br /> <br />Acres.</th> -<th class="tdc normal small bord_top bord_bot">Period,<br />Million<br />Gallons<br />per Acre<br />filtered<br />between<br />Scrapings.</th> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Altona</p></td> -<td class="tdl vertb">March,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1,620</td> -<td class="tdr bord_right vertb">4.44</td> -<td class="tdr bord_right vertb">3.08</td> -<td class="tdr bord_right vertb">1.45</td> -<td class="tdr bord_right vertb">31.0</td> -<td class="tdc">52</td> -</tr> -<tr> - -<td class="tdl vertb">March,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1,730</td> -<td class="tdr bord_right vertb">4.75</td> -<td class="tdr bord_right vertb">3.08</td> -<td class="tdr bord_right vertb">1.55</td> -<td class="tdr bord_right vertb">48.5</td> -<td class="tdc">36</td> -</tr> -<tr> - -<td class="tdl vertb">March,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1,960</td> -<td class="tdr bord_right vertb">5.40</td> -<td class="tdr bord_right vertb">3.08</td> -<td class="tdr bord_right vertb">1.75</td> -<td class="tdr bord_right vertb">44.0</td> -<td class="tdc">45</td> -</tr> -<tr> - -<td class="tdl vertb">March,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">1,940</td> -<td class="tdr bord_right vertb">5.30</td> -<td class="tdr bord_right vertb">3.08</td> -<td class="tdr bord_right vertb">1.72</td> -<td class="tdr bord_right vertb">36.5</td> -<td class="tdc">53</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="3"><p class="indent">Amsterdam, River</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">1,390</td> -<td class="tdr bord_right vertb">3.80</td> -<td class="tdr bord_right vertb">5.43</td> -<td class="tdr bord_right vertb">0.71</td> -<td class="tdr bord_right vertb">23</td> -<td class="tdc">62</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1,490</td> -<td class="tdr bord_right vertb">4.08</td> -<td class="tdr bord_right vertb">5.43</td> -<td class="tdr bord_right vertb">0.75</td> -<td class="tdr bord_right vertb">48</td> -<td class="tdc">31</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1,600</td> -<td class="tdr bord_right vertb">4.40</td> -<td class="tdr bord_right vertb">5.43</td> -<td class="tdr bord_right vertb">0.81</td> -<td class="tdr bord_right vertb">30</td> -<td class="tdc">53</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="3"><p class="indent">Amsterdam, Dunes</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">2,330</td> -<td class="tdr bord_right vertb">6.40</td> -<td class="tdr bord_right vertb">4.94</td> -<td class="tdr bord_right vertb">1.29</td> -<td class="tdr bord_right vertb">116</td> -<td class="tdc">20</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">2,360</td> -<td class="tdr bord_right vertb">6.50</td> -<td class="tdr bord_right vertb">4.75</td> -<td class="tdr bord_right vertb">1.37</td> -<td class="tdr bord_right vertb">90</td> -<td class="tdc">26</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">2,290</td> -<td class="tdr bord_right vertb">6.25</td> -<td class="tdr bord_right vertb">4.75</td> -<td class="tdr bord_right vertb">1.31</td> -<td class="tdr bord_right vertb">109</td> -<td class="tdc">21</td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Ashland, Wis</p></td> -<td class="tdl vertb">Feb.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">398</td> -<td class="tdr bord_right vertb">1.09</td> -<td class="tdr bord_right vertb">0.50</td> -<td class="tdr bord_right vertb">2.18</td> -<td class="tdr bord_right vertb">4.83</td> -<td class="tdc">83</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="3"><p class="indent">Berlin, total</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">13,000</td> -<td class="tdr bord_right vertb">35.60</td> -<td class="tdr bord_right vertb">25.10</td> -<td class="tdr bord_right vertb">1.42</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">12,900</td> -<td class="tdr bord_right vertb">35.40</td> -<td class="tdr bord_right vertb">25.10</td> -<td class="tdr bord_right vertb">1.40</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">13,200</td> -<td class="tdr bord_right vertb">36.20</td> -<td class="tdr bord_right vertb">27.00</td> -<td class="tdr bord_right vertb">1.34</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Bremen</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1,190</td> -<td class="tdr bord_right vertb">3.27</td> -<td class="tdr bord_right vertb">2.51</td> -<td class="tdr bord_right vertb">1.31</td> -<td class="tdr bord_right vertb">50</td> -<td class="tdc">24</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1,220</td> -<td class="tdr bord_right vertb">3.34</td> -<td class="tdr bord_right vertb">3.21</td> -<td class="tdr bord_right vertb">1.04</td> -<td class="tdr bord_right vertb">32.5</td> -<td class="tdc">38</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1,280</td> -<td class="tdr bord_right vertb">3.50</td> -<td class="tdr bord_right vertb">3.21</td> -<td class="tdr bord_right vertb">1.09</td> -<td class="tdr bord_right vertb">25.2</td> -<td class="tdc">50</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">1,400</td> -<td class="tdr bord_right vertb">4.10</td> -<td class="tdr bord_right vertb">3.21</td> -<td class="tdr bord_right vertb">1.28</td> -<td class="tdr bord_right vertb">34.0</td> -<td class="tdc">41</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Breslau</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">2,840</td> -<td class="tdr bord_right vertb">7.80</td> -<td class="tdr bord_right vertb">5.12</td> -<td class="tdr bord_right vertb">1.52</td> -<td class="tdr bord_right vertb">45</td> -<td class="tdc">64</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">2,960</td> -<td class="tdr bord_right vertb">8.10</td> -<td class="tdr bord_right vertb">5.12</td> -<td class="tdr bord_right vertb">1.58</td> -<td class="tdr bord_right vertb">40.0</td> -<td class="tdc">74</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">2,990</td> -<td class="tdr bord_right vertb">8.20</td> -<td class="tdr bord_right vertb">5.12</td> -<td class="tdr bord_right vertb">1.60</td> -<td class="tdr bord_right vertb">37</td> -<td class="tdc">81</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">3,060</td> -<td class="tdr bord_right vertb">8.40</td> -<td class="tdr bord_right vertb">5.12</td> -<td class="tdr bord_right vertb">1.64</td> -<td class="tdr bord_right vertb">43</td> -<td class="tdc">71</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="2"><p class="indent">Brunn</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1,110</td> -<td class="tdr bord_right vertb">3.04</td> -<td class="tdr bord_right vertb">1.62</td> -<td class="tdr bord_right vertb">1.87</td> -<td class="tdr bord_right vertb">8.6</td> -<td class="tdc">128</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1,190</td> -<td class="tdr bord_right vertb">3.25</td> -<td class="tdr bord_right vertb">1.62</td> -<td class="tdr bord_right vertb">2.00</td> -<td class="tdr bord_right vertb">9.1</td> -<td class="tdc">131</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Brunswick</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">815</td> -<td class="tdr bord_right vertb">2.23</td> -<td class="tdr bord_right vertb">1.48</td> -<td class="tdr bord_right vertb">1.51</td> -<td class="tdr bord_right vertb">14.8</td> -<td class="tdc">55</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">840</td> -<td class="tdr bord_right vertb">2.30</td> -<td class="tdr bord_right vertb">1.48</td> -<td class="tdr bord_right vertb">1.56</td> -<td class="tdr bord_right vertb">13.3</td> -<td class="tdc">63</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">820</td> -<td class="tdr bord_right vertb">2.25</td> -<td class="tdr bord_right vertb">1.48</td> -<td class="tdr bord_right vertb">1.52</td> -<td class="tdr bord_right vertb">13.7</td> -<td class="tdc">60</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">870</td> -<td class="tdr bord_right vertb">2.38</td> -<td class="tdr bord_right vertb">1.48</td> -<td class="tdr bord_right vertb">1.61</td> -<td class="tdr bord_right vertb">11.9</td> -<td class="tdc">73</td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Budapest</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1892</td> -<td class="tdr bord_right vertb">7,360</td> -<td class="tdr bord_right vertb">20.20</td> -<td class="tdr bord_right vertb">3.00</td> -<td class="tdr bord_right vertb">6.70</td> -<td class="tdr bord_right vertb">254</td> -<td class="tdc">29</td> -</tr> -<tr> -<td class="tdl bord_right vertt" rowspan="3"><span class="pagenum" id="Page_242">[Pg 242]</span><p class="indent">Copenhagen</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">2,330</td> -<td class="tdr bord_right vertb">6.40</td> -<td class="tdr bord_right vertb">2.88</td> -<td class="tdr bord_right vertb">2.22</td> -<td class="tdr bord_right vertb">45</td> -<td class="tdc">52</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">2,490</td> -<td class="tdr bord_right vertb">6.80</td> -<td class="tdr bord_right vertb">2.88</td> -<td class="tdr bord_right vertb">2.35</td> -<td class="tdr bord_right vertb">52</td> -<td class="tdc">48</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">2,580</td> -<td class="tdr bord_right vertb">7.10</td> -<td class="tdr bord_right vertb">2.88</td> -<td class="tdr bord_right vertb">2.47</td> -<td class="tdr bord_right vertb">54</td> -<td class="tdc">48</td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Dordrecht</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">365</td> -<td class="tdr bord_right vertb">1.00</td> -<td class="tdr bord_right vertb">0.56</td> -<td class="tdr bord_right vertb">1.79</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="3"><p class="indent">Frankfort on Oder</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">310</td> -<td class="tdr bord_right vertb">0.85</td> -<td class="tdr bord_right vertb">0.37</td> -<td class="tdr bord_right vertb">2.28</td> -<td class="tdr bord_right vertb">2.9</td> -<td class="tdc">107</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">325</td> -<td class="tdr bord_right vertb">0.89</td> -<td class="tdr bord_right vertb">0.37</td> -<td class="tdr bord_right vertb">2.40</td> -<td class="tdr bord_right vertb">7.4</td> -<td class="tdc">44</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">356</td> -<td class="tdr bord_right vertb">0.98</td> -<td class="tdr bord_right vertb">0.37</td> -<td class="tdr bord_right vertb">2.65</td> -<td class="tdr bord_right vertb">8.8</td> -<td class="tdc">41</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="5"><p class="indent">Hamburg</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">11,450</td> -<td class="tdr bord_right vertb">31.40</td> -<td class="tdr bord_right vertb">34.0</td> -<td class="tdr bord_right vertb">0.92</td> -<td class="tdr bord_right vertb">350</td> -<td class="tdc">33</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">11,700</td> -<td class="tdr bord_right vertb">32.10</td> -<td class="tdr bord_right vertb">34.0</td> -<td class="tdr bord_right vertb">0.94</td> -<td class="tdr bord_right vertb">275</td> -<td class="tdc">43</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">11,500</td> -<td class="tdr bord_right vertb">31.70</td> -<td class="tdr bord_right vertb">34.0</td> -<td class="tdr bord_right vertb">0.93</td> -<td class="tdr bord_right vertb">266</td> -<td class="tdc">43</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">12,000</td> -<td class="tdr bord_right vertb">32.70</td> -<td class="tdr bord_right vertb">34.0</td> -<td class="tdr bord_right vertb">0.96</td> -<td class="tdr bord_right vertb">285</td> -<td class="tdc">42</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">11,900</td> -<td class="tdr bord_right vertb">32.60</td> -<td class="tdr bord_right vertb">43.0</td> -<td class="tdr bord_right vertb">0.76</td> -<td class="tdr bord_right vertb">246</td> -<td class="tdc">48</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="3"><p class="indent">Hudson, N. Y.</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1892</td> -<td class="tdr bord_right vertb">697</td> -<td class="tdr bord_right vertb">1.91</td> -<td class="tdr bord_right vertb">0.74</td> -<td class="tdr bord_right vertb">2.58</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1893</td> -<td class="tdr bord_right vertb">543</td> -<td class="tdr bord_right vertb">1.49</td> -<td class="tdr bord_right vertb">0.74</td> -<td class="tdr bord_right vertb">2.01</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">535</td> -<td class="tdr bord_right vertb">1.46</td> -<td class="tdr bord_right vertb">0.74</td> -<td class="tdr bord_right vertb">1.98</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Ilion, N. Y.</p></td> -<td class="tdl vertb">Feb.,</td> -<td class="tdr bord_right vertb">1899</td> -<td class="tdr bord_right vertb">182</td> -<td class="tdr bord_right vertb">0.50</td> -<td class="tdr bord_right vertb">0.14</td> -<td class="tdr bord_right vertb">3.57</td> -<td class="tdr bord_right vertb">1.40</td> -<td class="tdc">130</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Königsberg</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1,060</td> -<td class="tdr bord_right vertb">2.90</td> -<td class="tdr bord_right vertb">2.70</td> -<td class="tdr bord_right vertb">1.07</td> -<td class="tdr bord_right vertb">38.5</td> -<td class="tdc">27</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1,085</td> -<td class="tdr bord_right vertb">2.97</td> -<td class="tdr bord_right vertb">2.70</td> -<td class="tdr bord_right vertb">1.10</td> -<td class="tdr bord_right vertb">35.0</td> -<td class="tdc">31</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1,085</td> -<td class="tdr bord_right vertb">2.97</td> -<td class="tdr bord_right vertb">2.70</td> -<td class="tdr bord_right vertb">1.10</td> -<td class="tdr bord_right vertb">41.0</td> -<td class="tdc">27</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">1,140</td> -<td class="tdr bord_right vertb">3.12</td> -<td class="tdr bord_right vertb">2.70</td> -<td class="tdr bord_right vertb">1.16</td> -<td class="tdr bord_right vertb">44.0</td> -<td class="tdc">26</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Lawrence</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">1,050</td> -<td class="tdr bord_right vertb">2.88</td> -<td class="tdr bord_right vertb">2.50</td> -<td class="tdr bord_right vertb">1.15</td> -<td class="tdr bord_right vertb">10</td> -<td class="tdc">105</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1,097</td> -<td class="tdr bord_right vertb">3.00</td> -<td class="tdr bord_right vertb">2.50</td> -<td class="tdr bord_right vertb">1.20</td> -<td class="tdr bord_right vertb">27</td> -<td class="tdc">41</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1,101</td> -<td class="tdr bord_right vertb">3.02</td> -<td class="tdr bord_right vertb">2.50</td> -<td class="tdr bord_right vertb">1.20</td> -<td class="tdr bord_right vertb">30</td> -<td class="tdc">37</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1,114</td> -<td class="tdr bord_right vertb">3.06</td> -<td class="tdr bord_right vertb">2.50</td> -<td class="tdr bord_right vertb">1.22</td> -<td class="tdr bord_right vertb">41</td> -<td class="tdc">27</td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Liverpool</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">8,520</td> -<td class="tdr bord_right vertb">23.40</td> -<td class="tdr bord_right vertb">10.92</td> -<td class="tdr bord_right vertb">2.14</td> -<td class="tdr bord_right vertb">158</td> -<td class="tdc">54</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="6"> -<p class="indent"><a id="FNanchor_53" href="#Footnote_53" class="fnanchor">[53]</a> -London, all filters -but not including -ground water</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1892</td> -<td class="tdr bord_right vertb">65,783</td> -<td class="tdr bord_right vertb">180</td> -<td class="tdr bord_right vertb">109.75</td> -<td class="tdr bord_right vertb">1.64</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc">90</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1893</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdr bord_right vertb">195</td> -<td class="tdr bord_right vertb">116.00</td> -<td class="tdr bord_right vertb">1.68</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">68,700</td> -<td class="tdr bord_right vertb">188</td> -<td class="tdr bord_right vertb">117.00</td> -<td class="tdr bord_right vertb">1.60</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">76,900</td> -<td class="tdr bord_right vertb">210</td> -<td class="tdr bord_right vertb">123.75</td> -<td class="tdr bord_right vertb">1.70</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">72,482</td> -<td class="tdr bord_right vertb">198</td> -<td class="tdr bord_right vertb">123.75</td> -<td class="tdr bord_right vertb">1.60</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">73,340</td> -<td class="tdr bord_right vertb">201</td> -<td class="tdr bord_right vertb">125.00</td> -<td class="tdr bord_right vertb">1.61</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">London, Chelsea</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">5,370</td> -<td class="tdr bord_right vertb">14.70</td> -<td class="tdr bord_right vertb">8.00</td> -<td class="tdr bord_right vertb">1.85</td><td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">E. London</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">18,000</td> -<td class="tdr bord_right vertb">49.00</td> -<td class="tdr bord_right vertb">31.00</td> -<td class="tdr bord_right vertb">1.58</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Grand Junction</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">8,560</td> -<td class="tdr bord_right vertb">23.40</td> -<td class="tdr bord_right vertb">21.75</td> -<td class="tdr bord_right vertb">1.07</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Lambeth</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">10,370</td> -<td class="tdr bord_right vertb">28.40</td> -<td class="tdr bord_right vertb">12.25</td> -<td class="tdr bord_right vertb">2.30</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">New River</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">15,750</td> -<td class="tdr bord_right vertb">43.00</td> -<td class="tdr bord_right vertb">16.50</td> -<td class="tdr bord_right vertb">2.60</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Southwark & Vauxhall</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">14,800</td> -<td class="tdr bord_right vertb">40.50</td> -<td class="tdr bord_right vertb">20.50</td> -<td class="tdr bord_right vertb">1.98</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">West Middlesex</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">8,910</td> -<td class="tdr bord_right vertb">24.30</td> -<td class="tdr bord_right vertb">15.00</td> -<td class="tdr bord_right vertb">1.61</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Lübeck</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1,520</td> -<td class="tdr bord_right vertb">4.15</td> -<td class="tdr bord_right vertb">1.40</td> -<td class="tdr bord_right vertb">2.95</td> -<td class="tdr bord_right vertb">16.2</td> -<td class="tdc">94</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1,600</td> -<td class="tdr bord_right vertb">4.38</td> -<td class="tdr bord_right vertb">1.40</td> -<td class="tdr bord_right vertb">3.13</td> -<td class="tdr bord_right vertb">24.4</td> -<td class="tdc">66</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1,650</td> -<td class="tdr bord_right vertb">4.50</td> -<td class="tdr bord_right vertb">1.40</td> -<td class="tdr bord_right vertb">3.22</td> -<td class="tdr bord_right vertb">27.0</td> -<td class="tdc">61</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">1,750</td> -<td class="tdr bord_right vertb">4.80</td> -<td class="tdr bord_right vertb">1.40</td> -<td class="tdr bord_right vertb">3.42</td> -<td class="tdr bord_right vertb">38.5</td> -<td class="tdc">45</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Magdeburg</p><span class="pagenum" id="Page_243">[Pg 243]</span></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1880</td> -<td class="tdr bord_right vertb">5.15</td> -<td class="tdr bord_right vertb">3.76</td> -<td class="tdr bord_right vertb">1.37</td> -<td class="tdr bord_right vertb">47.5</td> -<td class="tdc">40</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1950</td> -<td class="tdr bord_right vertb">5.35</td> -<td class="tdr bord_right vertb">3.76</td> -<td class="tdr bord_right vertb">1.42</td> -<td class="tdr bord_right vertb">65.0</td> -<td class="tdc">30</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1880</td> -<td class="tdr bord_right vertb">5.15</td> -<td class="tdr bord_right vertb">3.76</td> -<td class="tdr bord_right vertb">1.37</td> -<td class="tdr bord_right vertb">59.0</td> -<td class="tdc">32</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">2070</td> -<td class="tdr bord_right vertb">5.66</td> -<td class="tdr bord_right vertb">3.76</td> -<td class="tdr bord_right vertb">1.50</td> -<td class="tdr bord_right vertb">63.0</td> -<td class="tdc">33</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Mt. Vernon, N. Y</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">493</td> -<td class="tdr bord_right vertb">1.35</td> -<td class="tdr bord_right vertb">1.10</td> -<td class="tdr bord_right vertb">1.22</td> -<td class="tdr bord_right vertb">7.3</td> -<td class="tdc">68</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">608</td> -<td class="tdr bord_right vertb">1.66</td> -<td class="tdr bord_right vertb">1.10</td> -<td class="tdr bord_right vertb">1.51</td> -<td class="tdr bord_right vertb">9.2</td> -<td class="tdc">66</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">808</td> -<td class="tdr bord_right vertb">2.21</td> -<td class="tdr bord_right vertb">1.10</td> -<td class="tdr bord_right vertb">2.00</td> -<td class="tdr bord_right vertb">16.6</td> -<td class="tdc">49</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">933</td> -<td class="tdr bord_right vertb">2.56</td> -<td class="tdr bord_right vertb">1.10</td> -<td class="tdr bord_right vertb">2.34</td> -<td class="tdr bord_right vertb">18.4</td> -<td class="tdc">51</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Posen</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">305</td> -<td class="tdr bord_right vertb">0.84</td> -<td class="tdr bord_right vertb">0.70</td> -<td class="tdr bord_right vertb">1.20</td> -<td class="tdr bord_right vertb">10.3</td> -<td class="tdc">30</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">346</td> -<td class="tdr bord_right vertb">0.94</td> -<td class="tdr bord_right vertb">0.70</td> -<td class="tdr bord_right vertb">1.35</td> -<td class="tdr bord_right vertb">10.4</td> -<td class="tdc">33</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">325</td> -<td class="tdr bord_right vertb">0.89</td> -<td class="tdr bord_right vertb">0.70</td> -<td class="tdr bord_right vertb">1.27</td> -<td class="tdr bord_right vertb">10.1</td> -<td class="tdc">32</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">360</td> -<td class="tdr bord_right vertb">0.99</td> -<td class="tdr bord_right vertb">0.70</td> -<td class="tdr bord_right vertb">1.42</td> -<td class="tdr bord_right vertb">9.6</td> -<td class="tdc">38</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="7"><p class="indent">Poughkeepsie</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1892</td> -<td class="tdr bord_right vertb">696</td> -<td class="tdr bord_right vertb">1.91</td> -<td class="tdr bord_right vertb">0.68</td> -<td class="tdr bord_right vertb">2.81</td> -<td class="tdr bord_right vertb">14.0</td> -<td class="tdc">50</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1893</td> -<td class="tdr bord_right vertb">667</td> -<td class="tdr bord_right vertb">1.83</td> -<td class="tdr bord_right vertb">0.68</td> -<td class="tdr bord_right vertb">2.70</td> -<td class="tdr bord_right vertb">12.0</td> -<td class="tdc">56</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">633</td> -<td class="tdr bord_right vertb">1.73</td> -<td class="tdr bord_right vertb">0.68</td> -<td class="tdr bord_right vertb">2.55</td> -<td class="tdr bord_right vertb">14</td> -<td class="tdc">45</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">686</td> -<td class="tdr bord_right vertb">1.88</td> -<td class="tdr bord_right vertb">0.68</td> -<td class="tdr bord_right vertb">2.77</td> -<td class="tdr bord_right vertb">14</td> -<td class="tdc">49</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">664</td> -<td class="tdr bord_right vertb">1.82</td> -<td class="tdr bord_right vertb">0.68</td> -<td class="tdr bord_right vertb">2.68</td> -<td class="tdr bord_right vertb">9</td> -<td class="tdc">73</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">615</td> -<td class="tdr bord_right vertb">1.69</td> -<td class="tdr bord_right vertb">1.36</td> -<td class="tdr bord_right vertb">1.24</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">611</td> -<td class="tdr bord_right vertb">1.67</td> -<td class="tdr bord_right vertb">1.36</td> -<td class="tdr bord_right vertb">1.23</td> -<td class="tdr bord_right vertb">10.88</td> -<td class="tdc">57</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="2"><p class="indent">Rostock</p></td> -<td class="tdl vertb">June,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">560</td> -<td class="tdr bord_right vertb">1.54</td> -<td class="tdr bord_right vertb">1.11</td> -<td class="tdr bord_right vertb">1.38</td> -<td class="tdr bord_right vertb">9.3</td> -<td class="tdc">60</td> -</tr> -<tr> - -<td class="tdl vertb">June,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">625</td> -<td class="tdr bord_right vertb">1.71</td> -<td class="tdr bord_right vertb">1.11</td> -<td class="tdr bord_right vertb">1.55</td> -<td class="tdr bord_right vertb">9.0</td> -<td class="tdc">70</td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Rotterdam</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1893</td> -<td class="tdr bord_right vertb">4850</td> -<td class="tdr bord_right vertb">13.30</td> -<td class="tdr bord_right vertb">6.30</td> -<td class="tdr bord_right vertb">2.11</td> -<td class="tdr bord_right vertb"> </td> -<td class="tdc"> </td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Stettin</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1130</td> -<td class="tdr bord_right vertb">3.10</td> -<td class="tdr bord_right vertb">2.26</td> -<td class="tdr bord_right vertb">1.37</td> -<td class="tdr bord_right vertb">26.5</td> -<td class="tdc">43</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1030</td> -<td class="tdr bord_right vertb">2.83</td> -<td class="tdr bord_right vertb">2.26</td> -<td class="tdr bord_right vertb">1.25</td> -<td class="tdr bord_right vertb">15.5</td> -<td class="tdc">66</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">980</td> -<td class="tdr bord_right vertb">2.70</td> -<td class="tdr bord_right vertb">2.26</td> -<td class="tdr bord_right vertb">1.19</td> -<td class="tdr bord_right vertb">16.1</td> -<td class="tdc">61</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">1020</td> -<td class="tdr bord_right vertb">2.80</td> -<td class="tdr bord_right vertb">2.26</td> -<td class="tdr bord_right vertb">1.24</td> -<td class="tdr bord_right vertb">20.3</td> -<td class="tdc">50</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="3"><p class="indent">Stockholm</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">2375</td> -<td class="tdr bord_right vertb">6.50</td> -<td class="tdr bord_right vertb">2.78</td> -<td class="tdr bord_right vertb">2.33</td> -<td class="tdr bord_right vertb">70.0</td> -<td class="tdc">34</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">2500</td> -<td class="tdr bord_right vertb">6.85</td> -<td class="tdr bord_right vertb">2.78</td> -<td class="tdr bord_right vertb">2.45</td> -<td class="tdr bord_right vertb">68.0</td> -<td class="tdc">37</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">2750</td> -<td class="tdr bord_right vertb">7.50</td> -<td class="tdr bord_right vertb">3.60</td> -<td class="tdr bord_right vertb">2.08</td> -<td class="tdr bord_right vertb">76.0</td> -<td class="tdc">36</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="2"><p class="indent">Stralsund</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">215</td> -<td class="tdr bord_right vertb">0.59</td> -<td class="tdr bord_right vertb">1.11</td> -<td class="tdr bord_right vertb">0.53</td> -<td class="tdr bord_right vertb">16.0</td> -<td class="tdc">13</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">210</td> -<td class="tdr bord_right vertb">0.58</td> -<td class="tdr bord_right vertb">1.11</td> -<td class="tdr bord_right vertb">0.51</td> -<td class="tdr bord_right vertb">17.3</td> -<td class="tdc">12</td> -</tr> -<tr> - -<td class="tdl bord_right vertt" rowspan="4"><p class="indent">Stuttgart</p></td> -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">1040</td> -<td class="tdr bord_right vertb">2.85</td> -<td class="tdr bord_right vertb">1.46</td> -<td class="tdr bord_right vertb">1.96</td> -<td class="tdr bord_right vertb">13.7</td> -<td class="tdc">76</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">1220</td> -<td class="tdr bord_right vertb">3.34</td> -<td class="tdr bord_right vertb">1.66</td> -<td class="tdr bord_right vertb">2.04</td> -<td class="tdr bord_right vertb">17.7</td> -<td class="tdc">69</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">1270</td> -<td class="tdr bord_right vertb">3.48</td> -<td class="tdr bord_right vertb">2.32</td> -<td class="tdr bord_right vertb">1.50</td> -<td class="tdr bord_right vertb">18.7</td> -<td class="tdc">68</td> -</tr> -<tr> - -<td class="tdl vertb">Mar.,</td> -<td class="tdr bord_right vertb">1898</td> -<td class="tdr bord_right vertb">1320</td> -<td class="tdr bord_right vertb">3.60</td> -<td class="tdr bord_right vertb">2.32</td> -<td class="tdr bord_right vertb">1.54</td> -<td class="tdr bord_right vertb">20.2</td> -<td class="tdc">65</td> -</tr> -<tr> - -<td class="tdl bord_right vertb"><p class="indent">Utrecht</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">510</td> -<td class="tdr bord_right vertb">1.40</td> -<td class="tdr bord_right vertb">0.60</td> -<td class="tdr bord_right vertb">2.33</td> -<td class="tdr bord_right vertb">31</td> -<td class="tdc">16</td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot vertt" rowspan="8"><p class="indent">Zürich</p></td> -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1891</td> -<td class="tdr bord_right vertb">2010</td> -<td class="tdr bord_right vertb">5.50</td> -<td class="tdr bord_right vertb">0.84</td> -<td class="tdr bord_right vertb">6.50</td> -<td class="tdr bord_right vertb">8</td> -<td class="tdc">250</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1892</td> -<td class="tdr bord_right vertb">2150</td> -<td class="tdr bord_right vertb">5.90</td> -<td class="tdr bord_right vertb">0.84</td> -<td class="tdr bord_right vertb">7.00</td> -<td class="tdr bord_right vertb">10</td> -<td class="tdc">215</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1893</td> -<td class="tdr bord_right vertb">2310</td> -<td class="tdr bord_right vertb">6.38</td> -<td class="tdr bord_right vertb">1.19</td> -<td class="tdr bord_right vertb">5.35</td> -<td class="tdr bord_right vertb">13</td> -<td class="tdc">177</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1894</td> -<td class="tdr bord_right vertb">2250</td> -<td class="tdr bord_right vertb">6.15</td> -<td class="tdr bord_right vertb">1.19</td> -<td class="tdr bord_right vertb">5.18</td> -<td class="tdr bord_right vertb">17</td> -<td class="tdc">133</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1895</td> -<td class="tdr bord_right vertb">2460</td> -<td class="tdr bord_right vertb">6.70</td> -<td class="tdr bord_right vertb">1.19</td> -<td class="tdr bord_right vertb">5.62</td> -<td class="tdr bord_right vertb">27</td> -<td class="tdc">91</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1896</td> -<td class="tdr bord_right vertb">2360</td> -<td class="tdr bord_right vertb">6.45</td> -<td class="tdr bord_right vertb">1.66</td> -<td class="tdr bord_right vertb">3.88</td> -<td class="tdr bord_right vertb">30</td> -<td class="tdc">79</td> -</tr> -<tr> - -<td class="tdl vertb">Dec.,</td> -<td class="tdr bord_right vertb">1897</td> -<td class="tdr bord_right vertb">2500</td> -<td class="tdr bord_right vertb">6.84</td> -<td class="tdr bord_right vertb">1.66</td> -<td class="tdr bord_right vertb">4.13</td> -<td class="tdr bord_right vertb">35</td> -<td class="tdc">71</td> -</tr> -<tr> - -<td class="tdl vertb bord_bot">Dec.,</td> -<td class="tdr bord_right bord_bot vertb">1898</td> -<td class="tdr bord_right bord_bot vertb">2730</td> -<td class="tdr bord_right bord_bot vertb">7.50</td> -<td class="tdr bord_right bord_bot vertb">1.66</td> -<td class="tdr bord_right bord_bot vertb">4.50</td> -<td class="tdr bord_right bord_bot vertb">47</td> -<td class="tdc bord_bot vertb">58</td> -</tr> -</table> - -<p class="padt1 padb1"><span class="pagenum" id="Page_244">[Pg 244]</span></p> - -<table class="autotable" summary="cities using sand filters"> -<tr> -<th class="tdc normal" colspan="6" id="LIST_OF_CITIES_USING_SAND_FILTERS">PARTIAL LIST OF CITIES USING SAND FILTERS.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Place.</th> -<th class="tdc normal small bord_top bord_right bord_bot">When<br />Built.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Population.<br />1890.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Area<br />of<br />Filters.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Number<br />of<br />Filters.</th> -<th class="tdc normal small bord_top bord_bot">Average<br />Daily<br />Consumption.</th> -</tr> -<tr> -<td class="tdc" colspan="6">UNITED STATES.</td> -</tr> -<tr> -<td class="tdl bord_right">Poughkeepsie. N. Y.</td> -<td class="tdc bord_right">1872</td> -<td class="tdr bord_right">24,000</td> -<td class="tdc bord_right">1.36</td> -<td class="tdc bord_right">3</td> -<td class="tdc">1.67</td> -</tr> -<tr> -<td class="tdl bord_right">Hudson, N. Y.</td> -<td class="tdc bord_right">1874</td> -<td class="tdr bord_right">9,970</td> -<td class="tdc bord_right">0.74</td> -<td class="tdc bord_right">2</td> -<td class="tdc">1.50</td> -</tr> -<tr> -<td class="tdl bord_right">St. Johnsbury, Vt.</td> -<td class="tdc bord_right">187(?)</td> -<td class="tdr bord_right">3,857</td> -<td class="tdc bord_right">0.14</td> -<td class="tdc bord_right">3</td> -<td class="tdc">0.70</td> -</tr> -<tr> -<td class="tdl bord_right">Nantucket, Mass.</td> -<td class="tdc bord_right">1893</td> -<td class="tdr bord_right">3,268</td> -<td class="tdc bord_right">0.11</td> -<td class="tdc bord_right">1</td> -<td class="tdc">0.09</td> -</tr> -<tr> -<td class="tdl bord_right">Lawrence, Mass.</td> -<td class="tdc bord_right">1893</td> -<td class="tdr bord_right">44,654</td> -<td class="tdc bord_right">2.50</td> -<td class="tdc bord_right">1</td> -<td class="tdc">3.00</td> -</tr> -<tr> -<td class="tdl bord_right">Ilion, N. Y.</td> -<td class="tdc bord_right">1893</td> -<td class="tdr bord_right">4,057</td> -<td class="tdc bord_right">0.14</td> -<td class="tdc bord_right">2</td> -<td class="tdc">0.50</td> -</tr> -<tr> -<td class="tdl bord_right">Mount Vernon, N. Y.</td> -<td class="tdc bord_right">1894</td> -<td class="tdr bord_right">10,830</td> -<td class="tdc bord_right">1.10</td> -<td class="tdc bord_right">3</td> -<td class="tdc">1.66</td> -</tr> -<tr> -<td class="tdl bord_right">Grand Forks, N. D.</td> -<td class="tdc bord_right">1894</td> -<td class="tdr bord_right">4,979</td> -<td class="tdc bord_right">0.42</td> -<td class="tdc bord_right">1</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Milford, Mass.</td> -<td class="tdc bord_right">1895</td> -<td class="tdr bord_right">9,956</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right">1</td> -<td class="tdc">0.70</td> -</tr> -<tr> -<td class="tdl bord_right">Ashland, Wis.</td> -<td class="tdc bord_right">1895</td> -<td class="tdr bord_right">9,956</td> -<td class="tdc bord_right">0.50</td> -<td class="tdc bord_right">3</td> -<td class="tdc">1.09</td> -</tr> -<tr> -<td class="tdl bord_right">Hamilton, N. Y.</td> -<td class="tdc bord_right">1895</td> -<td class="tdr bord_right">1,744</td> -<td class="tdc bord_right">0.12</td> -<td class="tdc bord_right">1</td> -<td class="tdc">0.03</td> -</tr> -<tr> -<td class="tdl bord_right">Lambertville, N. J.</td> -<td class="tdc bord_right">1896</td> -<td class="tdr bord_right">4,142</td> -<td class="tdc bord_right">0.28</td> -<td class="tdc bord_right">2</td> -<td class="tdc">0.25</td> -</tr> -<tr> -<td class="tdl bord_right">Far Rockaway, N. Y.</td> -<td class="tdc bord_right">1896</td> -<td class="tdr bord_right">2,288</td> -<td class="tdc bord_right">0.92</td> -<td class="tdc bord_right">2</td> -<td class="tdc">0.93</td> -</tr> -<tr> -<td class="tdl bord_right">Red Bank, N. J.</td> -<td class="tdc bord_right">1897</td> -<td class="tdr bord_right">500</td> -<td class="tdc bord_right">0.03</td> -<td class="tdc bord_right">2</td> -<td class="tdc">0.10</td> -</tr> -<tr> -<td class="tdl bord_right">Somersworth, N. H.</td> -<td class="tdc bord_right">1897</td> -<td class="tdr bord_right">6,207</td> -<td class="tdc bord_right">0.50</td> -<td class="tdc bord_right">1</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Little Falls, N. Y.</td> -<td class="tdc bord_right">1898</td> -<td class="tdr bord_right">8,783</td> -<td class="tdc bord_right">0.76</td> -<td class="tdc bord_right">1</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Berwyn, Penna.</td> -<td class="tdc bord_right">1898</td> -<td class="tdr bord_right">826</td> -<td class="tdc bord_right">0.52</td> -<td class="tdc bord_right">3</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Harrisburg, Penna.</td> -<td class="tdc bord_right">1899</td> -<td class="tdr bord_right">1,200</td> -<td class="tdc bord_right">0.12</td> -<td class="tdc bord_right">2</td> -<td class="tdc">0.15</td> -</tr> -<tr> -<td class="tdl bord_right">Albany, N. Y.</td> -<td class="tdc bord_right">1899</td> -<td class="tdr bord_right">94,923</td> -<td class="tdc bord_right">5.60</td> -<td class="tdc bord_right">8</td> -<td class="tdc">11.00<a id="FNanchor_54" href="#Footnote_54" class="fnanchor">[54]</a></td> -</tr> -<tr> -<td class="tdl bord_right">Rock Island, Illinois</td> -<td class="tdc bord_right">1899</td> -<td class="tdr bord_right bord_bot">13,634</td> -<td class="tdc bord_right bord_bot">1.20</td> -<td class="tdc bord_right bord_bot">3</td> -<td class="tdc bord_bot">3.50</td> -</tr> -<tr> -<td class="tdl bord_right">Total</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">259,774</td> -<td class="tdc bord_right">17.31</td> -<td class="tdc bord_right">45</td> -<td class="tdc">26.87</td> -</tr> -<tr> -<td class="tdc" colspan="6">BRITISH COLUMBIA.</td> -</tr> -<tr> -<td class="tdl bord_right">Victoria</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">16,841</td> -<td class="tdc bord_right">0.82</td> -<td class="tdc bord_right">3</td> -<td class="tdc">1.80</td> -</tr> -<tr> -<td class="tdc" colspan="6">SOUTH AMERICA.</td> -</tr> -<tr> -<td class="tdl bord_right">Buenos Ayres</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">500,000</td> -<td class="tdc bord_right">4.15</td> -<td class="tdc bord_right">3</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Montevidio</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">....</td> -<td class="tdc bord_right">Filters</td> -<td class="tdc bord_right">reported</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdc" colspan="6">HOLLAND.</td> -</tr> -<tr> -<td class="tdl bord_right">Amsterdam</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">555,821</td> -<td class="tdc bord_right">10.18</td> -<td class="tdc bord_right">12</td> -<td class="tdc">11.20</td> -</tr> -<tr> -<td class="tdl bord_right">Rotterdam</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">290,000</td> -<td class="tdc bord_right">6.30</td> -<td class="tdc bord_right">18</td> -<td class="tdc">13.00</td> -</tr> -<tr> -<td class="tdl bord_right">The Hague</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">191,000</td> -<td class="tdc bord_right">2.88</td> -<td class="tdc bord_right">6</td> -<td class="tdc">4.20</td> -</tr> -<tr> -<td class="tdl bord_right">Schiedam</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">25,300</td> -<td class="tdc bord_right">1.33</td> -<td class="tdc bord_right">5</td> -<td class="tdc">0.68</td> -</tr> -<tr> -<td class="tdl bord_right">Utrecht</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">140,000</td> -<td class="tdc bord_right">0.60</td> -<td class="tdc bord_right">....</td> -<td class="tdc">1.40</td> -</tr> -<tr> -<td class="tdl bord_right">Groningen</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">57,900</td> -<td class="tdc bord_right">0.59</td> -<td class="tdc bord_right">2</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Dordrecht</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">34,100</td> -<td class="tdc bord_right">0.56</td> -<td class="tdc bord_right">2</td> -<td class="tdc">1.00</td> -</tr> -<tr> -<td class="tdl bord_right">Leeuwarden</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">30,700</td> -<td class="tdc bord_right">0.31</td> -<td class="tdc bord_right">2</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Vlaardingen</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Sliedrecht</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Gorinchem</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">10,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Zutphen</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">18,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Leyden</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">44,200</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Enschede</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Middelburg</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">17,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Total</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">1,414,021</td> -<td class="tdc bord_right">22.75</td> -<td class="tdc bord_right">47</td> -<td class="tdc">31.48</td> -</tr> -<tr> -<td class="tdc" colspan="6"><span class="pagenum" id="Page_246">[Pg 246]</span> -GREAT BRITAIN.</td> -</tr> -<tr> -<td class="tdl bord_right">London</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">5,030,267</td> -<td class="tdc bord_right">125.00</td> -<td class="tdc bord_right">120</td> -<td class="tdc">200.00</td> -</tr> -<tr> -<td class="tdl bord_right">Liverpool</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">790,000</td> -<td class="tdc bord_right">10.92</td> -<td class="tdc bord_right">....</td> -<td class="tdc">26.67</td> -</tr> -<tr> -<td class="tdl bord_right">Dublin</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">349,000</td> -<td class="tdc bord_right">5.00</td> -<td class="tdc bord_right">10</td> -<td class="tdc">18.00</td> -</tr> -<tr> -<td class="tdl bord_right">Leeds</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">420,000</td> -<td class="tdc bord_right">6.00</td> -<td class="tdc bord_right">8</td> -<td class="tdc">17.99</td> -</tr> -<tr> -<td class="tdl bord_right">Bradford</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">436,260</td> -<td class="tdc bord_right">4.62</td> -<td class="tdc bord_right">6</td> -<td class="tdc">13.31</td> -</tr> -<tr> -<td class="tdl bord_right">Leicester</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">220,005</td> -<td class="tdc bord_right">2.50</td> -<td class="tdc bord_right">....</td> -<td class="tdc">4.75</td> -</tr> -<tr> -<td class="tdl bord_right">York</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">72,083</td> -<td class="tdc bord_right">2.04</td> -<td class="tdc bord_right">6</td> -<td class="tdc">3.00</td> -</tr> -<tr> -<td class="tdl bord_right">Edinburgh</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">292,364</td> -<td class="tdc bord_right">2.00</td> -<td class="tdc bord_right">4</td> -<td class="tdc">18.00</td> -</tr> -<tr> -<td class="tdl bord_right">Darlington</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">43,000</td> -<td class="tdc bord_right">1.32</td> -<td class="tdc bord_right">7</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Wakefield</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">36,815</td> -<td class="tdc bord_right">1.25</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Carlisle</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">40,000</td> -<td class="tdc bord_right">0.90</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Dumfries</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">17,821</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Accrington</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">42,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Birmingham</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">680,140</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">19.05</td> -</tr> -<tr> -<td class="tdl bord_right">Blackburn</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">130,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">4.10</td> -</tr> -<tr> -<td class="tdl bord_right">Bolton</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">250,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">6.60</td> -</tr> -<tr> -<td class="tdl bord_right">Chester</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">40,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Halifax</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">217,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">5.18</td> -</tr> -<tr> -<td class="tdl bord_right">Hereford</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">20,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Middlesborough</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">187,331</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">11.39</td> -</tr> -<tr> -<td class="tdl bord_right">Newcastle</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">320,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">14.00</td> -</tr> -<tr> -<td class="tdl bord_right">Oldham</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">145,800</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">5.30</td> -</tr> -<tr> -<td class="tdl bord_right">Oxford</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">53,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">1.59</td> -</tr> -<tr> -<td class="tdl bord_right">Preston</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">113,864</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">4.20</td> -</tr> -<tr> -<td class="tdl bord_right">Reading</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">71,558</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">3.00</td> -</tr> -<tr> -<td class="tdl bord_right">Southampton</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">76,430</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">3.45</td> -</tr> -<tr> -<td class="tdl bord_right">Wigan</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">60,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">1.22</td> -</tr> -<tr> -<td class="tdl bord_right">Worcester</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right bord_bot">45,000</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdc bord_bot">1.93</td> -</tr> -<tr> -<td class="tdl bord_right">Total</td> -<td class="tdc bord_right">....