,,radio-,,active ,,substances4 ,,by ,,mdme4 ,,sklodowska ,,curie4 ,thesis presented to the ,facult des ,sciences de ,paris4 ,reprinted from the ,,chemical ,,news4 7,,second ,,edition74 ,,london3 ,,chemical ,,news ,,office1 #af1 ,,newcastle ,,street1 ,,farringdon ,,street1 ,e4,c4 #aijd4 ,d4 ,,van ,,nostrand ,,company1 #bc ,,murray ,,and #bg ,,warren ,,streets1 ,,new ,,york4 ---------------------------------------- -------------------------------- ,a4 ,c4 ,,cossor1 #ed1 ,farringdon ,road1 ,e4,c4 ,illustration ,,spinthariscopes1 ,,as ,,devised ,,by ,,sir ,,william ,,crookes4 ,showing the ,scintillations of ,radium4 ,,price #bas4 each4 ,illustration ,,pure ,,radium ,,bromide1 when available ,,pitchblende and ,,thorium ,,nitrate4 ,illustration ,,ozone ,,generator1 ,complete1 ,with #a in4 spark coil1 #b #ags4 #f;d4 ,,crookes',s ,,high ,,vacuum ,,tubes1 showing the fluorescence of various minerals4 ,a good selection always in stock1 including several specialities4 ,,spectrum ,,tubes1 ,,glass ,,blowing1 8,x-,,ray0 ,,outfits and ,,tubes1 ,,high ,,frequency ,,apparatus and ,,applicators1 and other ,scientific ,instruments4 ,experimental work of any kind in ,glass or ,metal4 99 99 99 99 99 ,,radium ,,salts and ,other ,preparations and ,minerals4 ,radium ,bromide1 ,radium-,barium ,bromide1 ,radium-,barium ,chloride1 in ,tubes of various quantities and strengths4 ,phosphorescent ,zinc ,sulphide1 #a grm4 and #e grm4 ,tubes1 and per oz4 ,phosphorescent ,zinc ,sulphide1 ,screens4 ,radium1 ,active ,screens for ,photographic effects4 ,uranium ,platino-cyanide ,screens1 from #g #e to #ae #aa4 ,pitchblende1 ,selected ,radio-,active4 ,willemite1 ,autunite1 and other ,fluorescent ,minerals4 ,salts of ,uranium1 ,thorium1 ,calcium1 and other ,x-,ray ,materials4 7,,subject ,,to ,,being ,,unsold47 ,chemicals for ,scientific ,investigation and ,laboratory ,work4 ,,harrington ,,bros41 #d1 ,oliver's ,yard1 ,city ,road1 ,london1 ,e4,c4 ,,manufacturing ,,chemists4 ---------------------------------------- -------------------------------- ,,radio-,,active ,,substances ,,by ,,mdme4 ,,sklodowska ,,curie ,thesis presented to the ,facult des ,sciences de ,paris4 ,reprinted from the ,,chemical ,,news4 7,,second ,,edition74 ,,london3 ,,chemical ,,news ,,office1 #af1 ,,newcastle ,,street1 ,,farringdon ,,street1 ,e4,c4 #aijd4 ,d4 ,,van ,,nostrand ,,company1 ,,new ,,york4 ,,london3 ,,printed ,,by ,,edwin ,,john ,,davey1 #af1 ,,newcastle ,,street1 ,,farringdon ,,street1 ,e4,c4 ---------------------------------------- -------------------------------- ,reprinted from the ,,chemical ,,news1 #aijc1 ,vol4 #hh1 p4 #he et seq4 ,,radio-,,active ,,substances4 ,,introduction4 ,the object of the present work is the publication of researches which ,i have been carrying on for more than four years on radio-active bodies4 ,i began these researches by a study of the phosphorescence of uranium1 discovered by ,m4 ,becquerel4 ,the results to which ,i was led by this work promised to afford so interesting a field that ,m4 ,curie put aside the work on which he was engaged1 and joined me1 our object being the extraction of new radio-active substances and the further study of their properties4 ,since the commencement of our research we thought it well to hand over specimens of the substances1 discovered and prepared by ourselves1 to certain physicists1 in the first place to ,m4 ,becquerel1 to whom is due the discovery of the uranium rays4 ,in this way we ourselves facilitated the research by others besides ourselves on the new radio-active bodies4 ,at the termination of our first publications1 ,m4 ,giesel1 in ,germany1 also began to prepare these substances1 and passed on specimens of them to several ,german scientists4 ,finally1 these substances were placed on sale in ,france and ,germany1 and the subject growing in importance gave rise to a scientific movement1 such that numerous memoirs have appeared1 and are constantly appearing on radio-active bodies1 principally abroad4 ,the results of the various ,french and foreign researches are necessarily confused1 as is the case with all new subjects in course of investigation1 the aspect of the question becoming modified from day to day4 ,from the chemical point of view1 however1 one point is definitely established3--i4e41 the existence of a new element1 strongly radio-active1 viz41 radium4 ,the preparation of the pure chloride of radium and the determination of the atomic weight of radium form the chief part of my own work4 ,whilst this work adds to the elements actually known with certainty a new element with very curious properties1 a new method of chemical research is at the same time established and justified4 ,this method1 based on the consideration of radio-activity as an atomic property of matter1 is just that which enabled ,m4 ,curie and myself to discover the existence of