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+The Project Gutenberg EBook of A Handbook of Laboratory Glass-Blowing, by 
+Bernard D. Bolas
+
+This eBook is for the use of anyone anywhere 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
+
+
+Title: A Handbook of Laboratory Glass-Blowing
+
+Author: Bernard D. Bolas
+
+Illustrator: Naomi Bolas
+
+Release Date: June 24, 2010 [EBook #32962]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK HANDBOOK--LABORATORY GLASS-BLOWING ***
+
+
+
+
+Produced by 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.)
+
+
+
+
+
+
+
+A HANDBOOK OF LABORATORY GLASS-BLOWING
+
+
+      _To my Friends
+        Eric Reid
+            and
+      Sidney Wilkinson_
+
+
+
+
+A Handbook of Laboratory Glass-Blowing
+
+BY
+
+BERNARD D. BOLAS
+
+WITH NUMEROUS DIAGRAMS IN THE TEXT
+
+BY NAOMI BOLAS
+
+[Illustration]
+
+LONDON
+GEORGE ROUTLEDGE & SONS, LTD
+NEW YORK: E. P. DUTTON & CO.
+1921
+
+
+
+
+CONTENTS
+
+
+    CHAP.                                                           PAGE
+
+    I. Introduction and Preliminary Remarks--General Principles
+    to be observed in Glass Working--Choice of Apparatus--Tools
+    and Appliances--Glass                                              1
+
+    II. Easy Examples of Laboratory Glass-Blowing--Cutting and
+    Sealing Tubes, Tubes for High Temperature
+    Experiments--Thermometer-Bulbs, Bulbs of Special Glass,
+    Pipettes, Absorption-Bulbs or Washing Bulbs--Joining Tubes,
+    Branches, Exhaustion-Branches, Branches of Dissimilar Glass,
+    Blowing Bulbs, A Thistle Funnel, Cracking and Breaking Glass,
+    Leading and Direction of Cracks--Use of Glass Rod or Strips
+    of Window-Glass, Joining Rod, Feet and Supports--Gripping
+    Devices for use in Corrosive Solutions--The Building up of
+    Special Forms from Solid Glass                                    10
+
+    III. Internal Seals, Air-Traps, Spray Arresters,
+    Filter-Pumps--Sprays, Condensers; plain, double surface, and
+    spherical--Soxhlet Tubes and Fat Extraction Apparatus--Vacuum
+    Tubes, Electrode Work, Enclosed Thermometers, Alarm
+    Thermometers ... Recording Thermometers, "Spinning" Glass 32
+
+    IV. Glass, its Composition and
+    Characteristics--Annealing--Drilling, Grinding, and Shaping
+    Glass by methods other than Fusion--Stopcocks--Marking
+    Glass--Calibration and Graduation of
+    Apparatus--Thermometers--Exhaustion of Apparatus--Joining
+    Glass and Metal--Silvering Glass                                  55
+
+    V. Extemporised Glass-Blowing Apparatus--The use of Oil or
+    other Fuels--Making Small Rods and Tubes from Glass
+    Scraps--The Examination of Manufactured Apparatus with a view
+    to Discovering the Methods used in Manufacture--Summary of
+    Conditions necessary for Successful Glass-Blowing                  80
+
+    Index                                                             105
+
+
+
+
+
+PREFACE
+
+
+To cover the whole field of glass-blowing in a small handbook would be
+impossible. To attempt even a complete outline of the methods used in
+making commercial apparatus would involve more than could be undertaken
+without omitting the essential details of manipulation that a novice
+needs. I have, therefore, confined myself as far as possible to such
+work as will find practical application in the laboratory and will, I
+hope, prove of value to those whose interests lie therein.
+
+The method of treatment and somewhat disjointed style of writing have
+been chosen solely with the view to economy of space without the undue
+sacrifice of clearness.
+
+                                              BERNARD D. BOLAS.
+
+
+
+
+Handbook of Laboratory Glass-Blowing
+
+
+
+
+CHAPTER I
+
+     Introduction and Preliminary Remarks--General Principles to
+     be observed in Glass Working--Choice of Apparatus--Tools and
+     Appliances--Glass.
+
+
+Glass-blowing is neither very easy nor very difficult; there are
+operations so easy that the youngest laboratory boy should be able to
+repeat them successfully after once having been shown the way, there are
+operations so difficult that years are needed to train eye and hand and
+judgment to carry them out; but the greater number of scientific needs
+lie between these two extremes. Yet a surprisingly large number of
+scientific workers fail even to join a glass tube or make a T piece that
+will not crack spontaneously, and the fault is rather one of
+understanding than of lack of ability to carry out the necessary
+manipulation.
+
+In following the scheme of instruction adopted in this handbook, it will
+be well for the student to pay particular attention to the reason given
+for each detail of the desirable procedure, and, as far as may be, to
+memorise it. Once having mastered the underlying reason, he can evolve
+schemes of manipulation to suit his own particular needs, although, as a
+rule, those given in the following pages will be found to embody the
+result of many years' experience.
+
+There is a wide choice of apparatus, from a simple mouth-blowpipe and a
+candle flame to a power-driven blower and a multiple-jet heating device.
+All are useful, and all have their special applications, but, for the
+present, we will consider the ordinary types of bellows and blowpipes,
+such as one usually finds in a chemical or physical laboratory.
+
+The usual, or Herepath, type of gas blowpipe consists of an outer tube
+through which coal gas can be passed and an inner tube through which a
+stream of air may be blown. Such a blowpipe is shown in section by Fig.
+1. It is desirable to have the three centring screws as shown, in order
+to adjust the position of the air jet and obtain a well-shaped flame,
+but these screws are sometimes omitted. Fig. 1, _a_ and _b_ show the
+effects of defective centring of the air jet, _c_ shows the effect of
+dirt or roughness in the inside of the air jet, _d_ shows a satisfactory
+flame.
+
+[Illustration: Fig 1]
+
+For many purposes, it is an advantage to have what is sometimes known
+as a "quick-change" blowpipe; that is one in which jets of varying size
+may be brought into position without stopping the work for more than a
+fraction of a second. Such a device is made by Messrs. Letcher, and is
+shown by _e_, and in section by _f_ Fig. 1. It is only necessary to
+rotate the desired jet into position in order to connect it with both
+gas and air supplies. A small bye-pass ignites the gas, and adjustment
+of gas and air may be made by a partial rotation of the cylinder which
+carries the jets.
+
+For specially heavy work, where it is needed to heat a large mass of
+glass, a multiple blowpipe jet of the pattern invented by my father,
+Thomas Bolas, as the result of a suggestion derived from a study of the
+jet used in Griffin's gas furnace, is of considerable value. This jet
+consists of a block of metal in which are drilled seven holes, one being
+central and the other six arranged in a close circle around the central
+hole. To each of these holes is a communication way leading to the gas
+supply, and an air jet is arranged centrally in each. Each hole has also
+an extension tube fitted into it, the whole effect being that of seven
+blowpipes. In order to provide a final adjustment for the flame, a
+perforated plate having seven holes which correspond in size and
+position to the outer tubes is arranged to slide on parallel guides in
+front of these outer tubes.
+
+[Illustration: Fig. 2]
+
+The next piece of apparatus for consideration is the bellows, of which
+there are three or more types on the market, although all consist of two
+essential parts, the blower or bellows proper and the wind chamber or
+reservoir. Two patterns are shown in Fig. 2; _a_, is the form which is
+commonly used by jewellers and metal workers to supply the air blast
+necessary for heating small furnaces. Such a bellows may be obtained at
+almost any jewellers' supply dealer in Clerkenwell, but it not
+infrequently happens that the spring in the wind chamber is too strong
+for glass-blowing, and hence the air supply tends to vary in pressure.
+This can be improved by fitting a weaker spring, but an easier way and
+one that usually gives fairly satisfactory results, is to place an
+ordinary screw-clip on the rubber tube leading from the bellows to the
+blowpipe, and to tighten this until an even blast is obtained.
+
+Another form of bellows, made by Messrs. Fletcher and Co., and common in
+most laboratories, is shown by _b_; the wind chamber consists of a disc
+of india-rubber clamped under a circular frame or tied on to a circular
+rim. This form is shown by Fig. 2, _b_.
+
+The third form, and one which my own experience has caused me to prefer
+to any other, is cylindrical, and stands inside the pedestal of the
+blowpipe-table. A blowpipe-table of this description is made by Enfer of
+Paris.
+
+There is no need, however, to purchase an expensive table for laboratory
+use. All the work described in this book can quite well be done with a
+simple foot bellows and a quick-change blowpipe. Nearly all of it can be
+done with a single jet blowpipe, such as that described first, or even
+with the still simpler apparatus mentioned on page 84, but I do not
+advise the beginner to practise with quite so simple a form at first,
+and for that reason have postponed a description of it until the last
+chapter.
+
+Glass-blowers' tools and appliances are many and various, quite a number
+of them are better rejected than used, but there are a few essentials.
+These are,--file, glass-knife, small turn-pin, large turn-pin, carbon
+cones, carbon plate, rubber tube of small diameter, various sizes of
+corks, and an asbestos heat reflector. For ordinary work, an annealing
+oven is not necessary, but one is described on page 60 in connection
+with the special cases where annealing is desirable.
+
+Fig. 3 illustrates the tools and appliances. _a_ is an end view of the
+desirable form of file, and shows the best method of grinding the edges
+in order to obtain a highly satisfactory tool. _b_ is a glass knife,
+shown both in perspective and end view, it is made of glass-hard steel
+and should be sharpened on a rough stone, such as a scythe-stone, in
+order to give a slightly irregular edge. _c_ is a small turn-pin which
+may be made by flattening and filing the end of a six-inch nail. _d_ is
+the large turn-pin and consists of a polished iron spike, about five
+inches long and a quarter of an inch diameter at its largest part. This
+should be mounted in a wooden handle. _e_ and _f_ are carbon cones. A
+thin rubber tube is also useful; it may be attached to the work and
+serve as a blowing tube, thus obviating the necessity of moving the work
+to the mouth when internal air pressure is to be applied. In order to
+avoid undue repetition, the uses of these tools and appliances will be
+described as they occur.
+
+[Illustration: Fig. 3]
+
+Glass, as usually supplied by chemical apparatus dealers is of the
+composition known as "soda-glass." They also supply "hard" or
+"combustion" glass, but this is only used for special purposes, as it is
+too infusible for convenient working in the ordinary blowpipe flame.
+
+Soda-glass consists primarily of silicate of sodium with smaller
+quantities of silicate of aluminum and potassium. Its exact composition
+varies. It is not blackened, as lead glass is, by exposure to the
+reducing gases which are present in the blue cone of a blowpipe flame,
+and hence is easier for a beginner to work without producing
+discolouration.
+
+Further notes on glasses will be found on page 55, but for ordinary
+purposes soda-glass will probably be used.
+
+
+
+
+CHAPTER II
+
+     Easy Examples of Laboratory Glass-Blowing--Cutting and
+     Sealing Tubes for Various Purposes; Test-Tubes,
+     Pressure-Tubes, Tubes for High Temperature
+     Experiments--Thermometer-Bulbs, Bulbs of Special Glass,
+     Pipettes, Absorption-Bulbs or Washing-Bulbs--Joining Tubes;
+     Branches, Exhaustion-Branches, Branches of Dissimilar
+     Glass--Blowing Bulbs; A Thistle Funnel; Cracking and
+     Breaking Glass; Leading and Direction of Cracks--Use of
+     Glass Rod or Strips of Window-Glass; Joining Rod, Feet and
+     Supports--Gripping Devices for use in Corrosive
+     Solutions--The Building Up of Special Forms from Solid
+     Glass.
+
+
+Perhaps the most common need of the glass-blower whose work is connected
+with that of the laboratory is for a sealed tube; and the sealing of a
+tube is an excellent preliminary exercise in glass-blowing.
+
+We will assume that the student has adjusted the blowpipe to give a
+flame similar to that shown in _d_, Fig. 1, and that he has learned to
+maintain a steady blast of air with the bellows; further, we will assume
+that the tube he wishes to seal is of moderate size, say not more than
+half an inch in diameter and with walls of from one-tenth to one-fifth
+of an inch thick.
+
+[Illustration: Fig. 4]
+
+A convenient length of tube for the first trial is about one foot; this
+should be cut off from the longer piece, in which it is usually
+supplied, as follows:--lay the tube on a flat surface and make a deep
+cut with the edge of a file. Do not "saw" the file to and fro over the
+glass. If the file edge has been ground as shown in _a_, Fig. 3, such a
+procedure will be quite unnecessary and only involve undue wear; one
+movement with sufficient pressure to make the file "bite" will give a
+deep cut. Now rotate the tube through about one-eighth of a turn and
+make another cut in continuation of the first. Take the tube in the
+hands, as shown in _a_, Fig. 4, and apply pressure with the thumbs, at
+the same time straining at the ends. The tube should break easily. If it
+does not, do not strain too hard, as it may shatter and cause serious
+injuries to the hands, but repeat the operation with the file and so
+deepen the original cuts. In holding a tube for breaking, it is
+important to place the hands as shown in sketch, as this method is least
+likely to cause shattering and also minimises the risk of injury even if
+the tube should shatter. To cut a large tube, or one having very thick
+walls, it is better to avoid straining altogether and to break by
+applying a small bead of intensely heated glass to the file cut. If the
+walls are very thin, a glass-blower's knife should be used instead of a
+file. The tube and glass-blower's knife should be held in the hand, and
+the tube rotated against the edge of the knife; this will not produce a
+deep cut, but is less likely to break the tube. A bead of hot glass
+should be used to complete the work.
+
+The next operation is to heat the glass tube in the middle; this must be
+done gradually and evenly; that is to say the tube must be rotated
+during heating and held some considerable distance in front of the flame
+at first; otherwise the outer surface of the glass will expand before
+the interior is affected and the tube will break. From two to five
+minutes, heating at a distance of about eight inches in front of the
+flame will be found sufficient in most cases, and another minute should
+be taken in bringing the tube into the flame. Gradual heating is
+important, but even heating is still more important and this can only be
+obtained by uniform and steady rotation. Until the student can rotate a
+tube steadily _without thinking about it_, real progress in
+glass-blowing is impossible.
+
+When the tube is in the flame it must be held just in front of the blue
+cone and rotated until the glass is soft enough to permit the ends to be
+drawn apart. Continue to separate the ends and, at the same time, move
+the tube very slightly along its own axis, so that the flame tends to
+play a little more on the thicker part than on the drawn-out portion. If
+this is done carefully, the drawn-out portion can be separated off,
+leaving only a slight "bleb" on the portion it is desired to seal. This
+is illustrated by _b_, Fig. 4.
+
+To convert the seal at _b_, Fig. 4., into the ordinary form of test-tube
+seal, it is only necessary to heat the "bleb" a little more strongly,
+blow gently into the tube until the thick portion is slightly expanded,
+re-heat the whole of the rounded end until it is beginning to collapse,
+and give a final shaping by careful blowing after it has commenced to
+cool. In each case the glass must be removed from the flame before
+blowing. The finished seal is shown by _c_, Fig. 4. If desired, the open
+end may now be finished by heating and rotating the soft glass against
+the large turn-pin, as illustrated in _d_, but the turn-pin must not be
+allowed to become too hot, as if this happens it will stick to the
+glass. After turning out the end, the lip of glass must be heated to
+redness and allowed to cool without coming in contact with anything;
+otherwise it will be in a condition of strain and liable to crack
+spontaneously. The finished test-tube is shown by _e_.
+
+When it is necessary to seal a substance inside a glass tube, the bottom
+of the tube is first closed, as explained above, and allowed to cool;
+the substance, if a solid, is now introduced, but should not come to
+within less than two inches of the point where the second seal is to be
+made. If the substance is a liquid it can more conveniently be
+introduced at a later stage.
+
+Now bring the tube into the blowpipe flame gradually, and rotate it,
+while heating, at the place where it is to be closed. Allow the glass to
+soften and commence to run together until the diameter of the tube is
+reduced to about half its original size. Remove from the flame and draw
+the ends apart, this should give a long, thick extension as shown by
+_f_, Fig. 4. If any liquid is to be introduced, it may now be done by
+inserting a thin rubber or other tube through the opening and running
+the liquid in. A glass tube should be used with caution for introducing
+the liquid, as any hard substance will tend to scratch the inside of the
+glass and cause cracking. The final closure is made by melting the
+drawn-out extension in the blowpipe flame; the finished seal being shown
+by _g_, Fig. 4.
+
+If the sealed tube has to stand internal pressure, it is desirable to
+allow the glass to thicken somewhat more before drawing out, and the
+bottom seal should also be made thicker. For such a tube, and especially
+when it has to stand heating, as in a Carius determination of chlorine,
+each seal should be cooled very slowly by rotating it in a gas flame
+until the surface is covered with a thick layer of soot, and it should
+then be placed aside in a position where the hot glass will not come in
+contact with anything, and where it will be screened from all draughts.
+
+_Joining Tube._--We will now consider the various forms of join in glass
+tubing which are met with in the laboratory. First, as being easiest, we
+will deal with the end-to-end joining of two tubes of similar glass.
+_a_, _b_, and _c_, Fig. 5, illustrate this. One end of one of the tubes
+should be closed, a lip should be turned out on each of the ends to be
+joined, and both lips heated simultaneously until the glass is
+thoroughly soft. Now bring the lips together gently, until they are in
+contact at all points and there are no places at which air can escape;
+remove from the flame, and blow slowly and very cautiously until the
+joint is expanded as shown in _b_, Fig. 5. Reheat in the flame until
+the glass has run down to rather less than the original diameter of the
+tube, and give a final shaping by re-blowing. The chief factors of
+success in making such a join are, thorough heating of the glass before
+bringing the two tubes together, and avoidance of hard or sudden blowing
+when expanding the joint. The finished work is shown by _c_, Fig. 5.
+
+[Illustration: Fig. 5]
+
+To join a small glass tube to the end of a large one, the large tube
+should first be sealed, a small spot on the extreme end of the seal
+heated, and air pressure used to expand the heated spot as shown in _d_.
+This expanded spot is then re-heated and blown out until it bursts as
+shown in _e_, the thin fragments of glass are removed and the end of the
+small tube turned out as shown in _f_. After this the procedure is
+similar to that used in jointing two tubes of equal size.
+
+When these two forms of joint have been mastered, a T piece will present
+but little difficulty. It is made in three stages as shown in Fig. 5,
+and the procedure is similar to that used in joining a large and small
+tube. Care should be taken to avoid softening the top of the "T" too
+much, or the glass will bend and distort the finished work; although a
+slight bend can be rectified by re-heating and bending back. Local
+re-heating is often useful in giving the joint its final shape.
+
+An exhaustion branch is often made by a totally different method. This
+method is shown by _g_, _h_, and _i_, Fig. 5; _g_ is the tube on which
+the branch is to be made. The end of a rod of similar glass should be
+heated until a mass of thoroughly liquid glass has collected, as shown,
+and at the same time a spot should be heated on that part of the tube
+where it is desired to make the branch. The mass of hot glass on the rod
+is now brought in contact with the heated spot on the tube and expanded
+by blowing as shown by _h_. The air pressure in the tube is still
+maintained while the rod is drawn away as shown by _i_. This will give a
+hollow branch which may be cut off at any desired point, and is then
+ready for connection to the vacuum pump.
+
+If the rod used is of a dissimilar glass, the branch should be blown
+much thinner. Such a branch will often serve as a useful basis for
+joining two tubes of different composition, as the ordinary type of
+branch is more liable to crack when made with two glasses having
+different coefficients of expansion.
+
+_Blowing Bulbs._--A bulb may be blown on a closed tube such as that
+shown by _c_, Fig. 5, by rotating it in the blowpipe flame until the end
+is softened, removing it from the flame and blowing cautiously. It is
+desirable to continue the rotation during blowing. In the case of a very
+small tube, it is sufficient to melt the end without previous sealing,
+rotate it in the flame until enough glass has collected, remove from the
+flame and blow while keeping the tube in rotation.
+
+_Thermometer Bulbs._--If the thermometer is to be filled with mercury,
+it is desirable to use a rubber bulb for blowing, as moisture is liable
+to condense inside the tube when the mouth is used, and this moisture
+will cause the mercury thread to break. In any case, a slight pressure
+should be maintained inside the thermometer tube while it is in the
+flame; otherwise the fine capillary tube will close and it will be very
+difficult to expand the heated glass into a bulb.
+
+_Large Bulbs._--When a large bulb is needed on a small or medium sized
+tube, it is often necessary to provide more glass than would be obtained
+if the bulb were blown in the ordinary way. One method is to expand the
+tube in successive stages along its axis, as shown by _a_, Fig. 6. These
+expanded portions are then re-heated, so that they run together into one
+hollow mass from which the bulb is blown; _b_ and _c_, illustrate this.
+Another method, and one which is useful for very large bulbs, is to
+fuse on a length of large, thick-walled, tubing. The heat reflector,
+_g_, Fig. 3, should be used, if necessary, when making large bulbs. It
+consists of a sheet of asbestos mounted in a foot, and is used by being
+placed close to the mass of glass on the side away from the blowpipe
+flame while the glass is being heated.
+
+[Illustration: Fig. 6]
+
+_Bulbs of Dissimilar Glass._--These may be made by the second method
+given under "Large Bulbs," but the joint should be blown as thin as
+possible. Further instructions in the use of unlike glasses are given on
+page 94.
+
+_A Bulb in the Middle of a Tube._--Unless the bulb is to be quite small,
+it will be necessary to join in a piece of thick glass tubing, or to
+draw the thin tube out from a larger piece, thus leaving a thick mass in
+the middle as shown by _d_, Fig. 6. This mass of glass should now be
+rotated in the blowpipe flame until it is quite soft and on the point of
+running together. Considerable practice will be necessary before the two
+ends of the tube can be rotated at the same speed and without
+"wobbling," but this power must be acquired. When the glass is
+thoroughly hot, remove from the flame, hold in a horizontal position,
+and expand by blowing. It is essential to continue the rotation while
+this is done. Should one part of the bulb tend to expand more than the
+other, turn the expanded part to the bottom, pause for about a second,
+both in rotating and blowing, in order that the lower portion may be
+cooled by ascending air-currents; then continue blowing and turning as
+before.
+
+_Absorption Bulbs or Washing Bulbs._--These are made by an elaboration
+of the processes given in the last paragraph, _g_, _h_, and _i_, Fig. 6,
+illustrate this.
+
+_A Thistle Funnel._--This is made by blowing a fairly thick-walled bulb
+on a glass tube, bursting a hole by heating and blowing, and enlarging
+the burst-out part by heating and rotating against a turn-pin.
+
+_Bending Glass Tube._--Small tubing may be bent in a flat flame gas
+burner and offers no special difficulty. Large or thin-walled tubing
+should be heated in the blowpipe flame and a slight bend made; another
+zone of the tube, just touching the first bend, should now be heated and
+another slight bend made. In this way it is possible to avoid flattening
+and a bend having any required angle can gradually be produced. A final
+shaping of the bend may be made by heating in a large blowpipe flame and
+expanding slightly by air pressure.
+
+_Glass Spirals._--If a tube is heated by means of a long, flat-flame
+burner, the softened tube may be wound on to an iron mandrel which has
+previously been covered with asbestos. The mandrel should be made
+slightly conical in order to facilitate withdrawal. It is desirable to
+heat the surface of the asbestos almost to redness by means of a second
+burner, and thus avoid undue chilling of the glass and the consequent
+production of internal strain.
+
+[Illustration: Fig. 7]
+
+_A Thermo-Regulator for Gas._--Fig. 7, _a-e_, shows an easily
+constructed thermo-regulator. The mercury reservoir, _a_, and the upper
+part, _b_, are made by joining two larger pieces of tubing on to the
+capillary. The gas inlet passes through a rubber stopper, in order to
+allow of adjustment for depth of insertion, and the bye-pass branches,
+_d_ and _e_, are connected by a piece of rubber tubing which can be
+compressed by means of a screw clip, thus providing a means of
+regulating the bye-pass.
+
+_Use of Glass Rod._--Apart from its most common laboratory use for
+stirring; glass rod may be used in building up such articles as
+insulating feet for electrical apparatus or acid-resisting cages for
+chemical purposes. Such a cage is shown by _f_, _g_ and _h_, Fig. 7.
+Further, by an elaboration of the method of making an exhaustion branch,
+given on page 18, blown articles may also be constructed from rod. Note
+the added parts of _e_, Fig. 9.
+
+_A Simple Foot._--The form of foot shown by Fig. 7, _k_, is easy to make
+and has many uses. First join a glass rod to a length of glass tubing as
+shown (the joint should be expanded slightly by blowing), cut off the
+tube and heat the piece remaining on the rod until it can be turned out
+as shown by _i_. This should be done with the large turn-pin, and care
+should be taken not to heat the supporting rod too strongly, otherwise
+the piece of tube will become bent and distorted; it is better to
+commence by heating the edge of the piece of tube and turn out a lip,
+then extend the heating by degrees and turn out more and more until the
+foot looks like that shown by _i_.
+
+We now need to make three projections of glass rod. These are produced
+as follows:--Heat the end of the glass rod until a thoroughly melted
+mass of glass has accumulated (the rod must be rotated while this is
+being done, otherwise the glass will drop off); when sufficient melted
+glass has been obtained, the edge of the turned-out foot should be
+heated to dull redness over about one-third of its circumference, and
+the melted glass on the rod should be drawn along the heated portion
+until both are so completely in contact as to form one mass of
+semi-fluid glass. The rod should now be drawn away slowly, and, finally,
+separated by melting off, thus producing a flat projection. A repetition
+of the process will give the other two projections, and the finished
+foot may be adjusted to stand upright by heating the projections
+slightly and standing it on the carbon plate mentioned on page 7. After
+the foot is adjusted it should be annealed slightly by heating to just
+below the softening point of the glass and then rotating in a smoky gas
+flame until it is covered with a deposit of carbon, after which it
+should be allowed to cool in a place free from draughts and where the
+hot glass will not come in contact with anything. The finished foot is
+shown by _k_, Fig. 7.
+
+_Building up from Glass Rod._--A glass skeleton-work can be constructed
+from rod without much difficulty, and is sometimes useful as a container
+for a substance which has to be treated with acid, or for similar
+purposes. The method is almost sufficiently explained by the
+illustration in Fig. 7; _f_ shows the initial stage, _g_ the method of
+construction of the net-work, and _h_ the finished container. It is
+convenient to introduce the substance at the stage indicated by _g_. The
+important points to observe in making this contrivance are that the
+glass rod must be kept hot by working while it is actually in the flame,
+and that the skeleton must be made as thin as possible with the
+avoidance of heavy masses of glass at any place. If these details are
+neglected it will be almost certain to crack.
+
+_Stirrers._--These are usually made from glass rod, and no special
+instructions are necessary for their construction, except that the glass
+should be in a thoroughly fused condition before making any joins and
+the finished join should be annealed slightly by covering with a deposit
+of soot, as explained on page 16. The flat ends shown in _a_, Fig. 8,
+are made by squeezing the soft glass rod between two pieces of carbon,
+and should be re-heated to dull redness after shaping. Fig. 8 also shows
+various forms of stirrer.
+
+In order to carry out stirring operations in the presence of a gas or
+mixture of gases other than air, some form of gland or seal may be
+necessary where the stirrer passes through the bearing in which it runs.
+A flask to which is fitted a stirrer and gas seal is shown in section by
+_b_, Fig. 8. The liquid used in this seal may be mercury, petroleum, or
+any other that the experimental conditions indicate.
+
+[Illustration: Fig. 8]
+
+If the bearing for a stirrer is made of glass tube, it is desirable to
+lubricate rather freely; otherwise heat will be produced by the
+friction of the stirrer and the tube will probably crack. Such
+lubrication may be supplied by turning out the top of the bearing tube
+and filling the turned-out portion with petroleum jelly mixed with a
+small quantity of finely ground or, better, colloidal graphite, and the
+bearing should also be lubricated with the same composition. Care
+should be taken not to employ so soft a lubricant or so large an excess
+as to cause it to run down the stirrer into the liquid which is being
+stirred.
+
+_Leading a Crack._--It sometimes happens that a large bulb or specially
+thin-walled tube has to be divided. In such a case it is scarcely
+practicable to use the method recommended for small tubes on page 12,
+but it is quite easy to lead a crack in any desired direction. A
+convenient starting point is a file cut; this is touched with hot glass
+until a crack is initiated. A small flame or a bead of hot glass is now
+used to heat the article at a point about a quarter of an inch from the
+end of the crack and in whatever direction it has to be led. The crack
+will now extend towards the source of heat, which should be moved
+farther away as the crack advances. In this manner a crack may be caused
+to take any desired path and can be led round a large bulb.
+
+_Cutting Glass with the Diamond._--Slips of window-glass can be used in
+place of glass rod for some purposes, and as cutting them involves the
+use of the glaziers' diamond or a wheel-cutter, they may well be
+mentioned under this heading.
+
+In cutting a sheet of glass with the diamond, one needs a flat surface
+on which to rest the glass, and a rule against which to guide the
+diamond. The diamond should be held in an almost vertical position, and
+drawn over the surface of the glass with slight pressure. While this is
+being done the angle of the diamond should be changed by bringing the
+top of the handle forward until the sound changes from one of scratching
+to a clear singing note. When this happens the diamond is cutting. A few
+trials will teach the student the correct angle for the diamond with
+which he works, and the glass, if properly cut, will break easily. If
+the cut fails it is better to turn the glass over and make a
+corresponding cut on the other side rather than make any attempt to
+improve the original cut. The diamond is seldom used for cutting small
+glass tubes.
+
+The use of the wheel-cutter calls for no special mention as it will cut
+at any angle, although the pressure required is somewhat greater than
+that needed by most diamonds.
+
+
+
+
+CHAPTER III
+
+     Internal Seals, Air-Traps, Spray Arresters,
+     Filter-Pumps--Sprays, Condensers; Plain, Double Surface, and
+     Spherical--Soxhlet Tubes and Fat Extraction
+     Apparatus--Vacuum Tubes, Electrode Work, Enclosed
+     Thermometers, Alarm Thermometers, Recording Thermometers,
+     "Spinning" Glass.
+
+
+_Internal Seals._--It is convenient to class those cases in which a
+glass tube passes through the wall of another tube or bulb under the
+heading of "Internal Seals." These are met with in barometers, spray
+arresters, and filter pumps, in condensers and some forms of vacuum
+tube. The two principal methods of making such seals will be considered
+first and their special application afterwards.
+
+_An Air Trap on a Barometer Tube._--This involves the use of the first
+method, and is perhaps the simplest example that can be given. Fig. 9,
+_a_, _a1_ and _a2_, show the stages by which this form of internal seal
+is made. For the first trials, it is well to work with fairly
+thick-walled tubing, which should be cut into two pieces, each being
+about eight inches long.
+
+[Illustration: Fig. 9]
+
+First seal the end of one tube as described on page 13, heat the sealed
+end and expand to a thick walled bulb. Fuse the end of the other tube,
+attach a piece of glass rod to serve as a handle, and draw out; cut off
+the drawn-out portion: leaving an end like _a_.
+
+Now heat a small spot at the end of the bulb, blow, burst out, and
+remove the thin fragments of glass. Heat a zone on the other tube at the
+point where the drawn-out portion commences and expand as shown by _a1_.
+
+The next stage is to join the tubes. Heat the ragged edges of the
+burst-out portion until they are thoroughly rounded. At the same time
+heat the drawn-out tube to just below softening point. Then, while the
+rounded edges of the burst-out portion are still soft, insert the other
+tube; rotate the join in the blowpipe flame until it is quite soft, and
+expand by blowing. If necessary, re-heat and expand again. The finished
+seal, which should be slightly annealed by smoking in a sooty flame, is
+shown by _a2_.
+
+_A Spray Arrester._--This is made by the second method, in which the
+piece of tube which projects inside the bulb is fused in position first
+and the outer tube is then joined on. The various stages of making are
+illustrated by _b_, _b1_ and _b2_, Fig. 9.
+
+A bulb is blown between two tubes by the method given on page 22, the
+larger tube is then cut off and the small piece of tube introduced into
+the bulb after having been shaped as shown in by _b_, Fig. 9. The
+opening in the bulb is sealed as shown by _b1_. The sealed part is now
+heated and the bulb inclined downwards until the inner tube comes in
+contact with the seal and is fused in position. This operation requires
+some practice in order to prevent the inner tube either falling through
+the soft glass or becoming unsymmetrical. The end of the bulb, where the
+inner tube comes in contact with it, is now perforated by heating and
+blowing, thus giving the form shown by _b2_, and the outer tube is
+joined on. The finished spray arrester is shown by _b3_. Practice alone
+will give the power to produce a symmetrical and stable piece of work.
+
+_Two Forms of Filter Pump._--That illustrated by _d_, Fig. 9, is made by
+the method explained under "An Air Trap on a Barometer Tube." That
+illustrated by _c_ is made by the method explained under "A Spray
+Arrester." No new manipulation is involved, and the construction should
+be clear from a study of the drawings.
+
+_Multiple and Branched Internal Seals._--A fuller consideration of these
+will be found on page 39, but one general principle may well be borne in
+mind; that, as far as is possible, a tube having both ends fastened
+inside another tube or bulb should be curved or have a spiral or bulb at
+some point in its length, otherwise any expansion or contraction will
+put great strain on the joints.
+
+_Sprays._--A spray which is easy to make, easy to adjust, and easy to
+clean after use is shown by _e_, Fig. 9. The opening on the top of the
+bulb is made by melting on a bead of glass, expanding, bursting, and
+fusing the ragged edges. The two branches which form the spray producing
+junction are made by the method used for an exhaustion branch and
+described on page 18.
+
+A spray which can be introduced through the neck of a bottle is shown by
+_h_, Fig. 9. The various stages in making this are illustrated by _f_,
+and _g_. If the inner tube is made by drawing out from a larger piece of
+glass so that two supporting pieces are left on each side of the place
+where it is intended to make the final bend, that bend can be made in a
+flat-flame gas burner without causing the inner tube to come in contact
+with the walls of the outer tube. Care must be taken when joining on the
+side piece that the inner tube is not heated enough to fuse it. The
+small hole in the side of the outer tube is produced by heating and
+bursting.
+
+_A Liebig's Condenser._--This consists of a straight glass tube passing
+through an outer cooling jacket. In practice it is better to make the
+jacket as a separate piece, and to effect a water-tight junction by
+means of two short rubber tubes. It may, however, be made with two
+internal seals of the class described under "A Spray Arrester." There is
+much less risk of these seals cracking if the inner tube is made in the
+form of a spiral or has a number of bulbs blown on it in order to give a
+certain amount of elasticity.
+
+_A Double-Surface Condenser._--Fig. 10 shows a condenser of this nature
+which is supplied by Messrs. Baird and Tatlock. It may be built up in
+stages as shown by _a_, _b_, and _c_, but the work involved requires
+considerable skill, and the majority of laboratory workers will find it
+cheaper to buy than to make.
+
+[Illustration: Fig. 10]
+
+_A Spherical Condenser._--Such a condenser as that shown by _f_, Fig 10,
+involves a method which may find application in a number of cases. The
+outer bulb is blown from a thick piece of tubing which has been inserted
+in a smaller piece (see _d_, Fig. 6); then the inner bulb by similar
+method. It is now necessary to introduce the smaller bulb into the
+larger, and for this purpose the larger bulb must be cut into halves. A
+small but deep cut is made with the file or glass-blowers' knife in the
+middle of the larger bulb, and at right angles to the axis of the tube
+on which it is blown. A minute bead of intensely heated glass is now
+brought in contact with the cut in order to start a crack. This crack
+may now be led round the bulb as described on page 30. If the work is
+carried out with care, it is possible to obtain the bulb in two halves
+as shown by _d_, and these two halves will correspond so exactly that
+when the cut edges are placed in contact they will be almost air-tight.
+The two tubes from the smaller bulb should be cut to such a length that
+they will just rest inside the larger, and the ends should be expanded.
+Place the inner bulb in position and fit the two halves of the outer
+bulb together, taking great care not to chip the edges. If the length of
+the tubes on the inner bulb has been adjusted properly, the inner bulb
+will be supported in position by their contact with the tubes on the
+outer bulb. Now rotate the cracked portion of the outer bulb in front
+of a blowpipe flame and press the halves together very gently as the
+glass softens. Expand slightly by blowing if necessary. If a small
+pin-hole develops at the joint it is sometimes possible to close this
+with a bead of hot glass; but if the bulb has been cut properly there
+should be no pin-holes formed. The condenser is finished by joining on
+the side tubes and sealing the inner tube through by the methods already
+given. In order to blow bulbs large enough to make a useful condenser,
+it will be convenient to employ the multiple-jet blowpipe described on
+page 4.
+
+_A Soxhlet-Tube or Extraction Apparatus._--This involves the
+construction of a re-entrant join where the syphon flows into the lower
+tube. It is of considerable value as an exercise and the complete
+apparatus is easy to make.
+
+A large tube is sealed at the bottom and the top is lipped, as in making
+a test-tube. A smaller tube is then joined on by a method similar to
+that given on page 18, but without making a perforation in the bottom of
+the large tube. Heating and expanding by air pressure, first through the
+large tube, then through the smaller tube and then again through the
+large tube, will give a satisfactory finish to this part of the work.
+
+[Illustration: Fig. 11]
+
+The syphon tube is now joined on to the large tube as shown by _a_, Fig.
+11, care being taken to seal the other end of the syphon tube before
+joining. The details of the final and re-entrant joint of the syphon
+tube are shown at the lower part of _a_. This join is made by expanding
+the sealed end of the syphon tube into a small, thick-walled bulb, and
+the bottom of this bulb is burst out by local heating and blowing; the
+fragments of glass are removed and the edges made smooth by melting. A
+similar operation is carried out on the side of the tube to which the
+syphon tube is to be joined. This stage is shown by _a_. Now heat the
+syphon tube at the upper bend until it is flexible, and press the bulb
+at its end into the opening on the side of the other tube. Hold the
+glass thus until the syphon is no longer flexible. The final join is
+made by heating the two contacting surfaces, if necessary pressing the
+edges in contact with the end of a turn-pin, fusing together and
+expanding. The finished apparatus is shown by _c_.
+
+_Electrodes._--A thin platinum wire may be sealed into a capillary tube
+without any special precautions being necessary. The capillary tube may
+be drawn out from the side of a larger tube by heating a spot on the
+glass, touching with a glass rod and drawing the rod away; or the
+exhaustion branch described on page 18 may be used for the introduction
+of an electrode. It is convenient sometimes to carry out the exhaustion
+through the same tube that will afterwards serve for the electrode. The
+electrode wire is laid inside the branch before connecting to the
+exhaustion pump. When exhaustion is completed the tube is heated until
+the soft glass flows round the platinum and makes the seal air-tight.
+The branch is now cut off close to the seal on the pump side, a loop is
+made in the projecting end of the platinum wire, and the seal is
+finished by melting the cut-off end.
+
+Platinum is usually employed for such work, but if care is taken to
+avoid oxidation it is not impossible to make fairly satisfactory seals
+with clean iron or nickel wire. Hard rods of fine graphite, such as are
+used in some pencils, may also be sealed into glass, but it seems
+probable that air would diffuse through the graphite in the course of
+time.