</td> -<td class="tdl">10,199,738</td> -<td class="tdr bord_right">161.80</td> -<td class="tdc bord_right">161</td> -<td class="tdc">382.73</td> -</tr> -<tr> -<td class="tdc" colspan="6">GERMANY.</td> -</tr> -<tr> -<td class="tdl bord_right">Hamburg</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">661,200</td> -<td class="tdc bord_right">42.00</td> -<td class="tdc bord_right">22</td> -<td class="tdc">33.00</td> -</tr> -<tr> -<td class="tdl bord_right">Berlin</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">1,746,424</td> -<td class="tdc bord_right">31.45</td> -<td class="tdc bord_right">55</td> -<td class="tdc">36.00</td> -</tr> -<tr> -<td class="tdl bord_right">Breslau</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">380,000</td> -<td class="tdc bord_right">5.12</td> -<td class="tdc bord_right">5</td> -<td class="tdc">8.20</td> -</tr> -<tr> -<td class="tdl bord_right">Magdeburg</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">217,067</td> -<td class="tdc bord_right">3.76</td> -<td class="tdc bord_right">11</td> -<td class="tdc">5.66</td> -</tr> -<tr> -<td class="tdl bord_right">Bremen</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">157,500</td> -<td class="tdc bord_right">3.21</td> -<td class="tdc bord_right">12</td> -<td class="tdc">3.50</td> -</tr> -<tr> -<td class="tdl bord_right">Altona</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">162,427</td> -<td class="tdc bord_right">3.08</td> -<td class="tdc bord_right">13</td> -<td class="tdc">5.40</td> -</tr> -<tr> -<td class="tdl bord_right">Königsberg</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">176,000</td> -<td class="tdc bord_right">2.70</td> -<td class="tdc bord_right">7</td> -<td class="tdc">3.00</td> -</tr> -<tr> -<td class="tdl bord_right">Stuttgart</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">162,516</td> -<td class="tdc bord_right">2.32</td> -<td class="tdc bord_right">....</td> -<td class="tdc">4.00</td> -</tr> -<tr> -<td class="tdl bord_right">Stettin</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">145,000</td> -<td class="tdc bord_right">2.26</td> -<td class="tdc bord_right">9</td> -<td class="tdc">3.00</td> -</tr> -<tr> -<td class="tdl bord_right">Lübeck</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">70,000</td> -<td class="tdc bord_right">1.40</td> -<td class="tdc bord_right">6</td> -<td class="tdc">4.50</td> -</tr> -<tr> -<td class="tdl bord_right">Brunswick</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">100,883</td> -<td class="tdc bord_right">1.48</td> -<td class="tdc bord_right">4</td> -<td class="tdc">2.30</td> -</tr> -<tr> -<td class="tdl bord_right">Stralsund</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">30,105</td> -<td class="tdc bord_right">1.11</td> -<td class="tdc bord_right">6</td> -<td class="tdc">0.60</td> -</tr> -<tr> -<td class="tdl bord_right">Rostock</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">49,891</td> -<td class="tdc bord_right">1.11</td> -<td class="tdc bord_right">3</td> -<td class="tdc">1.54</td> -</tr> -<tr> -<td class="tdl bord_right">Lignitz</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">46,852</td> -<td class="tdc bord_right">0.96</td> -<td class="tdc bord_right">6</td> -<td class="tdc">1.40</td> -</tr> -<tr> -<td class="tdl bord_right">Posen</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">75,000</td> -<td class="tdc bord_right">0.70</td> -<td class="tdc bord_right">4</td> -<td class="tdc">0.90</td> -</tr> -<tr> -<td class="tdl bord_right">Schwerin</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">36,000</td> -<td class="tdc bord_right">0.65</td> -<td class="tdc bord_right">4</td> -<td class="tdc">0.50</td> -</tr> -<tr> -<td class="tdl bord_right">Chemnitz</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">164,743</td> -<td class="tdc bord_right">0.59</td> -<td class="tdc bord_right">3</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Worms</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">30,000</td> -<td class="tdc bord_right">0.50</td> -<td class="tdc bord_right">3</td> -<td class="tdc">0.64</td> -</tr> -<tr> -<td class="tdl bord_right">Ratibor</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">20,729</td> -<td class="tdc bord_right">0.42</td> -<td class="tdc bord_right">3</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Frankfort on Oder</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">59,161</td> -<td class="tdc bord_right">0.37</td> -<td class="tdc bord_right">5</td> -<td class="tdc">0.89</td> -</tr> -<tr> -<td class="tdl bord_right">Kiel</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">69,214</td> -<td class="tdc bord_right">0.31</td> -<td class="tdc bord_right">....</td> -<td class="tdc">1.50</td> -</tr> -<tr> -<td class="tdl bord_right">Tilsit</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">30,000</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right">....</td> -<td class="tdc">0.20</td> -</tr> -<tr> -<td class="tdl bord_right">Brieg</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">20,154</td> -<td class="tdc bord_right">0.20</td> -<td class="tdc bord_right">4</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Gluckstadt</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">6,214</td> -<td class="tdc bord_right">0.14</td> -<td class="tdc bord_right">....</td> -<td class="tdc">0.10</td> -</tr> -<tr> -<td class="tdl bord_right">Wandsbeck</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right bord_bot">22,000</td> -<td class="tdc bord_right bord_bot">0.13</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdc bord_bot">0.30</td> -</tr> -<tr> -<td class="tdl bord_right">Total</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">4,639,080</td> -<td class="tdc bord_right">106.22</td> -<td class="tdc bord_right">185</td> -<td class="tdc">117.13</td> -</tr> -<tr> -<td class="tdc" colspan="6">OTHER EUROPEAN FILTERS.</td> -</tr> -<tr> -<td class="tdl bord_right">Warsaw</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">500,000</td> -<td class="tdc bord_right">6.20</td> -<td class="tdc bord_right">12</td> -<td class="tdc">6.00</td> -</tr> -<tr> -<td class="tdl bord_right">St. Petersburg</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">954,000</td> -<td class="tdc bord_right">5.85</td> -<td class="tdc bord_right">11</td> -<td class="tdc">39.00</td> -</tr> -<tr> -<td class="tdl bord_right">Odessa</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">380,000</td> -<td class="tdc bord_right">4.75</td> -<td class="tdc bord_right">5</td> -<td class="tdc">8.00</td> -</tr> -<tr> -<td class="tdl bord_right">Choisy le Roi and</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right" rowspan="2"><span class="double">}</span>200,000<span class="double">{</span></td> -<td class="tdc bord_right">3.85</td> -<td class="tdc bord_right">25</td> -<td class="tdc">10.00</td> -</tr> -<tr> -<td class="tdl bord_right">Neuilly sur Marne</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">2.31</td> -<td class="tdc bord_right">15</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Copenhagen</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">340,000</td> -<td class="tdc bord_right">2.88</td> -<td class="tdc bord_right">9</td> -<td class="tdc">6.80</td> -</tr> -<tr> -<td class="tdl bord_right">Stockholm</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">274,000</td> -<td class="tdc bord_right">2.78</td> -<td class="tdc bord_right">....</td> -<td class="tdc">7.00</td> -</tr> -<tr> -<td class="tdl bord_right">Antwerp</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">240,000</td> -<td class="tdc bord_right">2.10</td> -<td class="tdc bord_right">8</td> -<td class="tdc">2.00</td> -</tr> -<tr> -<td class="tdl bord_right">Zürich</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">96,839</td> -<td class="tdc bord_right">1.66</td> -<td class="tdc bord_right">....</td> -<td class="tdc">7.00</td> -</tr> -<tr> -<td class="tdl bord_right">Brunn</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">1.62</td> -<td class="tdc bord_right">....</td> -<td class="tdc">3.04</td> -</tr> -<tr> -<td class="tdl bord_right">Constantinople, South side</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdc bord_right bord_bot">0.74</td> -<td class="tdc bord_right bord_bot">3</td> -<td class="tdc bord_bot">....</td> -</tr> -<tr> -<td class="tdl bord_right">Total</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">2,984,839</td> -<td class="tdc bord_right">34.74</td> -<td class="tdc bord_right">88</td> -<td class="tdc">88.84</td> -</tr> -<tr> -<td class="tdc" colspan="6">ASIA.</td> -</tr> -<tr> -<td class="tdl bord_right">Blandarwada, India</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdl bord_right">1.97</td> -<td class="tdl bord_right">6</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Agra, India</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">1.37</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Bombay, India</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">821,000</td> -<td class="tdc bord_right">1.22</td> -<td class="tdc bord_right">4</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Shanghai, China</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">0.88</td> -<td class="tdc bord_right">4</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Hong Kong</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">0.67</td> -<td class="tdc bord_right">6</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Yokohama, Japan</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">110,000</td> -<td class="tdc bord_right">0.58</td> -<td class="tdc bord_right">3</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Calcutta, India</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">466,000</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Tokyo, Japan</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Baroda, India</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right">....</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Allahabad, India</td> -<td class="tdc bord_right">....</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdc bord_bot">....</td> -</tr> -<tr> -<td class="tdl bord_right">Total</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">1,397,000</td> -<td class="tdc bord_right">6.69</td> -<td class="tdc bord_right">23</td> -</tr> -<tr> -<td class="tdc" colspan="6">SUMMARY.</td> -</tr> -<tr> -<td class="tdl bord_right">United States</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">259,774</td> -<td class="tdc bord_right">17.31</td> -<td class="tdc bord_right">45</td> -<td class="tdc">26.87</td> -</tr> -<tr> -<td class="tdl bord_right">British Columbia</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">16,841</td> -<td class="tdc bord_right">0.82</td> -<td class="tdc bord_right">3</td> -<td class="tdc">1.80</td> -</tr> -<tr> -<td class="tdl bord_right">South America</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">500,000</td> -<td class="tdl bord_right">4.15</td> -<td class="tdc bord_right">3</td> -<td class="tdc">....</td> -</tr> -<tr> -<td class="tdl bord_right">Holland</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">1,414,021</td> -<td class="tdc bord_right">22.75</td> -<td class="tdc bord_right">47</td> -<td class="tdc">31.48</td> -</tr> -<tr> -<td class="tdl bord_right">Great Britain</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">10,199,738</td> -<td class="tdc bord_right">161.80</td> -<td class="tdc bord_right">161</td> -<td class="tdc">382.73</td> -</tr> -<tr> -<td class="tdl bord_right">Germany</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">4,639,080</td> -<td class="tdc bord_right">106.22</td> -<td class="tdc bord_right">185</td> -<td class="tdc">117.13</td> -</tr> -<tr> -<td class="tdl bord_right">Other European countries</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right">2,984,839</td> -<td class="tdc bord_right">34.74</td> -<td class="tdc bord_right">88</td> -<td class="tdc">88.84</td> -</tr> -<tr> -<td class="tdl bord_right">Asia</td> -<td class="tdc bord_right">....</td> -<td class="tdr bord_right bord_bot">1,397,000</td> -<td class="tdc bord_right bord_bot">6.69</td> -<td class="tdc bord_right bord_bot">23</td> -<td class="tdc bord_bot">....</td> -</tr> -<tr> -<td class="tdl bord_right bord_bot">Total</td> -<td class="tdc bord_right bord_bot">....</td> -<td class="tdr bord_right bord_bot">21,411,293</td> -<td class="tdc bord_right bord_bot">354.48</td> -<td class="tdc bord_right bord_bot">555</td> -<td class="tdc bord_bot">648.85</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_247">[Pg 247]</span></p> - -<table class="autotable" summary="mechanical filters"> -<tr> -<th class="tdc normal" colspan="7">LIST OF CITIES AND TOWNS USING MECHANICAL FILTERS.<br /> -ARRANGED BY POPULATIONS.</th> -</tr> -<tr> -<th class="tdl normal small" colspan="7"><p>Abbreviations.--P., Pressure filters; G., Gravity filters; J., Jewell system; N. Y., New York system; -W., Warren system; C., Continental system; Am., American system.</p></th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Place.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Population,<br />1890.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Filters<br />First<br />Installed.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Nominal<br />Capacity<br />of Filters,<br />1899.<br />Million<br />Gallons.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Average<br />Consumption,<br />Million<br />Gallons:<br />Water Works<br />Manual.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Area of<br />Filters,<br />Sq. Ft.,<br />1899.</th> -<th class="tdc normal small bord_top bord_bot">Filter<br />System.</th> -</tr> -<tr> -<td class="tdl bord_right">Denver, Col.</td> -<td class="tdr bord_right">108,204</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">2260</td> -<td class="tdc">Special.</td> -</tr> -<tr> -<td class="tdl bord_right">Atlanta, Ga.</td> -<td class="tdr bord_right">65,533</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">8</td> -<td class="tdc bord_right">4.54</td> -<td class="tdc bord_right">2056</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">St. Joseph, Mo.</td> -<td class="tdr bord_right">52,324</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">10.2</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">3842</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Oakland, Cal.</td> -<td class="tdr bord_right">48,682</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">5</td> -<td class="tdc bord_right">10</td> -<td class="tdc bord_right">1960</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Kansas City, Kan.</td> -<td class="tdr bord_right">38,316</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">6</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">2260</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Wilkesbarre, Pa.<a id="FNanchor_55" href="#Footnote_55" class="fnanchor">[55]</a></td> -<td class="tdr bord_right">37,718</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">10</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">3166</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Norfolk, Va.</td> -<td class="tdr bord_right">34,871</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">6</td> -<td class="tdc bord_right">3.5</td> -<td class="tdc bord_right">2112</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Augusta, Ga.</td> -<td class="tdr bord_right">33,300</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">6</td> -<td class="tdc bord_right">3.8</td> -<td class="tdc bord_right">2112</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Quincy. Ill.</td> -<td class="tdr bord_right">30,494</td> -<td class="tdc bord_right">1892</td> -<td class="tdc bord_right">4</td> -<td class="tdc bord_right">1.2</td> -<td class="tdc bord_right">1582</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Dubuque, Iowa<a id="FNanchor_56" href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">30,311</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">880</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Terre Haute, Ind.</td> -<td class="tdr bord_right">30,217</td> -<td class="tdc bord_right">1890</td> -<td class="tdc bord_right">4</td> -<td class="tdc bord_right">3<span class="double">{</span></td> -<td class="tdc bord_right">1076<br />226</td> -<td class="tdc">N. Y. P.<br />J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Elmira, N. Y.</td> -<td class="tdr bord_right">29,708</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">6</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">2034</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Chattanooga, Tenn.</td> -<td class="tdr bord_right">29,100</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">9</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">2080</td> -<td class="tdc">J. & N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Davenport, Iowa</td> -<td class="tdr bord_right">26,872</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">7.5</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">2380</td> -<td class="tdc">Am. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Little Rock, Ark.</td> -<td class="tdr bord_right">25,874</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">5.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">1544</td> -<td class="tdc">Am., J., & N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Winnipeg, Mann.</td> -<td class="tdr bord_right">25,642</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">390</td> -<td class="tdc bord_right">N. Y.</td> -<td class="tdc">P.</td> -</tr> -<tr> -<td class="tdl bord_right">Oshkosh, Wis.</td> -<td class="tdr bord_right">22,836</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">2.4</td> -<td class="tdc bord_right">2.1</td> -<td class="tdc bord_right">550</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Macon, Ga.</td> -<td class="tdr bord_right">22,746</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">4</td> -<td class="tdc bord_right">1.65</td> -<td class="tdc bord_right">1437</td> -<td class="tdl">J., W., & N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Burlington, Ia.</td> -<td class="tdr bord_right">22,565</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">3.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">1243</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Knoxville, Tenn.</td> -<td class="tdr bord_right">22,535</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">5</td> -<td class="tdc bord_right">1.93</td> -<td class="tdc bord_right">1404</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Lexington, Ky.</td> -<td class="tdr bord_right">21,567</td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">1.2</td> -<td class="tdc bord_right">678</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Kingston, N. Y.</td> -<td class="tdr bord_right">21,261</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">4</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">1120</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">York, Penna.</td> -<td class="tdr bord_right">20,793</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">4</td> -<td class="tdc bord_right">2.37</td> -<td class="tdc bord_right">1408</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Biddeford, Maine</td> -<td class="tdr bord_right">20,500</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">780</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Newport, R. I.</td> -<td class="tdr bord_right">19,467</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">4</td> -<td class="tdc bord_right">2.1</td> -<td class="tdc bord_right"> </td> -<td class="tdc">Special.</td> -</tr> -<tr> -<td class="tdl bord_right">Bangor, Maine</td> -<td class="tdr bord_right">19,103</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">5</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">1404</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Cedar Rapids, Ia.</td> -<td class="tdr bord_right">18,020</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">2.5</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">905</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Elgin, Ill.</td> -<td class="tdr bord_right">17,823</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">4.3</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">780</td> -<td class="tdc">Am. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Decatur, Ill.</td> -<td class="tdr bord_right">16,841</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">1008</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Belleville, Ill.</td> -<td class="tdr bord_right">15,361</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.6</td> -<td class="tdc bord_right">339</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Columbia, S. C.</td> -<td class="tdr bord_right">15,353</td> -<td class="tdc bord_right">1892</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">678</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Keokuk, Ia.</td> -<td class="tdr bord_right">14,101</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">980</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Ottumwa, Ia.</td> -<td class="tdr bord_right">14,001</td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">1.2</td> -<td class="tdc bord_right">678</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Rock Island, Ill.<a href="#Footnote_55" class="fnanchor">[55]</a></td> -<td class="tdr bord_right">13,634</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">3.5</td> -<td class="tdc bord_right">452</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Raleigh, N. C.</td> -<td class="tdr bord_right">12,678</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">296</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Shreveport, La.</td> -<td class="tdr bord_right">11,979</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">312</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">New Castle, Penna</td> -<td class="tdr bord_right">11,600</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">4</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">1408</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right"><span class="pagenum" id="Page_248">[Pg 248]</span>Charlotte, N. C.</td> -<td class="tdr bord_right">11,557</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">530</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Nebraska City, Neb.</td> -<td class="tdr bord_right">11,494</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right">0.7</td> -<td class="tdc bord_right">116</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Streator, Ill.</td> -<td class="tdr bord_right">11,414</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">1.3</td> -<td class="tdc bord_right">100</td> -<td class="tdc">Western & Am. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Hornelsville, N. Y.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">10,966</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">700</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Augusta, Maine</td> -<td class="tdr bord_right">10,527</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">0.6</td> -<td class="tdc bord_right">1.6</td> -<td class="tdc bord_right">100</td> -<td class="tdc">W.</td> -</tr> -<tr> -<td class="tdl bord_right">St. Thomas, Ont.</td> -<td class="tdr bord_right">10,370</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">2.5</td> -<td class="tdc bord_right">0.6</td> -<td class="tdc bord_right">700</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Cairo, Ill.</td> -<td class="tdr bord_right">10,324</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.8</td> -<td class="tdc bord_right">2.5</td> -<td class="tdc bord_right">197</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Alton, Ill.</td> -<td class="tdr bord_right">10,294</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">1056</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Asheville, N. C.</td> -<td class="tdr bord_right">10,235</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.35</td> -<td class="tdc bord_right">312</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Greenwich, Conn.</td> -<td class="tdr bord_right">10,131</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right">592</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Huntington, W. Va.</td> -<td class="tdr bord_right">10,108</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">704</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Beaver Falls, Pa.</td> -<td class="tdr bord_right">9,735</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">4.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc">N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Champaign, Ill.<a href="#Footnote_55" class="fnanchor">[55]</a></td> -<td class="tdr bord_right">9,719</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.75</td> -<td class="tdc bord_right"> </td> -<td class="tdc">N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Chatham, Ont.</td> -<td class="tdr bord_right">9,052</td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right">280</td> -<td class="tdl">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Adrian, Mich.</td> -<td class="tdr bord_right">8,756</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">1.75</td> -<td class="tdc bord_right">0.45</td> -<td class="tdc bord_right">565</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Athens, Ga.</td> -<td class="tdr bord_right">8,639</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.45</td> -<td class="tdc bord_right">420</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">East Providence, R. I.</td> -<td class="tdr bord_right">8,422</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">176</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Winston, N. C.</td> -<td class="tdr bord_right">8,018</td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right">156</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Danville, Penna.</td> -<td class="tdr bord_right">7,998</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">226</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Clarksville, Tenn.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">7,924</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">704</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Stevens Point, Wis.</td> -<td class="tdr bord_right">7,896</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Carlisle, Pa.</td> -<td class="tdr bord_right">7,620</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">339</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Calais, Me.</td> -<td class="tdr bord_right">7,290</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">0.85</td> -<td class="tdc bord_right">275</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Long Branch, N. J.</td> -<td class="tdr bord_right">7,231</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">1.3</td> -<td class="tdc bord_right">904</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Creston, Ia.</td> -<td class="tdr bord_right">7,200</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right">150</td> -<td class="tdc">J.</td> -</tr> -<tr> -<td class="tdl bord_right">St. Hyacinthe, Que.</td> -<td class="tdr bord_right">7,016</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.84</td> -<td class="tdc bord_right">294</td> -<td class="tdc">J. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Rome, Ga.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">6,957</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">1.3</td> -<td class="tdc bord_right">528</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Westerly, R. I.</td> -<td class="tdr bord_right">6,813</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">0.375</td> -<td class="tdc bord_right">396</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Merrill, Wis.</td> -<td class="tdr bord_right">6,809</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">339</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Dennison, Ohio<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">6,767</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">1.25</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">528</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Parsons, Kan.</td> -<td class="tdr bord_right">6,736</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">0.6</td> -<td class="tdc bord_right">452</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Waterloo, Iowa</td> -<td class="tdr bord_right">6,674</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">0.7</td> -<td class="tdc bord_right">565</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Somerville, N. J.</td> -<td class="tdr bord_right">6,417</td> -<td class="tdc bord_right">1885</td> -<td class="tdc bord_right">1.9</td> -<td class="tdc bord_right">0.75</td> -<td class="tdc bord_right">552</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Athol, Mass.</td> -<td class="tdr bord_right">6,319</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">350</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Owego, N. Y.</td> -<td class="tdr bord_right">6,200</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.75</td> -<td class="tdc bord_right">234</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Brunswick, Maine</td> -<td class="tdr bord_right">6,012</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">0.6</td> -<td class="tdc bord_right">0.33</td> -<td class="tdc bord_right">100</td> -<td class="tdc">W.</td> -</tr> -<tr> -<td class="tdl bord_right">Bucyrus, Ohio</td> -<td class="tdr bord_right">5,974</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.55</td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Warren, Ohio</td> -<td class="tdr bord_right">5,973</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">462</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Hopkinsville, Ky.</td> -<td class="tdr bord_right">5,833</td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.15</td> -<td class="tdc bord_right">140</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Brainerd, Minn.</td> -<td class="tdr bord_right">5,703</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">New Brighton, Pa.</td> -<td class="tdr bord_right">5,616</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Niagara Falls, N. Y.</td> -<td class="tdr bord_right">5,502</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">4.5</td> -<td class="tdc bord_right">2.62</td> -<td class="tdc bord_right">1019</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right"><span class="pagenum" id="Page_249">[Pg 249]</span>Durham, N. C.</td> -<td class="tdr bord_right">5485</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">0.9</td> -<td class="tdc bord_right">0.7</td> -<td class="tdc bord_right">252</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Winfield, Kan.</td> -<td class="tdr bord_right">5184</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">336</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Louisiana, Mo.</td> -<td class="tdr bord_right">5090</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">0.8</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">242</td> -<td class="tdc">N. Y. P. & G.</td> -</tr> -<tr> -<td class="tdl bord_right">Trenton, Mo.</td> -<td class="tdr bord_right">5039</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">128</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Lorain, Ohio</td> -<td class="tdr bord_right">4863</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">3</td> -<td class="tdc bord_right">1.5</td> -<td class="tdc bord_right">1356</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Sidney, Ohio<a href="#Footnote_55" class="fnanchor">[55]</a></td> -<td class="tdr bord_right">4850</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc">N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Mexico, Mo.</td> -<td class="tdr bord_right">4789</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right">66</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Mt. Clemens, Mich.</td> -<td class="tdr bord_right">4748</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.6</td> -<td class="tdc bord_right">251</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Riverside, Cal.</td> -<td class="tdr bord_right">4683</td> -<td class="tdc bord_right">1892</td> -<td class="tdc bord_right">0.09</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">20</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Columbus, Miss.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">4559</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.175</td> -<td class="tdc bord_right">176</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Winchester, Ky.</td> -<td class="tdr bord_right">4519</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">0.75</td> -<td class="tdc bord_right">0.107</td> -<td class="tdc bord_right">152</td> -<td class="tdc">J. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Salisbury, N. C.</td> -<td class="tdr bord_right">4418</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.35</td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Eufaula, Ala.</td> -<td class="tdr bord_right">4394</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">140</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Greenville, Tex.</td> -<td class="tdr bord_right">4330</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">0.8</td> -<td class="tdc bord_right">0.175</td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Exeter, N. H.</td> -<td class="tdr bord_right">4284</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">0.114</td> -<td class="tdc bord_right">0.179</td> -<td class="tdc bord_right">34</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Bordentown, N. J.</td> -<td class="tdr bord_right">4232</td> -<td class="tdc bord_right">1890</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Lake Forest, Ill.</td> -<td class="tdr bord_right">4203</td> -<td class="tdc bord_right">1892</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">168</td> -<td class="tdc">J. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Henderson, N. C.</td> -<td class="tdr bord_right">4191</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">118</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Reading, Mass.</td> -<td class="tdr bord_right">4088</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.198</td> -<td class="tdc bord_right">336</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Goldsboro, N. C.</td> -<td class="tdr bord_right">4017</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.1</td> -<td class="tdc bord_right">156</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Rich Hill, Mo.</td> -<td class="tdr bord_right">4008</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.24</td> -<td class="tdc bord_right">140</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Mt. Pleasant, Ia.</td> -<td class="tdr bord_right">3997</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Murphysboro, Ill.</td> -<td class="tdr bord_right">3880</td> -<td class="tdc bord_right">1890</td> -<td class="tdc bord_right">0.2</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">60</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Brandon, Manitoba</td> -<td class="tdr bord_right">3778</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.36</td> -<td class="tdc bord_right">240</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Danville, Ky.</td> -<td class="tdr bord_right">3766</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.1</td> -<td class="tdc bord_right">140</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Royersford, Pa.</td> -<td class="tdr bord_right">3612</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.08</td> -<td class="tdc bord_right">226</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Warsaw, Ind.</td> -<td class="tdr bord_right">3514</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Ashbury Park, N. J.</td> -<td class="tdr bord_right">3500</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">2</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">670</td> -<td class="tdc">C.</td> -</tr> -<tr> -<td class="tdl bord_right">Keyport, N. J.</td> -<td class="tdr bord_right">3411</td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.06</td> -<td class="tdc bord_right">156</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Deseronto, Ont.</td> -<td class="tdr bord_right">3338</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.84</td> -<td class="tdc bord_right">147</td> -<td class="tdc">J. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Milledgeville, Ga.</td> -<td class="tdr bord_right">3322</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Carlinville, Ill.</td> -<td class="tdr bord_right">3293</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">38</td> -<td class="tdc">Am. or Jackson.</td> -</tr> -<tr> -<td class="tdl bord_right">Gettysburg, Pa.</td> -<td class="tdr bord_right">3221</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right">0.075</td> -<td class="tdc bord_right">78</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Independence, Kan.</td> -<td class="tdr bord_right">3127</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">0.75</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right">129</td> -<td class="tdc">Am. P.</td> -</tr> -<tr> -<td class="tdl bord_right">LaGrange, Ga.</td> -<td class="tdr bord_right">3090</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">34</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Paola, Kan.</td> -<td class="tdr bord_right">2943</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right">0.45</td> -<td class="tdc bord_right">66</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Benwood, W. Va.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">2934</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">306</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Gadsden, Ala.</td> -<td class="tdr bord_right">2901</td> -<td class="tdc bord_right">1887</td> -<td class="tdc bord_right">1.325</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">430</td> -<td class="tdc">N. Y. P. & G.</td> -</tr> -<tr> -<td class="tdl bord_right">Lamar, Mo.</td> -<td class="tdr bord_right">2860</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">78</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Longueuil, Que.</td> -<td class="tdr bord_right">2757</td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right">100</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Washington, Mo.</td> -<td class="tdr bord_right">2725</td> -<td class="tdc bord_right">1888</td> -<td class="tdc bord_right">0.2</td> -<td class="tdc bord_right">0.075</td> -<td class="tdc bord_right">50</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Renfrew, Ont.</td> -<td class="tdr bord_right">2611</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">0.432</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">100</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right"><span class="pagenum" id="Page_250">[Pg 250]</span>Oswego, Kan.</td> -<td class="tdr bord_right">2574</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right">140</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Holden, Mo.</td> -<td class="tdr bord_right">2520</td> -<td class="tdc bord_right">1893</td> -<td class="tdc bord_right">0.2</td> -<td class="tdc bord_right">0.05</td> -<td class="tdc bord_right">100</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Burlington, Kan.</td> -<td class="tdr bord_right">2239</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">79</td> -<td class="tdc">J.</td> -</tr> -<tr> -<td class="tdl bord_right">Council Grove, Kan.</td> -<td class="tdr bord_right">2211</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right">0.08</td> -<td class="tdc bord_right">78</td> -<td class="tdc">N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Wakefield, R. I.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right">2170</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.15</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right"> </td> -<td class="tdc">N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Catonsville, Md.</td> -<td class="tdr bord_right">2115</td> -<td class="tdc bord_right">1890</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">78</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Attica, N. Y.</td> -<td class="tdr bord_right">1994</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">100</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Hightstown, N. J.</td> -<td class="tdr bord_right">1875</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right">0.025</td> -<td class="tdc bord_right">78</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">No. Berwick, Me.</td> -<td class="tdr bord_right">1803</td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">78</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Dunnville, Ont.</td> -<td class="tdr bord_right">1776</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">140</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Rogers Park, Ill.</td> -<td class="tdr bord_right">1708</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.4</td> -<td class="tdc bord_right">0.35</td> -<td class="tdc bord_right">100</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Eatonton, Ga.</td> -<td class="tdr bord_right">1682</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">132</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Caldwell, Kan.</td> -<td class="tdr bord_right">1642</td> -<td class="tdc bord_right">1890</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">LaGrange, Tex.</td> -<td class="tdr bord_right">1626</td> -<td class="tdc bord_right">1891</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">34</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Richfield Springs, N. Y.</td> -<td class="tdr bord_right">1623</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.35</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">100</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Valatie, N. Y.</td> -<td class="tdr bord_right">1437</td> -<td class="tdc bord_right">1894</td> -<td class="tdc bord_right">0.15</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">50</td> -<td class="tdc">N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Tunkhannock, Pa.</td> -<td class="tdr bord_right">1253</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right"> </td> -<td class="tdc">N. Y.</td> -</tr> -<tr> -<td class="tdl bord_right">Mechanics Falls, Me.</td> -<td class="tdr bord_right">1030</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">0.72</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">176</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">New Bethlehem, Pa.</td> -<td class="tdr bord_right">1026</td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">50</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Fairmount, W. Va.</td> -<td class="tdr bord_right">1023</td> -<td class="tdc bord_right">1898</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">280</td> -<td class="tdl">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Atlantic Highlands, N. J.</td> -<td class="tdr bord_right">945</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.3</td> -<td class="tdc bord_right">0.109</td> -<td class="tdc bord_right">130</td> -<td class="tdc">C.</td> -</tr> -<tr> -<td class="tdl bord_right">Rumford Falls, Me.</td> -<td class="tdr bord_right">898</td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">113</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Lakewood, N. J.</td> -<td class="tdr bord_right">730</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">156</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Veazie, Me.</td> -<td class="tdr bord_right">650</td> -<td class="tdc bord_right">1889</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.1</td> -<td class="tdc bord_right">176</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Portersville, Cal.</td> -<td class="tdr bord_right">606</td> -<td class="tdc bord_right">1890</td> -<td class="tdc bord_right">0.151</td> -<td class="tdc bord_right">0.060</td> -<td class="tdc bord_right">34</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Holmesburg, Pa.</td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">1</td> -<td class="tdc bord_right">0.046</td> -<td class="tdc bord_right">280</td> -<td class="tdc">N. Y. P.</td> -</tr> -<tr> -<td class="tdl bord_right">Pickering Creek, Pa.</td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right">1896</td> -<td class="tdc bord_right">0.75</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">234</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Overbrook, Penna.</td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right">1895</td> -<td class="tdc bord_right">0.25</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">78</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Vandergrift, Pa.</td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right">1897</td> -<td class="tdc bord_right">0.5</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">156</td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Frazerville, P. Q.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.2</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">78</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Arnate, Pa.</td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">0.12</td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">50</td> -<td class="tdc">N. Y. G.</td> -</tr> -<tr> -<td class="tdl bord_right">Chihuahua, Mex.<a href="#Footnote_56" class="fnanchor">[56]</a></td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right">1899</td> -<td class="tdc bord_right">1</td><td class="tdc bord_right"> </td> -<td class="tdc bord_right">612</td> -<td class="tdc">J. G.</td> -</tr> -<tr> -<td class="tdl bord_right">West Reading, Pa.</td> -<td class="tdr bord_right"> </td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right"> </td> -<td class="tdc bord_right">0.07</td> -<td class="tdc bord_right"> </td> -<td class="tdc">W. G.