,libraries47 ,a ,,brief ,,account ,,of ,,radio-,,activity ,,by ,,francis ,p4 ,,venable1 ,,ph4,d41 ,d4,,sc41 ,,ll4,d4 ,,professor ,,of ,,chemistry1 ,,university ,,of ,,north ,,carolina ,,author ,,of ,a ,,short ,,history ,,of ,,chemistry1 ,,periodic ,,law1 ,,etc4 ,d4 ,c4 ,,heath ,,co41 ,,publishers ,,boston ,,new ,,york ,,chicago ,,copyright1 #aiag1 ,,by ,d4 ,c4 ,,heath ,,co4 ,,ia#g ,,preface ,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 chemistry4 ,such a course dealing with the composition and structure of matter is left unfinished and in the air1 as it were1 unless the marvellous facts and deductions from the study of radio-activity are presented and discussed4 ,the usual page or two given in the present text-books are too condensed in their treatment to afford any intelligent grasp of the subject1 so ,i have put in book form the lectures which ,i have hitherto felt forced to give4 ,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 treatises4 ,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 treatment4 ,i have made free use of the writings of ,rutherford1 ,soddy1 and ,j4 ,j4 ,thomson1 and would here express my debt to them--just a part of that indebtedness which we all feel to these masters4 ,i wish also to acknowledge my obligations to ,professor ,bertram ,b4 ,boltwood for his helpful suggestions in connection with this work4 ,,contents ,,chapter ,i ,,discovery ,,of ,,radio-,,activity ,,page ,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 #a ,,chapter ,,ii ,,properties ,,of ,,the ,,radiations ,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 #g ,,chapter ,,iii ,,changes ,,in ,,radio-,,active ,,bodies ,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 #ag ,,chapter ,,iv ,,nature ,,of ,,the ,,alpha ,,particle ,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 #be ,,chapter ,v ,,the ,,structure ,,of ,,the ,,atom ,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 #cb ,,chapter ,,vi ,,radio-,,activity ,,and ,,chemical ,,theory ,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 #da ,,index #ec ,a ,,brief ,,account ,,of ,,radio-,,activity ,,chapter ,i ,,discovery ,,of ,,radio-,,activity ,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 science4 ,mathematical processes will be omitted1 as it is sufficient to give the assured results from calculations which are likely to be beyond the training of the reader4 ,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 science4 ,theories cannot be avoided1 but the facts remain while theories grow old and are discarded for others more in accord with the facts4 ,the ,beginning ,as so often happens in the history of science1 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 lead4 ,in #ahie1 ,rntgen modestly announced his discovery of the ,x rays4 ,this attracted immediate and intense interest4 ,among those who undertook to follow up these phenomena was ,becquerel1 who1 because of the apparent connection with phosphorescence1 tried the action of a number of phosphorescent substances upon the photographic plate1 the most striking characteristic of the ,x rays being their effect upon such sensitive plates4 ,in these experiments he obtained no results until he tried salts of uranium1 recalling previous observations of his as to their phosphorescence4 ,distinct action was noted4 ,furthermore1 he proved that this had no connection with the phenomenon of phosphorescence1 as both uranic and uranous salts were active and the latter show no phosphorescence4 ,becquerel announced his discoveries in #ahif and this was the beginning of the new science of radio-activity4 ,radio-active bodies ,the rays given off by uranium and its salts were found to differ from the ,x rays4 ,they showed no appreciable variation in intensity1 no previous exposure of the substance to light was necessary1 and neither changes of temperature nor any other physical or chemical agency affected them4 ,at first uranium and its compounds were the only known source of these new radiations1 but many other substances were examined and two years later thorium and its compounds were added to the list4 ,in general the discharging action seemed about the same4 ,other elements and ordinary substances show a minute activity4 ,only potassium and rubidium have a greater activity than this1 and theirs is only about one-thousandth that of uranium4 ,an ,atomic ,property ,in the examination of uranium and thorium compounds it was found that the activity was determined by the uranium and thorium present2 it was proportto the amount ofional these elements present and independent of the nature of the other elements composing the compound4 ,the conclusion was1 therefore1 that the activity was an inherent property of the atoms of uranium and thorium1 that is1 an atomic property4 ,this was a long step forward and introduced into science the conception of a new property of matter1 or at least of certain forms of matter4 ,discovery of ,new ,radio-active ,bodies ,in examining a large number of minerals containing uranium and thorium1 ,mme4 ,curie made the important observation that many of these were more active than the elements themselves4 ,in measuring the activity she made use of the electrical method which will be described later4 ,in the following table giving her results for uranium minerals the numbers under i give the maximum current in amperes4 ,they serve simply for comparison4 i ,pitchblende from ,joachimsthal #g4j #aj-aa ,clevite #a4d #aj-aa ,chalcolite #e4b #aj-aa ,autunite #b4g #aj-aa ,carnotite #f4b #aj-aa ,uranium #b4c #aj-aa ,uranium and potassium sulphate #j4g #aj-aa ,uranium and copper phosphate #j4i #aj-aa ,the last three are pure uranium and compounds of that element given for comparison with the first five1 which are naturally occurring minerals4 ,the last compound has the same composition as chalcolite and is simply the artificially prepared mineral4 ,it has the activity which would be calculated from the proportion of uranium present1 the copper and phosphoric acid contributing no activity4 ,since the activity is not dependent upon the composition but upon the amount of uranium present1 the activity in all of the minerals should be less than that of uranium4 ,on the contrary1 it is several times greater4 ,natural and artificial chalcolite also show a marked difference in favor of the former4 ,the supposition was a natural one1 therefore1 that these minerals contained small quantities of an element1 or elements1 undetected by ordinary analysis and having a much greater activity than uranium4 ,similar results were obtained in the examination of thorium minerals and thorium salts4 ,discovery of ,polonium ,following up this supposition1 ,m4 and ,mme4 ,curie set themselves the task of separating this unknown substance4 ,starting with pitchblende1 a systematic chemical examination was made4 ,this is an exceedingly complex mineral1 containing many elements4 ,the processes were laborious and demanded much time and minute care4 ,they need not be described here4 ,it is sufficient to say that along with bismuth a very active substance was separated1 to which ,mme4 ,curie gave the name of polonium for ,poland1 her native land4 ,its complete isolation is very difficult and sufficient quantities of the pure substance have not been obtained to determine its atomic weight and other properties1 but some of the lines of its spectrum have been determined4 ,chemically it is very closely analogous to bismuth4 ,discovery of ,radium ,in a similar manner a barium precipitate was obtained from pitchblende which contained a highly active substance4 ,the pure chloride of this body and barium can be prepared together and then separated by fractional crystallization4 ,to the new body thus found the name of radium was given4 ,it is similar in chemical properties to barium4 ,its atomic weight has been determined by several careful investigators and is accepted as #bbf4 ,its spectrum has been mapped and its general properties are known4 ,it is a silvery white1 oxidizable metal4 ,in one ton of pitchblende about #j4b gram of radium is present2 this is about #ejjj times greater than the amount of polonium present4 ,the activity of the products was depended upon as the guide in these separations4 ,the radium found is relatively enormously more active than the pitchblende or uranium4 ,other ,radio-active ,bodies ,found ,in the above separations use was made of relationships to bismuth and barium4 ,similarly1 by taking advantage of chemical relationship to the iron group of elements1 another body was partially separated by ,debierne1 to which he gave the name actinium4 ,boltwood discovered in uranium minerals the presence of a body which he named ionium1 and which is so similar to thorium that it cannot be separated from it4 ,it1 however1 far exceeds thorium in activity4 ,the lead which is present in uranium