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diff --git a/32307-h/32307-h.htm b/32307-h/32307-h.htm new file mode 100644 index 0000000..60a81c0 --- /dev/null +++ b/32307-h/32307-h.htm @@ -0,0 +1,2369 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" /> + <title> + The Project Gutenberg eBook of A Brief Account of Radio-activity, by Francis P. Venable. + </title> + <style type="text/css"> + + p { margin-top: .75em; + text-align: justify; + margin-bottom: .75em; + } + h1,h2,h3,h4,h5,h6 { + text-align: center; /* all headings centered */ + clear: both; + } + hr { width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: auto; + margin-right: auto; + clear: both; + } + + table {margin-left: auto; margin-right: auto;} + + body{margin-left: 10%; + margin-right: 10%; + } + + .pagenum { /* uncomment the next line for invisible page numbers */ + /* visibility: hidden; */ + position: absolute; + left: 92%; + font-size: smaller; + text-align: right; + } /* page numbers */ + + .blockquot{margin-left: 5%; margin-right: 10%;} + .sidenote {width: 20%; padding-bottom: .5em; padding-top: .5em; + padding-left: .5em; padding-right: .5em; margin-right: 1em; + float: left; clear: left; margin-top: 1em; + font-size: smaller; color: black; background: #eeeeee; border: dashed 1px;} + + .center {text-align: center;} + .smcap {font-variant: small-caps;} + + .caption {font-weight: bold;} + + .figcenter {margin: auto; text-align: center;} + + .figright {float: right; clear: right; margin-left: 1em; margin-bottom: 1em; + margin-top: 1em; margin-right: 0; padding: 0; text-align: center;} + + .footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + .footnote .label {position: absolute; right: 84%; text-align: right;} + .fnanchor {vertical-align: super; font-size: .8em; text-decoration: none;} + + </style> + </head> +<body> + + +<pre> + +The Project Gutenberg EBook of A Brief Account of Radio-activity, by +Francis Preston Venable + +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 Brief Account of Radio-activity + +Author: Francis Preston Venable + +Release Date: May 9, 2010 [EBook #32307] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK A BRIEF ACCOUNT OF RADIO-ACTIVITY *** + + + + +Produced by The Online Distributed Proofreading Team at +http://www.pgdp.net (This file was produced from images +generously made available by The Internet Archive/American +Libraries.) + + + + + + +</pre> + + + + +<h1>A BRIEF ACCOUNT OF<br /> +RADIO-ACTIVITY</h1> + +<h4>BY</h4> + +<h2><span class="smcap">FRANCIS P. VENABLE, Ph.D., D.Sc., LL.D.</span></h2> + +<h5>PROFESSOR OF CHEMISTRY, UNIVERSITY OF NORTH CAROLINA<br /> +AUTHOR OF<br /> +"A SHORT HISTORY OF CHEMISTRY,"<br /> +"PERIODIC LAW," ETC.</h5> + +<h3>D. C. HEATH & CO., PUBLISHERS<br /> +<small>BOSTON NEW YORK CHICAGO</small></h3> + + + +<h4><span class="smcap">Copyright, 1917,<br /> +By D. C. Heath & Co.</span><br /> +<br /> +IA7</h4> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'>[Pg iii]</span></p> +<h2>PREFACE</h2> + + +<p>I have gathered the material for this little book because I have found +it a necessary filling out of the course for my class in general +chemistry. Such a course dealing with the composition and structure of +matter is left unfinished and in the air, as it were, unless the +marvellous facts and deductions from the study of radio-activity are +presented and discussed. The usual page or two given in the present +text-books are too condensed in their treatment to afford any +intelligent grasp of the subject, so I have put in book form the +lectures which I have hitherto felt forced to give.</p> + +<p>Perhaps the book may prove useful also to busy men in other branches +of science who wish to know something of radio-activity and have scant +leisure in which to read the larger treatises.</p> + +<p>It is needless to say that there is nothing original in the book +unless it be in part the grouping of facts and order of their +treatment. I have made free use of the writings of Rutherford, Soddy, +and J. J. Thomson, and would here express my debt to them—just a part +of that indebtedness which we all feel to these masters. I wish also +to acknowledge my obligations to Professor Bertram B. Boltwood for his +helpful suggestions in connection with this work. +<span class='pagenum'>[Pg iv]</span></p> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'>[Pg v]</span></p> +<h2>CONTENTS</h2> + + +<table border="0" cellpadding="5" cellspacing="0" summary="Table of Contents" width="80%"> +<tr> + <td colspan="2" align="center"><a href="#CHAPTER_I"><b>CHAPTER I</b></a></td> +</tr> +<tr> + <td align="center"><b>DISCOVERY OF RADIO-ACTIVITY</b></td> + <td align="right"><small>PAGE</small></td> +</tr> +<tr> + <td>The beginning—Radio-active bodies—An atomic property—Discovery +of new radio-active bodies—Discovery of Polonium—Discovery +of Radium—Other radio-active bodies found</td> + <td align="right"><a href="#Page_1">1</a></td> +</tr> +<tr> + <td colspan="2" align="center"><a href="#CHAPTER_II"><b>CHAPTER II</b></a></td> +</tr> +<tr> + <td colspan="2" align="center"><b>PROPERTIES OF THE RADIATIONS</b></td> +</tr> +<tr> + <td>Ionization of Gases—Experimental confirmation—Application of +electric field—Size and nature of ions—Photographing the +track of the ray—Action of radiations on photographic plates—Discharge +of electrified bodies—Scintillations on phosphorescent +bodies—Penetrating power—Magnetic deflection—Three +types of rays—Alpha rays—Beta rays—Gamma rays—Measurement +of radiations—Identifications of the rays</td> + <td align="right"><a href="#Page_7">7</a></td> +</tr> +<tr> + <td colspan="2" align="center"><a href="#CHAPTER_III"><b>CHAPTER III</b></a></td> +</tr> +<tr> + <td colspan="2" align="center"><b>CHANGES IN RADIO-ACTIVE BODIES</b></td> +</tr> +<tr> + <td>Radio-activity a permanent property—Induced activity—Discovery +of Uranium X—Conclusions drawn—Search for new radio-active +bodies—Methods of investigation—Nature of the +radiations—Life-periods—Equilibrium series</td> + <td align="right"><a href="#Page_17">17</a></td> +</tr> +<tr> + <td colspan="2" align="center"><a href="#CHAPTER_IV"><b>CHAPTER IV</b></a></td> +</tr> +<tr> + <td colspan="2" align="center"><b>NATURE OF THE ALPHA PARTICLE</b></td> +</tr> +<tr> + <td>Disintegrating of the elements—Identification of the rays—The +alpha rays—Alpha rays consist of solid particles—Electrical +charge—Helium formed from alpha particles—Discovery of +Helium—Characteristics of Helium—Table of constants</td> + <td align="right"><a href="#Page_25">25</a></td> +</tr> +<tr> + <td colspan="2" align="center"><a href="#CHAPTER_V"><b>CHAPTER V</b></a><span class='pagenum'>[Pg vi]</span></td> +</tr> +<tr> + <td colspan="2" align="center"><b>THE STRUCTURE OF THE ATOM</b></td> +</tr> +<tr> + <td>Properties of Radium—Energy evolved by radium—Necessity for a +disintegration theory—Disintegration theory—Constitution +of the atom—Rutherford's atom—Scattering of alpha particles—Stopping +power of substances</td> + <td align="right"><a href="#Page_32">32</a></td> +</tr> +<tr> + <td colspan="2" align="center"><a href="#CHAPTER_VI"><b>CHAPTER VI</b></a></td> +</tr> +<tr> + <td colspan="2" align="center"><b>RADIO-ACTIVITY AND CHEMICAL THEORY</b></td> +</tr> +<tr> + <td>Influence upon chemical theory—The periodic system—Basis of the +periodic system—Influence of positive nucleus—Determination +of the atomic number—Use of X-ray spectra—Changes caused +by ray-emission—Atomic weight losses—Lead the end product—Changes +of position in the periodic system—Changes from +loss of beta particles—Isotopes—Radio-activity in nature—Radio-active +products in the earth's crust—Presence in air and +soil waters—Cosmical radio-activity</td> + <td align="right"><a href="#Page_41">41</a></td> +</tr> +<tr> + <td><a href="#INDEX"><span class="smcap">Index</span></a></td> + <td align="right"><a href="#Page_53">53</a></td> +</tr> +</table> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'>[Pg vii]</span></p> +<h2>A BRIEF ACCOUNT OF<br /> +RADIO-ACTIVITY</h2> + +<p><span class='pagenum'>[Pg viii]</span></p> + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> +<h1>A BRIEF ACCOUNT OF<br /> +RADIO-ACTIVITY</h1> + +<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I</h2> + +<h3>DISCOVERY OF RADIO-ACTIVITY</h3> + + +<p>The object of this brief treatise is to give a simple +account of the development of our knowledge of radio-activity +and its bearing on chemical and physical +science. Mathematical processes will be omitted, as +it is sufficient to give the assured results from calculations +which are likely to be beyond the training of +the reader. Experimental evidence will be given in +detail wherever it is fundamental and necessary to a +confident grasp of some of the marvelous deductions +in this new branch of science. Theories cannot be +avoided, but the facts remain while theories grow old +and are discarded for others more in accord with the +facts.</p> + +<div class="sidenote">The Beginning</div> + +<p>As so often happens in the history of science, the +opening up of this new field with its fascinating disclosures +was due to an investigation undertaken +for another purpose but painstakingly +carried out with a mind open to the truth wherever it +might lead.</p> + +<p><span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span> +In 1895, Röntgen modestly announced his discovery +of the <i>X</i> rays. This attracted immediate and intense +interest. Among those who undertook to follow up +these phenomena was Becquerel, who, because of the +apparent connection with phosphorescence, tried the +action of a number of phosphorescent substances upon +the photographic plate, the most striking characteristic +of the <i>X</i> rays being their effect upon such sensitive +plates. In these experiments he obtained no results +until he tried salts of uranium, recalling previous +observations of his as to their phosphorescence. Distinct +action was noted. Furthermore, he proved that +this had no connection with the phenomenon of phosphorescence, +as both uranic and uranous salts were +active and the latter show no phosphorescence. Becquerel +announced his discoveries in 1896 and this was +the beginning of the new science of radio-activity.</p> + +<div class="sidenote">Radio-active bodies</div> + +<p>The rays given off by uranium and its salts were +found to differ from the <i>X</i> rays. They showed no +appreciable variation in intensity, no previous +exposure of the substance to light +was necessary, and neither changes of temperature +nor any other physical or chemical agency affected +them.</p> + +<p>At first uranium and its compounds were the only +known source of these new radiations, but many other +substances were examined and two years later thorium +and its compounds were added to the list. In general +the discharging action seemed about the same. Other +<span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span> +elements and ordinary substances show a minute +activity. Only potassium and rubidium have a greater +activity than this, and theirs is only about one-thousandth +that of uranium.</p> + +<div class="sidenote">An Atomic Property</div> + +<p>In the examination of uranium and thorium compounds +it was found that the activity was determined +by the uranium and thorium present; it +was proportto the amount ofional these +elements present and independent of the nature of the +other elements composing the compound. The conclusion +was, therefore, that the activity was an inherent +property of the atoms of uranium and thorium, that is, +an atomic property. This was a long step forward and +introduced into science the conception of a new property +of matter, or at least of certain forms of matter.