+
+Another method for the introduction of an electrode is illustrated by
+_d_, _e_, _f_ and _g_, Fig. 11. In this case the bulb or thin-walled
+tube into which the electrode is to be sealed is perforated by a quick
+stab with an intensely heated wire--preferably of platinum--which is
+then withdrawn before the glass has had time to harden, and thus a
+minute circular hole is made. The electrode is coated with a layer of
+similar glass, or of the specially made enamel which is sold for this
+purpose, inserted into the bulb or tube by any convenient opening, and
+adjusted by careful shaking until the platinum wire projects through the
+small hole. The bulb or tube is then fused to the coating of the
+electrode and the whole spot expanded slightly by blowing. The
+appearance of the finished seal is shown by _g_. It is well to anneal
+slightly by smoking.
+
+_Thermometers._--Apart from the notes on page 20 with respect to the
+blowing of a suitable bulb on capillary tubing there is little to say in
+connection with the glass working needed in making a plain thermometer.
+The size desirable for the bulb will be determined by the bore of the
+capillary tube, the coefficient of expansion of the liquid used for
+filling, and the range of temperature for which the thermometer is
+intended.
+
+Filling may be carried out as follows:--Fit a small funnel to the open
+end of the capillary by means of a rubber tube, and pour into the funnel
+rather more than enough of the liquid to be used than is required to
+fill the bulb. Mercury or alcohol will be used in practice, most
+probably. Warm the bulb until a few air bubbles have escaped through
+the liquid and then allow to cool. This will suck a certain amount of
+liquid into the bulb. Now heat the bulb again, and at the same time heat
+the capillary tube over a second burner. The liquid will boil and sweep
+out the residual air, but it is necessary to heat the capillary tube as
+well in order to prevent condensation. Allow the bulb and tube to cool,
+then repeat the heating once more. By this time the bulb and tube should
+be free from air, and cooling should give a completely filled
+thermometer. Remove the funnel and heat the thermometer to a few degrees
+above the maximum temperature for which it is to be used; the mercury or
+other filling liquid will overflow from the top, and, as the temperature
+falls, will recede, thus allowing the end of the capillary to be drawn
+out. Reheat again until the liquid rises to the top of the tube, then
+seal by means of the blowpipe flame. The thermometer is now finished
+except for graduation; this is dealt with on page 75.
+
+_An Alarm Thermometer._--A thermometer which will complete an electric
+circuit when a certain temperature is reached may be made by sealing an
+electrode in the bulb and introducing a wire into the top, which in this
+case is not sealed. Naturally, this thermometer will be filled with
+mercury. There is considerable difficulty in filling such a bulb without
+causing it to crack.
+
+Several elaborations of this form are made, in which electrodes are
+sealed through the walls of the capillary tube, thus making it possible
+to detect electrically the variation of temperature when it exceeds any
+given limits.
+
+_An Enclosed or Floating Thermometer._--The construction of this type of
+thermometer is shown by _h_ and _i_, Fig 11. It is made in the following
+stages:--A bulb is blown on the drawn-out end of a thin-walled tube as
+shown by _h_. A small bulb is blown on the end of a capillary tube,
+burst, and turned out to form a lip which will rest in the drawn-out
+part of the thin-walled tube but is just too large to enter the bulb.
+The capillary tube is introduced and sealed in position, care being
+taken to expand the joint a little. The thermometer is filled and the
+top of the capillary tube closed by the use of a small blowpipe flame. A
+paper scale having the necessary graduations is inserted, and the top
+of the outer tube is closed as shown by _i_.
+
+_A Maximum and Minimum Thermometer._--If a small dumb-bell-shaped rod of
+glass or metal is introduced into the capillary tube of a horizontally
+placed, mercury-filled thermometer in such a position that the rising
+mercury column will come in contact with it, the rod will be pushed
+forward. When the mercury falls again the rod will be left behind and
+thus indicate the maximum temperature attained. If a similar
+dumb-bell-shaped rod is introduced into an alcohol-filled thermometer
+and pushed down until it is within the alcohol column, it will be drawn
+down by surface tension as the column falls; but the rising column will
+flow passed it without causing any displacement; thus the minimum
+temperature will be recorded.
+
+Six's combined maximum and minimum thermometer is shown by _b_, Fig. 11.
+In this case both maximum and minimum records are obtained from a
+mercury column, although the thermometer bulb is filled with alcohol. It
+is an advantage to make the dumb-bell-shaped rods of iron, as the
+thermometer can then be reset by the use of a small magnet, another
+advantage consequent on the use of metal being that the rods can be
+easily adjusted, by slight bending, so as to remain stationary in the
+tubes when the thermometer is hanging vertically, and yet to move with
+sufficient freedom to yield to the pressure of the recording column.
+
+The thermometer may be filled by the following method:--When the
+straight tube has been made the first dumb-bell is introduced and shaken
+down well towards the lower bulb, the tube is now bent to its final
+shape and the whole thermometer filled with alcohol as described on page
+44. Now heat the thermometer to a little above the maximum temperature
+that it is intended to record, and pour clean mercury into the open bulb
+while holding the thermometer vertically. Allow to cool, and the mercury
+will be sucked down. The second dumb-bell is now introduced, sufficient
+alcohol being allowed to remain in the open bulb to about half fill it,
+and the alcohol in this bulb is boiled to expel air. The tube through
+which the bulb was filled in now sealed.
+
+_Clinical Thermometers._--The clinical thermometer is a maximum
+thermometer of a different type. In this case there is a constriction
+of the bore at a point just above the bulb. When the mercury in the bulb
+commences to contract, the mercury column breaks at the constriction and
+remains stationary in the tube, thus showing the maximum temperature to
+which it has risen.
+
+_Vacuum Tubes._--There are so many forms of these that it is scarcely
+practicable or desirable to give detailed instructions for making them;
+but an application of the various methods of glass-working which have
+already been explained should enable the student to construct most of
+the simpler varieties. An interesting vacuum tube is made which has no
+electrodes, but contains a quantity of mercury. When the tube is rocked
+so as to cause friction between the mercury and the glass sufficient
+charge is produced to cause the tube to glow.
+
+_A Sprengel Pump._--This, in its simplest form, is illustrated by _a_,
+Fig. 12. Such a form, although highly satisfactory in action, needs
+constant watching while in action, as should the mercury funnel become
+empty air will enter the exhausted vessel. Obviously, the fall-tube must
+be made not less than thirty inches long; the measurement being taken
+from the junction of the exhaustion branch with the fall-tube to the top
+of the turned-up end.
+
+[Illustration: Fig. 12]
+
+_A Macleod Pump._--One form of this is illustrated by _b_, Fig. 12. It
+has the advantage that the mercury reservoir may be allowed to become
+empty without affecting the vacuum in the vessel being exhausted.
+
+_"Spinning" Glass._--By the use of suitable appliances, it is quite
+possible to draw out a continuous thread of glass, which is so thin as
+to have almost the flexibility and apparent softness of woollen fibre; a
+mass of such threads constitutes the "glass wool" of commerce.
+
+The appliances necessary are:--a blowpipe capable of giving a
+well-formed flame of about six or eight inches in length, a wheel of
+from eighteen inches to three feet in diameter and having a flat rim of
+about three inches wide, and a device for rotating the wheel at a speed
+of about three hundred revolutions per minute.
+
+A very satisfactory arrangement may be made from an old bicycle; the
+back wheel having the tyre removed and a flat rim of tin fastened on in
+its place. The chain drive should be retained, but one of the cranks
+removed and a handle substituted for the remaining pedal. The whole
+device is shown by Fig. 13.
+
+[Illustration: Fig. 13]
+
+The procedure in "spinning" glass is as follows:--First melt the end of
+a glass rod and obtain a large mass of thoroughly softened glass, now
+spin the wheel at such a speed that its own momentum will keep it
+spinning for several seconds. Touch the end of the melted rod with
+another piece of glass and, without withdrawing the original rod from
+the blowpipe flame, draw out a thread of molten glass and twist it round
+the spinning wheel. If this is done properly, the thread of glass will
+grip on the flat rim, and by continuing to turn the wheel by hand it is
+possible to draw out a continuous thread from the melted rod, which must
+be advanced in the blowpipe flame as it is drawn on the wheel. If the
+rod is not advanced sufficiently the thread will melt off, if it is
+advanced too much, so as to heat the thick part and allow the glass to
+become too cool at the point of drawing out, then the thread will become
+too thick, but it is easy after a little practice to obtain the right
+conditions. Practice is necessary also in order to find the right speed
+for the wheel.
+
+When sufficient glass has been "spun," the whole "hank" of thin thread
+may be removed by drawing the thumb-nail across the wheel at any point
+on its flat rim, thus breaking the threads, and allowing the "hank" to
+open.
+
+_Brushes for Use with Strong Acids._--Glass wool, if of fine enough
+texture to be highly flexible, can be used to make acid-resisting
+brushes. A convenient method for mounting the spun glass is to melt the
+ends of the threads together into a bead, and then to fuse the bead on
+to a rod; thus giving a brush. If a pointed brush is necessary, the
+point may be ground on an ordinary grindstone or carborundum wheel by
+pressing the loose end of the spun glass against the grinding wheel with
+a thin piece of cardboard.
+
+When using brushes of this description, it is well to bear in mind the
+fact that there is always a liability of a few threads of glass breaking
+off during use.
+
+
+
+
+CHAPTER IV
+
+     Glass, Its Composition and Characteristics. Annealing.
+     Drilling, Grinding, and Shaping Glass by methods other than
+     Fusion. Stopcocks. Marking Glass. Calibration and Graduation
+     of Apparatus. Thermometers. Exhaustion of Apparatus. Joining
+     Glass and Metal. Silvering Glass.
+
+
+There are three kinds of glass rod and tubing which are easily
+obtainable; these are soda-glass, which is that usually supplied by
+chemical apparatus dealers when no particular glass is specified;
+combustion-glass, which is supplied for work requiring a glass that does
+not so easily soften or fuse as soda-glass; and lead-glass, which is
+less common. There are also resistance-glass, made for use where very
+slight solubility in water or other solutions is desirable, and a number
+of other special glasses; but of these soda-glass, combustion-glass,
+lead-glass, and resistance-glass are the most important to the
+glass-blower whose work is connected with laboratory needs.
+
+_Soda-Glass._--Consists chiefly of sodium silicate, but contains
+smaller quantities of aluminum silicate, and often of calcium silicate;
+there may also be traces of several other compounds.
+
+The ordinary soda-glass tubing melts easily in the blowpipe flame, it
+has not a long intermediate or viscous stage during fusion, but becomes
+highly fluid rather suddenly; it does not blacken in the reducing flame.
+Bad soda-glass or that which has been kept for many years, tends to
+devitrify when worked. That is to say the glass becomes more or less
+crystalline and infusible while it is in the flame; and in this case it
+is often impossible to do good work with that particular sample of
+glass; although the devitrification may sometimes be remedied by heating
+the devitrified glass to a higher temperature. The presence of aluminum
+compounds appears to have some influence on the tendency of the glass to
+resist devitrification. Soda-glass, as a rule, is more liable to crack
+by sudden heating than lead-glass, and articles made from soda-glass
+often tend to crack spontaneously if badly made or, in the case of
+heavier and thicker articles, if insufficiently annealed.
+
+_Combustion-Glass._--Is usually a glass containing more calcium silicate
+and potassium silicate than the ordinary "soft" soda-glass. It is much
+less fusible than ordinary soda-glass, and passes through a longer
+intermediate or viscous stage when heated. Such a glass is not very
+suitable for use with the blowpipe owing to the difficulty experienced
+in obtaining a sufficiently high temperature. If, however, a certain
+amount of oxygen is mixed with the air used in producing the blowpipe
+flame this difficulty is minimised.
+
+_Resistance-Glass._--May contain zinc, magnesium, and other substances.
+As a rule it is harder than ordinary soda-glass, and less suitable for
+working in the blowpipe flame. It should have very little tendency to
+dissolve in water, and hence is used when traces of alkali or silicates
+would prove injurious in the solutions for which the glass vessels are
+to be used.
+
+_Lead-Glass._--This, or "flint" glass as it is often called from the
+fact that silica in the form of crushed and calcined flint was often
+used in making the English lead-glasses, contains a considerable
+proportion of lead silicate. Such a glass has, usually, a particularly
+bright appearance, a high refractive index, and is specially suitable
+for the production of the heavy "cut-glass" ware.
+
+Lead-glass tubing is easy to work in the blowpipe flame, melts easily,
+but does not become fluid quite so suddenly as most soda-glasses;
+articles made from it are remarkably stable and free from tendency to
+spontaneous cracking, although, as is essential for all the heavy or
+"glass-house" work, the massive articles need annealing in the oven.
+
+The two chief disadvantages of lead-glass for laboratory work are that
+it is blackened by the reducing gases if held too near to the blue cone
+of the blowpipe flame, and that it is rather easily attacked by chemical
+reagents; thus ammonium sulphide will cause blackening.
+
+The effect of the reducing flame on lead is not altogether a
+disadvantage, however; because a little care in adjusting the blowpipe
+and a little care in holding the glass in the right position will enable
+the student to work lead-glass without producing the faintest trace of
+blackening. This, in addition to being a valuable exercise in
+manipulation, will teach him to keep his blowpipe in good order, and
+prove a useful aid in his early efforts to judge as to the condition of
+the flame. It prevents discouragement if the student does his
+preliminary work with the soda-glass, but he should certainly make
+experiments with lead-glass as soon as he has acquired reasonable
+dexterity with soda-glass.
+
+_Annealing._--Annealing is a process by which any condition of strain
+which has been set up in a glass article, either by rapid cooling of one
+part while another part still remains hot, or by the application of
+mechanical stress after cooling is relieved. Annealing is carried out by
+subjecting the article to a temperature just below the softening point
+of the glass, maintaining that temperature until the whole article has
+become heated through the thicker part, and then reducing the
+temperature very gradually; thus avoiding any marked cooling of the
+thinner and outer parts first.
+
+For thin glass apparatus of the lamp-blown or blowpipe-made variety in
+which there are no marked difference of thickness, such as joins on
+tubes, ordinary seals, bulbs, etc., there is little need for annealing;
+and even those having rather marked changes of thickness, such as
+filter pumps, can be annealed sufficiently by taking care that the last
+step in making is heating to just below visible redness in the blowpipe
+flame and then rotating in a sooty gas flame until covered with a
+deposit of carbon. The article should then be allowed to cool in a place
+free from draughts and where the hot glass will not come in contact with
+anything.
+
+A few of the blowpipe-made articles, such, for example, as glass
+stopcocks, need more careful annealing, and for this purpose a small
+sheet-iron oven which can be heated to dull redness over a collection of
+gas burners will serve. Better still, a small clay muffle can be used.
+In either case, the article to be annealed should be laid on a clean,
+smooth, fireclay surface, the temperature should be maintained at a very
+dull red for two or three hours and then reduced steadily until the oven
+is cold. This cooling should take anything from three to twelve hours,
+according to the nature of the article to be annealed. A thick article,
+or one having great irregularities in thickness will need much longer
+annealing than one thinner or more regular. As a rule, soda-glass will
+need more annealing than lead-glass.
+
+_Drilling Glass._--Small holes may be drilled in glass by means of a rod
+of hard steel which has been broken off, thus giving a more or less
+irregular and crystalline end.
+
+There are several conditions necessary to enable the drilling of small
+holes to be carried out successfully:--the first of these is that the
+"drill" should be driven at a high speed. This may be done by means of a
+geared hand-drill such as the American pattern drill, although a
+somewhat higher speed than this will give is even more satisfactory. The
+second condition is that the pressure on the drill is neither too light
+nor too heavy; this is conveniently regulated by hand. The third
+condition is that the drill be prevented from "straying" over the
+surface of the glass; for this purpose a small metal guide is useful.
+The fourth condition is that a suitable lubricant be used; a strong
+solution of camphor in oil of turpentine is perhaps the most suitable.
+For commercial work, a diamond drill is often used, but this is scarcely
+necessary for the occasional work of a laboratory.
+
+_Larger Holes in Glass._--The method of drilling with a hard steel rod
+is not highly satisfactory for anything but small holes. When a larger
+hole, say one of an eighth of an inch or more, is needed it is better to
+use a copper or brass tube. This tube may be held in an American
+hand-drill, but a mixture of carborundum or emery and water is supplied
+to the rotating end. Tube or drill must be lifted at frequent intervals
+in order to allow a fresh supply of the grinding material to reach the
+end. In this case, also, a guide is quite essential in the early stages
+of drilling; otherwise the end of the tube will stray. The speed of
+cutting may be increased slightly by making a number of radial slots in
+the end of the tube; these serve to hold a supply of the grinding
+material.
+
+_Grinding Lenses._--This is scarcely within the scope of a book on
+glass-blowing for laboratory purposes, but it may be said that the lens
+may be ground by means of a permutating mould of hard lead or
+type-metal. The rough shaping is done with coarse carborundum or emery,
+and successive stages are carried on with finer and finer material. The
+last polishing is by the use of jewellers' rouge on the mould, now
+lined with a fine textile.
+
+_Filing Glass._--If a new file, thoroughly lubricated with a solution of
+camphor in oil of turpentine, is used, there is but little difficulty in
+filing the softer glasses. A slow movement of the file, without
+excessive pressure but without allowing the file to slip, is desirable.
+After a time the cutting edges of the file teeth will wear down and it
+will be necessary to replace the file by another.
+
+_Grinding Stoppers._--This is, perhaps, the most common form of grinding
+that the laboratory worker will need to perform, and for that reason,
+rather full details of the procedure are desirable.
+
+A very crude form of ground-in stopper may be made by drawing out the
+neck and the mass of glass which is intended to form the stopper to
+approximately corresponding angles, wetting the surfaces with a mixture
+of the abrasive material and water, and grinding the stopper in by hand.
+Frequent lifting of the stopper is necessary during grinding, in order
+to allow fresh supplies of abrasive material to reach the contacts. When
+an approximate fit is obtained, the coarse abrasive should be washed
+off, care being taken that the washing is complete, and a finer abrasive
+substituted. After a while, this is replaced in its turn by a still
+finer grinding material.
+
+Such a method of grinding may give a satisfactory stoppering if the
+angles of the plug and socket correspond very closely before grinding is
+commenced; but if there is a wide difference in the original angles,
+then no amount of grinding by this method will produce a good result.
+The reason for this is that the plug will become so worn in the
+preliminary grinding as to assume the form of a highly truncated cone;
+the socket will assume a reverse form, and the end result will be a
+loose-fitting plug and socket.
+
+Satisfactory grinding may be carried out by the use of copper or
+type-metal cones for the preliminary shaping. Such cones should be
+mounted on a mandrel which will fit into the chuck of the American
+hand-drill and turned on the lathe to the desirable angle for
+stoppering. A number of these cones will be necessary. A number of
+similar moulds, that is to say blocks of type-metal or hard lead in
+which is a hole corresponding in size and angle to the plug desired,
+should be made also. These must be rotated, either in the lathe or by
+other means, and are used for the preliminary shaping of the plug. If
+but few plugs are to be ground it is unnecessary to provide a means of
+rotating the moulds, as the plug may be held in the hand and ground into
+the mould in a manner similar to that used in the first method of
+stoppering.
+
+[Illustration: Fig. 14]
+
+When the socket and plug have been ground, by the successive use of
+cones and moulds, to the desired angle, so that they correspond almost
+exactly, the plug is given its final fitting into the socket by
+grinding-in with a fine abrasive, in the manner first described.
+
+_Stopcocks._--Although it would be more strictly in keeping with the
+form of this book to divide the making of stopcocks into two parts;
+shaping by heat and grinding, we will consider the whole operation here,
+and take for our example a simple stopcock such as that illustrated by
+Fig. 14.
+
+The "blank," _f_, that is the socket before grinding, is made by drawing
+out a piece of fairly thick-walled tubing into the form shown by _a_.
+Two zones on this tube are then heated by means of a small, pointed
+flame, and the tube is compressed along its axis, thus producing two
+raised rings as shown by _b_. Two zones, slightly towards the outer
+sides of these two raised rings are heated and the tube is drawn while
+air pressure is maintained within. This produces two thin-walled bulbs
+or extensions similar to those shown by _c_. One of these extensions is
+now broken off by means of a sharp blow with the edge of a file or
+other piece of metal, and the edges of the broken glass are rounded in
+the flame. The other extension is left to serve as a handle. We have now
+a piece of glass like that shown by _d_. Now heat a spot on the side of
+this, medially between the raised rings, until the glass is on the point
+of becoming deformed, and bring the intensely heated end of a smaller
+tube in contact with the heated spot. Without disturbing the relative
+positions of the two tubes, press the smaller tube down on a thin steel
+wire, so that the wire passes along the tube and enters the soft glass;
+thus forming a projection inside the sockets as shown by _e_. The wire
+must be withdrawn, again immediately. When the wire has been withdrawn,
+heat the place where it entered to dull redness, in order to relieve any
+strain; break off the thin extension, which up to the present has served
+as a handle, round off the broken edges in the flame, and join on and
+indent a similar piece of small tubing to the opposite side of the
+socket; the socket at this stage being shown by _f_. The "blank" for the
+socket is now completed, but it must be heated to dull redness in order
+to relieve strain and be placed in an annealing oven, where it should
+be annealed for some hours.
+
+The "blank" for the plug offers no special difficulty; it is made by
+heating a glass rod and compressing it axially until a mass having the
+form shown by _g_, Fig. 14, is produced; the end of this is heated
+intensely and brought in contact with the rather less heated side of a
+glass tube which has been drawn to the shape desired for the handle;
+when contact is made a slight air pressure is maintained in the glass
+tube, thus producing a hollow join. The ends of the tube are sealed and
+the bottom of the plug is drawn off, thus giving the finished "blank" as
+shown by _h_. This blank is now held in a pair of asbestos-covered
+tongs, heated to dull redness all over, and transferred to the annealing
+oven.
+
+When cold, the socket is ground out by the second method given under
+"Grinding Stoppers"; that is to say, by means of type-metal or copper
+cone, and the plug is ground to fit in a corresponding mould. When the
+fit is almost perfect, the transverse hole is drilled in the plug, and
+the final finishing is made with fine abrasive powder. Great care must
+be taken in the final grinding that there is no accumulation of
+abrasive material in the transverse hole of the plug; if this is allowed
+to occur there will be a ring ground out of the socket where the holes
+move, and the tightness of the finished stopcock will be lost.
+
+_Marking Glass._--As a preliminary to a consideration of the methods of
+graduating and calibrating glass apparatus, it is convenient to consider
+the various methods which are available for marking glass. Among these
+are, the writing diamond, the carborundum or abrasive pencil, the
+cutting-wheel, and etching by means of hydrofluoric acid. Each produces
+a different class of marking and each is worthy of independent
+consideration.
+
+_The Writing Diamond._--This is the name given to a small irregular
+fragment of "bort" which is usually mounted in a thin brass rod. Such a
+diamond, if properly selected, has none of the characteristics of a
+cutting diamond; although one occasionally finds so-called "writing
+diamonds" which will produce a definite cut. These should be rejected.
+
+The writing diamond is used in much the same way as a pencil, but is
+held more perpendicularly to the object, and a certain amount of
+pressure is necessary. The mark produced is a thin scratch which,
+although fairly definite, lacks breadth, and this is a disadvantage
+where the marking has to be read at a distance. This disadvantage may to
+some extent be overcome by making a number of parallel scratches.
+
+_The Abrasive Pencil._--A rod of carborundum composition may be ground
+or filed to a point, and this forms a very useful pencil for general
+work. The marking produced is rather less definite than that produced by
+a writing diamond, but has the advantage of being broader.
+
+_The Cutting Wheel._--"Cutting" in this case is scarcely the ideal
+expression, it should rather be "grinding," but "cutting" is more
+commonly used. Exceedingly good graduations may be made by the edge of a
+small, thin, abrasive wheel which is mounted on the end of a small
+mandrel and driven by a flexible shaft from an electric motor or any
+other convenient source of power. The depth of the mark can be
+controlled, and very light pressure will suffice.
+
+_Etching._--This is often the quickest and easiest way of marking glass
+apparatus. The object to be marked should first be warmed and coated
+very thoroughly with a thin film of paraffin wax. When cold, the marking
+is made through the paraffin wax by means of a needle point, and the
+object is then exposed to the action of hydrofluoric acid. If a shallow
+but clearly visible marking is desired, it is well to use the vapour of
+the acid; this may be done by bending up a sheet-lead trough on which
+the object can rest with the marked surface downwards. A little of the
+commercial hydrofluoric acid, or a mixture of a fluoride and sulphuric
+acid, is distributed over the bottom of the trough, and the whole
+arrangement is allowed to stand for about an hour. The object is washed
+thoroughly and the paraffin wax removed, either by melting and wiping
+off or by the use of a solvent, and the marking is finished.
+
+If a deep marking is desired, in order that it may afterwards be filled
+with some pigment, a better result is obtained by the use of liquid
+commercial hydrofluoric acid, which is a solution of hydrogen fluoride
+in water. The acid is mopped on to the object after the markings have
+been made on the paraffin wax film, and allowed to remain in contact for
+a few minutes. It is advantageous to repeat the mopping-on process at
+intervals during the etching.
+
+In all cases where hydrofluoric acid is used, or stored, it is of great
+importance to keep it well away from any optical instruments, as the
+most minute trace of vapour in the air will produce a highly destructive
+corrosion of any glass surfaces.
+
+_Methods of Calibration._--In the case of apparatus for volumetric work,
+this is usually carried out by weighing, although some of the smaller
+subdivisions are often made by measurement. When the subdivisions are
+made in this way it is of importance to see that the walls of the tube
+or vessel to be calibrated are parallel. Great errors arise in some of
+the commercial apparatus from neglect of this precaution. A convenient
+method of testing for parallelism, in the case of a wide tube, is to
+close one end and to weigh in successive quantities of mercury. An
+observation of the length occupied by each successive quantity will
+indicate any change in the bore. In the case of capillary tubes, it is
+convenient to introduce an unweighed quantity of mercury, measure its
+length accurately, and then to move it along the tube in stages, either
+by tilting the tube or by the application of air pressure. A measurement
+of the length at each stage will indicate whether the bore is
+approximately parallel or not. Neither of these methods is to be relied
+on without a careful examination of the tube, as it may happen that
+there are local irregularities in the bore which compensate for each
+other, and do not, therefore, affect the volume of a given length.
+Obviously, the smaller the quantity of mercury with which the test is
+carried out and the greater the number of observations made, the less
+risk will there be of such an error. A liquid, such as water or alcohol,
+which wets the glass is not suitable for such a test, unless special
+precautions are taken.
+
+When, however, a pipette or burette has to be calibrated to deliver a
+certain volume of water, the final calibration must be made with this
+liquid. Thus, the burette would first be calibrated by weighing in
+definite quantities of mercury of say 13.54 grammes (1 cc at 15°C.),
+each of the 1 cc divisions should be marked by some temporary marking.
+The burette is now filled with a solution of potassium bichromate and
+sulphuric acid and allowed to soak for some time; the bichromate is
+washed out and distilled water is put in. Successive quantities of water
+are run out of the jet, a fixed time being allowed for draining, and the
+weights of the quantities delivered are noted. This procedure will give
+the necessary data for altering the marking so that it may correspond to
+1 cc _delivered_. Each 1 cc division is now divided into tenths by the
+method described below. A final verification of the markings should be
+made when the subdivision is completed.
+
+_Subdivision of Graduations._--Mark out the spaces to be subdivided on a
+sheet of paper. Take a reliable ruler on which any convenient length is
+divided into the desired number and place it across the lines at such an
+angle that the limits noted on the rule exactly bridge the gap. Now draw
+parallel lines through the markings.
+
+_Copying a Scale._--When a scale has been prepared on paper and it is
+necessary to copy that scale on the waxed-glass surface for etching, a
+convenient method is to employ a long wooden bar having a sharp needle
+passing through it at either end. The scale and object to be marked are
+fastened in line with one another, and the caliper bar is used from step
+to step. The mark is made by moving the bar through a minute portion of
+a circle, which provided that the bar is two or three feet in length,
+will not introduce any perceptible error in a scale of say a quarter of
+an inch in width. The arrangement is shown by Fig. 15.
+
+[Illustration: Fig. 15]
+
+_Graduating a Thermometer._--Assuming that the thermometer has been made
+of carefully selected tubing in which the bore is parallel and free from
+any small irregularities, we have only to fix the freezing point and
+boiling point. The intervening space may then be divided into 100 (if
+the thermometer is to be Centigrade) or 180 (if Fahrenheit). This
+division may be carried out by the method given under "Subdivisions of
+Graduations." A thermometer should not be calibrated until some weeks
+after making, as the glass bulb tends to contract.
+
+_Joining Glass and Metal._--It sometimes happens that one needs to make
+a more permanent and less flexible joint between a glass and metal tube
+than can be obtained by means of a rubber tube. To this end, any one of
+three slightly different methods may be employed. In the method of
+Chatelier one first coats the glass with platinum or silver, which may
+be done by moistening the glass with platinum chloride or silver nitrate
+and then heating to redness; a layer of copper is then deposited
+electrolytically on the treated surface of the glass, and soldering is
+carried out in the usual manner.
+
+McKelvy and Taylor call attention to two other methods in the _Journal
+of the Chemical Society_ for September, 1920. In one of these methods
+the glass is coated with platinum by covering it with a suspension of
+platinum chloride in oil of lavender and heating until the oil is burnt
+off. The metal tube is then tinned on its inner side and soldered to the
+prepared glass, slightly acid zinc chloride being used as a flux.
+
+In the second method, a joint is made by means of the Kraus flux, which
+consists of equal weights of zinc oxide, borax, and powdered soda-glass
+fused together. This is coated on the inner surface of the metal tube,
+and the hot glass tube, which has had the end slightly flanged to give
+support, is inserted. Fusion of the flux is completed by heating the
+outside of metal tube.
+
+_Silvering Glass._--In all cases where it is intended to deposit a
+silver mirror on a glass surface, thorough cleaning is essential.
+Prolonged soaking in a hot solution of potassium bichromate which has
+been acidified with sulphuric acid will often prove useful. The glass
+should then be washed thoroughly, rinsed in distilled water, and the
+solution should then be used.
+
+There are many formulæ for the silvering solution, but that used in
+Martin's method may be given:--
+
+        A--Nitrate of Silver      40 grammes
+           Distilled Water      1000 c. cm.
+
+        B--Nitrate of Ammonium    60 grammes
+           Distilled Water      1000 c. cm.
+
+        C--Pure Caustic Potash   100 grammes
+           Distilled Water      1000 c. cm.
+
+        D--Pure Sugar Candy      100 grammes
+           Distilled Water      1000 c. cm.
+
+     Dissolve and add:--
+
+           Tartaric Acid          23 grammes
+
+     Boil for ten minutes, and when cool add:--
+
+           Alcohol               200 c. cm.
+           Distilled Water to   2000 c. cm.
+
+For use take equal parts of A and B. Mix together also equal parts of C
+and D in another vessel. Then mix both liquids together in the silvering
+vessel and suspend the glass to be silvered face downwards in the
+solution. Or if a vessel has to be silvered on the inside, the solution
+is poured in. In this case, the deposition of silver may be hastened by
+immersing the vessel to be silvered in warm water.
+
+In working with a silver solution containing ammonia or ammonium salts
+there is sometimes the possibility of forming an explosive silver
+compound. It is well, therefore, to avoid keeping such solutions longer
+than is necessary, and to bear in mind that any deposit formed by
+solutions containing both silver and ammonia may have explosive
+properties, especially when dry.
+
+
+
+
+CHAPTER V
+
+     Extemporised Glass-Blowing Apparatus--The Use of Oil or
+     other Fuels--Making Small Rods and Tubes from Glass
+     Scrap--The Examination of Manufactured Apparatus with the
+     View to Discovering the Methods Used in Manufacture--Summary
+     of Conditions Necessary for Successful Glass-Blowing.
+
+
+If, in the early stages of his study of glass-blowing, the student
+should attempt to work with the very simplest appliances, it is probable
+that his progress will be hindered; the use of the apparatus will
+require an undue amount of care and his attention will be distracted
+from the actual manipulation of the glass. The case is widely different
+after he has acquired a certain facility in glass-blowing.
+
+_A Simple Form of Blowpipe._--Although there are even more simple forms
+than that described here, we are not concerned with them. The form
+described is the simplest with which any considerable amount of
+glass-blowing can be carried out with certainty.
+
+This form consists of a tube through which air may be blown with the
+mouth, a condensation chamber in which any moisture from the breath can
+condense, a blowpipe jet, a supporting piece and a source of flame.
+
+The tube, condensation chamber, and jet are combined in the ordinary
+Black's blowpipe, such as is used for blowpipe tests in qualitative
+analysis; it consists of a conical tin tube having a mouthpiece at the
+small end and a side tube which carries a brass jet. A support for such
+a blowpipe may be cut out of a piece of brass or tin-plate, and should
+be fastened to a small, flat, wooden board. A source of flame may
+consist of an ordinary brass elbow, such as is used on gas fittings, and
+into which a piece of thin brass tube (the body of a fish-tail burner
+from which the perforated non-metallic plug has been removed will serve
+quite well) has been fitted. It is an advantage to flatten the brass
+tube somewhat and to file the flattened end to a slope which corresponds
+with the angle at which the blowpipe jet enters the burner. The whole
+source of the flame should be mounted on a separate base, in order that
+it may be moved while adjusting the apparatus to the best relative
+positions of flame and blowpipe jet. The complete apparatus is shown by
+_a_, Fig. 16.
+
+[Illustration: Fig. 16]
+
+In order to take full advantage of this blowpipe, it is desirable that
+the student should learn to maintain a steady steam of air with his
+mouth and, at the same time, be able to breathe. This requires a little
+practice.
+
+As a first exercise in breathing, before trying to breathe while using
+the mouth blowpipe, the student should close his mouth and inflate his
+cheeks with air; now, still keeping his cheeks tightly inflated, he
+should attempt to breathe through the nose. At first, this may be found
+rather difficult, but it becomes remarkably easy after a little
+practice. When he has mastered this, the student may practise the same
+operation, but with the blowpipe. It is important to bear in mind that
+the cheeks, not the lungs, form the reservoir for air used in
+maintaining the blowpipe flame. After a while, the student will find
+that he can maintain a steady air pressure and yet breathe with complete
+comfort.
+
+In adjusting the flame, care should be taken not to blow so hard as to
+produce a ragged and noisy cone of fire. A small jet, such as that
+commonly used on a mouth blowpipe, will with care give a pointed and
+quiet flame, having an appearance similar to that shown in the
+illustration.
+
+With a blowpipe like this, it is quite easy to seal glass tubes up to an
+inch in diameter, to join tubes up to half an inch in diameter, to bend
+tubes, to blow small bulbs, and to make the simpler forms of internal
+seal; but the provision for condensation of moisture is not ideal, and
+prolonged use of such a blowpipe also tends to produce undue fatigue.
+
+_A Mouth Blowpipe With an Expanding Reservoir._--This form of blowpipe
+can be made to give most excellent results; it is highly portable, and
+does not produce nearly so much fatigue when used continuously as the
+blowpipe described in the last section. Various slight modifications
+have been made in its construction during the last eighty years, but
+that described below will be found quite satisfactory.
+
+The apparatus consists of a tube through which air is blown from the
+mouth, a valve through which the air passes into an expanding reservoir,
+and a blowpipe jet in communication with the reservoir.
+
+In making the valve, several essentials have to be remembered; it must
+allow a free passage of air into the reservoir, it must open easily, and
+must close quickly. A satisfactory form of valve is that shown by _b_,
+Fig. 16. The moving part consists of a light glass bulb of about
+three-eights of an inch diameter and having a glass stem of rather under
+one-eighth diameter and about an inch and a half long. This stem rests
+in a guide at the end of a brass tube, the bulb contacting against the
+other end which is approximately shaped. The bulb and its seating are
+ground air-tight. A very light spring holds the bulb in position.
+
+This valve is fitted into a metal or glass T piece, one limb of which
+leads to the air reservoir and the other limb leads to the blowpipe jet;
+the limb containing the valve leads to the tube through which the air is
+blown in.
+
+A convenient reservoir may be made from a fairly large football bladder.
+A network of string should be fitted over the outside of the bladder and
+the strings should terminate in a hook on which a weight can be hung, in
+order to provide a means of adjusting the pressure at which the air is
+delivered to the jet. This bladder should be washed out and allowed to
+drain after use.
+
+The air tube which passes from the valve to the mouth may conveniently
+be made of brass, but, in order to avoid the continued contact of metal
+with the lips of the operator, it should be fitted with a non-metallic
+mouthpiece. It is an advantage from the point of view of portability to
+have the air tube easily detachable from the T piece containing the
+valve.
+
+The blowpipe jets, of which there may be several with advantage, may be
+made of glass tubing, bent to the most convenient angle and having an
+enlargement or bulb at some point in the tube. This bulb serves as a
+final condensing place for any traces of moisture that may escape from
+the larger reservoir.
+
+The whole device, blowing tube, reservoir, and T piece may be fastened
+to a clamp, so that it can be secured on the edge of any table where
+blowpipe work is to be carried out. If the blowpipe is to be used with
+gas, the form of burner described under. "A Simple Form of Blowpipe"
+will be found quite satisfactory.
+
+_The Use of Oil, or Other Non-Gaseous Fuels._--Although gas, when
+available, is usually preferred on account of its convenience, there are
+several other fuels which give a hotter flame. They have, also, the
+additional advantage of not requiring any connecting pipes; but each has
+its own disadvantage.
+
+One liquid fuel deserves special mention as being rather less desirable
+than the others; this is alcohol. Although very convenient in use, it
+has the disadvantage of being rather too highly inflammable and capable
+of burning without a wick, thus involving a certain fire risk; the flame
+is scarcely visible in a bright light, and the heat given by either the
+ordinary flame or the blowpipe flame produced from alcohol is
+considerably less than that from a similar flame in which coal gas is
+used. For small work, however, the facility with which a spirit lamp may
+be lighted may more than counterbalance these disadvantages at times.
+
+_Paraffin Wax._--Where there is no coal gas available and the blowpipe
+is only required at intervals, and especially where high portability is
+required, there are few fuels so convenient as paraffin wax. This may be
+obtained in pieces of a satisfactory size by cutting paraffin candles,
+from which the wick has been withdrawn, into lengths of about half an
+inch. These cut pieces have the advantage over any oily fuel, such as
+colza oil, that they can be wrapped in paper or carried in a cardboard
+box; further they will keep indefinitely, even in the presence of air,
+without undergoing any perceptible change.
+
+_Forms of Lamp for Paraffin Wax._--Probably, the best form is that
+devised by Thomas Bolas, and described by him in the _Journal of the
+Society of Arts_, December 2nd, 1898. This lamp consists of a small open
+tray of iron, through which pass three or more flat tubes, and between
+these tubes are placed small flat pieces of wick, the fit being such
+that the pieces of wick may be adjusted easily by means of a pair of
+pointed tweezers.
+
+The flame thus obtained, instead of having one large hollow, is broken
+or divided so that the combustion is concentrated into a smaller area,
+and the air blast, which is directed across the flame, carries the flame
+with it in a more complete manner than is the case with the ordinary
+flame; a more thorough combustion being realised by this arrangement.