radium4 ,if1 from the chemical point of view1 the question that we undertook primarily may be looked upon as solved1 the study of the physical properties of the radio-active bodies is in full evolution4 ,certain important points have been established1 but a large number of the conclusions are still of a provisional character4 ,this is not surprising when we consider the complexity of the phenomena due to radio-activity1 and the differences existing between the various radio-active substances4 ,the researches of physicists on these substances constantly meet and overlap4 ,whilst endeavouring to keep strictly to the limits of this work and to publish my individual research only1 ,i have been obliged at the same time to mention results of other researches1 the knowledge of which is indispensable4 ,i desired1 moreover1 to make this work an inclusive survey of the actual position of the question4 ,i indicate at the end the particular questions with which ,i am specially concerned1 and those which ,i investigated in conjunction with ,m4 ,curie4 ,i carried on the work in the laboratories of the ,school of ,physics and ,chemistry in ,paris1 with the permission of ,schtzenberger1 late ,director of the ,school1 and ,m4 ,lauth1 actual ,director4 ,i take this opportunity of expressing my gratitude for the kind hospitality received in this school4 ,historical4 ,the discovery of the phenomena of radio-activity is connected with researches followed1 since the discovery of the ,rntgen rays1 upon the photographic effects of phosphorescent and fluorescent substances4 ,the first tubes for producing ,rntgen rays were without the metallic anticathode4 ,the source of the ,rntgen rays was the glass surface impinged upon by the cathode rays2 this surface was at the same time actively fluorescent4 ,the question then was whether the emission of ,rntgen rays necessarily accompanied the production of fluorescence1 whatever might be the cause of the latter4 ,this idea was first enunciated by ,m4 ,henri ,poincar4 ,shortly afterwards1 ,m4 ,henry announced that he had obtained photographic impressions through black paper by means of phosphorescent zinc sulphide4 ,m4 ,niewenglowski obtained the same phenomenon with calcium sulphide exposed to the light4 ,finally1 ,m4 ,troost obtained strong photographic impressions with zinc sulphide artificially phosphorescent acting across black paper and thick cardboard4 ,the experiences just cited have not been reproduced1 in spite of numerous attempts to this end4 ,it cannot therefore be considered as proved that zinc sulphide and calcium sulphide are capable of emitting1 under the action of light1 invisible rays which traverse black paper and act on photographic plates4 ,m4 ,becquerel has made similar experiments on the salts of uranium1 some of which are fluorescent4 ,he obtained photographic impressions through black paper with the double sulphate of uranium and potassium4 ,m4 ,becquerel at first believed that this salt1 which is fluorescent1 behaved like the sulphides of zinc and calcium in the experiments of ,,mm4 ,henry1 ,niewenglowski1 and ,troost4 ,but the conclusion of his experiments showed that the phenomenon observed was in no way related to the fluorescence4 ,it is not necessary that the salt should be fluorescent2 further1 uranium and all its compounds1 fluorescent or not1 act in the same manner1 and metallic uranium is the most active4 ,m4 ,becquerel finally found that by placing uranium compounds in complete darkness1 they continue acting on photographic plates through black paper for years4 ,m4 ,becquerel allows that uranium and its compounds emit peculiar rays--uranium rays4 ,he proved that these rays can penetrate thin metallic screens1 and that they discharge electrified bodies4 ,he also made experiments from which he concluded that uranium rays undergo reflection1 refraction1 and polarisation4 ,the work of other physicists 7,elster and ,geitel1 ,lord ,kelvin1 ,schmidt1 ,rutherford1 ,beattie1 and ,smoluchowski7 confirms and extends the results of the researches of ,m4 ,becquerel1 with the exception of those relating to the reflection1 refraction1 and polarisation of uranium rays1 which in this respect behave like ,rntgen rays1 as has been recognised first by ,mr4 ,rutherford and then by ,m4 ,becquerel himself4 ,,chapter ,i4 ,,radio-,,activity ,,of ,,uranium ,,and ,,thorium4 ,,radio-,,active ,,minerals4 ,becquerel ,rays4--,the uranium rays discovered by ,m4 ,becquerel act upon photographic plates screened from the light2 they can penetrate all solid1 liquid1 and gaseous substances1 provided that the thickness is sufficiently reduced2 in passing through a gas1 they cause it to become a feeble conductor of electricity4 ,these properties of the uranium compounds are not due to any known cause4 ,the radiation seems to be spontaneous2 it loses