and thorium minerals--apparently in fairly definite ratio to the amount of uranium and thorium--is found1 on separation and purification1 to possess radio-active properties4 ,this activity is due to the presence of a very small proportion of an active constituent called radio-lead1 which has chemical properties identical with those of ordinary lead4 ,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 mineral4 ,a large number of other radio-active substances have been separated and some of their properties determined1 but these were found by different means and will be noted in their proper place4 ,they number in all more than thirty4 ,the sources or parents of these are the original uranium or thorium1 and the products form regular series with distinctive properties for each member4 ,,chapter ,,ii ,,properties ,,of ,,the ,,radiations ,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 cause4 ,ionization of ,gases ,one of these phenomena is the power of forming ions or carriers of electricity by the passage of the rays through a gas1 thus ionizing the gas4 ,the details of an experiment will serve to make the meaning of this ionization clear4 ,illustration3 ,,fig4 #a4--;,,ionization ,,of ,,gases4 ,when this apparatus is set up a minute current will be observed without the introduction of any radio-active matter4 ,this1 as ,rutherford says1 has been found due mainly to a slight natural radio-activity of the matter composing the plates4 ,if radio-active matter is spread on plate ,a1 which is connected with one pole of a grounded battery1 and if plate ,b is connected with an electrometer which is also connected with the earth1 a current is caused which increases rapidly with the difference of potential between the plates1 then more slowly until a value is reached that changes only slightly with a larger increase in the voltage4 ,according to the theory of ionization1 the radiation produces ions at a constant rate4 ,the ions carrying a positive charge are attracted to plate ,b1 while those negatively charged are attracted to plate ,a1 thus causing a current4 ,these ions will recombine and neutralize their charges if the opportunity is given4 ,the number1 therefore1 increases to a point at which the ions produced balance the number recombining4 ,when an electric field is produced between the plates1 the velocity of the ions between the plates is increased in proportion to the strength of the electric field4 ,in a weak field the ions travel so slowly that most of them recombine on the way and consequently the observed current is very small4 ,on increasing the voltage the speed of the ions is increased1 fewer recombine1 the current increases1 and1 when the condition for recombination is practically removed1 it will have a maximum value4 ,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 ,p4,d4 or saturation voltage4 ,the picture1 then1 is this4 ,the radiations separate the components of the gas into ions1 or carriers of electricity1 half of which are charged negatively and half positively4 ,in the electric field those negatively charged seek the positive plate and those positively charged seek the negative plate4 ,if time is given1 these ions meet and recombine1 their charges are neutralized1 and there is no current4 ,experimental ,confirmation ,this theory of the ionization of gases has been most interestingly confirmed by direct experiment4 ,for instance1 the ions may form nuclei for the condensation of water1 and in this way the existence of the separate ions in the gas may be shown and the number present actually counted4 ,when air saturated with water vapor is allowed to expand suddenly1 the water present forms a mist of small globules4 ,there are always small dust particles in air and around these as nuclei the drops are formed4 ,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 expansions4 ,if now the radiation from a radio-active body be introduced into the condensation vessel1 a new cloud is produced in which the water drops are finer and more numerous according to the intensity of the rays4 ,on passing a strong beam of light through the condensation chamber1 the drops can readily be seen4 ,these drops form on the ions produced by the radiation4 ,application of ,electric ,field ,if the condensation chamber has two parallel plates for the application of an electric field like that already described1 the ions will be carried at once to the electrodes and disappear4 ,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 formed4 ,if there is no electric field1 a cloud can be produced some time after the shutting off of the source of radiation1 showing that time is required for the recombination of the ions4 ,size and ,nature of ,ions ,if the drops are counted 7there being special methods for this7 and the total current carried accurately measured1 then the charge carried by each ion may be calculated4 ,this has been determined4 ,the mass of an ion compared with the mass of the molecules of gas in which it was produced can also be approximately estimated4 ,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 it4 ,it is roughly estimated that about thirty molecules of the gas cluster around each charged ion4 ,photographing the ,track of the ,ray ,utilizing the fact that these ions with their clusters of molecules form nuclei for the condensation of water vapor1 ,c4 ,t4 ,r4 ,wilson has by instantaneous photography been able to photograph the track of an ionizing ray through air4 ,the number of the ions produced1 and hence the number of drops1 is so great that the trail is shown as a continuous line4 ,in the copy of this photograph it will be seen that at some distance from its source the straight trail is slightly but abruptly bent4 ,near the end of its course there is another abrupt and much sharper bend4 ,these bends show where the ionizing ray1 in this case an alpha particle1 has been deflected by more or less direct collision with an atom4 ,these collisions and the final disappearance of the ray will be discussed later4 ,illustration3 ,,fig4 #b4--,,photograph ,,of ,,the ,,track ,,of ,,an ,,ionizing ,,ray4 ,action of ,radiations on ,photographic ,plates ,taking up now other means of examining these radiations1 it is well to consider their action upon a photographic or sensitive plate4 ,it will be recalled that this was the method by which their existence was originally detected4 ,to illustrate the method1 the following account of how one such photograph was taken may be given4 ,the plate was wrapped in two thicknesses of black paper4 ,the objects were placed upon this and the radio-active ore1 separated by a board one inch thick1 was placed above4 ,the exposure lasted five days4 ,the action is much less rapid and the result not so clearly defined as in the case of photographs taken by ,x rays4 ,of course1 the removal of the board and the use of more concentrated preparations of radium would give quicker and better results4 ,the method1 however1 on account of time consumed and lack of definition is ill adapted to accurate work4 ,illustration3 ,,fig4 #c--,,photograph ,,of ,,various ,,objects ,,taken ,,by ,,means ,,of ,,pitchblende ,discharge of ,electrified ,bodies ,the radiations from radio-active bodies can discharge both positively and negatively electrified bodies by making the air surrounding them a conductor of electricity4 ,to demonstrate this1 use is made of an electroscope4 ,if the hinged leaf of such an instrument be electrically charged and a radio-active body be brought into its neighborhood1 the electricity will be discharged and the leaf return to its original position4 ,the rapidity of this discharge is used to measure the degree of activity of the body giving off the radiation4 ,illustration3 ,,fig4 #d4--;,,gold-,,leaf ,,electroscope4 ,the gold-leaf ,l is attached to a flat rod ,r and is insulated inside the vessel by a piece of amber ,s supported from the rod ,p4 ,the system is charged by a bent rod ,,cc' passing through an ebonite stopper4 ,after charging1 it is removed from contact with the gold-leaf system4 ,the rods ,p and ,c and the cylinder are then connected with the earth4 ,scintillations on ,phosphorescent ,bodies ,it was found by ,crookes that a screen covered with phosphorescent zinc sulphide was brightly lighted up when exposed to the radiations4 ,this is due to the bombardment of the zinc sulphide by a type of ray called the alpha ray4 ,under a magnifying glass this light is seen to be made up of a number of scintillating points of light and is not continuous1 each scintillation being of very short duration4 ,by proper subdivision of the field under the lens1 the number of scintillations can be counted with close accuracy4 ,a simple form of apparatus called the spinthariscope has been devised to show these scintillations4 ,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 