</p> + +<div class="sidenote">Discovery of New Radio-active Bodies</div> + +<p>In examining a large number of minerals containing +uranium and thorium, Mme. Curie made the +important observation that many of these +were more active than the elements themselves. +In measuring the activity she +made use of the electrical method which will be described +later. In the following table giving her results +for uranium minerals the numbers under <i>i</i> give the +maximum current in amperes. They serve simply for +comparison.</p> + + +<table border="0" cellpadding="2" cellspacing="0" summary="Uranium Minerals" width="80%"> +<tr> + <td align="center"> </td> + <td align="center"><i>i</i></td> +</tr> +<tr> + <td>Pitchblende from Joachimsthal</td> + <td align="center">7.0 × 10<sup>-11</sup></td> +</tr> +<tr> + <td>Clevite</td> + <td align="center">1.4 × 10<sup>-11</sup></td> +</tr> +<tr> + <td>Chalcolite</td> + <td align="center">5.2 × 10<sup>-11</sup></td> +</tr> +<tr> + <td>Autunite</td> + <td align="center">2.7 × 10<sup>-11</sup></td> +</tr> +<tr> + <td>Carnotite</td> + <td align="center">6.2 × 10<sup>-11</sup></td> +</tr> +<tr> + <td>Uranium</td> + <td align="center">2.3 × 10<sup>-11</sup></td> +</tr> +<tr> + <td>Uranium and potassium sulphate</td> + <td align="center">0.7 × 10<sup>-11</sup></td> +</tr> +<tr> + <td>Uranium and copper phosphate</td> + <td align="center">0.9 × 10<sup>-11</sup></td> +</tr> +</table> + +<p><span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span> +The last three are pure uranium and compounds of +that element given for comparison with the first five, +which are naturally occurring minerals. The last compound +has the same composition as chalcolite and is +simply the artificially prepared mineral. It has the +activity which would be calculated from the proportion +of uranium present, the copper and phosphoric +acid contributing no activity.</p> + +<p>Since the activity is not dependent upon the composition +but upon the amount of uranium present, the activity +in all of the minerals should be less than that of +uranium. On the contrary, it is several times greater. +Natural and artificial chalcolite also show a marked +difference in favor of the former. The supposition +was a natural one, therefore, that these minerals contained +small quantities of an element, or elements, +undetected by ordinary analysis and having a much +greater activity than uranium. Similar results were +obtained in the examination of thorium minerals and +thorium salts.</p> + +<div class="sidenote">Discovery of Polonium</div> + +<p>Following up this supposition, M. and Mme. Curie set themselves the task of +separating this unknown substance. Starting with pitchblende, a systematic chemical +examination was made. This is an exceedingly complex mineral, containing +<span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span> +many elements. The processes were laborious and demanded much time and +minute care. They need not be described here. It is sufficient to say +that along with bismuth a very active substance was separated, to +which Mme. Curie gave the name of polonium for Poland, her native +land. Its complete isolation is very difficult and sufficient +quantities of the pure substance have not been obtained to determine +its atomic weight and other properties, but some of the lines of its +spectrum have been determined. Chemically it is very closely analogous +to bismuth.</p> + +<div class="sidenote">Discovery of Radium</div> + +<p>In a similar manner a barium precipitate was obtained from pitchblende +which contained a highly active substance. The pure chloride of this +body and barium can be prepared together and then separated by +fractional crystallization. To the new body thus found the name of +radium was given. It is similar in chemical properties to barium. Its +atomic weight has been determined by several careful investigators and +is accepted as 226. Its spectrum has been mapped and its general +properties are known. It is a silvery white, oxidizable metal. In one +ton of pitchblende about 0.2 gram of radium is present; this is about +5000 times greater than the amount of polonium present. The activity +of the products was depended upon as the guide in these separations. +The radium found is relatively enormously more active than the +pitchblende or uranium.</p> + +<div class="sidenote">Other Radio-active Bodies Found</div> + +<p>In the above separations use was made of relationships +<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span> +to bismuth and barium. Similarly, by taking advantage of chemical +relationship to the iron group of elements, another body was partially +separated by Debierne, to which he gave the name actinium. Boltwood +discovered in uranium minerals the presence of a body which he named +ionium, and which is so similar to thorium that it cannot be separated +from it. It, however, far exceeds thorium in activity.</p> + +<p>The lead which is present in uranium and thorium +minerals—apparently in fairly definite ratio to the amount of +uranium and thorium—is found, on separation and purification, to +possess radio-active properties. This activity is due to the presence +of a very small proportion of an active constituent called radio-lead, +which has chemical properties identical with those of ordinary lead. +The bulk of the lead obtained from radio-active minerals differs in +atomic weight from ordinary lead and appears also to be different +according to whether its source is a thorium or a uranium mineral.</p> + +<p>A large number of other radio-active substances have been separated +and some of their properties determined, but these were found by +different means and will be noted in their proper place. They number +in all more than thirty. The sources or parents of these are the +original uranium or thorium, and the products form regular series with +distinctive properties for each member.</p> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span></p> +<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II</h2> + +<h3>PROPERTIES OF THE RADIATIONS</h3> + + +<p>The activity of these radio-active bodies consists in the emission of +certain radiations which may be separated into rays and studied +through the phenomena which they cause.</p> + +<div class="sidenote">Ionization of Gases</div> + +<p>One of these phenomena is the power of forming ions or carriers of +electricity by the passage of the rays through a gas, thus ionizing +the gas. The details of an experiment will serve to make the meaning +of this ionization clear.</p> + +<div class="figcenter" style="width: 60%;"> +<img src="images/i015.jpg" width="100%" alt="Fig. 1." title="Fig. 1." /> +<span class="caption"><span class="smcap">Fig. 1.—Ionization of Gases.</span></span> +</div> + +<p>When this apparatus is set up a minute current will be observed +without the introduction of any radio-active matter. This, as +Rutherford says, has been found due mainly to a slight natural +radio-activity of the matter composing the plates. If radio-active matter +<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span> +is spread on plate <i>A</i>, which is connected with one pole of a grounded +battery, and if plate <i>B</i> is connected with an electrometer which is +also connected with the earth, a current is caused which increases +rapidly with the difference of potential between the plates, then more +slowly until a value is reached that changes only slightly with a +larger increase in the voltage.</p> + +<p>According to the theory of ionization, the radiation produces ions at +a constant rate. The ions carrying a positive charge are attracted to +plate <i>B</i>, while those negatively charged are attracted to plate <i>A</i>, +thus causing a current. These ions will recombine and neutralize their +charges if the opportunity is given. The number, therefore, increases +to a point at which the ions produced balance the number recombining.</p> + +<p>When an electric field is produced between the plates, the velocity of +the ions between the plates is increased in proportion to the strength +of the electric field. In a weak field the ions travel so slowly that +most of them recombine on the way and consequently the observed +current is very small. On increasing the voltage the speed of the ions +is increased, fewer recombine, the current increases, and, when the +condition for recombination is practically removed, it will have a +maximum value. This maximum current is called the saturation current +and the value of the potential difference required to give this +maximum current is called the saturation P.D. or saturation voltage.</p> + +<p>The picture, then, is this. The radiations separate +<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span> +the components of the gas into ions, or carriers of electricity, half +of which are charged negatively and half positively. In the electric +field those negatively charged seek the positive plate and those +positively charged seek the negative plate. If time is given, these +ions meet and recombine, their charges are neutralized, and there is +no current.</p> + +<div class="sidenote">Experimental Confirmation</div> + +<p>This theory of the ionization of gases has been most interestingly +confirmed by direct experiment. For instance, the ions may form nuclei +for the condensation of water, and in this way the existence of the +separate ions in the gas may be shown and the number present actually +counted.</p> + +<p>When air saturated with water vapor is allowed to expand suddenly, the +water present forms a mist of small globules. There are always small +dust particles in air and around these as nuclei the drops are formed. +These drops will settle and thus by repeated small expansions all dust +nuclei may be removed and no mist or cloud will be formed by further +expansions.</p> + +<p>If now the radiation from a radio-active body be introduced into the +condensation vessel, a new cloud is produced in which the water drops +are finer and more numerous according to the intensity of the rays. On +passing a strong beam of light through the condensation chamber, the +drops can readily be seen. These drops form on the ions produced by +the radiation.</p> + +<div class="sidenote">Application of Electric Field</div> + +<p>If the condensation chamber has two parallel plates +for the application of an electric field like that already +<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span> +described, the ions will be carried at once to the electrodes and +disappear. The rapidity of this action depends upon the strength of +the electric field and experiment shows that the stronger the field +the smaller the number of condensation drops formed. If there is no +electric field, a cloud can be produced some time after the shutting +off of the source of radiation, showing that time is required for the +recombination of the ions.</p> + +<div class="sidenote">Size and Nature of Ions</div> + +<p>If the drops are counted (there being special methods for this) and +the total current carried accurately measured, then the charge carried +by each ion may be calculated. This has been determined. The mass of +an ion compared with the mass of the molecules of gas in which it was +produced can also be approximately estimated. In the study of these +ions the view has been held that the charged ion attracted to itself a +cluster of molecules which surrounded the charged nucleus and traveled +with it. It is roughly estimated that about thirty molecules of the +gas cluster around each charged ion.</p> + +<div class="figright" style="width: 20%;"> +<img src="images/i019.jpg" width="100%" alt="Fig. 2." title="Fig. 2." /> +<span class="caption"><span class="smcap">Fig. 2.—Photograph +of the Track of an Ionizing Ray.