</td> -</tr> -<tr> -<td class="tdl bord_right bord_right bord_bot"><span class="add2em">Totals</span></td> -<td class="tdr bord_top bord_right bord_bot">1,565,881</td> -<td class="tdc bord_right bord_bot"> </td> -<td class="tdc bord_top bord_right bord_bot">252</td> -<td class="tdc bord_top bord_right bord_bot">108</td> -<td class="tdc bord_top bord_right bord_bot">77,806</td> -<td class="tdc bord_bot"> </td> -</tr> -</table> - -<p>Special filters, neither sand nor mechanical: Wilmington, Del.; Pop., -61,431; area, 10,000 sq. ft.; nominal capacity, 10 million gallons. See -Eng. News, Vol. 40, p. 146.</p> - -<p><span class="pagenum" id="Page_251">[Pg 251]</span></p> - -<div class="section"> -<h3 class="nobreak" id="NOTES_REGARDING_SAND_FILTERS_IN_THE_UNITED_STATES"> -NOTES REGARDING SAND FILTERS IN THE UNITED STATES.</h3></div> - -<p><span class="smcap">Poughkeepsie, N. Y.</span> Designed by James P. Kirkwood, built -in 1872, was the earliest of its kind in the United States. It was -enlarged by the Superintendent, Charles E. Fowler, in 1896. The walls -of the original filters were of rubble, and in course of time developed -cracks and leaked badly. The walls of the new filter are of rubble, -faced with vitrified brick. The filters treat the water of the Hudson -River, which is sewage-polluted and more or less muddy. Description: -Jour. N. E. Water Works Assoc., Vol. 12, p. 209.</p> - -<p><span class="smcap">Hudson, N. Y.</span> Designed by James P. Kirkwood, built in 1874. -enlarged in 1888. The filters are open and are used for treating the -Hudson River water, which is sewage-polluted and more or less muddy. -Description: Eng. News, Vol. 31, p. 487.</p> - -<p><span class="smcap">St. Johnsbury, Vt.</span> (E. & T. Fairbanks & Co.) These filters -were built about 30 years ago, and have been recently enlarged. The -filters were originally open, but were afterwards covered with a roof. -The single roof proved inadequate to keep them from freezing, and a -second roof was added inside and under the main roof. They are used -for filtering pond water, which is quite clear and not subject to much -pollution. The water supply is one of two, the other is the town supply -and is taken from the Passumpsic River. No published description.</p> - -<p><span class="smcap">Nantucket, Mass.</span> Designed by J. B. Rider, built in 1892. This -filter is used to remove organisms from the reservoir water supply. It -is only used when the organisms are troublesome, and is satisfactory -in preventing the tastes and odors which formerly resulted from their -presence. Description: Jour. N. E. Water Works Assoc., Vol. 8, p. 171; -Eng. News, Vol. 31, p. 336.</p> - -<p><span class="smcap">Lawrence, Mass.</span> Designed by Hiram F. Mills, built in 1892-3, -and put in operation September, 1893. It is used for treating the -water of the Merrimac River, which contains a large amount<span class="pagenum" id="Page_252">[Pg 252]</span> of sewage. -Description: Report of the Mass. State Board of Health, 1893, p. 543; -Jour. N. E. Water Works Assoc., Vol. 9, p. 44; Eng. News, Vol. 30, p. -97.</p> - -<p><span class="smcap">Ilion, N. Y.</span> Designed by the Stanwix Engineering Company and -are used for treating reservoir water, which is generally clear and not -subject to pollution. Description: Eng. News, Vol. 31, p. 466.</p> - -<p><span class="smcap">Mount Vernon, N. Y.</span> (New York Suburban Water Company.) -Designed by J. N. Chester, built in 1894. These filters are similar in -general construction to the Lawrence filter, although the dimensions -both vertical and horizontal are reduced, and the area is divided into -three parts. The filters are used for treating reservoir water, which -is generally quite clear, but which is polluted by a considerable -amount of sewage. Since the use of filters the reduction in the typhoid -fever death-rate has been very great. Description: Eng. News, Vol. 32, -p. 155.</p> - -<p><span class="smcap">Milford, Mass.</span> Designed by F. L. Northrop. This filter is very -simple in construction, and is used for filtering Charles River water -as an auxiliary supply. Description: Jour. N. E. Water Works Assoc., -Vol. 10, p. 262.</p> - -<p><span class="smcap">Grand Forks, N. D.</span> Designed by W. S. Russell. These filters -are covered with roofs. They treat the water from the Red River, which -is very muddy, and also sewage-polluted, and which formerly caused -typhoid fever. Description: Eng. News, Vol. 33, p. 341.</p> - -<p><span class="smcap">Ashland, Wis.</span> Designed by William Wheeler, built in 1895. -The Ashland filters were the first vaulted masonry filters to be -constructed in the United States, and are used for treating the bay -water, which is polluted with sewage, and is at times muddy from the -river water discharging into the bay near the intake. The filters are -below the bay level, and receive water from it by gravity. Description: -Jour. N. E. Water Works Assoc., Vol. 11, p. 301; Eng. News, Vol. 38, p. -338.</p> - -<p><span class="smcap">Lambertville, N. J.</span> Designed by Churchill Hungerford, and<span class="pagenum" id="Page_253">[Pg 253]</span> -built in 1896. These are open filters with earth embankments, for -filtration of reservoir water. Description: Eng. News, Vol. 36, p. 4.</p> - -<p><span class="smcap">Far Rockaway, L. I.</span> (Queens County Water Company.) Designed by -Charles R. Bettes, Engineer in Charge; Charles B. Brush & Co., Chief -Engineers; and Allen Hazen, Consulting Engineer. Constructed in 1896. -These masonry filters were used for the removal of iron from well -waters. They are also designed to be suitable for the filtration of -certain brook waters which are available as auxiliary supplies, but the -brook water has been but rarely used. Description: Eng. Record, Vol. -40, p. 412.</p> - -<p><span class="smcap">Red Bank, N. J.</span> (Rumson Improvement Company.) Designed by -Allen Hazen, built in 1897. They are similar in construction to the Far -Rockaway filters, and are used for iron removal only. Description: Eng. -Record, Vol. 40, p. 412.</p> - -<p><span class="smcap">Hamilton, N. Y.</span> Designed by the Stanwix Engineering Company, -and were built in 1895 to filter lake water. Description: Eng. News, -Vol. 39, p. 254.</p> - -<p><span class="smcap">Little Falls, N. Y.</span> Designed by Stephen E. Babcock. These -filters are open, and were built in 1898, and are used for filtering -river water. Description: Eng. Record, Vol. 38, p. 7.</p> - -<p><span class="smcap">Somersworth, N. H.</span> Designed by William Wheeler. These were the -second vaulted filters to be built in the United States. The supply is -from the Salmon Falls River and flows to the filters by gravity, the -filters being below the river level. Description: Eng. News, Vol 40, p. -358; Eng. Record, Vol. 38, p. 270.</p> - -<p><span class="smcap">Berwyn, Penna.</span> Designed by J. W. Ledoux. These open filters -are used for filtering creek water. Description: Eng. News, Vol. 41, p. -150.</p> - -<p><span class="smcap">Harrisburg, Penna.</span> (State Lunatic Hospital.) Designed by Allen -Hazen; open masonry filters, used for treating the water from a small -creek which is often muddy and is subject to pollution. No published -description.</p> - -<p><span class="pagenum" id="Page_254">[Pg 254]</span></p> - -<p><span class="smcap">Albany, N. Y.</span> Designed by Allen Hazen. Constructed 1898-99. -This was the third and is the largest vaulted masonry filter plant yet -constructed in the United States. It is used for filtering the Hudson -River water, which is slightly muddy and much polluted by sewage. -Description: Eng. News, Vol. 39, p. 91; Vol. 40, p. 254.</p> - -<p><span class="smcap">Rock Island, Ill.</span> Designed by Jacob A. Harman. Open filters -with embankments, used for filtering the Mississippi River water, which -is very muddy and also polluted by sewage. No published description.</p> - -<hr class="tb" /> - -<div class="section"> -<h3 class="nobreak" id="CAPACITY_OF_FILTERS">CAPACITY OF FILTERS.</h3></div> - -<p>Estimating the total additional area of sand filters for which figures -are not available at 100 acres, and the maximum capacity of sand -filters at three million gallons per acre daily, and of mechanical -filters at three million gallons per thousand square feet of filtering -area, the total filtering capacity of all the filters in the world used -for public water supplies in 1899 is nearly 1600 million gallons daily, -of which 15 per cent is represented by mechanical filters and 85 per -cent by sand filters. In the United States, including Wilmington, the -total filtering capacity is nearly 300 million gallons daily, of which -18 per cent is represented by sand filters, 79 per cent by mechanical -filters, and 3 per cent by a special type of filters.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_255">[Pg 255]</span></p> - -<h2 class="nobreak" id="APPENDIX_V">APPENDIX V.<br /> -<br /> - -<span class="small">LONDON’S WATER-SUPPLY.</span></h2></div> - -<p><span class="smcap">London</span> alone among great capitals is supplied with water by private -companies. They are, however, under government supervision, and -the rates charged for water are regulated by law. There are eight -companies, each of which supplies its own separate district, so that -there is no competition whatever. One of the companies supplying -460,000 people uses only ground-water drawn from deep wells in the -chalk, but the other seven companies depend mainly upon the rivers -Thames and Lea for their water. All water so drawn is filtered, and -must be satisfactory to the water examiner, who is required to inspect -the water supplied by each company at frequent intervals, and the -results of the examinations are published each month.</p> - -<p>In 1893 the average daily supply was 235,000,000 gallons, of which -about 40,000,000 were drawn from the chalk, 125,000,000 from the -Thames, and 70,000,000 from the Lea. Formerly some of the water -companies drew water from the Thames within the city where it was -grossly polluted, and the plagues and cholera which formerly ravaged -London were in part due to this fact. These intakes were abandoned -many years ago, and all the companies now draw their water from points -outside of the city and its immediate suburbs.</p> - -<p>The area of the watershed of the Thames above the intakes of the water -companies is 3548 square miles, and the population living upon it in -1891 was 1,056,415. The Thames Conservancy Board has control of the -main river for its whole length, and of all tributaries within ten -miles in a straight line of the main river, but has no<span class="pagenum" id="Page_256">[Pg 256]</span> jurisdiction -over the more remote feeders. The area drained is essentially -agricultural, with but little manufacturing, and there are but few -large towns. In the area coming under the conservators there are but -six towns with populations above 10,000 and an aggregate population -of 170,000, and there are but two or three other large towns on the -remaining area more than ten miles from the river. These principal -towns are as follows:</p> - -<table class="autotable" summary="principal towns more than 10 miles from Thames"> -<tr> -<th class="tdc normal small">Town.</th> -<th class="tdc normal small">Population 1891.</th> -<th class="tdc normal small">Distance above<br />Water Intakes.</th> -</tr> -<tr> -<td class="tdl">Reading</td> -<td class="tdc">60,054</td> -<td class="tdc"> 49 miles</td> -</tr> -<tr> - -<td class="tdl">Oxford</td> -<td class="tdc">45,791</td> -<td class="tdc"> 87 miles</td> -</tr> -<tr> - -<td class="tdl">New Swindon</td> -<td class="tdc">27,295</td> -<td class="tdc">116 miles</td> -</tr> -<tr> - -<td class="tdl">High Wycomb</td> -<td class="tdc">13,435</td> -<td class="tdc"> 33 miles</td> -</tr> -<tr> - -<td class="tdl">Windsor</td> -<td class="tdc">12,327</td> -<td class="tdc"> 18 miles</td> -</tr> -<tr> - -<td class="tdl">Maidenhead</td> -<td class="tdc">10,607</td> -<td class="tdc"> 25 miles</td> -</tr> -<tr> - -<td class="tdl">Guildford</td> -<td class="tdc">14,319</td> -<td class="tdc"> 20 miles</td> -</tr> -</table> - -<p>Guildford is outside of the conservators’ area. All of the above towns -treat their sewage by irrigation.</p> - -<p>Among the places that are regarded as the most dangerous are Chertsey -and Staines, with populations of 9215 and 5060, only 8 and 11 miles -above the intakes respectively. These towns are only partially sewered -and still depend mainly on cesspools. An attempt is made to treat the -little sewage which they produce upon land, but the work has not as yet -been systematically carried out. There are also several small towns of -3000 inhabitants or less upon the upper river which do not treat their -sewage so far as they have any, but, owing to their great distance, -the danger from them is much less than from Chertsey and Staines. -Twenty-one of the principal towns upon the watershed have sewage farms, -and there are no chemical precipitation plants now in use.</p> - -<p>Boats upon the river are not allowed to drain into it, but are -compelled to provide receptacles for their sewage, and facilities -are provided for removing and disposing of it; and as an additional -precaution no boat is allowed to anchor within five miles of the -intakes.</p> - -<p><span class="pagenum" id="Page_257">[Pg 257]</span></p> - -<p>The conservators of the river Lea have control of its entire drainage -area, which is about 460 square miles, measured from the East London -water intakes, and has a population of 189,287. On this watershed there -is but a single town with more than 10,000 inhabitants, this being -Lutton near the headwaters of the river, with a population of 30,005. -The sewage from Lutton and from seventeen smaller places is treated -upon land. No crude sewage is known to be ordinarily discharged into -the river. At Hereford, eleven miles above the East London intakes, -there is a chemical precipitation plant. The conservators do not -regard this treatment as satisfactory, and have recently conducted -an expensive lawsuit against the local authorities to compel them to -further treat their effluent. The suit was lost, the court holding that -no actual injury to health had been shown. It is especially interesting -to note that of the thirty-nine places on the Thames and the Lea giving -their sewage systematic treatment there is but a single place using -chemical precipitation, and there it is not considered satisfactory. -Formerly quite a number of these towns used other processes than land -treatment, but in every case but Hereford land treatment has been -substituted.</p> - -<p>In regard to the efficiency of the sewage farms, it is believed that -in ordinary weather the whole of the sewage percolates through the -land, and the inspectors of the Conservancy Boards strongly object to -its being allowed to pass over the surface into the streams. The land, -however, is for the most part impervious, as compared to Massachusetts -and German sewage farms, and in times of heavy storms the land often -has all the water it can take without receiving even the ordinary flow -of sewage, and much less the increased storm-flow. At such times the -sewage either does go over the surface, or perhaps more frequently -is discharged directly into the rivers without even a pretence of -treatment. The conservators apparently regard this as an unavoidable -evil and do not vigorously oppose it. It is the theory that, owing -to the increased dilution with the storm-flows, the matter is -comparatively harmless,<span class="pagenum" id="Page_258">[Pg 258]</span> although it would seem that the reduced time -required for it to reach the water-works intakes might largely offset -the effect of increased dilution.</p> - -<p>The water companies have large storage and sedimentation basins with -an aggregate capacity equal to nine days’ supply, but the proportion -varies widely with the different companies. It is desired that the -water held in reserve shall be alone used while the river is in flood, -as, owing to its increased pollution, it is regarded as far more -dangerous than the water at other times; but as no record is kept of -the times when raw sewage is discharged, and no exact information is -available in regard to the times when the companies do not take in -raw water, it can safely be assumed that a considerable amount of raw -sewage does become mixed with the water which is drawn by the companies.</p> - -<p>The water drawn from the river is filtered through 113 filters having -an area of 116 acres. None of the filters are covered, and with an -average January temperature of 39° but little trouble with ice is -experienced. A few new filters are provided with appliances for -regulating the rate on each filter separately and securing regular and -determined rates of filtration, but nearly all of the filters are of -the simple type described on page 48, and the rates of filtration are -subject to more or less violent fluctuation, the extent of which cannot -be determined.</p> - -<p>The area of filters is being continually increased to meet increasing -consumption; the approximate areas of filters in use having been as -follows:</p> - -<table class="autotable" summary="approximate areas of filters in use"> -<tr> - -<td class="tdl">1839</td> -<td class="tdl">First filters built</td> -</tr> -<tr> - -<td class="tdl">1855</td> -<td class="tdl"> 37 acres</td> -</tr> -<tr> - -<td class="tdl">1866</td> -<td class="tdl"> 47 acres</td> -</tr> -<tr> - -<td class="tdl">1876</td> -<td class="tdl"> 77 acres</td> -</tr> -<tr> - -<td class="tdl">1886</td> -<td class="tdl">104 acres</td> -</tr> -<tr> - -<td class="tdl">1894</td> -<td class="tdl">116 acres</td> -</tr> -</table> - -<p>There has been a tendency to reduce somewhat the rate of filtration. In -1868, with 51 acres of filters, the average daily quantity of<span class="pagenum" id="Page_259">[Pg 259]</span> water -filtered was 111,000,000 gallons, or 2,180,000 gallons per acre. In -1884, with 97 acres of filter surface, the daily quantity filtered was -157,000,000 gallons, or 1,620,000 gallons per acre; and in 1893, with -116 acres of filter surface and 195,000,000 gallons daily, the yield -per acre was 1,680,000 gallons.</p> - -<p>Owing to the area of filter surface out of use while being cleaned, -the variations in consumption of water, and the imperfections of the -regulating apparatus, the actual rates of filtration are often very -much higher and at times may easily be double the figures given.</p> - -<p>Evidence regarding the healthfulness of the filtered river-water was -collected and examined in a most exhaustive manner in 1893 by a Royal -Commission appointed to consider the water-supply of the metropolis in -all its aspects with reference to future needs. This commission was -unable to obtain any evidence whatever that the water as then supplied -was unhealthy or likely to become so, and they report that the rivers -can safely be depended upon for many years to come.</p> - -<p class="padb1">The numbers of deaths from all causes and from typhoid fever annually -per million of inhabitants for the years 1885-1891 in the populations -receiving their waters from different sources in London were as follows:</p> - -<table class="autotable" summary="london deaths from typhoid 1885 to 1891"> -<tr> - -<th class="tdc normal small">Water used.</th> -<th class="tdc normal small">Deaths from All Causes.</th> -<th class="tdc normal small">Deaths from Typhoid Fever.</th> -</tr> -<tr> - -<td class="tdl">Filtered Thames water only</td> -<td class="tdc">19,501</td> -<td class="tdc">125</td> -</tr> -<tr> - -<td class="tdl">Filtered Lea water only</td> -<td class="tdc">21,334</td> -<td class="tdc">167</td> -</tr> -<tr> - -<td class="tdl">Kent wells only</td> -<td class="tdc">18,001</td> -<td class="tdc">123</td> -</tr> -<tr> - -<td class="tdl">Thames and Lea jointly</td> -<td class="tdc">18,945</td> -<td class="tdc">138</td> -</tr> -<tr> - -<td class="tdl">Thames and Kent jointly</td> -<td class="tdc">18,577</td> -<td class="tdc">133</td> -</tr> -</table> - -<p class="padt1">The population supplied exclusively from the Lea by the East London -Company is of a poorer class than that of the rest of London, and this -may account for the slightly higher death-rate in this section. Aside -from this the rate is remarkably uniform and shows no great difference -between the section drinking ground-water only and those drinking -filtered river-waters. The death-rate from<span class="pagenum" id="Page_260">[Pg 260]</span> typhoid fever is also very -uniform and, although higher than that of some Continental cities with -excellent water-supplies (Berlin, Vienna, Munich, Dresden), is very -low—lower than in any American city of which I have records.</p> - -<p>In this connection, it was shown by the Registrar-General that there -is only a very small amount of typhoid fever on the watersheds of -the Thames and Lea, so that the danger of infection of the water as -distinct from pollution is less than would otherwise be the case. Thus -for the seven years above mentioned the numbers of deaths from typhoid -fever per million of population were only 105 and 120 on the watersheds -of the Thames and the Lea respectively, as against 176 for the whole of -England and Wales.</p> - -<table class="autotable" summary="london filters 1896"> -<tr> -<th class="tdc normal" colspan="8">LONDON FILTERS, 1896.</th> -</tr> -<tr> -<th class="tdc normal small" colspan="8">Twenty-sixth Annual Report of the Local Government Board, pages 206-213.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Company.</th> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Amount<br />of<br />Storage<br />Raw<br />Water,<br />Days.</th> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Average<br />Thickness of<br />Sand,<br />Feet.</th> -<th class="tdc normal small bord_top bord_right bord_bot" colspan="2">Average Rate<br />of<br />Filtration.</th> -<th class="tdc normal small bord_top bord_bot" colspan="3">Bacterial Efficiency.</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">Imperial<br />Gallons<br />per<br />Square<br />Foot<br />per Hour.</th> -<th class="tdc normal small bord_right bord_bot">Millions<br />U. S.<br />Gallons<br />per Acre<br />Daily.</th> -<th class="tdc normal small bord_right bord_bot">Maximum.</th> -<th class="tdc normal small bord_right bord_bot">Minimum.</th> -<th class="tdc normal small bord_bot">Average.</th> -</tr> -<tr> - -<td class="tdl bord_right vertt">Chelsea</td> -<td class="tdc vertb bord_right">12.0</td> -<td class="tdc vertb bord_right">4.0</td> -<td class="tdc vertb bord_right">1.75</td> -<td class="tdc vertb bord_right">2.19</td> -<td class="tdc vertb bord_right">99.92</td> -<td class="tdc vertb bord_right">99.62</td> -<td class="tdc vertb">99.86</td> -</tr> -<tr> - -<td class="tdl bord_right vertt">West Middlesex</td> -<td class="tdc vertb bord_right">5.6</td> -<td class="tdc vertb bord_right">2.75</td> -<td class="tdc vertb bord_right">1.25</td> -<td class="tdc vertb bord_right">1.56</td> -<td class="tdc vertb bord_right">99.94</td> -<td class="tdc vertb bord_right">91.48</td> -<td class="tdc vertb">99.79</td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Southwark & Vauxhall</td> -<td class="tdc vertb bord_right">4.1</td> -<td class="tdc vertb bord_right">2.5</td> -<td class="tdc vertb bord_right">1.5</td> -<td class="tdc vertb bord_right">1.88</td> -<td class="tdc vertb bord_right">100.00</td> -<td class="tdc vertb bord_right">84.33</td> -<td class="tdc vertb">97.77</td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Grand Junction</td> -<td class="tdc vertb bord_right">3.3</td> -<td class="tdc vertb bord_right">2.25</td> -<td class="tdc vertb bord_right">1.63</td> -<td class="tdc vertb bord_right">2.05</td> -<td class="tdc vertb bord_right">99.98</td> -<td class="tdc vertb bord_right">84.03</td> -<td class="tdc vertb">99.31</td> -</tr> -<tr> - -<td class="tdl bord_right vertt">Lambeth</td> -<td class="tdc vertb bord_right">6.0</td> -<td class="tdc vertb bord_right">2.8</td> -<td class="tdc vertb bord_right">2.08</td> -<td class="tdc vertb bord_right">2.60</td> -<td class="tdc vertb bord_right">99.97</td> -<td class="tdc vertb bord_right">96.45</td> -<td class="tdc vertb">99.81</td> -</tr> -<tr> - -<td class="tdl bord_right vertt">New River</td> -<td class="tdc vertb bord_right">2.2</td> -<td class="tdc vertb bord_right">4.4</td> -<td class="tdc vertb bord_right">1.89</td> -<td class="tdc vertb bord_right">2.37</td> -<td class="tdc vertb bord_right">100.00</td> -<td class="tdc vertb bord_right">77.14</td> -<td class="tdc vertb">99.07</td> -</tr> -<tr> - -<td class="tdl bord_right bord_bot">East London</td> -<td class="tdc vertb bord_right bord_bot">15.0</td> -<td class="tdc vertb bord_right bord_bot">2.0</td> -<td class="tdc vertb bord_right bord_bot">1.33</td> -<td class="tdc vertb bord_right bord_bot">1.67</td> -<td class="tdc vertb bord_right bord_bot">99.93</td> -<td class="tdc vertb bord_right bord_bot">97.03</td> -<td class="tdc vertb bord_bot">99.56</td> -</tr> -</table> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_261">[Pg 261]</span></p> - -<h2 class="nobreak" id="APPENDIX_VI">APPENDIX VI.<br /> -<br /> - -<span class="small">THE BERLIN WATER-WORKS.</span></h2></div> - -<p><span class="smcap">The</span> original works were built by an English company in 1856, and were -sold to the city in 1873 for $7,200,000.</p> - -<p>The water was taken from the river Spree at the Stralau Gate, which -was then above, but is now surrounded by, the growing city. The water -was always filtered, and the original filters remained in use until -1893, when they were supplanted by the new works at Lake Müggel. Soon -after acquiring the works the city introduced water from wells by Lake -Tegel as a supplementary supply, but much trouble was experienced from -crenothrix, an organism growing in ground-waters containing iron, and -in 1883 this supply was replaced by filtered water from Lake Tegel. -With rapidly-increasing pollution of the Spree at Stralau the purity -of this source was questioned, and in 1893 it was abandoned (although -still held as a reserve in case of urgent necessity), the supply now -being taken from the river ten miles higher up, at Müggel.</p> - -<p>The watershed of the Spree above Stralau, as I found by map -measurement, is about 3800 square miles; the average rainfall is about -25 inches yearly. At extreme low water the river discharges 457 cubic -feet per second, or 295 million gallons daily, and when in flood 5700 -cubic feet per second may be discharged. The city is allowed by law to -take 46 million gallons daily for water-supply, and this quantity can -be drawn either at Stralau or at Müggel.</p> - -<p>Above Stralau the river is polluted by numerous manufactories and -washing establishments, and by the effluent from a considerable part -of the city’s extensive sewage farms. The shipping on this part of the -river also is heavy, and sewage from the boats is discharged<span class="pagenum" id="Page_262">[Pg 262]</span> directly -into the river. The average number of bacteria in the Spree at this -point is something over ten thousand per cubic centimeter, and 99.6 per -cent of them were removed by the filters in 1893.</p> - -<p>The watershed of the Spree above the new water-works at Müggel I found -by map measurement to be 2800 square miles, and the low water-discharge -is said to be 269 million gallons daily. The river at this point flows -through Lake Müggel, which forms a natural sedimentation-basin, and the -raw water is quite clear except in windy weather.</p> - -<p>There were 16 towns on the watershed with populations above 2000 each -in 1890, and an aggregate population of 132,000, which does not include -the population of the smaller places or country districts. None of -these places purify their sewage so far as they have any. Fürstenwalde -with a population of 12,935, and 22 miles above Müggel, has surface -sewers discharging directly into the river. Above Fürstenwalde the -river runs through numerous lakes which probably remove the effect -of the pollution from the more distant cities. There is considerable -shipping on the river for some miles above Fürstenwalde (which forms a -section of the Friedrich Wilhelm Canal), but hardly any between Müggel -and Fürstenwalde. The raw water at Müggel contains two or three hundred -bacteria per cubic centimeter, and is thus a comparatively pure water -before filtration. It is slightly peaty and the filtered water has a -light straw color.</p> - -<p>Lake Tegel, which supplies the other part of the city’s supply, is an -enlargement of the river Havel. The watershed above Tegel I find to be -about 1350 square miles, and the annual rainfall is about 22 inches. -The low water-discharge is said to be 182 million gallons daily, and -the city is allowed by law to take 23 million gallons for water-supply.</p> - -<p>There were ten towns upon the watershed with populations above 2000 -each in 1890, and with an aggregate population of 44,000. Of these -Tegel is directly upon the lake with a population of 3000,<span class="pagenum" id="Page_263">[Pg 263]</span> and -Oranienburg, 14 miles above, has a population of 6000 and is rapidly -increasing. The shipping on the lake and river is heavy. The lake water -ordinarily contains two or three hundred bacteria per cubic centimeter. -The lake is shallow and becomes turbid in windy weather.</p> - -<p>There are 21 filter-beds at Tegel with a combined area of 12.40 acres -to furnish a maximum of 23 million gallons of water daily, and 22 -filters at Müggel with a combined area of 12.7 acres to deliver the -same quantity. Twenty-two more filters will be built at Müggel within -a few years to purify the full quantity which can be taken from the -river. All of these filters are covered with brick arches supported by -pillars about 16 feet apart from centre to centre in each direction, -and the whole is covered by nearly 3 feet of earth, making them quite -frost-proof. The original filters at Stralau were open, but much -difficulty was experienced with them in winter.</p> - -<p>The bottom of the filters at Tegel consists of 8 inches of concrete -above 20 inches of packed clay and with 2 inches of cement above, and -slopes slightly from each side to the centre. The central drain goes -the whole length of the filters and has a uniform cross-section of -about <sup>1</sup>⁄<sub>7300</sub> of the area of the whole bed. There are no lateral drains, -but the water is brought to the central drain by a twelve-inch layer -of stones as large as a man’s fist; above this there is another foot -of gravel of graded sizes supporting two feet of fine sand, which is -reduced by scraping to half its thickness before the sand is replaced. -The average depth of water above the sand is nearly 5 feet. The filters -are not allowed to filter at a rate above 2.57 million gallons per -acre daily, and at this rate with 70 per cent of the area in service -the whole legal quantity of water can be filtered. The filters work -at precisely the same rate day and night, and the filtered water -is continuously pumped as filtered to ample storage reservoirs at -Charlottenburg. The pumps which lift the water from the lake to the -filters work against a head of 14 feet. The apparatus for regulating -the rate of filtration was described on page 51.</p> - -<p>As yet no full description of the Müggel works has been published,<span class="pagenum" id="Page_264">[Pg 264]</span> but -they resemble closely the Tegel works. Both were designed by or under -the direction of the late director of the water-works, Mr. Henry Gill.</p> - -<p>The average daily quantity of water supplied for the fiscal year ending -March 31, 1893, was 29,000,000 gallons daily, which estimate allows -10 percent for the slip of the pumps. Of this quantity 9,650,000 was -furnished by Stralau and 19,350,000 by Tegel. The greatest consumption -in a single day was 43,300,000 gallons, or 26.6 gallons per head, -while the average quantity for the year was 18.4 gallons per head. All -water without exception is sold by meter, the prices ranging from 27.2 -cents a thousand gallons for small consumers to 13.6 cents for large -consumers and manufacturers. The average receipts for all water pumped, -including that used for public purposes and not paid for, were 15.4 -cents a thousand gallons, against the cost of production, 9.8 cents, -which covers operating expenses, interest on capital, and provision for -sinking fund. This leaves a handsome net profit to the city. On account -of the comparatively high price of the city water and the ease with -which well-water is obtained, the latter is almost exclusively used -for running engines, manufacturing purposes, etc., and this in part -explains the very low per-capita consumption.</p> - -<p>The volume of sewage, however, for the same year, including rain-water, -except during heavy showers, was only 29 gallons per head, showing even -with the private water-supplies an extraordinarily low consumption.</p> - -<p>The friction of the water in the 4.75 miles of 3-foot pipe between -Tegel and the reservoir at Charlottenburg presents an interesting -point. When well-water with crenothrix was pumped, the friction rose -to 34.5 feet, when the velocity was 2.46 feet per second. According to -Herr Anklamm, who had charge of the works at the time, the friction was -reduced to 19.7 feet when filtered water was used and after the pipe -had been flushed, and this has not increased with continued use. He -calculated the friction for the velocity according to Darcy 15.0 feet, -Lampe 17.8 feet, Weisbach 18.7 feet, and Prony 21.5 feet.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_265">[Pg 265]</span></p> - -<h2 class="nobreak" id="APPENDIX_VII">APPENDIX VII.<br /> -<br /> - -<span class="small">ALTONA WATER-WORKS.</span></h2></div> - -<p><span class="smcap">The</span> Altona water-works are specially interesting as an example of -a water drawn from a source polluted to a most unusual extent: the -sewage from cities with a population of 770,000, including its own, is -discharged into the river Elbe within ten miles above the intake and -upon the same side.</p> - -<p>The area of the watershed of the Elbe above Altona is about 52,000 -square miles, and the average rainfall is estimated to be about -28 inches, varying from 24 or less near its mouth to much higher -quantities in the mountains far to the south. On this watershed there -are 46 cities, which in 1890 had populations of over 20,000 each, -and in addition there is a permanent population upon the river-boats -estimated at 20,000, making in all 5,894,000 inhabitants, without -including either country districts or the numberless cities with less -than 20,000 inhabitants each. The sewage from about 1,700,000 of these -people is purified before being discharged; and assuming that as many -people living in cities smaller than 20,000 are connected with sewers -as live in larger places without being so connected, the sewage of -over four million people is discharged untreated into the Elbe and its -tributaries.</p> - -<p class="padb1">The more important of these sources of pollution are the following:</p> - -<table class="autotable" summary="elbe pollution"> -<tr> - -<th class="tdc normal small">City</th> -<th class="tdc normal small">Population<br />in 1890.</th> -<th class="tdc normal small">On what<br />River.</th> -<th class="tdc normal small">Approximate<br /> Distance, Miles.</th> -</tr> -<tr> - -<td class="tdl">Shipping</td> -<td class="tdr vertb">20,000</td> -<td class="tdc">——</td> -<td class="tdc">——</td> -</tr> -<tr> - -<td class="tdl">Altona</td> -<td class="tdr vertb">143,353</td> -<td class="tdl">Elbe</td> -<td class="tdc"> 6</td> -</tr> -<tr> - -<td class="tdl">Hamburg</td> -<td class="tdr vertb">570,534</td> -<td class="tdl">Elbe</td> -<td class="tdc"> 7</td> -</tr> -<tr> - -<td class="tdl">Wandsbeck</td> -<td class="tdr vertb">20,586</td> -<td class="tdl">Elbe</td> -<td class="tdc"> 8</td> -</tr> -<tr> - -<td class="tdl">Harburg</td> -<td class="tdr vertb">35,101</td> -<td class="tdl">Elbe</td> -<td class="tdc"> 11</td> -</tr> -<tr> - -<td class="tdl">Magdeburg</td> -<td class="tdr vertb">202,325</td> -<td class="tdl">Elbe</td> -<td class="tdc">185</td> -</tr> -<tr> - -<td class="tdl">Dresden</td> -<td class="tdr vertb">276,085</td> -<td class="tdl">Elbe</td> -<td class="tdc">354</td> -</tr> -<tr> - -<td class="tdl">Berlin and suburbs</td> -<td class="tdr vertb">1,787,859</td> -<td class="tdl">Havel</td> -<td class="tdc">243</td> -</tr> -<tr> - -<td class="tdl">Halle</td> -<td class="tdr vertb">101,401</td> -<td class="tdl">Saale</td> -<td class="tdc">272</td> -</tr> -<tr> - -<td class="tdl">Leipzig</td> -<td class="tdr vertb">355,485</td> -<td class="tdl">Elster</td> -<td class="tdc">305</td> -</tr> -<tr> - -<td class="tdl">Chemnitz</td> -<td class="tdr vertb">138,955</td> -<td class="tdl">Mulde</td> -<td class="tdc">340</td> -</tr> -<tr> - -<td class="tdl">Prague</td> -<td class="tdr vertb">310,483</td> -<td class="tdl">Moldau</td> -<td class="tdc">500</td> -</tr> -</table> - -<p class="padt1">The sewage of Berlin and of most of its suburbs is treated before being -discharged, and in addition the Havel flows through a series of lakes -below the city, allowing better opportunities for natural purification -than in the case of any of the other cities. Halle treats less than a -tenth of its sewage. Magdeburg will treat its sewage in the course of -a few years. Leipzig, Chemnitz, and other places are thinking more or -less seriously of purification.</p> - -<p>The number of bacteria in the raw water at Altona fluctuates with the -tide and is extremely variable; numbers of 50,000 and 100,000 are not -infrequent, but 10,000 to 40,000 is perhaps about the usual range.</p> - -<p>The works were originally built by an English company in 1860, and have -since been greatly extended. They were bought by the city some years -ago. The water is pumped directly from the river to a settling-basin -upon a hill 280 feet above the river. From this it flows by gravity -through the filters to the slightly lower pure-water reservoir and -to the city without further pumping. The filters are open, with -nearly vertical masonry walls, as described in Kirkwood’s report. The -cross-section of the main underdrain is <sup>1</sup>⁄<sub>2800</sub> of the area of the beds.</p> - -<p>Considerable trouble has been experienced from frost. With continued -cold weather it is extremely difficult to satisfactorily scrape the -filters, and very irregular rates of filtration may result at such -times. In the last few years, with systematic bacterial investigation, -it has been found that greatly decreased efficiency<span class="pagenum" id="Page_267">[Pg 267]</span> frequently follows -continued cold weather, and the mild epidemics of typhoid fever -from which the city has long suffered have generally occurred after -these times. Thus a light epidemic of typhoid in 1886 came in March, -following a light epidemic in Hamburg. In 1887 a severe epidemic in -February followed a severe epidemic in Hamburg in December and January. -In 1888 a severe epidemic in March followed an epidemic in Hamburg -lasting from November to January. Hamburg’s epidemic of 1889, coming in -warm weather, September and October, was followed by only a very slight -increase in Altona. In 1891 Altona suffered again in February from a -severe epidemic, although very little typhoid had been in Hamburg. A -less severe outbreak also came in February, 1892, and a still slighter -one in February, 1893. In the ten years 1882-1892, of five well-marked -epidemics, three broke out in February and two in March, while two -smaller outbreaks came in December and January. No important outbreak -has ever occurred in summer or in the fall months, when typhoid -is usually most prevalent, thus showing clearly the bad effect of -frost upon open filters (see Appendix II). With steadily increasing -consumption the sedimentation-basin capacity of late years has become -insufficient as well as the filtering area, and it is not unlikely that -with better conditions a much better result could be obtained in winter -even with open filters.<a id="FNanchor_63" href="#Footnote_63" class="fnanchor">[63]</a></p> - -<p>The brilliant achievement of the Altona filters was in the summer of -1892, when they protected the city from the cholera which<span class="pagenum" id="Page_268">[Pg 268]</span> -so ravaged Hamburg, although the raw water at Altona must have -contained a vastly greater quantity of infectious matter than that -which worked such havoc in Hamburg.</p> - -<p>From these records it appears that for about nine months of the year -the Altona filters protect the city from the impurities of the Elbe -water, but that during cold weather, with continued mean temperatures -below the freezing-point, such protection is not completely afforded, -and bad effects have occasionally resulted. Notwithstanding the recent -construction of open filters in Hamburg it appears to me that there -must always be more or less danger from open filters in such a climate. -Hamburg’s danger, however, will be much less than Altona’s on account -of its better intake above the outlets of the sewers of Hamburg and -Altona, which are the most important points of pollution at Altona.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_269">[Pg 269]</span></p> - -<h2 class="nobreak" id="APPENDIX_VIII">APPENDIX VIII.<br /> -<br /> - -<span class="small">HAMBURG WATER-WORKS.</span></h2></div> - -<p><span class="smcap">The</span> source and quality of the water previously supplied has been -sufficiently indicated in Appendix II. It was originally intended to -filter the water, but the construction of filters was postponed from -time to time until the fall of 1890, when the project was seriously -taken up, and work was commenced in the spring of 1891. Three years -were allowed for construction. In 1892, however, the epidemic of -cholera came, killing 8605 residents and doing incalculable damage to -the business interests of the city. The health authorities found that -the principal cause of this epidemic was the polluted water-supply. -To prevent a possible recurrence of cholera in 1893, the work of -construction of the filters was pressed forward much more rapidly than -had been intended. Electric lights were provided to allow the work to -proceed nights as well as days, and as a result the plant was put in -operation May 27, 1893, a full year before the intended time. Owing to -the forced construction the cost was materially increased.</p> - -<p>The new works take the raw water from a point one and a half miles -farther up-stream, where it is believed the tide can never carry the -city’s own sewage, as it did frequently to the old intake. The water -is pumped from the river to settling-basins against heads varying with -tide and the water-level in the basins from 8 to 22 feet. Each of the -four settling-basins has an area of about 10 acres, and, with the water -6.56 feet deep, holds 20,500,000 gallons, or 82,000,000 gallons in -all. The works are intended to supply a maximum of 48,000,000 gallons -daily, but the present average consumption is only about 35,000,000 -gallons (1892), or 59 gallons per<span class="pagenum" id="Page_270">[Pg 270]</span> head for 600,000 population. -This consumption is regarded as excessive, and it is hoped that it -will be reduced materially by the more general use of meters. The -sedimentation-basins are surrounded by earthen embankments with slopes -of 1:3, the inner sides being paved with brick above a clay layer. The -water flows by gravity from these basins to the filters, a distance -of 1<sup>1</sup>⁄<sub>2</sub> miles, through a conduit 8<sup>1</sup>⁄<sub>2</sub> feet in diameter. The flow of -the water out of the basins and from the lower end of the conduit is -regulated by automatic gates connected with floats, shown by Fig. 11, -page 60.</p> - -<p>The filters are 18 in number, and each has an effective area of 1.89, -or 34 acres in all. They are planned to filter at a rate of 1.60 -million gallons per acre daily, which with 16 filters in use gives a -daily quantity of 48,000,000 gallons as the present limit of the works. -The sides of the filters are embankments with 1:2 slopes. Both sides -and bottoms have 20 inches of packed clay, above which are 4 inches of -puddle, supporting a brick pavement laid in cement. The bricks are laid -flat on the bottom, but edge-wise on the sides where they will come in -contact with ice.</p> - -<p>The main effluent-drain has a cross-section for the whole length of -the filter of 4.73 square feet, or <sup>1</sup>⁄<sub>17000</sub> of the area of the filter; -and even at the low rate of filtration proposed, the velocity in the -drain will reach 0.97 foot. The drain has brick sides, 1.80 feet -high, covered with granite slabs. The lateral drains are all of brick -with numerous large openings for admission of water. They are not -ventilated, and I am unable to learn that any bad results follow this -omission.</p> - -<p>The filling of the filters consists of 2 feet of gravel, the top being -of course finer than the bottom layers, above which are 40 inches of -sand, which are to be reduced to 24 inches by scraping before being -refilled. The water over the sand, when the latter is of full depth, -is 43 inches deep, and will be increased to 59 inches with the minimum -sand-thickness. The apparatus for regulating the rate of filtration was -described page 52. The cost of the entire plant, including 34 acres -effective filter-surface, 40 acres of sedimentation-basins,<span class="pagenum" id="Page_271">[Pg 271]</span> over 2 -miles of 8<sup>1</sup>⁄<sub>2</sub>-foot conduit, pumping-machinery, sand-washing apparatus, -laboratory, etc., was about 9,500,000 marks, or $2,280,000. This all -reckoned on the effective filter area is $67,000 per acre, or $3.80 per -head for a population of 600,000.</p> - -<p class="padb1">The death-rate since the introduction of filtered water has been lower -than ever before in the history of the city, but as it is thought that -other conditions may help to this result, no conclusions are as yet -drawn.</p> - -<table class="autotable" summary="deaths in hamburg"> -<tr> -<th class="tdc normal" colspan="4">DEATHS IN HAMBURG FROM ALL CAUSES, AND FROM TYPHOID FEVER, BEFORE AND AFTER THE INTRODUCTION OF FILTERS.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot">Year.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Deaths from<br />all Causes<br />per 1000<br />Living.</th> -<th class="tdc normal small bord_top bord_right bord_bot">Deaths from<br />Typhoid<br />Fever per<br />100,000<br />Living.