nothing in intensity1 even on keeping the compounds in complete darkness for several years2 hence there is no question of the phosphorescence being specially produced by light4 ,the spontaneity and persistence of the uranium radiation appear as a quite unique physical phenomenon4 ,m4 ,becquerel kept a piece of uranium for several years in the dark1 and he has affirmed that at the end of this time the action upon a photographic plate had not sensibly altered4 ,,mm4 ,elster and ,geitel made a similar experiment1 and also found the action to remain constant4 ,i measured the intensity of radiation of uranium by the effect of this radiation on the conductivity of air4 ,the method of measurement will be explained later4 ,i also obtained figures which prove the persistence of radiation within the limits of accuracy of the experiments4 ,for these measurements a metallic plate was used covered with a layer of powdered uranium2 this plate was not otherwise kept in the dark2 this precaution1 according to the experimenters already quoted1 being of no importance4 ,the number of measurements taken with this plate is very great1 and they actually extend over a period of five years4 ,some researches were conducted to discover whether other substances were capable of acting similarly to the uranium compounds4 ,m4 ,schmidt was the first to publish that thorium and its compounds possess exactly the same property4 ,a similar research1 made contemporaneously1 gave me the same result4 ,i published this not knowing at the time of ,schmidt's publication4 ,we shall say that uranium1 thorium1 and their compounds emit ,becquerel rays4 ,i have called radio-active those substances which generate emissions of this nature4 ,this name has since been adopted generally4 ,in their photographic and electric effects1 the ,becquerel rays approximate to the ,rntgen rays4 ,they also1 like the latter1 possess the faculty of penetrating all matter4 ,but their capacity for penetration is very different2 the rays of uranium and of thorium are arrested by some millimetres of solid matter1 and cannot traverse in air a distance greater than a few centimetres2 this at least is the case for the greater part of the radiation4 ,the researches of different physicists1 and primarily of ,mr4 ,rutherford1 have shown that the ,becquerel rays undergo neither regular reflection1 nor refraction1 nor polarisation4 ,the feeble penetrating power of uranium and thorium rays would point to their similarity to the secondary rays produced by the ,rntgen rays1 and which have been investigated by ,m4 ,sagnac1 rather than to the ,rntgen rays themselves4 ,for the rest1 the ,becquerel rays might be classified as cathode rays propagated in the air4 ,it is now known that these different analogies are all legitimate4 ,measurement of the ,intensity of ,radiation4 ,illustration3 ,,fig4 #a4 ,the method employed consists in measuring the conductivity acquired by air under the action of radio-active bodies2 this method possesses the advantage of being rapid and of furnishing figures which are comparable4 ,the apparatus employed by me for the purpose consists essentially of a plate condenser1 ,a ,b 7,fig4 #a74 ,the active body1 finely powered1 is spread over the plate ,b1 making the air between the plates a conductor4 ,in order to measure the conductivity1 the plate ,b is raised to a high potential by connecting it with one pole of a battery of small accumulators1 ,p1 of which the other pole is connected to earth4 ,the plate ,a being maintained at the potential of the earth by the connection ,c ,d1 an electric current is set up between the two plates4 ,the potential of plate ,a is recorded by an electrometer1 ,e4 ,if the earth connection be broken at ,c1 the plate ,a becomes charged1 and this charge causes a deflection of the electrometer4 ,the velocity of the deflection is proportional to the intensity of the current1 and serves to measure the latter4 ,but a preferable method of measurement is that of compensating the charge on plate ,a1 so as to cause no deflection of the electrometer4 ,the charges in question are extremely weak2 they may be compensated by means of a quartz electric balance1 ,q1 one sheath of which is connected to plate ,a and the other to earth4 ,the quartz lamina is subjected to a known tension1 produced by placing weights in a plate1 2 the tension is produced progressively1 and has the effect of generating progressively a known quantity of electricity during the time observed4 ,the operation can be so regulated that1 at each instant1 there is compensation between the quantity of electricity that traverses the condenser and that of the opposite kind furnished by the quartz4 ,in this way1 the quantity of electricity passing through the condenser for a given time1 i4e41 the intensity of the current1 can be measured in absolute