</span></span> +</div> + +<div class="sidenote">Photographing the Track of the Ray</div> + +<p>Utilizing the fact that these ions with their clusters of molecules +form nuclei for the condensation of water vapor, C. T. R. Wilson has +by instantaneous photography been able to photograph the track of an +ionizing ray through air. The number of the ions produced, and hence +the number of drops, is so great that the trail is shown as a +continuous line. In the copy of this photograph it will be seen +<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span> +that at some distance from its source the straight trail is slightly +but abruptly bent. Near the end of its course there is another abrupt +and much sharper bend. These bends show where the ionizing ray, in +this case an alpha particle, has been deflected by more or less direct +collision with an atom. These collisions and the final disappearance +of the ray will be discussed later.</p> + +<div class="sidenote">Action of Radiations on Photographic Plates</div> + +<p>Taking up now other means of examining these radiations, it is well to +consider their action upon a photographic or sensitive plate. It will +be recalled that this was the method by which their existence was +originally detected. To illustrate the method, the following account +of how one such photograph was taken may be given.</p> + +<p>The plate was wrapped in two thicknesses of black paper. The objects +were placed upon this and the radio-active ore, separated by a board +one inch thick, was placed above. The exposure lasted five days. The +action is much less rapid and the result not so clearly defined as in +the case of photographs taken by <i>X</i> rays. Of course, the removal of +the board and the use of more concentrated preparations of radium +would give quicker and better results. The method, however, on +<span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span> +account of time consumed and lack of definition is ill adapted to +accurate work.</p> + +<div class="sidenote">Discharge of Electrified Bodies</div> + +<p>The radiations from radio-active bodies can discharge +both positively and negatively electrified bodies by +making the air surrounding them a conductor +of electricity. To demonstrate this, +use is made of an electroscope. If the +hinged leaf of such an instrument be electrically charged +and a radio-active body be brought into its neighborhood, +the electricity will be discharged and the leaf +return to its original position. The rapidity of this +discharge is used to measure the degree of activity of +the body giving off the radiation.</p> + +<div class="figcenter" style="width: 70%;"> +<img src="images/i021.jpg" width="100%" alt="Fig. 3." title="Fig. 3." /> +<span class="caption"><span class="smcap">Fig. 3—Photograph of Various Objects +taken by means of Pitchblende</span></span> +</div> + + +<div class="figcenter" style="width: 50%;"> +<img src="images/i020.jpg" width="100%" alt="Fig. 4." title="Fig. 4." /> +<span class="caption"><span class="smcap">Fig. 4.—Gold-leaf Electroscope.</span></span> +</div> + +<div class="blockquot"><p>The gold-leaf <i>L</i> is attached to a flat rod <i>R</i> +and is insulated inside the vessel by a piece of amber <i>S</i> supported +from the rod <i>P</i>. The system is charged by a bent rod <i>CC'</i> passing +through an ebonite stopper. After charging, it is removed from contact +with the gold-leaf system. The rods <i>P</i> and <i>C</i> and the cylinder are +then connected with the earth.</p></div> + + +<p><span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span></p> + +<div class="sidenote">Scintillations on Phosphorescent Bodies</div> + +<p>It was found by Crookes that a screen covered with phosphorescent zinc +sulphide was brightly lighted up when exposed to the radiations. This +is due to the bombardment of the zinc sulphide by a type of ray called +the alpha ray. Under a magnifying glass this light is seen to be made +up of a number of scintillating points of light and is not continuous, +each scintillation being of very short duration. By proper subdivision +of the field under the lens, the number of scintillations can be +counted with close accuracy.</p> + +<p>A simple form of apparatus called the spinthariscope has been devised +to show these scintillations. A zinc sulphide screen is fixed in one +end of a small tube and a plate carrying a trace of radium is placed +very close to it. The scintillations can be observed through an +adjustable lens at the other end of the tube. Outer light should be +cut off, as in a dark room. The screen then appears to be covered with +brilliant flashes of light. Other phosphorescent substances, such as +barium platino-cyanide, may be substituted for the zinc sulphide, but +they do not answer so well.</p> + +<div class="sidenote">Penetrating Power</div> + +<p>By penetrating power is meant the power exhibited by the rays of +passing through solids of different thicknesses and gases of various +depths. This power varies with different radiations and with the nature +of the solid or gas. For instance, a sheet of metallic foil may be used +and the effect of aluminum will differ from that of gold and the different +<span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span> +rays vary in penetrating power. In the case of gases air will differ +from hydrogen, and it is noticed that certain rays disappear after +penetrating a short distance, while others can penetrate further +before being lost.</p> + +<div class="sidenote">Magnetic Deflection</div> + +<p>If the radiations are subjected to the action of a strong magnetic +field, it is found that part of them are much deflected in the +magnetic field and describe circular orbits, part are only slightly +deflected and in the opposite direction from the first, and the +remaining rays are entirely unaffected.</p> + +<div class="figcenter" style="width: 60%;"> +<img src="images/i024.jpg" width="100%" alt="Fig. 5." title="Fig. 5." /> +<span class="caption"><span class="smcap">Fig. 5.—Showing Magnetic Deflection +of</span> α, β, <span class="smcap">and</span> γ <span class="smcap">Rays</span>.</span> +</div> + + +<div class="sidenote">Three Types of Rays</div> + +<p>By the use of these methods of investigation it is learned that the +radiations consist of three types of rays. These have been named the +alpha, beta, and gamma rays, respectively. Some radio-active bodies +emit all three types, some two, and some only one. The distinguishing +characteristic of these types of rays may be summed up as follows: +<span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span></p> + +<div class="sidenote">Alpha Rays</div> + +<p>The alpha rays have a positive electrical charge and a comparatively +low penetrating power. They are slightly deflected in strong magnetic +and electric fields. They have a great ionizing power and a velocity +about one-fifteenth that of light.</p> + +<div class="sidenote">Beta Rays</div> + +<p>The beta rays are negatively charged and have a greater penetrating +power than the alpha rays. They show a strong deflection in magnetic +and electric fields, have less ionizing power than the alpha rays, and +a velocity of the same order as light.</p> + +<div class="sidenote">Gamma Rays</div> + +<p>The gamma rays are very penetrating and are not deflected in the +magnetic or electric fields. They have the least ionizing power and a +very great velocity.</p> + +<p>The penetrating power of each type is complex and varies with the +source, so the statements given are but generalizations. The alpha +rays are projected particles which lose energy in penetrating matter. +As to the power of ionizing gases, if that for the α rays is +taken as 10,000, then the β rays would be approximately 100 and +the γ rays 1.</p> + +<div class="sidenote">Measurement of Radiations</div> + +<p>The rays are examined and measured in several ways: 1. By their action +on the sensitive photographic plates. The use of this method is +laborious, consumes time, and for comparative measurements of +intensity is uncertain as to effect.</p> + +<p>2. By electrical methods, using electroscopes, quadrant +<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> +electrometers, etc. These are the methods most used.</p> + +<p>3. By exposure to magnetic and electric fields, noting extent and +direction of deflection.</p> + +<p>4. By their relative absorption by solids and gases.</p> + +<p>5. By the scintillations on a zinc sulphide screen.</p> + +<div class="sidenote">Identification of the Rays</div> + +<p>The alpha rays have been identified as similar to the so-called canal +rays. These were first observed in the study of the <i>X</i> rays. When an +electrical discharge is passed through a vacuum tube with a cathode +having holes in it, luminous streams pass through the holes toward the +side away from the anode and the general direction of the stream. They +travel in straight lines and render certain substances phosphorescent. +These rays are slightly deflected by a magnetic field and in an +opposite direction from that taken by the cathode rays in their +deflection. The rays seem to be positive ions with masses never less +than that of the hydrogen atom. Their source is uncertain, but they +may be derived from the electrodes.</p> + +<p>The beta rays are identical in type with the cathode rays and are +negative electrons.</p> + +<p>The gamma rays are analogous to the <i>X</i> rays and are of the order of +light. They are in general considerably more penetrating than <i>X</i> +rays. For example, the gamma rays sent out by 30 milligrams of radium +can be detected by an electroscope after passing through 30 +centimeters of iron, a much greater thickness than +can be penetrated by the ordinary <i>X</i> rays.</p> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span></p> +<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III</h2> + +<h3>CHANGES IN RADIO-ACTIVE BODIES</h3> + + +<div class="sidenote">Is Radio-activity a Permanent Property?</div> + +<p>Is this power of emitting radiations a permanent property or is it +lost with the passage of time? The first investigations of the +activity of uranium and thorium showed no loss of intensity at the end +of several years, and radium also seemed to show no decrease in its +enormous activity. Polonium, however, was found to lose most of its +activity in a year, and later it appeared that some radio-active +substances lost most of their activity in the course of a few minutes +or hours.</p> + +<div class="sidenote">Induced Activity</div> + +<p>A phenomenon called induced or secondary radio-activity was also +observed. Thus a metal plate or wire exposed to the action of thorium +oxide for some hours became itself active. This induced activity was +not permanent but decreased to half its value in about eleven hours +and practically disappeared within a week. Similar phenomena were +observed when radium was substituted for thorium.</p> + +<div class="sidenote">Discovery of Uranium X</div> + +<p>In 1900 Crookes precipitated a solution of an active uranium +salt with ammonium carbonate. The precipitate was dissolved so +far as possible in an excess of the reagent, leaving an insoluble +residue. This residue was many hundred times more +<span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span> +active, weight for weight, than the original salt, and the solution +containing the salt was practically inactive. At the end of a year the +uranium salt had regained its activity while the residue had become +inactive.</p> + +<p>Another method of obtaining the same result is to dissolve +crystallized uranium nitrate in ether. Two layers of solution are +formed, one ether and the other water coming from the water of +crystallization. The aqueous layer is active, while the water layer is +inactive. Similarly, by adding barium chloride solution to a solution +of a salt of uranium and then precipitating the barium as sulphate, +the activity is transferred to this precipitate. These experiments +give proof of the formation and separation of a radio-active body by +ordinary chemical operations.