</th> -<th class="tdc normal small bord_top bord_bot"> </th> -</tr> -<tr> - -<td class="tdl bord_right">1880</td> -<td class="tdc bord_right">24.9</td> -<td class="tdc bord_right">26</td> -<td> </td> -</tr> -<tr> - -<td class="tdl bord_right">1881</td> -<td class="tdc bord_right">24.1</td> -<td class="tdc bord_right">30</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1882</td> -<td class="tdc bord_right">23.7</td> -<td class="tdc bord_right">27</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1883</td> -<td class="tdc bord_right">25.2</td> -<td class="tdc bord_right">25</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1884</td> -<td class="tdc bord_right">25.1</td> -<td class="tdc bord_right">26</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1885</td> -<td class="tdc bord_right">25.3</td> -<td class="tdc bord_right">42</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1886</td> -<td class="tdc bord_right">29.0</td> -<td class="tdc bord_right">71</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1887</td> -<td class="tdc bord_right">26.6</td> -<td class="tdc bord_right">88</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1888</td> -<td class="tdc bord_right">24.5</td> -<td class="tdc bord_right">54</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1889</td> -<td class="tdc bord_right">23.5</td> -<td class="tdc bord_right">43</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1890</td> -<td class="tdc bord_right">22.0</td> -<td class="tdc bord_right">27</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1891</td> -<td class="tdc bord_right">23.4</td> -<td class="tdc bord_right">24</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1892</td> -<td class="tdc bord_right">41.1</td> -<td class="tdc bord_right">34</td> -<td class="tdl">Cholera year.</td> -</tr> -<tr> - -<td class="tdl bord_right vertt">1893</td> -<td class="tdc bord_right vertt">20.2</td> -<td class="tdc bord_right vertt">18</td> -<td class="tdl vertb">Filtered water from May 28.</td> -</tr> -<tr> - -<td class="tdl bord_right">1894</td> -<td class="tdc bord_right">17.9</td> -<td class="tdc bord_right">7</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1895</td> -<td class="tdc bord_right">19.0</td> -<td class="tdc bord_right">11</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1896</td> -<td class="tdc bord_right">17.3</td> -<td class="tdc bord_right">6</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1897</td> -<td class="tdc bord_right">17.0</td> -<td class="tdc bord_right">7</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right">1898</td> -<td class="tdc bord_right">17.5</td> -<td class="tdc bord_right">5</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right"><p class="indent">Average for 5 years, excluding cholera year, before -filtration, 1887 to 1891</p></td> -<td class="tdc bord_right vertb">24.0</td> -<td class="tdc bord_right vertb">47.2</td> -<td> </td></tr> -<tr> - -<td class="tdl bord_right bord_bot"><p class="indent">Average for 5 years with -filtration, 1894 to 1898</p></td> -<td class="tdc bord_right bord_bot vertb">17.7</td> -<td class="tdc bord_right bord_bot vertb">7.2</td> -<td class="tdl bord_bot"> </td></tr> -</table> - -<div class="chapter"> -<p><span class="pagenum" id="Page_272">[Pg 272]</span></p> - -<h2 class="nobreak" id="APPENDIX_IX">APPENDIX IX.<br /> -<br /> - -<span class="small">NOTES ON SOME OTHER EUROPEAN WATER-SUPPLIES.</span></h2></div> - -<p><b>Amsterdam.</b>—The water is derived from open canals in the dunes. -These canals have an aggregate length of about 15 miles, and drain -about 6200 acres. The water, as it enters the canals from the fine -dune-sand, contains iron, but this is oxidized and deposited in the -canals. The water after collection is filtered. It has been suggested -that by using covered drains instead of open canals for collecting the -water, the filtration would be unnecessary; but, on the other hand, -the cost of building and maintaining covered drains in the very fine -sand would be much greater than that of the canals, and it is believed, -also, that the water so collected would contain iron, the removal of -which might prove as expensive as the present filtration. In 1887 -filters were built to take water from the river Vecht, but the city has -refused to allow the English company which owns the water-works to sell -this water for domestic purposes, and it is only used for public and -manufacturing purposes, only a fraction of the available supply being -required. Leyden, the Hague, and some other Dutch cities have supplies -like the dune supply of Amsterdam, and they are invariably filtered.</p> - -<p><b>Antwerp</b> is also supplied by an English company. The raw water -is drawn from a small tidal river, which at times is polluted by the -sewage of Brussels. It is treated by metallic iron in Anderson revolver -purifiers, and is afterward filtered at a rather low average rate. The -hygienic results are closely watched by the city authorities, and are -said to be satisfactory.</p> - -<p><b>Rotterdam.</b>—The raw water is drawn from the Maas, as the<span class="pagenum" id="Page_273">[Pg 273]</span> Dutch -call the main stream of the Rhine after it crosses their border. The -population upon the river and its tributaries in Switzerland, Germany, -Holland, France, and Belgium is very great; but the flow is also great, -and the low water flow is exceptionally large in proportion to the -average flow, on account of the melting snow in summer in Switzerland, -where it has its origin.</p> - -<p>The original filters had wooden under-drains, and there was constant -trouble with crenothrix until the filters were reconstructed without -wood, since which time there has been no farther trouble. The present -filters are large and well managed. There is ample preliminary -sedimentation.</p> - -<p><b>Schiedam.</b>—The filters at Schiedam are comparatively small, -but are of unusual interest on account of the way in which they are -operated. The intake is from the Maas just below Rotterdam. The city -was unable to raise the money to seek a more distant source of supply, -and the engineer, H. P. N. Halbertsma, was unwilling to recommend a -supply from so doubtful a source without more thorough treatment than -simple sand-filtration was then thought to be. The plan adopted is to -filter the supply after preliminary sedimentation through two filters -of 0.265 acre each, and the resulting effluent is then passed through -three other filters of the same size. River sand is used for the first, -and the very fine dune sand for the second filtration. The cost both of -construction and operation was satisfactory to the city, and much below -that of any other available source; and the hygienic results have been -equally satisfactory, notwithstanding the unfavorable position of the -intake.</p> - -<p><b>Magdeburg.</b>—The supply is drawn from the Elbe, and is filtered -through vaulted filters after preliminary sedimentation. The pollution -of the river is considerable, although less than at Altona or even at -Hamburg. The city has been troubled at times by enormous discharges of -salt solution from salt-works farther up, which at extreme low water -have sometimes rendered the whole river brackish and unpleasant to the -taste; but arrangements have<span class="pagenum" id="Page_274">[Pg 274]</span> now been made which, it is hoped, will -prevent the recurrence of this trouble.</p> - -<p><b>Breslau</b> is supplied with filtered water from the river Oder, -which has a watershed of 8200 square miles above the intake, and is -polluted by the sewage from cities with an aggregate population of -about 200,000, some of which are in Galicia, where cholera is often -prevalent. In recent years the city has been free from cholera, and -from more than a very limited number of typhoid-fever cases; but the -pollution is so great as to cause some anxiety, notwithstanding the -favorable record of the filters, and there is talk of the desirability -of securing another supply. Until 1893 there were four filter-beds, -with areas of 1.03 acres each, and not covered. In 1893 a fifth bed was -added. This is covered by vaulting and is divided into four sections, -which are separately operated, so that it is really four beds of 0.25 -acre each. The vaulting is concrete arches, supported by steel I beams -in one direction.</p> - -<p><b>Budapest.</b>—A great variety of temporary water-supplies have at -different times been used by this rapidly growing city. The filters -which for some years have supplied a portion of the supply have not -been altogether satisfactory; but perhaps this was due to lack of -preliminary sedimentation for the extremely turbid Danube water, and -also to inadequate filter-area. The city is rapidly building and -extending works for a supply of ground-water, and in 1894 the filters -were only used as was necessary to supplement this supply, and it was -hoped that enough well-water would be obtained to allow the filters to -be abandoned in the near future. The Danube above the intake receives -the sewage of Vienna and innumerable smaller cities, but the volume of -the river is very great compared to other European streams, so that the -relative pollution is not so great as in many other places.</p> - -<p><b>Zürich.</b>—The raw water is drawn by the city from the Lake of -Zürich near its outlet, and but a few hundred feet from the heart of -the city. Although no public sewers discharge into the<span class="pagenum" id="Page_275">[Pg 275]</span> lake, there -is some pollution from boats and bathers and other sources, and, -judging by the number of bacteria in the raw water, this pollution is -increasing. The raw water is extremely free from sediment, and the -filters only become clogged very slowly. The rate of filtration is -high, habitually reaching 7,000,000 gallons per acre daily; but, with -the clear lake water and long periods between scrapings, the results -are excellent even at this rate. The filters are all covered with -concrete groined arches.</p> - -<p>Filtration was commenced in 1886, and was followed by a sharp decline -in the amount of typhoid fever, which, up to that time, had been rather -increasing; for the six years before the change there were sixty-nine -deaths from this cause annually per 100,000 living, and for the six -years after only ten, or one seventh as many; and this reduction is -attributed by the local authorities to the filtration.<a id="FNanchor_64" href="#Footnote_64" class="fnanchor">[64]</a></p> - -<p><b>St. Petersburg.</b>—The supply is drawn from the Neva River by an -English company, and is filtered through vaulted filters at a very high -rate.</p> - -<p><b>Warsaw.</b>—The supply is drawn from the Weichsel River by the city, -and is filtered through vaulted filters after preliminary sedimentation -at a rate never exceeding 2,570,000 gallons per acre daily.</p> - -<div class="section"> -<h3 class="nobreak" id="THE_USE_OF_UNFILTERED_SURFACE_WATERS">THE USE OF UNFILTERED SURFACE-WATERS.</h3></div> - -<p>The use of surface-water without filtration in Europe is comparatively -limited. In Germany this use is now prohibited by the Imperial Board -of Health. In Great Britain, Glasgow draws its supply unfiltered from -Loch Katrine; and Manchester and some other towns use unfiltered -waters from lakes or impounding reservoirs the watersheds of which are -entirely free from population. The best English practice, however, as -in Germany, requires the filtration of such waters even if they are not -known to receive sewage, and the<span class="pagenum" id="Page_276">[Pg 276]</span> -unpolluted supplies of Liverpool, Bradford, Dublin, and many other -cities are filtered before use.</p> - -<div class="section"> -<h3 class="nobreak" id="THE_USE_OF_GROUND_WATER">THE USE OF GROUND-WATER.<a id="FNanchor_65" href="#Footnote_65" class="fnanchor">[65]</a></h3></div> - -<p>Ground-waters are extensively used in Europe, and apparently in -some localities the geological formations are unusually favorable -to this kind of supply. Paris derives all the water it now uses for -domestic purposes from springs, but has a supplementary supply from -the river for other purposes. Vienna and Munich also obtain their -entire supplies from springs, while Budapest, Cologne, Leipzig, -Dresden, Frankfurt, many of the great French cities, Brussels, a part -of London, and many other English cities derive their supplies from -wells or filter-galleries, and among the smaller cities all over Europe -ground-water supplies are more numerous than other kinds.</p> -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_277">[Pg 277]</span></p> - -<h2 class="nobreak" id="APPENDIX_X">APPENDIX X.<br /> -<br /> - -<span class="small">LITERATURE OF FILTRATION.</span></h2></div> - -<p class="padb1"><span class="smcap">The</span> following is a list of a number of articles on filtration. The -list is not complete, but it is believed that it contains the greater -part of articles upon slow sand-filtration, and that it will prove -serviceable to those who wish to study the subject more in detail.</p> - -<p class="indent6"><span class="smcap">Anklamm.</span> Glasers Annalen, 1886, p. 48.</p> -<p>A description of the Tegel filters at Berlin, with excellent plans.</p> - -<p class="indent6"><span class="smcap">Baker.</span> Engineering News.</p> - -<p>Water purification in America: a series of descriptions of filters, as -follows: Aug. 3, 1893, Lawrence filter and description of apparatus of -screening sand and gravel; Apr. 26, 1894, filter at Nantucket, Mass.; -June 7, 1894, filters at Ilion, N. Y., plans; June 14, 1894, filters -at Hudson, N. Y.; July 12, 1894, filters at Zürich, Switzerland, -plans; Aug. 23, 1894, filters at Mt. Vernon, N. Y., plans.</p> - -<p class="indent6"><span class="smcap">Bertschinger.</span> Journal für Gas- und Wasserversorgung, 1889, p. -1126.</p> - -<p>A record of experiments made at Zürich upon the effect of rate of -filtration, scraping, and the influence of vaulting. Rate and vaulting -were found to be without effect, but poorer results followed scraping. -The numbers of bacteria in the lake-water were too low to allow -conclusive results.</p> - -<p class="indent6">—— Journal für Gas- und Wasserversorgung, 1891, p. 684.</p> - -<p>A farther account of the Zürich results, with full analyses and a -criticism of Fränkel and Piefke’s experiments.</p> - -<p class="indent6"><span class="smcap">Bolton.</span> Pamphlet, 1884.</p> - -<p>Descriptions and statistics of London filters.</p> - -<p class="indent6"><span class="smcap">Böttcher</span> and <span class="smcap">Ohnesorge</span>. Zeitschrift für Bauwesen, -1876, p. 343.</p> - -<p>A description of the Bremen works, with full plans.</p> - -<p class="indent6"><span class="smcap">Burton.</span> Water-supply of Towns. London, 1894.</p> - -<p>Pages 94-115 are upon filtration and mention a novel method of regulating the rate.</p> - -<p class="indent6"><span class="smcap">Codd.</span> Engineering News, Apr. 26, 1894.</p> - -<p>A description of a filter at Nantucket, Mass.</p> - -<p><span class="pagenum" id="Page_278">[Pg 278]</span></p> - -<p class="indent6"><span class="smcap">Cramer.</span> Centralblatt für Bauwesen, 1886, p. 42.</p> - -<p>A description of filters built at Brieg, Germany.</p> - -<p class="indent6"><span class="smcap">Crook.</span> London Water-supply. London, 1883.</p> - -<p class="indent6"><span class="smcap">Delbruck.</span> Allgemeine Bauzeitung, 1853, p. 103.</p> - -<p>A general article on filtration; particularly valuable for notices of -early attempts at filtration and of the use of alum.</p> - -<p>Deutsche Verein von Gas- und Wasserfachmänner.</p> - -<p>Stenographic reports of the proceedings of this society are printed -regularly in the <cite>Journal für Gas- und Wasserversorgung</cite>, and the -discussions of papers are often most interesting.</p> - -<p class="indent6"><span class="smcap">Drown.</span> Journal Association Eng. Societies, 1890, p. 356.</p> - -<p>Filtration of natural waters.</p> - -<p class="indent6"><span class="smcap">Fischer.</span> Vierteljahresschrift für Gesundheitspflege, 1891, p. -82.</p> - -<p>Discussion of papers on water-filtration.</p> - -<p class="indent6"><span class="smcap">Fränkel.</span> Vierteljahresschrift für Gesundheitspflege, 1891, p. -38.</p> - -<p>On filters for city water-works.</p> - -<p class="indent6"><span class="smcap">Fränkel</span> and <span class="smcap">Piefke</span>. Zeitschrift für Hygiene, 1891, p. -38, Leistungen der Sandfiltern.</p> - -<p class="indent6"><span class="smcap">E. Frankland.</span> Report in regard to the London filters for -1893 in the Annual Summary of Births, Deaths, and Causes of Death in -London and Other Great Towns, 1893. Published by authority of the -Registrar-General.</p> - -<p class="indent6"><span class="smcap">P. Frankland.</span> Proc. Royal Society, 1885, p. 379.</p> - -<p>The removal of micro-organisms from water.</p> - -<p>—— Proceedings Inst. Civil Engineers, 1886, lxxxv. p. 197.</p> - -<p>Water-purification; its biological and chemical basis.</p> - -<p>—— Trans. of Sanitary Institute of Great Britain, 1886.</p> - -<p>Filtration of water for town supply.</p> - -<p class="indent6"><span class="smcap">Frühling.</span> Handbuch der Ingenieurwissenschaften, vol. ii.</p> - -<p>Chapter on water-filtration gives general account of filtration, with -details of Königsberg filters built by the author and not elsewhere -published.</p> - -<p> -<span style="margin-left: 1em;"><span class="smcap">Fuller.</span> Report Mass. State Board of Health, 1892, p. 449.</span><br /> -<span style="margin-left: 9.5em;">Report Mass. State Board of Health, 1893, p. 453.</span><br /> -</p> - -<p>Accounts of the Lawrence experiments upon water-filtration for 1892 -and 1893.</p> - -<p>—— American Public Health Association, 1893, p. 152.</p> - -<p>On the removal of pathogenic bacteria from water by sand filtration.</p> - -<p>—— American Public Health Association, 1894, p. 64.</p> - -<p>Sand filtration of water with special reference to results obtained at -Lawrence, Mass.</p> - -<p><span class="pagenum" id="Page_279">[Pg 279]</span></p> - -<p class="indent6"><span class="smcap">Gill.</span> Deutsche Bauzeitung, 1881, p. 567.</p> - -<p>On American rapid filters. The author shows that they are not to be -thought of for Berlin, as they would be more expensive as well as -probably less efficient than the usual procedure.</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1892, p. 596.</p> - -<p>A general account of the extension of the Berlin filters at Müggel. No -drawings.</p> - -<p class="indent6"><span class="smcap">Grahn.</span> Journal für Gas- und Wasserversorgung, 1877, p. 543.</p> - -<p>On the filtration of river-waters.</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1890, p. 511.</p> - -<p>Filters for city water-works.</p> - -<p>—— Vierteljahresschrift für Gesundsheitpflege, 1891, p. 76.</p> - -<p>Discussion of papers presented on filtration.</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1894, p. 185.</p> - -<p>A history of the “Rules for Water-filtration” (Appendix I), with some -discussion of them.</p> - -<p class="indent6"><span class="smcap">Grahn</span> and <span class="smcap">Meyer</span>. Reiseberichte über künstliche -central Sandfiltration. Hamburg, 1876.</p> - -<p>An account of the observations of the authors in numerous cities, -especially in England.</p> - -<p class="indent6"><span class="smcap">Grenzmer.</span> Centralblatt der Bauverwaltung, 1888, p. 148.</p> - -<p>A description of new filters at Amsterdam, with plans.</p> - -<p class="indent6"><span class="smcap">Gruber.</span> Centralblatt für Bakteriologie, 1893, p. 488.</p> - -<p>Salient points in judging of the work of sand-filters.</p> - -<p class="indent6"><span class="smcap">Halbertsma.</span> Journal für Gas- und Wasserversorgung, 1892, p. 43.</p> - -<p>Filter-works in Holland. Gives sand, gravel, and water thickness, with -diagrams.</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1892, p. 686.</p> - -<p>Description of filters built by the author at Leeuwarden, Holland, -with plans.</p> - -<p class="indent6"><span class="smcap">Hart.</span> Proceedings Inst. of Civil Engineers, 1890, c. p. 217.</p> - -<p>Description of filters at Shanghai.</p> - -<p class="indent6"><span class="smcap">Hausen.</span> Journal für Gas- und Wasserversorgung, 1892, p. 332.</p> - -<p>An account of experiments made for one year with three 16-inch filters -at Helsingfors, Finland, with weekly analyses of effluents.</p> - -<p class="indent6"><span class="smcap">Hazen.</span> Report of Mass. State Board of Health, 1891, p. 601.</p> - -<p>Experiments upon the filtration of water.</p> - -<p>—— Report of Mass. State Board of Health, 1892, p. 539.</p> - -<p>Physical properties of sands and gravels with reference to their use -in filtration. (Appendix III.)</p> - -<p class="indent6"><span class="smcap">Hunter.</span> Engineering, 1892, vol. 53, p. 621.</p> - -<p>Description of author’s sand-washing apparatus.</p> - -<p><span class="pagenum" id="Page_280">[Pg 280]</span></p> - -<p class="indent6"><span class="smcap">Kirkwood.</span> Filtration of River-waters. New York, 1869.</p> - -<p>A report upon European filters for the St. Louis Water Board in 1866. -Contains a full account of thirteen filtration-works visited by the -author, and of a number of filter-galleries, with a project for -filters for St. Louis. This project was never executed, but the report -is a wonderful work which appeared a generation before the American -public was able to appreciate it. It was translated into German, and -the German edition was widely circulated and known.</p> - -<p class="indent6"><span class="smcap">Koch.</span> Zeitschrift für Hygiene, 1893.</p> - -<p>Water-filtration and Cholera: a discussion of the Hamburg epidemic of -1892 in reference to the effect of filtration.</p> - -<p class="indent6"><span class="smcap">Kröhnke.</span> Journal für Gas- und Wasserversorgung, 1893, p. 513.</p> - -<p>An account of experiments made at Hamburg, as a result of which the -author recommends the addition of cuprous chloride to the water before -filtration to secure greater bacterial efficiency.</p> - -<p class="indent6"><span class="smcap">Kümmel.</span> Journal für Gas- und Wasserversorgung, 1877, p. 452.</p> - -<p>Operation of the Altona filters, with analyses.</p> - -<p>—— Vierteljahresschrift für Gesundheitspflege, 1881, p. 92.</p> - -<p>The water-works of the city of Altona.</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1887, p. 522.</p> - -<p>An article opposing the use of rapid filters (David’s process).</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1890, p. 531.</p> - -<p>A criticism of Fränkel and Piefke’s results, with some statistics of -German and English filters. (The English results are taken without -credit from Kirkwood.)</p> - -<p>—— Vierteljahresschrift für Gesundheitspflege, 1891, p. 87.</p> - -<p>Discussion of papers on filtration, with some statistics.</p> - -<p>—— Vierteljahresschrift für Gesundheitspflege, 1892, p. 385.</p> - -<p>The epidemic of typhoid-fever in Altona in 1891.</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1893, p. 161.</p> - -<p>Results of experiments upon filtration made at Altona, and bacterial -results of the Altona filters in connection with typhoid death-rates.</p> - -<p>—— Trans. Am. Society of Civil Engineers, 1893, xxx. p. 330.</p> - -<p>Questions of water-filtration.</p> - -<p class="indent6"><span class="smcap">Leslie.</span> Trans. Inst. Civil Engineers, 1883, lxxiv. p. 110.</p> - -<p>A short description of filters at Edinburgh.</p> - -<p class="indent6"><span class="smcap">Lindley.</span> A report for the commissioners of the Paris -Exposition of 1889 upon the purification of river-waters, and published -in French or German in a number of journals, among them <cite>Journal für -Gas- und Wasserversorgung</cite>, 1890, p. 501.</p> - -<p><span class="pagenum" id="Page_281">[Pg 281]</span></p> - -<p>This is a most satisfactory discussion of the conditions which modern -experience has shown to be essential to successful filtration.</p> - -<p class="indent6"><span class="smcap">Mason.</span> Engineering News, Dec. 7, 1893.</p> - -<p>Filters at Stuttgart, Germany, with plans.</p> - -<p class="indent6"><span class="smcap">Meyer</span> and <span class="smcap">Samuelson</span>. Deutsche Bauzeitung, 1881, p. -340.</p> - -<p>Project for filters for Hamburg, with diagrams. Except in detail, this -project is the same as that executed twelve years later.</p> - -<p class="indent6"><span class="smcap">Meyer.</span> Deutsche Bauzeitung, 1892, p. 519.</p> - -<p>Description of the proposed Hamburg filters, with diagrams.</p> - -<p>—— The Water-works of Hamburg.</p> - - -<p>A paper presented to the International Health Congress at Rome, March -1894, and published as a monograph. It contains a full description of -the filters as built, with drawings and views in greater detail than -the preceding paper.</p> - -<p class="indent6"><span class="smcap">Mills.</span> Special Report Mass. State Board of Health on the -Purification of Sewage and Water, 1890, p. 601.</p> - -<p>An account of the Lawrence experiments, 1888-1890.</p> - -<p>—— Report Mass. State Board of Health, 1893, p. 543.</p> - -<p>The Filter of the Water-supply of the City of Lawrence and its Results.</p> - -<p>—— Trans. Am. Society of Civil Engineers, 1893, xxx. p. 350.</p> - -<p>Purification of Sewage and Water by Filtration.</p> - -<p class="indent6"><span class="smcap">Neville.</span> Engineering, 1878, xxvi. p. 324.</p> - -<p>A description of the Dublin filters, with plans.</p> - -<p class="indent6"><span class="smcap">Nichols.</span> Report Mass. State Board of Health, 1878, p. 137.</p> - -<p>The filtration of potable water.</p> - -<p class="indent6"><span class="smcap">Oester.</span> Gesundheits-Ingenieur, 1893, p. 505.</p> - -<p>What is the Rate of Filtration? A purely theoretical discussion.</p> - -<p class="indent6"><span class="smcap">Orange.</span> Trans. Inst. Civil Engineers, 1890, c. p. 268.</p> - -<p>Filters at Hong Kong.</p> - -<p class="indent6"><span class="smcap">Pfeffer.</span> Deutsche Bauzeitung, 1880, p. 399.</p> - -<p>A description of filters at Liegnitz, Germany.</p> - -<p class="indent6"><span class="smcap">Piefke.</span> Results of Natural and Artificial Filtration. Berlin, -1881.</p> - -<p>Pamphlet.</p> - -<p>—— Journal für Gas- und Wasserversorgung, 1887, p. 595. Die Principien -der Reinwassergewinnung vermittelst Filtration.</p> - -<p>A sketch of the theory and practical application of filtration.</p> - -<p>—— Zeitschrift für Hygiene, 1889, p. 128. Aphorismen über -Wasserversorgung.</p> - -<p>A discussion of the theory of filtration, with a number of experiments -on the thickness of sand-layers, etc.</p> - -<p><span class="pagenum" id="Page_282">[Pg 282]</span></p> - -<p class="indent6"><span class="smcap">Piefke.</span> Vierteljahresschrift für Gesundheitspflege, 1891, p. -59.</p> - -<p>On filters for city water-works.</p> - -<p class="indent6"><span class="smcap">Fränkel</span> and <span class="smcap">Piefke</span>. Zeitschrift für Hygiene, 1891, p. -38.</p> - -<p>Leistungen der Sandfiltern. An account of the partial obstruction of -the Stralau filters by ice, and a typhoid epidemic which followed. -Experiments were then made upon the passage of cholera and typhoid -germs through small filters.</p> - -<p class="indent6"><span class="smcap">Piefke.</span> Journal für Gas- und Wasserversorgung, 1891, p. 208. -Neue Ermittelungen über Sandfiltration.</p> - -<p>The above mentioned experiments being objected to on certain -grounds, they were repeated by Piefke alone, confirming the previous -observations on the passage of bacteria through filters, but under -other conditions.</p> - -<p>—— Zeitschrift für Hygiene, 1894, p. 151, Über Betriebsführung von -Sandfiltern.</p> - -<p>A full account of the operation of the Stralau filters in 1893, with -discussion of the efficiency of filtration, etc.</p> - -<p class="indent6"><span class="smcap">Plagge and Proskauer.</span> Zeitschrift für Hygiene, 11. p. 403.</p> - -<p>Examination of water before and after filtration at Berlin, with -theory of filtration.</p> - -<p class="indent6"><span class="smcap">Reincke.</span> Bericht über die Medicinische Statistik des -Hamburgischen Staates für 1892.</p> - -<p>Contains a most valuable discussion of the relations of filtration to -cholera, typhoid fever, and diarrhœa, with numerous tables and charts. -(Abstract in Appendix II.)</p> - -<p class="indent6"><span class="smcap">Reinsch.</span> Centralblatt für Bakteriologie, 1895, p. 881.</p> - -<p>An account of the operation of the Altona filters. High numbers of -bacteria in the effluents have often resulted from the discharge of -sludge from the sedimentation-basins onto the filters, due to the -interference of ice on the action of the floating outlet for the -basins, and this, rather than the direct effect of cold, is believed -to be the direct cause of the low winter efficiency. The author urges -the necessity of a deeper sand-layers in no case less than 18 inches -thick.</p> - -<p class="indent6"><span class="smcap">Renk.</span> Gesundheits-Ingenieur, 1886, p. 54.</p> - -<p>—— Über die Ziele der künstliche Wasserfiltration.</p> - -<p class="indent6"><span class="smcap">Ruhlmann.</span> Wochenblatt für Baukunde, 1887, p. 409.</p> - -<p>A description of filters at Zürich.</p> - -<p class="indent6"><span class="smcap">Salbach.</span> Glaser’s Annalen, 1882.</p> - -<p>Filters at Groningen, Holland, built in 1880. Alum used.</p> - -<p class="indent6"><span class="smcap">Samuelson.</span> Translation of Kirkwood’s “Filtration of -River-waters” into German, with additional notes especially on the -theory of filtration and the sand to be employed. Hamburg, 1876.</p> - -<p><span class="pagenum" id="Page_283">[Pg 283]</span></p> - -<p class="indent6"><span class="smcap">Samuelson.</span> Filtration and constant water-supply. Pamphlet. -Hamburg, 1882.</p> - -<p>—— Journal f. Gas- und Wasserversorgung, 1892, p. 660.</p> - -<p>A discussion of the best materials and arrangement for sand-filters.</p> - -<p class="indent6"><span class="smcap">Schmetzen.</span> Deutsche Bauzeitung, 1878, p. 314.</p> - -<p>Notice and extended criticism of Samuelson’s translation of Kirkwood.</p> - -<p class="indent6"><span class="smcap">Sedden.</span> Jour. Asso. Eng. Soc., 1889, p. 477.</p> - -<p>In regard to the sedimentation of river-waters.</p> - -<p class="indent6"><span class="smcap">Sedgwick.</span> New England Water-works Association, 1892, p. 103.</p> - -<p>European methods of Filtration with Reference to American Needs.</p> - -<p class="indent6"><span class="smcap">Sokal.</span> Wochenschrift der östreichen Ingenieur-Verein, 1890, p. -386.</p> - -<p>A short description of the filters at St. Petersburg, and a comparison -with those at Warsaw.</p> - -<p class="indent6"><span class="smcap">Sturmhöfel.</span> Zeitschrift f. Bauwesen, 1880, p. 34.</p> - -<p>A description of the Magdeburg filters, with plans.</p> - -<p class="indent6"><span class="smcap">Tomlinson.</span> American Water-works Association, 1888.</p> - -<p>A paper on filters at Bombay and elsewhere.</p> - -<p class="indent6"><span class="smcap">Turner.</span> Proc. Inst. Civil Engineers, 1890, c. p. 285.</p> - -<p>Filters at Yokohama.</p> - -<p class="indent6"><span class="smcap">Van der Tak.</span> Tijdschrift van de Maatschapping van Bouwkunde, -1875(?).</p> - -<p>A description (in Dutch) of the Rotterdam water-works, including the -wooden drains which caused the trouble with crenothrix, and which have -since been removed. Diagrams.</p> - -<p class="indent6"><span class="smcap">Van Ijsselsteyn.</span> Tijdschrift van het Koninklijk Instituut van -Ingenieurs, 1892-5, p. 173.</p> - -<p>A description of the new Rotterdam filters, with full drawings.</p> - -<p class="indent6"><span class="smcap">Veitmeyer.</span> Verhandlungen d. polyt. Gesell. zu Berlin, April, -1880.</p> - -<p>Filtration and purification of water.</p> - -<p class="indent6"><span class="smcap">Wolffhügel.</span> Arbeiten aus dem Kaiserliche Gesundheitsamt, 1886, -p. 1.</p> - -<p>Examinations of Berlin water for 1884-5, with remarks showing superior -bacterial efficiency with open filters.</p> - -<p>—— Journal für Gas- u. Wasserversorgung, 1890, p. 516.</p> - -<p>On the bacterial efficiency of the Berlin filters, with diagrams.</p> - -<p class="indent6"><span class="smcap">Zobel.</span> Zeitschrift des Vereins deutsche Ingenieure, 1884, p. -537.</p> - -<p>Description of filters at Stuttgart.</p> -<p><span class="pagenum" id="Page_284">[Pg 284]</span></p> - -<p class="center">OTHER LITERATURE.</p> - -<p>Many scientific and engineering journals publish from time to time -short articles or notices on filtration which are not included in the -above list. Among such journals none gives more attention to filtration -than the <cite>Journal für Gasbeleuchtung und Wasserversorgung</cite>, which -publishes regularly reports upon the operation of many German filters, -and gives short notices of new construction. The first articles upon -filtration in this journal were a series of descriptions of German -water-works in 1870-73, including descriptions of filters at Altona, -Brunswick, Lübeck, etc. Stenographic reports of many scientific -meetings have been published, particularly since 1890, and since 1892 -there has been much discussion in regard to the “Rules for Filtration” -given in Appendix I.</p> - -<p>A Report of a Royal Commission to inquire into the water-supply of the -metropolis, with minutes of evidence, appendices, and maps (London, -1893-4), contains much valuable material in regard to filtration.</p> - -<p>The monthly reports of the water examiner, and other papers published -by the Local Government Board, London, are often of interest.</p> - -<p>The German “Verein von Gas- u. Wasserfachmänner” prints without -publishing a most useful annual summary of German water-works -statistics for distribution to members. Many of the statistics given in -this volume are from this source.</p> - -<p>Description of the filters at Worms was given in the <cite>Deutsche -Bauzeitung</cite>, 1892, p. 508; of the filters at Liverpool in -<cite>Engineering</cite>, 1889, p. 152, and 1892, p. 739. The latter journal -also has given a number of descriptions of filters built in various -parts of the world by English engineers, but, excepting the articles -mentioned in the above list, the descriptions are not given in detail.</p> - -<p><span class="pagenum" id="Page_285">[Pg 285]</span></p> - -<p class="center">MORE RECENT ARTICLES.</p> - -<p>The following are a few of the more important articles which have -appeared since the first edition of this book. In addition many -articles of current interest have appeared in the technical journals, -particularly in the journals mentioned above.</p> - -<p class="indent6"><span class="smcap">Clark.</span> Reports of Mass. State Board of Health, 1894 to 1897, -inclusive.</p> - -<p>Articles on the filtration of water, giving accounts of experiments at -the Lawrence Experiment Station, and records of the operation of the -Lawrence city filter. These experiments are directed principally to -the removal of bacteria from sewage-polluted waters.</p> - -<p>—— Jour. New England Water Works Assoc., XI., p. 277.</p> - -<p>Removal of Iron from Ground Waters. A description of certain -experiments.</p> - -<p class="indent6"><span class="smcap">Fowler.</span> Jour. New England Water Works Assoc., XII., p. 209.</p> - -<p>The Operation of a Slow Sand Filter. A most helpful and thorough -description of the operation of sand filters at Poughkeepsie for a -long period of years.</p> - -<p class="indent6"><span class="smcap">Fuller.</span> Water Purification at Louisville. D. Van Nostrand Co., -1898.</p> - -<p>A report upon a series of most exhaustive experiments carried out at -Louisville, directed principally to the clarification of excessively -muddy waters. Contains a full account of methods of coagulation, and -of experiments with the electrical treatment of water.</p> - -<p>—— Report on Water Filtration at Cincinnati. City document, 1899.</p> - -<p>Account of experiments with sand filters, with and without coagulants, -and with other processes applied to the Ohio River water at Cincinnati.</p> - -<p class="indent6"><span class="smcap">Gill.</span> Filters at Muggel. Proc. Institute of Civil Engineers, -1894-5; vol. 119, p. 236.</p> - -<p>A description of the new vaulted filter plant designed by the author -for Berlin, Germany. Plans and views.</p> - -<p class="indent6"><span class="smcap">Goetze.</span> Journal für Gasbeleuchtung und Wasserversorgung, 1897, -p. 169.</p> - -<p>Selbstthätige Wasseraustrittsregler besonders für Filter. A -description of the automatic regulating device for filters used at -Bremen.</p> - -<p>—— Zeitschrift des Vereines deutscher Ingenieure, XXX.</p> - -<p>Reinigung des Trinkwassers in Bremen durch mehrmalige Sandfiltration. -A description of the method of double filtration used at Bremen, -giving results obtained in full. No drawings.</p> - - -<p><span class="pagenum" id="Page_286">[Pg 286]</span></p> - -<p class="indent6"><span class="smcap">Grahn.</span> Journal für Gasbeleuchtung und Wasserversorgung, 1895.</p> - -<p>Water purification plant at the city of Magdeburg. A description of -the old plant, and the changes which have been made in it to increase -its capacity, and make it conform to the requirements of the German -official instructions regarding filtration. Many illustrations and -plans.</p> - -<p class="indent6"><span class="smcap">Halbertsma.</span> Journal für Gasbeleuchtung und Wasserversorgung, -1896.</p> - -<p>Die Resultate der doppelten Filtration zu Schiedam. A description of -double filtration at Schiedam, with the bacterial results for the two -years, 1894 and 1895, showing an average bacterial efficiency of 99.76 -per cent.</p> - -<p class="indent6"><span class="smcap">Hazen.</span> Report to Filtration Commission, Pittsburgh. City -document, 1899.</p> - -<p>A description of experiments upon the treatment of the Allegheny River -water by sand and mechanical filters.</p> - -<p>—— Ohio State Board of Health Report, 1897, p. 154.</p> - -<p>Report on the Mechanical Filtration of the Public Water Supply -of Lorain. Gives the results of a five-weeks test of the Jewell -mechanical filters at Lorain, treating Lake Erie water.</p> - -<p class="indent6"><span class="smcap">Kemna.</span> The Biology of Sand Filtration. Read before the annual -convention of the British Association of Water Works Engineers. -Abstract in Engineering News, XLI., p. 419.</p> - -<p>Describing organisms which develop in open sand filters, both animal -and vegetable, and their effects upon the process. A quite full -account of the author’s extended experience, and the only paper -treating this subject.</p> - -<p class="indent6"><span class="smcap">Magar.</span> Journal für Gasbeleuchtung und Wasserversorgung, 1897, -p. 4.</p> - -<p>Reinigungsbetrieb der offener Sandfilter des Hamburger Filterwerkes in -Frostzeiten. A new method of cleaning open filters in winter without -the removal of the ice.</p> - -<p class="indent6"><span class="smcap">Panwitz.</span> Arbeiten aus dem Kaiserlichen Gesundheitsamte, XIV., -p. 153.</p> - -<p>Die Filtration von Oberflächenwasser in den deutschen Wasserwerken -während der Jahre 1894 bis 1896.</p> - -<p>A description of the filtration works in Germany, and the results -obtained from them, particularly from the point of view of bacterial -efficiency. Results are graphically shown by a series of charts.</p> - -<p class="indent6"><span class="smcap">Reynard.</span> Le Génie Civil, 1896, XXVIII., p. 321.</p> - -<p>Purification of water with the aid of metallic iron. Describing the -works of the Compagnie Général des Eaux for supplying the suburbs -of Paris with filtered water, the capacity of the works being over -23,000,000 gallons daily.</p> - -<p><span class="pagenum" id="Page_287">[Pg 287]</span></p> - -<p class="indent6"><span class="smcap">Weston.</span> Rhode Island State Board of Health, 1894.</p> - -<p>Report of the Results Obtained with Experimental Filters at the -Pattaconset Pumping Station of the Providence Water Works. Relates -particularly to the bacterial purification obtained with rapid -filtration aided by sulphate of alumina. These were the first -systematic experiments made with mechanical filters.</p> - -<p class="indent6"><span class="smcap">Wheeler.</span> Journal of the New England Water Works Assoc., XI., -p. 301. Covered Sand Filter at Ashland, Wis.</p> - -<p>A description of the covered filters built by the author at Ashland -Wis. for the purification of the bay water. Views and drawings.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_288">[Pg 288]</span></p> - -<h2 class="nobreak" id="APPENDIX_XI">APPENDIX XI.<br /> -<br /> - -<span class="small">THE ALBANY WATER-FILTRATION PLANT.</span><br /> -<br /> -<span class="smallest">(Abridged from Proceedings American Society of Civil Engineers, Nov. -1899.)</span></h2></div> - -<p><span class="smcap">Albany</span>, N. Y., was originally supplied with water by gravity from -certain reservoirs on small streams west and north of the city. In -time, with increasing consumption, the supply obtained from these -sources became inadequate, and an additional supply from the Hudson -River was introduced. The water was obtained from the river through -a tunnel under the Erie Basin, and a pumping-station was erected in -Quackenbush Street to pump it to reservoirs, one of which served also -as the distributing point for one of the gravity supplies. The intake, -which was used first in 1873, drew water from the river opposite the -heart of the city. In recent years, the amount of water drawn from this -source has greatly exceeded that obtained from the gravity sources.</p> - -<p>The Hudson River, at the point of intake, has a drainage area of 8240 -square miles. Of this, 4541 square miles are tributary to the Hudson -above Troy, 3493 are tributary to the Mohawk, and 168 are tributary to -the Hudson below the Mohawk.</p> - -<p>The minimum flow may be estimated at 1657 cubic feet per second, or -1,060,000,000 gallons per 24 hours, or at least fifty times the maximum -consumption.</p> - -<p>The cities and larger towns upon the river above the intake, with -estimated populations and distances, are as follows:</p> - -<p><span class="pagenum" id="Page_289">[Pg 289]</span></p> - -<table class="autotable" summary="important places on the hudson watershed above albany"> -<tr> -<th class="tdc normal" colspan="6">MOST IMPORTANT CITIES, TOWNS, AND VILLAGES ON THE WATERSHED OF THE -HUDSON ABOVE ALBANY.</th> -</tr> -<tr> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Place.</th> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">County.</th> -<th class="tdc normal small bord_top bord_right bord_bot" rowspan="2">Approximate<br />Distance<br />above<br />Intake,<br />Miles.</th> -<th class="tdc normal small bord_top bord_bot" colspan="3">Population in</th> -</tr> -<tr> -<th class="tdc normal small bord_right bord_bot">1880.</th> -<th class="tdc normal small bord_right bord_bot">1890.</th> -<th class="tdc normal small bord_bot">1900.<br />(Estimated.)</th> -</tr> -<tr> -<td class="tdl bord_right">Troy</td> -<td class="tdl bord_right">Rensselaer</td> -<td class="tdc bord_right"> 4</td> -<td class="tdc bord_right"> 56,747</td> -<td class="tdc bord_right"> 60,956</td> -<td class="tdc"> 65,470</td> -</tr> -<tr> -<td class="tdl bord_right">Watervliet</td> -<td class="tdl bord_right">Albany</td> -<td class="tdc bord_right"> 4</td> -<td class="tdc bord_right"> 8,820</td> -<td class="tdc bord_right"> 12,967</td> -<td class="tdc"> 19,040</td> -</tr> -<tr> -<td class="tdl bord_right">Green Island</td> -<td class="tdl bord_right">Rensselaer</td> -<td class="tdc bord_right"> 5</td> -<td class="tdc bord_right"> 4,160</td> -<td class="tdc bord_right"> 4,463</td> -<td class="tdc"> 4,788</td> -</tr> -<tr> -<td class="tdl bord_right">Cohoes</td> -<td class="tdl bord_right">Albany</td> -<td class="tdc bord_right"> 8</td> -<td class="tdc bord_right"> 19,416</td> -<td class="tdc bord_right"> 22,509</td> -<td class="tdc"> 26,450</td> -</tr> -<tr> -<td class="tdl bord_right">Lansingburg</td> -<td class="tdl bord_right">Rensselaer</td> -<td class="tdc bord_right"> 8</td> -<td class="tdc bord_right"> 7,432</td> -<td class="tdc bord_right"> 10,550</td> -<td class="tdc"> 14,980</td> -</tr> -<tr> -<td class="tdl bord_right">Waterford</td> -<td class="tdl bord_right">Saratoga</td> -<td class="tdc bord_right"> 9</td> -<td class="tdc bord_right"> (1,822)</td> -<td class="tdc bord_right"> 1,822</td> -<td class="tdc"> (1,822)</td> -</tr> -<tr> -<td class="tdl bord_right">Schenectady</td> -<td class="tdl bord_right">Schenectady</td> -<td class="tdc bord_right"> 28</td> -<td class="tdc bord_right"> 13,655</td> -<td class="tdc bord_right"> 19,002</td> -<td class="tdc"> 26,450</td> -</tr> -<tr> -<td class="tdl bord_right">Hoosic Falls</td> -<td class="tdl bord_right">Rensselaer</td> -<td class="tdc bord_right"> 44</td> -<td class="tdc bord_right"> 4,530</td> -<td class="tdc bord_right"> 7,014</td> -<td class="tdc"> 10,860</td> -</tr> -<tr> -<td class="tdl bord_right">Amsterdam</td> -<td class="tdl bord_right">Montgomery</td> -<td class="tdc bord_right"> 44</td> -<td class="tdc bord_right"> 9,466</td> -<td class="tdc bord_right"> 17,336</td> -<td class="tdc"> 31,730</td> -</tr> -<tr> -<td class="tdl bord_right">Glens Falls</td> -<td class="tdl bord_right">Warren</td> -<td class="tdc bord_right"> 49</td> -<td class="tdc bord_right"> 4,900</td> -<td class="tdc bord_right"> 9,509</td> -<td class="tdc"> 18,450</td> -</tr> -<tr> -<td class="tdl bord_right">Saratoga Springs</td> -<td class="tdl bord_right">Saratoga</td> -<td class="tdc bord_right"> 51</td> -<td class="tdc bord_right"> 8,421</td> -<td class="tdc bord_right"> 11,975</td> -<td class="tdc"> 17,010</td> -</tr> -<tr> -<td class="tdl bord_right">Johnstown</td> -<td class="tdl bord_right">Fulton</td> -<td class="tdc bord_right"> 56</td> -<td class="tdc bord_right"> 5,013</td> -<td class="tdc bord_right"> 7,768</td> -<td class="tdc"> 12,040</td> -</tr> -<tr> -<td class="tdl bord_right">Gloversville</td> -<td class="tdl bord_right">Fulton</td> -<td class="tdc bord_right"> 58</td> -<td class="tdc bord_right"> 7,133</td> -<td class="tdc bord_right"> 13,864</td> -<td class="tdc"> 26,930</td> -</tr> -<tr> -<td class="tdl bord_right">North Adams, Mass.</td> -<td class="tdl bord_right">Berkshire</td> -<td class="tdc bord_right">68</td> -<td class="tdc bord_right"> 10,191</td> -<td class="tdc bord_right"> 16,074</td> -<td class="tdc"> 25,340</td> -</tr> -<tr> -<td class="tdl bord_right">Adams, Mass.