it4 ,the scintillations can be observed through an adjustable lens at the other end of the tube4 ,outer light should be cut off1 as in a dark room4 ,the screen then appears to be covered with brilliant flashes of light4 ,other phosphorescent substances1 such as barium platino-cyanide1 may be substituted for the zinc sulphide1 but they do not answer so well4 ,penetrating ,power ,by penetrating power is meant the power exhibited by the rays of passing through solids of different thicknesses and gases of various depths4 ,this power varies with different radiations and with the nature of the solid or gas4 ,for instance1 a sheet of metallic foil may be used and the effect of aluminum will differ from that of gold and the different rays vary in penetrating power4 ,in the case of gases air will differ from hydrogen1 and it is noticed that certain rays disappear after penetrating a short distance1 while others can penetrate further before being lost4 ,magnetic ,deflection ,if the radiations are subjected to the action of a strong magnetic field1 it is found that part of them are much deflected in the magnetic field and describe circular orbits1 part are only slightly deflected and in the opposite direction from the first1 and the remaining rays are entirely unaffected4 ,illustration3 ,,fig4 #e4--,,showing ,,magnetic ,,deflection ,,of alpha1 beta1 ,,and gamma ,,rays4 ,three ,types of ,rays ,by the use of these methods of investigation it is learned that the radiations consist of three types of rays4 ,these have been named the alpha1 beta1 and gamma rays1 respectively4 ,some radio-active bodies emit all three types1 some two1 and some only one4 ,the distinguishing characteristic of these types of rays may be summed up as follows3 ,alpha ,rays ,the alpha rays have a positive electrical charge and a comparatively low penetrating power4 ,they are slightly deflected in strong magnetic and electric fields4 ,they have a great ionizing power and a velocity about one-fifteenth that of light4 ,beta ,rays ,the beta rays are negatively charged and have a greater penetrating power than the alpha rays4 ,they show a strong deflection in magnetic and electric fields1 have less ionizing power than the alpha rays1 and a velocity of the same order as light4 ,gamma ,rays ,the gamma rays are very penetrating and are not deflected in the magnetic or electric fields4 ,they have the least ionizing power and a very great velocity4 ,the penetrating power of each type is complex and varies with the source1 so the statements given are but generalizations4 ,the alpha rays are projected particles which lose energy in penetrating matter4 ,as to the power of ionizing gases1 if that for the alpha rays is taken as #aj1jjj1 then the beta rays would be approximately #ajj and the gamma rays #a4 ,measurement of ,radiations ,the rays are examined and measured in several ways3 #a4 ,by their action on the sensitive photographic plates4 ,the use of this method is laborious1 consumes time1 and for comparative measurements of intensity is uncertain as to effect4 #b4 ,by electrical methods1 using electroscopes1 quadrant electrometers1 etc4 ,these are the methods most used4 #c4 ,by exposure to magnetic and electric fields1 noting extent and direction of deflection4 #d4 ,by their relative absorption by solids and gases4 #e4 ,by the scintillations on a zinc sulphide screen4 ,identification of the ,rays ,the alpha rays have been identified as similar to the so-called canal rays4 ,these were first observed in the study of the ,x rays4 ,when an electrical discharge is passed through a vacuum tube with a cathode having holes in it1 luminous streams pass through the holes toward the side away from the anode and the general direction of the stream4 ,they travel in straight lines and render certain substances phosphorescent4 ,these rays are slightly deflected by a magnetic field and in an opposite direction from that taken by the cathode rays in their deflection4 ,the rays seem to be positive ions with masses never less than that of the hydrogen atom4 ,their source is uncertain1 but they may be derived from the electrodes4 ,the beta rays are identical in type with the cathode rays and are negative electrons4 ,the gamma rays are analogous to the ,x rays and are of the order of light4 ,they are in general considerably more penetrating than ,x rays4 ,for example1 the gamma rays sent out by #cj milligrams of radium can be detected by an electroscope after passing through #cj centimeters of iron1 a much greater thickness than can be penetrated by the ordinary ,x rays4 ,,chapter ,,iii ,,changes ,,in ,,radio-,,active ,,bodies ,is ,radio-activity a ,permanent ,property8 ,is this power of emitting radiations a permanent property or is it lost with the passage of time8 ,the first investigations of the activity of uranium and thorium showed no loss of intensity at the end of several years1 and radium also seemed to show no decrease in its enormous activity4 ,polonium1 however1 was found to lose most of its activity in a year1 and later it appeared that some radio-active substances lost most of their activity in the course of a few minutes or hours4 ,induced ,activity ,a phenomenon called induced or secondary radio-activity was also observed4 ,thus a metal plate or wire exposed to the action of thorium oxide for some hours became itself active4 ,this induced activity was not permanent but decreased to half its value in about eleven hours and practically disappeared within a week4 ,similar phenomena were observed when radium was substituted for thorium4 ,discovery of ,uranium ,x ,in #aijj ,crookes precipitated a solution of an active uranium salt with ammonium carbonate4 ,the precipitate was dissolved so far as possible in an excess of the reagent1 leaving an insoluble residue4 ,this residue was many hundred times more active1 weight for weight1 than the original salt1 and the solution containing the salt was practically inactive4 ,at the end of a year the uranium salt had regained its activity while the residue had become inactive4 ,another method of obtaining the same result is to dissolve crystallized uranium nitrate in ether4 ,two layers of solution are formed1 one ether and the other water coming from the water of crystallization4 ,the aqueous layer is active1 while the water layer is inactive4 ,similarly1 by adding barium chloride solution to a solution of a salt of uranium and then precipitating the barium as sulphate1 the activity is transferred to this precipitate4 ,these experiments give proof of the formation and separation of a radio-active body by ordinary chemical operations4 ,so1 too1 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 salt4 ,after standing a month1 the separated material has lost its activity and the thorium salt has regained it4 ,here1 again1 there is the formation1 separation1 and loss of a radio-active body4 ,conclusions ,drawn ,now1 these are ordinary chemical processes for the separation of distinct chemical individuals4 ,the results1 therefore1 lead naturally to the conclusions3 7#a7 it would seem that uranium and thorium are themselves inactive and the activity is due to some other substance formed by these elements2 7#b7 this active substance is produced by some transformation in those elements1 for on standing the activity is regained4 ,this latter conclusion is startling1 for it indicates a change in the atom which1 up to the time of this discovery1 was deemed unchangeable under the influence of such physical and chemical changes as were known to us4 ,search for ,new ,radio-active ,bodies ,the search for new radio-active bodies and the study of their characteristics has been systematically and successfully carried on4 ,the bodies obtained in the above experiments were named uranium ,x and thorium ,x1 respectively4 ,further1 it became clear from the investigation of uranium minerals that radium1 polonium1 actinium1 and ionium originated from uranium4 ,from thorium minerals a body was separated called mesothorium1 which was analogous to radium4 ,both thorium and radium were found to give off a radio-active gas4 ,the first lost half of its activity in less than one minute4 ,the second was more stable and lost half of its activity in about four days4 ,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 gases1 such as helium1 argon1 neon1 etc41 which had been discovered by ,ramsay4 ,in some cases the chemical action was determined and these new bodies were found analogous to well-known elements1 as radium to barium1 polonium to bismuth4 ,the physical properties were investigated and1 where possible1 spectra were mapped and atomic weights determined4 ,it is clear1 therefore1 that these bodies are elemental in character and as such are made up of distinct1 similar atoms1 just as the commonly recognized elements are believed to be4 ,in this way more than