+
+Another advantage is the ease with which the wick may be changed and a
+larger or smaller wick inserted to suit the flame to any size of air
+jet.
+
+This form of lamp may be used for oily fuel, although it is specially
+suitable for paraffin wax.
+
+Two small pieces of bent tin-plate may be used as side covers, and these
+serve to adjust the flame within certain limits. A tin-plate cover which
+fits easily over the whole lamp serves as an extinguisher. The complete
+lamp is shown by _d_, Fig. 16, and this figure shows also a quick-change
+air-jet device, the whole arrangement forming a blowpipe for use where a
+non-gaseous fuel is to be employed.
+
+Although the lamp just described is desirable when complete control over
+the size of the flame is necessary, and if the ideal conditions and
+maximum heat are to be obtained, yet a simpler form of lamp will be
+found to give very good results. Such a lamp may consist of a flat tin
+tray, having a diameter of about three and a half inches and a depth of
+about one inch. In this tray is a tin support for the wick, and the wick
+itself may consist of a bundle of soft cotton, for example, a loosely
+rolled piece of cotton cloth, but in either case the top of the wick
+should be cut to approximately the same angle as that at which the
+blowpipe jet meets the flame.
+
+In using paraffin wax as a fuel, it is necessary to see that sufficient
+wax reaches the wick to prevent charring during the first few minutes
+before the bulk of the wax is melted.
+
+_Animal and Vegetable Oils._--Almost any oil may be used as a fuel, but
+many tend to become hard and gummy if allowed to stand in the air for
+any considerable time. When this happens, the wick becomes clogged and
+it is impossible to obtain a good flame. A number of the oils tend,
+also, to produce rather strongly smelling smoke.
+
+_A Flame-Guard for Use With Non-Gaseous Fuels._--In order to avoid the
+eye-strain produced by the luminous base of the flame from a wick
+burning paraffin wax or oil, it is often advantageous to make a small
+tunnel of tin-plate, which can be rested on the sides of the lamp and
+rises over the top of the wick. Such a flame guard is shown by _e_, Fig.
+16.
+
+_Small Rods and Tubes from Glass Scrap_:--It is scarcely practicable to
+make small quantities of good glass with the blowpipe flame as the only
+source of heat, but it is less difficult to make small rods or tubes
+from glass scrap, and the ability to do this is sometimes of
+considerable value when a small tube has to be joined on to some special
+piece of apparatus made of glass of unknown composition. It may be
+possible to obtain some fragments of similar glass, either from a broken
+part of the apparatus or from a similar piece, and from these fragments
+small tubes or rods can be made.
+
+The fragments of glass may be melted together on the end of a clay
+pipe-stem, care being taken to avoid trapping air bubbles as fresh
+fragments are added to the molten mass. When a sufficient quantity of
+glass has been accumulated, the viscous mass may be drawn out into a rod
+by bringing another pipe-stem into contact with the hot mass, rotating
+both pipe-stems steadily, and separating them until a rod of the desired
+size has been obtained.
+
+If, on the other hand, it is desired to produce a tube from the mass of
+heated glass, the mass should be blown hollow before the pipe-stems
+supporting it are separated.
+
+_Methods of Manufacture._--When the student has familiarised himself
+with the more common operations and processes used in glass-blowing, he
+will be in a position to increase his skill and knowledge of special
+methods by a critical examination of various examples of commercial
+work. There are few exercises more valuable than such an examination,
+combined with an attempt to reconstruct the stages and the methods by
+which the article chosen for examination was made.
+
+Obviously, it is impossible to give full details of all constructions in
+a small text-book; but it is easy to give an example of the
+constructional methods employed in the making of almost any piece of
+light blown-glass apparatus, and these methods should prove of special
+value when apparatus of a new pattern has to be evolved for the purposes
+of research. That is to say, one designs the apparatus required, applies
+known methods of construction as far as possible, and, by the
+examination of commercial apparatus having similar features, evolves the
+new methods required. For an exercise in such a process of
+reconstruction we may well take an ordinary commercial vacuum tube, such
+as that shown by _a_, Fig. 17.
+
+[Illustration: Fig. 17]
+
+In the tube from which this drawing was made, it was found that the
+spiral in the middle bulb was of a slightly yellowish colour and gave a
+green fluorescence when the electric discharge was passed through the
+tube; that is to say, the spiral is made of uranium-glass, which is
+usually a soda-glass containing trace of uranium, and hence differing
+slightly in composition from the ordinary glasses. The two enclosed
+tubes which are bent into a series of S bends gave a pink fluorescence,
+which indicates lead-glass; and the remainder of the tube fluoresced
+with an apple-green colour; this suggests ordinary soda-glass. We have,
+therefore, a piece of apparatus in which three dissimilar glasses are
+joined, while, at the same time, that apparatus contains a number of
+internal seals, and it is not probable that the dissimilar glasses will
+have their coefficients of expansion so nearly alike as to permit of a
+stable internal seal being made if one part of the seal consists of a
+glass differing from that of the other part.
+
+These considerations lead us to a closer examination of the joins where
+the dissimilar glasses are introduced, and we find that in no case is
+the internal seal made between dissimilar glasses, but that a soda-glass
+extension is joined on to both the uranium-glass tube and the lead-glass
+tubes at a point about half an inch before the internal seal commences.
+Careful examination of these joins shows that the change from one glass
+to another is not abrupt but gradual. Such a transitional joint may be
+made by taking a length of soda-glass tubing, sealing the end and fusing
+a minute bead of the other glass on to the sealed end, the end is then
+expanded and another bead of the other glass added, this bead is
+expanded and the operation is repeated, thus building up a tube, and,
+finally, the tube of the other glass is joined on to the end of this.
+
+We are now concerned with the question of the insertion of the
+uranium-glass spiral into the bulb (see p. 38). Obviously the spiral is
+too large to pass through the necks of the bulb, and it is difficult to
+imagine that the spiral was obtained by the insertion of a length of
+straight tubing which was bent after entering the bulb; therefore, the
+only remaining method is that the spiral was made first and the
+soda-glass extensions fastened on, and that the bulb was blown, cut in
+halves and the spiral inserted, and the two halves were then rejoined.
+That this was actually the case is confirmed by traces of a join which
+are just visible round the middle of the bulb. The insertion of the
+spiral and the making of the first internal seal are shown by _b_, and
+_c_.
+
+There is one detail in making the second join of the spiral to the bulb
+which calls for attention, and the small branch, similar to an
+exhaustion branch, at the side of the bulb provides a clue to this. If
+an attempt were made to complete the second internal seal through a
+closed bulb it would be impossible to obtain a good result, as the
+air-pressure in the bulb would not be under control when once union was
+effected, and further heating of the air in the bulb would cause
+expansion and perforate the wall near the second internal seal; we
+therefore make a small branch which can be left open and through which
+such air-pressure as may be found necessary can be maintained.
+
+The third join, by which the lead-glass tube is joined to the soda-glass
+is made in stages similar to those in which the soda-glass and
+uranium-glass were joined; but the internal seal is most conveniently
+made by sliding a length of tubing over the lead-glass and fusing this
+tubing to the large diameter soda-glass tube to which the lead-glass is
+already joined. The first stage of this operation is illustrated by _d_.
+When this seal is completed, the end of the soda-glass tube is drawn off
+and sealed as shown in _e_, and at this stage a side tube or branch is
+joined on. The sealed end of the outer and large diameter soda-glass
+tube is heated until it contracts and fuses to the enlargement that has
+previously been joined to the lead-glass tube, and the end is burst out
+as shown in _f_. Another length of soda-glass is then joined on to the
+burst-out end, and this length of soda-glass tubing is drawn out to a
+thin-walled contraction; the non-contracted part is expanded to form the
+bulb, and a small exhaustion branch made on the side, the drawn-out
+portion being cut off, and an electrode, previously prepared by coating
+a part of its length with a suitable enamel, is introduced. The tube is
+tilted to keep the electrode away from the drawn-out end, which is
+melted off and sealed. A small perforation is made with a hot platinum
+or iron wire in the sealed end, the electrode is shaken into position,
+and the sealing is completed as explained on page 42.
+
+The remainder of the tube, that is to say the lead-glass tube and the
+bulb on the other side of the middle bulb, is completed in a similar
+manner.
+
+
+SUMMARY OF CONDITIONS NECESSARY FOR SUCCESS IN GLASS-BLOWING.
+
+For the convenience of the student, it may be well to summarise the
+chief essentials for success in glass-blowing, and at the same time to
+add such brief notes on the various methods as may seem desirable.
+
+_Adjustment of Blowpipe._--The air jet should be clean internally, and
+so centered as to give a flame having a well-defined blue portion, the
+tip of the flame should not be only slightly luminous but purple in
+colour. In the case of a blowpipe burning oil or wax fuel the flame may
+be a trifle more ragged without disadvantage.
+
+_Bellows and Blowing._--The bellows should be adjusted to deliver air at
+constant pressure, either by insertion of a tap or, better, by attention
+to the wind reservoir if necessary. The movement of the foot in blowing
+should be steady, not jerky.
+
+_Heating Glass._--The tube or rod should be heated cautiously until it
+has reached its softening point in its thickest part. Steady rotation of
+the glass during the heating is almost essential.
+
+_Blowing a Bulb or Expanding a Join._--Prolonged heating is necessary in
+order that the thick parts may be heated completely through. Blowing
+should take place by stages, in order that the thin parts, which tend
+to expand first, have time to cool. The thick parts can then be expanded
+by further blowing and thus a bulb or expansion of even thickness can be
+obtained.
+
+_Cutting Glass._--The most useful method for general use is by means of
+the file or glass-blowers' knife. Either file or knife must be kept
+sharp by grinding. Neither file nor knife should be used on hot glass.
+The diamond and wheel cutter are useful for cutting sheet-glass, and
+when the diamond is employed a singing noise is an indication of a
+satisfactory cut.
+
+_Leading a Crack._--A crack may be led in any desired direction by means
+of a bead of hot glass or a small gas flame. The glass which it is
+desired to crack should be heated at a point slightly in advance of the
+crack, which will extend in the direction of the source of the heat.
+
+_Turning Out the End of a Tube._--This is done by heating the end of the
+tube and rotating it against an iron rod. The rod must be kept polished
+and free from rust, and it must not be allowed to become too hot while
+in use, otherwise the glass will stick to it.
+
+_Joining Unlike Glasses._--Joints between unlike glasses are often
+unstable. When such joints are made it is desirable to blow them as thin
+as possible, and to avoid the junction of unlike glasses in any complex
+joint, such as an internal seal. A transitional portion of tubing may be
+built up by the successive addition and interfusion of beads of one of
+the glasses to the end of a sealed tube consisting of the other glass.
+
+_Joining a Tube to a Very Thin Bulb._--The bulb may be thickened at the
+point of union by fusing on a bead of glass and expanding this slightly.
+A small central portion of the expanded part may then be perforated by
+bursting and the tube joined on.
+
+_Insertion of One Bulb Within Another._--A bulb may be divided into two
+halves by leading a crack round it and the inner bulb is then
+introduced. The two halves of the outer bulb may be fitted together
+(care being taken to avoid any damage to the edges), and the bulb may be
+completed by rotating the contacting edges before the blowpipe until
+they are soft, and then expanding slightly by means of air-pressure.
+
+_Annealing._--For most purposes, in the case of thin, blowpipe-made or
+lamp-blown glass apparatus, it is sufficient to cool slowly by rotating
+the finished article over a smoky flame and setting it aside in a place
+free from draughts, and where the hot glass will not come in contact
+with anything.
+
+Simple bulbs and joints do not even need this smoking; but thick
+articles, and especially those that are to be subjected to the stress of
+grinding, need more prolonged annealing in a special oven.
+
+_Use of Lead-Glass._--When lead-glass is to be used, the blowpipe flame
+should be in good adjustment and the glass should not be allowed to
+approach so near to the blue cone as to be blackened. Slight blackening
+may often be removed by heating the glass in the extreme end of the
+flame.
+
+Lead-glass articles tend to be rather more stable than similar articles
+of soda-glass.
+
+_Combustion-Glass._--This may be worked more easily if a small
+percentage of oxygen is introduced into the air with which the blowpipe
+flame is produced. If the air is replaced entirely by oxygen there is a
+risk of damaging the blowpipe jet, unless a special blowpipe is
+employed.
+
+_Internal Seal._--There are two ways of making these, one, in which the
+inner portion of the tube is fused on to the inside of the bulb or tube
+through which it is to pass, an opening is made by bursting and the
+outer tube is joined on. This is a quick and in some ways more
+satisfactory method than the other, in which there is no separate inner
+piece.
+
+_Rubber Blowing Tube._--In complicated work it is often convenient to
+use a thin rubber blowing-tube which is connected with the work either
+by a cork and piece of glass tubing or by fitting over a drawn-out end.
+The use of such a blowing-tube avoids the inconvenience of raising the
+work to the mouth when internal air-pressure is required. One end of the
+rubber tube is retained in the mouth during work.
+
+_General Notes._--A large amount of glass-blowing is spoiled through
+carelessness in arranging the work beforehand. The student should have
+every detail of his manipulation clearly in mind before he commences the
+work; he should not trust to evolving the method during the actual
+manipulation.
+
+Undue haste is another fruitful source of failure. Practically every
+operation in glass-blowing can be carried out in a perfectly leisurely
+manner, and it is better to err rather on the side of deliberation than
+on the side of haste.
+
+If, as will doubtless happen at times, a piece of work gives trouble and
+it is necessary to pause and consider the whole question, or if for any
+other reason it is necessary to stop during the construction of a
+partially finished join or other operation, great care should be taken
+not to allow the work to cool. A large, brush-like flame may be produced
+by increasing the amount of gas admitted to the blowpipe, and the work
+should be held just in front of the current of hot air produced by such
+a flame.
+
+It will then be possible to continue work on this without causing it to
+crack when further heat is applied.
+
+As time goes on, the student will find an increasing confidence in his
+ability to manipulate the soft glass, and with increasing confidence
+will come rapidly increasing power of manipulation. Perhaps the greatest
+obstacle to success in glass-blowing is undue haste in manipulation.
+
+
+
+
+INDEX
+
+
+Absorption bulbs, 21, 23.
+
+Airtube, flexible, 8, 102.
+
+Alarm thermometer, 45.
+
+Annealing, 7, 60.
+
+
+Bellows, adjusting pressure of, 5, 6.
+
+Bellows, foot, 5, 6.
+
+Bending tubes, 23.
+
+Blackening, 58, 101.
+
+Branching, 18, 19.
+
+Brushes of spun glass, 53.
+
+Blowpipe flame, quality of, 3.
+
+Blowpipe for mouth blast, 80, 82, 84.
+
+Blowpipe, for paraffin wax, 82, 88.
+
+Blowpipe, Herepath's, 2.
+
+Blowpipe jet, centring, 3, 98.
+
+Blowpipe jet, dirt in, 3.
+
+Blowpipe jet, multiple, 4, 40.
+
+Blowpipe, Letcher's, change, 4.
+
+Blowpipe, simple form of, 80.
+
+Bulb, medially on tube, 22.
+
+Bulbs, 19, 20, 22, 38, 98.
+
+Bulbs, absorption, (Liebig's), 21, 23.
+
+Bulbs, dividing, 39, 95.
+
+Bulbs from rod, 25.
+
+Bulbs, internal, 38.
+
+Bulbs, thick, 21.
+
+
+Cages, from glass rod, 24, 25, 27.
+
+Calibration, 72.
+
+Carius tubes, 16.
+
+Condenser, Liebig's, 37.
+
+Condensers, various, 37, 38.
+
+Cone, carbon, 8.
+
+Crack, leading, 30, 99.
+
+Cracking, subversive, 103.
+
+Cutting glass with diamond, 30.
+
+Cutting tubes, 11, 99.
+
+
+Diamond (glazier's), use of, 30.
+
+Dissimilar glass, joining of, 22, 94.
+
+Drilling, 61.
+
+
+Electrodes, sealing in, 42, 97.
+
+Etching glass, 70.
+
+Extemporised appliances, 80.
+
+Examination of apparatus, 93.
+
+
+Failure, Haste chief Source of, 103.
+
+Failures, Notes as to, 97.
+
+File, with oblique ground edge, 7.
+
+Filing glass, 63.
+
+Filter pumps, 35
+
+Foot, 25
+
+Fuels various, 82, 86, 87, 89.
+
+Funnel, thistle, 23.
+
+
+General principles and precautions, 1, 97
+
+Glass, varieties of, 9, 55, 91-97.
+
+Graduation, 72-76
+
+
+Haste, Source of Failure, 103
+
+Heat reflector, asbestos, 7.
+
+Heating, intensive, 7, 57.
+
+Heating precautions, 12, 98
+
+
+Joining dissimilar glass, 22.
+
+Joining glass to metal, 76.
+
+Joining tubes, 16, 94, 100.
+
+
+Knife, Glass blower's, 7, 99.
+
+
+Lenses, grinding, 63.
+
+
+Marking glass, 69.
+
+Methods, analytic study of, 91, 93.
+
+
+Oxygen for intensive heating, 57, 101.
+
+
+Precautions and General Principles, 1, 97.
+
+Pumps, Filter, 35.
+
+Pumps, Sprengel, 49, 50.
+
+
+Re-entering branch, 40.
+
+Reflector of heat, asbestos, 7.
+
+Rod, uses and articles from, 17, 25, 27, 28.
+
+Rod, blowing to hollow, 17, 25, 26, 91.
+
+
+Scrap glass, working, 90.
+
+Sealing tubes, 12, 13, 14.
+
+Sealed tubes for pressure, 15, 16.
+
+Sealing in of Electrodes, 42, 97.
+
+Seals, internal (airtraps), 32, 102.
+
+Silvering glass, 77.
+
+Soldering glass, 76.
+
+Soxhlet-tube, 40.
+
+Spirals, 23, 95.
+
+Spray arrester, 34.
+
+Spray producers, 36.
+
+Sprengel pumps, 49, 50.
+
+Spinning glass, 51.
+
+Stopcocks, 60, 66.
+
+Stoppering, 63.
+
+Stirrers, 28, 29.
+
+Summary as to precautions and failures, 97.
+
+
+Taps, 60, 66.
+
+Thermometers, Various, 44-49.
+
+Thermo-regulator, 24.
+
+Thistle Funnel, 23.
+
+Tools, Various small, 7.
+
+Turn-pins, 7, 8, 99.
+
+Turning out open ends, 14, 99.
+
+
+PRINTED IN GREAT BRITAIN BY
+W. JOLLY & SONS, LTD., PRINTERS, ABERDEEN.
+
+
+
+
+
+End of the Project Gutenberg EBook of A Handbook of Laboratory Glass-Blowing, by 
+Bernard D. Bolas
+
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+  <head>
+    <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" />
+    <title>
+      The Project Gutenberg eBook of A Handbook Of Laboratory Glass-blowing, by Bernard D. Bolas.
+    </title>
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+
+<pre>
+
+The Project Gutenberg EBook of A Handbook of Laboratory Glass-Blowing, by 
+Bernard D. Bolas
+
+This eBook is for the use of anyone anywhere 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
+
+
+Title: A Handbook of Laboratory Glass-Blowing
+
+Author: Bernard D. Bolas
+
+Illustrator: Naomi Bolas
+
+Release Date: June 24, 2010 [EBook #32962]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK HANDBOOK--LABORATORY GLASS-BLOWING ***
+
+
+
+
+Produced by 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.)
+
+
+
+
+
+
+</pre>
+
+
+
+<h1>A HANDBOOK OF LABORATORY GLASS-BLOWING</h1>
+
+
+<p class="center">
+<i>To my Friends<br />
+Eric Reid<br />
+and<br />
+Sidney Wilkinson</i><br />
+</p>
+
+
+
+<hr style="width: 65%;" />
+<h1>A Handbook of Laboratory Glass-Blowing</h1>
+
+<h3>BY</h3>
+
+<h2>BERNARD D. BOLAS</h2>
+
+<h4>WITH NUMEROUS DIAGRAMS IN THE TEXT</h4>
+
+<h2>BY NAOMI BOLAS</h2>
+
+<div class="figcenter" style="width: 120px;">
+<img src="images/deco.jpg" width="120" height="160" alt="" title="" />
+</div>
+
+<p class="center">
+LONDON<br />
+GEORGE ROUTLEDGE &amp; SONS, LTD<br />
+<span class="smcap">New York</span>: E. P. DUTTON &amp; CO.<br />
+1921<br />
+</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_v" id="Page_v">[Pg v]</a></span></p>
+<h2>CONTENTS</h2>
+
+
+<p>
+CHAP.                             <span class="tocnum">PAGE</span>
+<br />
+    I. Introduction and Preliminary Remarks&mdash;General
+    Principles to be observed in Glass Working&mdash;Choice of
+    Apparatus&mdash;Tools and Appliances&mdash;Glass <span class="tocnum"><a href='#Page_1'>1</a></span><br />
+
+<br />
+    II. Easy Examples of Laboratory Glass-Blowing&mdash;Cutting
+    and Sealing Tubes, Tubes for High Temperature
+    Experiments&mdash;Thermometer-Bulbs, Bulbs of Special Glass,
+    Pipettes, Absorption-Bulbs or Washing Bulbs&mdash;Joining
+    Tubes, Branches, Exhaustion-Branches, Branches of Dissimilar
+    Glass, Blowing Bulbs, A Thistle Funnel, Cracking and Breaking
+    Glass, Leading and Direction of Cracks&mdash;Use of Glass Rod
+    or Strips of Window-Glass, Joining Rod, Feet and
+    Supports&mdash;Gripping Devices for use in Corrosive
+    Solutions&mdash;The Building up of Special Forms from Solid
+    Glass <span class="tocnum"><a href='#Page_10'>10</a></span><br />
+
+<br />
+    III. Internal Seals, Air-Traps, Spray Arresters,
+    Filter-Pumps&mdash;Sprays, Condensers; plain, double surface,
+    and spherical&mdash;Soxhlet Tubes and Fat Extraction
+    Apparatus&mdash;Vacuum Tubes, Electrode Work, Enclosed
+    Thermometers, Alarm Thermometers ... Recording Thermometers,
+    "Spinning" Glass <span class="tocnum"><a href='#Page_32'>32</a></span><br />
+
+    <br /> IV. Glass, its Composition and
+    Characteristics&mdash;Annealing&mdash;Drilling, Grinding, and
+    Shaping <span class='pagenum'><a name="Page_vi" id="Page_vi">[Pg vi]</a></span>Glass by methods other than
+    Fusion&mdash;Stopcocks&mdash;Marking Glass&mdash;Calibration
+    and Graduation of
+    Apparatus&mdash;Thermometers&mdash;Exhaustion of
+    Apparatus&mdash;Joining Glass and Metal&mdash;Silvering Glass
+    <span class="tocnum"><a href='#Page_55'>55</a></span><br /> <br /> V. Extemporised Glass-Blowing Apparatus&mdash;The use of
+    Oil or other Fuels&mdash;Making Small Rods and Tubes from
+    Glass Scraps&mdash;The Examination of Manufactured Apparatus
+    with a view to Discovering the Methods used in
+    Manufacture&mdash;Summary of Conditions necessary for
+    Successful Glass-Blowing <span class="tocnum"><a href='#Page_80'>80</a></span><br /> <br />
+
+Index                               <span class="tocnum"><a href='#Page_105'>105</a></span>
+</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p>
+<h2>PREFACE</h2>
+
+
+<p>To cover the whole field of glass-blowing in a small handbook would be
+impossible. To attempt even a complete outline of the methods used in
+making commercial apparatus would involve more than could be undertaken
+without omitting the essential details of manipulation that a novice
+needs. I have, therefore, confined myself as far as possible to such
+work as will find practical application in the laboratory and will, I
+hope, prove of value to those whose interests lie therein.</p>
+
+<p>The method of treatment and somewhat disjointed style of writing have
+been chosen solely with the view to economy of space without the undue
+sacrifice of clearness.</p>
+
+<p class="right">
+BERNARD D. BOLAS.<br />
+</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
+<h2>Handbook of Laboratory Glass-Blowing</h2>
+
+
+
+<hr style="width: 65%;" />
+<h2>CHAPTER I</h2>
+
+<div class="blockquot"><p>Introduction and Preliminary Remarks&mdash;General Principles to
+be observed in Glass Working&mdash;Choice of Apparatus&mdash;Tools and
+Appliances&mdash;Glass.</p></div>
+
+
+<p>Glass-blowing is neither very easy nor very difficult; there are
+operations so easy that the youngest laboratory boy should be able to
+repeat them successfully after once having been shown the way, there are
+operations so difficult that years are needed to train eye and hand and
+judgment to carry them out; but the greater number of scientific needs
+lie between these two extremes. Yet a surprisingly large number of
+scientific workers fail even to join a glass tube or make a <b>T</b> piece that
+will not crack spontaneously, and the fault is rather one of
+understanding than of lack of ability to carry out the necessary
+manipulation.<span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span></p>
+
+<p>In following the scheme of instruction adopted in this handbook, it will
+be well for the student to pay particular attention to the reason given
+for each detail of the desirable procedure, and, as far as may be, to
+memorise it. Once having mastered the underlying reason, he can evolve
+schemes of manipulation to suit his own particular needs, although, as a
+rule, those given in the following pages will be found to embody the
+result of many years' experience.</p>
+
+<p>There is a wide choice of apparatus, from a simple mouth-blowpipe and a
+candle flame to a power-driven blower and a multiple-jet heating device.
+All are useful, and all have their special applications, but, for the
+present, we will consider the ordinary types of bellows and blowpipes,
+such as one usually finds in a chemical or physical laboratory.</p>
+
+<p>The usual, or Herepath, type of gas blowpipe consists of an outer tube
+through which coal gas can be passed and an inner tube through which a
+stream of air may be blown. Such a blowpipe is shown in section by Fig.
+1. It is desirable to have the three centring screws as shown, in order
+to adjust the position<span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span> of the air jet and obtain a well-shaped flame,
+but these screws are sometimes omitted. Fig. 1, <i>a</i> and <i>b</i> show the
+effects of defective centring of the air jet, <i>c</i> shows the effect of
+dirt or roughness in the inside of the air jet, <i>d</i> shows a satisfactory
+flame.</p>
+
+<div class="figcenter" style="width: 490px;">
+<img src="images/fig1.jpg" width="490" height="500" alt="Fig 1" title="" />
+<span class="caption">Fig 1</span>
+</div>
+
+<p>For many purposes, it is an advantage to<span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span> have what is sometimes known
+as a "quick-change" blowpipe; that is one in which jets of varying size
+may be brought into position without stopping the work for more than a
+fraction of a second. Such a device is made by Messrs. Letcher, and is
+shown by <i>e</i>, and in section by <i>f</i> Fig. 1. It is only necessary to
+rotate the desired jet into position in order to connect it with both
+gas and air supplies. A small bye-pass ignites the gas, and adjustment
+of gas and air may be made by a partial rotation of the cylinder which
+carries the jets.</p>
+
+<p>For specially heavy work, where it is needed to heat a large mass of
+glass, a multiple blowpipe jet of the pattern invented by my father,
+Thomas Bolas, as the result of a suggestion derived from a study of the
+jet used in Griffin's gas furnace, is of considerable value. This jet
+consists of a block of metal in which are drilled seven holes, one being
+central and the other six arranged in a close circle around the central
+hole. To each of these holes is a communication way leading to the gas
+supply, and an air jet is arranged centrally in each. Each hole has also
+an extension tube fitted into it, the whole effect being that of<span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span> seven
+blowpipes. In order to provide a final adjustment for the flame, a
+perforated plate having seven holes which correspond in size and
+position to the outer tubes is arranged to slide on parallel guides in
+front of these outer tubes.</p>
+
+<div class="figcenter" style="width: 650px;">
+<img src="images/fig2.jpg" width="650" height="288" alt="Fig. 2" title="" />
+<span class="caption">Fig. 2</span>
+</div>
+
+<p>The next piece of apparatus for consideration is the bellows, of which
+there are three or more types on the market, although all consist of two
+essential parts, the blower or bellows proper and the wind chamber or
+reservoir. Two patterns are shown in Fig. 2; <i>a</i>, is the form which is
+commonly used by jewellers and metal workers to supply the air blast
+necessary for heating small furnaces. Such a bellows may be obtained at
+almost any jewellers' supply dealer in Clerkenwell, but it not
+infrequently happens that the spring in the wind<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span> chamber is too strong
+for glass-blowing, and hence the air supply tends to vary in pressure.
+This can be improved by fitting a weaker spring, but an easier way and
+one that usually gives fairly satisfactory results, is to place an
+ordinary screw-clip on the rubber tube leading from the bellows to the
+blowpipe, and to tighten this until an even blast is obtained.</p>
+
+<p>Another form of bellows, made by Messrs. Fletcher and Co., and common in
+most laboratories, is shown by <i>b</i>; the wind chamber consists of a disc
+of india-rubber clamped under a circular frame or tied on to a circular
+rim. This form is shown by Fig. 2, <i>b</i>.</p>
+
+<p>The third form, and one which my own experience has caused me to prefer
+to any other, is cylindrical, and stands inside the pedestal of the
+blowpipe-table. A blowpipe-table of this description is made by Enfer of
+Paris.</p>
+
+<p>There is no need, however, to purchase an expensive table for laboratory
+use. All the work described in this book can quite well be done with a
+simple foot bellows and a quick-change blowpipe. Nearly all of it can be
+done with a single jet blowpipe, such as that described<span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span> first, or even
+with the still simpler apparatus mentioned on page 84, but I do not
+advise the beginner to practise with quite so simple a form at first,
+and for that reason have postponed a description of it until the last
+chapter.</p>
+
+<p>Glass-blowers' tools and appliances are many and various, quite a number
+of them are better rejected than used, but there are a few essentials.
+These are,&mdash;file, glass-knife, small turn-pin, large turn-pin, carbon
+cones, carbon plate, rubber tube of small diameter, various sizes of
+corks, and an asbestos heat reflector. For ordinary work, an annealing
+oven is not necessary, but one is described on page 60 in connection
+with the special cases where annealing is desirable.</p>
+
+<p>Fig. 3 illustrates the tools and appliances. <i>a</i> is an end view of the
+desirable form of file, and shows the best method of grinding the edges
+in order to obtain a highly satisfactory tool. <i>b</i> is a glass knife,
+shown both in perspective and end view, it is made of glass-hard steel
+and should be sharpened on a rough stone, such as a scythe-stone, in
+order to give a slightly irregular edge. <i>c</i> is a small turn-pin which
+may be made by flattening and filing the<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span> end of a six-inch nail. <i>d</i> is
+the large turn-pin and consists of a polished iron spike, about five
+inches long and a quarter of an inch diameter at its largest part. This
+should be mounted in a wooden handle. <i>e</i> and <i>f</i> are carbon cones. A
+thin rubber tube is also useful; it may be attached to the work and
+serve as a blowing tube, thus obviating the necessity of moving the work
+to the mouth when internal air pressure is to be applied. In order to
+avoid undue repetition, the uses of these tools and appliances will be
+described as they occur.<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span></p>
+
+<div class="figcenter" style="width: 650px;">
+<img src="images/fig3.jpg" width="650" height="547" alt="Fig. 3" title="" />
+<span class="caption">Fig. 3</span>
+</div>
+
+<p>Glass, as usually supplied by chemical apparatus dealers is of the
+composition known as "soda-glass." They also supply "hard" or
+"combustion" glass, but this is only used for special purposes, as it is
+too infusible for convenient working in the ordinary blowpipe flame.</p>
+
+<p>Soda-glass consists primarily of silicate of sodium with smaller
+quantities of silicate of aluminum and potassium. Its exact composition
+varies. It is not blackened, as lead glass is, by exposure to the
+reducing gases which are present in the blue cone of a blowpipe flame,
+and hence is easier for a beginner to work without producing
+discolouration.</p>
+
+<p>Further notes on glasses will be found on page 55, but for ordinary
+purposes soda-glass will probably be used.</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span></p>
+<h2>CHAPTER II</h2>
+
+<div class="blockquot"><p>Easy Examples of Laboratory Glass-Blowing&mdash;Cutting and
+Sealing Tubes for Various Purposes; Test-Tubes,
+Pressure-Tubes, Tubes for High Temperature
+Experiments&mdash;Thermometer-Bulbs, Bulbs of Special Glass,
+Pipettes, Absorption-Bulbs or Washing-Bulbs&mdash;Joining Tubes;
+Branches, Exhaustion-Branches, Branches of Dissimilar
+Glass&mdash;Blowing Bulbs; A Thistle Funnel; Cracking and
+Breaking Glass; Leading and Direction of Cracks&mdash;Use of
+Glass Rod or Strips of Window-Glass; Joining Rod, Feet and
+Supports&mdash;Gripping Devices for use in Corrosive
+Solutions&mdash;The Building Up of Special Forms from Solid
+Glass.</p></div>
+
+
+<p>Perhaps the most common need of the glass-blower whose work is connected
+with that of the laboratory is for a sealed tube; and the sealing of a
+tube is an excellent preliminary exercise in glass-blowing.</p>
+
+<p>We will assume that the student has adjusted the blowpipe to give a
+flame similar to that shown in <i>d</i>, Fig. 1, and that he has learned to
+maintain a steady blast of air with the bellows; further, we will assume
+that the tube he wishes to seal is of moderate size, say not more than
+half an inch in diameter and with<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span> walls of from one-tenth to one-fifth
+of an inch thick.</p>
+
+<div class="figcenter" style="width: 650px;">
+<img src="images/fig4.jpg" width="650" height="423" alt="Fig. 4" title="" />
+<span class="caption">Fig. 4</span>
+</div>
+
+<p>A convenient length of tube for the first trial is about one foot; this
+should be cut off from the longer piece, in which it is usually
+supplied, as follows:&mdash;lay the tube on a flat surface and make a deep
+cut with the edge of a file. Do not "saw" the file to and fro over the
+glass. If the file edge has been ground as shown in <i>a</i>, Fig. 3, such a
+procedure will be quite unnecessary and only involve undue wear; one
+movement with sufficient pressure to make the file "bite" will give a
+deep cut. Now rotate the tube through about one-eighth of a turn and<span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span>
+make another cut in continuation of the first. Take the tube in the
+hands, as shown in <i>a</i>, Fig. 4, and apply pressure with the thumbs, at
+the same time straining at the ends. The tube should break easily. If it
+does not, do not strain too hard, as it may shatter and cause serious
+injuries to the hands, but repeat the operation with the file and so
+deepen the original cuts. In holding a tube for breaking, it is
+important to place the hands as shown in sketch, as this method is least
+likely to cause shattering and also minimises the risk of injury even if
+the tube should shatter. To cut a large tube, or one having very thick
+walls, it is better to avoid straining altogether and to break by
+applying a small bead of intensely heated glass to the file cut. If the
+walls are very thin, a glass-blower's knife should be used instead of a
+file. The tube and glass-blower's knife should be held in the hand, and
+the tube rotated against the edge of the knife; this will not produce a
+deep cut, but is less likely to break the tube. A bead of hot glass
+should be used to complete the work.</p>
+
+<p>The next operation is to heat the glass tube in the middle; this must be
+done gradually<span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span> and evenly; that is to say the tube must be rotated
+during heating and held some considerable distance in front of the flame
+at first; otherwise the outer surface of the glass will expand before
+the interior is affected and the tube will break. From two to five
+minutes, heating at a distance of about eight inches in front of the
+flame will be found sufficient in most cases, and another minute should
+be taken in bringing the tube into the flame. Gradual heating is
+important, but even heating is still more important and this can only be
+obtained by uniform and steady rotation. Until the student can rotate a
+tube steadily <i>without thinking about it</i>, real progress in
+glass-blowing is impossible.</p>
+
+<p>When the tube is in the flame it must be held just in front of the blue
+cone and rotated until the glass is soft enough to permit the ends to be
+drawn apart. Continue to separate the ends and, at the same time, move
+the tube very slightly along its own axis, so that the flame tends to
+play a little more on the thicker part than on the drawn-out portion. If
+this is done carefully, the drawn-out portion can be separated off,
+leaving only a slight "bleb" on<span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span> the portion it is desired to seal. This
+is illustrated by <i>b</i>, Fig. 4.</p>
+
+<p>To convert the seal at <i>b</i>, Fig. 4., into the ordinary form of test-tube
+seal, it is only necessary to heat the "bleb" a little more strongly,
+blow gently into the tube until the thick portion is slightly expanded,
+re-heat the whole of the rounded end until it is beginning to collapse,
+and give a final shaping by careful blowing after it has commenced to
+cool. In each case the glass must be removed from the flame before
+blowing. The finished seal is shown by <i>c</i>, Fig. 4. If desired, the open
+end may now be finished by heating and rotating the soft glass against
+the large turn-pin, as illustrated in <i>d</i>, but the turn-pin must not be
+allowed to become too hot, as if this happens it will stick to the
+glass. After turning out the end, the lip of glass must be heated to
+redness and allowed to cool without coming in contact with anything;
+otherwise it will be in a condition of strain and liable to crack
+spontaneously. The finished test-tube is shown by <i>e</i>.</p>
+
+<p>When it is necessary to seal a substance inside a glass tube, the bottom
+of the tube is<span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span> first closed, as explained above, and allowed to cool;
+the substance, if a solid, is now introduced, but should not come to
+within less than two inches of the point where the second seal is to be
+made. If the substance is a liquid it can more conveniently be
+introduced at a later stage.</p>
+
+<p>Now bring the tube into the blowpipe flame gradually, and rotate it,
+while heating, at the place where it is to be closed. Allow the glass to
+soften and commence to run together until the diameter of the tube is
+reduced to about half its original size. Remove from the flame and draw
+the ends apart, this should give a long, thick extension as shown by
+<i>f</i>, Fig. 4. If any liquid is to be introduced, it may now be done by
+inserting a thin rubber or other tube through the opening and running
+the liquid in. A glass tube should be used with caution for introducing
+the liquid, as any hard substance will tend to scratch the inside of the
+glass and cause cracking. The final closure is made by melting the
+drawn-out extension in the blowpipe flame; the finished seal being shown
+by <i>g</i>, Fig. 4.</p>
+
+<p>If the sealed tube has to stand internal<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> pressure, it is desirable to
+allow the glass to thicken somewhat more before drawing out, and the
+bottom seal should also be made thicker. For such a tube, and especially
+when it has to stand heating, as in a Carius determination of chlorine,
+each seal should be cooled very slowly by rotating it in a gas flame
+until the surface is covered with a thick layer of soot, and it should
+then be placed aside in a position where the hot glass will not come in
+contact with anything, and where it will be screened from all draughts.</p>
+
+<p><i>Joining Tube.</i>&mdash;We will now consider the various forms of join in glass
+tubing which are met with in the laboratory. First, as being easiest, we
+will deal with the end-to-end joining of two tubes of similar glass.