</td> -<td class="tdl bord_right">Berkshire</td> -<td class="tdc bord_right"> 75</td> -<td class="tdc bord_right"> 5,591</td> -<td class="tdc bord_right"> 9,213</td> -<td class="tdc"> 15,181</td> -</tr> -<tr> -<td class="tdl bord_right">Little Falls</td> -<td class="tdl bord_right">Herkimer</td> -<td class="tdc bord_right"> 82</td> -<td class="tdc bord_right"> 6,910</td> -<td class="tdc bord_right"> 8,783</td> -<td class="tdc"> 11,160</td> -</tr> -<tr> -<td class="tdl bord_right">Utica</td> -<td class="tdl bord_right">Oneida</td> -<td class="tdc bord_right">107</td> -<td class="tdc bord_right"> 33,914</td> -<td class="tdc bord_right"> 44,007</td> -<td class="tdc"> 57,090</td> -</tr> -<tr> -<td class="tdl bord_right">Rome</td> -<td class="tdl bord_right">Oneida</td> -<td class="tdc bord_right">127</td> -<td class="tdc bord_right"> 12,194</td> -<td class="tdc bord_right"> 14,991</td> -<td class="tdc"> 18,430</td> -</tr> -<tr> -<td class="tdl bord_right bord_bot">32 villages</td> -<td class="tdl bord_right bord_bot"> </td> -<td class="tdl bord_right bord_bot"> </td> -<td class="tdc bord_right bord_bot"> 52,523</td> -<td class="tdc bord_right bord_bot"> 61,869</td> -<td class="tdc bord_bot"> 76,194</td> -</tr> -<tr> -<td class="tdl bord_right" colspan="3"><span class="add2em">Total, not including rural population</span></td> -<td class="tdc bord_right">272,838</td> -<td class="tdc bord_right">354,672</td> -<td class="tdc">479,415</td> -</tr> -<tr> -<td class="tdl bord_right bord_bot" colspan="3"><span class="add2em">Per square mile</span></td> -<td class="tdc bord_bot bord_right"> 33</td> -<td class="tdc bord_bot bord_right"> 43</td> -<td class="tdc bord_bot"> 59</td> -</tr> -</table> - -<p class="padt1">Without entering into a detailed discussion, it may be said that the -amount of sewage, with reference to the size of the river and the -volume of flow, is a fraction less than that at Lawrence, Mass., -where a filter-plant has also been constructed, but the pollution is -much greater than that of most American rivers from which municipal -water-supplies are taken.</p> - -<p>The filtration-plant completed in 1899 takes the water from a point -about two miles above the old intake. Pumps lift the water to the -sedimentation-basin, from which it flows to the filters and thence -through a conduit to the pumping-station previously used.</p> - -<div class="section"> -<h3 class="nobreak" id="DESCRIPTION_OF_PLANT">DESCRIPTION OF PLANT.</h3></div> - -<p><b>Intake.</b>—The intake consists of a simple concrete structure in -the form of a box, having an open top covered with rails 6 inches -apart, and connected below, through a 36-inch pipe, with<span class="pagenum" id="Page_291">[Pg 291]</span> a well -in the pumping-station. Before going to the pumps the water passes -through a screen with bars 2 inches apart, so arranged as to be raked -readily. The rails over the intake and this screen are intended to -stop matters which might obstruct the passageways of the pumps, but no -attempt is made to stop fish, leaves, or other floating matters which -may be in the water. The arrangement, in this respect, is like that of -the filter at Lawrence, Mass., where the raw water is not subjected to -close screening. There is room, however, to place finer screens in the -pump-well, should they be found desirable.</p> - -<div class="figcenter padt1 padb1 illowp48" id="image290" style="max-width: 80.9375em;"> - <img class="w100" src="images/image290.jpg" alt="" /> - <p class="caption"><span class="sans large">HUDSON RIVER</span><br /> - -<span class="sans">NEAR INTAKE</span><br /> - -<span class="smcap">Fig. 1.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing290_1" style="max-width: 97.9375em;"> - <img class="w100" src="images/facing290_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Sedimentation-basin, Pumping-station, and -Outlets.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing290_2" style="max-width: 98.0625em;"> - <img class="w100" src="images/facing290_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Sedimentation-basin, an Outlet, and Laboratory.</span></p> - -<p class="right"> -[<em>To face page 290.</em>]</p></div> - -<p><b>Pumping-station.</b>—The centrifugal pumps have a guaranteed -capacity of 16,000,000 gallons per 24 hours against a lift of 18 feet, -or 12,000,000 gallons per 24 hours against a lift of 24 feet. The -ordinary pumping at low water is against the higher lift, and under -these conditions either pump can supply the ordinary consumption, the -other pump being held in reserve.</p> - -<p>The pumping-station building, to a point above the highest flood-level, -is of massive concrete construction, without openings. Nearly all -the machinery is necessarily below this level, and in high water -the sluice-gates are closed, and the machinery is thus protected -from flooding. The superstructure is of pressed brick, with granite -trimmings.</p> - -<p><b>Meter for Raw Water.</b>—Upon leaving the pumping-station the water -passes through a 36-inch Venturi meter having a throat diameter of 17 -inches, the throat area being two ninths of the area of the pipe. The -meter records the quantity of water pumped, and is also arranged to -show on gauges in the pumping-station the rate of pumping.</p> - -<p><b>Aeration.</b>—After leaving the meter, the water passes to the -sedimentation-basin through eleven outlets. These outlets consist of -12-inch pipes on end, the tops of which are 4 feet above the nominal -flow-line of the sedimentation-basin. Each of these outlet-pipes is -pierced with 296 <sup>3</sup>⁄<sub>8</sub>-inch holes extending from 0.5 to 3.5 feet below -the top of the pipe. These holes are computed<span class="pagenum" id="Page_293">[Pg 293]</span> so that when 11,000,000 -gallons of water per day are pumped all the water will pass through the -holes, the water in the pipes standing flush with the tops. The water -is thus thrown out in 3256 small streams, and becomes aerated. When -more than the above amount is pumped, the excess flows over the tops of -the outlet-pipes in thin sheets, which are broken by the jets.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image292" style="max-width: 125em;"> - <img class="w100" src="images/image292.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 2.</span></p></div> - -<p>Regarding the necessity for aeration, no observations have been taken -upon the Hudson River, but, judging from experience with the Merrimac -at Lawrence, where the conditions are in many respects similar, the -water is at all times more or less aerated, and, for the greater -part of the year, it is nearly saturated with oxygen, and aeration -is not necessary. During low water in summer, however, there is much -less oxygen in the water, and at these times aeration is a distinct -advantage. Further, the river-water will often have a slight odor, and -aeration will tend to remove it. The outlets are arranged so that they -can be removed readily in winter if they are not found necessary at -that season.</p> - -<p><b>Sedimentation-basin.</b>—The sedimentation-basin has an area of -5 acres and is 9 feet deep. To the overflow it has a capacity of -14,600,000 gallons, and to the flow-line of the filters 8,900,000 -gallons. There is thus a reserve capacity of 5,700,000 gallons between -these limits, and this amount can be drawn upon, without inconvenience, -for maintaining the filters in service while the pumps are shut down. -This allows a freedom in the operation of the pumps which would not -exist with the water supplied direct to the filters.</p> - -<p>The water enters the sedimentation-basin from eleven inlets along -one side, and is withdrawn from eleven outlets directly opposite. -The inlets and aerating devices described previously bring the water -into the basin without current and evenly distributed along one -side. Both inlets and outlets are controlled by gates, so that any -irregularities in distribution can be avoided. The concrete floor of -the sedimentation-basin is built with even slopes from the toe of each -embankment to a sump, the heights of<span class="pagenum" id="Page_295">[Pg 295]</span> these slopes being 1 foot, -whatever their lengths. The sump is connected with a 24-inch pipe -leading to a large manhole in which there is a gate through which water -can be drawn to empty the basin. There is an overflow from the basin -to this manhole which makes it impossible to fill the basin above the -intended level.</p> - - <div class="figcenter padt1 padb1 illowp100" id="image294" style="max-width: 125em;"> - <img class="w100" src="images/image294.jpg" alt="" /> - <p class="caption"><span class="sans">LONGITUDINAL SECTION ON</span> <em>a-b-c-d-e-f-g-h</em><br /> - -<span class="sans large">FILTER BEDS</span><br /> - -<span class="sans small">PLAN AND SECTION OF FILTER NO. 2</span><br /> - -<span class="smcap large">Fig. 3.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing294_1" style="max-width: 98.875em;"> - <img class="w100" src="images/facing294_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Outside Wall, ready for Concrete Backing.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing294_2" style="max-width: 99.125em;"> - <img class="w100" src="images/facing294_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Sedimentation-basin: showing Construction of Floor.</span></p> - -<p class="right">[<em>To face page 294.</em>]</p></div> - -<p><b>Filters.</b>—The filters are of masonry, and are covered to protect -them against the winters, which are quite severe in Albany. The piers, -cross-walls, and linings of the outside walls, entrances, etc., are of -vitrified brick. All other masonry is concrete. The average depth of -excavation for the filters was 4 feet, and the material at the bottom -was usually blue or yellow clay. In some places shale was encountered. -In one place soft clay was found, and there the foundations were made -deeper. The floors consisted of inverted, groined, concrete arches, -arranged to distribute the weight of the walls and vaulting over the -whole area of the bottom.</p> - -<p>The groined arch-vaulting is of concrete with a clear span of 11 feet -11 inches, a rise of 2<sup>1</sup>⁄<sub>2</sub> feet, and a thickness of 6 inches at the -crown. It was put in in squares, the joints being on the crowns of the -arches parallel with the lines of the piers, and each pier being the -centre of one square. The manholes are in alternate sections, and are -of concrete, built in steel forms with castings at the tops, securely -jointed to the concrete.</p> - -<p>Above the vaulting there are 2 feet of earth and soil, grassed on -top. The tops of the manholes are 6 inches above the soil to prevent -rain-water from entering them. The drainage of the soil is effected -by a depression of the vaulting over each pier, partially filled with -gravel and sand, from which water is removed by a 2-inch tile-drain -going down the centre of the pier and discharging through its side just -above the top of the sand in the filter.</p> - -<p>In order to provide ready access to each filter, a part of the vaulting -near one side is elevated and made cylindrical in shape, making an -inclined runway from the sand-level to a door the threshold of which is -6 inches above the level of the overflow.</p> - -<p><span class="pagenum" id="Page_296">[Pg 296]</span></p> - -<div class="figcenter padt1 padb1 illowp100" id="image296" style="max-width: 100em;"> - <img class="w100" src="images/image296.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 4.</span></p></div> - -<p><span class="pagenum" id="Page_297">[Pg 297]</span></p> - -<p>This sand-run is provided with permanent timber runways and with secure -doors.</p> - -<div class="figcenter padt1 padb1 illowp93" id="image297" style="max-width: 86.5em;"> - <img class="w100" src="images/image297.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 5.—Entrance to a Filter.</span></p></div> - -<p>The manholes of the filters are provided with double covers of steel -plates to exclude the cold. The covers also exclude light. When -cleaning the filters, light can be admitted by removing the covers. -Supports for electric lights are placed in the vaulting, so that the -filters can be lighted by electricity and the work of cleaning can be -done at night, and in winter under heavy snow, without removing the -covers. The electric lights have not yet been installed.</p> - -<p>The regulator-houses, the entrances to the sand-runs, and all exposed -work are of pressed brick with Milford granite trimmings and slate -roofs. The regulator-houses have double walls and double windows and -a tight ceiling in the roof, to make them as warm as possible and to -avoid the necessity of artificial heat to prevent freezing.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image298" style="max-width: 100em;"> - <img class="w100" src="images/image298.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 6.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing298_1" style="max-width: 99.4375em;"> - <img class="w100" src="images/facing298_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Placing the Floor of a Filter.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing298_2" style="max-width: 99.75em;"> - <img class="w100" src="images/facing298_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Building the Brick Piers.</span></p> - -<p class="right">[<em>To face page 298.</em>]</p></div> - -<p>The main underdrains for removing the filtered water are of<span class="pagenum" id="Page_299">[Pg 299]</span> -vitrified pipe surrounded by concrete and are entirely below the floors -of the filters.</p> - -<p>Connections with the main drain are made through thirty-eight 6-inch -outlets in each filter, passing through the floor and connected with -6-inch lateral drains running through the whole width of the filter. -These drains were made with pipes having one side of the bell cut off -so that they would lie flat on the floor and make concentric joints, -without support and without having to be wedged. They were laid with a -space of about 1 inch between the barrels, leaving a large opening for -the admission of water from the gravel.</p> - -<p>The underdrainage system is so designed that, when starting a filter -after cleaning, the friction of the sand is about 50 mm. at a rate of -3,000,000 gallons per acre daily, and the friction of the underdrainage -system is estimated at 10 mm. This very low friction, which is -necessary, is obtained by the use of ample sizes for the underdrains -and low velocities in them. In the outlet and measuring devices -moderate losses of head are not objectionable, and the sizes of the -pipes and connections are, therefore, smaller than the main underdrains.</p> - -<p>The gravel surrounding the underdrains is of three grades. The material -was obtained from the river-bed by dredging, and was of the same stock -as that used for preparing ballast for the concrete. It was separated -and cleaned by a special, cylindrical, revolving screen. The coarsest -grade of gravel was that which would not pass round holes 1 inch in -diameter, and free from stones more than about 2 inches in diameter. At -first it was required to pass a screen with holes 2 inches in diameter, -but this screen removed many stones which it was desired to retain, and -the screen was afterward changed to have holes 3 inches in diameter. -The intermediate grades of gravel passed the 1-inch holes, and were -retained by a screen with round holes 3<sup>3</sup>⁄<sub>8</sub> inch in diameter. The finest -gravel passed the above screens and was retained by a screen with -round holes <sup>3</sup>⁄<sub>16</sub> inch in diameter. The gravel was washed, until free -from sand and dirt, by water played upon it during the<span class="pagenum" id="Page_301">[Pg 301]</span> process of -screening, and it was afterward taken over screens in the chutes, where -it was separated from the dirty water, and, when necessary, further -quantities of water were played upon it at these points.</p> - -<div class="figcenter padt1 padb1 illowp100" id="image300" style="max-width: 112.5em;"> - <img class="w100" src="images/image300.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 7.</span></p></div> - -<p>The average mechanical analyses of the three grades of gravel are shown -by Fig. 8. Their effective sizes were 23, 8, and 3 mm. respectively, -and for convenience they are designated by these numbers. The average -uniformity coefficient for each grade was about 1.8.</p> - -<p>The 23-mm. gravel entirely surrounded the 6-inch pipe-drains, and was -carried slightly above their tops. In some cases it was used to cover -nearly the whole of the floor, but this was not insisted upon.</p> - -<p>The 8-mm. gravel was obtained in larger quantity than the other sizes, -and was used to fill all spaces up to a plane 2<sup>1</sup>⁄<sub>2</sub> inches below the -finished surface of the gravel, this layer being about 2 inches thick -over the tops of the drains, and somewhat thicker elsewhere.</p> - -<p>The 3-mm. gravel was then applied in a layer 2<sup>1</sup>⁄<sub>2</sub> inches deep, and the -surface levelled.</p> - -<p>The preliminary estimates of cost were based upon the use of -filter-sand from a bank near the filter-site. Further examination -showed that this sand contained a considerable quantity of lime, and -it was found by experiment with a small filter constructed for that -purpose that the use of this sand would harden the water by about 2 -parts in 100,000, and the amount of lime contained in the sand, namely, -about 7 per cent, was sufficient to continue this hardening action -for a considerable number of years. This was regarded as a serious -objection to its use, and the specifications were drawn limiting the -amount of lime in the sand. This excluded all of the local bank sands. -The river-sands which were used were nearly free from lime, and in the -end the sand as secured was probably not only free from lime, but more -satisfactory<span class="pagenum" id="Page_302">[Pg 302]</span> in other ways, and also cheaper than the bank-sand would -have been.</p> - -<div class="figcenter padt1 padb1 illowp95" id="image302" style="max-width: 98.375em;"> - <img class="w100" src="images/image302.jpg" alt="" /> - <p class="caption"><em>Diameters in Millimeters</em><br /> - <span class="sans large">MECHANICAL COMPOSITION OF FILTER SAND AND GRAVELS.</span><br /> - <span class="sans small">(ARROWS SHOW REQUIREMENT OF SPECIFICATION)</span><br /> - <span class="smcap">Fig. 8.</span></p></div> - -<p>The specifications of the filter-sand require that “The filter-sand -shall be clean river-, beach-, or bank-sand, with either sharp or -rounded grains. It shall be entirely free from clay, dust, or organic -impurities, and shall, if necessary, be washed to remove such materials -from it. The grains shall, all of them, be of hard material which will -not disintegrate, and shall be of the following diameters: Not more -than 1 per cent, by weight, less than 0.13 mm., nor more than 10 per -cent less than 0.27 mm.; at least 10 per cent, by weight, shall be -less than 0.36 mm., and at least 70 per cent, by weight, shall be less -than 1 mm., and no particles shall be more than 5 mm. in diameter. -The diameters of the sand-grains will be computed as the diameters of -spheres of<span class="pagenum" id="Page_304">[Pg 304]</span> equal volume. The sand shall not contain more than 2 per -cent, by weight, of lime and magnesia taken together and calculated as -carbonates.”</p> - -<div class="figcenter padt1 padb1 illowp100" id="facing302_1" style="max-width: 97.6875em;"> - <img class="w100" src="images/facing302_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Placing the Concrete Vaulting.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing302_2" style="max-width: 99em;"> - <img class="w100" src="images/facing302_2.jpg" alt="" /> - <p class="caption"><span class="smcap">General View of Vaulting, under Construction.</span></p> - -<p class="right"> -[<em>To face page 302.</em></p></div> - -<div class="figcenter padb1 illowp100" id="image303" style="max-width: 125em;"> - <img class="w100" src="images/image303.jpg" alt="" /> - <p class="caption"><span class="smcap">Fig. 9.</span></p></div> - -<p>The sand was obtained from the river at various places by dredging. -It was first taken up by dipper-dredges, and brought in scows to a -point in the back channel a little north of the filter-plant. It was -there dumped in a specially prepared place in the bottom of the river, -from which it was lifted by a hydraulic dredge and pumped through a -15-inch pipe an average distance of 525 feet to points selected, and -varied from time to time, on the flats north of the filters. The water -containing the sand was then put through screens having meshes which -excluded all stones 5 mm. in diameter and over, and was then taken into -basins where the sand was deposited and afterward carted to the filters.</p> - -<p>Two ejector sand-washing machines, shown in Fig. 9, are provided at -convenient places between the filters. In them the dirty sand is mixed -with water, and is thrown up by an ejector, after which it runs through -a chute into a receptacle, from which it is again lifted by another -ejector. It passes in all through five ejectors, part of the dirty -water being wasted each time. The sand is finally collected from the -last ejector, where it is allowed to deposit from the water.</p> - -<p>Water is admitted to each filter through a 20-inch pipe from a pipe -system connecting with the sedimentation-basin. Just inside of the -filter-wall is placed a standard gate, and beyond that a balanced -valve connected with an adjustable float to shut off the water when -it reaches the desired height on the filter. These valves and floats -were constructed from special designs, and are similar in principle to -valves used for the same purpose in the Berlin water-filters.</p> - -<p>Each filter is provided with an overflow, so arranged that it cannot be -closed, which prevents the water-level from exceeding a fixed limit in -case the balanced valve fails to act. An outlet is also provided near -the sand-run, so that unfiltered water can be<span class="pagenum" id="Page_305">[Pg 305]</span> removed quickly from the -surface of the filter, should it be necessary, to facilitate cleaning.</p> - -<p>The outlet of each filter is through a 20-inch gate controlled by a -standard graduated to show the exact distance the gate is open. The -water rises in a chamber and flows through an orifice in a brass plate -4 by 24 inches, the centre of which is 1 foot below the level of the -sand-line. At the nominal rate of filtration, 3,000,000 gallons per -acre daily, 1 foot of head is required to force the water through the -orifice. With other rates the head increases or decreases approximately -as the square of the rate and forms a measure of it. With water -standing in the lower chamber, so that the orifice is submerged, it is -assumed that the same rates will be obtained with a given difference -in level between the water on the two sides of the orifice as from an -equal head above the centre of the orifice when discharging into air.</p> - -<p><b>Measurement of Effluent.</b>—In order to show the rate of filtration -two floats are connected with the water on the two sides of the -orifice. These floats are counterbalanced; one carries a graduated -scale, and the other a marker which moves in front of the scale and -shows the rate of filtration corresponding to the difference in level -of the water on the two sides. When the water in the lower chamber -falls below the centre of the orifice, the water in the float-chamber -is nevertheless maintained at this level. This is accomplished by -making the lower part of the tube water-tight, with openings just at -the desired level, so that when the water falls below this point in the -outer chamber it does not fall in the float-chamber.</p> - -<p>To prevent the loss of water in the float-chamber by evaporation or -from other causes, a lead pipe is brought from the other chamber and -supplies a driblet of water to it constantly; this overflows through -the openings, and maintains the water-level at precisely the desired -point. The floats thus indicate the difference in water-level on the -two sides of the orifice whenever the water in the lower chamber is -above the centre of the orifice; otherwise<span class="pagenum" id="Page_306">[Pg 306]</span> they indicate the height of -water in the upper chamber above the centre of the orifice, regardless -of the water-level in the lower chamber. The scale is graduated to show -the rates of filtration in millions of gallons per acre of filtering -area. In computing this scale the area of the filters is taken as 0.7 -acre, and the coefficient of discharge as 0.61.</p> - -<p>At the ordinary rates of filtration the errors introduced by the -different conditions under which the orifice operates will rarely -amount to as much as 100,000 gallons per acre daily, or one thirtieth -of the ordinary rate of filtration. Usually they are much less than -this. The apparatus thus shows directly, and with substantial accuracy, -the rate of filtration under all conditions.</p> - -<p><b>Measurement of Loss of Head.</b>—Two other floats with similar -connections show the difference in level between the water standing on -the filter and the water in the main drain-pipe back of the gate, or, -in other words, the frictional resistance of the filter, including the -drains. This is commonly called the loss of head, and increases from -0.2 foot or less, with a perfectly clean filter, to 4 feet with the -filter ready for cleaning. When the loss of head exceeds 4 feet the -rate of filtration cannot be maintained at 3,000,000 gallons per acre -daily with the outlet devices provided, and, in order to maintain the -rate, the filter must be cleaned.</p> - -<p><b>Adjustment of Gauges.</b>—The adjustment of the gauges showing the -rate of filtration and loss of head is extremely simple. When a filter -is put in service the gates from the lower chamber to the pure-water -reservoir and to the drain are closed, the outlet of the filter opened, -and both chambers allowed to fill to the level of the water on the -filter. The length of the wire carrying the gauge is then adjusted so -that the gauge will make the desired run without hitting at either end, -and then the marker is adjusted. As both the rate of filtration and -loss of head are zero under these conditions, it is only necessary to -set the markers to read zero on the gauges to adjust them. The gates -can then be opened for regular operation, and the readings on the -gauges will be correct.</p> - -<div class="figcenter padt1 padb1 illowp100" id="facing306_1" style="max-width: 99.375em;"> - <img class="w100" src="images/facing306_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Interior of a Filter: Drain, Gravel and Sand -Layers.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing306_2" style="max-width: 99em;"> - <img class="w100" src="images/facing306_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Interior of a Filter, Ready for Use.</span></p> - -<p class="right">[<em>To face page 306.</em>]</p></div> - -<p><span class="pagenum" id="Page_307">[Pg 307]</span></p> - -<p>It is necessary to use wires which are light, flexible, and which will -not stretch. At first piano-wire, No. 27 B. & S. gauge, was used, and -was well adapted to the purpose, except that it rusted rapidly. Because -of the rusting it was found necessary to substitute another wire, -and cold-drawn copper wire, No. 24 B. & S. gauge, was used with fair -results. Stretching is less serious than it would otherwise be, as the -correctness of the adjustment can be observed and corrected readily -every time a filter is out of service.</p> - -<p>From the lower chambers in the regulator-houses the water flows -through gates to the pipe system leading to the pure-water reservoir. -Drain-pipes are also provided which allow the water to be entirely -drawn out of each filter, should that be necessary for any reason, -and without interfering with the other filters or with the pure-water -reservoir.</p> - -<p>The outlets of the filters are connected in pairs, so that filtered -water can be used for filling the underdrains and sand of the filters -from below prior to starting, thus avoiding the disturbance which -results from bringing dirty water upon the sand of a filter not filled -with water.</p> - -<p><b>Laboratory Building.</b>—The scientific control of filters is -regarded as one of the essentials to the best results, and to provide -for this there is a laboratory building at one end of the central court -between the filters and close to the sedimentation-basin, supplied -with the necessary equipment for full bacterial examinations, and also -with facilities for observing the colors and turbidities of raw and -filtered waters, and for making such chemical examinations as may be -necessary. This building also provides a comfortable office, dark room, -and storage room for tools, etc., used in the work.</p> - -<p><b>Pure-water Reservoir.</b>—A small pure-water reservoir, 94 -feet square and holding about 600,000 gallons, is provided at the -filter-plant. The construction is similar to that of the filters, but -the shapes of the piers and vaulting were changed slightly, as there -was no necessity for the ledges about the bottoms of the piers and<span class="pagenum" id="Page_308">[Pg 308]</span> -walls; while provision is made for taking the rain-water, falling upon -the vaulting above, to the nearest filters instead of allowing it to -enter the reservoir. The floor and roof of the reservoir are at the -same levels as those of the filters.</p> - -<div class="section"> -<h3 class="nobreak" id="CAPACITY_OF_PLANT_AND_MEANS_OF_REGULATION">CAPACITY OF PLANT AND MEANS OF REGULATION.</h3></div> - -<p>The various filters have effective filtering areas of from 0.702 to -0.704 acre, depending upon slight differences in the thickness of the -walls in different places. For the purpose of computation, the area of -each filter is taken at 0.7 acre. The nominal rate of filtration is -taken as 3,000,000 gallons per acre daily, at which rate each filter -will yield 2,100,000 gallons daily, and, with one filter out of use -for the purpose of being cleaned, seven filters normally in use will -yield 14,700,000 gallons. The entrances and outlets are all made of -sufficient size, so that rates 50 per cent greater than the foregoing -are possible. The capacities of the intake, pumping-station, and piping -are such as to supply any quantity of water which the filters can -take, up to an extreme maximum of 25,000,000 gallons in 24 hours. The -pure-water conduit from the filters to Quackenbush Street is nominally -rated at 25,000,000 gallons per 24 hours, after it has become old and -somewhat tuberculated. In its present excellent condition it will carry -a larger quantity,</p> - -<p>At the pumping-station at Quackenbush Street there are three Allis -pumps, each capable of pumping 5,000,000 gallons per 24 hours. In -addition to the above there are the old reserve pumps with a nominal -capacity of 10,000,000 gallons per 24 hours, which can be used if -necessary, but which require so much coal that they are seldom used. -For practical purposes the 15,000,000 gallons represents the pumping -capacity of this station and also the capacity of the filters, but -the arrangements are such that in case of emergency the supply can be -increased to 20,000,000 or even 25,000,000 gallons for a short time.</p> - -<p><span class="pagenum" id="Page_309">[Pg 309]</span></p> - -<p>The water is pumped through rising mains to reservoirs holding -37,000,000 gallons, not including the Tivoli low-service reservoir, -which is usually supplied from gravity sources. The reservoir capacity -is such that the pumping can be suspended at Quackenbush Street -for considerable periods if necessary, and in practice it has been -suspended at certain times, especially on Sundays. The amount of water -required is also somewhat irregular. The drainage areas supplying the -gravity reservoirs are much larger, relatively, than the reservoirs, -and at flood periods the volume of the gravity supply is much greater -than that which can be drawn in dry weather. Thus it happens that, at -certain seasons of the year, the amount of water to be pumped is but a -fraction of the nominal capacity of the pumps, and at these times it is -possible to shut the pumps down for greater lengths of time.</p> - -<p><b>Capacity of Pure-water Reservoir.</b>—The storage capacity provided -between the filters and the Quackenbush Street pumps is comparatively -small, namely, 600,000 gallons, or one hour’s supply at the full -nominal rate. A larger basin, holding as much as one third or one -half of a day’s supply, would be in many respects desirable in this -position, but the conditions were such as to make it practically -impossible. The bottom of the reservoir could not be put lower without -deepening and increasing greatly the expense of the conduit-line. On -the other hand, the flow-line of the reservoir could not be raised -without raising the level of the filters, which was hardly possible -upon the site selected. The available depth of the reservoir was thus -limited between very narrow bounds, and to secure a large capacity -would have necessitated a very large area, and consequently a great -expense. Under these circumstances, and especially in view of the -abundant storage capacity for filtered water in the distributing -reservoirs, it was not deemed necessary to provide a large storage, and -only so much was provided as would allow the pumps to be started at -the convenience of the engineer, and give a reasonable length of time -for the filters to be brought into operation. For this the pure-water<span class="pagenum" id="Page_310">[Pg 310]</span> -reservoir is ample, but it is not enough to balance any continued -fluctuations in the rate of pumping.</p> - -<p><b>Method of Regulating and Changing the Rate of Filtration.</b>—With -all the Allis pumps running at their nominal capacity, the quantity -of water required will just about equal the nominal capacity of the -filters. When only one or two pumps are running, the rate of filtration -can be reduced. With the plant operating up to its full capacity, the -water-level in the pure-water reservoir will be below the level of -the standard orifices in the filter outlets. When the rate of pumping -is reduced, if no change is made in the gates controlling the filter -outlets, the water will gradually rise in the pure-water reservoir and -in the various regulator chambers, and will submerge the orifices and -gradually reduce the head on the filters, and consequently the rates -of filtration, until those rates equal the quantity pumped. In case -the pumping is stopped altogether, the filters will keep on delivering -at gradually reduced rates until the water-level in the pure-water -reservoir reaches that of the water on the filters.</p> - -<p>When the pumps are started up, after such stoppage or reduced rate -of pumping, the water-levels in the pure-water reservoir and in the -gate-chambers will be lowered gradually, and the filters will start -to operate it first with extremely low rates, which will increase -gradually until the water is depressed below the orifices, when they -will again reach the rates at which they were last set. The regulators -during all this time will show the rate of filtration on each filter, -and, if any inequalities occur which demand correction, the gates on -the various outlets can be adjusted accordingly.</p> - -<div class="figcenter padt1 padb1 illowp100" id="facing310_1" style="max-width: 99.375em;"> - <img class="w100" src="images/facing310_1.jpg" alt="" /> - <p class="caption"><span class="smcap">Central Court, showing Sand-washer, Dirty Sand, -etc.</span></p></div> - -<div class="figcenter padb1 illowp100" id="facing310_2" style="max-width: 98.1875em;"> - <img class="w100" src="images/facing310_2.jpg" alt="" /> - <p class="caption"><span class="smcap">Sedimentation Basin, Filters, etc.</span></p> - -<p class="right">[<em>To face page 310.</em></p></div> - -<p>The arrangement, in this respect, combines some of the features of -the English and German plants. In the English plants the filters are -usually connected directly with the clear-water basin, and that in turn -with the pumps, and the speed of filtration is required to respond -to the speed of the pumps, increasing and decreasing with it, being -regulated at all times by the height of water in the pure-water -reservoir. This arrangement has been subject to severe criticism, -because the rate of filtration fluctuates with the consumption, and -especially because the rates of filtration obtained simultaneously in -different filters may be different. There was no way to determine at -what rate any individual filter was working, and there was always a -tendency for a freshly scraped filter to operate much more rapidly than -those which had not been scraped for some time.</p> - -<p>This led to the procedure, first formulated by the Commission of German -Water-works Engineers in 1894, and provided for in most of the German -works built or remodelled since that time, of providing pure-water -storage sufficient in amount to make the rate of filtration entirely -independent of the operation of the pumps. Each filter was to be -controlled by itself, be independent of the others, and deliver its -water into a pure-water reservoir lower than itself, so that it could -never be affected by back-water, and so large that there would never be -a demand for sudden changes in the rate of filtration.</p> - -<p>This procedure has given excellent results in the German works; but -it leads oftentimes to expensive construction. It involves, in the -first place, a much greater loss of head in passing through the works, -because the pure-water reservoir must be lower than the filters, and -the cost of the pure-water reservoir is increased greatly because -of its large size. The regulation of the filters is put upon the -attendants entirely, or upon automatic devices, and regulation by what -is known as “responding to the pumps” is eliminated.</p> - -<p>More recently, the German authorities have shown less disposition to -insist rigidly upon the principles advanced in 1894. In a compilation -of the results of several years’ experience with German water-filters, -Dr. Pannwiz<a id="FNanchor_66" href="#Footnote_66" class="fnanchor">[66]</a> makes a statement of particular interest, of which a -free translation is as follows:</p> - -<p>“Most of the German works have sufficient pure-water reservoir capacity -to balance the normal fluctuations in consumption,<span class="pagenum" id="Page_312">[Pg 312]</span> -so that the rate of filtration is at least independent of the hourly -fluctuations in consumption. Of especial importance is the superficial -area of the pure-water reservoir. If it is sufficiently large, there is -no objection to allowing the water-level in it to rise to that of the -water upon the filters. With very low rates of consumption during the -night the filters may work slowly and even stop, without damage to the -sediment layers when the stopping and starting take place slowly and -regularly, because of the ample reservoir area.”</p> - -<p>“The very considerable fluctuations from day to day, especially those -arising from unusual and unforeseen occurrences, are not provided for -entirely by even very large and well-arranged reservoirs. To provide -for these without causing shock, the rate of filtration must be changed -carefully and gradually, and the first essential to success is a good -regulation apparatus.”</p> - -<p>“Responding to the pumps” has a great deal to recommend it. It allows -the pure-water reservoir to be put at the highest possible level, it -reduces to a minimum the loss of head in the plant, and yet provides -automatically, and without the slightest trouble on the part of the -attendants, for the delivery of the required quantity of water by the -filters at all times. If the filters are connected directly to the -pumps there is a tendency for the pulsations of the pumps to disturb -their operation, which is highly objectionable, even if the pumps are -far removed; and this exists where filters are connected directly to -the pumps, and a pure-water reservoir is attached to them indirectly. -By taking all the water through the pure-water reservoir and having no -connection except through it, this condition is absolutely avoided, and -the pull on the filters is at all times perfectly steady.</p> - -<p>Much has been said as to the effect of variation in the rate of -filtration upon the efficiency of filters. Experiments have been made -at Lawrence and elsewhere which have shown that, as long as the maximum -rate does not exceed a proper one, and under reasonable regulations, -and with the filter in all respects in good<span class="pagenum" id="Page_313">[Pg 313]</span> order, no marked decrease -in efficiency results from moderate fluctuations in rate. There is -probably a greater decrease in efficiency by stopping the filter -altogether, especially if it is done suddenly, than by simply reducing -the rate. The former sometimes results in loosening air-bubbles in the -sand, which rise to the surface and cause disturbances, but this is not -often caused by simple change in rate.</p> - -<p>On the whole, there is little evidence to show that, within reasonable -limits, fluctuations in rate are objectionable, or should be excluded -entirely, especially in such cases as at Albany, where arrangements to -prevent them would have resulted in very greatly increased first cost. -The inferior results sometimes obtained with the system of “responding -to the pumps” as it existed in earlier works, and still exists in many -important places, undoubtedly arises from the fact that there is no -means of knowing and controlling the simultaneous rate of filtration in -different filters, and that one filter may be filtering two or three -times as fast as another, with nothing to indicate it.</p> - -<p>This contingency is fully provided for in the Albany plant. The -orifices are of such size that even with a filter just scraped and -put in service, with the minimum loss of head, with the outlet-gate -wide open, and with the water-level in the pure-water reservoir clear -down—that is, with the most unfavorable conditions which could possibly -exist—the rate of filtration cannot exceed 5,000,000 or 6,000,000 -gallons per acre daily, or double the nominal rate. This rate, while -much too high for a filter which has just been cleaned, is not nearly -as high as was possible, and in fact actually occurred in the old -Stralau filters at Berlin, and in many English works; and, further, -such a condition could only occur through the gross negligence of -the attendants, because the rate of filtration is indicated clearly -at all times by the gauges. These regulating-devices have been -specially designed to show the rate with unmistakable clearness, so -that no attendant, however stupid, can make an error by an incorrect -computation from the<span class="pagenum" id="Page_314">[Pg 314]</span> gauge heights. It is believed that the advantage -of clearness by this procedure is much more important than any -increased accuracy which might be secured by refinements in the method -of computation, which should take into account variations in the value -of the coefficient of discharge, but which would render direct readings -impossible.</p> - -<p>In designing the Albany plant the object has been to combine the best -features of German regulation with the economical and convenient -features of the older English system, and filters are allowed to -respond to the pumps within certain limits, while guarding against the -dangers ordinarily incident thereto.</p> - -<div class="section"> -<h3 class="nobreak" id="RESULTS_OF_OPERATION">RESULTS OF OPERATION.</h3></div> - -<p>The filters were designed to remove from the water the bacteria which -cause disease. They have already reached a bacterial efficiency of over -99 per cent, and it is expected that their use will result in a great -reduction in the death-rate from water-borne diseases in the city. They -also remove a part of the color and all of the suspended matters and -turbidity, so that the water is satisfactory in its physical properties.</p> - -<p>The filters have reached with perfect ease their rated capacity, and -on several occasions have been operated to deliver one third more than -this amount; that is to say, at a rate of 4,000,000 gallons per acre, -daily.</p> - -<div class="section"> -<h3 class="nobreak" id="COST_OF_CONSTRUCTION">COST OF CONSTRUCTION.</h3></div> - -<p class="padb1">The approximate cost of the filtration-plant complete was as follows:</p> - -<table class="autotable" summary="albany cost of plant"> -<tr> -<td class="tdl">Land</td> -<td class="tdr vertb">$8,290</td> -</tr> -<tr> -<td class="tdl"><p class="indent">Pumping-station and intake</p></td> -<td class="tdr vertb">49,745</td> -</tr> -<tr> -<td class="tdl"><p class="indent">Filters and sedimentation-basin, with piping</p></td> -<td class="tdr vertb">323,960</td> -</tr> -<tr> -<td class="tdl"><p class="indent">Pure-water conduit and connection with Quackenbush Street pumping-station</p></td> -<td class="tdr vertb">86,638</td> -</tr> -<tr> -<td class="tdl"><p class="indent">Engineering and minor expenses</p></td> -<td class="tdr vertb">28,000</td> -</tr> -<tr> -<td class="tdl">Total</td> -<td class="tdr bord_top">$496,633</td> -</tr> -</table> - -<p><span class="pagenum" id="Page_315">[Pg 315]</span></p> - -<p class="padt1">The filters, sedimentation-basin, and pure-water reservoir are -connected in such a way as to make an exact separation of their -costs impossible; but, approximately, the sedimentation-basin cost -$60,000, the pure-water reservoir $9,000, and the filters $255,000. -The sedimentation-basin thus cost $4,100 per million gallons capacity; -and the filters complete cost $45,600 per acre of net filtering area, -including all piping, office and laboratory building, but exclusive of -land and engineering.</p> - - -<p class="center padt1 padb1">ACKNOWLEDGMENT.</p> - -<p>The general plan and location of the plant were first conceived by the -Superintendent of Water-works, George I. Bailey, M. Am. Soc. C. E., and -the successful execution is largely due to his efforts. The members -of the Water Board, and especially the Construction Committee, have -followed the work in detail closely and personally, and their interest -and support have been essential factors in the results accomplished. In -the designs and specifications for the pure-water conduit the author -is greatly indebted to Emil Kuichling, M. Am. Soc. C. E., and also for -most valuable suggestions relative to the performance of this part of -the work. To William Wheeler, M. Am. Soc. C. E., of Boston, the author -is indebted for advice upon the vaulting and cross-sections of the -walls, and these matters were submitted to him before the plans were -put in final shape. All the architectural designs have been supplied -by Mr. A. W. Fuller, of Albany. W. B. Fuller, M. Am. Soc. C. E., as -Resident Engineer, has been in direct charge of the work, and its -success is largely due to his interest in it and the close attention -which he and the assistant engineers have given it.</p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> - -<h2 class="nobreak" id="FOOTNOTES">FOOTNOTES:</h2> -</div> - -<div class="footnote"> - -<p><a id="Footnote_1" href="#FNanchor_1" class="label">[1]</a> The American gallon is 231 cubic inches or 0.8333 of the -imperial gallon. In this work American gallons are always used, and -English quantities are stated in American, not imperial, gallons.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_2" href="#FNanchor_2" class="label">[2]</a> Filtration of River Waters. Van Nostrand & Co., 1869.