units4 ,the measurement is independent of the sensitiveness of the electrometer4 ,in carrying out a certain number of measurements of this kind1 it is seen that radio-activity is a phenomenon capable of being measured with a certain accuracy4 ,it varies little with temperature2 it is scarcely affected by variations in the temperature of the surroundings2 it is not influenced by incandescence of the active substance4 ,the intensity of the current which traverses the condenser increases with the surface of the plates4 ,for a given condenser and a given substance the current increases with the difference of potential between the plates1 with the pressure of the gas which fills the condenser1 and with the distance of the plates 7provided this distance be not too great in comparison with the diameter74 ,in every case1 for great differences of potential the current attains a limiting value1 which is practically constant4 ,this is the current of saturation1 or limiting current4 ,similarly1 for a certain sufficiently great distance between the plates the current hardly varies any longer with the distance4 ,it is the current obtained under these conditions that was taken as the measure of radio-activity in my researches1 the condenser being placed in air at atmospheric pressure4 ,i append curves which represent the intensity of the current as a function of the field established between the plates for two different plate distances4 ,plate ,b was covered with a thin layer of powdered metallic uranium2 plate ,a1 connected with the electrometer1 was provided with a guard-ring4 ,illustration3 ,,fig4 #b4 ,illustration3 ,,fig4 #c4 ,fig4 #b shows that the intensity of the current becomes constant for high potential differences between the plates4 ,fig4 #c represents the same curves on another scale1 and comprehends only relative results for small differences of potential4 ,at the origin1 the curve is rectilinear2 the ratio of the intensity of the current to the difference of potential is constant for weak forces1 and represents the initial conduction between the plates4 ,two important characteristic constants of the observed phenomenon are therefore to be recognised3--7#a7 ,the initial conduction for small differences of potential2 7#b7 the limiting current for great potential differences4 ,the limiting current has been adopted as the measure of the radio-activity4 ,besides the difference of potential established between the two plates1 there exists between them an electromotive force of contact1 and these two sources of current combine their effects2 for this reason1 the absolute value of the intensity of the current changes with the sign of the external difference of potential4 ,in every case1 for considerable potential differences1 the effect of the electromotive force of contact is negligible1 and the intensity of the current is therefore the same whatever be the direction of the field between the plates4 ,the investigation of the conductivity of air and other gases subjected to the action of ,becquerel rays has been undertaken by several physicists4 ,a very complete research upon the subject has been published by ,mr4 ,rutherford4 ,the laws of the conductivity produced in gases by the ,becquerel rays are the same as those found for the ,rntgen rays4 ,the mechanics of the phenomenon appear to be the same in both cases4 ,the theory of ionisation of the gases by the action of the ,rntgen or ,becquerel rays agrees well with the observed facts4 ,this theory will not be put forward here4 ,i will merely record the results to which they point3-- ,firstly1 the number of ions produced per second in the gas is considered proportional to the energy of radiation absorbed by the gas4 ,secondly1 in order to obtain the limiting current relatively to a given radiation1 it is necessary1 on the one hand1 to cause complete absorption of this radiation by the gas by employing a sufficient mass of it2 on the other hand1 it is necessary for the production of the current to use all the ions generated by establishing an electric field of such strength that the number of the ions which recombine may be a negligible fraction of the total number of ions produced in the same time1 most of which are carried by the current to the electrodes4 ,the strength of the electric field necessary to give this result is proportional to the amount of ionisation4 ,according to the recent researches of ,mr4 ,townsend1 the phenomenon is more complex when the pressure of the gas is low4 ,at first the current appears to approach to a constant limiting value with increasing difference of potential2 but after a certain point has been reached1 the current begins again to increase with the field1 and with very great rapidity4 ,mr4 ,townsend ascribes this increase to a new ionisation produced by the ions themselves when1 