</p> + +<p>So, too, in the case of thorium salts a substance can be obtained by +means of ammonium hydroxide which is several thousand times more +active than an equal weight of the original salt. After standing a +month, the separated material has lost its activity and the thorium +salt has regained it. Here, again, there is the formation, separation, +and loss of a radio-active body.</p> + +<div class="sidenote">Conclusions Drawn</div> + +<p>Now, these are ordinary chemical processes for the separation of +distinct chemical individuals. The results, therefore, lead naturally +to the conclusions: (1) it would seem that uranium and thorium are +themselves inactive and the activity is due to some other substance +formed by these elements; (2) this active substance is produced by some +<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span> +transformation in those elements, for on standing the activity is +regained. This latter conclusion is startling, for it indicates a +change in the atom which, up to the time of this discovery, was deemed +unchangeable under the influence of such physical and chemical changes +as were known to us.</p> + +<div class="sidenote">Search for New Radio-active Bodies</div> + +<p>The search for new radio-active bodies and the study of their +characteristics has been systematically and successfully carried on. +The bodies obtained in the above experiments were named uranium <i>X</i> +and thorium <i>X</i>, respectively. Further, it became clear from the +investigation of uranium minerals that radium, polonium, actinium, and +ionium originated from uranium. From thorium minerals a body was +separated called mesothorium, which was analogous to radium. Both +thorium and radium were found to give off a radio-active gas. The +first lost half of its activity in less than one minute. The second +was more stable and lost half of its activity in about four days. The +name radium emanation was given to the latter and it was found +chemically and physically to belong to the class of monatomic or noble +gases, such as helium, argon, neon, etc., which had been discovered by +Ramsay. In some cases the chemical action was determined and these new +bodies were found analogous to well-known elements, as radium to +barium, polonium to bismuth. The physical properties were investigated +and, where possible, spectra were mapped and atomic weights +determined.</p> + +<p><span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span> +It is clear, therefore, that these bodies are elemental in character +and as such are made up of distinct, similar atoms, just as the +commonly recognized elements are believed to be. In this way more than +thirty new elements have been added to the list. These new elements +are called radio-active elements, but it is an open question whether +all atoms do not possess this property in greater or less degree. +Certainly, it is possessed in varying degree by four of the old +elements widely separated in the Periodic System, namely, uranium, +thorium, rubidium, and potassium. The last two, while feebly active +themselves, do not form any secondary radio-active substance so far as +is known. Only two of the elements, then, can definitely be said to go +through these transformations. It is just possible that radio-activity +may be found to be a common property of all atoms and of all matter.</p> + +<div class="sidenote">Methods of Investigation</div> + +<p>It is important to know how these new bodies were discovered and +distinguished from one another. Two properties are relied upon. One is +the nature of the rays emitted and the other is the duration of the +activity. Of course, knowledge of the physical and chemical properties +is also of great importance whenever obtainable.</p> + +<div class="sidenote">Nature of the Radiations</div> + +<p>The nature of the radiation is a distinguishing characteristic, +though similarity here does not prove identity of substances. +Some emit α rays only, some emit β rays, some emit +two of the possible rays, as for instance, β and γ, and +<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span> +some emit all three. The rays may also differ in the velocity with +which they are emitted by different radio-active substances. Thus, in +the case of one substance the α rays may have a slightly greater +or less penetrating power than those emitted by some other substance, +and this may be true also of the other rays.</p> + +<div class="sidenote">Life Periods</div> + +<p>The duration of the activity is called the life period. This is +absolutely fixed for each body and furnishes the most important mode +of differentiating among them. It measures the relative stability and +is the time which must elapse before their activity is lost and they, +changing into something else, entirely disappear. The measure usually +adopted is the half-value period. Two hypotheses are made use of:</p> + +<p>1. That there is a constant production of fresh radio-active matter by +the radio-active body.</p> + +<p>2. That the activity of the matter so formed decreases according to an +exponential law with the time from the moment of its formation.</p> + +<p>These hypotheses agree with the experimental results. The decrease and +rise of activity, for example, of uranium and uranium <i>X</i>, and also of +thorium and thorium <i>X</i>, have been measured, plotted, and the +equations worked out.</p> + +<p>Manifestly, a state of equilibrium will be reached +when the rate of loss of activity of the matter already +produced is balanced by the activity of the new matter +<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span> +produced. This equilibrium and the knowledge of the rate of decrease +in general will have little value if this rate, like chemical changes, +is subject to the influence of chemical and physical conditions. The +rate of decrease has been found to be unaltered by any known chemical +or physical agency. For instance, neither the highest temperatures +applicable nor the cold of liquid air have any appreciable effect.</p> + +<div class="sidenote">Equilibrium Series</div> + +<p>In order to measure the disintegration of a radio-active body in units +of time so that the rate may be comparable with that of other +radio-active bodies, the relation between the amounts under +consideration must be a definite one. For this purpose equal weights +of the bodies are not taken, but use is made of the amounts which are +in equilibrium with a fixed amount of the parent substance.</p> + +<p>One gram of radium has been settled upon as the standard for that +series and a unit known as the "curie" has been adopted to express the +equilibrium quantity of radium emanation. Thus, a curie of radium +emanation (or niton) is the weight (or, as this is a gas, the volume +at standard pressure and temperature) of the emanation in equilibrium +with one gram of radium. This, by calculation and experiment, is found +to be 0.63 cubic millimeter. When this amount has been produced by one +gram of radium, the formation and decay will exactly balance one +another. This is, therefore, one curie of emanation.</p> + +<p><span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span> +The measurement of the rate of decay is difficult but can be carried +out with great accuracy, even down to seconds, in the case of certain +short-lived bodies. Errors crept in at first from the failure to +completely separate the substances produced in the series, and +sometimes because of the simultaneous production of two substances.</p> + +<p>As stated, the decay follows an exponential law. The time required for +the decay of activity to half-value does not mean, therefore, that +there will be total decay in twice that time. Thus the half-value +period for uranium <i>X</i> is about 22 days. The period for complete decay +is about 160 days. This half-value period corresponds to the +half-value recovery period of uranium, which is also 22 days.</p> + +<p>These were the earlier figures obtained for uranium <i>X</i> and they +illustrate some of the difficulties surrounding such determinations. +It was found later that the body examined as uranium <i>X</i> was really a +constant mixture and of course the decay and recovery periods were +also composite. It required later and very skilful work to separate +them into the bodies indicated in the disintegration series.</p> + +<p>The half-value period for thorium <i>X</i> is much shorter, namely, a +little over four days, and this is also the recovery period for +thorium <i>X</i>. The plotted decay and recovery curves will intersect at +this point.</p> + +<p>The consecutive disintegration series, with the +half-value periods, for the uranium and thorium series as +<span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span> +given by Soddy are seen in the following tables. They are probably +subject to some changes on further and more accurate determination. +The nature of the rays emitted is also given.</p> + +<div class="figcenter" style="width: 80%;"> +<img src="images/i034.jpg" width="100%" alt="Fig. 6." title="Fig. 6." /> +<span class="caption"><span class="smcap">Fig. 6.—Disintegration Series for Uranium, Actinium, +and Thorium, as Given by Soddy.</span></span> +</div> + + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span></p> +<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV</h2> + +<h3>NATURE OF THE ALPHA PARTICLE</h3> + + +<div class="sidenote">Disintegration of the Elements</div> + +<p>The remarkable disintegrations related in the last chapter, in which +the heaviest known elementary atom—that of uranium (at. wt. +238)—is by successive stages changed into others of lower atomic +weight, afford a clue to the nature of the atom and to that goal of +the chemist, the final constitution of matter. The composite nature of +the atom and some sort of interrelation of the elements had previously +been made apparent from a study of the Periodic System and data +gathered still earlier, but all attempts at working out a so-called +genesis of the elements had proved vague and unsatisfactory.</p> + +<div class="sidenote">Identification of the Rays</div> + +<p>To get an understanding of the disintegration occurring in +radio-active substances, the nature of the rays produced must be +known. These rays are the cause of the activity and their emission +accompanies the changes or disintegration. They have for the sake of +convenience been called the alpha, beta, and gamma rays. The gamma +rays have been identified with the <i>X</i> rays discovered by Röntgen +and are a form of energy analogous to light. The beta rays are +particles of negative electricity or electrons. With +<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> +these, then, we have some degree of familiarity. But what are the +alpha rays? An answer to this question should make clearer the +character of the changes taking place, and should give some insight +into the composition and mechanism of the atom.</p> + +<div class="sidenote">The Alpha Rays</div> + +<p>It has already been stated that these alpha rays are similar or +analogous to the canal rays, but this advances the matter very little, +as the nature of these canal rays has not been fully determined. The +full identity with them, if proved, should have an important +theoretical bearing.</p> + +<div class="sidenote">Alpha Rays Consist of Solid Particles</div> + +<p>In the first place, these alpha rays have been found to be made up of +solid particles, that is, of what we are accustomed to call matter. +Since it has become more and more difficult to draw a clear +distinction between matter and energy, it would perhaps be better to +say that these particles appear to have some of the properties +hitherto attributed solely to matter. The best evidence that these +particles are of atomic mass is furnished by their deflection in +electric and magnetic fields.