+<i>a</i>, <i>b</i>, and <i>c</i>, Fig. 5, illustrate this. One end of one of the tubes
+should be closed, a lip should be turned out on each of the ends to be
+joined, and both lips heated simultaneously until the glass is
+thoroughly soft. Now bring the lips together gently, until they are in
+contact at all points and there are no places at which air can escape;
+remove from the flame, and blow slowly and very cautiously until the
+joint is expanded<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span> as shown in <i>b</i>, Fig. 5. Reheat in the flame until
+the glass has run down to rather less than the original diameter of the
+tube, and give a final shaping by re-blowing. The chief factors of
+success in making such a join are, thorough heating of the glass before
+bringing the two tubes together, and avoidance of hard or sudden blowing
+when expanding the joint. The finished work is shown by <i>c</i>, Fig. 5.</p>
+
+<div class="figcenter" style="width: 650px;">
+<img src="images/fig5.jpg" width="650" height="546" alt="Fig. 5" title="" />
+<span class="caption">Fig. 5</span>
+</div>
+
+<p>To join a small glass tube to the end of a<span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span> large one, the large tube
+should first be sealed, a small spot on the extreme end of the seal
+heated, and air pressure used to expand the heated spot as shown in <i>d</i>.
+This expanded spot is then re-heated and blown out until it bursts as
+shown in <i>e</i>, the thin fragments of glass are removed and the end of the
+small tube turned out as shown in <i>f</i>. After this the procedure is
+similar to that used in jointing two tubes of equal size.</p>
+
+<p>When these two forms of joint have been mastered, a <b>T</b> piece will present
+but little difficulty. It is made in three stages as shown in Fig. 5,
+and the procedure is similar to that used in joining a large and small
+tube. Care should be taken to avoid softening the top of the "<b>T</b>" too
+much, or the glass will bend and distort the finished work; although a
+slight bend can be rectified by re-heating and bending back. Local
+re-heating is often useful in giving the joint its final shape.</p>
+
+<p>An exhaustion branch is often made by a totally different method. This
+method is shown by <i>g</i>, <i>h</i>, and <i>i</i>, Fig. 5; <i>g</i> is the tube on which
+the branch is to be made. The end of a rod of similar glass should be
+heated until a<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span> mass of thoroughly liquid glass has collected, as shown,
+and at the same time a spot should be heated on that part of the tube
+where it is desired to make the branch. The mass of hot glass on the rod
+is now brought in contact with the heated spot on the tube and expanded
+by blowing as shown by <i>h</i>. The air pressure in the tube is still
+maintained while the rod is drawn away as shown by <i>i</i>. This will give a
+hollow branch which may be cut off at any desired point, and is then
+ready for connection to the vacuum pump.</p>
+
+<p>If the rod used is of a dissimilar glass, the branch should be blown
+much thinner. Such a branch will often serve as a useful basis for
+joining two tubes of different composition, as the ordinary type of
+branch is more liable to crack when made with two glasses having
+different coefficients of expansion.</p>
+
+<p><i>Blowing Bulbs.</i>&mdash;A bulb may be blown on a closed tube such as that
+shown by <i>c</i>, Fig. 5, by rotating it in the blowpipe flame until the end
+is softened, removing it from the flame and blowing cautiously. It is
+desirable to continue the rotation during blowing. In the case of a very
+small tube, it is sufficient to melt the end<span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span> without previous sealing,
+rotate it in the flame until enough glass has collected, remove from the
+flame and blow while keeping the tube in rotation.</p>
+
+<p><i>Thermometer Bulbs.</i>&mdash;If the thermometer is to be filled with mercury,
+it is desirable to use a rubber bulb for blowing, as moisture is liable
+to condense inside the tube when the mouth is used, and this moisture
+will cause the mercury thread to break. In any case, a slight pressure
+should be maintained inside the thermometer tube while it is in the
+flame; otherwise the fine capillary tube will close and it will be very
+difficult to expand the heated glass into a bulb.</p>
+
+<p><i>Large Bulbs.</i>&mdash;When a large bulb is needed on a small or medium sized
+tube, it is often necessary to provide more glass than would be obtained
+if the bulb were blown in the ordinary way. One method is to expand the
+tube in successive stages along its axis, as shown by <i>a</i>, Fig. 6. These
+expanded portions are then re-heated, so that they run together into one
+hollow mass from which the bulb is blown; <i>b</i> and <i>c</i>, illustrate this.
+Another method, and one which is useful for very large bulbs, is to<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span>
+fuse on a length of large, thick-walled, tubing. The heat reflector,
+<i>g</i>, Fig. 3, should be used, if necessary, when making large bulbs. It
+consists of a sheet of asbestos mounted in a foot, and is used by being
+placed close to the mass of glass on the side away from the blowpipe
+flame while the glass is being heated.<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span></p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig6.jpg" width="500" height="522" alt="Fig. 6" title="" />
+<span class="caption">Fig. 6</span>
+</div>
+
+<p><i>Bulbs of Dissimilar Glass.</i>&mdash;These may be made by the second method
+given under "Large Bulbs," but the joint should be blown as thin as
+possible. Further instructions in the use of unlike glasses are given on
+page 94.</p>
+
+<p><i>A Bulb in the Middle of a Tube.</i>&mdash;Unless the bulb is to be quite small,
+it will be necessary to join in a piece of thick glass tubing, or to
+draw the thin tube out from a larger piece, thus leaving a thick mass in
+the middle as shown by <i>d</i>, Fig. 6. This mass of glass should now be
+rotated in the blowpipe flame until it is quite soft and on the point of
+running together. Considerable practice will be necessary before the two
+ends of the tube can be rotated at the same speed and without
+"wobbling," but this power must be acquired. When the glass is
+thoroughly hot, remove from the flame, hold in a horizontal position,
+and expand by blowing. It is essential to continue the rotation while
+this is done. Should one part of the bulb tend to expand more than the
+other, turn the expanded part to the bottom, pause for about a second,
+both in rotating and blowing, in order that the lower portion may<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span> be
+cooled by ascending air-currents; then continue blowing and turning as
+before.</p>
+
+<p><i>Absorption Bulbs or Washing Bulbs.</i>&mdash;These are made by an elaboration
+of the processes given in the last paragraph, <i>g</i>, <i>h</i>, and <i>i</i>, Fig. 6,
+illustrate this.</p>
+
+<p><i>A Thistle Funnel.</i>&mdash;This is made by blowing a fairly thick-walled bulb
+on a glass tube, bursting a hole by heating and blowing, and enlarging
+the burst-out part by heating and rotating against a turn-pin.</p>
+
+<p><i>Bending Glass Tube.</i>&mdash;Small tubing may be bent in a flat flame gas
+burner and offers no special difficulty. Large or thin-walled tubing
+should be heated in the blowpipe flame and a slight bend made; another
+zone of the tube, just touching the first bend, should now be heated and
+another slight bend made. In this way it is possible to avoid flattening
+and a bend having any required angle can gradually be produced. A final
+shaping of the bend may be made by heating in a large blowpipe flame and
+expanding slightly by air pressure.</p>
+
+<p><i>Glass Spirals.</i>&mdash;If a tube is heated by means of a long, flat-flame
+burner, the softened tube may be wound on to an iron mandrel<span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span> which has
+previously been covered with asbestos. The mandrel should be made
+slightly conical in order to facilitate withdrawal. It is desirable to
+heat the surface of the asbestos almost to redness by means of a second
+burner, and thus avoid undue chilling of the glass and the consequent
+production of internal strain.</p>
+
+<div class="figcenter" style="width: 650px;">
+<img src="images/fig7.jpg" width="650" height="551" alt="Fig. 7" title="" />
+<span class="caption">Fig. 7</span>
+</div>
+
+<p><i>A Thermo-Regulator for Gas.</i>&mdash;Fig. 7, <i>a-e</i>, shows an easily
+constructed thermo-regulator.<span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span> The mercury reservoir, <i>a</i>, and the upper
+part, <i>b</i>, are made by joining two larger pieces of tubing on to the
+capillary. The gas inlet passes through a rubber stopper, in order to
+allow of adjustment for depth of insertion, and the bye-pass branches,
+<i>d</i> and <i>e</i>, are connected by a piece of rubber tubing which can be
+compressed by means of a screw clip, thus providing a means of
+regulating the bye-pass.</p>
+
+<p><i>Use of Glass Rod.</i>&mdash;Apart from its most common laboratory use for
+stirring; glass rod may be used in building up such articles as
+insulating feet for electrical apparatus or acid-resisting cages for
+chemical purposes. Such a cage is shown by <i>f</i>, <i>g</i> and <i>h</i>, Fig. 7.
+Further, by an elaboration of the method of making an exhaustion branch,
+given on page 18, blown articles may also be constructed from rod. Note
+the added parts of <i>e</i>, Fig. 9.</p>
+
+<p><i>A Simple Foot.</i>&mdash;The form of foot shown by Fig. 7, <i>k</i>, is easy to make
+and has many uses. First join a glass rod to a length of glass tubing as
+shown (the joint should be expanded slightly by blowing), cut off the
+tube and heat the piece remaining on the rod until it can be turned out
+as shown by <i>i</i>. This should be<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> done with the large turn-pin, and care
+should be taken not to heat the supporting rod too strongly, otherwise
+the piece of tube will become bent and distorted; it is better to
+commence by heating the edge of the piece of tube and turn out a lip,
+then extend the heating by degrees and turn out more and more until the
+foot looks like that shown by <i>i</i>.</p>
+
+<p>We now need to make three projections of glass rod. These are produced
+as follows:&mdash;Heat the end of the glass rod until a thoroughly melted
+mass of glass has accumulated (the rod must be rotated while this is
+being done, otherwise the glass will drop off); when sufficient melted
+glass has been obtained, the edge of the turned-out foot should be
+heated to dull redness over about one-third of its circumference, and
+the melted glass on the rod should be drawn along the heated portion
+until both are so completely in contact as to form one mass of
+semi-fluid glass. The rod should now be drawn away slowly, and, finally,
+separated by melting off, thus producing a flat projection. A repetition
+of the process will give the other two projections, and the finished
+foot may be adjusted to stand upright by heating the<span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span> projections
+slightly and standing it on the carbon plate mentioned on page 7. After
+the foot is adjusted it should be annealed slightly by heating to just
+below the softening point of the glass and then rotating in a smoky gas
+flame until it is covered with a deposit of carbon, after which it
+should be allowed to cool in a place free from draughts and where the
+hot glass will not come in contact with anything. The finished foot is
+shown by <i>k</i>, Fig. 7.</p>
+
+<p><i>Building up from Glass Rod.</i>&mdash;A glass skeleton-work can be constructed
+from rod without much difficulty, and is sometimes useful as a container
+for a substance which has to be treated with acid, or for similar
+purposes. The method is almost sufficiently explained by the
+illustration in Fig. 7; <i>f</i> shows the initial stage, <i>g</i> the method of
+construction of the net-work, and <i>h</i> the finished container. It is
+convenient to introduce the substance at the stage indicated by <i>g</i>. The
+important points to observe in making this contrivance are that the
+glass rod must be kept hot by working while it is actually in the flame,
+and that the skeleton must be made as thin as<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span> possible with the
+avoidance of heavy masses of glass at any place. If these details are
+neglected it will be almost certain to crack.</p>
+
+<p><i>Stirrers.</i>&mdash;These are usually made from glass rod, and no special
+instructions are necessary for their construction, except that the glass
+should be in a thoroughly fused condition before making any joins and
+the finished join should be annealed slightly by covering with a deposit
+of soot, as explained on page 16. The flat ends shown in <i>a</i>, Fig. 8,
+are made by squeezing the soft glass rod between two pieces of carbon,
+and should be re-heated to dull redness after shaping. Fig. 8 also shows
+various forms of stirrer.</p>
+
+<p>In order to carry out stirring operations in the presence of a gas or
+mixture of gases other than air, some form of gland or seal may be
+necessary where the stirrer passes through the bearing in which it runs.
+A flask to which is fitted a stirrer and gas seal is shown in section by
+<i>b</i>, Fig. 8. The liquid used in this seal may be mercury, petroleum, or
+any other that the experimental conditions indicate.</p>
+
+<div class="figcenter" style="width: 487px;">
+<img src="images/fig8.jpg" width="487" height="500" alt="Fig. 8" title="" />
+<span class="caption">Fig. 8</span>
+</div>
+
+<p>If the bearing for a stirrer is made of glass tube, it is desirable to
+lubricate rather freely;<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span> otherwise heat will be produced by the
+friction of the stirrer and the tube will probably crack. Such
+lubrication may be supplied by turning out the top of the bearing tube
+and filling the turned-out portion with petroleum jelly mixed with a
+small quantity of finely ground or, better, colloidal graphite, and the
+bearing should also<span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span> be lubricated with the same composition. Care
+should be taken not to employ so soft a lubricant or so large an excess
+as to cause it to run down the stirrer into the liquid which is being
+stirred.</p>
+
+<p><i>Leading a Crack.</i>&mdash;It sometimes happens that a large bulb or specially
+thin-walled tube has to be divided. In such a case it is scarcely
+practicable to use the method recommended for small tubes on page 12,
+but it is quite easy to lead a crack in any desired direction. A
+convenient starting point is a file cut; this is touched with hot glass
+until a crack is initiated. A small flame or a bead of hot glass is now
+used to heat the article at a point about a quarter of an inch from the
+end of the crack and in whatever direction it has to be led. The crack
+will now extend towards the source of heat, which should be moved
+farther away as the crack advances. In this manner a crack may be caused
+to take any desired path and can be led round a large bulb.</p>
+
+<p><i>Cutting Glass with the Diamond.</i>&mdash;Slips of window-glass can be used in
+place of glass rod for some purposes, and as cutting them involves the
+use of the glaziers' diamond or a wheel-cutter,<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span> they may well be
+mentioned under this heading.</p>
+
+<p>In cutting a sheet of glass with the diamond, one needs a flat surface
+on which to rest the glass, and a rule against which to guide the
+diamond. The diamond should be held in an almost vertical position, and
+drawn over the surface of the glass with slight pressure. While this is
+being done the angle of the diamond should be changed by bringing the
+top of the handle forward until the sound changes from one of scratching
+to a clear singing note. When this happens the diamond is cutting. A few
+trials will teach the student the correct angle for the diamond with
+which he works, and the glass, if properly cut, will break easily. If
+the cut fails it is better to turn the glass over and make a
+corresponding cut on the other side rather than make any attempt to
+improve the original cut. The diamond is seldom used for cutting small
+glass tubes.</p>
+
+<p>The use of the wheel-cutter calls for no special mention as it will cut
+at any angle, although the pressure required is somewhat greater than
+that needed by most diamonds.</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span></p>
+<h2>CHAPTER III</h2>
+
+<div class="blockquot"><p>Internal Seals, Air-Traps, Spray Arresters,
+Filter-Pumps&mdash;Sprays, Condensers; Plain, Double Surface, and
+Spherical&mdash;Soxhlet Tubes and Fat Extraction
+Apparatus&mdash;Vacuum Tubes, Electrode Work, Enclosed
+Thermometers, Alarm Thermometers, Recording Thermometers,
+"Spinning" Glass.</p></div>
+
+
+<p><i>Internal Seals.</i>&mdash;It is convenient to class those cases in which a
+glass tube passes through the wall of another tube or bulb under the
+heading of "Internal Seals." These are met with in barometers, spray
+arresters, and filter pumps, in condensers and some forms of vacuum
+tube. The two principal methods of making such seals will be considered
+first and their special application afterwards.</p>
+
+<p><i>An Air Trap on a Barometer Tube.</i>&mdash;This involves the use of the first
+method, and is perhaps the simplest example that can be given. Fig. 9,
+<i>a</i>, <i>a1</i> and <i>a2</i>, show the stages by which this form of internal seal
+is made. For the first trials, it is well to work with fairly
+thick-walled<span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span> tubing, which should be cut into two pieces, each being
+about eight inches long.</p>
+
+<div class="figcenter" style="width: 546px;">
+<img src="images/fig9.jpg" width="546" height="700" alt="Fig. 9" title="" />
+<span class="caption">Fig. 9</span>
+</div>
+
+<p>First seal the end of one tube as described on page 13, heat the sealed
+end and expand to a<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> thick walled bulb. Fuse the end of the other tube,
+attach a piece of glass rod to serve as a handle, and draw out; cut off
+the drawn-out portion: leaving an end like <i>a</i>.</p>
+
+<p>Now heat a small spot at the end of the bulb, blow, burst out, and
+remove the thin fragments of glass. Heat a zone on the other tube at the
+point where the drawn-out portion commences and expand as shown by <i>a1</i>.</p>
+
+<p>The next stage is to join the tubes. Heat the ragged edges of the
+burst-out portion until they are thoroughly rounded. At the same time
+heat the drawn-out tube to just below softening point. Then, while the
+rounded edges of the burst-out portion are still soft, insert the other
+tube; rotate the join in the blowpipe flame until it is quite soft, and
+expand by blowing. If necessary, re-heat and expand again. The finished
+seal, which should be slightly annealed by smoking in a sooty flame, is
+shown by <i>a2</i>.</p>
+
+<p><i>A Spray Arrester.</i>&mdash;This is made by the second method, in which the
+piece of tube which projects inside the bulb is fused in position first
+and the outer tube is then joined<span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span> on. The various stages of making are
+illustrated by <i>b</i>, <i>b1</i> and <i>b2</i>, Fig. 9.</p>
+
+<p>A bulb is blown between two tubes by the method given on page 22, the
+larger tube is then cut off and the small piece of tube introduced into
+the bulb after having been shaped as shown in by <i>b</i>, Fig. 9. The
+opening in the bulb is sealed as shown by <i>b1</i>. The sealed part is now
+heated and the bulb inclined downwards until the inner tube comes in
+contact with the seal and is fused in position. This operation requires
+some practice in order to prevent the inner tube either falling through
+the soft glass or becoming unsymmetrical. The end of the bulb, where the
+inner tube comes in contact with it, is now perforated by heating and
+blowing, thus giving the form shown by <i>b2</i>, and the outer tube is
+joined on. The finished spray arrester is shown by <i>b3</i>. Practice alone
+will give the power to produce a symmetrical and stable piece of work.</p>
+
+<p><i>Two Forms of Filter Pump.</i>&mdash;That illustrated by <i>d</i>, Fig. 9, is made by
+the method explained under "An Air Trap on a Barometer Tube." That
+illustrated by <i>c</i> is made by the method explained under "A Spray<span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span>
+Arrester." No new manipulation is involved, and the construction should
+be clear from a study of the drawings.</p>
+
+<p><i>Multiple and Branched Internal Seals.</i>&mdash;A fuller consideration of these
+will be found on page 39, but one general principle may well be borne in
+mind; that, as far as is possible, a tube having both ends fastened
+inside another tube or bulb should be curved or have a spiral or bulb at
+some point in its length, otherwise any expansion or contraction will
+put great strain on the joints.</p>
+
+<p><i>Sprays.</i>&mdash;A spray which is easy to make, easy to adjust, and easy to
+clean after use is shown by <i>e</i>, Fig. 9. The opening on the top of the
+bulb is made by melting on a bead of glass, expanding, bursting, and
+fusing the ragged edges. The two branches which form the spray producing
+junction are made by the method used for an exhaustion branch and
+described on page 18.</p>
+
+<p>A spray which can be introduced through the neck of a bottle is shown by
+<i>h</i>, Fig. 9. The various stages in making this are illustrated by <i>f</i>,
+and <i>g</i>. If the inner tube is made by drawing out from a larger piece of
+glass so<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span> that two supporting pieces are left on each side of the place
+where it is intended to make the final bend, that bend can be made in a
+flat-flame gas burner without causing the inner tube to come in contact
+with the walls of the outer tube. Care must be taken when joining on the
+side piece that the inner tube is not heated enough to fuse it. The
+small hole in the side of the outer tube is produced by heating and
+bursting.</p>
+
+<p><i>A Liebig's Condenser.</i>&mdash;This consists of a straight glass tube passing
+through an outer cooling jacket. In practice it is better to make the
+jacket as a separate piece, and to effect a water-tight junction by
+means of two short rubber tubes. It may, however, be made with two
+internal seals of the class described under "A Spray Arrester." There is
+much less risk of these seals cracking if the inner tube is made in the
+form of a spiral or has a number of bulbs blown on it in order to give a
+certain amount of elasticity.</p>
+
+<p><i>A Double-Surface Condenser.</i>&mdash;Fig. 10 shows a condenser of this nature
+which is supplied by Messrs. Baird and Tatlock. It may be built up in
+stages as shown by <i>a</i>, <i>b</i>,<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span> and <i>c</i>, but the work involved requires
+considerable skill, and the majority of laboratory workers will find it
+cheaper to buy than to make.</p>
+
+<div class="figcenter" style="width: 550px;">
+<img src="images/fig10.jpg" width="550" height="650" alt="Fig. 10" title="" />
+<span class="caption">Fig. 10</span>
+</div>
+
+<p><i>A Spherical Condenser.</i>&mdash;Such a condenser as that shown by <i>f</i>, Fig 10,
+involves a method which may find application in a number of cases. The
+outer bulb is blown from a thick piece of tubing which has been inserted
+in a<span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span> smaller piece (see <i>d</i>, Fig. 6); then the inner bulb by similar
+method. It is now necessary to introduce the smaller bulb into the
+larger, and for this purpose the larger bulb must be cut into halves. A
+small but deep cut is made with the file or glass-blowers' knife in the
+middle of the larger bulb, and at right angles to the axis of the tube
+on which it is blown. A minute bead of intensely heated glass is now
+brought in contact with the cut in order to start a crack. This crack
+may now be led round the bulb as described on page 30. If the work is
+carried out with care, it is possible to obtain the bulb in two halves
+as shown by <i>d</i>, and these two halves will correspond so exactly that
+when the cut edges are placed in contact they will be almost air-tight.
+The two tubes from the smaller bulb should be cut to such a length that
+they will just rest inside the larger, and the ends should be expanded.
+Place the inner bulb in position and fit the two halves of the outer
+bulb together, taking great care not to chip the edges. If the length of
+the tubes on the inner bulb has been adjusted properly, the inner bulb
+will be supported in position by their contact with the tubes on the
+outer bulb.<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> Now rotate the cracked portion of the outer bulb in front
+of a blowpipe flame and press the halves together very gently as the
+glass softens. Expand slightly by blowing if necessary. If a small
+pin-hole develops at the joint it is sometimes possible to close this
+with a bead of hot glass; but if the bulb has been cut properly there
+should be no pin-holes formed. The condenser is finished by joining on
+the side tubes and sealing the inner tube through by the methods already
+given. In order to blow bulbs large enough to make a useful condenser,
+it will be convenient to employ the multiple-jet blowpipe described on
+page 4.</p>
+
+<p><i>A Soxhlet-Tube or Extraction Apparatus.</i>&mdash;This involves the
+construction of a re-entrant join where the syphon flows into the lower
+tube. It is of considerable value as an exercise and the complete
+apparatus is easy to make.</p>
+
+<p>A large tube is sealed at the bottom and the top is lipped, as in making
+a test-tube. A smaller tube is then joined on by a method similar to
+that given on page 18, but without making a perforation in the bottom of
+the large tube. Heating and expanding by air pressure, first through the
+large tube, then through the<span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span> smaller tube and then again through the
+large tube, will give a satisfactory finish to this part of the work.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/fig11.jpg" width="600" height="523" alt="Fig. 11" title="" />
+<span class="caption">Fig. 11</span>
+</div>
+
+<p>The syphon tube is now joined on to the large tube as shown by <i>a</i>, Fig.
+11, care being taken to seal the other end of the syphon tube before
+joining. The details of the final and re-entrant joint of the syphon
+tube are shown at the lower part of <i>a</i>. This join is made by expanding
+the sealed end of the syphon tube into a small, thick-walled bulb, and
+the bottom<span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span> of this bulb is burst out by local heating and blowing; the
+fragments of glass are removed and the edges made smooth by melting. A
+similar operation is carried out on the side of the tube to which the
+syphon tube is to be joined. This stage is shown by <i>a</i>. Now heat the
+syphon tube at the upper bend until it is flexible, and press the bulb
+at its end into the opening on the side of the other tube. Hold the
+glass thus until the syphon is no longer flexible. The final join is
+made by heating the two contacting surfaces, if necessary pressing the
+edges in contact with the end of a turn-pin, fusing together and
+expanding. The finished apparatus is shown by <i>c</i>.</p>
+
+<p><i>Electrodes.</i>&mdash;A thin platinum wire may be sealed into a capillary tube
+without any special precautions being necessary. The capillary tube may
+be drawn out from the side of a larger tube by heating a spot on the
+glass, touching with a glass rod and drawing the rod away; or the
+exhaustion branch described on page 18 may be used for the introduction
+of an electrode. It is convenient sometimes to carry out the exhaustion
+through the same tube that will afterwards serve for the electrode. The<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span>
+electrode wire is laid inside the branch before connecting to the
+exhaustion pump. When exhaustion is completed the tube is heated until
+the soft glass flows round the platinum and makes the seal air-tight.
+The branch is now cut off close to the seal on the pump side, a loop is
+made in the projecting end of the platinum wire, and the seal is
+finished by melting the cut-off end.</p>
+
+<p>Platinum is usually employed for such work, but if care is taken to
+avoid oxidation it is not impossible to make fairly satisfactory seals
+with clean iron or nickel wire. Hard rods of fine graphite, such as are
+used in some pencils, may also be sealed into glass, but it seems
+probable that air would diffuse through the graphite in the course of
+time.</p>
+
+<p>Another method for the introduction of an electrode is illustrated by
+<i>d</i>, <i>e</i>, <i>f</i> and <i>g</i>, Fig. 11. In this case the bulb or thin-walled
+tube into which the electrode is to be sealed is perforated by a quick
+stab with an intensely heated wire&mdash;preferably of platinum&mdash;which is
+then withdrawn before the glass has had time to harden, and thus a
+minute circular hole is made. The electrode is coated with a layer of
+similar glass,<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span> or of the specially made enamel which is sold for this
+purpose, inserted into the bulb or tube by any convenient opening, and
+adjusted by careful shaking until the platinum wire projects through the
+small hole. The bulb or tube is then fused to the coating of the
+electrode and the whole spot expanded slightly by blowing. The
+appearance of the finished seal is shown by <i>g</i>. It is well to anneal
+slightly by smoking.</p>
+
+<p><i>Thermometers.</i>&mdash;Apart from the notes on page 20 with respect to the
+blowing of a suitable bulb on capillary tubing there is little to say in
+connection with the glass working needed in making a plain thermometer.
+The size desirable for the bulb will be determined by the bore of the
+capillary tube, the coefficient of expansion of the liquid used for
+filling, and the range of temperature for which the thermometer is
+intended.</p>
+
+<p>Filling may be carried out as follows:&mdash;Fit a small funnel to the open
+end of the capillary by means of a rubber tube, and pour into the funnel
+rather more than enough of the liquid to be used than is required to
+fill the bulb. Mercury or alcohol will be used in practice, most
+probably. Warm the bulb until a few air<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span> bubbles have escaped through
+the liquid and then allow to cool. This will suck a certain amount of
+liquid into the bulb. Now heat the bulb again, and at the same time heat
+the capillary tube over a second burner. The liquid will boil and sweep
+out the residual air, but it is necessary to heat the capillary tube as
+well in order to prevent condensation. Allow the bulb and tube to cool,
+then repeat the heating once more. By this time the bulb and tube should
+be free from air, and cooling should give a completely filled
+thermometer. Remove the funnel and heat the thermometer to a few degrees
+above the maximum temperature for which it is to be used; the mercury or
+other filling liquid will overflow from the top, and, as the temperature
+falls, will recede, thus allowing the end of the capillary to be drawn
+out. Reheat again until the liquid rises to the top of the tube, then
+seal by means of the blowpipe flame. The thermometer is now finished
+except for graduation; this is dealt with on page 75.</p>
+
+<p><i>An Alarm Thermometer.</i>&mdash;A thermometer which will complete an electric
+circuit when a certain temperature is reached may be made by<span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span> sealing an
+electrode in the bulb and introducing a wire into the top, which in this
+case is not sealed. Naturally, this thermometer will be filled with
+mercury. There is considerable difficulty in filling such a bulb without
+causing it to crack.</p>
+
+<p>Several elaborations of this form are made, in which electrodes are
+sealed through the walls of the capillary tube, thus making it possible
+to detect electrically the variation of temperature when it exceeds any
+given limits.</p>
+
+<p><i>An Enclosed or Floating Thermometer.</i>&mdash;The construction of this type of
+thermometer is shown by <i>h</i> and <i>i</i>, Fig 11. It is made in the following
+stages:&mdash;A bulb is blown on the drawn-out end of a thin-walled tube as
+shown by <i>h</i>. A small bulb is blown on the end of a capillary tube,
+burst, and turned out to form a lip which will rest in the drawn-out
+part of the thin-walled tube but is just too large to enter the bulb.
+The capillary tube is introduced and sealed in position, care being
+taken to expand the joint a little. The thermometer is filled and the
+top of the capillary tube closed by the use of a small blowpipe flame. A
+paper scale having the necessary graduations is inserted,<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span> and the top
+of the outer tube is closed as shown by <i>i</i>.</p>
+
+<p><i>A Maximum and Minimum Thermometer.</i>&mdash;If a small dumb-bell-shaped rod of
+glass or metal is introduced into the capillary tube of a horizontally
+placed, mercury-filled thermometer in such a position that the rising
+mercury column will come in contact with it, the rod will be pushed
+forward. When the mercury falls again the rod will be left behind and
+thus indicate the maximum temperature attained. If a similar
+dumb-bell-shaped rod is introduced into an alcohol-filled thermometer
+and pushed down until it is within the alcohol column, it will be drawn
+down by surface tension as the column falls; but the rising column will
+flow passed it without causing any displacement; thus the minimum
+temperature will be recorded.</p>
+
+<p>Six's combined maximum and minimum thermometer is shown by <i>b</i>, Fig. 11.
+In this case both maximum and minimum records are obtained from a
+mercury column, although the thermometer bulb is filled with alcohol. It
+is an advantage to make the dumb-bell-shaped rods of iron, as the
+thermometer can then be reset by the use of a small magnet, another<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span>
+advantage consequent on the use of metal being that the rods can be
+easily adjusted, by slight bending, so as to remain stationary in the
+tubes when the thermometer is hanging vertically, and yet to move with
+sufficient freedom to yield to the pressure of the recording column.</p>
+
+<p>The thermometer may be filled by the following method:&mdash;When the
+straight tube has been made the first dumb-bell is introduced and shaken
+down well towards the lower bulb, the tube is now bent to its final
+shape and the whole thermometer filled with alcohol as described on page
+44. Now heat the thermometer to a little above the maximum temperature
+that it is intended to record, and pour clean mercury into the open bulb
+while holding the thermometer vertically. Allow to cool, and the mercury
+will be sucked down. The second dumb-bell is now introduced, sufficient
+alcohol being allowed to remain in the open bulb to about half fill it,
+and the alcohol in this bulb is boiled to expel air. The tube through
+which the bulb was filled in now sealed.</p>
+
+<p><i>Clinical Thermometers.</i>&mdash;The clinical thermometer is a maximum
+thermometer of a<span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span> different type. In this case there is a constriction
+of the bore at a point just above the bulb. When the mercury in the bulb
+commences to contract, the mercury column breaks at the constriction and
+remains stationary in the tube, thus showing the maximum temperature to
+which it has risen.</p>
+
+<p><i>Vacuum Tubes.</i>&mdash;There are so many forms of these that it is scarcely
+practicable or desirable to give detailed instructions for making them;
+but an application of the various methods of glass-working which have
+already been explained should enable the student to construct most of
+the simpler varieties. An interesting vacuum tube is made which has no
+electrodes, but contains a quantity of mercury. When the tube is rocked
+so as to cause friction between the mercury and the glass sufficient
+charge is produced to cause the tube to glow.</p>
+
+<p><i>A Sprengel Pump.</i>&mdash;This, in its simplest form, is illustrated by <i>a</i>,
+Fig. 12. Such a form, although highly satisfactory in action, needs
+constant watching while in action, as should the mercury funnel become
+empty air will enter the exhausted vessel. Obviously, the fall-tube must
+be made not less than thirty<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span> inches long; the measurement being taken
+from the junction of the exhaustion branch with the fall-tube to the top
+of the turned-up end.</p>
+
+<div class="figcenter" style="width: 506px;">
+<img src="images/fig12.jpg" width="506" height="650" alt="Fig. 12" title="" />
+<span class="caption">Fig. 12</span>
+</div>
+
+<p><i>A Macleod Pump.</i>&mdash;One form of this is illustrated by <i>b</i>, Fig. 12. It
+has the advantage<span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span> that the mercury reservoir may be allowed to become
+empty without affecting the vacuum in the vessel being exhausted.</p>
+
+<p><i>"Spinning" Glass.</i>&mdash;By the use of suitable appliances, it is quite
+possible to draw out a continuous thread of glass, which is so thin as
+to have almost the flexibility and apparent softness of woollen fibre; a
+mass of such threads constitutes the "glass wool" of commerce.</p>
+
+<p>The appliances necessary are:&mdash;a blowpipe capable of giving a
+well-formed flame of about six or eight inches in length, a wheel of
+from eighteen inches to three feet in diameter and having a flat rim of
+about three inches wide, and a device for rotating the wheel at a speed
+of about three hundred revolutions per minute.</p>
+
+<p>A very satisfactory arrangement may be made from an old bicycle; the
+back wheel having the tyre removed and a flat rim of tin fastened on in
+its place. The chain drive should be retained, but one of the cranks
+removed and a handle substituted for the remaining pedal. The whole
+device is shown by Fig. 13.</p>
+
+<div class="figcenter" style="width: 550px;">
+<img src="images/fig13.jpg" width="550" height="523" alt="Fig. 13" title="" />
+<span class="caption">Fig. 13</span>
+</div>
+
+<p>The procedure in "spinning" glass is as<span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span> follows:&mdash;First melt the end of
+a glass rod and obtain a large mass of thoroughly softened glass, now
+spin the wheel at such a speed that its own momentum will keep it
+spinning for several seconds. Touch the end of the melted rod with
+another piece of glass and, without withdrawing the original rod from
+the blowpipe flame, draw out a thread of molten glass and twist it round
+the spinning wheel. If this is done properly, the thread of glass will
+grip<span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span> on the flat rim, and by continuing to turn the wheel by hand it is
+possible to draw out a continuous thread from the melted rod, which must
+be advanced in the blowpipe flame as it is drawn on the wheel. If the
+rod is not advanced sufficiently the thread will melt off, if it is
+advanced too much, so as to heat the thick part and allow the glass to
+become too cool at the point of drawing out, then the thread will become
+too thick, but it is easy after a little practice to obtain the right
+conditions. Practice is necessary also in order to find the right speed
+for the wheel.</p>
+
+<p>When sufficient glass has been "spun," the whole "hank" of thin thread
+may be removed by drawing the thumb-nail across the wheel at any point
+on its flat rim, thus breaking the threads, and allowing the "hank" to
+open.</p>
+
+<p><i>Brushes for Use with Strong Acids.</i>&mdash;Glass wool, if of fine enough
+texture to be highly flexible, can be used to make acid-resisting
+brushes. A convenient method for mounting the spun glass is to melt the
+ends of the threads together into a bead, and then to fuse the bead on
+to a rod; thus giving a brush. If a pointed brush is necessary, the
+point may be ground on<span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span> an ordinary grindstone or carborundum wheel by
+pressing the loose end of the spun glass against the grinding wheel with
+a thin piece of cardboard.</p>
+
+<p>When using brushes of this description, it is well to bear in mind the
+fact that there is always a liability of a few threads of glass breaking
+off during use.</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_55" id="Page_55">[Pg 55]</a></span></p>
+<h2>CHAPTER IV</h2>
+
+<div class="blockquot"><p>Glass, Its Composition and Characteristics. Annealing.
+Drilling, Grinding, and Shaping Glass by methods other than
+Fusion. Stopcocks. Marking Glass. Calibration and Graduation
+of Apparatus. Thermometers. Exhaustion of Apparatus. Joining
+Glass and Metal. Silvering Glass.</p></div>
+
+
+<p>There are three kinds of glass rod and tubing which are easily
+obtainable; these are soda-glass, which is that usually supplied by
+chemical apparatus dealers when no particular glass is specified;
+combustion-glass, which is supplied for work requiring a glass that does
+not so easily soften or fuse as soda-glass; and lead-glass, which is
+less common. There are also resistance-glass, made for use where very
+slight solubility in water or other solutions is desirable, and a number
+of other special glasses; but of these soda-glass, combustion-glass,
+lead-glass, and resistance-glass are the most important to the
+glass-blower whose work is connected with laboratory needs.</p>
+
+<p><i>Soda-Glass.</i>&mdash;Consists chiefly of sodium<span class='pagenum'><a name="Page_56" id="Page_56">[Pg 56]</a></span> silicate, but contains
+smaller quantities of aluminum silicate, and often of calcium silicate;
+there may also be traces of several other compounds.</p>
+
+<p>The ordinary soda-glass tubing melts easily in the blowpipe flame, it
+has not a long intermediate or viscous stage during fusion, but becomes
+highly fluid rather suddenly; it does not blacken in the reducing flame.
+Bad soda-glass or that which has been kept for many years, tends to
+devitrify when worked. That is to say the glass becomes more or less
+crystalline and infusible while it is in the flame; and in this case it
+is often impossible to do good work with that particular sample of
+glass; although the devitrification may sometimes be remedied by heating
+the devitrified glass to a higher temperature. The presence of aluminum
+compounds appears to have some influence on the tendency of the glass to
+resist devitrification. Soda-glass, as a rule, is more liable to crack
+by sudden heating than lead-glass, and articles made from soda-glass
+often tend to crack spontaneously if badly made or, in the case of
+heavier and thicker articles, if insufficiently annealed.<span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span></p>
+
+<p><i>Combustion-Glass.</i>&mdash;Is usually a glass containing more calcium silicate
+and potassium silicate than the ordinary "soft" soda-glass. It is much
+less fusible than ordinary soda-glass, and passes through a longer
+intermediate or viscous stage when heated. Such a glass is not very
+suitable for use with the blowpipe owing to the difficulty experienced
+in obtaining a sufficiently high temperature. If, however, a certain
+amount of oxygen is mixed with the air used in producing the blowpipe
+flame this difficulty is minimised.</p>
+
+<p><i>Resistance-Glass.</i>&mdash;May contain zinc, magnesium, and other substances.