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_3" href="#FNanchor_3" class="label">[3]</a> Annual Report of Albert F. Noyes, City Engineer for 1891.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_4" href="#FNanchor_4" class="label">[4]</a> Rept. Mass. State Board of Health, 1892, p. 541. See -Appendix III.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_5" href="#FNanchor_5" class="label">[5]</a> The method of calculating the size is given in Appendix -III.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_6" href="#FNanchor_6" class="label">[6]</a> A full table of frictions with various velocities and -gravels was given in the Rept. of Mass. State Board of Health, 1892, p. -555.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_7" href="#FNanchor_7" class="label">[7]</a> Frühling, Handbuch der Ingenieurwissenschaften, II. Band, -VI. Kapitel.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_8" href="#FNanchor_8" class="label">[8]</a> The American gallon is used throughout this book; the -English gallon is one fifth larger.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_9" href="#FNanchor_9" class="label">[9]</a> Piefke, <cite>Zeitschrift für Hygiene</cite>, 1894, p. 177.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_10" href="#FNanchor_10" class="label">[10]</a> <cite>Zeitschrift für Hygiene</cite>, 1891, page 38.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_11" href="#FNanchor_11" class="label">[11]</a> <cite>Journal für Gas- u. Wasserversorgung</cite>, 1891, 208 -and 228.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_12" href="#FNanchor_12" class="label">[12]</a> <cite>Journal für Gas- u. Wasserversorgung</cite>, 1893, 161.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_13" href="#FNanchor_13" class="label">[13]</a> Samuelson’s translation of Kirkwood’s “Filtration -of River-waters;” Lindley, Die Nutzbarmachung des Flusswassers, -<cite>Journal für Gas- u. Wasserversorgung</cite>, 1890, 501; Kaiserlichen -Gesundheitsamt, Grundsätze für die Reinigung von Oberflächenwasser -durch Sandfiltration; <cite>Journal für Gas- u. Wasserversorgung</cite>, -1894, Appendix I.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_14" href="#FNanchor_14" class="label">[14]</a> Lindley, <cite>Journal für Gas- u. Wasserversorgung</cite>, -1890, 501; Grahn, <cite>Journal für Gas- u. Wasserversorgung</cite>, 1890, -511; Halbertsma, <cite>Journal für Gas- u. Wasserversorgung</cite>, 1892, -686; Piefke, <cite>Zeitschrift für Hygiene</cite>, 1894, 151; and others.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_15" href="#FNanchor_15" class="label">[15]</a> Appendix I.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_16" href="#FNanchor_16" class="label">[16]</a> The Water Supply of Towns. London, 1894.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_17" href="#FNanchor_17" class="label">[17]</a> A special species of bacteria artificially added to -secure more precise information in regard to the passage of germs -through the filter.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_18" href="#FNanchor_18" class="label">[18]</a> <cite>Zeitschrift für Hygiene</cite>, 1894, p. 173.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_19" href="#FNanchor_19" class="label">[19]</a> Report Mass. State Board of Health for 1891, p. 438; -1892, page 409.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_20" href="#FNanchor_20" class="label">[20]</a> Appendix IV.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_21" href="#FNanchor_21" class="label">[21]</a> Piefke, <cite>Zeitschrift für Hygiene</cite>, 1894, p, 177.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_22" href="#FNanchor_22" class="label">[22]</a> <cite>Journal für Gas- und Wasserversorgung</cite>, 1887, p. -595.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_23" href="#FNanchor_23" class="label">[23]</a> <cite>Zeitschrift für Hygiene</cite>, 1894, p. 172.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_24" href="#FNanchor_24" class="label">[24]</a> Appendix IV.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_25" href="#FNanchor_25" class="label">[25]</a> Appendix I.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_26" href="#FNanchor_26" class="label">[26]</a> <cite>Glaser’s Annalen</cite>, 1886, p. 48; <cite>Zeit. f. -Hygiene</cite>, 1889, p. 128.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_27" href="#FNanchor_27" class="label">[27]</a> <cite>Vierteljahresschrift für öffentliche -Gesundheitspflege</cite>, 1891, p. 59.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_28" href="#FNanchor_28" class="label">[28]</a> <cite>Journal für Gas- und Wasserversorgung</cite>, 1891, 108.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_29" href="#FNanchor_29" class="label">[29]</a> <cite>Zeitschrift für Hygiene</cite>, 1894, 182.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_30" href="#FNanchor_30" class="label">[30]</a> I am informed that several other filters upon the same -principle have been more recently built.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_31" href="#FNanchor_31" class="label">[31]</a> Report on Water Purification at Cincinnati, page 378.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_32" href="#FNanchor_32" class="label">[32]</a> Translation in German in Dingler’s Polytechnical Journal, -1832, 386.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_33" href="#FNanchor_33" class="label">[33]</a> Water Purification at Louisville, page 378.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_34" href="#FNanchor_34" class="label">[34]</a> Special Report Mass. State Board of Health 1890, -Purification of Sewage and Water, page 747.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_35" href="#FNanchor_35" class="label">[35]</a> Water Purification at Cincinnati, p. 485.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_36" href="#FNanchor_36" class="label">[36]</a> Jour. of the New England Water Works Assoc., Vol. -<span class="allsmcap">VIII</span>, page 183.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_37" href="#FNanchor_37" class="label">[37]</a> Report of the Pittsburg Filtration Commission, 1899, page -55.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_38" href="#FNanchor_38" class="label">[38]</a> Rhode Island State Board of Health Report for 1894.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_39" href="#FNanchor_39" class="label">[39]</a> Report of the Rhode Island State Board of Health for -1894.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_40" href="#FNanchor_40" class="label">[40]</a> Report on the Investigations into the Purification of the -Ohio River Water at Louisville, Kentucky. D. Van Nostrand & Co., 1898.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_41" href="#FNanchor_41" class="label">[41]</a> Ohio State Board of Health Report, 1897, page 154.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_42" href="#FNanchor_42" class="label">[42]</a> Report of the Pittsburg Filtration Commission, City -Document, 1899.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_43" href="#FNanchor_43" class="label">[43]</a> Fuller, Water Purification at Louisville, page 425.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_44" href="#FNanchor_44" class="label">[44]</a> Warren, Feb. 9; June 1; July 6. Jewell, July 1; Feb. 9, -16, 17.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_45" href="#FNanchor_45" class="label">[45]</a> “Removal of Iron from Ground Waters,” Journal of the New -England Water Works Association, Vol. xi, 1897, page 277.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_46" href="#FNanchor_46" class="label">[46]</a> Journal of the New England Water Works Association, Vol. -ii, page 294. Description of plant by Supt. Lewis M. Bancroft.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_47" href="#FNanchor_47" class="label">[47]</a> This number was the result of numerous counts made from -fæces from persons suffering with typhoid fever in the Lawrence City -Hospital in 1891 and 1892. Mr. G. W. Fuller afterward made at the -Lawrence Experiment Station some further investigation of fæces from -healthy people in which the numbers were considerably lower, usually -less than 200,000,000, per gram and sometimes as low as 10,000,000 per -gram.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_48" href="#FNanchor_48" class="label">[48]</a> These experiments, so far as they have come to the notice -of the author, have been made with water sterilized by heating, usually -in small tubes stoppered with cotton-wool or other organic matter. In -this case the water, no matter how carefully purified in the first -place, becomes an infusion of organic matters capable of supporting -bacterial growths, and not at all to be compared to natural waters.</p> - -<p>In experiments often repeated under my direction, carefully distilled -water in bottles, <em>most scrupulously clean</em>, with glass stoppers, -and protected from dust, but <em>not sterilized</em>, has uniformly -refused to support bacterial growths even when cautiously seeded at -the start, and the same is usually true of pure natural waters. Some -further experiments showed hardly any bacterial growth even of the most -hardy water bacteria in a solution 1 part of peptone in 1,000,000,000 -parts of distilled water, and solutions ten times as strong only gave -moderate growths.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_49" href="#FNanchor_49" class="label">[49]</a> The Water-supply of Chicago: Its Source and Sanitary -Aspects. By Arthur R. Reynolds, M.D., Commissioner of Health of -Chicago, and Allen Hazen. <cite>American Public Health Association</cite>, -1893. Page 146.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_50" href="#FNanchor_50" class="label">[50]</a> <cite>Journal für Gas- u. Wasserversorgung</cite>, 1893, 694.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_51" href="#FNanchor_51" class="label">[51]</a> <cite>Journal für Gas- u. Wasserversorgung</cite>, 1894, 185.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_52" href="#FNanchor_52" class="label">[52]</a> The method of making this determination was given in the -<cite>American Chemical Journal</cite>, vol. 12, p. 427.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_53" href="#FNanchor_53" class="label">[53]</a> Some of the companies secure some ground water which they -mix with the filtered water, and this is included in the quantities for -the separate companies, but is excluded from the totals for all the -companies by years.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_54" href="#FNanchor_54" class="label">[54]</a> Exclusive of gravity supplies.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_55" href="#FNanchor_55" class="label">[55]</a> Not in use.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_56" href="#FNanchor_56" class="label">[56]</a> Under construction.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_57" href="#FNanchor_57" class="label">[57]</a> Not in use.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_58" href="#FNanchor_58" class="label">[58]</a> Under construction.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_59" href="#FNanchor_59" class="label">[59]</a> Not in use.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_60" href="#FNanchor_60" class="label">[60]</a> Under construction.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_61" href="#FNanchor_61" class="label">[61]</a> Not in use.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_62" href="#FNanchor_62" class="label">[62]</a> Under construction.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_63" href="#FNanchor_63" class="label">[63]</a> In the <cite>Centralblatt für Bakteriologie</cite>, 1895, page -881, Reinsch discusses at length the cause of the inferior results -at Altona in winter, and has apparently discovered a new factor in -producing them. Owing to defective construction of the outlets for the -sedimentation-basins they have failed to act properly in presence of -excessive quantities of ice, and the sediment from the basins has been -discharged in large quantity upon the filters, and a small fraction of -the many millions of bacteria in it have passed through the filters. He -has experimented with this sediment applied to small filters, and has -become convinced that to secure good work under all conditions a much -deeper layer of sand than that generally considered necessary must be -used, and his work emphasizes the importance of the action of the sand -in distinction from the action of the sediment layer, which has often -been thought to be the sole, or at least the principal, requirement of -good filtration.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_64" href="#FNanchor_64" class="label">[64]</a> Licht- u. Wasserwerke, Zürich, 1892, page 32.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_65" href="#FNanchor_65" class="label">[65]</a> Descriptions of some of the leading European ground-water -supplies were given by the author in the Jour. Asso. Eng. Soc., Feb. -1895, p. 113.</p> - -</div> - -<div class="footnote"> - -<p><a id="Footnote_66" href="#FNanchor_66" class="label">[66]</a> “<cite>Arbeiten aus dem Kaiserlichen Gesundheitsamte</cite>,” -vol. xiv. p. 260.</p> - -</div> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_317">[Pg 317]</span></p> -<h2 class="nobreak" id="INDEX">INDEX.</h2> -</div> - -<ul class="index"> -<li class="ifrst">Albany, N. Y., filters at, <a href="#Page_254">254</a>, <a href="#Page_288">288</a>.</li> - -<li class="indx">Alkalinity, <a href="#Page_155">155</a>.</li> - -<li class="indx">Altona, double filtration at, <a href="#Page_198">198</a>.</li> -<li class="isub3">filters at, <a href="#Page_265">265</a>.</li> - -<li class="indx">Alum, use of, in filtration, <a href="#Page_92">92</a>, <a href="#Page_144">144</a>.</li> - -<li class="indx">American cities, water-supplies of, and typhoid fever in, <a href="#Page_211">211</a>.</li> - -<li class="indx">Amsterdam, filters at, <a href="#Page_272">272</a>.</li> -<li class="isub3">iron removal at, <a href="#Page_192">192</a>.</li> - -<li class="indx">Anderson process, <a href="#Page_147">147</a>.</li> - -<li class="indx">Antwerp, filters at, <a href="#Page_272">272</a>.</li> - -<li class="indx">Asbestos as filtering material, <a href="#Page_181">181</a>.</li> - -<li class="indx">Asbury Park, iron removal at, <a href="#Page_192">192</a>.</li> - -<li class="indx">Ashland, Wis., filters at, <a href="#Page_252">252</a>.</li> - -<li class="indx">Area of filters to be provided, <a href="#Page_47">47</a>.</li> - -<li class="ifrst">Bacteria, apparent and actual removal of, by filters, <a href="#Page_87">87</a>.</li> -<li class="isub3">from underdrains, <a href="#Page_87">87</a>.</li> -<li class="isub3">in Elbe at Altona, <a href="#Page_228">228</a>.</li> -<li class="isub3">in fæces, <a href="#Page_215">215</a>.</li> -<li class="isub3">in water, <a href="#Page_84">84</a>.</li> -<li class="isub3">number to be allowed in filtered water, <a href="#Page_222">222</a>.</li> -<li class="isub3">of cholera in river water, <a href="#Page_231">231</a>.</li> -<li class="isub3">of typhoid fever, life of, in water, <a href="#Page_216">216</a>.</li> -<li class="isub3">of special kinds to test efficiency of filtration, <a href="#Page_86">86</a>.</li> -<li class="isub3">to be determined daily, <a href="#Page_222">222</a>.</li> - -<li class="indx">Bacterial examination of water, <a href="#Page_93">93</a>.</li> - -<li class="indx">Berlin, regulation of depth of water, <a href="#Page_59">59</a>.</li> -<li class="isub3">cholera infantum from water, <a href="#Page_229">229</a>.</li> -<li class="isub3">friction in underdrains, <a href="#Page_44">44</a>.</li> -<li class="isub3">regulation of rate, <a href="#Page_53">53</a>, <a href="#Page_55">55</a>.</li> -<li class="isub3">water works, <a href="#Page_261">261</a>.</li> - -<li class="indx">Berwyn, Penn., filters at, <a href="#Page_253">253</a>.</li> - -<li class="indx">Boston, protection of purity of water-supply, <a href="#Page_110">110</a>.</li> -<li class="isub3">experimental filters at, <a href="#Page_73">73</a>.</li> - -<li class="indx">Bremen, double filtration at, <a href="#Page_198">198</a>.</li> - -<li class="indx">Breslau, filters at, <a href="#Page_274">274</a>.</li> - -<li class="indx">Brussels, ground-water, supply of, <a href="#Page_276">276</a>.</li> - -<li class="indx">Budapest, filters at, <a href="#Page_274">274</a>.</li> - -<li class="indx">Burton, regulation of rate at Tokyo, Japan, <a href="#Page_58">58</a>.</li> - -<li class="ifrst">Carpenter, Prof. L. G., <a href="#Page_24">24</a>.</li> - -<li class="indx">Chemnitz, intermittent filtration at, <a href="#Page_107">107</a>.</li> - -<li class="indx">Chicago, reduced death-rate with new intake, <a href="#Page_217">217</a>.</li> - -<li class="indx">Cholera infantum from impure water, <a href="#Page_226">226</a>.</li> - -<li class="indx">Cholera, in Hamburg from water, <a href="#Page_230">230</a>.</li> -<li class="isub3">caused by water, <a href="#Page_214">214</a>.</li> - -<li class="indx">Clarification, definition of, <a href="#Page_113">113</a>.</li> - -<li class="indx">Clark, H. W., <a href="#Page_24">24</a>, <a href="#Page_190">190</a>.</li> - -<li class="indx">Clark’s process for softening water, <a href="#Page_92">92</a>, <a href="#Page_145">145</a>.</li> - -<li class="indx">Clay particles, size of, <a href="#Page_123">123</a>.</li> - -<li class="indx">Cleaning filters, <a href="#Page_68">68</a>.</li> - -<li class="indx">Coagulant, absorption of, by suspended matters, <a href="#Page_154">154</a>.</li> -<li class="isub3">successive applications of, <a href="#Page_154">154</a>.</li> - -<li class="indx">Coagulants used in practice, <a href="#Page_150">150</a>.</li> - -<li class="indx">Coagulation of waters, <a href="#Page_144">144</a>.</li> - -<li class="indx">Cologne, water-supply of, from wells, <a href="#Page_276">276</a>.</li> - -<li class="indx">Color, <a href="#Page_113">113</a>.</li> -<li class="isub3">amount of coagulant required to remove, <a href="#Page_153">153</a>.</li> -<li class="isub3">amount of, in various waters, <a href="#Page_115">115</a>.</li> -<li class="isub3"><span class="pagenum" id="Page_318">[Pg 318]</span>measurement of, <a href="#Page_114">114</a>.</li> - -<li class="ifrst">Color, removal of, <a href="#Page_117">117</a>.</li> - -<li class="indx">Continuous filters, <a href="#Page_5">5</a>.</li> -<li class="isub3">filtration, nature of, <a href="#Page_83">83</a>, <a href="#Page_92">92</a>.</li> - -<li class="indx">Cost of filters and filtration, <a href="#Page_4">4</a>, <a href="#Page_48">48</a>, <a href="#Page_102">102</a>, <a href="#Page_200">200</a>, <a href="#Page_314">314</a>.</li> - -<li class="indx">Covered filters, efficiency of, <a href="#Page_17">17</a>.</li> - -<li class="indx">Covers for filters, <a href="#Page_12">12</a>, <a href="#Page_15">15</a>.</li> -<li class="isub3">at Albany, <a href="#Page_295">295</a>.</li> -<li class="isub3">in the United States, <a href="#Page_17">17</a>.</li> -<li class="isub3">omitted at Lawrence, <a href="#Page_101">101</a>.</li> - -<li class="indx">Crenothrix, <a href="#Page_105">105</a>, <a href="#Page_186">186</a>.</li> - -<li class="ifrst">Diarrhœa from impure water, <a href="#Page_226">226</a>.</li> - -<li class="indx">Dibden, W. J., <a href="#Page_129">129</a>.</li> - -<li class="indx">Disease from water, <a href="#Page_210">210</a>.</li> - -<li class="indx">Double filtration at Schiedam, <a href="#Page_273">273</a>.</li> - -<li class="indx">Drainage areas of a number of rivers, <a href="#Page_133">133</a>.</li> - -<li class="indx">Dresden, water-supply of, from filter-gallery, <a href="#Page_276">276</a>.</li> - -<li class="indx">Drown, Dr. Thomas M., <a href="#Page_150">150</a>, <a href="#Page_191">191</a>.</li> - -<li class="ifrst">Effective size of sand, <a href="#Page_21">21</a>, <a href="#Page_238">238</a>.</li> -<li class="isub3">European sands, <a href="#Page_25">25</a>.</li> - -<li class="indx">Efficiency of filtration, <a href="#Page_83">83</a>, <a href="#Page_88">88</a>, <a href="#Page_91">91</a>.</li> -<li class="isub3">effect of rate upon, <a href="#Page_50">50</a>.</li> -<li class="isub3">effect of size of sand-grain upon, <a href="#Page_30">30</a>.</li> -<li class="isub3">effect of thickness of sand layer upon, <a href="#Page_34">34</a>.</li> -<li class="isub3">at Lawrence, <a href="#Page_106">106</a>.</li> -<li class="isub3">European filters, <a href="#Page_91">91</a>, <a href="#Page_260">260</a>.</li> - -<li class="indx">Effluents, wasting after scraping, <a href="#Page_74">74</a>.</li> - -<li class="ifrst">Fæces, number of bacteria in, <a href="#Page_215">215</a>.</li> - -<li class="indx">Far Rockaway, L. I., filters at, <a href="#Page_193">193</a>, <a href="#Page_253">253</a>.</li> - -<li class="indx">Filling sand with water from below, <a href="#Page_68">68</a>, <a href="#Page_307">307</a>.</li> - -<li class="indx">Filter beds, bottoms of, must be water-tight, <a href="#Page_12">12</a>.</li> -<li class="isub3">covers for, <a href="#Page_12">12</a>.</li> -<li class="isub3">form of, <a href="#Page_11">11</a>.</li> -<li class="isub3">size of, <a href="#Page_10">10</a>.</li> - -<li class="indx">Filters, aggregate capacity of, <a href="#Page_254">254</a>.</li> -<li class="isub3">depths of waters on, <a href="#Page_45">45</a>.</li> -<li class="isub3">list of cities using, <a href="#Page_244">244</a>.</li> -<li class="isub3">reserve area required, <a href="#Page_47">47</a>.</li> -<li class="isub3">first constructed at London, <a href="#Page_83">83</a>.</li> -<li class="isub3">for household use, <a href="#Page_183">183</a>.</li> -<li class="isub3">general arrangement of, <a href="#Page_6">6</a>.</li> - -<li class="indx">Filters, statistics of, at various cities, <a href="#Page_241">241</a>.</li> - -<li class="indx">Filtration, cost of, <a href="#Page_200">200</a>.</li> -<li class="isub3">degree of purification required, <a href="#Page_5">5</a>.</li> -<li class="isub3">general nature of, <a href="#Page_92">92</a>.</li> - -<li class="indx">Fischer tile system, <a href="#Page_181">181</a>.</li> - -<li class="indx">FitzGerald, Desmond, <a href="#Page_73">73</a>, <a href="#Page_111">111</a>, <a href="#Page_196">196</a>.</li> - -<li class="indx">Flood flows not taken for supply, <a href="#Page_10">10</a>.</li> - -<li class="indx">Fränkel and Piefke, experiments on removal of disease germs, <a href="#Page_86">86</a>.</li> - -<li class="indx">Frankfort on Main, water supply of, from springs, <a href="#Page_276">276</a>.</li> - -<li class="indx">Frankland, Dr. Percy, <a href="#Page_84">84</a>.</li> - -<li class="indx">Friction of filtered water in pipes, <a href="#Page_264">264</a>.</li> -<li class="isub3">water in gravel, <a href="#Page_37">37</a>.</li> -<li class="isub3">water in sand, <a href="#Page_22">22</a>.</li> -<li class="isub3">water in underdrains, <a href="#Page_40">40</a>.</li> - -<li class="indx">Frost, effect of, upon filters, <a href="#Page_12">12</a>, <a href="#Page_229">229</a>, <a href="#Page_266">266</a>.</li> - -<li class="indx">Frühling, on the heating of water by sunshine, <a href="#Page_16">16</a>.</li> -<li class="isub3">underdraining at Königsberg, <a href="#Page_39">39</a>.</li> - -<li class="indx">Fuller, G. W., <a href="#Page_118">118</a>, <a href="#Page_123">123</a>, <a href="#Page_131">131</a>, <a href="#Page_139">139</a>, <a href="#Page_140">140</a>, <a href="#Page_145">145</a>, <a href="#Page_152">152</a>, <a href="#Page_154">154</a>, <a href="#Page_161">161</a>, <a href="#Page_165">165</a>.</li> - -<li class="ifrst">German Imperial Board of Health, <a href="#Page_34">34</a>, <a href="#Page_51">51</a>, <a href="#Page_54">54</a>, <a href="#Page_75">75</a>, <a href="#Page_95">95</a>.</li> -<li class="isub3">regulations in regard to filtration, <a href="#Page_221">221</a>.</li> - -<li class="indx">Gill, apparatus for regulation, <a href="#Page_55">55</a>.</li> - -<li class="indx">Glasgow, water-supply of, from Loch Katrine, <a href="#Page_275">275</a>.</li> - -<li class="indx">Gravel at Albany, <a href="#Page_299">299</a>.</li> -<li class="isub3">layers, <a href="#Page_35">35</a>.</li> -<li class="isub3">friction of water in, <a href="#Page_37">37</a>.</li> -<li class="isub3">screening of, for filters, <a href="#Page_37">37</a>.</li> - -<li class="indx">Grand Forks, N. D., filters at, <a href="#Page_252">252</a>.</li> - -<li class="indx">Ground-water supplies, <a href="#Page_3">3</a>.</li> -<li class="isub3">the use of, in Europe, <a href="#Page_276">276</a>.</li> - -<li class="ifrst">Halbertsma, H. P. N., <a href="#Page_54">54</a>, <a href="#Page_59">59</a>.</li> - -<li class="indx">Hamburg, apparatus for regulating depth of water, <a href="#Page_59">59</a>.</li> -<li class="isub3">health of, <a href="#Page_226">226</a>, <a href="#Page_271">271</a>.</li> -<li class="isub3">regulation of rate of filtration, <a href="#Page_56">56</a>.</li> -<li class="isub3">underdrains of filters at, <a href="#Page_42">42</a>.</li> -<li class="isub3">water-supply of, <a href="#Page_269">269</a>.</li> - -<li class="indx">Hamilton, N. Y., filters at, <a href="#Page_253">253</a>.</li> - -<li class="indx">Hardness, removal of, <a href="#Page_92">92</a>, <a href="#Page_145">145</a>.</li> - -<li class="indx">Harrisburg, Penn., filters at, <a href="#Page_253">253</a>.</li> - -<li class="indx">Hermany, Charles, <a href="#Page_161">161</a>.</li> - -<li class="indx"><span class="pagenum" id="Page_319">[Pg 319]</span> High rates of filtration without coagulant, <a href="#Page_182">182</a>.</li> - -<li class="indx">Household filters, <a href="#Page_183">183</a>.</li> - -<li class="indx">Hudson, N. Y., filters at, <a href="#Page_251">251</a>.</li> - -<li class="ifrst">Ice on filters, <a href="#Page_13">13</a>.</li> - -<li class="indx">Inlet regulators, <a href="#Page_59">59</a>.</li> - -<li class="indx">Impounding reservoirs, <a href="#Page_2">2</a>.</li> - -<li class="indx">Intermittent filtration, <a href="#Page_97">97</a>.</li> -<li class="isub3">application of, <a href="#Page_111">111</a>, <a href="#Page_197">197</a>.</li> -<li class="isub3">at Chemnitz, <a href="#Page_107">107</a>.</li> -<li class="isub3">at Lawrence, <a href="#Page_100">100</a>.</li> -<li class="isub3">of Pegan Brook, <a href="#Page_110">110</a>.</li> - -<li class="indx">Iron, compounds of, as coagulants, <a href="#Page_146">146</a>.</li> -<li class="isub3">in ground-waters, <a href="#Page_186">186</a>.</li> -<li class="isub3">in ground-water at Lawrence, <a href="#Page_105">105</a>.</li> -<li class="isub3">metallic, the Anderson process, <a href="#Page_147">147</a>.</li> -<li class="isub3">present as ferrous sulphate, <a href="#Page_191">191</a>.</li> -<li class="isub3">removal plants in operation, <a href="#Page_192">192</a>.</li> - -<li class="indx">Iron waters, treatment of, <a href="#Page_189">189</a>.</li> - -<li class="ifrst">Jewel filter, <a href="#Page_151">151</a>, <a href="#Page_161">161</a>, <a href="#Page_162">162</a>, <a href="#Page_172">172</a>, <a href="#Page_173">173</a>.</li> - -<li class="ifrst">Kirkwood, James P., <a href="#Page_8">8</a>, <a href="#Page_36">36</a>, <a href="#Page_47">47</a>, <a href="#Page_51">51</a>, <a href="#Page_55">55</a>, <a href="#Page_61">61</a>, <a href="#Page_63">63</a>, <a href="#Page_67">67</a>.</li> - -<li class="indx">Kümmel, <a href="#Page_50">50</a>, <a href="#Page_51">51</a>, <a href="#Page_86">86</a>.</li> - -<li class="ifrst">Lambertsville, N. J., filters at, <a href="#Page_252">252</a>.</li> - -<li class="indx">Lawrence City filter, description of, <a href="#Page_100">100</a>.</li> - -<li class="indx">Lawrence Experiment Station, <a href="#Page_97">97</a>.</li> -<li class="isub3">air in water filtered in winter at, <a href="#Page_46">46</a>.</li> -<li class="isub3">depth of sand removed at, <a href="#Page_70">70</a>.</li> -<li class="isub3">depth of water on filters, <a href="#Page_46">46</a>.</li> -<li class="isub3">effect of loss of head upon efficiency, <a href="#Page_61">61</a>.</li> -<li class="isub3">effect of size of sand-grain upon efficiency, <a href="#Page_32">32</a>.</li> -<li class="isub3">effect of size of sand-grain upon frequency of scraping, <a href="#Page_32">32</a>.</li> -<li class="isub3">efficiency of filters at various rates, <a href="#Page_50">50</a>.</li> -<li class="isub3">efficiency of filtration at, <a href="#Page_86">86</a>, <a href="#Page_89">89</a>.</li> -<li class="isub3">experiments with continuous filtration, <a href="#Page_110">110</a>.</li> -<li class="isub3">filters of fine sand, <a href="#Page_31">31</a>.</li> -<li class="isub3">filters of various sand-grain sizes, <a href="#Page_32">32</a>.</li> -<li class="isub3">gravel for filters at, <a href="#Page_39">39</a>.</li> -<li class="isub3">growth of bacteria in sterilized sand at, <a href="#Page_85">85</a>.</li> -<li class="isub3">intermittent filtration investigated, <a href="#Page_97">97</a>.</li> - -<li class="indx">Lawrence Experiment Station, method of sand analysis at, <a href="#Page_20">20</a>.</li> -<li class="isub3">quantities of water filtered at various losses of head, <a href="#Page_66">66</a>.</li> -<li class="isub3">wasting effluents not necessary, <a href="#Page_75">75</a>.</li> - -<li class="indx">Lawrence, typhoid fever at, <a href="#Page_102">102</a>.</li> - -<li class="indx">Leipzig, water-supply of, from wells, <a href="#Page_276">276</a>.</li> - -<li class="indx">Lime in sand, <a href="#Page_29">29</a>.</li> -<li class="isub3">sterilizing effect of, <a href="#Page_146">146</a>.</li> -<li class="isub3">as a coagulant, <a href="#Page_145">145</a>.</li> -<li class="isub3">application of, to water, <a href="#Page_157">157</a>.</li> - -<li class="indx">Lindley, <a href="#Page_43">43</a>, <a href="#Page_51">51</a>, <a href="#Page_54">54</a>, <a href="#Page_57">57</a>, <a href="#Page_81">81</a>.</li> - -<li class="indx">Literature on filtration, <a href="#Page_277">277</a>, <a href="#Page_285">285</a>.</li> - -<li class="indx">Little Falls, N. Y., filters at, <a href="#Page_253">253</a>.</li> - -<li class="indx">Loam in filters, <a href="#Page_35">35</a>.</li> - -<li class="indx">London, cost of operating filters at, <a href="#Page_202">202</a>.</li> -<li class="isub3">water-supply of, <a href="#Page_255">255</a>.</li> - -<li class="indx">Long, Prof., <a href="#Page_131">131</a>.</li> - -<li class="indx">Lorain, tests of mechanical filters, <a href="#Page_161">161</a>.</li> - -<li class="indx">Loss of head, <a href="#Page_52">52</a>.</li> -<li class="isub3">limit to, <a href="#Page_60">60</a>, <a href="#Page_67">67</a>.</li> -<li class="isub3">reasons for allowing high, <a href="#Page_65">65</a>.</li> - -<li class="indx">Louisville, mechanical filters at, <a href="#Page_161">161</a>.</li> - -<li class="ifrst">Magdeburg, filters at, <a href="#Page_273">273</a>.</li> - -<li class="indx">Maignen system, <a href="#Page_181">181</a>.</li> - -<li class="indx">Manchester, water-supply of, <a href="#Page_275">275</a>.</li> - -<li class="indx">Manganese, compounds of, as coagulants, <a href="#Page_148">148</a>.</li> -<li class="isub3">in ground-waters, <a href="#Page_188">188</a>.</li> - -<li class="indx">Massachusetts State Board of Health, see Lawrence Experiment</li> -<li class="isub4">Station.</li> - -<li class="indx">Mechanical filters, <a href="#Page_159">159</a>.</li> -<li class="isub3">application of, <a href="#Page_199">199</a>.</li> -<li class="isub3">efficiency of, <a href="#Page_179">179</a>.</li> -<li class="isub3">list of, <a href="#Page_247">247</a>.</li> -<li class="isub3">pressure filters, <a href="#Page_180">180</a>.</li> -<li class="isub3">rates of filtration used, <a href="#Page_175">175</a>.</li> -<li class="isub3">types of, <a href="#Page_172">172</a>.</li> -<li class="isub3">wasting effluent after washing, <a href="#Page_163">163</a>.</li> - -<li class="indx">Millford, Mass., filters at, <a href="#Page_252">252</a>.</li> - -<li class="indx">Mills, H. F., <a href="#Page_97">97</a>, <a href="#Page_99">99</a>, <a href="#Page_102">102</a>.</li> - -<li class="indx">Mount Vernon, N. Y., filters at, <a href="#Page_252">252</a>.</li> - -<li class="indx">Mud, see turbidity.</li> - -<li class="indx">Muddy waters, <a href="#Page_113">113</a>.</li> - -<li class="indx">Munich, water-supply of, from springs, <a href="#Page_275">275</a>.</li> - -<li class="ifrst"><span class="pagenum" id="Page_320">[Pg 320]</span>Nichols, Prof., suspended matters in European streams, <a href="#Page_131">131</a>.</li> - -<li class="indx">Nitrification, effect of, upon bacteria, <a href="#Page_98">98</a>.</li> - -<li class="ifrst">Odors, removal of, by filtration, <a href="#Page_112">112</a>.</li> - -<li class="indx">Organic matters in water, <a href="#Page_83">83</a>.</li> -<li class="isub3">removed by intermittent filters, <a href="#Page_98">98</a>.</li> - -<li class="ifrst">Paper manufacturing, filtration of water for, <a href="#Page_5">5</a>.</li> - -<li class="indx">Paris, ground-water supply of, <a href="#Page_276">276</a>.</li> - -<li class="indx">Palmer, Prof., <a href="#Page_131">131</a>.</li> - -<li class="indx">Passages through the sand in filters, <a href="#Page_67">67</a>.</li> - -<li class="indx">Pegan Brook, purification of, <a href="#Page_110">110</a>.</li> - -<li class="indx">Period, how computed and length of, <a href="#Page_72">72</a>.</li> -<li class="isub3">length of, dependent upon turbidity, <a href="#Page_137">137</a>.</li> - -<li class="indx">Piefke, <a href="#Page_48">48</a>, <a href="#Page_50">50</a>, <a href="#Page_54">54</a>, <a href="#Page_63">63</a>, <a href="#Page_69">69</a>, <a href="#Page_73">73</a>, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_80">80</a>, <a href="#Page_84">84</a>, <a href="#Page_85">85</a>, <a href="#Page_90">90</a>.</li> - -<li class="indx">Pittsburgh, experiments with mechanical filters, <a href="#Page_162">162</a>.</li> - -<li class="indx">Plägge and Proskauer, <a href="#Page_84">84</a>.</li> - -<li class="indx">Plymouth, Penn., typhoid fever at, <a href="#Page_208">208</a>.</li> - -<li class="indx">Pollution of European water-supplies, <a href="#Page_93">93</a>.</li> - -<li class="indx">Polluted waters, utilization of excessively, <a href="#Page_111">111</a>.</li> - -<li class="indx">Porcelain filters for household use, <a href="#Page_183">183</a>.</li> - -<li class="indx">Poughkeepsie, N. Y., filters at, <a href="#Page_251">251</a>.</li> - -<li class="indx">Pressure filters, <a href="#Page_180">180</a>.</li> - -<li class="indx">Providence, mechanical filters at, <a href="#Page_159">159</a>.</li> - -<li class="ifrst">Rate of filtration, <a href="#Page_47">47</a>, <a href="#Page_224">224</a>.</li> -<li class="isub3">at various places, <a href="#Page_241">241</a>.</li> -<li class="isub3">effect of, upon cost, <a href="#Page_48">48</a>.</li> -<li class="isub3">effect of, upon efficiency, <a href="#Page_50">50</a>.</li> -<li class="isub3">lower after scraping, <a href="#Page_76">76</a>.</li> -<li class="isub3">regulation of, <a href="#Page_52">52</a>.</li> - -<li class="indx">Red Bank, N. J., filters at, <a href="#Page_193">193</a>, <a href="#Page_253">253</a>.</li> - -<li class="indx">Regulation of filters, <a href="#Page_52">52</a>.</li> -<li class="isub3">old forms of regulators, <a href="#Page_52">52</a>.</li> -<li class="isub3">modern forms of regulators, <a href="#Page_54">54</a>.</li> -<li class="isub3">at Albany, <a href="#Page_305">305</a>, <a href="#Page_308">308</a>, <a href="#Page_310">310</a>.</li> -<li class="isub3">of mechanical filters, <a href="#Page_178">178</a>.</li> - -<li class="indx">Reincke, Dr., report on health of Hamburg for 1892, <a href="#Page_226">226</a>.</li> - -<li class="indx">Reinsch on the cause of poor filtration at Altona, <a href="#Page_267">267</a>.</li> - -<li class="indx">Reserve area required in case of ice, <a href="#Page_18">18</a>.</li> - -<li class="indx">Reservoirs, purposes served by, <a href="#Page_133">133</a>.</li> - -<li class="indx">Rock Island, Ill., filters at, <a href="#Page_254">254</a>.</li> - -<li class="indx">Roofs for filters, <a href="#Page_16">16</a>.</li> - -<li class="indx">Rotterdam, filters at, <a href="#Page_272">272</a>.</li> - -<li class="ifrst">St. Johnsbury, Vt., filters at, <a href="#Page_251">251</a>.</li> - -<li class="indx">St. Louis, regulators for proposed filters, <a href="#Page_55">55</a>.</li> - -<li class="indx">St. Petersburg, filters at, <a href="#Page_275">275</a>.</li> - -<li class="indx">Samuelson, <a href="#Page_51">51</a>.</li> - -<li class="indx">Sand, <a href="#Page_20">20</a>.</li> -<li class="isub3">at Albany, <a href="#Page_301">301</a>.</li> -<li class="isub3">analysis of European, <a href="#Page_25">25</a>.</li> -<li class="isub3">analysis of, from leading works, <a href="#Page_28">28</a>.</li> -<li class="isub3">appliances for moving, <a href="#Page_68">68</a>.</li> -<li class="isub3">compactness of, in natural banks, <a href="#Page_61">61</a>.</li> -<li class="isub3">depth of, in filters, <a href="#Page_34">34</a>.</li> -<li class="isub3">depth to be removed from filters, <a href="#Page_69">69</a>.</li> -<li class="isub3">dune, <a href="#Page_26">26</a>.</li> -<li class="isub3">dune, washing of, impossible, <a href="#Page_82">82</a>.</li> -<li class="isub3">effect of grain-size upon frequency of scraping, <a href="#Page_32">32</a>.</li> -<li class="isub3">effect of grain-size upon the efficiency, <a href="#Page_30">30</a>.</li> -<li class="isub3">effective size of, <a href="#Page_21">21</a>, <a href="#Page_238">238</a>.</li> -<li class="isub3">extra scraping before replacing fresh, <a href="#Page_71">71</a>.</li> -<li class="isub3">for filtration, <a href="#Page_20">20</a>, <a href="#Page_33">33</a>.</li> -<li class="isub3">for mechanical filters, <a href="#Page_175">175</a>.</li> -<li class="isub3">friction of water in, <a href="#Page_22">22</a>.</li> -<li class="isub3">grain-size of, <a href="#Page_20">20</a>, <a href="#Page_233">233</a>.</li> -<li class="isub3">in European filters, <a href="#Page_24">24</a>.</li> -<li class="isub3">in Lawrence filters, two sizes of, <a href="#Page_100">100</a>.</li> -<li class="isub3">lime in, <a href="#Page_29">29</a>.</li> -<li class="isub3">method of analysis of, <a href="#Page_233">233</a>.</li> -<li class="isub3">quantity to be removed by scraping, <a href="#Page_74">74</a>.</li> -<li class="isub3">replacing, <a href="#Page_71">71</a>.</li> -<li class="isub3">selection of, <a href="#Page_33">33</a>.</li> -<li class="isub3">size of passages between grains of, <a href="#Page_6">6</a>.</li> -<li class="isub3">sterilized, experiments with, <a href="#Page_85">85</a>.</li> -<li class="isub3">thickness of layer, <a href="#Page_34">34</a>.</li> -<li class="isub3">uniformity coefficient, <a href="#Page_21">21</a>, <a href="#Page_238">238</a>.</li> - -<li class="indx">Sand washing, <a href="#Page_26">26</a>, <a href="#Page_76">76</a>, <a href="#Page_304">304</a>.</li> -<li class="isub3">cost of, <a href="#Page_81">81</a>.</li> -<li class="isub3">water for, <a href="#Page_80">80</a>.</li> - -<li class="indx">Sandstone filters for household use, <a href="#Page_183">183</a>.</li> - -<li class="indx">Schiedam, double filtration at, <a href="#Page_273">273</a>.</li> - -<li class="indx">Scraping filters, <a href="#Page_7">7</a>, <a href="#Page_68">68</a>.</li> - -<li class="indx"><span class="pagenum" id="Page_321">[Pg 321]</span> Scraping filters, amount of labor required for, <a href="#Page_81">81</a>.</li> -<li class="isub3">depth of sand removed, <a href="#Page_33">33</a>, <a href="#Page_66">66</a>, <a href="#Page_69">69</a>.</li> -<li class="isub3">frequency of, <a href="#Page_49">49</a>, <a href="#Page_72">72</a>, <a href="#Page_241">241</a>.</li> - -<li class="indx">Sedgwick, Prof. W. T., <a href="#Page_86">86</a>.</li> - -<li class="indx">Sediment, removal of, <a href="#Page_92">92</a>, <a href="#Page_133">133</a>.</li> - -<li class="indx">Sediment layer, <a href="#Page_6">6</a>, <a href="#Page_31">31</a>.</li> -<li class="isub3">influence of, upon bacterial purification, <a href="#Page_84">84</a>.</li> -<li class="isub3">thickness of, <a href="#Page_33">33</a>, <a href="#Page_66">66</a>, <a href="#Page_69">69</a>.</li> - -<li class="indx">Sedimentation basins, <a href="#Page_8">8</a>, <a href="#Page_133">133</a>, <a href="#Page_293">293</a>.</li> -<li class="isub3">effect of, <a href="#Page_134">134</a>.</li> - -<li class="indx">Sewage, number of bacteria in, <a href="#Page_215">215</a>.</li> - -<li class="indx">Simpson, James, <a href="#Page_83">83</a>.</li> - -<li class="indx">Soda-ash, application of, <a href="#Page_157">157</a>.</li> - -<li class="indx">Somersworth, N. H., filters at, <a href="#Page_253">253</a>.</li> - -<li class="indx">Storage for raw water, <a href="#Page_136">136</a>.</li> - -<li class="indx">Subsidence, limits to the use of, <a href="#Page_142">142</a>.</li> - -<li class="indx">Sulphate of alumina, action of, upon waters, <a href="#Page_144">144</a>.</li> - -<li class="indx">Surface-waters, use of, unfiltered, <a href="#Page_275">275</a>.</li> - -<li class="indx">Suspended matters, <a href="#Page_113">113</a>, <a href="#Page_117">117</a>.</li> -<li class="isub3">in relation to turbidities, <a href="#Page_122">122</a>.</li> -<li class="isub3">in various waters, <a href="#Page_129">129</a>.</li> - -<li class="ifrst">The Hague, iron removal at, <a href="#Page_192">192</a>.</li> - -<li class="indx">Tokyo, regulation of rate at, <a href="#Page_58">58</a>.</li> - -<li class="indx">Trenched bottoms for filters, <a href="#Page_36">36</a>, <a href="#Page_40">40</a>, <a href="#Page_100">100</a>.</li> - -<li class="indx">Turbidity, <a href="#Page_92">92</a>, <a href="#Page_113">113</a>.</li> -<li class="isub3">amount which is noticeable, <a href="#Page_121">121</a>.</li> -<li class="isub3">amount in several streams, <a href="#Page_124">124</a>.</li> -<li class="isub3">duration of, <a href="#Page_128">128</a>.</li> -<li class="isub3">in relation to suspended matters, <a href="#Page_122">122</a>.</li> -<li class="isub3">measurement of, <a href="#Page_117">117</a>.</li> -<li class="isub3">power of sand filters to remove, <a href="#Page_139">139</a>.</li> -<li class="isub3">preliminary processes to remove, <a href="#Page_133">133</a>.</li> -<li class="isub3">source of, <a href="#Page_123">123</a>.</li> - -<li class="indx">Typhoid fever in Berlin and Altona, <a href="#Page_12">12</a>, <a href="#Page_85">85</a>, <a href="#Page_267">267</a>.</li> -<li class="isub3">in American cities, <a href="#Page_211">211</a>.</li> - -<li class="indx">Typhoid fever in Hamburg, <a href="#Page_271">271</a>.</li> -<li class="isub3">in Lawrence, <a href="#Page_102">102</a>.</li> -<li class="isub3">in London, <a href="#Page_259">259</a>.</li> -<li class="isub3">in Zürich, <a href="#Page_275">275</a>.</li> - -<li class="indx">Typhoid-fever germs, life of, in water, <a href="#Page_216">216</a>.</li> - -<li class="ifrst">Underdrains, <a href="#Page_35">35</a>, <a href="#Page_39">39</a>.</li> -<li class="isub3">bacteria from, <a href="#Page_87">87</a>.</li> -<li class="isub3">friction of, at Albany, <a href="#Page_299">299</a>.</li> -<li class="isub3">size of, <a href="#Page_41">41</a>.</li> -<li class="isub3">ventilators for, <a href="#Page_44">44</a>.</li> - -<li class="indx">Uniformity coefficient of sand, <a href="#Page_21">21</a>, <a href="#Page_238">238</a>.</li> - -<li class="ifrst">Ventilators for underdrains, <a href="#Page_44">44</a>.</li> - -<li class="indx">Vienna, water-supply of, from springs, <a href="#Page_276">276</a>.</li> - -<li class="ifrst">Warren filter, <a href="#Page_151">151</a>, <a href="#Page_161">161</a>, <a href="#Page_162">162</a>, <a href="#Page_172">172</a>, <a href="#Page_176">176</a>, <a href="#Page_177">177</a>.</li> - -<li class="indx">Warsaw, filters at, <a href="#Page_275">275</a>.</li> -<li class="isub3">friction in underdrains, <a href="#Page_43">43</a>.</li> -<li class="isub3">regulation of rate at, <a href="#Page_57">57</a>.</li> - -<li class="indx">Wasting effluents, <a href="#Page_74">74</a>.</li> - -<li class="indx">Water, depth of, on filters, <a href="#Page_45">45</a>, <a href="#Page_59">59</a>.</li> -<li class="isub3">heating of, in filters, <a href="#Page_45">45</a>.</li> -<li class="isub3">organic matters in, <a href="#Page_83">83</a>.</li> - -<li class="indx">Water-supplies of American cities, <a href="#Page_211">211</a>.</li> - -<li class="indx">Water-supply and disease, <a href="#Page_210">210</a>.</li> - -<li class="indx">Waters, what require filtration, <a href="#Page_207">207</a>.</li> - -<li class="indx">Weston, E. B., <a href="#Page_153">153</a>, <a href="#Page_154">154</a>, <a href="#Page_159">159</a>.</li> - -<li class="indx">Weston, R. S., <a href="#Page_153">153</a>, <a href="#Page_189">189</a>.</li> - -<li class="indx">West Superior, iron in ground-water at, <a href="#Page_189">189</a>.</li> - -<li class="indx">Winter, effect of, upon filtration, <a href="#Page_12">12</a>.</li> -<li class="isub3">temperatures of places having open and covered filters, <a href="#Page_15">15</a>.</li> - -<li class="indx">Worms tile system, <a href="#Page_181">181</a>.</li> - -<li class="ifrst">Zürich, filters at, <a href="#Page_274">274</a>.</li> -</ul> - -<p><span class="pagenum" id="Page_1A">[Pg 1]</span></p> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="chapter"> -<h2 class="nobreak" id="SHORT_TITLE_CATALOGUE"><span class="sansbold largest">SHORT-TITLE CATALOGUE</span><br /> - -<span class="smaller"><b>OF THE</b></span><br /> - -<span class="larger"><b>PUBLICATIONS</b></span><br /> - -<span class="smaller"><b>OF</b></span><br /> - -<span class="largest"><b>JOHN WILEY & SONS,</b></span><br /> - -<span class="sansbold smcap">New York.</span><br /> - -<span class="smcap small"><b>London: CHAPMAN & HALL, Limited.</b></span></h2></div> - -<p class="center padt1 padb1"><b>ARRANGED UNDER SUBJECTS.</b></p> - -<p class="small">Descriptive circulars sent on application. Books marked with an -asterisk (*) are sold at <em>net</em> prices only, a double asterisk (**) -books sold under the rules of the American Publishers’ Association at -<em>net</em> prices subject to an extra charge for postage. All books are -bound in cloth unless otherwise stated.</p> - -<table class="autotable" summary="advertismenta"> -<tr> -<th class="tdc normal" colspan="4">AGRICULTURE.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Armsby’s Manual of Cattle-feeding</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">$1 75</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Principles of Animal Nutrition</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Budd and Hansen’s American Horticultural Manual:</p></td> -<td class="tdr vertb"> </td> -<td class="tdr vertb"> </td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part I. Propagation, Culture, and Improvement</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Systematic Pomology</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Downing’s Fruits and Fruit-trees of America</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Elliott’s Engineering for Land Drainage</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Practical Farm Drainage</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Green’s Principles of American Forestry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl" colspan="2"><p class="indent">Grotenfelt’s Principles of Modern Dairy Practice. (Woll.