under the action of the electric field1 they acquire a velocity such that a molecule of gas encountering one of them becomes broken down into its constituent ions4 ,a strong electric field and a low pressure are favourable to the production of this ionisation by ions already present1 and1 as soon as the action is set up1 the intensity of the current increases uniformly with the field between the plates4 ,the limiting current could1 therefore1 only be obtained under conditions of ionisation of which the intensity does not exceed a certain value1 and in such a manner that saturation corresponds to fields in which1 from multiplicity of ions1 ionisation can no longer take place4 ,this condition has occurred in my experiments4 ,the order of magnitude of the saturation currents obtained with uranium compounds is #aj-aa ampres for a condenser in which the plates have a diameter of #h c4m41 and are at a distance of #c c4m4 ,thorium compounds give rise to currents of the same order of magnitude1 and the activity of the oxides of uranium and thorium is very similar4 ,radio-activity of the ,compounds of ,uranium and ,thorium4 ,the following are the figures ,i obtained with different uranium compounds4 ,i have represented the intensity of the current in ampres by the letter i3-- i #ajaa4 ,metallic uranium 7containing a little carbon7 #bc ,black oxide of uranium1 ,u#b,o#e #bf ,green oxide of uranium1 ,u#c,o#d #ah ,hydrated uranic acid #jf ,uranate of sodium #ab ,uranate of potassium #ab ,uranate of ammonium #ac ,uranium sulphate #jg ,sulphate of uranium and potassium #jg ,nitrate of uranium #jg ,phosphate of copper and uranium #ji ,oxysulphide of uranium #ab ,the thickness of the layer of the uranium compound used has little effect1 provided that the layer is uniform4 ,the following illustrate this point3-- ,thickness of layer4 i #ajaa4 ,m4m4 ,uranium oxide #je #bg ,uranium oxide #cj #cj ,ammonium uranate #je #ac ,ammonium uranate #cj #ad ,it may be concluded from this that the absorption of uranium rays by the substance which generates them is very great1 since the rays proceeding from deep layers produce no significant effect4 ,the figures ,i obtained with thorium compounds enable me to state3-- ,firstly1 that the thickness of the layer used has considerable effect1 especially in the case of the oxide4 ,secondly1 that the action is only regular if a sufficiently thin layer is used 7e4g41 #jbe m4m474 ,on the contrary1 when a thick layer of the substance is used 7#f m4m471 the figures obtained vary between two extreme limits1 especially in the case of the oxide3-- ,thickness of layer4 i #ajaa4 ,m4m4 ,thorium oxide #jbe #bb ,thorium oxide #je #be ,thorium oxide #be #dg ,thorium oxide #cj #ee 7mean7 ,thorium oxide #fj #ee 7mean7 ,thorium sulphate #jbe #jh 7mean7 ,there is here some cause of irregularities which do not exist in the case of the uranium compounds4 ,the figures obtained for a layer of oxide #f m4m4 thick varied between #cg and #gc4 ,the experiments that ,i made on the absorption of uranium and thorium rays showed that those of thorium are more penetrating than those of uranium1 and that the rays emitted by the oxide of thorium in a thick layer are more penetrating than those emitted by a thin layer of the same4 ,the following figures 7p4 #ac7 give the fraction of the radiation transmitted by a sheet of aluminium #jja thick4 ,with the uranium compounds1 the absorption is the same whatever be the compound used1 which leads to the conclusion that the rays emitted by the different compounds are of the same nature4 ,radio-active substance4 ,fraction of radiation transmitted by the sheet4 ,uranium #jah ,uranium oxide1 ,u#b,o#e #jbj ,uranate of ammonium #jbj ,phosphate of uranium and copper #jba ,thorium oxide of thickness #jbe m4m4 #jch ,thorium oxide of thickness #je m4m4 #jdg ,thorium oxide of thickness #cj m4m4 #jgj ,thorium oxide of thickness #jfj m4m4 #jgj ,thorium sulphate #jbe m4m4 #jch ,the characteristics of the thorium radiation have formed the subject of very complete publications4 ,mr4 ,owens has demonstrated that a uniform current is only obtained after some time has elapsed1 with an enclosed apparatus1 and that the intensity of the current is greatly reduced under the influence of a current of air 7which does not occur with the compounds of uranium74 ,mr4 ,rutherford has made similar experiments1 and has explained them by the proposition that thorium and its compounds produce1 besides the ,becquerel rays1 another emanation1 composed of extremely minute particles1 which remain radio-active for some time after their emission1 and are capable of being swept along by a current of air4 ,the characteristics of the thorium radiation1 which have reference to the thickness of the layer employed and to the action of air currents1 have an intimate connection with the