+As a rule it is harder than ordinary soda-glass, and less suitable for
+working in the blowpipe flame. It should have very little tendency to
+dissolve in water, and hence is used when traces of alkali or silicates
+would prove injurious in the solutions for which the glass vessels are
+to be used.</p>
+
+<p><i>Lead-Glass.</i>&mdash;This, or "flint" glass as it is often called from the
+fact that silica in the form of crushed and calcined flint was often
+used in making the English lead-glasses, contains a considerable
+proportion of lead silicate. Such<span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span> a glass has, usually, a particularly
+bright appearance, a high refractive index, and is specially suitable
+for the production of the heavy "cut-glass" ware.</p>
+
+<p>Lead-glass tubing is easy to work in the blowpipe flame, melts easily,
+but does not become fluid quite so suddenly as most soda-glasses;
+articles made from it are remarkably stable and free from tendency to
+spontaneous cracking, although, as is essential for all the heavy or
+"glass-house" work, the massive articles need annealing in the oven.</p>
+
+<p>The two chief disadvantages of lead-glass for laboratory work are that
+it is blackened by the reducing gases if held too near to the blue cone
+of the blowpipe flame, and that it is rather easily attacked by chemical
+reagents; thus ammonium sulphide will cause blackening.</p>
+
+<p>The effect of the reducing flame on lead is not altogether a
+disadvantage, however; because a little care in adjusting the blowpipe
+and a little care in holding the glass in the right position will enable
+the student to work lead-glass without producing the faintest trace of
+blackening. This, in addition to being a valuable exercise in
+manipulation, will teach<span class='pagenum'><a name="Page_59" id="Page_59">[Pg 59]</a></span> him to keep his blowpipe in good order, and
+prove a useful aid in his early efforts to judge as to the condition of
+the flame. It prevents discouragement if the student does his
+preliminary work with the soda-glass, but he should certainly make
+experiments with lead-glass as soon as he has acquired reasonable
+dexterity with soda-glass.</p>
+
+<p><i>Annealing.</i>&mdash;Annealing is a process by which any condition of strain
+which has been set up in a glass article, either by rapid cooling of one
+part while another part still remains hot, or by the application of
+mechanical stress after cooling is relieved. Annealing is carried out by
+subjecting the article to a temperature just below the softening point
+of the glass, maintaining that temperature until the whole article has
+become heated through the thicker part, and then reducing the
+temperature very gradually; thus avoiding any marked cooling of the
+thinner and outer parts first.</p>
+
+<p>For thin glass apparatus of the lamp-blown or blowpipe-made variety in
+which there are no marked difference of thickness, such as joins on
+tubes, ordinary seals, bulbs, etc., there is little need for annealing;
+and even those having<span class='pagenum'><a name="Page_60" id="Page_60">[Pg 60]</a></span> rather marked changes of thickness, such as
+filter pumps, can be annealed sufficiently by taking care that the last
+step in making is heating to just below visible redness in the blowpipe
+flame and then rotating in a sooty gas flame until covered with a
+deposit of carbon. The article should then be allowed to cool in a place
+free from draughts and where the hot glass will not come in contact with
+anything.</p>
+
+<p>A few of the blowpipe-made articles, such, for example, as glass
+stopcocks, need more careful annealing, and for this purpose a small
+sheet-iron oven which can be heated to dull redness over a collection of
+gas burners will serve. Better still, a small clay muffle can be used.
+In either case, the article to be annealed should be laid on a clean,
+smooth, fireclay surface, the temperature should be maintained at a very
+dull red for two or three hours and then reduced steadily until the oven
+is cold. This cooling should take anything from three to twelve hours,
+according to the nature of the article to be annealed. A thick article,
+or one having great irregularities in thickness will need much longer
+annealing than one thinner<span class='pagenum'><a name="Page_61" id="Page_61">[Pg 61]</a></span> or more regular. As a rule, soda-glass will
+need more annealing than lead-glass.</p>
+
+<p><i>Drilling Glass.</i>&mdash;Small holes may be drilled in glass by means of a rod
+of hard steel which has been broken off, thus giving a more or less
+irregular and crystalline end.</p>
+
+<p>There are several conditions necessary to enable the drilling of small
+holes to be carried out successfully:&mdash;the first of these is that the
+"drill" should be driven at a high speed. This may be done by means of a
+geared hand-drill such as the American pattern drill, although a
+somewhat higher speed than this will give is even more satisfactory. The
+second condition is that the pressure on the drill is neither too light
+nor too heavy; this is conveniently regulated by hand. The third
+condition is that the drill be prevented from "straying" over the
+surface of the glass; for this purpose a small metal guide is useful.
+The fourth condition is that a suitable lubricant be used; a strong
+solution of camphor in oil of turpentine is perhaps the most suitable.
+For commercial work, a diamond drill is often used, but this is scarcely
+necessary for the occasional work of a laboratory.<span class='pagenum'><a name="Page_62" id="Page_62">[Pg 62]</a></span></p>
+
+<p><i>Larger Holes in Glass.</i>&mdash;The method of drilling with a hard steel rod
+is not highly satisfactory for anything but small holes. When a larger
+hole, say one of an eighth of an inch or more, is needed it is better to
+use a copper or brass tube. This tube may be held in an American
+hand-drill, but a mixture of carborundum or emery and water is supplied
+to the rotating end. Tube or drill must be lifted at frequent intervals
+in order to allow a fresh supply of the grinding material to reach the
+end. In this case, also, a guide is quite essential in the early stages
+of drilling; otherwise the end of the tube will stray. The speed of
+cutting may be increased slightly by making a number of radial slots in
+the end of the tube; these serve to hold a supply of the grinding
+material.</p>
+
+<p><i>Grinding Lenses.</i>&mdash;This is scarcely within the scope of a book on
+glass-blowing for laboratory purposes, but it may be said that the lens
+may be ground by means of a permutating mould of hard lead or
+type-metal. The rough shaping is done with coarse carborundum or emery,
+and successive stages are carried on with finer and finer material. The
+last polishing is by the<span class='pagenum'><a name="Page_63" id="Page_63">[Pg 63]</a></span> use of jewellers' rouge on the mould, now
+lined with a fine textile.</p>
+
+<p><i>Filing Glass.</i>&mdash;If a new file, thoroughly lubricated with a solution of
+camphor in oil of turpentine, is used, there is but little difficulty in
+filing the softer glasses. A slow movement of the file, without
+excessive pressure but without allowing the file to slip, is desirable.
+After a time the cutting edges of the file teeth will wear down and it
+will be necessary to replace the file by another.</p>
+
+<p><i>Grinding Stoppers.</i>&mdash;This is, perhaps, the most common form of grinding
+that the laboratory worker will need to perform, and for that reason,
+rather full details of the procedure are desirable.</p>
+
+<p>A very crude form of ground-in stopper may be made by drawing out the
+neck and the mass of glass which is intended to form the stopper to
+approximately corresponding angles, wetting the surfaces with a mixture
+of the abrasive material and water, and grinding the stopper in by hand.
+Frequent lifting of the stopper is necessary during grinding, in order
+to allow fresh supplies of abrasive material to reach the contacts. When
+an approximate fit is obtained,<span class='pagenum'><a name="Page_64" id="Page_64">[Pg 64]</a></span> the coarse abrasive should be washed
+off, care being taken that the washing is complete, and a finer abrasive
+substituted. After a while, this is replaced in its turn by a still
+finer grinding material.</p>
+
+<p>Such a method of grinding may give a satisfactory stoppering if the
+angles of the plug and socket correspond very closely before grinding is
+commenced; but if there is a wide difference in the original angles,
+then no amount of grinding by this method will produce a good result.
+The reason for this is that the plug will become so worn in the
+preliminary grinding as to assume the form of a highly truncated cone;
+the socket will assume a reverse form, and the end result will be a
+loose-fitting plug and socket.</p>
+
+<p>Satisfactory grinding may be carried out by the use of copper or
+type-metal cones for the preliminary shaping. Such cones should be
+mounted on a mandrel which will fit into the chuck of the American
+hand-drill and turned on the lathe to the desirable angle for
+stoppering. A number of these cones will be necessary. A number of
+similar moulds, that is to say blocks of type-metal or hard lead in
+which is a hole corresponding in size and angle<span class='pagenum'><a name="Page_65" id="Page_65">[Pg 65]</a></span> to the plug desired,
+should be made also. These must be rotated, either in the lathe or by
+other means, and are used for the preliminary shaping of the plug. If
+but few plugs are to be ground it is unnecessary to provide a means of
+rotating the moulds, as the plug may be held in the hand and ground into
+the mould in a manner similar to that used in the first method of
+stoppering.</p>
+
+<div class="figcenter" style="width: 561px;">
+<img src="images/fig14.jpg" width="561" height="550" alt="Fig. 14" title="" />
+<span class="caption">Fig. 14</span>
+</div><p><span class='pagenum'><a name="Page_66" id="Page_66">[Pg 66]</a></span></p>
+
+<p>When the socket and plug have been ground, by the successive use of
+cones and moulds, to the desired angle, so that they correspond almost
+exactly, the plug is given its final fitting into the socket by
+grinding-in with a fine abrasive, in the manner first described.</p>
+
+<p><i>Stopcocks.</i>&mdash;Although it would be more strictly in keeping with the
+form of this book to divide the making of stopcocks into two parts;
+shaping by heat and grinding, we will consider the whole operation here,
+and take for our example a simple stopcock such as that illustrated by
+Fig. 14.</p>
+
+<p>The "blank," <i>f</i>, that is the socket before grinding, is made by drawing
+out a piece of fairly thick-walled tubing into the form shown by <i>a</i>.
+Two zones on this tube are then heated by means of a small, pointed
+flame, and the tube is compressed along its axis, thus producing two
+raised rings as shown by <i>b</i>. Two zones, slightly towards the outer
+sides of these two raised rings are heated and the tube is drawn while
+air pressure is maintained within. This produces two thin-walled bulbs
+or extensions similar to those shown by <i>c</i>. One of these extensions is
+now broken off by means of a<span class='pagenum'><a name="Page_67" id="Page_67">[Pg 67]</a></span> sharp blow with the edge of a file or
+other piece of metal, and the edges of the broken glass are rounded in
+the flame. The other extension is left to serve as a handle. We have now
+a piece of glass like that shown by <i>d</i>. Now heat a spot on the side of
+this, medially between the raised rings, until the glass is on the point
+of becoming deformed, and bring the intensely heated end of a smaller
+tube in contact with the heated spot. Without disturbing the relative
+positions of the two tubes, press the smaller tube down on a thin steel
+wire, so that the wire passes along the tube and enters the soft glass;
+thus forming a projection inside the sockets as shown by <i>e</i>. The wire
+must be withdrawn, again immediately. When the wire has been withdrawn,
+heat the place where it entered to dull redness, in order to relieve any
+strain; break off the thin extension, which up to the present has served
+as a handle, round off the broken edges in the flame, and join on and
+indent a similar piece of small tubing to the opposite side of the
+socket; the socket at this stage being shown by <i>f</i>. The "blank" for the
+socket is now completed, but it must be heated to dull redness in order
+to relieve strain<span class='pagenum'><a name="Page_68" id="Page_68">[Pg 68]</a></span> and be placed in an annealing oven, where it should
+be annealed for some hours.</p>
+
+<p>The "blank" for the plug offers no special difficulty; it is made by
+heating a glass rod and compressing it axially until a mass having the
+form shown by <i>g</i>, Fig. 14, is produced; the end of this is heated
+intensely and brought in contact with the rather less heated side of a
+glass tube which has been drawn to the shape desired for the handle;
+when contact is made a slight air pressure is maintained in the glass
+tube, thus producing a hollow join. The ends of the tube are sealed and
+the bottom of the plug is drawn off, thus giving the finished "blank" as
+shown by <i>h</i>. This blank is now held in a pair of asbestos-covered
+tongs, heated to dull redness all over, and transferred to the annealing
+oven.</p>
+
+<p>When cold, the socket is ground out by the second method given under
+"Grinding Stoppers"; that is to say, by means of type-metal or copper
+cone, and the plug is ground to fit in a corresponding mould. When the
+fit is almost perfect, the transverse hole is drilled in the plug, and
+the final finishing is made with fine abrasive powder. Great care must
+be taken in the<span class='pagenum'><a name="Page_69" id="Page_69">[Pg 69]</a></span> final grinding that there is no accumulation of
+abrasive material in the transverse hole of the plug; if this is allowed
+to occur there will be a ring ground out of the socket where the holes
+move, and the tightness of the finished stopcock will be lost.</p>
+
+<p><i>Marking Glass.</i>&mdash;As a preliminary to a consideration of the methods of
+graduating and calibrating glass apparatus, it is convenient to consider
+the various methods which are available for marking glass. Among these
+are, the writing diamond, the carborundum or abrasive pencil, the
+cutting-wheel, and etching by means of hydrofluoric acid. Each produces
+a different class of marking and each is worthy of independent
+consideration.</p>
+
+<p><i>The Writing Diamond.</i>&mdash;This is the name given to a small irregular
+fragment of "bort" which is usually mounted in a thin brass rod. Such a
+diamond, if properly selected, has none of the characteristics of a
+cutting diamond; although one occasionally finds so-called "writing
+diamonds" which will produce a definite cut. These should be rejected.</p>
+
+<p>The writing diamond is used in much the same way as a pencil, but is
+held more perpendicularly<span class='pagenum'><a name="Page_70" id="Page_70">[Pg 70]</a></span> to the object, and a certain amount of
+pressure is necessary. The mark produced is a thin scratch which,
+although fairly definite, lacks breadth, and this is a disadvantage
+where the marking has to be read at a distance. This disadvantage may to
+some extent be overcome by making a number of parallel scratches.</p>
+
+<p><i>The Abrasive Pencil.</i>&mdash;A rod of carborundum composition may be ground
+or filed to a point, and this forms a very useful pencil for general
+work. The marking produced is rather less definite than that produced by
+a writing diamond, but has the advantage of being broader.</p>
+
+<p><i>The Cutting Wheel.</i>&mdash;"Cutting" in this case is scarcely the ideal
+expression, it should rather be "grinding," but "cutting" is more
+commonly used. Exceedingly good graduations may be made by the edge of a
+small, thin, abrasive wheel which is mounted on the end of a small
+mandrel and driven by a flexible shaft from an electric motor or any
+other convenient source of power. The depth of the mark can be
+controlled, and very light pressure will suffice.</p>
+
+<p><i>Etching.</i>&mdash;This is often the quickest and<span class='pagenum'><a name="Page_71" id="Page_71">[Pg 71]</a></span> easiest way of marking glass
+apparatus. The object to be marked should first be warmed and coated
+very thoroughly with a thin film of paraffin wax. When cold, the marking
+is made through the paraffin wax by means of a needle point, and the
+object is then exposed to the action of hydrofluoric acid. If a shallow
+but clearly visible marking is desired, it is well to use the vapour of
+the acid; this may be done by bending up a sheet-lead trough on which
+the object can rest with the marked surface downwards. A little of the
+commercial hydrofluoric acid, or a mixture of a fluoride and sulphuric
+acid, is distributed over the bottom of the trough, and the whole
+arrangement is allowed to stand for about an hour. The object is washed
+thoroughly and the paraffin wax removed, either by melting and wiping
+off or by the use of a solvent, and the marking is finished.</p>
+
+<p>If a deep marking is desired, in order that it may afterwards be filled
+with some pigment, a better result is obtained by the use of liquid
+commercial hydrofluoric acid, which is a solution of hydrogen fluoride
+in water. The acid is mopped on to the object after the<span class='pagenum'><a name="Page_72" id="Page_72">[Pg 72]</a></span> markings have
+been made on the paraffin wax film, and allowed to remain in contact for
+a few minutes. It is advantageous to repeat the mopping-on process at
+intervals during the etching.</p>
+
+<p>In all cases where hydrofluoric acid is used, or stored, it is of great
+importance to keep it well away from any optical instruments, as the
+most minute trace of vapour in the air will produce a highly destructive
+corrosion of any glass surfaces.</p>
+
+<p><i>Methods of Calibration.</i>&mdash;In the case of apparatus for volumetric work,
+this is usually carried out by weighing, although some of the smaller
+subdivisions are often made by measurement. When the subdivisions are
+made in this way it is of importance to see that the walls of the tube
+or vessel to be calibrated are parallel. Great errors arise in some of
+the commercial apparatus from neglect of this precaution. A convenient
+method of testing for parallelism, in the case of a wide tube, is to
+close one end and to weigh in successive quantities of mercury. An
+observation of the length occupied by each successive quantity will
+indicate any change in the bore. In the case of capillary tubes, it is<span class='pagenum'><a name="Page_73" id="Page_73">[Pg 73]</a></span>
+convenient to introduce an unweighed quantity of mercury, measure its
+length accurately, and then to move it along the tube in stages, either
+by tilting the tube or by the application of air pressure. A measurement
+of the length at each stage will indicate whether the bore is
+approximately parallel or not. Neither of these methods is to be relied
+on without a careful examination of the tube, as it may happen that
+there are local irregularities in the bore which compensate for each
+other, and do not, therefore, affect the volume of a given length.
+Obviously, the smaller the quantity of mercury with which the test is
+carried out and the greater the number of observations made, the less
+risk will there be of such an error. A liquid, such as water or alcohol,
+which wets the glass is not suitable for such a test, unless special
+precautions are taken.</p>
+
+<p>When, however, a pipette or burette has to be calibrated to deliver a
+certain volume of water, the final calibration must be made with this
+liquid. Thus, the burette would first be calibrated by weighing in
+definite quantities of mercury of say 13.54 grammes (1 cc at 15&deg;C.),
+each of the 1 cc divisions should be marked by<span class='pagenum'><a name="Page_74" id="Page_74">[Pg 74]</a></span> some temporary marking.
+The burette is now filled with a solution of potassium bichromate and
+sulphuric acid and allowed to soak for some time; the bichromate is
+washed out and distilled water is put in. Successive quantities of water
+are run out of the jet, a fixed time being allowed for draining, and the
+weights of the quantities delivered are noted. This procedure will give
+the necessary data for altering the marking so that it may correspond to
+1 cc <i>delivered</i>. Each 1 cc division is now divided into tenths by the
+method described below. A final verification of the markings should be
+made when the subdivision is completed.</p>
+
+<p><i>Subdivision of Graduations.</i>&mdash;Mark out the spaces to be subdivided on a
+sheet of paper. Take a reliable ruler on which any convenient length is
+divided into the desired number and place it across the lines at such an
+angle that the limits noted on the rule exactly bridge the gap. Now draw
+parallel lines through the markings.</p>
+
+<p><i>Copying a Scale.</i>&mdash;When a scale has been prepared on paper and it is
+necessary to copy that scale on the waxed-glass surface for etching, a
+convenient method is to employ a<span class='pagenum'><a name="Page_75" id="Page_75">[Pg 75]</a></span> long wooden bar having a sharp needle
+passing through it at either end. The scale and object to be marked are
+fastened in line with one another, and the caliper bar is used from step
+to step. The mark is made by moving the bar through a minute portion of
+a circle, which provided that the bar is two or three feet in length,
+will not introduce any perceptible error in a scale of say a quarter of
+an inch in width. The arrangement is shown by Fig. 15.</p>
+
+<div class="figcenter" style="width: 650px;">
+<img src="images/fig15.jpg" width="650" height="226" alt="Fig. 15" title="" />
+<span class="caption">Fig. 15</span>
+</div>
+
+<p><i>Graduating a Thermometer.</i>&mdash;Assuming that the thermometer has been made
+of carefully selected tubing in which the bore is parallel and free from
+any small irregularities, we have only to fix the freezing point and
+boiling point. The intervening space may then be divided into 100 (if
+the thermometer is to be Centigrade) or 180 (if Fahrenheit). This
+division may be carried out by the method given under<span class='pagenum'><a name="Page_76" id="Page_76">[Pg 76]</a></span> "Subdivisions of
+Graduations." A thermometer should not be calibrated until some weeks
+after making, as the glass bulb tends to contract.</p>
+
+<p><i>Joining Glass and Metal.</i>&mdash;It sometimes happens that one needs to make
+a more permanent and less flexible joint between a glass and metal tube
+than can be obtained by means of a rubber tube. To this end, any one of
+three slightly different methods may be employed. In the method of
+Chatelier one first coats the glass with platinum or silver, which may
+be done by moistening the glass with platinum chloride or silver nitrate
+and then heating to redness; a layer of copper is then deposited
+electrolytically on the treated surface of the glass, and soldering is
+carried out in the usual manner.</p>
+
+<p>McKelvy and Taylor call attention to two other methods in the <i>Journal
+of the Chemical Society</i> for September, 1920. In one of these methods
+the glass is coated with platinum by covering it with a suspension of
+platinum chloride in oil of lavender and heating until the oil is burnt
+off. The metal tube is then tinned on its inner side and soldered to the
+prepared<span class='pagenum'><a name="Page_77" id="Page_77">[Pg 77]</a></span> glass, slightly acid zinc chloride being used as a flux.</p>
+
+<p>In the second method, a joint is made by means of the Kraus flux, which
+consists of equal weights of zinc oxide, borax, and powdered soda-glass
+fused together. This is coated on the inner surface of the metal tube,
+and the hot glass tube, which has had the end slightly flanged to give
+support, is inserted. Fusion of the flux is completed by heating the
+outside of metal tube.</p>
+
+<p><i>Silvering Glass.</i>&mdash;In all cases where it is intended to deposit a
+silver mirror on a glass surface, thorough cleaning is essential.
+Prolonged soaking in a hot solution of potassium bichromate which has
+been acidified with sulphuric acid will often prove useful. The glass
+should then be washed thoroughly, rinsed in distilled water, and the
+solution should then be used.</p>
+
+<p>There are many formul&aelig; for the silvering solution, but that used in
+Martin's method may be given:<span class='pagenum'><a name="Page_78" id="Page_78">[Pg 78]</a></span>&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='right'>A&mdash;Nitrate of Silver</td><td align='right'>40</td><td align='left'> grammes</td></tr>
+<tr><td align='right'>Distilled Water</td><td align='right'>1000</td><td align='left'> c. cm.</td></tr>
+<tr><td align='right'>B&mdash;Nitrate of Ammonium</td><td align='right'>60</td><td align='left'> grammes</td></tr>
+<tr><td align='right'>Distilled Water</td><td align='right'>1000</td><td align='left'> c. cm.</td></tr>
+<tr><td align='right'>C&mdash;Pure Caustic Potash</td><td align='right'>100</td><td align='left'> grammes</td></tr>
+<tr><td align='right'>Distilled Water</td><td align='right'>1000</td><td align='left'> c. cm.</td></tr>
+<tr><td align='right'>D&mdash;Pure Sugar Candy</td><td align='right'>100</td><td align='left'> grammes</td></tr>
+<tr><td align='right'>Distilled Water</td><td align='right'>1000</td><td align='left'> c. cm.</td></tr>
+<tr><td colspan="3">Dissolve and add:&mdash;</td></tr>
+<tr><td align='right'>Tartaric Acid</td><td align='right'>23</td><td align='left'> grammes</td></tr>
+<tr><td colspan="3">Boil for ten minutes, and when cool add:&mdash;</td></tr>
+<tr><td align='right'>Alcohol</td><td align='right'>200</td><td align='left'> c. cm.</td></tr>
+<tr><td align='right'>Distilled Water to</td><td align='right'>2000</td><td align='left'> c. cm.</td></tr>
+</table></div>
+
+<p>For use take equal parts of A and B. Mix together also equal parts of C
+and D in another vessel. Then mix both liquids together in the silvering
+vessel and suspend the glass to be silvered face downwards in the
+solution. Or if a vessel has to be silvered on the inside, the solution
+is poured in. In this case, the deposition of silver may be hastened by
+immersing the vessel to be silvered in warm water.</p>
+
+<p>In working with a silver solution containing ammonia or ammonium salts
+there is sometimes the possibility of forming an explosive silver
+compound. It is well, therefore, to avoid keeping such solutions longer
+than is necessary, and to bear in mind that any deposit<span class='pagenum'><a name="Page_79" id="Page_79">[Pg 79]</a></span> formed by
+solutions containing both silver and ammonia may have explosive
+properties, especially when dry.</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_80" id="Page_80">[Pg 80]</a></span></p>
+<h2>CHAPTER V</h2>
+
+<div class="blockquot"><p>Extemporised Glass-Blowing Apparatus&mdash;The Use of Oil or
+other Fuels&mdash;Making Small Rods and Tubes from Glass
+Scrap&mdash;The Examination of Manufactured Apparatus with the
+View to Discovering the Methods Used in Manufacture&mdash;Summary
+of Conditions Necessary for Successful Glass-Blowing.</p></div>
+
+
+<p>If, in the early stages of his study of glass-blowing, the student
+should attempt to work with the very simplest appliances, it is probable
+that his progress will be hindered; the use of the apparatus will
+require an undue amount of care and his attention will be distracted
+from the actual manipulation of the glass. The case is widely different
+after he has acquired a certain facility in glass-blowing.</p>
+
+<p><i>A Simple Form of Blowpipe.</i>&mdash;Although there are even more simple forms
+than that described here, we are not concerned with them. The form
+described is the simplest with which any considerable amount of
+glass-blowing can be carried out with certainty.<span class='pagenum'><a name="Page_81" id="Page_81">[Pg 81]</a></span></p>
+
+<p>This form consists of a tube through which air may be blown with the
+mouth, a condensation chamber in which any moisture from the breath can
+condense, a blowpipe jet, a supporting piece and a source of flame.</p>
+
+<p>The tube, condensation chamber, and jet are combined in the ordinary
+Black's blowpipe, such as is used for blowpipe tests in qualitative
+analysis; it consists of a conical tin tube having a mouthpiece at the
+small end and a side tube which carries a brass jet. A support for such
+a blowpipe may be cut out of a piece of brass or tin-plate, and should
+be fastened to a small, flat, wooden board. A source of flame may
+consist of an ordinary brass elbow, such as is used on gas fittings, and
+into which a piece of thin brass tube (the body of a fish-tail burner
+from which the perforated non-metallic plug has been removed will serve
+quite well) has been fitted. It is an advantage to flatten the brass
+tube somewhat and to file the flattened end to a slope which corresponds
+with the angle at which the blowpipe jet enters the burner. The whole
+source of the flame should be mounted on a separate base, in order that
+it may be moved while adjusting the apparatus to<span class='pagenum'><a name="Page_82" id="Page_82">[Pg 82]</a></span> the best relative
+positions of flame and blowpipe jet. The complete apparatus is shown by
+<i>a</i>, Fig. 16.</p>
+
+<div class="figcenter" style="width: 554px;">
+<img src="images/fig16.jpg" width="554" height="650" alt="Fig. 16" title="" />
+<span class="caption">Fig. 16</span>
+</div>
+
+<p>In order to take full advantage of this blowpipe, it is desirable that
+the student should learn to maintain a steady steam of air with his<span class='pagenum'><a name="Page_83" id="Page_83">[Pg 83]</a></span>
+mouth and, at the same time, be able to breathe. This requires a little
+practice.</p>
+
+<p>As a first exercise in breathing, before trying to breathe while using
+the mouth blowpipe, the student should close his mouth and inflate his
+cheeks with air; now, still keeping his cheeks tightly inflated, he
+should attempt to breathe through the nose. At first, this may be found
+rather difficult, but it becomes remarkably easy after a little
+practice. When he has mastered this, the student may practise the same
+operation, but with the blowpipe. It is important to bear in mind that
+the cheeks, not the lungs, form the reservoir for air used in
+maintaining the blowpipe flame. After a while, the student will find
+that he can maintain a steady air pressure and yet breathe with complete
+comfort.</p>
+
+<p>In adjusting the flame, care should be taken not to blow so hard as to
+produce a ragged and noisy cone of fire. A small jet, such as that
+commonly used on a mouth blowpipe, will with care give a pointed and
+quiet flame, having an appearance similar to that shown in the
+illustration.</p>
+
+<p>With a blowpipe like this, it is quite easy to seal glass tubes up to an
+inch in diameter, to<span class='pagenum'><a name="Page_84" id="Page_84">[Pg 84]</a></span> join tubes up to half an inch in diameter, to bend
+tubes, to blow small bulbs, and to make the simpler forms of internal
+seal; but the provision for condensation of moisture is not ideal, and
+prolonged use of such a blowpipe also tends to produce undue fatigue.</p>
+
+<p><i>A Mouth Blowpipe With an Expanding Reservoir.</i>&mdash;This form of blowpipe
+can be made to give most excellent results; it is highly portable, and
+does not produce nearly so much fatigue when used continuously as the
+blowpipe described in the last section. Various slight modifications
+have been made in its construction during the last eighty years, but
+that described below will be found quite satisfactory.</p>
+
+<p>The apparatus consists of a tube through which air is blown from the
+mouth, a valve through which the air passes into an expanding reservoir,
+and a blowpipe jet in communication with the reservoir.</p>
+
+<p>In making the valve, several essentials have to be remembered; it must
+allow a free passage of air into the reservoir, it must open easily, and
+must close quickly. A satisfactory form of valve is that shown by <i>b</i>,
+Fig. 16. The moving part consists of a light glass bulb of<span class='pagenum'><a name="Page_85" id="Page_85">[Pg 85]</a></span> about
+three-eights of an inch diameter and having a glass stem of rather under
+one-eighth diameter and about an inch and a half long. This stem rests
+in a guide at the end of a brass tube, the bulb contacting against the
+other end which is approximately shaped. The bulb and its seating are
+ground air-tight. A very light spring holds the bulb in position.</p>
+
+<p>This valve is fitted into a metal or glass <b>T</b> piece, one limb of which
+leads to the air reservoir and the other limb leads to the blowpipe jet;
+the limb containing the valve leads to the tube through which the air is
+blown in.</p>
+
+<p>A convenient reservoir may be made from a fairly large football bladder.
+A network of string should be fitted over the outside of the bladder and
+the strings should terminate in a hook on which a weight can be hung, in
+order to provide a means of adjusting the pressure at which the air is
+delivered to the jet. This bladder should be washed out and allowed to
+drain after use.</p>
+
+<p>The air tube which passes from the valve to the mouth may conveniently
+be made of brass, but, in order to avoid the continued contact of metal
+with the lips of the operator, it should be<span class='pagenum'><a name="Page_86" id="Page_86">[Pg 86]</a></span> fitted with a non-metallic
+mouthpiece. It is an advantage from the point of view of portability to
+have the air tube easily detachable from the <b>T</b> piece containing the
+valve.</p>
+
+<p>The blowpipe jets, of which there may be several with advantage, may be
+made of glass tubing, bent to the most convenient angle and having an
+enlargement or bulb at some point in the tube. This bulb serves as a
+final condensing place for any traces of moisture that may escape from
+the larger reservoir.</p>
+
+<p>The whole device, blowing tube, reservoir, and <b>T</b> piece may be fastened
+to a clamp, so that it can be secured on the edge of any table where
+blowpipe work is to be carried out. If the blowpipe is to be used with
+gas, the form of burner described under. "A Simple Form of Blowpipe"
+will be found quite satisfactory.</p>
+
+<p><i>The Use of Oil, or Other Non-Gaseous Fuels.</i>&mdash;Although gas, when
+available, is usually preferred on account of its convenience, there are
+several other fuels which give a hotter flame. They have, also, the
+additional advantage of not requiring any connecting pipes; but each has
+its own disadvantage.</p>
+
+<p>One liquid fuel deserves special mention as<span class='pagenum'><a name="Page_87" id="Page_87">[Pg 87]</a></span> being rather less desirable
+than the others; this is alcohol. Although very convenient in use, it
+has the disadvantage of being rather too highly inflammable and capable
+of burning without a wick, thus involving a certain fire risk; the flame
+is scarcely visible in a bright light, and the heat given by either the
+ordinary flame or the blowpipe flame produced from alcohol is
+considerably less than that from a similar flame in which coal gas is
+used. For small work, however, the facility with which a spirit lamp may
+be lighted may more than counterbalance these disadvantages at times.</p>
+
+<p><i>Paraffin Wax.</i>&mdash;Where there is no coal gas available and the blowpipe
+is only required at intervals, and especially where high portability is
+required, there are few fuels so convenient as paraffin wax. This may be
+obtained in pieces of a satisfactory size by cutting paraffin candles,
+from which the wick has been withdrawn, into lengths of about half an
+inch. These cut pieces have the advantage over any oily fuel, such as
+colza oil, that they can be wrapped in paper or carried in a cardboard
+box; further they will keep indefinitely, even<span class='pagenum'><a name="Page_88" id="Page_88">[Pg 88]</a></span> in the presence of air,
+without undergoing any perceptible change.</p>
+
+<p><i>Forms of Lamp for Paraffin Wax.</i>&mdash;Probably, the best form is that
+devised by Thomas Bolas, and described by him in the <i>Journal of the
+Society of Arts</i>, December 2nd, 1898. This lamp consists of a small open
+tray of iron, through which pass three or more flat tubes, and between
+these tubes are placed small flat pieces of wick, the fit being such
+that the pieces of wick may be adjusted easily by means of a pair of
+pointed tweezers.</p>
+
+<p>The flame thus obtained, instead of having one large hollow, is broken
+or divided so that the combustion is concentrated into a smaller area,
+and the air blast, which is directed across the flame, carries the flame
+with it in a more complete manner than is the case with the ordinary
+flame; a more thorough combustion being realised by this arrangement.</p>
+
+<p>Another advantage is the ease with which the wick may be changed and a
+larger or smaller wick inserted to suit the flame to any size of air
+jet.</p>
+
+<p>This form of lamp may be used for oily fuel, although it is specially
+suitable for paraffin wax.<span class='pagenum'><a name="Page_89" id="Page_89">[Pg 89]</a></span></p>
+
+<p>Two small pieces of bent tin-plate may be used as side covers, and these
+serve to adjust the flame within certain limits. A tin-plate cover which
+fits easily over the whole lamp serves as an extinguisher. The complete
+lamp is shown by <i>d</i>, Fig. 16, and this figure shows also a quick-change
+air-jet device, the whole arrangement forming a blowpipe for use where a
+non-gaseous fuel is to be employed.</p>
+
+<p>Although the lamp just described is desirable when complete control over
+the size of the flame is necessary, and if the ideal conditions and
+maximum heat are to be obtained, yet a simpler form of lamp will be
+found to give very good results. Such a lamp may consist of a flat tin
+tray, having a diameter of about three and a half inches and a depth of
+about one inch. In this tray is a tin support for the wick, and the wick
+itself may consist of a bundle of soft cotton, for example, a loosely
+rolled piece of cotton cloth, but in either case the top of the wick
+should be cut to approximately the same angle as that at which the
+blowpipe jet meets the flame.</p>
+
+<p>In using paraffin wax as a fuel, it is necessary to see that sufficient
+wax reaches the<span class='pagenum'><a name="Page_90" id="Page_90">[Pg 90]</a></span> wick to prevent charring during the first few minutes
+before the bulk of the wax is melted.</p>
+
+<p><i>Animal and Vegetable Oils.</i>&mdash;Almost any oil may be used as a fuel, but
+many tend to become hard and gummy if allowed to stand in the air for
+any considerable time. When this happens, the wick becomes clogged and
+it is impossible to obtain a good flame. A number of the oils tend,
+also, to produce rather strongly smelling smoke.</p>
+
+<p><i>A Flame-Guard for Use With Non-Gaseous Fuels.</i>&mdash;In order to avoid the
+eye-strain produced by the luminous base of the flame from a wick
+burning paraffin wax or oil, it is often advantageous to make a small
+tunnel of tin-plate, which can be rested on the sides of the lamp and
+rises over the top of the wick. Such a flame guard is shown by <i>e</i>, Fig.
+16.</p>
+
+<p><i>Small Rods and Tubes from Glass Scrap</i>:&mdash;It is scarcely practicable to
+make small quantities of good glass with the blowpipe flame as the only
+source of heat, but it is less difficult to make small rods or tubes
+from glass scrap, and the ability to do this is sometimes of
+considerable value when a small tube has to be joined on to some special
+piece of apparatus<span class='pagenum'><a name="Page_91" id="Page_91">[Pg 91]</a></span> made of glass of unknown composition. It may be
+possible to obtain some fragments of similar glass, either from a broken
+part of the apparatus or from a similar piece, and from these fragments
+small tubes or rods can be made.</p>
+
+<p>The fragments of glass may be melted together on the end of a clay
+pipe-stem, care being taken to avoid trapping air bubbles as fresh
+fragments are added to the molten mass. When a sufficient quantity of
+glass has been accumulated, the viscous mass may be drawn out into a rod
+by bringing another pipe-stem into contact with the hot mass, rotating
+both pipe-stems steadily, and separating them until a rod of the desired
+size has been obtained.</p>
+
+<p>If, on the other hand, it is desired to produce a tube from the mass of
+heated glass, the mass should be blown hollow before the pipe-stems
+supporting it are separated.</p>
+
+<p><i>Methods of Manufacture.</i>&mdash;When the student has familiarised himself
+with the more common operations and processes used in glass-blowing, he
+will be in a position to increase his skill and knowledge of special
+methods by a critical examination of various examples of commercial
+work. There are few exercises<span class='pagenum'><a name="Page_92" id="Page_92">[Pg 92]</a></span> more valuable than such an examination,
+combined with an attempt to reconstruct the stages and the methods by
+which the article chosen for examination was made.</p>
+
+<p>Obviously, it is impossible to give full details of all constructions in
+a small text-book; but it is easy to give an example of the
+constructional methods employed in the making of almost any piece of
+light blown-glass apparatus, and these methods should prove of special
+value when apparatus of a new pattern has to be evolved for the purposes
+of research. That is to say, one designs the apparatus required, applies
+known methods of construction as far as possible, and, by the
+examination of commercial apparatus having similar features, evolves the
+new methods required. For an exercise in such a process of
+reconstruction we may well take an ordinary commercial vacuum tube, such
+as that shown by <i>a</i>, Fig. 17.</p>
+
+<div class="figcenter" style="width: 537px;">
+<img src="images/fig17.jpg" width="537" height="550" alt="Fig. 17" title="" />
+<span class="caption">Fig. 17</span>
+</div>
+
+<p>In the tube from which this drawing was made, it was found that the
+spiral in the middle bulb was of a slightly yellowish colour and gave a
+green fluorescence when the electric discharge was passed through the
+tube; that<span class='pagenum'><a name="Page_93" id="Page_93">[Pg 93]</a></span> is to say, the spiral is made of uranium-glass, which is
+usually a soda-glass containing trace of uranium, and hence differing
+slightly in composition from the ordinary glasses. The two enclosed
+tubes which are bent into a series of <b>S</b> bends gave a pink fluorescence,
+which indicates lead-glass; and the remainder of the tube fluoresced
+with an apple-green colour;<span class='pagenum'><a name="Page_94" id="Page_94">[Pg 94]</a></span> this suggests ordinary soda-glass. We have,
+therefore, a piece of apparatus in which three dissimilar glasses are
+joined, while, at the same time, that apparatus contains a number of
+internal seals, and it is not probable that the dissimilar glasses will
+have their coefficients of expansion so nearly alike as to permit of a
+stable internal seal being made if one part of the seal consists of a
+glass differing from that of the other part.</p>
+
+<p>These considerations lead us to a closer examination of the joins where
+the dissimilar glasses are introduced, and we find that in no case is
+the internal seal made between dissimilar glasses, but that a soda-glass
+extension is joined on to both the uranium-glass tube and the lead-glass
+tubes at a point about half an inch before the internal seal commences.
+Careful examination of these joins shows that the change from one glass
+to another is not abrupt but gradual. Such a transitional joint may be
+made by taking a length of soda-glass tubing, sealing the end and fusing
+a minute bead of the other glass on to the sealed end, the end is then
+expanded and another bead of the other glass added, this bead is
+expanded<span class='pagenum'><a name="Page_95" id="Page_95">[Pg 95]</a></span> and the operation is repeated, thus building up a tube, and,
+finally, the tube of the other glass is joined on to the end of this.</p>
+
+<p>We are now concerned with the question of the insertion of the
+uranium-glass spiral into the bulb (see p. 38). Obviously the spiral is
+too large to pass through the necks of the bulb, and it is difficult to
+imagine that the spiral was obtained by the insertion of a length of
+straight tubing which was bent after entering the bulb; therefore, the
+only remaining method is that the spiral was made first and the
+soda-glass extensions fastened on, and that the bulb was blown, cut in
+halves and the spiral inserted, and the two halves were then rejoined.