</p> + +<div class="sidenote">Electrical Charge</div> + +<p>It is not of first importance to discuss this or other proofs +of the material nature of these particles. That they carry a +charge of positive electricity is, however, a fact of very +great import. The value of this charge has been carefully +determined by a number of investigators working with different +sources of the alpha particles and has been found to +<span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span> +be 9.3 × 10<sup>-10</sup> electrostatic units (.000,000,000,93 e.s.). +From the consideration of the charge upon an electron previously obtained +by J. J. Thomson and others, it was concluded that the alpha particle +carried two unit positive charges; the fundamental unit charge, +therefore, is half this value, or 4.65 × 10<sup>-10</sup> e.s.</p> + +<div class="sidenote">Helium Formed from Alpha Particles</div> + +<p>To determine the nature of the alpha particle a crucial experiment was +carried out by Rutherford and Royds, which was described as follows:</p> + +<div class="figright" style="width: 30%;"> +<img src="images/i037.jpg" width="100%" alt="Fig. 7." title="Fig. 7." /> +<span class="caption"><span class="smcap">Fig. 7.—Apparatus +Used in Experiment by Rutherford and Royds.</span></span> +</div> + +<p>A large quantity of radium emanation was compressed into a fine glass +tube <i>A</i>, about 1.5 cm. long. This tube, which was sealed to a larger +capillary tube <i>B</i>, was sufficiently thin to allow the alpha particles +from the emanation and its products to pass through, but sufficiently +thick to withstand atmospheric pressure. The thickness of the glass +wall was in most cases less than .01 mm. On introducing the emanation +into the tube, the escape of the alpha particles from the emanation +was clearly seen by the scintillations produced at some distance on a +zinc sulphide screen. After this test the glass tube <i>A</i> was +surrounded by a glass tube <i>T</i> and a small spectrum tube +<i>V</i> attached to it. The tube +<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span> +<i>T</i> was exhausted to a charcoal vacuum. By means of the mercury column +<i>H</i>, the gases in the tube <i>T</i> could at any time be compressed into +the spectrum tube <i>V</i> and the nature of the gases which had been +produced determined spectroscopically. It was found that two days +after the introduction of the emanation into <i>A</i> the spectrum showed +the yellow line of helium, and after six days the whole helium +spectrum was observed. In order to be certain that the helium, coming +possibly from some other source, had not diffused through the thin +walls of the tube <i>A</i>, the emanation was pumped out and helium +substituted. No trace of helium could be observed in the vacuum tube +after several days, showing that the helium observed in the first +experiment must have originated from the alpha particles which had +been propelled through the thin glass tube into the outer tube.</p> + +<p>Most of the alpha particles are propelled with such force that they +penetrate some distance into the walls of the outer tube and some of +these gradually diffuse out into the exhausted space. The presence of +helium in the spectrum tube can be detected after a shorter interval +if a thin cylinder of lead is placed over the emanation tube, since +the particles fired into the lead diffuse out more rapidly than from +glass.</p> + +<p>A still more definite proof of the identity of the alpha particle with +the helium atom was obtained by removing the outer glass tube <i>T</i> and +placing a cylinder of lead over the emanation tube in the open air. Helium was +<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span> +always detected in the lead after it had remained several hours over +the thin tube containing a large quantity of the emanation. In order +to test for the presence of helium in the lead, the gases present were +released by melting the lead in a closed vessel. There can thus be no +doubt that the alpha particle becomes a helium atom when its positive +charge is neutralized.</p> + +<p>Thus the chemist was afforded the experience of the building up of at +least one element under his observation, and both the analysis and +synthesis of matter have been revealed through the discoveries of +radio-activity.</p> + +<div class="sidenote">Discovery of Helium</div> + +<p>It is of interest at this point to learn something of the history of +helium and its occurrence. In 1868 there was discovered by Janssen and +Lockyer a bright yellow line in the spectrum of the sun's +chromosphere. Because of its origin the name helium was given to the +supposed new element causing it. Later it was found in the spectra of +many of the stars, and because of its predominance in some of these +they were called helium stars. Its existence on our planet was not +detected for nearly thirty years.</p> + +<p>In 1895, in connection with the discovery of argon in the atmosphere, a +search was made to see if the latter element could be obtained from mineral +sources. In analyzing certain uranium minerals Hillebrand had found considerable +quantities of a gas which he took to be a peculiar form of nitrogen. +Ramsay made a further examination of the gas coming from these minerals and +<span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span> +the spectroscope revealed the yellow line of helium, thus at last +proving the presence of this element on the earth. It is known now to +be present in thorium minerals, in the waters of radio-active wells, +and in minute amounts in the atmosphere. Its occurrence in every case, +in the light of the experiment described above, would seem to be due +to the presence of radio-active changes.</p> + +<div class="sidenote">Characteristics of Helium</div> + +<p>Helium, on account of its chemical inactivity and physical properties, +is classed along with argon, neon, krypton, and xenon in the zero +group of the Periodic System, and forms with them the monatomic, inert +gases. In this class are now placed also the three radio-active gases, +emanating respectively from radium, thorium, and actinium. These are +generally known as radium emanation, thorium emanation, and actinium +emanation. The first mentioned was once called niton. Emanium was the +name originally proposed by Giesel for the body now known as actinium.</p> + +<p>The calculated rate of production of helium in the series in +equilibrium with one gram of radium is 158 cubic millimeters per year. +This corresponds quite well with the experimental results.</p> + +<div class="sidenote">Table of Constants</div> + +<p>Some of the more important atomic and radio-active constants +are given in the following table. They are recorded here to show +how helpful the study of radio-activity has been in working +out the composition of matter, and to give some idea of +<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span> +the magnitude of the numbers and the minuteness of the quantities +dealt with.</p> + +<table border="0" cellpadding="2" cellspacing="0" summary="Constants"> +<colgroup><col width="60%" /><col width="35%" /><col width="5%" /></colgroup> +<tr> + <td></td> + <td align="right"></td> + <td></td> +</tr> +<tr> + <td></td> + <td align="right"></td> + <td></td> +</tr> +<tr> + <td>Electric charge carried by each H atom inelectrolysis</td> + <td align="right">4.65 × 10<sup>-10</sup></td> + <td>e.s.<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></td> +</tr> +<tr> + <td>Electric charge carried by each α particle</td> + <td align="right">9.3 × 10<sup>-10</sup></td> + <td>e.s.</td> +</tr> +<tr> + <td>Number of atoms in 1 gram of H</td> + <td align="right">6.2 × 10<sup>23</sup></td> + <td></td> +</tr> +<tr> + <td>Mass of 1 atom of H</td> + <td align="right">1.6 × 10<sup>-24</sup></td> + <td>gram</td> +</tr> +<tr> + <td>Number of molecules per cc. of any gas at standard pressure and temperature</td> + <td align="right">2.72 × 10<sup>19</sup></td> + <td> </td> +</tr> +<tr> + <td>Number of α particles expelled per second per gram of radium itself</td> + <td align="right">3.6 × 10<sup>10</sup></td> + <td> </td> +</tr> +<tr> + <td>Number of α particles expelled per second per gram of radium in equilibrium with its products</td> + <td align="right">14.3 × 10<sup>10</sup></td> + <td> </td> +</tr> +</table> + +<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> The expression 10<sup>-10</sup> means multiplying by .000,000,000,1; 10<sup>10</sup> means +multiplying by 10,000,000,000.</p></div> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span></p> +<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V</h2> + +<h3>THE STRUCTURE OF THE ATOM</h3> + + +<div class="sidenote">Properties of Radium</div> + +<p>A study of the properties of radium will aid in throwing light upon +the question as to the building up of the atom. First to be considered +are the usual properties which distinguish an elementary body. +Metallic radium has been prepared by a method similar to that used in +the preparation of barium. It is a pure white metal, melting at +700°, and far more volatile than barium. It rapidly alters on +exposure to the air, probably forming a nitride. It energetically +decomposes water and the product dissolves in the water. Its atomic +weight is 226.</p> + +<p>Radium forms a series of salts analogous in appearance and chemical +action to those of barium. In the course of time they become colored, +especially if mixed barium salts. The radiations from radium produce +marked chemical effects in a number of substances. Carbon dioxide is +changed into carbon, oxygen, and carbon monoxide, and the latter is +changed into carbon and oxygen. Ammonia is dissociated into nitrogen and +hydrogen; hydrochloric acid into chlorine and hydrogen. Oxygen is condensed +into ozone. In general, the action upon gases appears to be similar to that +<span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span> +of the silent electric discharge. Water is decomposed into hydrogen +and oxygen. If moist radium chloride or a salt of radium containing +water of crystallization is sealed in a glass tube, the gradual +accumulation of hydrogen and oxygen will burst the tube.</p> + +<p>The radiations rapidly decompose organic matter with the evolution of +gases. Thus grease from stopcocks of apparatus used with radium or +paraffin will give off carbon dioxide. Under an intense alpha +radiation paraffin or vaseline become hard and infusible. White +phosphorus is changed into red.</p> + +<p>The action upon living tissue is most noteworthy, as its possible use +as a remedial agent is dependent upon this. A small amount of a radium +salt enclosed in a glass tube will cause a serious burn on flesh +exposed to it. It therefore has to be handled with care and undue +exposure to the radiations must be avoided. Cancer sacs shrivel up and +practically disappear under its action. Whether the destruction of +whatever causes the cancer is complete is at least open to serious +doubt.</p> + +<p>The coagulating effect upon globulin is interesting. When two +solutions of globulin from ox serum are taken and acetic acid added to +one while ammonia is added to the other, the opalescence in drops of +the former is rapidly diminished on exposure to radium, showing a more +complete solution, whereas the latter solution rapidly turns to a +jelly and becomes opaque, indicating a greatly decreased solubility.