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kemp’s Landscape Gardening</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Maynard’s Landscape Gardening as Applied to Home Decoration</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* McKay and Larsen’s Principles and Practice of Butter-making</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sanderson’s Insects Injurious to Staple Crops</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Insects Injurious to Garden Crops. (In preparation.)</p></td> -<td class="tdr vertb"> </td> -<td class="tdr vertb"> </td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Insects Injuring Fruits. (In preparation.)</p></td> -<td class="tdr vertb"> </td> -<td class="tdr vertb"> </td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Stockbridge’s Rocks and Soils</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Winton’s Microscopy of Vegetable Foods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Woll’s Handbook for Farmers and Dairymen</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 50</td> -</tr> - -<tr> -<th class="tdc normal" colspan="4">ARCHITECTURE.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Baldwin’s Steam Heating for Buildings</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bashore’s Sanitation of a Country House</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Berg’s Buildings and Structures of American Railroads</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Birkmire’s Planning and Construction of American Theatres</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Architectural Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Compound Riveted Girders as Applied in Buildings</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Planning and Construction of High Office Buildings</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Skeleton Construction in Buildings</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Brigg’s Modern American School Buildings</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Carpenter’s Heating and Ventilating of Buildings</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Freitag’s Architectural Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Fireproofing of Steel Buildings</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">French and Ives’s Stereotomy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_2A">[Pg 2]</span> -<p class="indent">Gerhard’s Guide to Sanitary House-inspection</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Theatre Fires and Panics</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Greene’s Structural Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Holly’s Carpenters’ and Joiners’ Handbook</p></td> -<td class="tdr vertb">18mo,</td> -<td class="tdr vertb">75</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s Statics by Algebraic and Graphic Methods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kidder’s Architects’ and Builders’ Pocket-book. Rewritten Edition</p></td> -<td class="tdr vertb">16mo, mor.,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merrill’s Stones for Building and Decoration</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Non-metallic Minerals: Their Occurrence and Uses</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Monckton’s Stair-building</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Patton’s Practical Treatise on Foundations</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Peabody’s Naval Architecture</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richey’s Handbook for Superintendents of Construction</p></td> -<td class="tdr vertb">16mo, mor.,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sabin’s Industrial and Artistic Technology of Paints and Varnish</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Siebert and Biggin’s Modern Stone-cutting and Masonry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Snow’s Principal Species of Wood</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sondericker’s Graphic Statics With Applications To Trusses, Beams, and Arches</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Towne’s Locks and Builders’ Hardware</p></td> -<td class="tdr vertb">18mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wait’s Engineering and Architectural Jurisprudence</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"> </td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">6 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Law of Operations Preliminary To Construction in Engineering and -Architecture</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"> </td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">5 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Law of Contracts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s Rustless Coatings: Corrosion and Electrolysis of Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Worcester and Atkinson’s Small Hospitals, Establishment and Maintenance, -Suggestions for Hospital Architecture, with Plans for a Small Hospital</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">The World’s Columbian Exposition of 1893</p></td> -<td class="tdr vertb">Large 4to,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> -<th class="tdc normal" colspan="4">ARMY AND NAVY.</th> -</tr> -<tr> -<td class="tdl vertt" colspan="2"><p class="indent">Bernadou’s Smokeless Powder, Nitro-cellulose, and the Theory of the Cellulose Molecule</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bruff’s Text-book Ordnance and Gunnery</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Chase’s Screw Propellers and Marine Propulsion</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Cloke’s Gunner’s Examiner</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Craig’s Azimuth</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Crehore and Squier’s Polarizing Photo-chronograph</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Davis’s Elements of Law</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Treatise on the Military Law of United States</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"> </td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">De Brack’s Cavalry Outposts Duties. (Carr.)</p></td> -<td class="tdr vertb">24mo, morocco,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dietz’s Soldier’s First Aid Handbook</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Dredge’s Modern French Artillery</p></td> -<td class="tdr vertb">4to, half morocco,</td> -<td class="tdr vertb">15 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Durand’s Resistance and Propulsion of Ships</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Dyer’s Handbook of Light Artillery</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Eissler’s Modern High Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Fiebeger’s Text-book on Field Fortification</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hamilton’s The Gunner’s Catechism</p></td> -<td class="tdr vertb">18mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Hoff’s Elementary Naval Tactics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ingalls’s Handbook of Problems in Direct Fire</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Ballistic Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Lyons’s Treatise on Electromagnetic Phenomena.</p></td> -<td class="tdr vertb">Vols. I. and II. 8vo, each,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Mahan’s Permanent Fortifications. (Mercur.)</p></td> -<td class="tdr vertb">8vo, half morocco,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Manual for Courts-martial</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Mercur’s Attack of Fortified Places</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Elements of the Art of War</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_3A">[Pg 3]</span> -<p class="indent">Metcalf’s Cost of Manufactures—And the Administration of Workshops</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Ordnance and Gunnery. 2 vols</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Murray’s Infantry Drill Regulations</p></td> -<td class="tdr vertb">18mo, paper,</td> -<td class="tdr vertb">10</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Nixon’s Adjutants’ Manual</p></td> -<td class="tdr vertb">24mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Peabody’s Naval Architecture</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Phelps’s Practical Marine Surveying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Powell’s Army Officer’s Examiner</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sharpe’s Art of Subsisting Armies in War</p></td> -<td class="tdr vertb">18mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Walke’s Lectures on Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Wheeler’s Siege Operations and Military Mining</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Winthrop’s Abridgment of Military Law</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Woodhull’s Notes on Military Hygiene</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Young’s Simple Elements of Navigation</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> -<th class="tdc normal" colspan="4">ASSAYING.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fletcher’s Practical Instructions in Quantitative Assaying with the Blowpipe</p></td> -<td class="tdr vertb">12mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Furman’s Manual of Practical Assaying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Lodge’s Notes on Assaying and Metallurgical Laboratory Experiments</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Low’s Technical Methods of Ore Analysis</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Miller’s Manual of Assaying</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Minet’s Production of Aluminum and its Industrial Use. (Waldo.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">O’Driscoll’s Notes on the Treatment of Gold Ores</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ricketts and Miller’s Notes on Assaying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Robine and Lenglen’s Cyanide Industry. (Le Clerc.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb"> </td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ulke’s Modern Electrolytic Copper Refining</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s Cyanide Processes</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Chlorination Process</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> -<th class="tdc normal" colspan="4">ASTRONOMY.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Comstock’s Field Astronomy for Engineers</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Craig’s Azimuth</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Doolittle’s Treatise on Practical Astronomy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Gore’s Elements of Geodesy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hayford’s Text-book of Geodetic Astronomy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman’s Elements of Precise Surveying and Geodesy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Michie and Harlow’s Practical Astronomy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* White’s Elements of Theoretical and Descriptive Astronomy</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> -<th class="tdc normal" colspan="4">BOTANY.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Davenport’s Statistical Methods, with Special Reference to Biological Variation</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thomé and Bennett’s Structural and Physiological Botany</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">2 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Westermaier’s Compendium of General Botany. (Schneider.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> -<th class="tdc normal" colspan="4">CHEMISTRY.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Adriance’s Laboratory Calculations and Specific Gravity Tables</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Allen’s Tables for Iron Analysis</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Arnold’s Compendium of Chemistry. (Mandel</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Austen’s Notes for Chemical Students</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bernadou’s Smokeless Powder.—Nitro-cellulose, and Theory of the Cellulose Molecule</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Browning’s Introduction to the Rarer Elements</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_4A">[Pg 4]</span> -<p class="indent">Brush and Penfield’s Manual of Determinative Mineralogy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Classen’s Quantitative Chemical Analysis by Electrolysis. (Boltwood.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Cohn’s Indicators and Test-papers</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Tests and Reagents</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Crafts’s Short Course in Qualitative Chemical Analysis. (Schaeffer.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dolezalek’s Theory of the Lead Accumulator (Storage Battery). (Von -Ende.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Drechsel’s Chemical Reactions. (Merrill.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Duhem’s Thermodynamics and Chemistry. (Burgess.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Eissler’s Modern High Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Effront’s Enzymes and their Applications. (Prescott.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Erdmann’s Introduction to Chemical Preparations. (Dunlap.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fletcher’s Practical Instructions in Quantitative Assaying with the Blowpipe.</p></td> -<td class="tdr vertb">12mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fowler’s Sewage Works Analyses</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fresenius’s Manual of Qualitative Chemical Analysis. (Wells.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Manual of Qualitative Chemical Analysis. Part I. Descriptive. (Wells.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">System of Instruction in Quantitative Chemical Analysis. (Cohn.) 2 vols</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">12 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fuertes’s Water and Public Health</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Furman’s Manual of Practical Assaying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Getman’s Exercises in Physical Chemistry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Gill’s Gas and Fuel Analysis for Engineers</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Grotenfelt’s Principles of Modern Dairy Practice. (Woll.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hammarsten’s Text-book of Physiological Chemistry. (Mandel.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Helm’s Principles of Mathematical Chemistry. (Morgan.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hering’s Ready Reference Tables (Conversion Factors)</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hind’s Inorganic Chemistry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Laboratory Manual for Students</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Holleman’s Text-book of Inorganic Chemistry. (Cooper.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Text-book of Organic Chemistry. (Walker and Mott.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Laboratory Manual of Organic Chemistry. (Walker.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hopkins’s Oil-chemists’ Handbook</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Jackson’s Directions for Laboratory Work in Physiological Chemistry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Keep’s Cast Iron</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ladd’s Manual of Quantitative Chemical Analysis</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Landauer’s Spectrum Analysis. (Tingle.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Langworthy and Austen. -The Occurrence of Aluminium in Vegetable -Products, Animal Products, and Natural Waters</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Lassar-Cohn’s Practical Urinary Analysis. (Lorenz.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Application of Some General Reactions to Investigations in Organic Chemistry. (Tingle.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Leach’s The Inspection and Analysis of Food with Special Reference to State Control</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Löb’s Electrochemistry of Organic Compounds. (Lorenz.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Lodge’s Notes on Assaying and Metallurgical Laboratory Experiments</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Low’s Technical Method of Ore Analysis</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Lunge’s Techno-chemical Analysis. (Cohn.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mandel’s Handbook for Bio-chemical Laboratory</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Martin’s Laboratory Guide to Qualitative Analysis with the Blowpipe</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">60</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mason’s Water-supply. (Considered Principally from a Sanitary Standpoint.) -3d Edition, Rewritten</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Examination of Water. (Chemical and Bacteriological.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Matthew’s The Textile Fibres</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Meyer’s Determination of Radicles in Carbon Compounds. (Tingle.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Miller’s Manual of Assaying</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Minet’s Production of Aluminum and its Industrial Use. (Waldo.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mixter’s Elementary Text-book of Chemistry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Morgan’s Elements of Physical Chemistry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">* Physical Chemistry for Electrical Engineers</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_5A">[Pg 5]</span><p class="indent">Morse’s Calculations used in Cane-sugar Factories</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mulliken’s General Method for the Identification of Pure Organic Compounds. Vol. I.</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">O’Brine’s Laboratory Guide in Chemical Analysis</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">O’Driscoll’s Notes on the Treatment of Gold Ores</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ostwald’s Conversations on Chemistry. Part One. (Ramsey.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ostwald’s Conversations on Chemistry. Part Two. (Turnbull.)</p></td> -<td class="tdr vertb">12mo, 2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Penfield’s Notes on Determinative Mineralogy and Record of Mineral Tests</p></td> -<td class="tdr vertb">8vo, paper,</td> -<td class="tdr vertb">50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Pictet’s The Alkaloids and their Chemical Constitution. (Biddle.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Pinner’s Introduction to Organic Chemistry. (Austen.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Poole’s Calorific Power of Fuels</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Prescott and Winslow’s Elements of Water Bacteriology, with Special -Reference to Sanitary Water Analysis</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Reisig’s Guide to Piece-dyeing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">25 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richards and Woodman’s Air, Water, and Food from a Sanitary Standpoint</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richards’s Cost of Living as Modified by Sanitary Science</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Cost of Food, a Study in Dietaries</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Richards and Williams’s The Dietary Computer</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ricketts and Russell’s Skeleton Notes upon Inorganic Chemistry. (Part I. Non-metallic Elements.)</p></td> -<td class="tdr vertb">8vo, morocco,</td> -<td class="tdr vertb">75</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ricketts and Miller’s Notes on Assaying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rideal’s Sewage and the Bacterial Purification of Sewage</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Disinfection and the Preservation of Food</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rigg’s Elementary Manual for the Chemical Laboratory</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Robine and Lenglen’s Cyanide Industry. (Le Clerc.)</p></td> -<td class="tdr vertb">8vo,</td> -<td> </td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rostoski’s Serum Diagnosis. (Bolduan.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ruddiman’s Incompatibilities in Prescriptions</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Whys in Pharmacy</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sabin’s Industrial and Artistic Technology of Paints and Varnish</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Salkowski’s Physiological and Pathological Chemistry. (Orndorff.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Schimpf’s Text-book of Volumetric Analysis</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Essentials of Volumetric Analysis</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Qualitative Chemical Analysis</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Spencer’s Handbook for Chemists of Beet-sugar Houses</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Handbook for Cane Sugar Manufacturers</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Stockbridge’s Rocks and Soils</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Tillman’s Elementary Lessons in Heat</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Descriptive General Chemistry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Treadwell’s Qualitative Analysis. (Hall.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Quantitative Analysis. (Hall.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Turneaure and Russell’s Public Water-supplies</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Van Deventer’s Physical Chemistry for Beginners. (Boltwood.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Walke’s Lectures on Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ware’s Beet-sugar Manufacture and Refining</p></td> -<td class="tdr vertb">Small 8vo, cloth,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Washington’s Manual of the Chemical Analysis of Rocks</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wassermann’s Immune Sera: Hæmolysins, Cytotoxins, and Precipitins. (Bolduan.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Well’s Laboratory Guide in Qualitative Chemical Analysis</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Short Course in Inorganic Qualitative Chemical Analysis for Engineering Students</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Text-book of Chemical Arithmetic</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Whipple’s Microscopy of Drinking-water</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s Cyanide Processes</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Chlorination Process</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Winton’s Microscopy of Vegetable Foods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wulling’s Elementary Course in Inorganic, Pharmaceutical, and Medical Chemistry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> -<th class="tdc normal" colspan="4"><span class="pagenum" id="Page_6A">[Pg 6]</span>CIVIL ENGINEERING.</th> -</tr> -<tr> -<th class="tdc small normal" colspan="4">BRIDGES AND ROOFS. HYDRAULICS. MATERIALS OF ENGINEERING.<br />RAILWAY ENGINEERING.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Baker’s Engineers’ Surveying Instruments</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bixby’s Graphical Computing Table</p></td> -<td class="tdr vertb">Paper 19<sup>1</sup>⁄<sub>2</sub> × 24<sup>1</sup>⁄<sub>4</sub> inches.</td> -<td class="tdr vertb">25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">** Burr’s Ancient and Modern Engineering and the Isthmian Canal. (Postage, 27 cents additional.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdr" colspan="2"><p class="indent">Comstock’s Field Astronomy for Engineers</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Davis’s Elevation and Stadia Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Elliott’s Engineering for Land Drainage</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Practical Farm Drainage</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdr" colspan="2"><p class="indent">* Fiebeger’s Treatise on Civil Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Folwell’s Sewerage. (Designing and Maintenance.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Freitag’s Architectural Engineering. 2d Edition, Rewritten</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">French and Ives’s Stereotomy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Goodhue’s Municipal Improvements</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 75</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Goodrich’s Economic Disposal of Towns’ Refuse</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Gore’s Elements of Geodesy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hayford’s Text-book of Geodetic Astronomy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hering’s Ready Reference Tables (Conversion Factors)</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Howe’s Retaining Walls for Earth</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s (J. B.) Theory and Practice of Surveying</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s (L. J.) Statics by Algebraic and Graphic Methods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Laplace’s Philosophical Essay on Probabilities. (Truscott and Emory.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mahan’s Treatise on Civil Engineering. (1873.) (Wood.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Descriptive Geometry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman’s Elements of Precise Surveying and Geodesy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman and Brooks’s Handbook for Surveyors</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Nugent’s Plane Surveying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ogden’s Sewer Design</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Patton’s Treatise on Civil Engineering</p></td> -<td class="tdr vertb">8vo half leather,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Reed’s Topographical Drawing and Sketching</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rideal’s Sewage and the Bacterial Purification of Sewage</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Siebert and Biggin’s Modern Stone-cutting and Masonry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s Manual of Topographical Drawing. (McMillan.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sondericker’s Graphic Statics, with Applications to Trusses, Beams, and Arches.</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Taylor and Thompson’s Treatise on Concrete, Plain and Reinforced</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Trautwine’s Civil Engineer’s Pocket-book</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wait’s Engineering and Architectural Jurisprudence</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td> </td> -<td> </td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">6 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Law of Operations Preliminary to Construction in Engineering and Architecture</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"> </td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">5 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Law of Contracts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Warren’s Stereotomy—Problems in Stone-cutting</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Webb’s Problems in the Use and Adjustment of Engineering Instruments.</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s Topographic Surveying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> -<th class="tdc normal small" colspan="4">BRIDGES AND ROOFS.</th> -</tr> -<tr> -<td class="tdl vertt" colspan="2"><p class="indent">Boller’s Practical Treatise on the Construction of Iron Highway Bridges</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Thames River Bridge</p></td> -<td class="tdr vertb">4to, paper,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Burr’s Course on the Stresses in Bridges and Roof Trusses, Arched Ribs, and Suspension Bridges</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_7A">[Pg 7]</span> -<p class="indent">Burr and Falk’s Influence Lines for Bridge and Roof Computations</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Design and Construction of Metallic Bridges</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Du Bois’s Mechanics of Engineering. Vol. II.</p></td> -<td class="tdr vertb">Small 4to,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Foster’s Treatise on Wooden Trestle Bridges</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fowler’s Ordinary Foundations</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Greene’s Roof Trusses</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Bridge Trusses</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Arches in Wood, Iron, and Stone</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Howe’s Treatise on Arches</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Design of Simple Roof-trusses in Wood and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson, Bryan, and Turneaure’s Theory and Practice in the Designing of -Modern Framed Structures</p></td> -<td class="tdr vertb">Small 4to,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman and Jacoby’s Text-book on Roofs and Bridges:</p></td> -<td> </td> -<td> </td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part I. Stresses in Simple Trusses</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Graphic Statics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part III. Bridge Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb"> 2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part IV. Higher Structures</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Morison’s Memphis Bridge</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Waddell’s de Pontibus, a Pocket-book for Bridge Engineers</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Specifications for Steel Bridges</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wright’s Designing of Draw-spans. Two Parts in one volume</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<th class="tdc normal small" colspan="4">HYDRAULICS.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bazin’s Experiments upon the Contraction of the Liquid Vein Issuing from -an Orifice. (Trautwine.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bovey’s Treatise on Hydraulics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Church’s Mechanics of Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Diagrams of Mean Velocity of Water in Open Channels</p></td> -<td class="tdr vertb">paper,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Hydraulic Motors</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Coffin’s Graphical Solution of Hydraulic Problems</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Flather’s Dynamometers, and the Measurement of Power</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Folwell’s Water-supply Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Frizell’s Water-power</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fuertes’s Water and Public Health</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Water-filtration Works</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ganguillet and Kutter’s General Formula for the Uniform Flow of Water in -Rivers and Other Channels. (Hering and Trautwine.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hazen’s Filtration of Public Water-supply</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hazlehurst’s Towers and Tanks for Water-works</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Herschel’s 115 Experiments on the Carrying Capacity of Large, Riveted, Metal Conduits</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mason’s Water-supply. (Considered Principally From a Sanitary Standpoint.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman’s Treatise on Hydraulics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Michie’s Elements of Analytical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Schuyler’s Reservoirs for Irrigation, Water-power, and Domestic -Water-supply</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">** Thomas and Watt’s Improvement of Rivers.</p></td> -<td class="tdr vertb">(Post., 44c. additional.) 4to,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Turneaure and Russell’s Public Water-supplies</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wegmann’s Design and Construction of Dams</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Water-supply of the City of New York From 1658 to 1895</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Williams and Hazen’s Hydraulic Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s Irrigation Engineering</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wolff’s Windmill as a Prime Mover</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s Turbines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Elements of Analytical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> -<th class="tdc normal small" colspan="4"><span class="pagenum" id="Page_8A">[Pg 8]</span>MATERIALS OF ENGINEERING.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Baker’s Treatise on Masonry Construction</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Roads and Pavements</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Black’s United States Public Works</p></td> -<td class="tdr vertb">Oblong 4to,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bovey’s Strength of Materials and Theory of Structures</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Burr’s Elasticity and Resistance of the Materials of Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Byrne’s Highway Construction</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Inspection of the Materials and Workmanship Employed in Construction.</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Church’s Mechanics of Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Du Bois’s Mechanics of Engineering. Vol. I.</p></td> -<td class="tdr vertb">Small 4to,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Eckel’s Cements, Limes, and Plasters</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s Materials of Construction</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fowler’s Ordinary Foundations</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Greene’s Structural Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Keep’s Cast Iron</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Lanza’s Applied Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Marten’s Handbook on Testing Materials. (Henning.) 2 vols.</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Maurer’s Technical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merrill’s Stones for Building and Decoration</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman’s Mechanics of Materials</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Strength of Materials</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Metcalf’s Steel. A Manual for Steel-users</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Patton’s Practical Treatise on Foundations</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richardson’s Modern Asphalt Pavements</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richey’s Handbook for Superintendents of Construction</p></td> -<td class="tdr vertb">16mo, mor.,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rockwell’s Roads and Pavements in France</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sabin’s Industrial and Artistic Technology of Paints and Varnish</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s Materials of Machines</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Snow’s Principal Species of Wood</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Spalding’s Hydraulic Cement</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Text-book on Roads and Pavements</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Taylor and Thompson’s Treatise on Concrete, Plain and Reinforced</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Materials of Engineering. 3 Parts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">8 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part I. Non-metallic Materials of Engineering and Metallurgy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their Constituents</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Text-book of the Materials of Construction</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Tillson’s Street Pavements and Paving Materials</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Waddell’s De Pontibus. (A Pocket-book for Bridge Engineers.)</p></td> -<td class="tdr vertb">16mo, mor.,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Specifications for Steel Bridges</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s (De V.) Treatise on the Resistance of Materials, and an Appendix on -the Preservation of Timber</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s (De V.) Elements of Analytical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<th class="tdc small normal" colspan="4">RAILWAY ENGINEERING.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Andrew’s Handbook for Street Railway Engineers</p></td> -<td class="tdr vertb">3×5 inches, morocco,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Berg’s Buildings and Structures of American Railroads</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Brook’s Handbook of Street Railroad Location</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Butt’s Civil Engineer’s Field-book</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Crandall’s Transition Curve</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Railway and Other Earthwork Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dawson’s “Engineering” and Electric Traction Pocket-book</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_9A">[Pg 9]</span><p class="indent">Dredge’s History of the Pennsylvania Railroad: (1879)</p></td> -<td class="tdr vertb">Paper,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Drinker’s Tunnelling, Explosive Compounds, and Rock Drills</p></td> -<td class="tdr vertb">4to, half mor.,</td> -<td class="tdr vertb">25 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fisher’s Table of Cubic Yards</p></td> -<td class="tdr vertb">Cardboard,</td> -<td class="tdr vertb">25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Godwin’s Railroad Engineers’ Field-book and Explorers’ Guide</p></td> -<td class="tdr vertb">16mo, mor.,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Howard’s Transition Curve Field-book</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hudson’s Tables for Calculating the Cubic Contents of Excavations and Embankments</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Molitor and Beard’s Manual for Resident Engineers</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Nagle’s Field Manual for Railroad Engineers</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Philbrick’s Field Manual for Engineers</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Searles’s Field Engineering</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Railroad Spiral</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Taylor’s Prismoidal Formulæ and Earthwork</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Trautwine’s Method of Calculating the Cube Contents of Excavations and Embankments by the Aid of Diagrams</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">The Field Practice of Laying Out Circular Curves for Railroads.</p></td> -<td class="tdr vertb">12mo, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Cross-section Sheet</p></td> -<td class="tdr vertb">Paper,</td> -<td class="tdr vertb">25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Webb’s Railroad Construction</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wellington’s Economic Theory of the Location of Railways</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">DRAWING.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Barr’s Kinematics of Machinery</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bartlett’s Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bartlett’s Mechanical Drawing Abridged Ed.</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Coolidge’s Manual of Drawing</p></td> -<td class="tdr vertb">8vo, paper,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Coolidge and Freeman’s Elements of General Drafting for Mechanical Engineers</p></td> -<td class="tdr vertb">Oblong 4to,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Durley’s Kinematics of Machines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Emch’s Introduction to Projective Geometry and its Applications</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hill’s Text-book on Shades and Shadows, and Perspective</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Jamison’s Elements of Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Advanced Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Jones’s Machine Design:</p></td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part I. Kinematics of Machinery</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Form, Strength, and Proportions of Parts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">MacCord’s Elements of Descriptive Geometry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Kinematics; or, Practical Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Mechanical Drawing</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Velocity Diagrams</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">MacLeod’s Descriptive Geometry</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Mahan’s Descriptive Geometry and Stone-cutting</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Industrial Drawing. (Thompson.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Moyer’s Descriptive Geometry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Reed’s Topographical Drawing and Sketching</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Reid’s Course in Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Text-book of Mechanical Drawing and Elementary Machine Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Robinson’s Principles of Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Schwamb and Merrill’s Elements of Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s (R. S.) Manual of Topographical Drawing. (McMillan.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith (A. W.) and Marx’s Machine Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Warren’s Elements of Plane and Solid Free-hand Geometrical Drawing</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Drafting Instruments and Operations</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Manual of Elementary Projection Drawing</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Manual of Elementary Problems in the Linear Perspective of Form and Shadow</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Plane Problems in Elementary Geometry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_10A">[Pg 10]</span><p class="indent">Warren’s Primary Geometry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">75</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Elements of Descriptive Geometry, Shadows, and Perspective</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">General Problems of Shades and Shadows</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Elements of Machine Construction and Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Problems, Theorems, and Examples in Descriptive Geometry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Weisbach’s Kinematics and Power of Transmission. (Hermann and Klein.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Whelpley’s Practical Instruction in the Art of Letter Engraving</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s (H. M.) Topographic Surveying</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s (V. T.) Free-hand Perspective</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s (V. T.) Free-hand Lettering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Woolf’s Elementary Course in Descriptive Geometry</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">3 00</td> - -</tr> -<tr> -<th class="tdc normal" colspan="4">ELECTRICITY AND PHYSICS.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Anthony and Brackett’s Text-book of Physics. (Magie.)</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Anthony’s Lecture-notes on the Theory of Electrical Measurements</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Benjamin’s History of Electricity</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Voltaic Cell</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Classen’s Quantitative Chemical Analysis by Electrolysis. (Boltwood.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Crehore and Squier’s Polarizing Photo-chronograph</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dawson’s “Engineering” and Electric Traction Pocket-book</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dolezalek’s Theory of the Lead Accumulator (Storage Battery). (Von Ende.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Duhem’s Thermodynamics and Chemistry. (Burgess.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Flather’s Dynamometers, and the Measurement of Power</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Gilbert’s De Magnete. (Mottelay.