thirty new elements have been added to the list4 ,these new elements are called radio-active elements1 but it is an open question whether all atoms do not possess this property in greater or less degree4 ,certainly1 it is possessed in varying degree by four of the old elements widely separated in the ,periodic ,system1 namely1 uranium1 thorium1 rubidium1 and potassium4 ,the last two1 while feebly active themselves1 do not form any secondary radio-active substance so far as is known4 ,only two of the elements1 then1 can definitely be said to go through these transformations4 ,it is just possible that radio-activity may be found to be a common property of all atoms and of all matter4 ,methods of ,investigation ,it is important to know how these new bodies were discovered and distinguished from one another4 ,two properties are relied upon4 ,one is the nature of the rays emitted and the other is the duration of the activity4 ,of course1 knowledge of the physical and chemical properties is also of great importance whenever obtainable4 ,nature of the ,radiations ,the nature of the radiation is a distinguishing characteristic1 though similarity here does not prove identity of substances4 ,some emit alpha rays only1 some emit beta rays1 some emit two of the possible rays1 as for instance1 beta and gamma1 and some emit all three4 ,the rays may also differ in the velocity with which they are emitted by different radio-active substances4 ,thus1 in the case of one substance the alpha rays may have a slightly greater or less penetrating power than those emitted by some other substance1 and this may be true also of the other rays4 ,life ,periods ,the duration of the activity is called the life period4 ,this is absolutely fixed for each body and furnishes the most important mode of differentiating among them4 ,it measures the relative stability and is the time which must elapse before their activity is lost and they1 changing into something else1 entirely disappear4 ,the measure usually adopted is the half-value period4 ,two hypotheses are made use of3 #a4 ,that there is a constant production of fresh radio-active matter by the radio-active body4 #b4 ,that the activity of the matter so formed decreases according to an exponential law with the time from the moment of its formation4 ,these hypotheses agree with the experimental results4 ,the decrease and rise of activity1 for example1 of uranium and uranium ,x1 and also of thorium and thorium ,x1 have been measured1 plotted1 and the equations worked out4 ,manifestly1 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 produced4 ,this equilibrium and the knowledge of the rate of decrease in general will have little value if this rate1 like chemical changes1 is subject to the influence of chemical and physical conditions4 ,the rate of decrease has been found to be unaltered by any known chemical or physical agency4 ,for instance1 neither the highest temperatures applicable nor the cold of liquid air have any appreciable effect4 ,equilibrium ,series ,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 bodies1 the relation between the amounts under consideration must be a definite one4 ,for this purpose equal weights of the bodies are not taken1 but use is made of the amounts which are in equilibrium with a fixed amount of the parent substance4 ,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 emanation4 ,thus1 a curie of radium emanation 7or niton7 is the weight 7or1 as this is a gas1 the volume at standard pressure and temperature7 of the emanation in equilibrium with one gram of radium4 ,this1 by calculation and experiment1 is found to be #j4fc cubic millimeter4 ,when this amount has been produced by one gram of radium1 the formation and decay will exactly balance one another4 ,this is1 therefore1 one curie of emanation4 ,the measurement of the rate of decay is difficult but can be carried out with great accuracy1 even down to seconds1 in the case of certain short-lived bodies4 ,errors crept in at first from the failure to completely separate the substances produced in the series1 and sometimes because of the simultaneous production of two substances4 ,as stated1 the decay follows an exponential law4 ,the time required for the decay of activity to half-value does not mean1 therefore1 that there will be total decay in twice that time4 ,thus the half-value period for uranium ,x is about #bb days4 ,the period for complete decay is about #afj days4 ,this half-value period corresponds to the half-value recovery period of uranium1 which is also #bb days4 ,these were the earlier figures obtained for uranium ,x and they illustrate some of the difficulties surrounding such determinations4 ,it was found later that the body examined as uranium ,x was really a constant mixture and of course the decay and recovery periods were also composite4 ,it required later and very skilful work to separate them into the bodies indicated in the disintegration series4 ,the half-value period for thorium ,x is much shorter1 namely1 a little over four days1 and this is also the recovery period for thorium ,x4 ,the plotted decay and recovery curves will intersect at this point4 ,the consecutive disintegration series1 with the half-value periods1 for the uranium and thorium series as given by ,soddy are seen in the following tables4 ,they are probably subject to some changes on further and more accurate determination4 ,the nature of the rays emitted is also given4 ,illustration3 ,uranium 7#h #aji years7 #bch4e - alpha - alpha _/ ,uranium ,x 7#ce4e days7 7#bcj4e7 - betagamma - 7beta7 _/ _/ _/ ,ionium 7#e #ajd to #ajf years7 7#bcj4e7 - alpha _/ ,radium 7#b1ejj years7 #bbf4d - alpha _/ ,emanation 7#e4eg days7 7#bbb4d7 - alpha _/ ,radium ,a 7#d4c minutes7 7#bah4d7 - alpha _/ ,radium ,b 7#ch4e minutes7 7#bad4d7 - 7beta7 _/ ,radium ,c#a 7#bh4a minutes7 7#bad4d7 - alpha - betagamma _/ ,radium ,c#b 7#a4i minutes7 7#baj4d7 - betagamma _/ ,radium ,d 7#bd years87 7#baj4d7 - 7beta7 _/ ,radium ,e 7#g4be days7 7#baj4d7 - betagamma _/ ,radium ,f 7,polonium #bjb days7 7#baj4d7 - alpha _/ ,radium ,g 7probably lead7 7#bjf4h7 ,actinium 787 _/ ,radio-,actinium 7#bh4a days7 - alpha - 7beta7 _/ ,actinium ,x 7#ae days7 - alpha _/ ,emanation 7#e4f seconds7 - alpha _/ ,actinium ,a 7#j4jjbi second7 - alpha _/ ,actinium ,b 7#eb4a minutes7 - 7beta7 _/ ,actinium ,c#a 7#c4aj mins47 - alpha _/ ,actinium ,c#b 787 - alpha _/ ,actinium ,d 7#g4d minutes7 - betagamma _/ ,actinium ,e 7unknown7 ,thorium 7#d #ajaj years87 #bcb4d - alpha787 _/ ,mesothorium#a 7#g4i years7 _/ ,mesothorium#b 7#h4i hours7 - betagamma _/ ,radiothorium 7#b4ia years87 - alpha _/ ,thorium ,x 7#e4ce days7 - alpha _/ ,emanation 7#gf seconds7 - alpha _/ ,thorium ,a 7#j4bjc second7 - alpha _/ ,thorium ,b 7#ae4c hours7 - 7beta7 _/ ,thorium ,c#a 7#gi minutes7 - alpha _/ ,thorium ,c#b 787 - alpha _/ ,thorium ,d 7#d4e minutes7 - betagamma _/ ,thorium ,e 7unknown7 ,,fig4 #f4--;,,disintegration ,,series ,,for ,,uranium1 ,,actinium1 ,,and ,,thorium1 ,,as ,,given ,,by ,,soddy4 ,,chapter ,,iv ,,nature ,,of ,,the ,,alpha ,,particle ,disintegration of the ,elements ,the remarkable disintegrations related in the last chapter1 in which the heaviest known elementary atom--that of uranium 7at4 wt4 #bch7--;is by successive stages changed into others of lower atomic weight1 afford a clue to the nature of the atom and to that goal of the chemist1 the final constitution of matter4 ,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 earlier1 but all attempts at working out a so-called genesis of the elements had proved vague and unsatisfactory4 ,identification of the ,rays ,to get an understanding of the disintegration occurring in radio-active substances1 the nature of the rays produced must be known4 ,these rays are the cause of the activity and their emission accompanies the changes or disintegration4 ,they have for the sake of convenience been called the alpha1 beta1 and gamma rays4 ,the gamma rays have been identified with the ,x rays discovered by ,rntgen and are a form of energy analogous to light4 ,the beta rays are particles of negative electricity or electrons4 ,with these1 then1 we have some degree of familiarity4 ,but what are the alpha rays8 ,an answer to this question should make clearer the character of the changes taking place1 and should give some insight into the composition and mechanism of the atom4 ,the ,alpha ,rays ,it has already been stated that these alpha rays are similar or analogous to the canal rays1 but this advances the matter very little1 as the nature of these canal rays has not been fully determined4 ,the full identity with them1 if proved1 should have an important theoretical bearing4 ,alpha ,rays ,consist of ,solid ,particles ,in the first place1 these alpha rays have been found to be made up of solid particles1 that is1 of what we are accustomed to call