</p> + +<div class="sidenote">Energy Evolved by Radium</div> + +<p>The greater part of the tremendous energy evolved +<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> +by radium is due to the emission of the alpha particles, and in +comparison the beta and gamma rays together supply only a small +fraction. This energy may be measured as heat. It was first observed +that a radium compound maintained a temperature several degrees higher +than that of the air around it. The rate of heat production was later +measured by means of an ice calorimeter and also by noting the +strength of the current required to raise a comparison tube of barium +salt to the same temperature. Both methods showed that the heat +produced was at the rate of about 135 gram calories per hour. As the +emission is continuous, one gram of radium would therefore emit about +1,180,000 gram calories in the course of a year. At the end of 2000 +years it would still emit 590,000 gram calories per year. Such a +production of energy so far surpasses all experience that it becomes +almost inconceivable. It is futile to speak of it in terms of the heat +evolved by the combustion of hydrogen, which is the greatest that can +be produced by chemical means.</p> + +<p>This effect is unaltered at low temperatures, as has been tested by +immersing a tube containing radium in liquid air. It should be stated that +these measurements were made after the radium had reached an equilibrium +with its products; that is, after waiting at least a month after its +preparation. The evolution of heat from radium and the radio-active +substances is, in a sense, a secondary effect, as it measures the radiant +<span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span> +energy transformed into heat energy by the active matter itself and +whatever surrounds it. Let us repeat, therefore, that the total amount +of energy pent up in a single atom of radium almost passes our powers +of conception.</p> + +<div class="sidenote">Necessity for a Disintegration Theory</div> + +<p>The facts gathered so far justify and necessitate a theory which shall +satisfactorily explain them, and since these phenomena are not caused +by nor subject to the influence of external agencies, they must refer +to changes taking place within the atom—in other words, a theory +of disintegration. In the main, these facts may be summed up as the +emission of certain radiations from known elemental matter: the +material alpha particles with positive charge, the beta particles or +negative electrons, and the gamma rays analogous to <i>X</i> rays. The +emission of these rays results in the production of great heat. Then +there is the law of transformations by which whole series of new +elements are generated from the original element and maintain a +constant equilibrium of growth and decay in the series. Lastly, we +have the production of helium from the alpha particles.</p> + +<div class="sidenote">Disintegration Theory</div> + +<p>In explanation of these phenomena, Rutherford offered the hypothesis +that the atoms of certain elements were unstable and subject to +disintegration. The only elements definitely known to come under this +description are the two having atoms of the greatest known mass, +thorium (232) and uranium (238).</p> + +<p><span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span> +The atoms of uranium, for instance, are supposed to be not permanent +but unstable systems. According to the hypothesis, about 1 atom in +every 10<sup>18</sup> becomes unstable each second and breaks up with a violent +explosion for so small a mass of matter. One, or possibly two alpha +particles are expelled with great velocity. This alpha particle +corresponds to an atom of helium with an atomic weight of 4, and its +loss reduces the original atomic weight to 234 with the formation of a +new element, having changed properties corresponding to the new atomic +weight. This new element is uranium <i>X</i><sub>1</sub>.</p> + +<p>These new atoms are far more unstable than those of uranium, and the +decomposition proceeds at a new rate of 1 in 10<sup>7</sup> per second. So at a +definite, measurable rate this stepwise disintegration proceeds. The +explosions are not in all cases equally violent in going from element +to element, nor are the results the same. Sometimes alpha particles +alone are expelled, sometimes beta, or two of them together, as alpha +and beta.</p> + +<p>The new product may remain with the unchanged part of the original +matter. Thus there would be an accumulation of it until its own decay +balances its production, resulting eventually in a state of +equilibrium.</p> + +<div class="sidenote">Constitution of the Atom</div> + +<p>In order to explain the electrical and optical properties +of matter, the hypothesis was made that the atom consisted of +positively and negatively electrified particles. Later it was +shown that negative electrons exist in all kinds of matter. +<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span> +Various attempts were made to work out a model of such an atom in +which these particles were held in equilibrium by electrical forces. +The atom of Lord Kelvin consisted of a uniform sphere of positive +electrification throughout which a number of negative electrons were +distributed, and J. J. Thomson has determined the properties of this +type as to the number of particles, their arrangement and stability.</p> + +<div class="sidenote">Rutherford's Atom</div> + +<p>According to Rutherford, the atom of uranium may be looked upon as +consisting of a central charge of positive electricity surrounded by a +number of concentric rings of negative electrons in rapid motion. The +positively charged centre is made up of a complicated system in +movement, consisting in part of charged helium and hydrogen atoms, and +practically the whole charge and mass of the atom is concentrated at +the centre. The central system of the atom is from some unknown cause +unstable, and one of the helium atoms escapes from the central mass as +an alpha particle.</p> + +<p>There are, confessedly, difficulties connected with this conception of +the atom which need not, however, be discussed here. Much remains to +be learned as to the mechanics of the atom, and the hypothesis +outlined above will probably have to be materially altered as +knowledge grows. Perhaps it may have to be entirely abandoned in favor +of some more satisfactory solution. Until such time it at least suffices +as a mental picture around which the known facts group themselves. In +<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span> +this picture energy and matter lose their old-time distinctness of +definition. Discrete subdivisions of energy are recognized which may +be called charged particles without losing their significance. Some of +these subdivisions charged in a certain way or with neutralized charge +exhibit the properties of so-called matter.</p> + +<div class="sidenote">Scattering of Alpha Particles</div> + +<p>This conception of the atom would doubtless fail of much support were +it not for certain experimental facts which lend great weight to it. +Certain suppositions can be based on this theory mathematically +reasoned out and tested by experiment. Predictions thus based on +mathematical reasoning and afterward confirmed by experiment give a +very convincing impression that truth lies at the bottom.</p> + +<p>The first of these experimental proofs comes under the head of what is +known as the scattering of the alpha particles, a phenomenon which, +when first observed, proved hard to explain. If an alpha particle in +its escape from the parent atom should come within the influence of +the supposed outer electrical field of some other atom, it should be +deflected from its course and, the intensity of the two charges being +known, the angle of deflection could be calculated. For instance, if +it came to what might be called a head-on collision with the positive +central nucleus of another atom, it would recoil if it were itself of +lesser mass, or would propel the other forward if that were the lighter.</p> + +<p><span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span> +The experiment is carried out by placing a thin metal foil over a +radio-active body, as radium <i>C</i>, which expels alpha particles with a +high velocity, and counting the number of alpha particles which are +scattered through an angle greater than 90° and so recoil toward +their source. This has been done by a number of investigators and it +has been found that the angle of scattering and the number of recoil +particles depend upon the atomic weight of the metal used as foil. For +example, if gold is used, the number of recoil atoms is one in +something less than 8,000.</p> + +<p>Taking the atomic weight of gold into consideration, Rutherford +calculated mathematically that this was about the number which should +be driven backward. But he went further and calculated also the number +which should be returned by aluminum, which has an atomic weight of +only about one-seventh that of gold. Two investigators determined +experimentally the number for aluminum and their results agreed with +Rutherford's calculations.</p> + +<p>The metals from aluminum to gold have been examined in this way. The +number of recoil particles increases with the atomic weight of the +metal. Comparing experiment with theory, the central charge in an atom +corresponds to about one-half the atomic weight multiplied by the +charge on an electron, or, as it is expressed, ½ Ae.</p> + +<p>There is only one lighter atom than helium, namely, +hydrogen, which has a mass only one-fourth as great. +<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> +When alpha particles are discharged into hydrogen, a few of the latter +atoms are found to be propelled to a distance four times as great as +that reached by the alpha particles.</p> + +<div class="sidenote">Stopping Power of Substances</div> + +<p>Parallel with the experiments mentioned, there is what is called the +stopping power of substances. This means the depth or thickness of a +substance necessary to put a stop to the course of the alpha +particles. This gives the range of the alpha particles in such +substances and is connected in a simple way with the atomic weight, +that is, it is again fixed by the mass of the opposing atom. This +stopping power of an atom for an alpha particle is approximately +proportional to the square root of its atomic weight.</p> + +<p>Considering gases, for instance, if the range in hydrogen be 1, then +the range in oxygen, the atomic weight of which is 16, is only +√(1/16) or ¼. Generally in the case of metals the weight of +matter per unit area required to stop the alpha particle is found to vary +according to the square root of the atomic weight of the +metal taken.</p> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span></p> +<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI</h2> + +<h3>RADIO-ACTIVITY AND CHEMICAL THEORY</h3> + + +<div class="sidenote">Influence upon Chemical Theory</div> + +<p>It can easily be seen that the revelations of radio-activity must have +a far-reaching effect upon chemical theory, throwing light upon, and +so bringing nearer, the solution of some of the problems which have +been long discussed without arriving at any satisfactory solution. The +so-called electro-chemical nature of the elements will certainly be +made much clearer. The changes in valence should become intelligible +and valence itself should be explained. A fuller understanding of the +ionization of electrolytes also becomes possible. As these matters are +debatable and the details are still unsettled, it is scarcely +appropriate to give here the hypotheses in detail or to enter into any +discussion of them. But the promise of solution in accord with the +facts is encouraging.</p> + +<div class="sidenote">The Periodic System</div> + +<p>Such progress has been made, however, in regard to a better +understanding of the Periodic System that the new facts and +their interpretation may well be given. No reliable clue to the +meaning of this system and the true relationship between the +<span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span> +elements had been found up to the time when new light was thrown upon +it by the discoveries of radio-activity. The underlying principle was +unknown and even the statement of what was sometimes erroneously +called the Periodic Law was manifestly incorrect and its terms were +ignored.