+That this was actually the case is confirmed by traces of a join which
+are just visible round the middle of the bulb. The insertion of the
+spiral and the making of the first internal seal are shown by <i>b</i>, and
+<i>c</i>.</p>
+
+<p>There is one detail in making the second join of the spiral to the bulb
+which calls for attention, and the small branch, similar to an
+exhaustion branch, at the side of the bulb provides a clue to this. If
+an attempt were made to complete the second internal seal<span class='pagenum'><a name="Page_96" id="Page_96">[Pg 96]</a></span> through a
+closed bulb it would be impossible to obtain a good result, as the
+air-pressure in the bulb would not be under control when once union was
+effected, and further heating of the air in the bulb would cause
+expansion and perforate the wall near the second internal seal; we
+therefore make a small branch which can be left open and through which
+such air-pressure as may be found necessary can be maintained.</p>
+
+<p>The third join, by which the lead-glass tube is joined to the soda-glass
+is made in stages similar to those in which the soda-glass and
+uranium-glass were joined; but the internal seal is most conveniently
+made by sliding a length of tubing over the lead-glass and fusing this
+tubing to the large diameter soda-glass tube to which the lead-glass is
+already joined. The first stage of this operation is illustrated by <i>d</i>.
+When this seal is completed, the end of the soda-glass tube is drawn off
+and sealed as shown in <i>e</i>, and at this stage a side tube or branch is
+joined on. The sealed end of the outer and large diameter soda-glass
+tube is heated until it contracts and fuses to the enlargement that has
+previously been joined to<span class='pagenum'><a name="Page_97" id="Page_97">[Pg 97]</a></span> the lead-glass tube, and the end is burst out
+as shown in <i>f</i>. Another length of soda-glass is then joined on to the
+burst-out end, and this length of soda-glass tubing is drawn out to a
+thin-walled contraction; the non-contracted part is expanded to form the
+bulb, and a small exhaustion branch made on the side, the drawn-out
+portion being cut off, and an electrode, previously prepared by coating
+a part of its length with a suitable enamel, is introduced. The tube is
+tilted to keep the electrode away from the drawn-out end, which is
+melted off and sealed. A small perforation is made with a hot platinum
+or iron wire in the sealed end, the electrode is shaken into position,
+and the sealing is completed as explained on page 42.</p>
+
+<p>The remainder of the tube, that is to say the lead-glass tube and the
+bulb on the other side of the middle bulb, is completed in a similar
+manner.</p>
+
+
+<h3><span class="smcap">Summary of Conditions Necessary for Success in Glass-Blowing.</span></h3>
+
+<p>For the convenience of the student, it may be well to summarise the
+chief essentials for<span class='pagenum'><a name="Page_98" id="Page_98">[Pg 98]</a></span> success in glass-blowing, and at the same time to
+add such brief notes on the various methods as may seem desirable.</p>
+
+<p><i>Adjustment of Blowpipe.</i>&mdash;The air jet should be clean internally, and
+so centered as to give a flame having a well-defined blue portion, the
+tip of the flame should not be only slightly luminous but purple in
+colour. In the case of a blowpipe burning oil or wax fuel the flame may
+be a trifle more ragged without disadvantage.</p>
+
+<p><i>Bellows and Blowing.</i>&mdash;The bellows should be adjusted to deliver air at
+constant pressure, either by insertion of a tap or, better, by attention
+to the wind reservoir if necessary. The movement of the foot in blowing
+should be steady, not jerky.</p>
+
+<p><i>Heating Glass.</i>&mdash;The tube or rod should be heated cautiously until it
+has reached its softening point in its thickest part. Steady rotation of
+the glass during the heating is almost essential.</p>
+
+<p><i>Blowing a Bulb or Expanding a Join.</i>&mdash;Prolonged heating is necessary in
+order that the thick parts may be heated completely through. Blowing
+should take place by stages, in order<span class='pagenum'><a name="Page_99" id="Page_99">[Pg 99]</a></span> that the thin parts, which tend
+to expand first, have time to cool. The thick parts can then be expanded
+by further blowing and thus a bulb or expansion of even thickness can be
+obtained.</p>
+
+<p><i>Cutting Glass.</i>&mdash;The most useful method for general use is by means of
+the file or glass-blowers' knife. Either file or knife must be kept
+sharp by grinding. Neither file nor knife should be used on hot glass.
+The diamond and wheel cutter are useful for cutting sheet-glass, and
+when the diamond is employed a singing noise is an indication of a
+satisfactory cut.</p>
+
+<p><i>Leading a Crack.</i>&mdash;A crack may be led in any desired direction by means
+of a bead of hot glass or a small gas flame. The glass which it is
+desired to crack should be heated at a point slightly in advance of the
+crack, which will extend in the direction of the source of the heat.</p>
+
+<p><i>Turning Out the End of a Tube.</i>&mdash;This is done by heating the end of the
+tube and rotating it against an iron rod. The rod must be kept polished
+and free from rust, and it must not be allowed to become too hot while
+in use, otherwise the glass will stick to it.<span class='pagenum'><a name="Page_100" id="Page_100">[Pg 100]</a></span></p>
+
+<p><i>Joining Unlike Glasses.</i>&mdash;Joints between unlike glasses are often
+unstable. When such joints are made it is desirable to blow them as thin
+as possible, and to avoid the junction of unlike glasses in any complex
+joint, such as an internal seal. A transitional portion of tubing may be
+built up by the successive addition and interfusion of beads of one of
+the glasses to the end of a sealed tube consisting of the other glass.</p>
+
+<p><i>Joining a Tube to a Very Thin Bulb.</i>&mdash;The bulb may be thickened at the
+point of union by fusing on a bead of glass and expanding this slightly.
+A small central portion of the expanded part may then be perforated by
+bursting and the tube joined on.</p>
+
+<p><i>Insertion of One Bulb Within Another.</i>&mdash;A bulb may be divided into two
+halves by leading a crack round it and the inner bulb is then
+introduced. The two halves of the outer bulb may be fitted together
+(care being taken to avoid any damage to the edges), and the bulb may be
+completed by rotating the contacting edges before the blowpipe until
+they are soft, and then expanding slightly by means of air-pressure.<span class='pagenum'><a name="Page_101" id="Page_101">[Pg 101]</a></span></p>
+
+<p><i>Annealing.</i>&mdash;For most purposes, in the case of thin, blowpipe-made or
+lamp-blown glass apparatus, it is sufficient to cool slowly by rotating
+the finished article over a smoky flame and setting it aside in a place
+free from draughts, and where the hot glass will not come in contact
+with anything.</p>
+
+<p>Simple bulbs and joints do not even need this smoking; but thick
+articles, and especially those that are to be subjected to the stress of
+grinding, need more prolonged annealing in a special oven.</p>
+
+<p><i>Use of Lead-Glass.</i>&mdash;When lead-glass is to be used, the blowpipe flame
+should be in good adjustment and the glass should not be allowed to
+approach so near to the blue cone as to be blackened. Slight blackening
+may often be removed by heating the glass in the extreme end of the
+flame.</p>
+
+<p>Lead-glass articles tend to be rather more stable than similar articles
+of soda-glass.</p>
+
+<p><i>Combustion-Glass.</i>&mdash;This may be worked more easily if a small
+percentage of oxygen is introduced into the air with which the blowpipe
+flame is produced. If the air is replaced entirely by oxygen there is a
+risk of damaging<span class='pagenum'><a name="Page_102" id="Page_102">[Pg 102]</a></span> the blowpipe jet, unless a special blowpipe is
+employed.</p>
+
+<p><i>Internal Seal.</i>&mdash;There are two ways of making these, one, in which the
+inner portion of the tube is fused on to the inside of the bulb or tube
+through which it is to pass, an opening is made by bursting and the
+outer tube is joined on. This is a quick and in some ways more
+satisfactory method than the other, in which there is no separate inner
+piece.</p>
+
+<p><i>Rubber Blowing Tube.</i>&mdash;In complicated work it is often convenient to
+use a thin rubber blowing-tube which is connected with the work either
+by a cork and piece of glass tubing or by fitting over a drawn-out end.
+The use of such a blowing-tube avoids the inconvenience of raising the
+work to the mouth when internal air-pressure is required. One end of the
+rubber tube is retained in the mouth during work.</p>
+
+<p><i>General Notes.</i>&mdash;A large amount of glass-blowing is spoiled through
+carelessness in arranging the work beforehand. The student should have
+every detail of his manipulation clearly in mind before he commences the
+work;<span class='pagenum'><a name="Page_103" id="Page_103">[Pg 103]</a></span> he should not trust to evolving the method during the actual
+manipulation.</p>
+
+<p>Undue haste is another fruitful source of failure. Practically every
+operation in glass-blowing can be carried out in a perfectly leisurely
+manner, and it is better to err rather on the side of deliberation than
+on the side of haste.</p>
+
+<p>If, as will doubtless happen at times, a piece of work gives trouble and
+it is necessary to pause and consider the whole question, or if for any
+other reason it is necessary to stop during the construction of a
+partially finished join or other operation, great care should be taken
+not to allow the work to cool. A large, brush-like flame may be produced
+by increasing the amount of gas admitted to the blowpipe, and the work
+should be held just in front of the current of hot air produced by such
+a flame.</p>
+
+<p>It will then be possible to continue work on this without causing it to
+crack when further heat is applied.</p>
+
+<p>As time goes on, the student will find an increasing confidence in his
+ability to manipulate the soft glass, and with increasing<span class='pagenum'><a name="Page_104" id="Page_104">[Pg 104]</a></span> confidence
+will come rapidly increasing power of manipulation. Perhaps the greatest
+obstacle to success in glass-blowing is undue haste in manipulation.</p>
+
+
+
+<hr style="width: 65%;" /><p><span class='pagenum'><a name="Page_105" id="Page_105">[Pg 105]</a></span></p>
+<h2>INDEX</h2>
+
+
+<p>
+Absorption bulbs, <a href='#Page_21'>21</a>, <a href='#Page_23'>23</a>.<br />
+<br />
+Airtube, flexible, <a href='#Page_8'>8</a>, <a href='#Page_102'>102</a>.<br />
+<br />
+Alarm thermometer, <a href='#Page_45'>45</a>.<br />
+<br />
+Annealing, <a href='#Page_7'>7</a>, <a href='#Page_60'>60</a>.<br />
+<br />
+<br />
+Bellows, adjusting pressure of, <a href='#Page_5'>5</a>, <a href='#Page_6'>6</a>.<br />
+<br />
+Bellows, foot, <a href='#Page_5'>5</a>, <a href='#Page_6'>6</a>.<br />
+<br />
+Bending tubes, <a href='#Page_23'>23</a>.<br />
+<br />
+Blackening, <a href='#Page_58'>58</a>, <a href='#Page_101'>101</a>.<br />
+<br />
+Branching, <a href='#Page_18'>18</a>, <a href='#Page_19'>19</a>.<br />
+<br />
+Brushes of spun glass, <a href='#Page_53'>53</a>.<br />
+<br />
+Blowpipe flame, quality of, <a href='#Page_3'>3</a>.<br />
+<br />
+Blowpipe for mouth blast, <a href='#Page_80'>80</a>, <a href='#Page_82'>82</a>, <a href='#Page_84'>84</a>.<br />
+<br />
+Blowpipe, for paraffin wax, <a href='#Page_82'>82</a>, <a href='#Page_88'>88</a>.<br />
+<br />
+Blowpipe, Herepath's, <a href='#Page_2'>2</a>.<br />
+<br />
+Blowpipe jet, centring, <a href='#Page_3'>3</a>, <a href='#Page_98'>98</a>.<br />
+<br />
+Blowpipe jet, dirt in, <a href='#Page_3'>3</a>.<br />
+<br />
+Blowpipe jet, multiple, <a href='#Page_4'>4</a>, <a href='#Page_40'>40</a>.<br />
+<br />
+Blowpipe, Letcher's, change, <a href='#Page_4'>4</a>.<br />
+<br />
+Blowpipe, simple form of, <a href='#Page_80'>80</a>.<br />
+<br />
+Bulb, medially on tube, <a href='#Page_22'>22</a>.<br />
+<br />
+Bulbs, <a href='#Page_19'>19</a>, <a href='#Page_20'>20</a>, <a href='#Page_22'>22</a>, <a href='#Page_38'>38</a>, <a href='#Page_98'>98</a>.<br />
+<br />
+Bulbs, absorption, (Liebig's), <a href='#Page_21'>21</a>, <a href='#Page_23'>23</a>.<br />
+<br />
+Bulbs, dividing, <a href='#Page_39'>39</a>, <a href='#Page_95'>95</a>.<br />
+<br />
+Bulbs from rod, <a href='#Page_25'>25</a>.<br />
+<br />
+Bulbs, internal, <a href='#Page_38'>38</a>.<br />
+<br />
+Bulbs, thick, <a href='#Page_21'>21</a>.<br />
+<br />
+<br />
+Cages, from glass rod, <a href='#Page_24'>24</a>, <a href='#Page_25'>25</a>, <a href='#Page_27'>27</a>.<br />
+<br />
+Calibration, <a href='#Page_72'>72</a>.<br />
+<br />
+Carius tubes, <a href='#Page_16'>16</a>.<br />
+<br />
+Condenser, Liebig's, <a href='#Page_37'>37</a>.<br />
+<br />
+Condensers, various, <a href='#Page_37'>37</a>, <a href='#Page_38'>38</a>.<br />
+<br />
+Cone, carbon, <a href='#Page_8'>8</a>.<br />
+<br />
+Crack, leading, <a href='#Page_30'>30</a>, <a href='#Page_99'>99</a>.<br />
+<br />
+Cracking, subversive, <a href='#Page_103'>103</a>.<br />
+<br />
+Cutting glass with diamond, <a href='#Page_30'>30</a>.<br />
+<br />
+Cutting tubes, <a href='#Page_11'>11</a>, <a href='#Page_99'>99</a>.<br />
+<br />
+<br />
+Diamond (glazier's), use of, <a href='#Page_30'>30</a>.<br />
+<br />
+Dissimilar glass, joining of, <a href='#Page_22'>22</a>, <a href='#Page_94'>94</a>.<br />
+<br />
+Drilling, <a href='#Page_61'>61</a>.<br />
+<br />
+<br />
+Electrodes, sealing in, <a href='#Page_42'>42</a>, <a href='#Page_97'>97</a>.<br />
+<br />
+Etching glass, <a href='#Page_70'>70</a>.<br />
+<br />
+Extemporised appliances, <a href='#Page_80'>80</a>.<br />
+<br />
+Examination of apparatus, <a href='#Page_93'>93</a>.<br />
+<br />
+<br />
+Failure, Haste chief Source of, <a href='#Page_103'>103</a>.<br />
+<br />
+Failures, Notes as to, <a href='#Page_97'>97</a>.<br />
+<br />
+File, with oblique ground edge, <a href='#Page_7'>7</a>.<br />
+<br />
+Filing glass, <a href='#Page_63'>63</a>.<br />
+<br />
+Filter pumps, <a href='#Page_35'>35</a><br />
+<br />
+Foot, <a href='#Page_25'>25</a><br />
+<br />
+Fuels various, <a href='#Page_82'>82</a>, <a href='#Page_86'>86</a>, <a href='#Page_87'>87</a>, <a href='#Page_89'>89</a>.<br />
+<br />
+Funnel, thistle, <a href='#Page_23'>23</a>.<br />
+<br />
+<br />
+General principles and precautions, <a href='#Page_1'>1</a>, <a href='#Page_97'>97</a><br />
+<br />
+Glass, varieties of, <a href='#Page_9'>9</a>, <a href='#Page_55'>55</a>, <a href='#Page_91'>91</a>-97.<br />
+<br />
+Graduation, <a href='#Page_72'>72</a>-76<br />
+<br />
+<br />
+Haste, Source of Failure, <a href='#Page_103'>103</a><br />
+<br />
+Heat reflector, asbestos, <a href='#Page_7'>7</a>.<br />
+<br />
+Heating, intensive, <a href='#Page_7'>7</a>, <a href='#Page_57'>57</a>.<br />
+<br />
+Heating precautions, <a href='#Page_12'>12</a>, <a href='#Page_98'>98</a><br />
+<br />
+<br />
+<span class='pagenum'><a name="Page_106" id="Page_106">[Pg 106]</a></span>Joining dissimilar glass, <a href='#Page_22'>22</a>.<br />
+<br />
+Joining glass to metal, <a href='#Page_76'>76</a>.<br />
+<br />
+Joining tubes, <a href='#Page_16'>16</a>, <a href='#Page_94'>94</a>, <a href='#Page_100'>100</a>.<br />
+<br />
+<br />
+Knife, Glass blower's, <a href='#Page_7'>7</a>, <a href='#Page_99'>99</a>.<br />
+<br />
+<br />
+Lenses, grinding, <a href='#Page_63'>63</a>.<br />
+<br />
+<br />
+Marking glass, <a href='#Page_69'>69</a>.<br />
+<br />
+Methods, analytic study of, <a href='#Page_91'>91</a>, <a href='#Page_93'>93</a>.<br />
+<br />
+<br />
+Oxygen for intensive heating, <a href='#Page_57'>57</a>, <a href='#Page_101'>101</a>.<br />
+<br />
+<br />
+Precautions and General Principles, <a href='#Page_1'>1</a>, <a href='#Page_97'>97</a>.<br />
+<br />
+Pumps, Filter, <a href='#Page_35'>35</a>.<br />
+<br />
+Pumps, Sprengel, <a href='#Page_49'>49</a>, <a href='#Page_50'>50</a>.<br />
+<br />
+<br />
+Re-entering branch, <a href='#Page_40'>40</a>.<br />
+<br />
+Reflector of heat, asbestos, <a href='#Page_7'>7</a>.<br />
+<br />
+Rod, uses and articles from, <a href='#Page_17'>17</a>, <a href='#Page_25'>25</a>, <a href='#Page_27'>27</a>, <a href='#Page_28'>28</a>.<br />
+<br />
+Rod, blowing to hollow, <a href='#Page_17'>17</a>, <a href='#Page_25'>25</a>, <a href='#Page_26'>26</a>, <a href='#Page_91'>91</a>.<br />
+<br />
+<br />
+Scrap glass, working, <a href='#Page_90'>90</a>.<br />
+<br />
+Sealing tubes, <a href='#Page_12'>12</a>, <a href='#Page_13'>13</a>, <a href='#Page_14'>14</a>.<br />
+<br />
+Sealed tubes for pressure, <a href='#Page_15'>15</a>, <a href='#Page_16'>16</a>.<br />
+<br />
+Sealing in of Electrodes, <a href='#Page_42'>42</a>, <a href='#Page_97'>97</a>.<br />
+<br />
+Seals, internal (airtraps), <a href='#Page_32'>32</a>, <a href='#Page_102'>102</a>.<br />
+<br />
+Silvering glass, <a href='#Page_77'>77</a>.<br />
+<br />
+Soldering glass, <a href='#Page_76'>76</a>.<br />
+<br />
+Soxhlet-tube, <a href='#Page_40'>40</a>.<br />
+<br />
+Spirals, <a href='#Page_23'>23</a>, <a href='#Page_95'>95</a>.<br />
+<br />
+Spray arrester, <a href='#Page_34'>34</a>.<br />
+<br />
+Spray producers, <a href='#Page_36'>36</a>.<br />
+<br />
+Sprengel pumps, <a href='#Page_49'>49</a>, <a href='#Page_50'>50</a>.<br />
+<br />
+Spinning glass, <a href='#Page_51'>51</a>.<br />
+<br />
+Stopcocks, <a href='#Page_60'>60</a>, <a href='#Page_66'>66</a>.<br />
+<br />
+Stoppering, <a href='#Page_63'>63</a>.<br />
+<br />
+Stirrers, <a href='#Page_28'>28</a>, <a href='#Page_29'>29</a>.<br />
+<br />
+Summary as to precautions and failures, <a href='#Page_97'>97</a>.<br />
+<br />
+<br />
+Taps, <a href='#Page_60'>60</a>, <a href='#Page_66'>66</a>.<br />
+<br />
+Thermometers, Various, <a href='#Page_44'>44</a>-49.<br />
+<br />
+Thermo-regulator, <a href='#Page_24'>24</a>.<br />
+<br />
+Thistle Funnel, <a href='#Page_23'>23</a>.<br />
+<br />
+Tools, Various small, <a href='#Page_7'>7</a>.<br />
+<br />
+Turn-pins, <a href='#Page_7'>7</a>, <a href='#Page_8'>8</a>, <a href='#Page_99'>99</a>.<br />
+<br />
+Turning out open ends, <a href='#Page_14'>14</a>, <a href='#Page_99'>99</a>.<br />
+</p>
+
+
+<p class="center"><span class='pagenum'><a name="Page_107" id="Page_107">[Pg 107]</a></span>
+<span class="smcap">Printed in Great Britain by<br />
+W. Jolly &amp; Sons, Ltd., Printers, Aberdeen.</span>
+</p>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of A Handbook of Laboratory Glass-Blowing, by 
+Bernard D. Bolas
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+</body>
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+The Project Gutenberg EBook of A Handbook of Laboratory Glass-Blowing, by
+Bernard D. Bolas
+
+This eBook is for the use of anyone anywhere 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
+
+
+Title: A Handbook of Laboratory Glass-Blowing
+
+Author: Bernard D. Bolas
+
+Illustrator: Naomi Bolas
+
+Release Date: June 24, 2010 [EBook #32962]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK HANDBOOK--LABORATORY GLASS-BLOWING ***
+
+
+
+
+Produced by 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.)
+
+
+
+
+
+
+
+A HANDBOOK OF LABORATORY GLASS-BLOWING
+
+
+      _To my Friends
+        Eric Reid
+            and
+      Sidney Wilkinson_
+
+
+
+
+A Handbook of Laboratory Glass-Blowing
+
+BY
+
+BERNARD D. BOLAS
+
+WITH NUMEROUS DIAGRAMS IN THE TEXT
+
+BY NAOMI BOLAS
+
+[Illustration]
+
+LONDON
+GEORGE ROUTLEDGE & SONS, LTD
+NEW YORK: E. P. DUTTON & CO.
+1921
+
+
+
+
+CONTENTS
+
+
+    CHAP.                                                           PAGE
+
+    I. Introduction and Preliminary Remarks--General Principles
+    to be observed in Glass Working--Choice of Apparatus--Tools
+    and Appliances--Glass                                              1
+
+    II. Easy Examples of Laboratory Glass-Blowing--Cutting and
+    Sealing Tubes, Tubes for High Temperature
+    Experiments--Thermometer-Bulbs, Bulbs of Special Glass,
+    Pipettes, Absorption-Bulbs or Washing Bulbs--Joining Tubes,
+    Branches, Exhaustion-Branches, Branches of Dissimilar Glass,
+    Blowing Bulbs, A Thistle Funnel, Cracking and Breaking Glass,
+    Leading and Direction of Cracks--Use of Glass Rod or Strips
+    of Window-Glass, Joining Rod, Feet and Supports--Gripping
+    Devices for use in Corrosive Solutions--The Building up of
+    Special Forms from Solid Glass                                    10
+
+    III. Internal Seals, Air-Traps, Spray Arresters,
+    Filter-Pumps--Sprays, Condensers; plain, double surface, and
+    spherical--Soxhlet Tubes and Fat Extraction Apparatus--Vacuum
+    Tubes, Electrode Work, Enclosed Thermometers, Alarm
+    Thermometers ... Recording Thermometers, "Spinning" Glass 32
+
+    IV. Glass, its Composition and
+    Characteristics--Annealing--Drilling, Grinding, and Shaping
+    Glass by methods other than Fusion--Stopcocks--Marking
+    Glass--Calibration and Graduation of
+    Apparatus--Thermometers--Exhaustion of Apparatus--Joining
+    Glass and Metal--Silvering Glass                                  55
+
+    V. Extemporised Glass-Blowing Apparatus--The use of Oil or
+    other Fuels--Making Small Rods and Tubes from Glass
+    Scraps--The Examination of Manufactured Apparatus with a view
+    to Discovering the Methods used in Manufacture--Summary of
+    Conditions necessary for Successful Glass-Blowing                  80
+
+    Index                                                             105
+
+
+
+
+
+PREFACE
+
+
+To cover the whole field of glass-blowing in a small handbook would be
+impossible. To attempt even a complete outline of the methods used in
+making commercial apparatus would involve more than could be undertaken
+without omitting the essential details of manipulation that a novice
+needs. I have, therefore, confined myself as far as possible to such
+work as will find practical application in the laboratory and will, I
+hope, prove of value to those whose interests lie therein.
+
+The method of treatment and somewhat disjointed style of writing have
+been chosen solely with the view to economy of space without the undue
+sacrifice of clearness.
+
+                                              BERNARD D. BOLAS.
+
+
+
+
+Handbook of Laboratory Glass-Blowing
+
+
+
+
+CHAPTER I
+
+     Introduction and Preliminary Remarks--General Principles to
+     be observed in Glass Working--Choice of Apparatus--Tools and
+     Appliances--Glass.
+
+
+Glass-blowing is neither very easy nor very difficult; there are
+operations so easy that the youngest laboratory boy should be able to
+repeat them successfully after once having been shown the way, there are
+operations so difficult that years are needed to train eye and hand and
+judgment to carry them out; but the greater number of scientific needs
+lie between these two extremes. Yet a surprisingly large number of
+scientific workers fail even to join a glass tube or make a T piece that
+will not crack spontaneously, and the fault is rather one of
+understanding than of lack of ability to carry out the necessary
+manipulation.
+
+In following the scheme of instruction adopted in this handbook, it will
+be well for the student to pay particular attention to the reason given
+for each detail of the desirable procedure, and, as far as may be, to
+memorise it. Once having mastered the underlying reason, he can evolve
+schemes of manipulation to suit his own particular needs, although, as a
+rule, those given in the following pages will be found to embody the
+result of many years' experience.
+
+There is a wide choice of apparatus, from a simple mouth-blowpipe and a
+candle flame to a power-driven blower and a multiple-jet heating device.
+All are useful, and all have their special applications, but, for the
+present, we will consider the ordinary types of bellows and blowpipes,
+such as one usually finds in a chemical or physical laboratory.
+
+The usual, or Herepath, type of gas blowpipe consists of an outer tube
+through which coal gas can be passed and an inner tube through which a
+stream of air may be blown. Such a blowpipe is shown in section by Fig.
+1. It is desirable to have the three centring screws as shown, in order
+to adjust the position of the air jet and obtain a well-shaped flame,
+but these screws are sometimes omitted. Fig. 1, _a_ and _b_ show the
+effects of defective centring of the air jet, _c_ shows the effect of
+dirt or roughness in the inside of the air jet, _d_ shows a satisfactory
+flame.
+
+[Illustration: Fig 1]
+
+For many purposes, it is an advantage to have what is sometimes known
+as a "quick-change" blowpipe; that is one in which jets of varying size
+may be brought into position without stopping the work for more than a
+fraction of a second. Such a device is made by Messrs. Letcher, and is
+shown by _e_, and in section by _f_ Fig. 1. It is only necessary to
+rotate the desired jet into position in order to connect it with both
+gas and air supplies. A small bye-pass ignites the gas, and adjustment
+of gas and air may be made by a partial rotation of the cylinder which
+carries the jets.
+
+For specially heavy work, where it is needed to heat a large mass of
+glass, a multiple blowpipe jet of the pattern invented by my father,
+Thomas Bolas, as the result of a suggestion derived from a study of the
+jet used in Griffin's gas furnace, is of considerable value. This jet
+consists of a block of metal in which are drilled seven holes, one being
+central and the other six arranged in a close circle around the central
+hole. To each of these holes is a communication way leading to the gas
+supply, and an air jet is arranged centrally in each. Each hole has also
+an extension tube fitted into it, the whole effect being that of seven
+blowpipes. In order to provide a final adjustment for the flame, a
+perforated plate having seven holes which correspond in size and
+position to the outer tubes is arranged to slide on parallel guides in
+front of these outer tubes.
+
+[Illustration: Fig. 2]
+
+The next piece of apparatus for consideration is the bellows, of which
+there are three or more types on the market, although all consist of two
+essential parts, the blower or bellows proper and the wind chamber or
+reservoir. Two patterns are shown in Fig. 2; _a_, is the form which is
+commonly used by jewellers and metal workers to supply the air blast
+necessary for heating small furnaces. Such a bellows may be obtained at
+almost any jewellers' supply dealer in Clerkenwell, but it not
+infrequently happens that the spring in the wind chamber is too strong
+for glass-blowing, and hence the air supply tends to vary in pressure.
+This can be improved by fitting a weaker spring, but an easier way and
+one that usually gives fairly satisfactory results, is to place an
+ordinary screw-clip on the rubber tube leading from the bellows to the
+blowpipe, and to tighten this until an even blast is obtained.
+
+Another form of bellows, made by Messrs. Fletcher and Co., and common in
+most laboratories, is shown by _b_; the wind chamber consists of a disc
+of india-rubber clamped under a circular frame or tied on to a circular
+rim. This form is shown by Fig. 2, _b_.
+
+The third form, and one which my own experience has caused me to prefer
+to any other, is cylindrical, and stands inside the pedestal of the
+blowpipe-table. A blowpipe-table of this description is made by Enfer of
+Paris.
+
+There is no need, however, to purchase an expensive table for laboratory
+use. All the work described in this book can quite well be done with a
+simple foot bellows and a quick-change blowpipe. Nearly all of it can be
+done with a single jet blowpipe, such as that described first, or even
+with the still simpler apparatus mentioned on page 84, but I do not
+advise the beginner to practise with quite so simple a form at first,
+and for that reason have postponed a description of it until the last
+chapter.
+
+Glass-blowers' tools and appliances are many and various, quite a number
+of them are better rejected than used, but there are a few essentials.
+These are,--file, glass-knife, small turn-pin, large turn-pin, carbon
+cones, carbon plate, rubber tube of small diameter, various sizes of
+corks, and an asbestos heat reflector. For ordinary work, an annealing
+oven is not necessary, but one is described on page 60 in connection
+with the special cases where annealing is desirable.
+
+Fig. 3 illustrates the tools and appliances. _a_ is an end view of the
+desirable form of file, and shows the best method of grinding the edges
+in order to obtain a highly satisfactory tool. _b_ is a glass knife,
+shown both in perspective and end view, it is made of glass-hard steel
+and should be sharpened on a rough stone, such as a scythe-stone, in
+order to give a slightly irregular edge. _c_ is a small turn-pin which
+may be made by flattening and filing the end of a six-inch nail. _d_ is
+the large turn-pin and consists of a polished iron spike, about five
+inches long and a quarter of an inch diameter at its largest part. This
+should be mounted in a wooden handle. _e_ and _f_ are carbon cones. A
+thin rubber tube is also useful; it may be attached to the work and
+serve as a blowing tube, thus obviating the necessity of moving the work
+to the mouth when internal air pressure is to be applied. In order to
+avoid undue repetition, the uses of these tools and appliances will be
+described as they occur.
+
+[Illustration: Fig. 3]
+
+Glass, as usually supplied by chemical apparatus dealers is of the
+composition known as "soda-glass." They also supply "hard" or
+"combustion" glass, but this is only used for special purposes, as it is
+too infusible for convenient working in the ordinary blowpipe flame.
+
+Soda-glass consists primarily of silicate of sodium with smaller
+quantities of silicate of aluminum and potassium. Its exact composition
+varies. It is not blackened, as lead glass is, by exposure to the
+reducing gases which are present in the blue cone of a blowpipe flame,
+and hence is easier for a beginner to work without producing
+discolouration.
+
+Further notes on glasses will be found on page 55, but for ordinary
+purposes soda-glass will probably be used.
+
+
+
+
+CHAPTER II
+
+     Easy Examples of Laboratory Glass-Blowing--Cutting and
+     Sealing Tubes for Various Purposes; Test-Tubes,
+     Pressure-Tubes, Tubes for High Temperature
+     Experiments--Thermometer-Bulbs, Bulbs of Special Glass,
+     Pipettes, Absorption-Bulbs or Washing-Bulbs--Joining Tubes;
+     Branches, Exhaustion-Branches, Branches of Dissimilar
+     Glass--Blowing Bulbs; A Thistle Funnel; Cracking and
+     Breaking Glass; Leading and Direction of Cracks--Use of
+     Glass Rod or Strips of Window-Glass; Joining Rod, Feet and
+     Supports--Gripping Devices for use in Corrosive
+     Solutions--The Building Up of Special Forms from Solid
+     Glass.
+
+
+Perhaps the most common need of the glass-blower whose work is connected
+with that of the laboratory is for a sealed tube; and the sealing of a
+tube is an excellent preliminary exercise in glass-blowing.
+
+We will assume that the student has adjusted the blowpipe to give a
+flame similar to that shown in _d_, Fig. 1, and that he has learned to
+maintain a steady blast of air with the bellows; further, we will assume
+that the tube he wishes to seal is of moderate size, say not more than
+half an inch in diameter and with walls of from one-tenth to one-fifth
+of an inch thick.
+
+[Illustration: Fig. 4]
+
+A convenient length of tube for the first trial is about one foot; this
+should be cut off from the longer piece, in which it is usually
+supplied, as follows:--lay the tube on a flat surface and make a deep
+cut with the edge of a file. Do not "saw" the file to and fro over the
+glass. If the file edge has been ground as shown in _a_, Fig. 3, such a
+procedure will be quite unnecessary and only involve undue wear; one
+movement with sufficient pressure to make the file "bite" will give a
+deep cut. Now rotate the tube through about one-eighth of a turn and
+make another cut in continuation of the first. Take the tube in the
+hands, as shown in _a_, Fig. 4, and apply pressure with the thumbs, at
+the same time straining at the ends. The tube should break easily. If it
+does not, do not strain too hard, as it may shatter and cause serious
+injuries to the hands, but repeat the operation with the file and so
+deepen the original cuts. In holding a tube for breaking, it is
+important to place the hands as shown in sketch, as this method is least
+likely to cause shattering and also minimises the risk of injury even if
+the tube should shatter. To cut a large tube, or one having very thick
+walls, it is better to avoid straining altogether and to break by
+applying a small bead of intensely heated glass to the file cut. If the
+walls are very thin, a glass-blower's knife should be used instead of a
+file. The tube and glass-blower's knife should be held in the hand, and
+the tube rotated against the edge of the knife; this will not produce a
+deep cut, but is less likely to break the tube. A bead of hot glass
+should be used to complete the work.
+
+The next operation is to heat the glass tube in the middle; this must be
+done gradually and evenly; that is to say the tube must be rotated
+during heating and held some considerable distance in front of the flame
+at first; otherwise the outer surface of the glass will expand before
+the interior is affected and the tube will break. From two to five
+minutes, heating at a distance of about eight inches in front of the
+flame will be found sufficient in most cases, and another minute should
+be taken in bringing the tube into the flame. Gradual heating is
+important, but even heating is still more important and this can only be
+obtained by uniform and steady rotation. Until the student can rotate a
+tube steadily _without thinking about it_, real progress in
+glass-blowing is impossible.
+
+When the tube is in the flame it must be held just in front of the blue
+cone and rotated until the glass is soft enough to permit the ends to be
+drawn apart. Continue to separate the ends and, at the same time, move
+the tube very slightly along its own axis, so that the flame tends to
+play a little more on the thicker part than on the drawn-out portion. If
+this is done carefully, the drawn-out portion can be separated off,
+leaving only a slight "bleb" on the portion it is desired to seal. This
+is illustrated by _b_, Fig. 4.
+
+To convert the seal at _b_, Fig. 4., into the ordinary form of test-tube
+seal, it is only necessary to heat the "bleb" a little more strongly,
+blow gently into the tube until the thick portion is slightly expanded,
+re-heat the whole of the rounded end until it is beginning to collapse,
+and give a final shaping by careful blowing after it has commenced to
+cool. In each case the glass must be removed from the flame before
+blowing. The finished seal is shown by _c_, Fig. 4. If desired, the open
+end may now be finished by heating and rotating the soft glass against
+the large turn-pin, as illustrated in _d_, but the turn-pin must not be
+allowed to become too hot, as if this happens it will stick to the
+glass. After turning out the end, the lip of glass must be heated to
+redness and allowed to cool without coming in contact with anything;
+otherwise it will be in a condition of strain and liable to crack
+spontaneously. The finished test-tube is shown by _e_.
+
+When it is necessary to seal a substance inside a glass tube, the bottom
+of the tube is first closed, as explained above, and allowed to cool;
+the substance, if a solid, is now introduced, but should not come to
+within less than two inches of the point where the second seal is to be
+made. If the substance is a liquid it can more conveniently be
+introduced at a later stage.
+
+Now bring the tube into the blowpipe flame gradually, and rotate it,
+while heating, at the place where it is to be closed. Allow the glass to
+soften and commence to run together until the diameter of the tube is
+reduced to about half its original size. Remove from the flame and draw
+the ends apart, this should give a long, thick extension as shown by
+_f_, Fig. 4. If any liquid is to be introduced, it may now be done by
+inserting a thin rubber or other tube through the opening and running
+the liquid in. A glass tube should be used with caution for introducing
+the liquid, as any hard substance will tend to scratch the inside of the
+glass and cause cracking. The final closure is made by melting the
+drawn-out extension in the blowpipe flame; the finished seal being shown
+by _g_, Fig. 4.
+
+If the sealed tube has to stand internal pressure, it is desirable to
+allow the glass to thicken somewhat more before drawing out, and the
+bottom seal should also be made thicker. For such a tube, and especially
+when it has to stand heating, as in a Carius determination of chlorine,
+each seal should be cooled very slowly by rotating it in a gas flame
+until the surface is covered with a thick layer of soot, and it should
+then be placed aside in a position where the hot glass will not come in
+contact with anything, and where it will be screened from all draughts.
+
+_Joining Tube._--We will now consider the various forms of join in glass
+tubing which are met with in the laboratory. First, as being easiest, we
+will deal with the end-to-end joining of two tubes of similar glass.
+_a_, _b_, and _c_, Fig. 5, illustrate this. One end of one of the tubes
+should be closed, a lip should be turned out on each of the ends to be
+joined, and both lips heated simultaneously until the glass is
+thoroughly soft. Now bring the lips together gently, until they are in
+contact at all points and there are no places at which air can escape;
+remove from the flame, and blow slowly and very cautiously until the
+joint is expanded as shown in _b_, Fig. 5. Reheat in the flame until
+the glass has run down to rather less than the original diameter of the
+tube, and give a final shaping by re-blowing. The chief factors of
+success in making such a join are, thorough heating of the glass before
+bringing the two tubes together, and avoidance of hard or sudden blowing
+when expanding the joint. The finished work is shown by _c_, Fig. 5.
+
+[Illustration: Fig. 5]
+
+To join a small glass tube to the end of a large one, the large tube
+should first be sealed, a small spot on the extreme end of the seal
+heated, and air pressure used to expand the heated spot as shown in _d_.
+This expanded spot is then re-heated and blown out until it bursts as
+shown in _e_, the thin fragments of glass are removed and the end of the
+small tube turned out as shown in _f_. After this the procedure is
+similar to that used in jointing two tubes of equal size.
+
+When these two forms of joint have been mastered, a T piece will present
+but little difficulty. It is made in three stages as shown in Fig. 5,
+and the procedure is similar to that used in joining a large and small
+tube. Care should be taken to avoid softening the top of the "T" too
+much, or the glass will bend and distort the finished work; although a
+slight bend can be rectified by re-heating and bending back. Local
+re-heating is often useful in giving the joint its final shape.