matter4 ,since it has become more and more difficult to draw a clear distinction between matter and energy1 it would perhaps be better to say that these particles appear to have some of the properties hitherto attributed solely to matter4 ,the best evidence that these particles are of atomic mass is furnished by their deflection in electric and magnetic fields4 ,electrical ,charge ,it is not of first importance to discuss this or other proofs of the material nature of these particles4 ,that they carry a charge of positive electricity is1 however1 a fact of very great import4 ,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 be #i4c #aj-aj electrostatic units 74#jjj1jjj1jjj1ic e4s474 ,from the consideration of the charge upon an electron previously obtained by ,j4 ,j4 ,thomson and others1 it was concluded that the alpha particle carried two unit positive charges2 the fundamental unit charge1 therefore1 is half this value1 or #d4fe #aj-aj e4s4 ,helium ,formed from ,alpha ,particles ,to determine the nature of the alpha particle a crucial experiment was carried out by ,rutherford and ,royds1 which was described as follows3 ,illustration3 ,,fig4 #g4--;,,apparatus ,,used ,,in ,,experiment ,,by ,,rutherford ,,and ,,royds4 ,a large quantity of radium emanation was compressed into a fine glass tube ,a1 about #a4e cm4 long4 ,this tube1 which was sealed to a larger capillary tube ,b1 was sufficiently thin to allow the alpha particles from the emanation and its products to pass through1 but sufficiently thick to withstand atmospheric pressure4 ,the thickness of the glass wall was in most cases less than 4#ja mm4 ,on introducing the emanation into the tube1 the escape of the alpha particles from the emanation was clearly seen by the scintillations produced at some distance on a zinc sulphide screen4 ,after this test the glass tube ,a was surrounded by a glass tube ,t and a small spectrum tube ,v attached to it4 ,the tube ,t was exhausted to a charcoal vacuum4 ,by means of the mercury column ,h1 the gases in the tube ,t could at any time be compressed into the spectrum tube ,v and the nature of the gases which had been produced determined spectroscopically4 ,it was found that two days after the introduction of the emanation into ,a the spectrum showed the yellow line of helium1 and after six days the whole helium spectrum was observed4 ,in order to be certain that the helium1 coming possibly from some other source1 had not diffused through the thin walls of the tube ,a1 the emanation was pumped out and helium substituted4 ,no trace of helium could be observed in the vacuum tube after several days1 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 tube4 ,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 space4 ,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 tube1 since the particles fired into the lead diffuse out more rapidly than from glass4 ,a still more definite proof of the identity of the alpha particle with the helium atom was obtained by removing the outer glass tube ,t and placing a cylinder of lead over the emanation tube in the open air4 ,helium was always detected in the lead after it had remained several hours over the thin tube containing a large quantity of the emanation4 ,in order to test for the presence of helium in the lead1 the gases present were released by melting the lead in a closed vessel4 ,there can thus be no doubt that the alpha particle becomes a helium atom when its positive charge is neutralized4 ,thus the chemist was afforded the experience of the building up of at least one element under his observation1 and both the analysis and synthesis of matter have been revealed through the discoveries of radio-activity4 ,discovery of ,helium ,it is of interest at this point to learn something of the history of helium and its occurrence4 ,in #ahfh there was discovered by ,janssen and ,lockyer a bright yellow line in the spectrum of the sun's chromosphere4 ,because of its origin the name helium was given to the supposed new element causing it4 ,later it was found in the spectra of many of the stars1 and because of its predominance in some of these they were called helium stars4 ,its existence on our planet was not detected for nearly thirty years4 ,in #ahie1 in connection with the discovery of argon in the atmosphere1 a search was made to see if the latter element could be obtained from mineral sources4 ,in analyzing certain uranium minerals ,hillebrand had found considerable quantities of a gas which he took to be a peculiar form of nitrogen4 ,ramsay made a further examination of the gas coming from these minerals and the spectroscope revealed the yellow line of helium1 thus at last proving the presence of this element on the earth4 ,it is known now to be present in thorium minerals1 in the waters of radio-active wells1 and in minute amounts in the atmosphere4 ,its occurrence in every case1 in the light of the experiment described above1 would seem to be due to the presence of radio-active changes4 ,characteristics of ,helium ,helium1 on account of its chemical inactivity and physical properties1 is classed along with argon1 neon1 krypton1 and xenon in the zero group of the ,periodic ,system1 and forms with them the monatomic1 inert gases4 ,in this class are now placed also the three radio-active gases1 emanating respectively from radium1 thorium1 and actinium4 ,these are generally known as radium emanation1 thorium emanation1 and actinium emanation4 ,the first mentioned was once called niton4 ,emanium was the name originally proposed by ,giesel for the body now known as actinium4 ,the calculated rate of production of helium in the series in equilibrium with one gram of radium is #aeh cubic millimeters per year4 ,this corresponds quite well with the experimental results4 ,table of ,constants ,some of the more important atomic and radio-active constants are given in the following table4 ,they are recorded here to show how helpful the study of radio-activity has been in working out the composition of matter1 and to give some idea of the magnitude of the numbers and the minuteness of the quantities dealt with4 ,electric charge carried by each ,h atom in electrolysis #d4fe #aj-aj e4s4#a ,electric charge carried by each alpha particle #i4c #aj-aj e4s4 ,number of atoms in #a gram of ,h #f4b #ajbc ,mass of #a atom of ,h #a4f #aj-bd gram ,number of molecules per cc4 of any gas at standard pressure and temperature #b4gb #ajai ,number of alpha particles expelled per second per gram of radium itself #c4f #ajaj ,number of alpha particles expelled per second per gram of radium in equilibrium with its products #ad4c #ajaj #a ,the expression #aj-aj means multiplying by 4#jjj1jjj1jjj1a2 #ajaj means multiplying by #aj1jjj1jjj1jjj4 ,,chapter ,v ,,the ,,structure ,,of ,,the ,,atom ,properties of ,radium ,a study of the properties of radium will aid in throwing light upon the question as to the building up of the atom4 ,first to be considered are the usual properties which distinguish an elementary body4 ,metallic radium has been prepared by a method similar to that used in the preparation of barium4 ,it is a pure white metal1 melting at #gjj1 and far more volatile than barium4 ,it rapidly alters on exposure to the air1 probably forming a nitride4 ,it energetically decomposes water and the product dissolves in the water4 ,its atomic weight is #bbf4 ,radium forms a series of salts analogous in appearance and chemical action to those of barium4 ,in the course of time they become colored1 especially if mixed barium salts4 ,the radiations from radium produce marked chemical effects in a number of substances4 ,carbon dioxide is changed into carbon1 oxygen1 and carbon monoxide1 and the latter is changed into carbon and oxygen4 ,ammonia is dissociated into nitrogen and hydrogen2 hydrochloric acid into chlorine and hydrogen4 ,oxygen is condensed into ozone4 ,in general1 the action upon gases appears to be similar to that of the silent electric discharge4 ,water is decomposed into hydrogen and oxygen4 ,if moist radium chloride or a salt of radium containing water of crystallization is sealed in a glass tube1 the gradual accumulation of hydrogen and oxygen will burst the tube4 ,the radiations rapidly decompose organic matter with the evolution of gases4 ,thus grease from stopcocks of apparatus used with radium or paraffin will give off carbon dioxide4 ,under an intense alpha radiation paraffin or vaseline become hard and infusible4 ,white phosphorus is changed into red4 ,the action upon living tissue is most noteworthy1 as its possible use as a remedial agent is dependent upon this4 ,a small amount of a radium salt enclosed in a glass tube will cause a serious burn on flesh exposed to it4 ,it therefore has to be handled with care and undue exposure to the radiations must be avoided4 ,cancer sacs shrivel up and practically