</p> + +<div class="sidenote">Basis of the Periodic System</div> + +<p>The ordinary statement of the fundamental principle of the Periodic +System has been that the properties of the elements were periodic +functions of the atomic weights, and that when the elements were +arranged in the order of their atomic weights they fell into a natural +series, taking their places in the proper related groups.</p> + +<p>In accepting this, the interpretation of function was both +unmathematical and vague, and the order of the atomic weights was not +strictly adhered to but unhesitatingly abandoned to force the group +relationship. Wherever consideration of the atomic weight would have +placed an element out of the grouping with other elements to which it +was clearly related in physical and chemical properties, the guidance +of these properties was accepted and that of the atomic weights +disregarded. Such shiftings are noted in the cases of tellurium and +iodine; cobalt and nickel; argon and potassium. It was most helpful +that, following the order of atomic weights, the majority of the +elements fell naturally into their places. Otherwise +the generalization known as the Periodic System might +<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span> +have remained for a long time undiscovered and the progress of +chemistry would have been greatly retarded.</p> + +<div class="sidenote">Influence of Positive Nucleus</div> + +<p>It is evident that the order of the elements is determined by +something else than their atomic weights. From the known facts of +radio-activity it would seem that this determining factor is the +positive nucleus. And this nucleus also determines the mass or weight +of the atom. Taking the elements in their order in the Periodic Series +and numbering the positions held by them in this series as 1, 2, 3, +etc., we get the position number or what is called the atomic number. +This designates the order or position of the element in the series. We +must learn that this number marks a position rather than a single +element, a statement which will be explained later.</p> + +<div class="sidenote">Determination of the Atomic Number</div> + +<p>Since the atomic weight is unreliable as a means of settling the +position of an element in the series and so fixing its atomic number, +how is this number to be determined? Of course, one answer to this +question is that we may rely upon a consideration of the general +properties, as has been done in the past. Fortunately, other methods +have been found by which this may be confirmed. For instance, the +stopping and scattering power of the element for alpha particles has +been suggested and successfully used.</p> + +<div class="sidenote">Use of X-Ray Spectra</div> + +<p>A most interesting method is due to Moseley's +<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span> +observations upon the <i>X</i>-ray spectra of the various elements. It has +been found that crystals, such as those of quartz, have the power of +reflecting and defining the <i>X</i> rays. The spectra given by these rays +can be photographed and the wave lengths measured. These <i>X</i> rays are +emitted by various substances under bombardment by the cathode rays +(negative electrons) and have great intensity and very minute wave +lengths. Moseley made use of various metals as anti-cathodes for the +production of these rays. These metals ranged from calcium to zinc in +the Periodic System. In each case he observed that two characteristic +types of <i>X</i> rays of definite intensity and different wave lengths +were emitted. From the frequency of these waves there is deduced a +simple relation connected with a fundamental quantity which increases +in units from one element to the next. This is due to the charge of +the positive central nucleus. The number found in this way is one less +than the atomic number. Thus the number for calcium is 19 instead of +20 and that for zinc is 29 instead of 30. So, by adding 1 to the +number found the atomic number is obtained.</p> + +<p>The atomic weight can usually be followed in fixing the atomic +number, but where doubt exists the method just given can be resorted +to. Thus doubt arises in the case of iron and nickel and cobalt. +This would be the order according to the atomic weights. The +<i>X</i>-ray method gives the order as iron, cobalt, and +<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span> +nickel, and this is the accepted order in the Periodic System.</p> + +<div class="sidenote">Changes Caused by Ray Emission</div> + +<p>On studying the properties of the elements in a transformation series +in connection with the ray emission which produced them, it was seen +that these properties were determined in each case by the nature of +the ray emitted from the preceding transformation product or parent +element.</p> + +<div class="sidenote">Atomic Weight Losses</div> + +<p>Each alpha particle emitted means a loss of 4 in the atomic weight. +This is the mass of a helium atom. Thus from uranium with an atomic +weight of 238 to radium there is a loss of three alpha particles. +Therefore, 12 must be subtracted from 238, leaving 226, which agrees +closely with the atomic weight of radium as actually determined by the +ordinary methods. Uranium <i>X</i><sub>1</sub>, then, would have an atomic weight of +234 and that of ionium would be 230. The other intermediate elements, +whose formation is due to the loss of beta particles only, show no +decrease in atomic weight.</p> + +<div class="sidenote">Lead the End Product</div> + +<p>From uranium to lead there is a loss of 8 alpha particles, or 32 units +in atomic weight. This would give for the final product an atomic +weight of 206. The atomic weight of lead is 207.17. It is not at all +certain that the final product of this series is ordinary lead. The +facts are such that they would lead one to think that it is not. +It is known only that the end product would probably be some +element closely resembling lead chemically and hence +<span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span> +difficult or impossible to separate from it. Several accurate +determinations of lead coming from uranium minerals, which always +carry this element and in an approximately definite ratio to the +amount of uranium present, show atomic weights of 206.40; 206.36; and +206.54. Even the most rigid methods of purification fail to change +these results. The lead in these minerals might therefore be +considered as coming in the main from the disintegration of the +uranium atom and, though chemically resembling lead, as being in +reality a different element with different atomic weight.</p> + +<p>Furthermore, in the thorium series 6 alpha particles are lost before +reaching the end product, which again is perhaps the chemical analogue +of lead. The atomic weight here should be 232 less 24, or 208. +Determinations of the atomic weight of lead from thorite, a thorium +mineral nearly free from uranium, gave 208.4.</p> + +<p>The end product of the actinium series is also an element resembling +lead, but both the beginning and ending of this series are still in +obscurity.</p> + +<div class="sidenote">Changes of Position in the Periodic System</div> + +<p>The loss of 4 units in the atomic weight of an element on the +expulsion of an alpha particle is accompanied by a change of chemical +properties which removes the new element two groups toward the +positive side in the Periodic System.</p> + +<p>Thus ionium is so closely related to thorium and so +resembles it chemically that it is properly classed along +with thorium as a quadrivalent element in the fourth +<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span> +group. Ionium expels an alpha particle and becomes radium, which is a +bivalent element resembling barium belonging to the second group. +Radium then expels an alpha particle and becomes the gas, radium +emanation, which is an analogue of argon and belongs to the zero +group. Other instances might be cited which go to show that in all +cases the loss of an alpha particle makes a change of two places +toward the left or positive side of the System.</p> + +<div class="sidenote">Changes from Loss of Beta Particles</div> + +<p>The loss of a beta particle causes no change in the atomic weight but +does cause a shift for each beta particle of one group toward the +right or negative side of the System. Two such losses, then, will +counterbalance the loss of an alpha particle and bring the new element +back to the group originally occupied by its progenitor. Thus uranium +in the sixth group loses an alpha particle and the product UX<sub>1</sub> falls +in the fourth group. One beta particle is then lost and UX<sub>2</sub> belonging +to the fifth group is formed. With the loss of one more beta particle +the new element returns to the sixth group from which the +transformation began.</p> + +<p>The table on page 48, as adapted from Soddy, affords a general view of +these changes.<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span></p> + +<div class="figcenter" style="width: 100%;"> +<img src="images/i058.jpg" width="100%" alt="Fig. 6." title="Fig. 6." /> +<span class="caption"><span class="smcap">Radio-active Elements from Uranium and Thorium Placed in the Periodic Systems</span><br /> +<small>Adapted from Soddy</small></span> +</div> + +<div class="sidenote">Isotopes</div> + +<p>An examination of the table will show a number of different +elements falling in the same position in a group of the Periodic +System irrespective of their atomic weights. These are +chemically inseparable so far as the present limitations of +<span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span> +chemical analysis are concerned. Even the spectra of these elements +seem to be identical so far as known. This identity extends to most of +the physical properties, but this demands much further investigation. +For this new phenomenon Soddy has suggested the word isotope for the +element and isotopic for the property, and these names have come into +general use.</p> + +<p>Manifestly, we have come across a phenomenon here which quite +eliminates the atomic weight as a determining factor as to position in +the Periodic or Natural System or of the elemental properties in +general. All of the properties of the bodies which we call elements, +and consequently of their compounds and hence of matter in general, +seem to depend upon the balance maintained between the charges of +negative and positive electricity which, according to Rutherford's +theory, go to make up the atom.</p> + +<p>It is evident that any study of chemical phenomena and chemical theory +is quite incomplete without a study of radio-activity and the +transformations which it produces.</p> + +<div class="sidenote">Radio-activity in Nature</div> + +<p>In concluding this outline of the main facts of radio-activity, +it is of interest to discuss briefly the presence +of radio-active material on this planet and +in the stars. Facts enough have been +gathered to show the probable universality of this +phenomenon of radio-activity. Whether this means +solely the disintegration of the uranium and thorium +<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span> +atoms, or whether other elements are also transformed under the +intensity of the agencies at work in the universe, is of course a +question as yet unsolved.