+
+An exhaustion branch is often made by a totally different method. This
+method is shown by _g_, _h_, and _i_, Fig. 5; _g_ is the tube on which
+the branch is to be made. The end of a rod of similar glass should be
+heated until a mass of thoroughly liquid glass has collected, as shown,
+and at the same time a spot should be heated on that part of the tube
+where it is desired to make the branch. The mass of hot glass on the rod
+is now brought in contact with the heated spot on the tube and expanded
+by blowing as shown by _h_. The air pressure in the tube is still
+maintained while the rod is drawn away as shown by _i_. This will give a
+hollow branch which may be cut off at any desired point, and is then
+ready for connection to the vacuum pump.
+
+If the rod used is of a dissimilar glass, the branch should be blown
+much thinner. Such a branch will often serve as a useful basis for
+joining two tubes of different composition, as the ordinary type of
+branch is more liable to crack when made with two glasses having
+different coefficients of expansion.
+
+_Blowing Bulbs._--A bulb may be blown on a closed tube such as that
+shown by _c_, Fig. 5, by rotating it in the blowpipe flame until the end
+is softened, removing it from the flame and blowing cautiously. It is
+desirable to continue the rotation during blowing. In the case of a very
+small tube, it is sufficient to melt the end without previous sealing,
+rotate it in the flame until enough glass has collected, remove from the
+flame and blow while keeping the tube in rotation.
+
+_Thermometer Bulbs._--If the thermometer is to be filled with mercury,
+it is desirable to use a rubber bulb for blowing, as moisture is liable
+to condense inside the tube when the mouth is used, and this moisture
+will cause the mercury thread to break. In any case, a slight pressure
+should be maintained inside the thermometer tube while it is in the
+flame; otherwise the fine capillary tube will close and it will be very
+difficult to expand the heated glass into a bulb.
+
+_Large Bulbs._--When a large bulb is needed on a small or medium sized
+tube, it is often necessary to provide more glass than would be obtained
+if the bulb were blown in the ordinary way. One method is to expand the
+tube in successive stages along its axis, as shown by _a_, Fig. 6. These
+expanded portions are then re-heated, so that they run together into one
+hollow mass from which the bulb is blown; _b_ and _c_, illustrate this.
+Another method, and one which is useful for very large bulbs, is to
+fuse on a length of large, thick-walled, tubing. The heat reflector,
+_g_, Fig. 3, should be used, if necessary, when making large bulbs. It
+consists of a sheet of asbestos mounted in a foot, and is used by being
+placed close to the mass of glass on the side away from the blowpipe
+flame while the glass is being heated.
+
+[Illustration: Fig. 6]
+
+_Bulbs of Dissimilar Glass._--These may be made by the second method
+given under "Large Bulbs," but the joint should be blown as thin as
+possible. Further instructions in the use of unlike glasses are given on
+page 94.
+
+_A Bulb in the Middle of a Tube._--Unless the bulb is to be quite small,
+it will be necessary to join in a piece of thick glass tubing, or to
+draw the thin tube out from a larger piece, thus leaving a thick mass in
+the middle as shown by _d_, Fig. 6. This mass of glass should now be
+rotated in the blowpipe flame until it is quite soft and on the point of
+running together. Considerable practice will be necessary before the two
+ends of the tube can be rotated at the same speed and without
+"wobbling," but this power must be acquired. When the glass is
+thoroughly hot, remove from the flame, hold in a horizontal position,
+and expand by blowing. It is essential to continue the rotation while
+this is done. Should one part of the bulb tend to expand more than the
+other, turn the expanded part to the bottom, pause for about a second,
+both in rotating and blowing, in order that the lower portion may be
+cooled by ascending air-currents; then continue blowing and turning as
+before.
+
+_Absorption Bulbs or Washing Bulbs._--These are made by an elaboration
+of the processes given in the last paragraph, _g_, _h_, and _i_, Fig. 6,
+illustrate this.
+
+_A Thistle Funnel._--This is made by blowing a fairly thick-walled bulb
+on a glass tube, bursting a hole by heating and blowing, and enlarging
+the burst-out part by heating and rotating against a turn-pin.
+
+_Bending Glass Tube._--Small tubing may be bent in a flat flame gas
+burner and offers no special difficulty. Large or thin-walled tubing
+should be heated in the blowpipe flame and a slight bend made; another
+zone of the tube, just touching the first bend, should now be heated and
+another slight bend made. In this way it is possible to avoid flattening
+and a bend having any required angle can gradually be produced. A final
+shaping of the bend may be made by heating in a large blowpipe flame and
+expanding slightly by air pressure.
+
+_Glass Spirals._--If a tube is heated by means of a long, flat-flame
+burner, the softened tube may be wound on to an iron mandrel which has
+previously been covered with asbestos. The mandrel should be made
+slightly conical in order to facilitate withdrawal. It is desirable to
+heat the surface of the asbestos almost to redness by means of a second
+burner, and thus avoid undue chilling of the glass and the consequent
+production of internal strain.
+
+[Illustration: Fig. 7]
+
+_A Thermo-Regulator for Gas._--Fig. 7, _a-e_, shows an easily
+constructed thermo-regulator. The mercury reservoir, _a_, and the upper
+part, _b_, are made by joining two larger pieces of tubing on to the
+capillary. The gas inlet passes through a rubber stopper, in order to
+allow of adjustment for depth of insertion, and the bye-pass branches,
+_d_ and _e_, are connected by a piece of rubber tubing which can be
+compressed by means of a screw clip, thus providing a means of
+regulating the bye-pass.
+
+_Use of Glass Rod._--Apart from its most common laboratory use for
+stirring; glass rod may be used in building up such articles as
+insulating feet for electrical apparatus or acid-resisting cages for
+chemical purposes. Such a cage is shown by _f_, _g_ and _h_, Fig. 7.
+Further, by an elaboration of the method of making an exhaustion branch,
+given on page 18, blown articles may also be constructed from rod. Note
+the added parts of _e_, Fig. 9.
+
+_A Simple Foot._--The form of foot shown by Fig. 7, _k_, is easy to make
+and has many uses. First join a glass rod to a length of glass tubing as
+shown (the joint should be expanded slightly by blowing), cut off the
+tube and heat the piece remaining on the rod until it can be turned out
+as shown by _i_. This should be done with the large turn-pin, and care
+should be taken not to heat the supporting rod too strongly, otherwise
+the piece of tube will become bent and distorted; it is better to
+commence by heating the edge of the piece of tube and turn out a lip,
+then extend the heating by degrees and turn out more and more until the
+foot looks like that shown by _i_.
+
+We now need to make three projections of glass rod. These are produced
+as follows:--Heat the end of the glass rod until a thoroughly melted
+mass of glass has accumulated (the rod must be rotated while this is
+being done, otherwise the glass will drop off); when sufficient melted
+glass has been obtained, the edge of the turned-out foot should be
+heated to dull redness over about one-third of its circumference, and
+the melted glass on the rod should be drawn along the heated portion
+until both are so completely in contact as to form one mass of
+semi-fluid glass. The rod should now be drawn away slowly, and, finally,
+separated by melting off, thus producing a flat projection. A repetition
+of the process will give the other two projections, and the finished
+foot may be adjusted to stand upright by heating the projections
+slightly and standing it on the carbon plate mentioned on page 7. After
+the foot is adjusted it should be annealed slightly by heating to just
+below the softening point of the glass and then rotating in a smoky gas
+flame until it is covered with a deposit of carbon, after which it
+should be allowed to cool in a place free from draughts and where the
+hot glass will not come in contact with anything. The finished foot is
+shown by _k_, Fig. 7.
+
+_Building up from Glass Rod._--A glass skeleton-work can be constructed
+from rod without much difficulty, and is sometimes useful as a container
+for a substance which has to be treated with acid, or for similar
+purposes. The method is almost sufficiently explained by the
+illustration in Fig. 7; _f_ shows the initial stage, _g_ the method of
+construction of the net-work, and _h_ the finished container. It is
+convenient to introduce the substance at the stage indicated by _g_. The
+important points to observe in making this contrivance are that the
+glass rod must be kept hot by working while it is actually in the flame,
+and that the skeleton must be made as thin as possible with the
+avoidance of heavy masses of glass at any place. If these details are
+neglected it will be almost certain to crack.
+
+_Stirrers._--These are usually made from glass rod, and no special
+instructions are necessary for their construction, except that the glass
+should be in a thoroughly fused condition before making any joins and
+the finished join should be annealed slightly by covering with a deposit
+of soot, as explained on page 16. The flat ends shown in _a_, Fig. 8,
+are made by squeezing the soft glass rod between two pieces of carbon,
+and should be re-heated to dull redness after shaping. Fig. 8 also shows
+various forms of stirrer.
+
+In order to carry out stirring operations in the presence of a gas or
+mixture of gases other than air, some form of gland or seal may be
+necessary where the stirrer passes through the bearing in which it runs.
+A flask to which is fitted a stirrer and gas seal is shown in section by
+_b_, Fig. 8. The liquid used in this seal may be mercury, petroleum, or
+any other that the experimental conditions indicate.
+
+[Illustration: Fig. 8]
+
+If the bearing for a stirrer is made of glass tube, it is desirable to
+lubricate rather freely; otherwise heat will be produced by the
+friction of the stirrer and the tube will probably crack. Such
+lubrication may be supplied by turning out the top of the bearing tube
+and filling the turned-out portion with petroleum jelly mixed with a
+small quantity of finely ground or, better, colloidal graphite, and the
+bearing should also be lubricated with the same composition. Care
+should be taken not to employ so soft a lubricant or so large an excess
+as to cause it to run down the stirrer into the liquid which is being
+stirred.
+
+_Leading a Crack._--It sometimes happens that a large bulb or specially
+thin-walled tube has to be divided. In such a case it is scarcely
+practicable to use the method recommended for small tubes on page 12,
+but it is quite easy to lead a crack in any desired direction. A
+convenient starting point is a file cut; this is touched with hot glass
+until a crack is initiated. A small flame or a bead of hot glass is now
+used to heat the article at a point about a quarter of an inch from the
+end of the crack and in whatever direction it has to be led. The crack
+will now extend towards the source of heat, which should be moved
+farther away as the crack advances. In this manner a crack may be caused
+to take any desired path and can be led round a large bulb.
+
+_Cutting Glass with the Diamond._--Slips of window-glass can be used in
+place of glass rod for some purposes, and as cutting them involves the
+use of the glaziers' diamond or a wheel-cutter, they may well be
+mentioned under this heading.
+
+In cutting a sheet of glass with the diamond, one needs a flat surface
+on which to rest the glass, and a rule against which to guide the
+diamond. The diamond should be held in an almost vertical position, and
+drawn over the surface of the glass with slight pressure. While this is
+being done the angle of the diamond should be changed by bringing the
+top of the handle forward until the sound changes from one of scratching
+to a clear singing note. When this happens the diamond is cutting. A few
+trials will teach the student the correct angle for the diamond with
+which he works, and the glass, if properly cut, will break easily. If
+the cut fails it is better to turn the glass over and make a
+corresponding cut on the other side rather than make any attempt to
+improve the original cut. The diamond is seldom used for cutting small
+glass tubes.
+
+The use of the wheel-cutter calls for no special mention as it will cut
+at any angle, although the pressure required is somewhat greater than
+that needed by most diamonds.
+
+
+
+
+CHAPTER III
+
+     Internal Seals, Air-Traps, Spray Arresters,
+     Filter-Pumps--Sprays, Condensers; Plain, Double Surface, and
+     Spherical--Soxhlet Tubes and Fat Extraction
+     Apparatus--Vacuum Tubes, Electrode Work, Enclosed
+     Thermometers, Alarm Thermometers, Recording Thermometers,
+     "Spinning" Glass.
+
+
+_Internal Seals._--It is convenient to class those cases in which a
+glass tube passes through the wall of another tube or bulb under the
+heading of "Internal Seals." These are met with in barometers, spray
+arresters, and filter pumps, in condensers and some forms of vacuum
+tube. The two principal methods of making such seals will be considered
+first and their special application afterwards.
+
+_An Air Trap on a Barometer Tube._--This involves the use of the first
+method, and is perhaps the simplest example that can be given. Fig. 9,
+_a_, _a1_ and _a2_, show the stages by which this form of internal seal
+is made. For the first trials, it is well to work with fairly
+thick-walled tubing, which should be cut into two pieces, each being
+about eight inches long.
+
+[Illustration: Fig. 9]
+
+First seal the end of one tube as described on page 13, heat the sealed
+end and expand to a thick walled bulb. Fuse the end of the other tube,
+attach a piece of glass rod to serve as a handle, and draw out; cut off
+the drawn-out portion: leaving an end like _a_.
+
+Now heat a small spot at the end of the bulb, blow, burst out, and
+remove the thin fragments of glass. Heat a zone on the other tube at the
+point where the drawn-out portion commences and expand as shown by _a1_.
+
+The next stage is to join the tubes. Heat the ragged edges of the
+burst-out portion until they are thoroughly rounded. At the same time
+heat the drawn-out tube to just below softening point. Then, while the
+rounded edges of the burst-out portion are still soft, insert the other
+tube; rotate the join in the blowpipe flame until it is quite soft, and
+expand by blowing. If necessary, re-heat and expand again. The finished
+seal, which should be slightly annealed by smoking in a sooty flame, is
+shown by _a2_.
+
+_A Spray Arrester._--This is made by the second method, in which the
+piece of tube which projects inside the bulb is fused in position first
+and the outer tube is then joined on. The various stages of making are
+illustrated by _b_, _b1_ and _b2_, Fig. 9.
+
+A bulb is blown between two tubes by the method given on page 22, the
+larger tube is then cut off and the small piece of tube introduced into
+the bulb after having been shaped as shown in by _b_, Fig. 9. The
+opening in the bulb is sealed as shown by _b1_. The sealed part is now
+heated and the bulb inclined downwards until the inner tube comes in
+contact with the seal and is fused in position. This operation requires
+some practice in order to prevent the inner tube either falling through
+the soft glass or becoming unsymmetrical. The end of the bulb, where the
+inner tube comes in contact with it, is now perforated by heating and
+blowing, thus giving the form shown by _b2_, and the outer tube is
+joined on. The finished spray arrester is shown by _b3_. Practice alone
+will give the power to produce a symmetrical and stable piece of work.
+
+_Two Forms of Filter Pump._--That illustrated by _d_, Fig. 9, is made by
+the method explained under "An Air Trap on a Barometer Tube." That
+illustrated by _c_ is made by the method explained under "A Spray
+Arrester." No new manipulation is involved, and the construction should
+be clear from a study of the drawings.
+
+_Multiple and Branched Internal Seals._--A fuller consideration of these
+will be found on page 39, but one general principle may well be borne in
+mind; that, as far as is possible, a tube having both ends fastened
+inside another tube or bulb should be curved or have a spiral or bulb at
+some point in its length, otherwise any expansion or contraction will
+put great strain on the joints.
+
+_Sprays._--A spray which is easy to make, easy to adjust, and easy to
+clean after use is shown by _e_, Fig. 9. The opening on the top of the
+bulb is made by melting on a bead of glass, expanding, bursting, and
+fusing the ragged edges. The two branches which form the spray producing
+junction are made by the method used for an exhaustion branch and
+described on page 18.
+
+A spray which can be introduced through the neck of a bottle is shown by
+_h_, Fig. 9. The various stages in making this are illustrated by _f_,
+and _g_. If the inner tube is made by drawing out from a larger piece of
+glass so that two supporting pieces are left on each side of the place
+where it is intended to make the final bend, that bend can be made in a
+flat-flame gas burner without causing the inner tube to come in contact
+with the walls of the outer tube. Care must be taken when joining on the
+side piece that the inner tube is not heated enough to fuse it. The
+small hole in the side of the outer tube is produced by heating and
+bursting.
+
+_A Liebig's Condenser._--This consists of a straight glass tube passing
+through an outer cooling jacket. In practice it is better to make the
+jacket as a separate piece, and to effect a water-tight junction by
+means of two short rubber tubes. It may, however, be made with two
+internal seals of the class described under "A Spray Arrester." There is
+much less risk of these seals cracking if the inner tube is made in the
+form of a spiral or has a number of bulbs blown on it in order to give a
+certain amount of elasticity.
+
+_A Double-Surface Condenser._--Fig. 10 shows a condenser of this nature
+which is supplied by Messrs. Baird and Tatlock. It may be built up in
+stages as shown by _a_, _b_, and _c_, but the work involved requires
+considerable skill, and the majority of laboratory workers will find it
+cheaper to buy than to make.
+
+[Illustration: Fig. 10]
+
+_A Spherical Condenser._--Such a condenser as that shown by _f_, Fig 10,
+involves a method which may find application in a number of cases. The
+outer bulb is blown from a thick piece of tubing which has been inserted
+in a smaller piece (see _d_, Fig. 6); then the inner bulb by similar
+method. It is now necessary to introduce the smaller bulb into the
+larger, and for this purpose the larger bulb must be cut into halves. A
+small but deep cut is made with the file or glass-blowers' knife in the
+middle of the larger bulb, and at right angles to the axis of the tube
+on which it is blown. A minute bead of intensely heated glass is now
+brought in contact with the cut in order to start a crack. This crack
+may now be led round the bulb as described on page 30. If the work is
+carried out with care, it is possible to obtain the bulb in two halves
+as shown by _d_, and these two halves will correspond so exactly that
+when the cut edges are placed in contact they will be almost air-tight.
+The two tubes from the smaller bulb should be cut to such a length that
+they will just rest inside the larger, and the ends should be expanded.
+Place the inner bulb in position and fit the two halves of the outer
+bulb together, taking great care not to chip the edges. If the length of
+the tubes on the inner bulb has been adjusted properly, the inner bulb
+will be supported in position by their contact with the tubes on the
+outer bulb. Now rotate the cracked portion of the outer bulb in front
+of a blowpipe flame and press the halves together very gently as the
+glass softens. Expand slightly by blowing if necessary. If a small
+pin-hole develops at the joint it is sometimes possible to close this
+with a bead of hot glass; but if the bulb has been cut properly there
+should be no pin-holes formed. The condenser is finished by joining on
+the side tubes and sealing the inner tube through by the methods already
+given. In order to blow bulbs large enough to make a useful condenser,
+it will be convenient to employ the multiple-jet blowpipe described on
+page 4.
+
+_A Soxhlet-Tube or Extraction Apparatus._--This involves the
+construction of a re-entrant join where the syphon flows into the lower
+tube. It is of considerable value as an exercise and the complete
+apparatus is easy to make.
+
+A large tube is sealed at the bottom and the top is lipped, as in making
+a test-tube. A smaller tube is then joined on by a method similar to
+that given on page 18, but without making a perforation in the bottom of
+the large tube. Heating and expanding by air pressure, first through the
+large tube, then through the smaller tube and then again through the
+large tube, will give a satisfactory finish to this part of the work.
+
+[Illustration: Fig. 11]
+
+The syphon tube is now joined on to the large tube as shown by _a_, Fig.
+11, care being taken to seal the other end of the syphon tube before
+joining. The details of the final and re-entrant joint of the syphon
+tube are shown at the lower part of _a_. This join is made by expanding
+the sealed end of the syphon tube into a small, thick-walled bulb, and
+the bottom of this bulb is burst out by local heating and blowing; the
+fragments of glass are removed and the edges made smooth by melting. A
+similar operation is carried out on the side of the tube to which the
+syphon tube is to be joined. This stage is shown by _a_. Now heat the
+syphon tube at the upper bend until it is flexible, and press the bulb
+at its end into the opening on the side of the other tube. Hold the
+glass thus until the syphon is no longer flexible. The final join is
+made by heating the two contacting surfaces, if necessary pressing the
+edges in contact with the end of a turn-pin, fusing together and
+expanding. The finished apparatus is shown by _c_.
+
+_Electrodes._--A thin platinum wire may be sealed into a capillary tube
+without any special precautions being necessary. The capillary tube may
+be drawn out from the side of a larger tube by heating a spot on the
+glass, touching with a glass rod and drawing the rod away; or the
+exhaustion branch described on page 18 may be used for the introduction
+of an electrode. It is convenient sometimes to carry out the exhaustion
+through the same tube that will afterwards serve for the electrode. The
+electrode wire is laid inside the branch before connecting to the
+exhaustion pump. When exhaustion is completed the tube is heated until
+the soft glass flows round the platinum and makes the seal air-tight.
+The branch is now cut off close to the seal on the pump side, a loop is
+made in the projecting end of the platinum wire, and the seal is
+finished by melting the cut-off end.
+
+Platinum is usually employed for such work, but if care is taken to
+avoid oxidation it is not impossible to make fairly satisfactory seals
+with clean iron or nickel wire. Hard rods of fine graphite, such as are
+used in some pencils, may also be sealed into glass, but it seems
+probable that air would diffuse through the graphite in the course of
+time.
+
+Another method for the introduction of an electrode is illustrated by
+_d_, _e_, _f_ and _g_, Fig. 11. In this case the bulb or thin-walled
+tube into which the electrode is to be sealed is perforated by a quick
+stab with an intensely heated wire--preferably of platinum--which is
+then withdrawn before the glass has had time to harden, and thus a
+minute circular hole is made. The electrode is coated with a layer of
+similar glass, or of the specially made enamel which is sold for this
+purpose, inserted into the bulb or tube by any convenient opening, and
+adjusted by careful shaking until the platinum wire projects through the
+small hole. The bulb or tube is then fused to the coating of the
+electrode and the whole spot expanded slightly by blowing. The
+appearance of the finished seal is shown by _g_. It is well to anneal
+slightly by smoking.
+
+_Thermometers._--Apart from the notes on page 20 with respect to the
+blowing of a suitable bulb on capillary tubing there is little to say in
+connection with the glass working needed in making a plain thermometer.
+The size desirable for the bulb will be determined by the bore of the
+capillary tube, the coefficient of expansion of the liquid used for
+filling, and the range of temperature for which the thermometer is
+intended.
+
+Filling may be carried out as follows:--Fit a small funnel to the open
+end of the capillary by means of a rubber tube, and pour into the funnel
+rather more than enough of the liquid to be used than is required to
+fill the bulb. Mercury or alcohol will be used in practice, most
+probably. Warm the bulb until a few air bubbles have escaped through
+the liquid and then allow to cool. This will suck a certain amount of
+liquid into the bulb. Now heat the bulb again, and at the same time heat
+the capillary tube over a second burner. The liquid will boil and sweep
+out the residual air, but it is necessary to heat the capillary tube as
+well in order to prevent condensation. Allow the bulb and tube to cool,
+then repeat the heating once more. By this time the bulb and tube should
+be free from air, and cooling should give a completely filled
+thermometer. Remove the funnel and heat the thermometer to a few degrees
+above the maximum temperature for which it is to be used; the mercury or
+other filling liquid will overflow from the top, and, as the temperature
+falls, will recede, thus allowing the end of the capillary to be drawn
+out. Reheat again until the liquid rises to the top of the tube, then
+seal by means of the blowpipe flame. The thermometer is now finished
+except for graduation; this is dealt with on page 75.
+
+_An Alarm Thermometer._--A thermometer which will complete an electric
+circuit when a certain temperature is reached may be made by sealing an
+electrode in the bulb and introducing a wire into the top, which in this
+case is not sealed. Naturally, this thermometer will be filled with
+mercury. There is considerable difficulty in filling such a bulb without
+causing it to crack.
+
+Several elaborations of this form are made, in which electrodes are
+sealed through the walls of the capillary tube, thus making it possible
+to detect electrically the variation of temperature when it exceeds any
+given limits.
+
+_An Enclosed or Floating Thermometer._--The construction of this type of
+thermometer is shown by _h_ and _i_, Fig 11. It is made in the following
+stages:--A bulb is blown on the drawn-out end of a thin-walled tube as
+shown by _h_. A small bulb is blown on the end of a capillary tube,
+burst, and turned out to form a lip which will rest in the drawn-out
+part of the thin-walled tube but is just too large to enter the bulb.
+The capillary tube is introduced and sealed in position, care being
+taken to expand the joint a little. The thermometer is filled and the
+top of the capillary tube closed by the use of a small blowpipe flame. A
+paper scale having the necessary graduations is inserted, and the top
+of the outer tube is closed as shown by _i_.
+
+_A Maximum and Minimum Thermometer._--If a small dumb-bell-shaped rod of
+glass or metal is introduced into the capillary tube of a horizontally
+placed, mercury-filled thermometer in such a position that the rising
+mercury column will come in contact with it, the rod will be pushed
+forward. When the mercury falls again the rod will be left behind and
+thus indicate the maximum temperature attained. If a similar
+dumb-bell-shaped rod is introduced into an alcohol-filled thermometer
+and pushed down until it is within the alcohol column, it will be drawn
+down by surface tension as the column falls; but the rising column will
+flow passed it without causing any displacement; thus the minimum
+temperature will be recorded.
+
+Six's combined maximum and minimum thermometer is shown by _b_, Fig. 11.
+In this case both maximum and minimum records are obtained from a
+mercury column, although the thermometer bulb is filled with alcohol. It
+is an advantage to make the dumb-bell-shaped rods of iron, as the
+thermometer can then be reset by the use of a small magnet, another
+advantage consequent on the use of metal being that the rods can be
+easily adjusted, by slight bending, so as to remain stationary in the
+tubes when the thermometer is hanging vertically, and yet to move with
+sufficient freedom to yield to the pressure of the recording column.
+
+The thermometer may be filled by the following method:--When the
+straight tube has been made the first dumb-bell is introduced and shaken
+down well towards the lower bulb, the tube is now bent to its final
+shape and the whole thermometer filled with alcohol as described on page
+44. Now heat the thermometer to a little above the maximum temperature
+that it is intended to record, and pour clean mercury into the open bulb
+while holding the thermometer vertically. Allow to cool, and the mercury
+will be sucked down. The second dumb-bell is now introduced, sufficient
+alcohol being allowed to remain in the open bulb to about half fill it,
+and the alcohol in this bulb is boiled to expel air. The tube through
+which the bulb was filled in now sealed.
+
+_Clinical Thermometers._--The clinical thermometer is a maximum
+thermometer of a different type. In this case there is a constriction
+of the bore at a point just above the bulb. When the mercury in the bulb
+commences to contract, the mercury column breaks at the constriction and
+remains stationary in the tube, thus showing the maximum temperature to
+which it has risen.
+
+_Vacuum Tubes._--There are so many forms of these that it is scarcely
+practicable or desirable to give detailed instructions for making them;
+but an application of the various methods of glass-working which have
+already been explained should enable the student to construct most of
+the simpler varieties. An interesting vacuum tube is made which has no
+electrodes, but contains a quantity of mercury. When the tube is rocked
+so as to cause friction between the mercury and the glass sufficient
+charge is produced to cause the tube to glow.
+
+_A Sprengel Pump._--This, in its simplest form, is illustrated by _a_,
+Fig. 12. Such a form, although highly satisfactory in action, needs
+constant watching while in action, as should the mercury funnel become
+empty air will enter the exhausted vessel. Obviously, the fall-tube must
+be made not less than thirty inches long; the measurement being taken
+from the junction of the exhaustion branch with the fall-tube to the top
+of the turned-up end.
+
+[Illustration: Fig. 12]
+
+_A Macleod Pump._--One form of this is illustrated by _b_, Fig. 12. It
+has the advantage that the mercury reservoir may be allowed to become
+empty without affecting the vacuum in the vessel being exhausted.
+
+_"Spinning" Glass._--By the use of suitable appliances, it is quite
+possible to draw out a continuous thread of glass, which is so thin as
+to have almost the flexibility and apparent softness of woollen fibre; a
+mass of such threads constitutes the "glass wool" of commerce.
+
+The appliances necessary are:--a blowpipe capable of giving a
+well-formed flame of about six or eight inches in length, a wheel of
+from eighteen inches to three feet in diameter and having a flat rim of
+about three inches wide, and a device for rotating the wheel at a speed
+of about three hundred revolutions per minute.
+
+A very satisfactory arrangement may be made from an old bicycle; the
+back wheel having the tyre removed and a flat rim of tin fastened on in
+its place. The chain drive should be retained, but one of the cranks
+removed and a handle substituted for the remaining pedal. The whole
+device is shown by Fig. 13.
+
+[Illustration: Fig. 13]
+
+The procedure in "spinning" glass is as follows:--First melt the end of
+a glass rod and obtain a large mass of thoroughly softened glass, now
+spin the wheel at such a speed that its own momentum will keep it
+spinning for several seconds. Touch the end of the melted rod with
+another piece of glass and, without withdrawing the original rod from
+the blowpipe flame, draw out a thread of molten glass and twist it round
+the spinning wheel. If this is done properly, the thread of glass will
+grip on the flat rim, and by continuing to turn the wheel by hand it is
+possible to draw out a continuous thread from the melted rod, which must
+be advanced in the blowpipe flame as it is drawn on the wheel. If the
+rod is not advanced sufficiently the thread will melt off, if it is
+advanced too much, so as to heat the thick part and allow the glass to
+become too cool at the point of drawing out, then the thread will become
+too thick, but it is easy after a little practice to obtain the right
+conditions. Practice is necessary also in order to find the right speed
+for the wheel.
+
+When sufficient glass has been "spun," the whole "hank" of thin thread
+may be removed by drawing the thumb-nail across the wheel at any point
+on its flat rim, thus breaking the threads, and allowing the "hank" to
+open.
+
+_Brushes for Use with Strong Acids._--Glass wool, if of fine enough
+texture to be highly flexible, can be used to make acid-resisting
+brushes. A convenient method for mounting the spun glass is to melt the
+ends of the threads together into a bead, and then to fuse the bead on
+to a rod; thus giving a brush. If a pointed brush is necessary, the
+point may be ground on an ordinary grindstone or carborundum wheel by
+pressing the loose end of the spun glass against the grinding wheel with
+a thin piece of cardboard.
+
+When using brushes of this description, it is well to bear in mind the
+fact that there is always a liability of a few threads of glass breaking
+off during use.
+
+
+
+
+CHAPTER IV
+
+     Glass, Its Composition and Characteristics. Annealing.
+     Drilling, Grinding, and Shaping Glass by methods other than
+     Fusion. Stopcocks. Marking Glass. Calibration and Graduation
+     of Apparatus. Thermometers. Exhaustion of Apparatus. Joining
+     Glass and Metal. Silvering Glass.
+
+
+There are three kinds of glass rod and tubing which are easily
+obtainable; these are soda-glass, which is that usually supplied by
+chemical apparatus dealers when no particular glass is specified;
+combustion-glass, which is supplied for work requiring a glass that does
+not so easily soften or fuse as soda-glass; and lead-glass, which is
+less common. There are also resistance-glass, made for use where very
+slight solubility in water or other solutions is desirable, and a number
+of other special glasses; but of these soda-glass, combustion-glass,
+lead-glass, and resistance-glass are the most important to the
+glass-blower whose work is connected with laboratory needs.
+
+_Soda-Glass._--Consists chiefly of sodium silicate, but contains
+smaller quantities of aluminum silicate, and often of calcium silicate;
+there may also be traces of several other compounds.
+
+The ordinary soda-glass tubing melts easily in the blowpipe flame, it
+has not a long intermediate or viscous stage during fusion, but becomes
+highly fluid rather suddenly; it does not blacken in the reducing flame.
+Bad soda-glass or that which has been kept for many years, tends to
+devitrify when worked. That is to say the glass becomes more or less
+crystalline and infusible while it is in the flame; and in this case it
+is often impossible to do good work with that particular sample of
+glass; although the devitrification may sometimes be remedied by heating
+the devitrified glass to a higher temperature. The presence of aluminum
+compounds appears to have some influence on the tendency of the glass to
+resist devitrification. Soda-glass, as a rule, is more liable to crack
+by sudden heating than lead-glass, and articles made from soda-glass
+often tend to crack spontaneously if badly made or, in the case of
+heavier and thicker articles, if insufficiently annealed.
+
+_Combustion-Glass._--Is usually a glass containing more calcium silicate
+and potassium silicate than the ordinary "soft" soda-glass. It is much
+less fusible than ordinary soda-glass, and passes through a longer
+intermediate or viscous stage when heated. Such a glass is not very
+suitable for use with the blowpipe owing to the difficulty experienced
+in obtaining a sufficiently high temperature. If, however, a certain
+amount of oxygen is mixed with the air used in producing the blowpipe
+flame this difficulty is minimised.
+
+_Resistance-Glass._--May contain zinc, magnesium, and other substances.
+As a rule it is harder than ordinary soda-glass, and less suitable for
+working in the blowpipe flame. It should have very little tendency to
+dissolve in water, and hence is used when traces of alkali or silicates
+would prove injurious in the solutions for which the glass vessels are
+to be used.
+
+_Lead-Glass._--This, or "flint" glass as it is often called from the
+fact that silica in the form of crushed and calcined flint was often
+used in making the English lead-glasses, contains a considerable
+proportion of lead silicate. Such a glass has, usually, a particularly
+bright appearance, a high refractive index, and is specially suitable
+for the production of the heavy "cut-glass" ware.
+
+Lead-glass tubing is easy to work in the blowpipe flame, melts easily,
+but does not become fluid quite so suddenly as most soda-glasses;
+articles made from it are remarkably stable and free from tendency to
+spontaneous cracking, although, as is essential for all the heavy or
+"glass-house" work, the massive articles need annealing in the oven.
+
+The two chief disadvantages of lead-glass for laboratory work are that
+it is blackened by the reducing gases if held too near to the blue cone
+of the blowpipe flame, and that it is rather easily attacked by chemical
+reagents; thus ammonium sulphide will cause blackening.
+
+The effect of the reducing flame on lead is not altogether a
+disadvantage, however; because a little care in adjusting the blowpipe
+and a little care in holding the glass in the right position will enable
+the student to work lead-glass without producing the faintest trace of
+blackening. This, in addition to being a valuable exercise in
+manipulation, will teach him to keep his blowpipe in good order, and
+prove a useful aid in his early efforts to judge as to the condition of
+the flame. It prevents discouragement if the student does his
+preliminary work with the soda-glass, but he should certainly make
+experiments with lead-glass as soon as he has acquired reasonable
+dexterity with soda-glass.
+
+_Annealing._--Annealing is a process by which any condition of strain
+which has been set up in a glass article, either by rapid cooling of one
+part while another part still remains hot, or by the application of
+mechanical stress after cooling is relieved. Annealing is carried out by
+subjecting the article to a temperature just below the softening point
+of the glass, maintaining that temperature until the whole article has
+become heated through the thicker part, and then reducing the
+temperature very gradually; thus avoiding any marked cooling of the
+thinner and outer parts first.
+
+For thin glass apparatus of the lamp-blown or blowpipe-made variety in
+which there are no marked difference of thickness, such as joins on
+tubes, ordinary seals, bulbs, etc., there is little need for annealing;
+and even those having rather marked changes of thickness, such as
+filter pumps, can be annealed sufficiently by taking care that the last
+step in making is heating to just below visible redness in the blowpipe
+flame and then rotating in a sooty gas flame until covered with a
+deposit of carbon. The article should then be allowed to cool in a place
+free from draughts and where the hot glass will not come in contact with
+anything.
+
+A few of the blowpipe-made articles, such, for example, as glass
+stopcocks, need more careful annealing, and for this purpose a small
+sheet-iron oven which can be heated to dull redness over a collection of
+gas burners will serve. Better still, a small clay muffle can be used.
+In either case, the article to be annealed should be laid on a clean,
+smooth, fireclay surface, the temperature should be maintained at a very
+dull red for two or three hours and then reduced steadily until the oven
+is cold. This cooling should take anything from three to twelve hours,
+according to the nature of the article to be annealed. A thick article,
+or one having great irregularities in thickness will need much longer
+annealing than one thinner or more regular. As a rule, soda-glass will
+need more annealing than lead-glass.
+
+_Drilling Glass._--Small holes may be drilled in glass by means of a rod
+of hard steel which has been broken off, thus giving a more or less
+irregular and crystalline end.
+
+There are several conditions necessary to enable the drilling of small
+holes to be carried out successfully:--the first of these is that the
+"drill" should be driven at a high speed. This may be done by means of a
+geared hand-drill such as the American pattern drill, although a
+somewhat higher speed than this will give is even more satisfactory. The
+second condition is that the pressure on the drill is neither too light
+nor too heavy; this is conveniently regulated by hand. The third
+condition is that the drill be prevented from "straying" over the
+surface of the glass; for this purpose a small metal guide is useful.
+The fourth condition is that a suitable lubricant be used; a strong
+solution of camphor in oil of turpentine is perhaps the most suitable.
+For commercial work, a diamond drill is often used, but this is scarcely
+necessary for the occasional work of a laboratory.
+
+_Larger Holes in Glass._--The method of drilling with a hard steel rod
+is not highly satisfactory for anything but small holes. When a larger
+hole, say one of an eighth of an inch or more, is needed it is better to
+use a copper or brass tube. This tube may be held in an American
+hand-drill, but a mixture of carborundum or emery and water is supplied
+to the rotating end. Tube or drill must be lifted at frequent intervals
+in order to allow a fresh supply of the grinding material to reach the
+end. In this case, also, a guide is quite essential in the early stages
+of drilling; otherwise the end of the tube will stray. The speed of
+cutting may be increased slightly by making a number of radial slots in
+the end of the tube; these serve to hold a supply of the grinding
+material.
+
+_Grinding Lenses._--This is scarcely within the scope of a book on
+glass-blowing for laboratory purposes, but it may be said that the lens
+may be ground by means of a permutating mould of hard lead or
+type-metal. The rough shaping is done with coarse carborundum or emery,
+and successive stages are carried on with finer and finer material. The
+last polishing is by the use of jewellers' rouge on the mould, now
+lined with a fine textile.
+
+_Filing Glass._--If a new file, thoroughly lubricated with a solution of
+camphor in oil of turpentine, is used, there is but little difficulty in
+filing the softer glasses. A slow movement of the file, without
+excessive pressure but without allowing the file to slip, is desirable.
+After a time the cutting edges of the file teeth will wear down and it
+will be necessary to replace the file by another.
+
+_Grinding Stoppers._--This is, perhaps, the most common form of grinding
+that the laboratory worker will need to perform, and for that reason,
+rather full details of the procedure are desirable.
+
+A very crude form of ground-in stopper may be made by drawing out the
+neck and the mass of glass which is intended to form the stopper to
+approximately corresponding angles, wetting the surfaces with a mixture
+of the abrasive material and water, and grinding the stopper in by hand.
+Frequent lifting of the stopper is necessary during grinding, in order
+to allow fresh supplies of abrasive material to reach the contacts. When
+an approximate fit is obtained, the coarse abrasive should be washed
+off, care being taken that the washing is complete, and a finer abrasive
+substituted. After a while, this is replaced in its turn by a still
+finer grinding material.
+
+Such a method of grinding may give a satisfactory stoppering if the
+angles of the plug and socket correspond very closely before grinding is
+commenced; but if there is a wide difference in the original angles,
+then no amount of grinding by this method will produce a good result.
+The reason for this is that the plug will become so worn in the
+preliminary grinding as to assume the form of a highly truncated cone;
+the socket will assume a reverse form, and the end result will be a
+loose-fitting plug and socket.