disappear under its action4 ,whether the destruction of whatever causes the cancer is complete is at least open to serious doubt4 ,the coagulating effect upon globulin is interesting4 ,when two solutions of globulin from ox serum are taken and acetic acid added to one while ammonia is added to the other1 the opalescence in drops of the former is rapidly diminished on exposure to radium1 showing a more complete solution1 whereas the latter solution rapidly turns to a jelly and becomes opaque1 indicating a greatly decreased solubility4 ,energy ,evolved by ,radium ,the greater part of the tremendous energy evolved by radium is due to the emission of the alpha particles1 and in comparison the beta and gamma rays together supply only a small fraction4 ,this energy may be measured as heat4 ,it was first observed that a radium compound maintained a temperature several degrees higher than that of the air around it4 ,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 temperature4 ,both methods showed that the heat produced was at the rate of about #ace gram calories per hour4 ,as the emission is continuous1 one gram of radium would therefore emit about #a1ahj1jjj gram calories in the course of a year4 ,at the end of #bjjj years it would still emit #eij1jjj gram calories per year4 ,such a production of energy so far surpasses all experience that it becomes almost inconceivable4 ,it is futile to speak of it in terms of the heat evolved by the combustion of hydrogen1 which is the greatest that can be produced by chemical means4 ,this effect is unaltered at low temperatures1 as has been tested by immersing a tube containing radium in liquid air4 ,it should be stated that these measurements were made after the radium had reached an equilibrium with its products2 that is1 after waiting at least a month after its preparation4 ,the evolution of heat from radium and the radio-active substances is1 in a sense1 a secondary effect1 as it measures the radiant energy transformed into heat energy by the active matter itself and whatever surrounds it4 ,let us repeat1 therefore1 that the total amount of energy pent up in a single atom of radium almost passes our powers of conception4 ,necessity for a ,disintegration ,theory ,the facts gathered so far justify and necessitate a theory which shall satisfactorily explain them1 and since these phenomena are not caused by nor subject to the influence of external agencies1 they must refer to changes taking place within the atom--in other words1 a theory of disintegration4 ,in the main1 these facts may be summed up as the emission of certain radiations from known elemental matter3 the material alpha particles with positive charge1 the beta particles or negative electrons1 and the gamma rays analogous to ,x rays4 ,the emission of these rays results in the production of great heat4 ,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 series4 ,lastly1 we have the production of helium from the alpha particles4 ,disintegration ,theory ,in explanation of these phenomena1 ,rutherford offered the hypothesis that the atoms of certain elements were unstable and subject to disintegration4 ,the only elements definitely known to come under this description are the two having atoms of the greatest known mass1 thorium 7#bcb7 and uranium 7#bch74 ,the atoms of uranium1 for instance1 are supposed to be not permanent but unstable systems4 ,according to the hypothesis1 about #a atom in every #ajah becomes unstable each second and breaks up with a violent explosion for so small a mass of matter4 ,one1 or possibly two alpha particles are expelled with great velocity4 ,this alpha particle corresponds to an atom of helium with an atomic weight of #d1 and its loss reduces the original atomic weight to #bcd with the formation of a new element1 having changed properties corresponding to the new atomic weight4 ,this new element is uranium ,x#a4 ,these new atoms are far more unstable than those of uranium1 and the decomposition proceeds at a new rate of #a in #ajg per second4 ,so at a definite1 measurable rate this stepwise disintegration proceeds4 ,the explosions are not in all cases equally violent in going from element to element1 nor are the results the same4 ,sometimes alpha particles alone are expelled1 sometimes beta1 or two of them together1 as alpha and beta4 ,the new product may remain with the unchanged part of the original matter4 ,thus there would be an accumulation of it until its own decay balances its production1 resulting eventually in a state of equilibrium4 ,constitution of the ,atom ,in order to explain the electrical and optical properties of matter1 the hypothesis was made that the atom consisted of positively and negatively electrified particles4 ,later it was shown that negative electrons exist in all kinds of matter4 ,various attempts were made to work out a model of such an atom in which these particles were held in equilibrium by electrical forces4 ,the atom of ,lord ,kelvin consisted of a uniform sphere of positive electrification throughout which a number of negative electrons were distributed1 and ,j4 ,j4 ,thomson has determined the properties of this type as to the number of particles1 their arrangement and stability4 ,rutherford's ,atom ,according to ,rutherford1 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 motion4 ,the positively charged centre is made up of a complicated system in movement1 consisting in part of charged helium and hydrogen atoms1 and practically the whole charge and mass of the atom is concentrated at the centre4 ,the central system of the atom is from some unknown cause unstable1 and one of the helium atoms escapes from the central mass as an alpha particle4 ,there are1 confessedly1 difficulties connected with this conception of the atom which need not1 however1 be discussed here4 ,much remains to be learned as to the mechanics of the atom1 and the hypothesis outlined above will probably have to be materially altered as knowledge grows4 ,perhaps it may have to be entirely abandoned in favor of some more satisfactory solution4 ,until such time it at least suffices as a mental picture around which the known facts group themselves4 ,in this picture energy and matter lose their old-time distinctness of definition4 ,discrete subdivisions of energy are recognized which may be called charged particles without losing their significance4 ,some of these subdivisions charged in a certain way or with neutralized charge exhibit the properties of so-called matter4 ,scattering of ,alpha ,particles ,this conception of the atom would doubtless fail of much support were it not for certain experimental facts which lend great weight to it4 ,certain suppositions can be based on this theory mathematically reasoned out and tested by experiment4 ,predictions thus based on mathematical reasoning and afterward confirmed by experiment give a very convincing impression that truth lies at the bottom4 ,the first of these experimental proofs comes under the head of what is known as the scattering of the alpha particles1 a phenomenon which1 when first observed1 proved hard to explain4 ,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 atom1 it should be deflected from its course and1 the intensity of the two charges being known1 the angle of deflection could be calculated4 ,for instance1 if it came to what might be called a head-on collision with the positive central nucleus of another atom1 it would recoil if it were itself of lesser mass1 or would propel the other forward if that were the lighter4 ,the experiment is carried out by placing a thin metal foil over a radio-active body1 as radium ,c1 which expels alpha particles with a high velocity1 and counting the number of alpha particles which are scattered through an angle greater than #ij and so recoil toward their source4 ,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 foil4 ,for example1 if gold is used1 the number of recoil atoms is one in something less than #h1jjj4 ,taking the atomic weight of gold into consideration1 ,rutherford calculated mathematically that this was about the number which should be driven backward4 ,but he went further and calculated also the number which should be returned by aluminum1 which has an atomic weight of only about one-seventh that of gold4 ,two investigators determined experimentally the number for aluminum and their results agreed with ,rutherford's calculations4 ,the metals from aluminum to gold have been examined in this way4 ,the number of recoil particles increases with the atomic weight of the metal4 ,comparing experiment with theory1 the central charge in an atom corresponds to about one-half the atomic weight multiplied by the charge on an electron1 or1 as it is expressed1 #a_/b ,ae4 ,there is only one lighter atom than helium1 namely1 hydrogen1 which has a mass only one-fourth as