</p> + +<div class="sidenote">Radio-active Products in the Earth's Crust</div> + +<p>The presence of uranium and thorium widely distributed throughout the +crust of the earth would lead to the conclusion that their +disintegration products would be found there also. Various rocks of +igneous origin have been examined revealing from 4.78 × 10<sup>-12</sup> to +0.31 × 10<sup>-12</sup> grams of radium per gram of the rock. Aqueous rocks +have shown a lesser amount, ranging from 2.92 × 10<sup>-12</sup> to 0.86 +× 10<sup>-12</sup> grams. As the soil is formed by the decomposition of +these rocks, radium is present in varying amounts in all kinds of +soil.</p> + +<div class="sidenote">Presence in Air and Soil Waters</div> + +<p>As radium is transformed into the gaseous emanation, this will escape +wherever the soil is not enclosed. For instance, a larger amount of +radio-activity is found in the soil of caves and cellars than in open +soils. If an iron pipe is sunk into a soil and the air of the soil +sucked up into a large electroscope, the latter instrument will show +the effect of the rays emitted and will measure the degree of +activity. Also the interior of the pipe will receive a deposit of the +radio-active material and will show appreciable radio-activity after +being removed from the soil.</p> + +<p>This radium emanation is dissolved in the soil waters, wells, springs, +and rivers, rendering them more or less radio-active, and sometimes +the muddy deposit at the bottom of a spring shows decided radio-activity.</p> + +<p><span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span> +The emanation also escapes into the air so that many observations made +in various places show that the radium emanation is everywhere present +in the atmosphere. Neither summer nor winter seems to affect this +emanation, and it extends certainly to a height of two or three miles. +Rain, falling through the air, dissolves some of the emanation, so +that it may be found in freshly-fallen rain water and also in +freshly-fallen snow. Radio-active deposits are found upon electrically +charged wires exposed near the earth's surface.</p> + +<p>As helium is the resulting product of the alpha particles emitted by +the emanation and other radio-active bodies, it is found in the soil +air, soil waters, and atmosphere.</p> + +<p>Average measurements of the radio-activity of the atmosphere have led +to the calculation that about one gram of radium per square kilometer +of the earth's surface is requisite to keep up the supply of the +emanation.</p> + +<p>A number of estimates have been given as to the heat produced by the +radio-active transformations going on in the material of this planet. +Actual data are scarce and mere assumptions unsatisfactory, so little +that is worth while can be deduced. It is possible that this source of +heat may have an appreciable effect upon or serve to balance the +earth's rate of cooling.</p> + +<div class="sidenote">Cosmical Radio-activity</div> + +<p>Meteorites of iron coming from other celestial bodies have not +shown the presence of radium. Aerolites or stone meteorites +have been found to contain as much as similar terrestrial rock. +<span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span> +Since the sun contains helium and some stars show its presence as +predominating, this suggests the presence of radio-active matter in +these bodies. In addition, the spectral lines of uranium, radium, and +the radium emanation have been reported as being found in the sun's +spectrum and also in the new star, <i>Nova Geminorum 2</i>. These +observations await further investigation and confirmation. So far as +the sun's chromosphere is concerned, the possible amount of radium +present would seem to be very small. If this is true, radio-active +processes could have little to do with the sun's heat. The statement +is made by Rutherford that indirect evidence obtained from the study +of the aurora suggests that the sun emits rays similar in type to the +alpha and beta rays. Such rays would be absorbed, and the gamma rays +likewise, in passing through the earth's atmosphere and so escape +ordinary observation. All of this is but further evidence of the unity +of matter and of forces in the universe.</p> + + + +<hr style="width: 65%;" /> +<p><span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span></p> +<h2><a name="INDEX" id="INDEX"></a>INDEX</h2> + +<p> +Actinium, discovery of, <a href="#Page_6">6</a><br /> +<br /> +Activity, induced, <a href="#Page_17">17</a><br /> +<br /> +Alpha particles, effect of loss on Atomic Weight, <a href="#Page_45">45</a><br /> +<span style="margin-left: 1em;">electrical charge of, <a href="#Page_26">26</a></span><br /> +<span style="margin-left: 1em;">form helium, <a href="#Page_27">27</a></span><br /> +<span style="margin-left: 1em;">nature of, <a href="#Page_25">25</a></span><br /> +<span style="margin-left: 1em;">penetrating power of, <a href="#Page_39">39</a></span><br /> +<span style="margin-left: 1em;">position of element changed by its loss, <a href="#Page_46">46</a></span><br /> +<span style="margin-left: 1em;">recoil, <a href="#Page_39">39</a></span><br /> +<span style="margin-left: 1em;">scattering of, <a href="#Page_38">38</a></span><br /> +<span style="margin-left: 1em;">solid, <a href="#Page_26">26</a></span><br /> +<br /> +Atom, constitution of, <a href="#Page_36">36</a><br /> +<span style="margin-left: 1em;">Kelvin's, <a href="#Page_37">37</a></span><br /> +<span style="margin-left: 1em;">models of, <a href="#Page_37">37</a></span><br /> +<span style="margin-left: 1em;">Rutherford's, <a href="#Page_37">37</a></span><br /> +<br /> +Atomic number, determination of, <a href="#Page_43">43</a><br /> +<br /> +<br /> +Becquerel's experiments, <a href="#Page_2">2</a><br /> +<br /> +Beta particles, change in position of element by loss of, <a href="#Page_47">47</a><br /> +<br /> +<br /> +Chalcolite, natural and artificial, <a href="#Page_4">4</a><br /> +<br /> +Constants, table of, <a href="#Page_31">31</a><br /> +<br /> +Curie unit, <a href="#Page_22">22</a><br /> +<br /> +<br /> +Disintegration of the element, <a href="#Page_25">25</a><br /> +<br /> +Disintegration series, <a href="#Page_24">24</a><br /> +<br /> +Disintegration theory, <a href="#Page_35">35</a><br /> +<br /> +<br /> +Electroscope, <a href="#Page_12">12</a><br /> +<br /> +Equilibrium series, <a href="#Page_22">22</a><br /> +<br /> +<br /> +Helium, characteristics of, <a href="#Page_30">30</a><br /> +<span style="margin-left: 1em;">discovery of, <a href="#Page_29">29</a></span><br /> +<br /> +<br /> +Ionium, discovery of, <a href="#Page_6">6</a><br /> +<br /> +Ionization, application of electric field to, <a href="#Page_10">10</a><br /> +<span style="margin-left: 1em;">experimental confirmation, <a href="#Page_9">9</a></span><br /> +<br /> +Ionization of gases, <a href="#Page_7">7</a><br /> +<span style="margin-left: 1em;">theory of, <a href="#Page_8">8</a></span><br /> +<br /> +Ions, size and nature of, <a href="#Page_10">10</a><br /> +<br /> +Isotopes, <a href="#Page_47">47</a><br /> +<br /> +<br /> +Lead, atomic weight varies with source, <a href="#Page_45">45</a><br /> +<span style="margin-left: 1em;">radio-active, <a href="#Page_6">6</a></span><br /> +<span style="margin-left: 1em;">the end product, <a href="#Page_45">45</a></span><br /> +<br /> +Life-periods of radio-active bodies, <a href="#Page_21">21</a><br /> +<br /> +<br /> +Periodic system, <a href="#Page_41">41</a><br /> +<span style="margin-left: 1em;">basis of, <a href="#Page_42">42</a></span><br /> +<br /> +Polonium, discovery of, <a href="#Page_4">4</a><br /> +<br /> +Positive nucleus, influence of, <a href="#Page_43">43</a><br /> +<br /> +Potassium, radio-activity of, <a href="#Page_3">3</a><br /> +<br /> +<br /> +Radiations, action on phosphorescent bodies, <a href="#Page_13">13</a><br /> +<span style="margin-left: 1em;">action on photographic plates, <a href="#Page_11">11</a></span><br /> +<span style="margin-left: 1em;">discharge electrified bodies, <a href="#Page_12">12</a></span><br /> +<span style="margin-left: 1em;">magnetic deflection of, <a href="#Page_14">14</a></span><br /> +<span style="margin-left: 1em;">measurements of, <a href="#Page_15">15</a></span><br /> +<span style="margin-left: 1em;">penetrating power of, <a href="#Page_13">13</a>, <a href="#Page_15">15</a></span><br /> +<span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span><br /> +Radio-active bodies, elemental nature of, <a href="#Page_20">20</a><br /> +<span style="margin-left: 1em;">examination of, <a href="#Page_20">20</a></span><br /> +<span style="margin-left: 1em;">life periods of, <a href="#Page_21">21</a></span><br /> +<br /> +Radio-activity, an atomic property, <a href="#Page_3">3</a><br /> +<span style="margin-left: 1em;">cosmical, <a href="#Page_51">51</a></span><br /> +<span style="margin-left: 1em;">influence on chemical theory, <a href="#Page_41">41</a></span><br /> +<span style="margin-left: 1em;">products in atmosphere, <a href="#Page_51">51</a></span><br /> +<span style="margin-left: 1em;">products in earth's crust, <a href="#Page_50">50</a></span><br /> +<span style="margin-left: 1em;">products in soil waters, <a href="#Page_50">50</a></span><br /> +<br /> +Radium, action on organic matter, etc., <a href="#Page_33">33</a><br /> +<span style="margin-left: 1em;">amount in pitchblende, <a href="#Page_5">5</a></span><br /> +<span style="margin-left: 1em;">discovery of, <a href="#Page_5">5</a></span><br /> +<span style="margin-left: 1em;">emanation, <a href="#Page_22">22</a></span><br /> +<span style="margin-left: 1em;">energy evolved by, <a href="#Page_34">34</a></span><br /> +<span style="margin-left: 1em;">properties of, <a href="#Page_5">5</a>, <a href="#Page_32">32</a></span><br /> +<br /> +Rays, alpha, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>, <a href="#Page_26">26</a><br /> +<span style="margin-left: 1em;">beta, <a href="#Page_15">15</a>, <a href="#Page_16">16</a></span><br /> +<span style="margin-left: 1em;">gamma, <a href="#Page_15">15</a>, <a href="#Page_16">16</a></span><br /> +<span style="margin-left: 1em;">identification of, <a href="#Page_16">16</a>, <a href="#Page_25">25</a></span><br /> +<span style="margin-left: 1em;">magnetic deflection of, <a href="#Page_14">14</a></span><br /> +<span style="margin-left: 1em;">photographing track of, <a href="#Page_10">10</a></span><br /> +<span style="margin-left: 1em;">types of, <a href="#Page_14">14</a></span><br /> +<br /> +Rubidium, radio-activity of, <a href="#Page_3">3</a><br /> +<br /> +<br /> +Spinthariscope, <a href="#Page_13">13</a><br /> +<br /> +Stopping power of substances, <a href="#Page_39">39</a><br /> +<br /> +<br /> +Thorium X, discovery of, <a href="#Page_18">18</a>, <a href="#Page_21">21</a><br /> +<br /> +<br /> +Uranium atom, disintegration of, <a href="#Page_36">36</a><br /> +<br /> +Uranium minerals, radio-activity of, <a href="#Page_3">3</a><br /> +<br /> +Uranium X, discovery of, <a href="#Page_17">17</a>, <a href="#Page_21">21</a>, <a href="#Page_23">23</a><br /> +<br /> +<br /> +X-ray spectra, <a href="#Page_44">44</a><br /> +<br /> +<br /> +Zinc sulphide screen, <a href="#Page_13">13</a><br /> +</p> + + + +<hr style="width: 65%;" /> +<h2>TRANSCRIBER'S NOTES</h2> + + +<p>Images have been moved from the middle of a paragraph to the +closest paragraph break. Other than that, the original text has been +reproduced as such.</p> + + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of A Brief Account of Radio-activity, by +Francis Preston Venable + +*** END OF THIS PROJECT GUTENBERG EBOOK A BRIEF ACCOUNT OF RADIO-ACTIVITY *** + +***** This file should be named 32307-h.htm or 32307-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/2/3/0/32307/ + +Produced by The Online Distributed Proofreading Team at +http://www.pgdp.net (This file was produced from images +generously made available by The Internet Archive/American +Libraries.) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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