+
+Satisfactory grinding may be carried out by the use of copper or
+type-metal cones for the preliminary shaping. Such cones should be
+mounted on a mandrel which will fit into the chuck of the American
+hand-drill and turned on the lathe to the desirable angle for
+stoppering. A number of these cones will be necessary. A number of
+similar moulds, that is to say blocks of type-metal or hard lead in
+which is a hole corresponding in size and angle to the plug desired,
+should be made also. These must be rotated, either in the lathe or by
+other means, and are used for the preliminary shaping of the plug. If
+but few plugs are to be ground it is unnecessary to provide a means of
+rotating the moulds, as the plug may be held in the hand and ground into
+the mould in a manner similar to that used in the first method of
+stoppering.
+
+[Illustration: Fig. 14]
+
+When the socket and plug have been ground, by the successive use of
+cones and moulds, to the desired angle, so that they correspond almost
+exactly, the plug is given its final fitting into the socket by
+grinding-in with a fine abrasive, in the manner first described.
+
+_Stopcocks._--Although it would be more strictly in keeping with the
+form of this book to divide the making of stopcocks into two parts;
+shaping by heat and grinding, we will consider the whole operation here,
+and take for our example a simple stopcock such as that illustrated by
+Fig. 14.
+
+The "blank," _f_, that is the socket before grinding, is made by drawing
+out a piece of fairly thick-walled tubing into the form shown by _a_.
+Two zones on this tube are then heated by means of a small, pointed
+flame, and the tube is compressed along its axis, thus producing two
+raised rings as shown by _b_. Two zones, slightly towards the outer
+sides of these two raised rings are heated and the tube is drawn while
+air pressure is maintained within. This produces two thin-walled bulbs
+or extensions similar to those shown by _c_. One of these extensions is
+now broken off by means of a sharp blow with the edge of a file or
+other piece of metal, and the edges of the broken glass are rounded in
+the flame. The other extension is left to serve as a handle. We have now
+a piece of glass like that shown by _d_. Now heat a spot on the side of
+this, medially between the raised rings, until the glass is on the point
+of becoming deformed, and bring the intensely heated end of a smaller
+tube in contact with the heated spot. Without disturbing the relative
+positions of the two tubes, press the smaller tube down on a thin steel
+wire, so that the wire passes along the tube and enters the soft glass;
+thus forming a projection inside the sockets as shown by _e_. The wire
+must be withdrawn, again immediately. When the wire has been withdrawn,
+heat the place where it entered to dull redness, in order to relieve any
+strain; break off the thin extension, which up to the present has served
+as a handle, round off the broken edges in the flame, and join on and
+indent a similar piece of small tubing to the opposite side of the
+socket; the socket at this stage being shown by _f_. The "blank" for the
+socket is now completed, but it must be heated to dull redness in order
+to relieve strain and be placed in an annealing oven, where it should
+be annealed for some hours.
+
+The "blank" for the plug offers no special difficulty; it is made by
+heating a glass rod and compressing it axially until a mass having the
+form shown by _g_, Fig. 14, is produced; the end of this is heated
+intensely and brought in contact with the rather less heated side of a
+glass tube which has been drawn to the shape desired for the handle;
+when contact is made a slight air pressure is maintained in the glass
+tube, thus producing a hollow join. The ends of the tube are sealed and
+the bottom of the plug is drawn off, thus giving the finished "blank" as
+shown by _h_. This blank is now held in a pair of asbestos-covered
+tongs, heated to dull redness all over, and transferred to the annealing
+oven.
+
+When cold, the socket is ground out by the second method given under
+"Grinding Stoppers"; that is to say, by means of type-metal or copper
+cone, and the plug is ground to fit in a corresponding mould. When the
+fit is almost perfect, the transverse hole is drilled in the plug, and
+the final finishing is made with fine abrasive powder. Great care must
+be taken in the final grinding that there is no accumulation of
+abrasive material in the transverse hole of the plug; if this is allowed
+to occur there will be a ring ground out of the socket where the holes
+move, and the tightness of the finished stopcock will be lost.
+
+_Marking Glass._--As a preliminary to a consideration of the methods of
+graduating and calibrating glass apparatus, it is convenient to consider
+the various methods which are available for marking glass. Among these
+are, the writing diamond, the carborundum or abrasive pencil, the
+cutting-wheel, and etching by means of hydrofluoric acid. Each produces
+a different class of marking and each is worthy of independent
+consideration.
+
+_The Writing Diamond._--This is the name given to a small irregular
+fragment of "bort" which is usually mounted in a thin brass rod. Such a
+diamond, if properly selected, has none of the characteristics of a
+cutting diamond; although one occasionally finds so-called "writing
+diamonds" which will produce a definite cut. These should be rejected.
+
+The writing diamond is used in much the same way as a pencil, but is
+held more perpendicularly to the object, and a certain amount of
+pressure is necessary. The mark produced is a thin scratch which,
+although fairly definite, lacks breadth, and this is a disadvantage
+where the marking has to be read at a distance. This disadvantage may to
+some extent be overcome by making a number of parallel scratches.
+
+_The Abrasive Pencil._--A rod of carborundum composition may be ground
+or filed to a point, and this forms a very useful pencil for general
+work. The marking produced is rather less definite than that produced by
+a writing diamond, but has the advantage of being broader.
+
+_The Cutting Wheel._--"Cutting" in this case is scarcely the ideal
+expression, it should rather be "grinding," but "cutting" is more
+commonly used. Exceedingly good graduations may be made by the edge of a
+small, thin, abrasive wheel which is mounted on the end of a small
+mandrel and driven by a flexible shaft from an electric motor or any
+other convenient source of power. The depth of the mark can be
+controlled, and very light pressure will suffice.
+
+_Etching._--This is often the quickest and easiest way of marking glass
+apparatus. The object to be marked should first be warmed and coated
+very thoroughly with a thin film of paraffin wax. When cold, the marking
+is made through the paraffin wax by means of a needle point, and the
+object is then exposed to the action of hydrofluoric acid. If a shallow
+but clearly visible marking is desired, it is well to use the vapour of
+the acid; this may be done by bending up a sheet-lead trough on which
+the object can rest with the marked surface downwards. A little of the
+commercial hydrofluoric acid, or a mixture of a fluoride and sulphuric
+acid, is distributed over the bottom of the trough, and the whole
+arrangement is allowed to stand for about an hour. The object is washed
+thoroughly and the paraffin wax removed, either by melting and wiping
+off or by the use of a solvent, and the marking is finished.
+
+If a deep marking is desired, in order that it may afterwards be filled
+with some pigment, a better result is obtained by the use of liquid
+commercial hydrofluoric acid, which is a solution of hydrogen fluoride
+in water. The acid is mopped on to the object after the markings have
+been made on the paraffin wax film, and allowed to remain in contact for
+a few minutes. It is advantageous to repeat the mopping-on process at
+intervals during the etching.
+
+In all cases where hydrofluoric acid is used, or stored, it is of great
+importance to keep it well away from any optical instruments, as the
+most minute trace of vapour in the air will produce a highly destructive
+corrosion of any glass surfaces.
+
+_Methods of Calibration._--In the case of apparatus for volumetric work,
+this is usually carried out by weighing, although some of the smaller
+subdivisions are often made by measurement. When the subdivisions are
+made in this way it is of importance to see that the walls of the tube
+or vessel to be calibrated are parallel. Great errors arise in some of
+the commercial apparatus from neglect of this precaution. A convenient
+method of testing for parallelism, in the case of a wide tube, is to
+close one end and to weigh in successive quantities of mercury. An
+observation of the length occupied by each successive quantity will
+indicate any change in the bore. In the case of capillary tubes, it is
+convenient to introduce an unweighed quantity of mercury, measure its
+length accurately, and then to move it along the tube in stages, either
+by tilting the tube or by the application of air pressure. A measurement
+of the length at each stage will indicate whether the bore is
+approximately parallel or not. Neither of these methods is to be relied
+on without a careful examination of the tube, as it may happen that
+there are local irregularities in the bore which compensate for each
+other, and do not, therefore, affect the volume of a given length.
+Obviously, the smaller the quantity of mercury with which the test is
+carried out and the greater the number of observations made, the less
+risk will there be of such an error. A liquid, such as water or alcohol,
+which wets the glass is not suitable for such a test, unless special
+precautions are taken.
+
+When, however, a pipette or burette has to be calibrated to deliver a
+certain volume of water, the final calibration must be made with this
+liquid. Thus, the burette would first be calibrated by weighing in
+definite quantities of mercury of say 13.54 grammes (1 cc at 15 deg.C.),
+each of the 1 cc divisions should be marked by some temporary marking.
+The burette is now filled with a solution of potassium bichromate and
+sulphuric acid and allowed to soak for some time; the bichromate is
+washed out and distilled water is put in. Successive quantities of water
+are run out of the jet, a fixed time being allowed for draining, and the
+weights of the quantities delivered are noted. This procedure will give
+the necessary data for altering the marking so that it may correspond to
+1 cc _delivered_. Each 1 cc division is now divided into tenths by the
+method described below. A final verification of the markings should be
+made when the subdivision is completed.
+
+_Subdivision of Graduations._--Mark out the spaces to be subdivided on a
+sheet of paper. Take a reliable ruler on which any convenient length is
+divided into the desired number and place it across the lines at such an
+angle that the limits noted on the rule exactly bridge the gap. Now draw
+parallel lines through the markings.
+
+_Copying a Scale._--When a scale has been prepared on paper and it is
+necessary to copy that scale on the waxed-glass surface for etching, a
+convenient method is to employ a long wooden bar having a sharp needle
+passing through it at either end. The scale and object to be marked are
+fastened in line with one another, and the caliper bar is used from step
+to step. The mark is made by moving the bar through a minute portion of
+a circle, which provided that the bar is two or three feet in length,
+will not introduce any perceptible error in a scale of say a quarter of
+an inch in width. The arrangement is shown by Fig. 15.
+
+[Illustration: Fig. 15]
+
+_Graduating a Thermometer._--Assuming that the thermometer has been made
+of carefully selected tubing in which the bore is parallel and free from
+any small irregularities, we have only to fix the freezing point and
+boiling point. The intervening space may then be divided into 100 (if
+the thermometer is to be Centigrade) or 180 (if Fahrenheit). This
+division may be carried out by the method given under "Subdivisions of
+Graduations." A thermometer should not be calibrated until some weeks
+after making, as the glass bulb tends to contract.
+
+_Joining Glass and Metal._--It sometimes happens that one needs to make
+a more permanent and less flexible joint between a glass and metal tube
+than can be obtained by means of a rubber tube. To this end, any one of
+three slightly different methods may be employed. In the method of
+Chatelier one first coats the glass with platinum or silver, which may
+be done by moistening the glass with platinum chloride or silver nitrate
+and then heating to redness; a layer of copper is then deposited
+electrolytically on the treated surface of the glass, and soldering is
+carried out in the usual manner.
+
+McKelvy and Taylor call attention to two other methods in the _Journal
+of the Chemical Society_ for September, 1920. In one of these methods
+the glass is coated with platinum by covering it with a suspension of
+platinum chloride in oil of lavender and heating until the oil is burnt
+off. The metal tube is then tinned on its inner side and soldered to the
+prepared glass, slightly acid zinc chloride being used as a flux.
+
+In the second method, a joint is made by means of the Kraus flux, which
+consists of equal weights of zinc oxide, borax, and powdered soda-glass
+fused together. This is coated on the inner surface of the metal tube,
+and the hot glass tube, which has had the end slightly flanged to give
+support, is inserted. Fusion of the flux is completed by heating the
+outside of metal tube.
+
+_Silvering Glass._--In all cases where it is intended to deposit a
+silver mirror on a glass surface, thorough cleaning is essential.
+Prolonged soaking in a hot solution of potassium bichromate which has
+been acidified with sulphuric acid will often prove useful. The glass
+should then be washed thoroughly, rinsed in distilled water, and the
+solution should then be used.
+
+There are many formulae for the silvering solution, but that used in
+Martin's method may be given:--
+
+        A--Nitrate of Silver      40 grammes
+           Distilled Water      1000 c. cm.
+
+        B--Nitrate of Ammonium    60 grammes
+           Distilled Water      1000 c. cm.
+
+        C--Pure Caustic Potash   100 grammes
+           Distilled Water      1000 c. cm.
+
+        D--Pure Sugar Candy      100 grammes
+           Distilled Water      1000 c. cm.
+
+     Dissolve and add:--
+
+           Tartaric Acid          23 grammes
+
+     Boil for ten minutes, and when cool add:--
+
+           Alcohol               200 c. cm.
+           Distilled Water to   2000 c. cm.
+
+For use take equal parts of A and B. Mix together also equal parts of C
+and D in another vessel. Then mix both liquids together in the silvering
+vessel and suspend the glass to be silvered face downwards in the
+solution. Or if a vessel has to be silvered on the inside, the solution
+is poured in. In this case, the deposition of silver may be hastened by
+immersing the vessel to be silvered in warm water.
+
+In working with a silver solution containing ammonia or ammonium salts
+there is sometimes the possibility of forming an explosive silver
+compound. It is well, therefore, to avoid keeping such solutions longer
+than is necessary, and to bear in mind that any deposit formed by
+solutions containing both silver and ammonia may have explosive
+properties, especially when dry.
+
+
+
+
+CHAPTER V
+
+     Extemporised Glass-Blowing Apparatus--The Use of Oil or
+     other Fuels--Making Small Rods and Tubes from Glass
+     Scrap--The Examination of Manufactured Apparatus with the
+     View to Discovering the Methods Used in Manufacture--Summary
+     of Conditions Necessary for Successful Glass-Blowing.
+
+
+If, in the early stages of his study of glass-blowing, the student
+should attempt to work with the very simplest appliances, it is probable
+that his progress will be hindered; the use of the apparatus will
+require an undue amount of care and his attention will be distracted
+from the actual manipulation of the glass. The case is widely different
+after he has acquired a certain facility in glass-blowing.
+
+_A Simple Form of Blowpipe._--Although there are even more simple forms
+than that described here, we are not concerned with them. The form
+described is the simplest with which any considerable amount of
+glass-blowing can be carried out with certainty.
+
+This form consists of a tube through which air may be blown with the
+mouth, a condensation chamber in which any moisture from the breath can
+condense, a blowpipe jet, a supporting piece and a source of flame.
+
+The tube, condensation chamber, and jet are combined in the ordinary
+Black's blowpipe, such as is used for blowpipe tests in qualitative
+analysis; it consists of a conical tin tube having a mouthpiece at the
+small end and a side tube which carries a brass jet. A support for such
+a blowpipe may be cut out of a piece of brass or tin-plate, and should
+be fastened to a small, flat, wooden board. A source of flame may
+consist of an ordinary brass elbow, such as is used on gas fittings, and
+into which a piece of thin brass tube (the body of a fish-tail burner
+from which the perforated non-metallic plug has been removed will serve
+quite well) has been fitted. It is an advantage to flatten the brass
+tube somewhat and to file the flattened end to a slope which corresponds
+with the angle at which the blowpipe jet enters the burner. The whole
+source of the flame should be mounted on a separate base, in order that
+it may be moved while adjusting the apparatus to the best relative
+positions of flame and blowpipe jet. The complete apparatus is shown by
+_a_, Fig. 16.
+
+[Illustration: Fig. 16]
+
+In order to take full advantage of this blowpipe, it is desirable that
+the student should learn to maintain a steady steam of air with his
+mouth and, at the same time, be able to breathe. This requires a little
+practice.
+
+As a first exercise in breathing, before trying to breathe while using
+the mouth blowpipe, the student should close his mouth and inflate his
+cheeks with air; now, still keeping his cheeks tightly inflated, he
+should attempt to breathe through the nose. At first, this may be found
+rather difficult, but it becomes remarkably easy after a little
+practice. When he has mastered this, the student may practise the same
+operation, but with the blowpipe. It is important to bear in mind that
+the cheeks, not the lungs, form the reservoir for air used in
+maintaining the blowpipe flame. After a while, the student will find
+that he can maintain a steady air pressure and yet breathe with complete
+comfort.
+
+In adjusting the flame, care should be taken not to blow so hard as to
+produce a ragged and noisy cone of fire. A small jet, such as that
+commonly used on a mouth blowpipe, will with care give a pointed and
+quiet flame, having an appearance similar to that shown in the
+illustration.
+
+With a blowpipe like this, it is quite easy to seal glass tubes up to an
+inch in diameter, to join tubes up to half an inch in diameter, to bend
+tubes, to blow small bulbs, and to make the simpler forms of internal
+seal; but the provision for condensation of moisture is not ideal, and
+prolonged use of such a blowpipe also tends to produce undue fatigue.
+
+_A Mouth Blowpipe With an Expanding Reservoir._--This form of blowpipe
+can be made to give most excellent results; it is highly portable, and
+does not produce nearly so much fatigue when used continuously as the
+blowpipe described in the last section. Various slight modifications
+have been made in its construction during the last eighty years, but
+that described below will be found quite satisfactory.
+
+The apparatus consists of a tube through which air is blown from the
+mouth, a valve through which the air passes into an expanding reservoir,
+and a blowpipe jet in communication with the reservoir.
+
+In making the valve, several essentials have to be remembered; it must
+allow a free passage of air into the reservoir, it must open easily, and
+must close quickly. A satisfactory form of valve is that shown by _b_,
+Fig. 16. The moving part consists of a light glass bulb of about
+three-eights of an inch diameter and having a glass stem of rather under
+one-eighth diameter and about an inch and a half long. This stem rests
+in a guide at the end of a brass tube, the bulb contacting against the
+other end which is approximately shaped. The bulb and its seating are
+ground air-tight. A very light spring holds the bulb in position.
+
+This valve is fitted into a metal or glass T piece, one limb of which
+leads to the air reservoir and the other limb leads to the blowpipe jet;
+the limb containing the valve leads to the tube through which the air is
+blown in.
+
+A convenient reservoir may be made from a fairly large football bladder.
+A network of string should be fitted over the outside of the bladder and
+the strings should terminate in a hook on which a weight can be hung, in
+order to provide a means of adjusting the pressure at which the air is
+delivered to the jet. This bladder should be washed out and allowed to
+drain after use.
+
+The air tube which passes from the valve to the mouth may conveniently
+be made of brass, but, in order to avoid the continued contact of metal
+with the lips of the operator, it should be fitted with a non-metallic
+mouthpiece. It is an advantage from the point of view of portability to
+have the air tube easily detachable from the T piece containing the
+valve.
+
+The blowpipe jets, of which there may be several with advantage, may be
+made of glass tubing, bent to the most convenient angle and having an
+enlargement or bulb at some point in the tube. This bulb serves as a
+final condensing place for any traces of moisture that may escape from
+the larger reservoir.
+
+The whole device, blowing tube, reservoir, and T piece may be fastened
+to a clamp, so that it can be secured on the edge of any table where
+blowpipe work is to be carried out. If the blowpipe is to be used with
+gas, the form of burner described under. "A Simple Form of Blowpipe"
+will be found quite satisfactory.
+
+_The Use of Oil, or Other Non-Gaseous Fuels._--Although gas, when
+available, is usually preferred on account of its convenience, there are
+several other fuels which give a hotter flame. They have, also, the
+additional advantage of not requiring any connecting pipes; but each has
+its own disadvantage.
+
+One liquid fuel deserves special mention as being rather less desirable
+than the others; this is alcohol. Although very convenient in use, it
+has the disadvantage of being rather too highly inflammable and capable
+of burning without a wick, thus involving a certain fire risk; the flame
+is scarcely visible in a bright light, and the heat given by either the
+ordinary flame or the blowpipe flame produced from alcohol is
+considerably less than that from a similar flame in which coal gas is
+used. For small work, however, the facility with which a spirit lamp may
+be lighted may more than counterbalance these disadvantages at times.
+
+_Paraffin Wax._--Where there is no coal gas available and the blowpipe
+is only required at intervals, and especially where high portability is
+required, there are few fuels so convenient as paraffin wax. This may be
+obtained in pieces of a satisfactory size by cutting paraffin candles,
+from which the wick has been withdrawn, into lengths of about half an
+inch. These cut pieces have the advantage over any oily fuel, such as
+colza oil, that they can be wrapped in paper or carried in a cardboard
+box; further they will keep indefinitely, even in the presence of air,
+without undergoing any perceptible change.
+
+_Forms of Lamp for Paraffin Wax._--Probably, the best form is that
+devised by Thomas Bolas, and described by him in the _Journal of the
+Society of Arts_, December 2nd, 1898. This lamp consists of a small open
+tray of iron, through which pass three or more flat tubes, and between
+these tubes are placed small flat pieces of wick, the fit being such
+that the pieces of wick may be adjusted easily by means of a pair of
+pointed tweezers.
+
+The flame thus obtained, instead of having one large hollow, is broken
+or divided so that the combustion is concentrated into a smaller area,
+and the air blast, which is directed across the flame, carries the flame
+with it in a more complete manner than is the case with the ordinary
+flame; a more thorough combustion being realised by this arrangement.
+
+Another advantage is the ease with which the wick may be changed and a
+larger or smaller wick inserted to suit the flame to any size of air
+jet.
+
+This form of lamp may be used for oily fuel, although it is specially
+suitable for paraffin wax.
+
+Two small pieces of bent tin-plate may be used as side covers, and these
+serve to adjust the flame within certain limits. A tin-plate cover which
+fits easily over the whole lamp serves as an extinguisher. The complete
+lamp is shown by _d_, Fig. 16, and this figure shows also a quick-change
+air-jet device, the whole arrangement forming a blowpipe for use where a
+non-gaseous fuel is to be employed.
+
+Although the lamp just described is desirable when complete control over
+the size of the flame is necessary, and if the ideal conditions and
+maximum heat are to be obtained, yet a simpler form of lamp will be
+found to give very good results. Such a lamp may consist of a flat tin
+tray, having a diameter of about three and a half inches and a depth of
+about one inch. In this tray is a tin support for the wick, and the wick
+itself may consist of a bundle of soft cotton, for example, a loosely
+rolled piece of cotton cloth, but in either case the top of the wick
+should be cut to approximately the same angle as that at which the
+blowpipe jet meets the flame.
+
+In using paraffin wax as a fuel, it is necessary to see that sufficient
+wax reaches the wick to prevent charring during the first few minutes
+before the bulk of the wax is melted.
+
+_Animal and Vegetable Oils._--Almost any oil may be used as a fuel, but
+many tend to become hard and gummy if allowed to stand in the air for
+any considerable time. When this happens, the wick becomes clogged and
+it is impossible to obtain a good flame. A number of the oils tend,
+also, to produce rather strongly smelling smoke.
+
+_A Flame-Guard for Use With Non-Gaseous Fuels._--In order to avoid the
+eye-strain produced by the luminous base of the flame from a wick
+burning paraffin wax or oil, it is often advantageous to make a small
+tunnel of tin-plate, which can be rested on the sides of the lamp and
+rises over the top of the wick. Such a flame guard is shown by _e_, Fig.
+16.
+
+_Small Rods and Tubes from Glass Scrap_:--It is scarcely practicable to
+make small quantities of good glass with the blowpipe flame as the only
+source of heat, but it is less difficult to make small rods or tubes
+from glass scrap, and the ability to do this is sometimes of
+considerable value when a small tube has to be joined on to some special
+piece of apparatus made of glass of unknown composition. It may be
+possible to obtain some fragments of similar glass, either from a broken
+part of the apparatus or from a similar piece, and from these fragments
+small tubes or rods can be made.
+
+The fragments of glass may be melted together on the end of a clay
+pipe-stem, care being taken to avoid trapping air bubbles as fresh
+fragments are added to the molten mass. When a sufficient quantity of
+glass has been accumulated, the viscous mass may be drawn out into a rod
+by bringing another pipe-stem into contact with the hot mass, rotating
+both pipe-stems steadily, and separating them until a rod of the desired
+size has been obtained.
+
+If, on the other hand, it is desired to produce a tube from the mass of
+heated glass, the mass should be blown hollow before the pipe-stems
+supporting it are separated.
+
+_Methods of Manufacture._--When the student has familiarised himself
+with the more common operations and processes used in glass-blowing, he
+will be in a position to increase his skill and knowledge of special
+methods by a critical examination of various examples of commercial
+work. There are few exercises more valuable than such an examination,
+combined with an attempt to reconstruct the stages and the methods by
+which the article chosen for examination was made.
+
+Obviously, it is impossible to give full details of all constructions in
+a small text-book; but it is easy to give an example of the
+constructional methods employed in the making of almost any piece of
+light blown-glass apparatus, and these methods should prove of special
+value when apparatus of a new pattern has to be evolved for the purposes
+of research. That is to say, one designs the apparatus required, applies
+known methods of construction as far as possible, and, by the
+examination of commercial apparatus having similar features, evolves the
+new methods required. For an exercise in such a process of
+reconstruction we may well take an ordinary commercial vacuum tube, such
+as that shown by _a_, Fig. 17.
+
+[Illustration: Fig. 17]
+
+In the tube from which this drawing was made, it was found that the
+spiral in the middle bulb was of a slightly yellowish colour and gave a
+green fluorescence when the electric discharge was passed through the
+tube; that is to say, the spiral is made of uranium-glass, which is
+usually a soda-glass containing trace of uranium, and hence differing
+slightly in composition from the ordinary glasses. The two enclosed
+tubes which are bent into a series of S bends gave a pink fluorescence,
+which indicates lead-glass; and the remainder of the tube fluoresced
+with an apple-green colour; this suggests ordinary soda-glass. We have,
+therefore, a piece of apparatus in which three dissimilar glasses are
+joined, while, at the same time, that apparatus contains a number of
+internal seals, and it is not probable that the dissimilar glasses will
+have their coefficients of expansion so nearly alike as to permit of a
+stable internal seal being made if one part of the seal consists of a
+glass differing from that of the other part.
+
+These considerations lead us to a closer examination of the joins where
+the dissimilar glasses are introduced, and we find that in no case is
+the internal seal made between dissimilar glasses, but that a soda-glass
+extension is joined on to both the uranium-glass tube and the lead-glass
+tubes at a point about half an inch before the internal seal commences.
+Careful examination of these joins shows that the change from one glass
+to another is not abrupt but gradual. Such a transitional joint may be
+made by taking a length of soda-glass tubing, sealing the end and fusing
+a minute bead of the other glass on to the sealed end, the end is then
+expanded and another bead of the other glass added, this bead is
+expanded and the operation is repeated, thus building up a tube, and,
+finally, the tube of the other glass is joined on to the end of this.
+
+We are now concerned with the question of the insertion of the
+uranium-glass spiral into the bulb (see p. 38). Obviously the spiral is
+too large to pass through the necks of the bulb, and it is difficult to
+imagine that the spiral was obtained by the insertion of a length of
+straight tubing which was bent after entering the bulb; therefore, the
+only remaining method is that the spiral was made first and the
+soda-glass extensions fastened on, and that the bulb was blown, cut in
+halves and the spiral inserted, and the two halves were then rejoined.
+That this was actually the case is confirmed by traces of a join which
+are just visible round the middle of the bulb. The insertion of the
+spiral and the making of the first internal seal are shown by _b_, and
+_c_.
+
+There is one detail in making the second join of the spiral to the bulb
+which calls for attention, and the small branch, similar to an
+exhaustion branch, at the side of the bulb provides a clue to this. If
+an attempt were made to complete the second internal seal through a
+closed bulb it would be impossible to obtain a good result, as the
+air-pressure in the bulb would not be under control when once union was
+effected, and further heating of the air in the bulb would cause
+expansion and perforate the wall near the second internal seal; we
+therefore make a small branch which can be left open and through which
+such air-pressure as may be found necessary can be maintained.
+
+The third join, by which the lead-glass tube is joined to the soda-glass
+is made in stages similar to those in which the soda-glass and
+uranium-glass were joined; but the internal seal is most conveniently
+made by sliding a length of tubing over the lead-glass and fusing this
+tubing to the large diameter soda-glass tube to which the lead-glass is
+already joined. The first stage of this operation is illustrated by _d_.
+When this seal is completed, the end of the soda-glass tube is drawn off
+and sealed as shown in _e_, and at this stage a side tube or branch is
+joined on. The sealed end of the outer and large diameter soda-glass
+tube is heated until it contracts and fuses to the enlargement that has
+previously been joined to the lead-glass tube, and the end is burst out
+as shown in _f_. Another length of soda-glass is then joined on to the
+burst-out end, and this length of soda-glass tubing is drawn out to a
+thin-walled contraction; the non-contracted part is expanded to form the
+bulb, and a small exhaustion branch made on the side, the drawn-out
+portion being cut off, and an electrode, previously prepared by coating
+a part of its length with a suitable enamel, is introduced. The tube is
+tilted to keep the electrode away from the drawn-out end, which is
+melted off and sealed. A small perforation is made with a hot platinum
+or iron wire in the sealed end, the electrode is shaken into position,
+and the sealing is completed as explained on page 42.
+
+The remainder of the tube, that is to say the lead-glass tube and the
+bulb on the other side of the middle bulb, is completed in a similar
+manner.
+
+
+SUMMARY OF CONDITIONS NECESSARY FOR SUCCESS IN GLASS-BLOWING.
+
+For the convenience of the student, it may be well to summarise the
+chief essentials for success in glass-blowing, and at the same time to
+add such brief notes on the various methods as may seem desirable.
+
+_Adjustment of Blowpipe._--The air jet should be clean internally, and
+so centered as to give a flame having a well-defined blue portion, the
+tip of the flame should not be only slightly luminous but purple in
+colour. In the case of a blowpipe burning oil or wax fuel the flame may
+be a trifle more ragged without disadvantage.
+
+_Bellows and Blowing._--The bellows should be adjusted to deliver air at
+constant pressure, either by insertion of a tap or, better, by attention
+to the wind reservoir if necessary. The movement of the foot in blowing
+should be steady, not jerky.
+
+_Heating Glass._--The tube or rod should be heated cautiously until it
+has reached its softening point in its thickest part. Steady rotation of
+the glass during the heating is almost essential.
+
+_Blowing a Bulb or Expanding a Join._--Prolonged heating is necessary in
+order that the thick parts may be heated completely through. Blowing
+should take place by stages, in order that the thin parts, which tend
+to expand first, have time to cool. The thick parts can then be expanded
+by further blowing and thus a bulb or expansion of even thickness can be
+obtained.
+
+_Cutting Glass._--The most useful method for general use is by means of
+the file or glass-blowers' knife. Either file or knife must be kept
+sharp by grinding. Neither file nor knife should be used on hot glass.
+The diamond and wheel cutter are useful for cutting sheet-glass, and
+when the diamond is employed a singing noise is an indication of a
+satisfactory cut.
+
+_Leading a Crack._--A crack may be led in any desired direction by means
+of a bead of hot glass or a small gas flame. The glass which it is
+desired to crack should be heated at a point slightly in advance of the
+crack, which will extend in the direction of the source of the heat.
+
+_Turning Out the End of a Tube._--This is done by heating the end of the
+tube and rotating it against an iron rod. The rod must be kept polished
+and free from rust, and it must not be allowed to become too hot while
+in use, otherwise the glass will stick to it.
+
+_Joining Unlike Glasses._--Joints between unlike glasses are often
+unstable. When such joints are made it is desirable to blow them as thin
+as possible, and to avoid the junction of unlike glasses in any complex
+joint, such as an internal seal. A transitional portion of tubing may be
+built up by the successive addition and interfusion of beads of one of
+the glasses to the end of a sealed tube consisting of the other glass.
+
+_Joining a Tube to a Very Thin Bulb._--The bulb may be thickened at the
+point of union by fusing on a bead of glass and expanding this slightly.
+A small central portion of the expanded part may then be perforated by
+bursting and the tube joined on.
+
+_Insertion of One Bulb Within Another._--A bulb may be divided into two
+halves by leading a crack round it and the inner bulb is then
+introduced. The two halves of the outer bulb may be fitted together
+(care being taken to avoid any damage to the edges), and the bulb may be
+completed by rotating the contacting edges before the blowpipe until
+they are soft, and then expanding slightly by means of air-pressure.
+
+_Annealing._--For most purposes, in the case of thin, blowpipe-made or
+lamp-blown glass apparatus, it is sufficient to cool slowly by rotating
+the finished article over a smoky flame and setting it aside in a place
+free from draughts, and where the hot glass will not come in contact
+with anything.
+
+Simple bulbs and joints do not even need this smoking; but thick
+articles, and especially those that are to be subjected to the stress of
+grinding, need more prolonged annealing in a special oven.
+
+_Use of Lead-Glass._--When lead-glass is to be used, the blowpipe flame
+should be in good adjustment and the glass should not be allowed to
+approach so near to the blue cone as to be blackened. Slight blackening
+may often be removed by heating the glass in the extreme end of the
+flame.
+
+Lead-glass articles tend to be rather more stable than similar articles
+of soda-glass.
+
+_Combustion-Glass._--This may be worked more easily if a small
+percentage of oxygen is introduced into the air with which the blowpipe
+flame is produced. If the air is replaced entirely by oxygen there is a
+risk of damaging the blowpipe jet, unless a special blowpipe is
+employed.
+
+_Internal Seal._--There are two ways of making these, one, in which the
+inner portion of the tube is fused on to the inside of the bulb or tube
+through which it is to pass, an opening is made by bursting and the
+outer tube is joined on. This is a quick and in some ways more
+satisfactory method than the other, in which there is no separate inner
+piece.
+
+_Rubber Blowing Tube._--In complicated work it is often convenient to
+use a thin rubber blowing-tube which is connected with the work either
+by a cork and piece of glass tubing or by fitting over a drawn-out end.
+The use of such a blowing-tube avoids the inconvenience of raising the
+work to the mouth when internal air-pressure is required. One end of the
+rubber tube is retained in the mouth during work.
+
+_General Notes._--A large amount of glass-blowing is spoiled through
+carelessness in arranging the work beforehand. The student should have
+every detail of his manipulation clearly in mind before he commences the
+work; he should not trust to evolving the method during the actual
+manipulation.
+
+Undue haste is another fruitful source of failure. Practically every
+operation in glass-blowing can be carried out in a perfectly leisurely
+manner, and it is better to err rather on the side of deliberation than
+on the side of haste.
+
+If, as will doubtless happen at times, a piece of work gives trouble and
+it is necessary to pause and consider the whole question, or if for any
+other reason it is necessary to stop during the construction of a
+partially finished join or other operation, great care should be taken
+not to allow the work to cool. A large, brush-like flame may be produced
+by increasing the amount of gas admitted to the blowpipe, and the work
+should be held just in front of the current of hot air produced by such
+a flame.
+
+It will then be possible to continue work on this without causing it to
+crack when further heat is applied.
+
+As time goes on, the student will find an increasing confidence in his
+ability to manipulate the soft glass, and with increasing confidence
+will come rapidly increasing power of manipulation. Perhaps the greatest
+obstacle to success in glass-blowing is undue haste in manipulation.
+
+
+
+
+INDEX
+
+
+Absorption bulbs, 21, 23.
+
+Airtube, flexible, 8, 102.
+
+Alarm thermometer, 45.
+
+Annealing, 7, 60.
+
+
+Bellows, adjusting pressure of, 5, 6.
+
+Bellows, foot, 5, 6.
+
+Bending tubes, 23.
+
+Blackening, 58, 101.
+
+Branching, 18, 19.
+
+Brushes of spun glass, 53.
+
+Blowpipe flame, quality of, 3.
+
+Blowpipe for mouth blast, 80, 82, 84.
+
+Blowpipe, for paraffin wax, 82, 88.
+
+Blowpipe, Herepath's, 2.
+
+Blowpipe jet, centring, 3, 98.
+
+Blowpipe jet, dirt in, 3.
+
+Blowpipe jet, multiple, 4, 40.
+
+Blowpipe, Letcher's, change, 4.
+
+Blowpipe, simple form of, 80.
+
+Bulb, medially on tube, 22.
+
+Bulbs, 19, 20, 22, 38, 98.
+
+Bulbs, absorption, (Liebig's), 21, 23.
+
+Bulbs, dividing, 39, 95.
+
+Bulbs from rod, 25.
+
+Bulbs, internal, 38.
+
+Bulbs, thick, 21.
+
+
+Cages, from glass rod, 24, 25, 27.
+
+Calibration, 72.
+
+Carius tubes, 16.
+
+Condenser, Liebig's, 37.
+
+Condensers, various, 37, 38.
+
+Cone, carbon, 8.
+
+Crack, leading, 30, 99.
+
+Cracking, subversive, 103.
+
+Cutting glass with diamond, 30.
+
+Cutting tubes, 11, 99.
+
+
+Diamond (glazier's), use of, 30.
+
+Dissimilar glass, joining of, 22, 94.
+
+Drilling, 61.
+
+
+Electrodes, sealing in, 42, 97.
+
+Etching glass, 70.
+
+Extemporised appliances, 80.
+
+Examination of apparatus, 93.
+
+
+Failure, Haste chief Source of, 103.
+
+Failures, Notes as to, 97.
+
+File, with oblique ground edge, 7.
+
+Filing glass, 63.
+
+Filter pumps, 35
+
+Foot, 25
+
+Fuels various, 82, 86, 87, 89.
+
+Funnel, thistle, 23.
+
+
+General principles and precautions, 1, 97
+
+Glass, varieties of, 9, 55, 91-97.
+
+Graduation, 72-76
+
+
+Haste, Source of Failure, 103
+
+Heat reflector, asbestos, 7.
+
+Heating, intensive, 7, 57.
+
+Heating precautions, 12, 98
+
+
+Joining dissimilar glass, 22.
+
+Joining glass to metal, 76.
+
+Joining tubes, 16, 94, 100.
+
+
+Knife, Glass blower's, 7, 99.
+
+
+Lenses, grinding, 63.
+
+
+Marking glass, 69.
+
+Methods, analytic study of, 91, 93.
+
+
+Oxygen for intensive heating, 57, 101.
+
+
+Precautions and General Principles, 1, 97.
+
+Pumps, Filter, 35.
+
+Pumps, Sprengel, 49, 50.
+
+
+Re-entering branch, 40.
+
+Reflector of heat, asbestos, 7.
+
+Rod, uses and articles from, 17, 25, 27, 28.
+
+Rod, blowing to hollow, 17, 25, 26, 91.
+
+
+Scrap glass, working, 90.
+
+Sealing tubes, 12, 13, 14.
+
+Sealed tubes for pressure, 15, 16.
+
+Sealing in of Electrodes, 42, 97.
+
+Seals, internal (airtraps), 32, 102.
+
+Silvering glass, 77.
+
+Soldering glass, 76.
+
+Soxhlet-tube, 40.
+
+Spirals, 23, 95.
+
+Spray arrester, 34.
+
+Spray producers, 36.
+
+Sprengel pumps, 49, 50.
+
+Spinning glass, 51.
+
+Stopcocks, 60, 66.
+
+Stoppering, 63.
+
+Stirrers, 28, 29.
+
+Summary as to precautions and failures, 97.
+
+
+Taps, 60, 66.
+
+Thermometers, Various, 44-49.
+
+Thermo-regulator, 24.
+
+Thistle Funnel, 23.
+
+Tools, Various small, 7.
+
+Turn-pins, 7, 8, 99.
+
+Turning out open ends, 14, 99.
+
+
+PRINTED IN GREAT BRITAIN BY
+W. JOLLY & SONS, LTD., PRINTERS, ABERDEEN.
+
+
+
+
+
+End of the Project Gutenberg EBook of A Handbook of Laboratory Glass-Blowing, by
+Bernard D. Bolas
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