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hanchett’s Alternating Currents Explained</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hering’s Ready Reference Tables (Conversion Factors)</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Holman’s Precision of Measurements</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Telescopic Mirror-scale Method, Adjustments, and Tests</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">75</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kinzbrunner’s Testing of Continuous-current Machines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Landauer’s Spectrum Analysis. (Tingle.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Le Chatelier’s High-temperature Measurements. (Boudouard—Burgess.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Löb’s Electrochemistry of Organic Compounds. (Lorenz.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Lyon’s Treatise on Electromagnetic Phenomena. Vols. I. and II.</p></td> -<td class="tdr vertb">8vo, each,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Michie’s Elements of Wave Motion Relating to Sound and Light</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Niaudet’s Elementary Treatise on Electric Batteries. (Fishback.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Rosenberg’s Electrical Engineering. (Haldane Gee—Kinzbrunner.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ryan, Norris, and Hoxie’s Electrical Machinery. Vol. I.</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Stationary Steam-engines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Tillman’s Elementary Lessons in Heat</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Tory and Pitcher’s Manual of Laboratory Physics</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ulke’s Modern Electrolytic Copper Refining</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> - -</tr> -<tr> -<th class="tdc normal" colspan="4">LAW.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Davis’s Elements of Law</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Treatise on the Military Law of United States</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2">*</td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Manual for Courts-martial</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wait’s Engineering and Architectural Jurisprudence</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2">*</td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">6 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Law of Operations Preliminary to Construction in Engineering and Architecture</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"> </td> -<td class="tdr vertb">Sheep,</td> -<td class="tdr vertb">5 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Law of Contracts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Winthrop’s Abridgment of Military Law</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4"><span class="pagenum" id="Page_11A">[Pg 11]</span>MANUFACTURES.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bernadou’s Smokeless Powder—Nitro-cellulose and Theory of the Cellulose Molecule</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bolland’s Iron Founder</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">“The Iron Founder,” Supplement</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Encyclopedia of Founding and Dictionary of Foundry Terms Used in the Practice of Moulding</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Eissler’s Modern High Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Effront’s Enzymes and their Applications. (Prescott.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fitzgerald’s Boston Machinist</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ford’s Boiler Making for Boiler Makers</p></td> -<td class="tdr vertb">18mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hopkin’s Oil-chemists’ Handbook</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Keep’s Cast Iron</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Leach’s The Inspection and Analysis of Food with Special Reference to State Control</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Matthews’s The Textile Fibres</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Metcalf’s Steel. A Manual for Steel-users</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Metcalfe’s Cost of Manufactures—And the Administration of Workshops</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Meyer’s Modern Locomotive Construction</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Morse’s Calculations used in Cane-sugar Factories</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Reisig’s Guide to Piece-dyeing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">25 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sabin’s Industrial and Artistic Technology of Paints and Varnish</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s Press-working of Metals</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Spalding’s Hydraulic Cement</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Spencer’s Handbook for Chemists of Beet-sugar Houses</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Handbook for Cane Sugar Manufacturers</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Taylor and Thompson’s Treatise on Concrete, Plain and Reinforced</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Manual of Steam-boilers, their Designs, Construction and Operation</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Walke’s Lectures on Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ware’s Beet-sugar Manufacture and Refining</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">West’s American Foundry Practice</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Moulder’s Text-book</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wolff’s Windmill as a Prime Mover</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s Rustless Coatings: Corrosion and Electrolysis of Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">MATHEMATICS.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Baker’s Elliptic Functions</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bass’s Elements of Differential Calculus</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Briggs’s Elements of Plane Analytic Geometry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Compton’s Manual of Logarithmic Computations</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Davis’s Introduction to the Logic of Algebra</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Dickson’s College Algebra</p></td> -<td class="tdr vertb">Large 12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt"><p class="indent">Introduction to the Theory of Algebraic Equations</p></td> -<td class="tdr vertb">Large 12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Emch’s Introduction to Projective Geometry and its Applications</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Halsted’s Elements of Geometry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 75</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Elementary Synthetic Geometry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Rational Geometry</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 75</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Johnson’s (J. B.) Three-place Logarithmic Tables:</p></td> -<td class="tdr vertb">Vest-pocket size paper,</td> -<td class="tdr vertb">15</td> -</tr> -<tr> -<td class="tdl vertt" colspan="2"> </td> -<td class="tdr vertb">100 copies for</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdr" colspan="2">Mounted on heavy cardboard, 8 × 10 inches,</td> -<td class="tdr vertb">25</td> -</tr> -<tr> - -<td class="tdr" colspan="3">10 copies for</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s (W. W.) Elementary Treatise on Differential Calculus</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_12A">[Pg 12]</span><p class="indent">Johnson’s (W. W.) Elementary Treatise on the Integral Calculus</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s (W. W.) Curve Tracing in Cartesian Co-ordinates</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s (W. W.) Treatise on Ordinary and Partial Differential Equations</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s (W. W.) Theory of Errors and the Method of Least Squares</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Johnson’s (W. W.) Theoretical Mechanics</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Laplace’s Philosophical Essay on Probabilities. (Truscott and Emory.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Ludlow and Bass. Elements of Trigonometry and Logarithmic and Other Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Trigonometry and Tables published separately</p></td> -<td class="tdr vertb">Each,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Ludlow’s Logarithmic and Trigonometric Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mathematical Monographs. Edited by Mansfield Merriman and Robert S. Woodward</p></td> -<td class="tdr vertb">Octavo,</td> -<td class="tdr vertb">each 1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt">No. 1. History of Modern Mathematics, by David Eugene Smith. -No. 2. Synthetic Projective Geometry, by George Bruce Halsted. -No. 3. Determinants, by Laenas Gifford Weld. -No. 4. Hyperbolic Functions, by James McMahon. -No. 5. Harmonic Functions, by William E. Byerly. -No. 6. Grassmann’s Space Analysis, by Edward W. Hyde. -No. 7. Probability and Theory of Errors, by Robert S. Woodward. -No. 8. Vector Analysis and Quaternions, by Alexander Macfarlane. -No. 9. Differential Equations, by William Woolsey Johnson. -No. 10. The Solution of Equations, by Mansfield Merriman. -No. 11. Functions of a Complex Variable, by Thomas S. Fiske.</td> -<td> </td> -<td> </td></tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Maurer’s Technical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman and Woodward’s Higher Mathematics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman’s Method of Least Squares</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rice and Johnson’s Elementary Treatise on the Differential Calculus</p></td> -<td class="tdr vertb">Sm. 8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Differential and Integral Calculus. 2 vols. in one</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s Elements of Co-ordinate Geometry</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Trigonometry: Analytical, Plane, and Spherical</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">MECHANICAL ENGINEERING.</th> -</tr> -<tr> -<th class="tdc normal small" colspan="4">MATERIALS OF ENGINEERING, STEAM-ENGINES AND BOILERS.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bacon’s Forge Practice</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Baldwin’s Steam Heating for Buildings</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Barr’s Kinematics of Machinery</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bartlett’s Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bartlett’s Mechanical Drawing Abridged Ed</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Benjamin’s Wrinkles and Recipes</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Carpenter’s Experimental Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Heating and Ventilating Buildings</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="4"><p class="indent">Cary’s Smoke Suppression in Plants using Bituminous Coal. (In Preparation.)</p></td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Clerk’s Gas and Oil Engine</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Coolidge’s Manual of Drawing</p></td> -<td class="tdr vertb">8vo, paper,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Coolidge and Freeman’s Elements of General Drafting for Mechanical Engineers</p></td> -<td class="tdr vertb">Oblong 4to,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Cromwell’s Treatise on Toothed Gearing</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Treatise on Belts and Pulleys</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Durley’s Kinematics of Machines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Flather’s Dynamometers and the Measurement of Power</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Rope Driving</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Gill’s Gas and Fuel Analysis for Engineers</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hall’s Car Lubrication</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hering’s Ready Reference Tables (Conversion Factors)</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_13A">[Pg 13]</span><p class="indent">Hutton’s The Gas Engine</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Jamison’s Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="4">Jones’s Machine Design:</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part I. Kinematics of Machinery</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Form, Strength, and Proportions of Parts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kent’s Mechanical Engineers’ Pocket-book</p></td> -<td class="tdr vertb">16mo, morocco,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kerr’s Power and Power Transmission</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Leonard’s Machine Shop, Tools, and Methods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Lorenz’s Modern Refrigerating Machinery. (Pope, Haven, and Dean.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">MacCord’s Kinematics; or, Practical Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Mechanical Drawing</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Velocity Diagrams</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">MacFarland’s Standard Reduction Factors for Gases</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mahan’s Industrial Drawing. (Thompson.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Poole’s Calorific Power of Fuels</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Reid’s Course in Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Text-book of Mechanical Drawing and Elementary Machine Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richard’s Compressed Air</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Robinson’s Principles of Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Schwamb and Merrill’s Elements of Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s (O.) Press-working of Metals</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith (A. W.) and Marx’s Machine Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Treatise on Friction and Lost Work in Machinery and Mill Work</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Animal as a Machine and Prime Motor, and the Laws of Energetics</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Warren’s Elements of Machine Construction and Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Weisbach’s Kinematics and the Power of Transmission. (Herrmann—Klein.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Machinery of Transmission and Governors. (Herrmann—Klein.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wolff’s Windmill as a Prime Mover</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s Turbines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">MATERIALS OF ENGINEERING.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bovey’s Strength of Materials and Theory of Structures</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Burr’s Elasticity and Resistance of the Materials of Engineering. 6th Edition. Reset</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Church’s Mechanics of Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Greene’s Structural Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s Materials of Construction</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Keep’s Cast Iron</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Lanza’s Applied Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Martens’s Handbook on Testing Materials. (Henning.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Maurer’s Technical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman’s Mechanics of Materials</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Strength of Materials</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Metcalf’s Steel. A manual for Steel-users</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sabin’s Industrial and Artistic Technology of Paints and Varnish</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s Materials of Machines</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Materials of Engineering 3 vols.,</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">8 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their Constituents</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Text-book of the Materials of Construction</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s (De V.) Treatise on the Resistance of Materials and an Appendix on the Preservation of Timber</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_14A">[Pg 14]</span><p class="indent">Wood’s (De V.) Elements of Analytical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s (M. P.) Rustless Coatings: Corrosion and Electrolysis of Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">STEAM-ENGINES AND BOILERS.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Berry’s Temperature-entropy Diagram</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Carnot’s Reflections on the Motive Power of Heat. (Thurston.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dawson’s “Engineering” and Electric Traction Pocket-book</p></td> -<td class="tdr vertb">16mo, mor.,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ford’s Boiler Making for Boiler Makers</p></td> -<td class="tdr vertb">18mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Goss’s Locomotive Sparks</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hemenway’s Indicator Practice and Steam-engine Economy</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hutton’s Mechanical Engineering of Power Plants</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Heat and Heat-engines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kent’s Steam boiler Economy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kneass’s Practice and Theory of the Injector</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">MacCord’s Slide-valves</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Meyer’s Modern Locomotive Construction</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Peabody’s Manual of the Steam-engine Indicator</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Tables of the Properties of Saturated Steam and Other Vapors</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Thermodynamics of the Steam-engine and Other Heat-engines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Valve-gears for Steam-engines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Peabody and Miller’s Steam-boilers</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Pray’s Twenty Years with the Indicator</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Pupin’s Thermodynamics of Reversible Cycles in Gases and Saturated Vapors. (Osterberg.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Reagan’s Locomotives: Simple Compound, and Electric</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rontgen’s Principles of Thermodynamics. (Du Bois.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sinclair’s Locomotive Engine Running and Management</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smart’s Handbook of Engineering Laboratory Practice</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Snow’s Steam-boiler Practice</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Spangler’s Valve-gears</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Notes on Thermodynamics</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Spangler, Greene, and Marshall’s Elements of Steam-engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Handy Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Manual of the Steam-engine</p></td> -<td class="tdr vertb">2 vols., 8vo,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part I. History, Structure, and Theory</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Design, Construction, and Operation</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Handbook of Engine and Boiler Trials, and the Use of the Indicator and the Prony Brake</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Stationary Steam-engines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Steam-boiler Explosions in Theory and in Practice</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Manual of Steam-boilers, their Designs, Construction, and Operation</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Weisbach’s Heat, Steam, and Steam-engines. (Du Bois.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Whitham’s Steam-engine Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s Treatise on Steam-boilers. (Flather.)</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s Thermodynamics, Heat Motors, and Refrigerating Machines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">MECHANICS AND MACHINERY.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Barr’s Kinematics of Machinery</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Bovey’s Strength of Materials and Theory of Structures</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Chase’s The Art of Pattern-making</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Church’s Mechanics of Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">6 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Notes and Examples in Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Compton’s First Lessons in Metal-working</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Compton and De Groodt’s The Speed Lathe</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_15A">[Pg 15]</span><p class="indent">Cromwell’s Treatise on Toothed Gearing</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Treatise on Belts and Pulleys</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dana’s Text-book of Elementary Mechanics for Colleges and Schools</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dingey’s Machinery Pattern Making</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dredge’s Record of the Transportation Exhibits Building of the World’s Columbian Exposition of 1893</p></td> -<td class="tdr vertb">4to half morocco,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="4"><p class="indent">Du Bois’s Elementary Principles of Mechanics:</p></td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Vol. I. Kinematics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Vol. II. Statics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Mechanics of Engineering. Vol. I.</p></td> -<td class="tdr vertb">Small 4to,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent"><span class="add11em">Vol. II.</span></p></td> -<td class="tdr vertb">Small 4to,</td> -<td class="tdr vertb">10 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Durley’s Kinematics of Machines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fitzgerald’s Boston Machinist</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Flather’s Dynamometers, and the Measurement of Power</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Rope Driving</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Goss’s Locomotive Sparks</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Greene’s Structural Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hall’s Car Lubrication</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Holly’s Art of Saw Filing</p></td> -<td class="tdr vertb">18mo,</td> -<td class="tdr vertb">75</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">James’s Kinematics of a Point and the Rational Mechanics of a Particle.</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Johnson’s (W. W.) Theoretical Mechanics</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Johnson’s (L. J.) Statics by Graphic and Algebraic Methods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="4">Jones’s Machine Design:</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part I. Kinematics of Machinery</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Form, Strength, and Proportions of Parts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kerr’s Power and Power Transmission</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Lanza’s Applied Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Leonard’s Machine Shop, Tools, and Methods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Lorenz’s Modern Refrigerating Machinery. (Pope, Haven, and Dean.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">MacCord’s Kinematics; or, Practical Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Velocity Diagrams</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Maurer’s Technical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merriman’s Mechanics of Materials</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt">*</td> -<td class="tdl vertt">Elements of Mechanics</td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Michie’s Elements of Analytical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Reagan’s Locomotives: Simple, Compound, and Electric</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Reid’s Course in Mechanical Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Text-book of Mechanical Drawing and Elementary Machine Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richards’s Compressed Air</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Robinson’s Principles of Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ryan, Norris, and Hoxie’s Electrical Machinery. Vol. I.</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Schwamb and Merrill’s Elements of Mechanism</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Sinclair’s Locomotive-engine Running and Management</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s (O.) Press-working of Metals</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s (A. W.) Materials of Machines</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith (A. W.) and Marx’s Machine Design</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Spangler, Greene, and Marshall’s Elements of Steam-engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Treatise on Friction and Lost Work in Machinery and Mill Work</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Animal as a Machine and Prime Motor, and the Laws of Energetics</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Warren’s Elements of Machine Construction and Drawing</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Weisbach’s Kinematics and Power of Transmission. (Herrmann—Klein.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Machinery of Transmission and Governors. (Herrmann—Klein.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wood’s Elements of Analytical Mechanics</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Principles of Elementary Mechanics</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Turbines</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">The World’s Columbian Exposition of 1893</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4"><span class="pagenum" id="Page_16A">[Pg 16]</span>METALLURGY.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="4"><p class="indent">Egleston’s Metallurgy of Silver, Gold, and Mercury:</p></td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Vol. I. Silver</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Vol. II. Gold and Mercury</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">** Iles’s Lead-smelting. (Postage 9 cents additional.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Keep’s Cast Iron</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kunhardt’s Practice of Ore Dressing in Europe</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Le Chatelier’s High-temperature Measurements. (Boudouard—Burgess.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Metcalf’s Steel. A Manual for Steel-users</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Minet’s Production of Aluminum and its Industrial Use. (Waldo.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Robine and Lenglen’s Cyanide Industry. (Le Clerc.)</p></td> -<td class="tdr vertb">8vo,</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Smith’s Materials of Machines</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Thurston’s Materials of Engineering. In Three Parts</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">8 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part II. Iron and Steel</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Part III. A Treatise on Brasses, Bronzes, and Other Alloys and their Constituents</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ulke’s Modern Electrolytic Copper Refining</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">MINERALOGY.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Barringer’s Description of Minerals of Commercial Value.</p></td> -<td class="tdr vertb">Oblong, morocco,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Boyd’s Resources of Southwest Virginia.</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Map of Southwest Virginia</p></td> -<td class="tdr vertb">Pocket-book form,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Brush’s Manual of Determinative Mineralogy. (Penfield.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Chester’s Catalogue of Minerals</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">paper,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdr" colspan="3">Cloth,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Dictionary of the Names of Minerals</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Dana’s System of Mineralogy</p></td> -<td class="tdr vertb">Large 8vo, half leather,</td> -<td class="tdr vertb">12 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">First Appendix to Dana’s New “System of Mineralogy.”</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Text-book of Mineralogy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Minerals and How to Study Them</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Catalogue of American Localities of Minerals</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Manual of Mineralogy and Petrography</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Douglas’s Untechnical Addresses on Technical Subjects</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Eakle’s Mineral Tables</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Egleston’s Catalogue of Minerals and Synonyms</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hussak’s The Determination of Rock-forming Minerals. (Smith.)</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Merrill’s Non-metallic Minerals: Their Occurrence and Uses</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Penfield’s Notes on Determinative Mineralogy and Record of Mineral Tests.</p></td> -<td class="tdr vertb">8vo, paper,</td> -<td class="tdr vertb">50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rosenbusch’s Microscopical Physiography of the Rock-making Minerals. (Iddings.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Tillman’s Text-book of Important Minerals and Rocks</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">MINING.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Beard’s Ventilation of Mines</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Boyd’s Resources of Southwest Virginia</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Map of Southwest Virginia</p></td> -<td class="tdr vertb">Pocket-book form,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Douglas’s Untechnical Addresses on Technical Subjects</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Drinker’s Tunneling, Explosive Compounds, and Rock Drills</p></td> -<td class="tdr vertb">4to, hf. mor.,</td> -<td class="tdr vertb">25 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Eissler’s Modern High Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_17A">[Pg 17]</span><p class="indent">Fowler’s Sewage Works Analyses</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Goodyear’s Coal-mines of the Western Coast of the United States</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ihlseng’s Manual of Mining</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Iles’s Lead-smelting. (Postage 9c. additional.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Kunhardt’s Practice of Ore Dressing in Europe</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">O’Driscoll’s Notes on the treatment of Gold Ores</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Robine and Lenglen’s Cyanide Industry. (Le Clerc.)</p></td> -<td class="tdr vertb">8vo,</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Walke’s Lectures on Explosives</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Wilson’s Cyanide Processes</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Chlorination Process</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Hydraulic and Placer Mining</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Treatise on Practical and Theoretical Mine Ventilation</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">SANITARY SCIENCE.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Bashore’s Sanitation of a Country House</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Folwell’s Sewerage. (Designing, Construction, and Maintenance.)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Water-supply Engineering</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Fuertes’s Water and Public Health</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Water-filtration Works</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Gerhard’s Guide to Sanitary House-inspection</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Goodrich’s Economic Disposal of Town’s Refuse</p></td> -<td class="tdr vertb">Demy 8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Hazen’s Filtration of Public Water-supplies</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Leach’s The Inspection and Analysis of Food with Special Reference to State Control</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mason’s Water-supply. (Considered principally from a Sanitary Standpoint)</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Examination of Water. (Chemical and Bacteriological.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ogden’s Sewer Design</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Prescott and Winslow’s Elements of Water Bacteriology, with Special Reference to Sanitary Water Analysis</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Price’s Handbook on Sanitation</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richards’s Cost of Food. A Study in Dietaries</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Cost of Living as Modified by Sanitary Science</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Richards and Woodman’s Air, Water, and Food from a Sanitary Standpoint</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">* Richards and Williams’s The Dietary Computer</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rideal’s Sewage and Bacterial Purification of Sewage</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Turneaure and Russell’s Public Water-supplies</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Von Behring’s Suppression of Tuberculosis. (Bolduan.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Whipple’s Microscopy of Drinking-water</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Winton’s Microscopy of Vegetable Foods</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">7 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Woodhull’s Notes on Military Hygiene</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">MISCELLANEOUS.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">De Fursac’s Manual of Psychiatry. (Rosanoff and Collins.)</p></td> -<td class="tdr vertb">Large 12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Emmons’s Geological Guide-book of the Rocky Mountain Excursion of the International Congress of Geologists</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ferrel’s Popular Treatise on the Winds</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">4 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Haines’s American Railway Management</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">2 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Mott’s Fallacy of the Present Theory of Sound</p></td> -<td class="tdr vertb">16mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Ricketts’s History of Rensselaer Polytechnic Institute, 1824-1894</p></td> -<td class="tdr vertb">Small 8vo,</td> -<td class="tdr vertb">3 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rostoski’s Serum Diagnosis. (Bolduan.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Rotherham’s Emphasized New Testament</p></td> -<td class="tdr vertb">Large 8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><span class="pagenum" id="Page_18A">[Pg 18]</span><p class="indent">Steel’s Treatise on the Diseases of the Dog</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">3 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">The World’s Columbian Exposition of 1893</p></td> -<td class="tdr vertb">4to,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Von Behring’s Suppression of Tuberculosis. (Bolduan.)</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Winslow’s Elements of Applied Microscopy</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 50</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Worcester and Atkinson. Small Hospitals, Establishment and Maintenance; Suggestions for Hospital Architecture: Plans for Small Hospital</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<th class="tdc normal" colspan="4">HEBREW AND CHALDEE TEXT-BOOKS.</th> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Green’s Elementary Hebrew Grammar</p></td> -<td class="tdr vertb">12mo,</td> -<td class="tdr vertb">1 25</td> -</tr> -<tr> - -<td class="tdl vertt"> </td> -<td class="tdl vertt"><p class="indent">Hebrew Chrestomathy</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Gesenius’s Hebrew and Chaldee Lexicon to the Old Testament Scriptures. (Tregelles.)</p></td> -<td class="tdr vertb">Small 4to, half morocco,</td> -<td class="tdr vertb">5 00</td> -</tr> -<tr> - -<td class="tdl vertt" colspan="2"><p class="indent">Letteris’s Hebrew Bible</p></td> -<td class="tdr vertb">8vo,</td> -<td class="tdr vertb">2 25</td> -</tr> -</table> - -<hr class="chap x-ebookmaker-drop" /> - -<div class="transnote chapter"><p>Transcriber’s Notes:—</p> - -<p class="noindent padt1 padb1">The spelling, hyphenation, punctuation and accentuation are as the -original, except for apparent typographical errors which have been -corrected.</p> - -<p class="noindent">The original table of contents is here:—</p> - -<table class="autotable" summary="original toc"> -<tr> -<th class="tdc normal" colspan="3">CONTENTS.</th> -</tr> -<tr> -<td class="tdr" colspan="3">PAGE</td> -</tr> -<tr> -<td class="tdl"> CHAPTER</td> -<td class="tdl">I. INTRODUCTION.</td> -<td class="tdl">1</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">II. CONTINUOUS FILTERS AND THEIR CONSTRUCTION</td> -<td class="tdl">5</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Sedimentation-basins</td> -<td class="tdl">8</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Size of Filter-beds</td> -<td class="tdl">10</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Covers for Filters</td> -<td class="tdl">12</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">III. FILTERING-MATERIALS</td> -<td class="tdl">20</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Sand</td> -<td class="tdl">20</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Gravel</td> -<td class="tdl">35</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Underdrains</td> -<td class="tdl">39</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Depth of Water on Filters</td> -<td class="tdl">45</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">IV. RATE OF FILTRATION AND LOSS OF HEAD</td> -<td class="tdl">47</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Rate of Filtration</td> -<td class="tdl">47</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Loss of Head and Apparatus for regulating it</td> -<td class="tdl">52</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Limit to the Loss of Head</td> -<td class="tdl">60</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">V. CLEANING FILTERS</td> -<td class="tdl">68</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Scraping</td> -<td class="tdl">68</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Frequency of Scraping</td> -<td class="tdl">72</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Sand-washing</td> -<td class="tdl">76</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">VI. THEORY AND EFFICIENCY OF FILTRATION</td> -<td class="tdl">83</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Bacterial Examination of Waters</td> -<td class="tdl">93</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">VII. INTERMITTENT FILTRATION</td> -<td class="tdl">97</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">The Lawrence Filter</td> -<td class="tdl">100</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">The Chemnitz Filter</td> -<td class="tdl">107</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">VIII. TURBIDITY AND COLOR, AND THE EFFECT OF MUD UPON</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">SAND FILTERS</td> -<td class="tdl">113</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Color</td> -<td class="tdl">114</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Turbidity</td> -<td class="tdl">117</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Preliminary Processes to remove Mud</td> -<td class="tdl">133</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Effect of Mud upon Sand Filters</td> -<td class="tdl">137</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">IX. COAGULATION OF WATERS</td> -<td class="tdl">144</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Substances used for Coagulation</td> -<td class="tdl">145</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Amount of Coagulant required to remove Turbidity</td> -<td class="tdl">150</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Amount of Coagulant required to remove Color</td> -<td class="tdl">153</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Successive Applications of Coagulant</td> -<td class="tdl">154</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Amount of Coagulant which Waters will receive</td> -<td class="tdl">155</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">X. MECHANICAL FILTERS</td> -<td class="tdl">159</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Influence of Amount of Coagulant on Bacterial</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Efficiency</td> -<td class="tdl">165</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Types of Mechanical Filters</td> -<td class="tdl">172</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">XI. OTHER METHODS OF FILTRATION</td> -<td class="tdl">181</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">XII. REMOVAL OF IRON FROM GROUND-WATERS</td> -<td class="tdl">186</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Cause of Iron in Ground-waters</td> -<td class="tdl">187</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Treatment of Iron-containing Waters</td> -<td class="tdl">189</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Iron-removal Plants in Operation</td> -<td class="tdl">192</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">XIII. TREATMENT OF WATERS</td> -<td class="tdl">197</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Cost of Filtration</td> -<td class="tdl">200</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">XIV. WATER-SUPPLY AND DISEASE</td> -<td class="tdl">210</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">APPENDIX I. GERMAN OFFICIAL REGULATION IN REGARD TO FILTRATION</td> -<td class="tdl">221</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">II. EXTRACTS FROM DR. REINCKE’S REPORT UPON THE HEALTH</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">OF HAMBURG FOR 1892</td> -<td class="tdl">226</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">III. METHODS OF SAND-ANALYSIS</td> -<td class="tdl">233</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">IV. STATISTICS OF SOME FILTERS</td> -<td class="tdl">241</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Results of Operation</td> -<td class="tdl">241</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">List of Sand Filters in Use</td> -<td class="tdl">244</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">List of Mechanical Filters in Use</td> -<td class="tdl">247</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Notes regarding Sand Filters in America</td> -<td class="tdl">251</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">Extent of the Use of Filters</td> -<td class="tdl">254</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">V. WATER-SUPPLY OF LONDON</td> -<td class="tdl">255</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">VI. WATER-SUPPLY OF BERLIN</td> -<td class="tdl">261</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">VII. WATER-SUPPLY OF ALTONA</td> -<td class="tdl">265</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">VIII. WATER-SUPPLY OF HAMBURG</td> -<td class="tdl">269</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">IX. NOTES ON SOME OTHER EUROPEAN SUPPLIES</td> -<td class="tdl">272</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">X. LITERATURE OF FILTRATION</td> -<td class="tdl">277</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">XI. THE ALBANY FILTRATION PLANT</td> -<td class="tdl">288</td> -</tr> -<tr> -<td class="tdl"></td> -<td class="tdl">INDEX</td> -<td class="tdl">317</td> -</tr> -</table> - -<p>In the table of “ANALYSES OF SANDS USED IN WATER FILTRATION” the place name “Owesty” has been corrested to read “Oswestry”.</p> - -<p>On page 270 the statement “the velocity in the drain will reach 0.97 -foot” should probably read “0.97 feet per second”.</p> - -</div> -<div style='display:block; margin-top:4em'>*** END OF THE PROJECT GUTENBERG EBOOK THE FILTRATION OF PUBLIC WATER-SUPPLIES ***</div> -<div style='text-align:left'> - -<div style='display:block; margin:1em 0'> -Updated editions will replace the previous one—the old editions will -be renamed. -</div> - -<div style='display:block; margin:1em 0'> -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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