great4 ,when alpha particles are discharged into hydrogen1 a few of the latter atoms are found to be propelled to a distance four times as great as that reached by the alpha particles4 ,stopping ,power of ,substances ,parallel with the experiments mentioned1 there is what is called the stopping power of substances4 ,this means the depth or thickness of a substance necessary to put a stop to the course of the alpha particles4 ,this gives the range of the alpha particles in such substances and is connected in a simple way with the atomic weight1 that is1 it is again fixed by the mass of the opposing atom4 ,this stopping power of an atom for an alpha particle is approximately proportional to the square root of its atomic weight4 ,considering gases1 for instance1 if the range in hydrogen be #a1 then the range in oxygen1 the atomic weight of which is #af1 is only 7#a_/af7a_/b or #a_/d4 ,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 taken4 ,,chapter ,,vi ,,radio-,,activity ,,and ,,chemical ,,theory ,influence upon ,chemical ,theory ,it can easily be seen that the revelations of radio-activity must have a far-reaching effect upon chemical theory1 throwing light upon1 and so bringing nearer1 the solution of some of the problems which have been long discussed without arriving at any satisfactory solution4 ,the so-called electro-chemical nature of the elements will certainly be made much clearer4 ,the changes in valence should become intelligible and valence itself should be explained4 ,a fuller understanding of the ionization of electrolytes also becomes possible4 ,as these matters are debatable and the details are still unsettled1 it is scarcely appropriate to give here the hypotheses in detail or to enter into any discussion of them4 ,but the promise of solution in accord with the facts is encouraging4 ,the ,periodic ,system ,such progress has been made1 however1 in regard to a better understanding of the ,periodic ,system that the new facts and their interpretation may well be given4 ,no reliable clue to the meaning of this system and the true relationship between the elements had been found up to the time when new light was thrown upon it by the discoveries of radio-activity4 ,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 ignored4 ,basis of the ,periodic ,system ,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 weights1 and that when the elements were arranged in the order of their atomic weights they fell into a natural series1 taking their places in the proper related groups4 ,in accepting this1 the interpretation of function was both unmathematical and vague1 and the order of the atomic weights was not strictly adhered to but unhesitatingly abandoned to force the group relationship4 ,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 properties1 the guidance of these properties was accepted and that of the atomic weights disregarded4 ,such shiftings are noted in the cases of tellurium and iodine2 cobalt and nickel2 argon and potassium4 ,it was most helpful that1 following the order of atomic weights1 the majority of the elements fell naturally into their places4 ,otherwise the generalization known as the ,periodic ,system might have remained for a long time undiscovered and the progress of chemistry would have been greatly retarded4 ,influence of ,positive ,nucleus ,it is evident that the order of the elements is determined by something else than their atomic weights4 ,from the known facts of radio-activity it would seem that this determining factor is the positive nucleus4 ,and this nucleus also determines the mass or weight of the atom4 ,taking the elements in their order in the ,periodic ,series and numbering the positions held by them in this series as #a1 #b1 #c1 etc41 we get the position number or what is called the atomic number4 ,this designates the order or position of the element in the series4 ,we must learn that this number marks a position rather than a single element1 a statement which will be explained later4 ,determination of the ,atomic ,number ,since the atomic weight is unreliable as a means of settling the position of an element in the series and so fixing its atomic number1 how is this number to be determined8 ,of course1 one answer to this question is that we may rely upon a consideration of the general properties1 as has been done in the past4 ,fortunately1 other methods have been found by which this may be confirmed4 ,for instance1 the stopping and scattering power of the element for alpha particles has been suggested and successfully used4 ,use of ,x-,ray ,spectra ,a most interesting method is due to ,moseley's observations upon the ,x-ray spectra of the various elements4 ,it has been found that crystals1 such as those of quartz1 have the power of reflecting and defining the ,x rays4 ,the spectra given by these rays can be photographed and the wave lengths measured4 ,these ,x rays are emitted by various substances under bombardment by the cathode rays 7negative electrons7 and have great intensity and very minute wave lengths4 ,moseley made use of various metals as anti-cathodes for the production of these rays4 ,these metals ranged from calcium to zinc in the ,periodic ,system4 ,in each case he observed that two characteristic types of ,x rays of definite intensity and different wave lengths were emitted4 ,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 next4 ,this is due to the charge of the positive central nucleus4 ,the number found in this way is one less than the atomic number4 ,thus the number for calcium is #ai instead of #bj and that for zinc is #bi instead of #cj4 ,so1 by adding #a to the number found the atomic number is obtained4 ,the atomic weight can usually be followed in fixing the atomic number1 but where doubt exists the method just given can be resorted to4 ,thus doubt arises in the case of iron and nickel and cobalt4 ,this would be the order according to the atomic weights4 ,the ,x-ray method gives the order as iron1 cobalt1 and nickel1 and this is the accepted order in the ,periodic ,system4 ,changes ,caused by ,ray ,emission ,on studying the properties of the elements in a transformation series in connection with the ray emission which produced them1 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 element4 ,atomic ,weight ,losses ,each alpha particle emitted means a loss of #d in the atomic weight4 ,this is the mass of a helium atom4 ,thus from uranium with an atomic weight of #bch to radium there is a loss of three alpha particles4 ,therefore1 #ab must be subtracted from #bch1 leaving #bbf1 which agrees closely with the atomic weight of radium as actually determined by the ordinary methods4 ,uranium ,x#a1 then1 would have an atomic weight of #bcd and that of ionium would be #bcj4 ,the other intermediate elements1 whose formation is due to the loss of beta particles only1 show no decrease in atomic weight4 ,lead the ,end ,product ,from uranium to lead there is a loss of #h alpha particles1 or #cb units in atomic weight4 ,this would give for the final product an atomic weight of #bjf4 ,the atomic weight of lead is #bjg4ag4 ,it is not at all certain that the final product of this series is ordinary lead4 ,the facts are such that they would lead one to think that it is not4 ,it is known only that the end product would probably be some element closely resembling lead chemically and hence difficult or impossible to separate from it4 ,several accurate determinations of lead coming from uranium minerals1 which always carry this element and in an approximately definite ratio to the amount of uranium present1 show atomic weights of #bjf4dj2 #bjf4cf2 and #bjf4ed4 ,even the most rigid methods of purification fail to change these results4 ,the lead in these minerals might therefore be considered as coming in the main from the disintegration of the uranium atom and1 though chemically resembling lead1 as being in reality a different element with different atomic weight4 ,furthermore1 in the thorium series #f alpha particles are lost before reaching the end product1 which again is perhaps the chemical analogue of lead4 ,the atomic weight here should be #bcb less #bd1 or #bjh4 ,determinations of the atomic weight of lead from thorite1 a thorium mineral nearly free from uranium1 gave #bjh4d4 ,the end product of the actinium series is also an element resembling lead1 but both the beginning and ending of this series are still in obscurity4 ,changes of ,position in the ,periodic ,system ,the loss of #d 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 ,system4 ,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 group4 ,ionium expels an alpha particle and becomes radium1 which is a bivalent element resembling barium belonging to the second group4 ,radium then expels an alpha particle and becomes the gas1 radium emanation1 which is an analogue of argon and belongs to the zero group4 ,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 ,system4 ,changes from ,loss of ,beta ,particles ,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 ,system4 ,two such losses1 then1 will counterbalance the loss of an alpha particle and bring the new element back to the group originally occupied by its progenitor4 ,thus uranium in the sixth group loses an alpha particle and the product ,,ux#a falls in the fourth group4 ,one beta particle is then lost and ,,ux#b belonging to the fifth group is formed4 ,with the loss of one more beta particle the new element returns to the sixth group from which the transformation began4 ,the table on page #dh1 as adapted from ,soddy1 affords a general view of these changes4 ,isotopes ,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 weights4 ,these are chemically inseparable so far as the present limitations of chemical analysis are concerned4 ,even the spectra of these elements seem to be identical so far as known4 ,this identity extends to most of the physical properties1 but this demands much further investigation4 ,for this new phenomenon ,soddy has suggested the word isotope for the element and isotopic for the property1 and these names have come into general use4 ,illustration3 ,,radio-,,active ,,elements ,,from ,,uranium ,,and ,,thorium ,,placed ,,in ,,the ,,periodic ,,systems ,adapted from ,soddy ,manifestly1 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 general4 ,all of the properties of the bodies which we call elements1 and consequently of their compounds and hence of matter in general1 seem to depend upon the balance maintained between the charges of negative and positive electricity which1 according to ,rutherford's theory1 go to make up the atom4 ,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 produces4 ,radio-activity in ,nature ,in concluding this outline of the main facts of radio-activity1 it is of interest to discuss briefly the presence of radio-active material on this planet and in the stars4 ,facts enough have been gathered to show the probable universality of this phenomenon of radio-activity4 ,whether this means solely the disintegration of the uranium and thorium atoms1 or whether other elements are also transformed under the intensity of the agencies at work in the universe1 is of course a question as yet unsolved4 ,radio-active ,products in the ,earth's ,crust ,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 also4 ,various rocks of igneous origin have been examined revealing from #d4gh #aj-ab to #j4ca #aj-ab grams of radium per gram of the rock4 ,aqueous rocks have shown a lesser amount1 ranging from #b4ib #aj-ab to #j4hf #aj-ab grams4 ,as the soil is formed by the decomposition of these rocks1 radium is present in varying amounts in all kinds of soil4 ,presence in ,air and ,soil ,waters ,as radium is transformed into the gaseous emanation1 this will escape wherever the soil is not enclosed4 ,for instance1 a larger amount of radio-activity is found in the soil of caves and cellars than in open soils4 ,if an iron pipe is sunk into a soil and the air of the soil sucked up into a large electroscope1 the latter instrument will show the effect of the rays emitted and will measure the degree of activity4 ,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 soil4 ,this radium emanation is dissolved in the soil waters1 wells1 springs1 and rivers1 rendering them more or less radio-active1 and sometimes the muddy deposit at the bottom of a spring shows decided radio-activity4 ,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 atmosphere4 ,neither summer nor winter seems to affect this emanation1 and it extends certainly to a height of two or three miles4 ,rain1 falling through the air1 dissolves some of the emanation1 so that it may be found in freshly-fallen rain water and also in freshly-fallen snow4 ,radio-active deposits are found upon electrically charged wires exposed near the earth's surface4 ,as helium is the resulting product of the alpha particles emitted by the emanation and other radio-active bodies1 it is found in the soil air1 soil waters1 and atmosphere4 ,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 emanation4 ,a number of estimates have been given as to the heat produced by the radio-active transformations going on in the material of this planet4 ,actual data are scarce and mere assumptions unsatisfactory1 so little that is worth while can be deduced4 ,it is possible that this source of heat may have an appreciable effect upon or serve to balance the earth's rate of cooling4 ,cosmical ,radio-activity ,meteorites of iron coming from other celestial bodies have not shown the presence of radium4 ,aerolites or stone meteorites have been found to contain as much as similar terrestrial rock4 ,since the sun contains helium and some stars show its presence as predominating1 this suggests the presence of radio-active matter in these bodies4 ,in addition1 the spectral lines of uranium1 radium1 and the radium emanation have been reported as being found in the sun's spectrum and also in the new star1 ,nova ,geminorum #b4 ,these observations await further investigation and confirmation4 ,so far as the sun's chromosphere is concerned1 the possible amount of radium present would seem to be very small4 ,if this is true1 radio-active processes could have little to do with the sun's heat4 ,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 rays4 ,such rays would be absorbed1 and the gamma rays likewise1 in passing through the earth's atmosphere and so escape ordinary observation4 ,all of this is but further evidence of the unity of matter and of forces in the universe4 ,,index ,actinium1 discovery of1 #f ,activity1 induced1 #ag ,alpha particles1 effect of loss on ,atomic ,weight1 #de electrical charge of1 #bf form helium1 #bg nature of1 #be penetrating power of1 #ci position of element changed by its loss1 #df recoil1 #ci scattering of1 #ch solid1 #bf ,atom1 constitution of1 #cf ,kelvin's1 #cg models of1 #cg ,rutherford's1 #cg ,atomic number1 determination of1 #dc ,becquerel's experiments1 #b ,beta particles1 change in position of element by loss of1 #dg ,chalcolite1 natural and artificial1 #d ,constants1 table of1 #ca ,curie unit1 #bb ,disintegration of the element1 #be ,disintegration series1 #bd ,disintegration theory1 #ce ,electroscope1 #ab ,equilibrium series1 #bb ,helium1 characteristics of1 #cj discovery of1 #bi ,ionium1 discovery of1 #f ,ionization1 application of electric field to1 #aj experimental confirmation1 #i ,ionization of gases1 #g theory of1 #h ,ions1 size and nature of1 #aj ,isotopes1 #dg ,lead1 atomic weight varies with source1 #de radio-active1 #f the end product1 #de ,life-periods of radio-active bodies1 #ba ,periodic system1 #da basis of1 #db ,polonium1 discovery of1 #d ,positive nucleus1 influence of1 #dc ,potassium1 radio-activity of1 #c ,radiations1 action on phosphorescent bodies1 #ac action on photographic plates1 #aa discharge electrified bodies1 #ab magnetic deflection of1 #ad measurements of1 #ae penetrating power of1 #ac1 #ae ,radio-active bodies1 elemental nature of1 #bj examination of1 #bj life periods of1 #ba ,radio-activity1 an atomic property1 #c cosmical1 #ea influence on chemical theory1 #da products in atmosphere1 #ea products in earth's crust1 #ej products in soil waters1 #ej ,radium1 action on organic matter1 etc41 #cc amount in pitchblende1 #e discovery of1 #e emanation1 #bb energy evolved by1 #cd properties of1 #e1 #cb ,rays1 alpha1 #ae1 #af1 #bf beta1 #ae1 #af gamma1 #ae1 #af identification of1 #af1 #be magnetic deflection of1 #ad photographing track of1 #aj types of1 #ad ,rubidium1 radio-activity of1 #c ,spinthariscope1 #ac ,stopping power of substances1 #ci ,thorium ,x1 discovery of1 #ah1 #ba ,uranium atom1 disintegration of1 #cf ,uranium minerals1 radio-activity of1 #c ,uranium ,x1 discovery of1 #ag1 #ba1 #bc ,x-ray spectra1 #dd ,zinc sulphide screen1 #ac ,,transcriber',s ,,notes #a4 ,passages in italics are surrounded by underscores4 #b4 ,images have been moved from the middle of a paragraph to the closest paragraph break4 #c4 ,the original text includes certain ,greek alphabets4 ,for this text version alpha1 beta1 gamma indicate first three letters of ,greek alphabet respectively4 #d4 ,in this version1 the number following carat character is to be interpreted as follows4 ,the expression #aj-b means multiplying by #j4ja2 #ajaj means multiplying by #aj1jjj1jjj1jjj4 #e4 ,in this version1 the subscripted text has been replaced by an underline character followed by the same with curly braces and 4 ,for example1 ,x#a indicates ,x with subscript #a4 #f4 ,the fractions are indicated with the help of forward character _/4 ,for example1 #a_/d indicates one-fourth4 #g4 ,other than the changes listed above1 the original text has been reproduced as such4