phenomenon of the radio-activity induced1 and of its propagation from place to place4 ,this phenomenon was observed for the first time with radium1 and will be described later4 ,the radio-activity of thorium and uranium compounds appears as an atomic property4 ,m4 ,becquerel has already observed that all uranium compounds are active1 and had concluded that their activity was due to the presence of the element uranium2 he also demonstrated that uranium was more active than its salts4 ,i have investigated1 from this point of view1 the compounds of thorium and uranium1 and have taken a great many measurements of their activity under different conditions4 ,the result of all these determinations shows the radio-activity of these substances to be decidedly an atomic property4 ,it seems to depend upon the presence of atoms of the two elements in question1 and is not influenced by any change of physical state or chemical decomposition4 ,the chemical combinations and mixtures containing uranium or thorium are active in proportion to the amount of the metal contained1 all inactive material acting as inert bodies and absorbing the radiation4 ,is ,atomic ,radio-activity a general ,phenomenon8 ,as ,i have said above1 ,i made experiments to discover whether substances other than compounds of uranium and thorium were radio-active4 ,i undertook this research with the idea that it was scarcely probable that radio-activity1 considered as an atomic property1 should belong to a certain kind of matter to the exclusion of all other4 ,the determinations ,i made permit me to say that1 for chemical elements actually considered as such1 including the rarest and most hypothetical1 the compounds ,i investigated were always at least #ajj times less active in my apparatus than metallic uranium4 ,the following is a summary of the substances experimented upon1 either as the element or in combination3-- #a4 ,all the metals or non-metals easily procurable1 and some1 more rare1 pure products obtained from the collection of ,m4 ,etard1 at the ,ecole de ,physique et de ,chimie ,industrielles de la ,ville de ,paris4 #b4 ,the following rare bodies3--,gallium1 germanium1 neodymium1 praseodymium1 niobium1 scandium1 gadolinium1 erbium1 samarium1 and rubidium 7specimens lent by ,m4 ,demaray71 yttrium1 ytterbium 7lent by ,m4 ,urbain74 #c4 ,a large number of rocks and minerals4 ,within the limits of sensitiveness of any apparatus1 ,i found no simple substance1 other than uranium and thorium1 possessing atomic radio-activity4 ,it will be suitable to add a few words here concerning phosphorus4 ,white moist phosphorus1 placed between the plates of the condenser1 causes the air between the plates to conduct4 ,however1 ,i do not consider this body radio-active in the same manner as thorium and uranium4 ,for1 under these conditions1 phosphorus becomes oxidised and emits luminous rays1 whilst uranium and thorium compounds are radio-active without showing any chemical change which can be detected by any known means4 ,further1 phosphorus is not active in the red variety1 nor in a state of combination4 ,in a recent work1 ,m4 ,bloch has demonstrated that phosphorus1 undergoing oxidation in air1 gives rise to slightly motile ions1 which make the air conduct1 and cause condensation of aqueous vapour4 ,uranium and thorium are elements which possess the highest atomic weights 7#bdj and #bcb72 they occur frequently in the same minerals4 ,radio-active ,minerals4 ,i have examined many minerals in my apparatus2 certain of them gave evidence of radio-activity1 e4g41 pitchblende1 thorite1 orangite1 fergusonite1 cleveite1 chalcolite1 autunite1 monazite1 c4 ,the following is a table giving in ampres the intensity1 i1 of the current obtained with metallic uranium and with different minerals3-- i #ajaa4 ,uranium #bc ,pitchblende from ,johanngeorgenstadt#hc ,pitchblende from ,joachimsthal #gj ,pitchblende from ,pzibran #fe ,pitchblende from ,cornwallis #af ,cleveite #ad ,chalcolite #eb ,autunite #bg ,various thorites #ja #jc #jg #ac #ad ,orangite #bj ,monazite #je ,xenotime #jjc schynite #jg ,fergusonite 7two samples7 #jd #ja ,samarskite #aa ,niobite 7two samples7 #ja #jc ,tantalite #jjb ,carnotite #fb ,the current obtained with orangite 7native oxide of thorium7 varied greatly with the thickness of the layer4 ,by increasing this thickness from #jbe m4m4 to #f m4m4 the current increased from #ah to #bc4 ,all the minerals which showed radio-activity contained uranium or thorium3 their activity is therefore not surprising1 but the intensity of the action in certain cases is unexpected4 ,thus pitchblendes 7ores of uranium oxide7 are found which are four times as active as metallic uranium4 ,chalcolite 7double phosphate of copper and uranium7 is twice as active as uranium4 ,autunite 7phosphate of uranium and calcium7 is as active as uranium4 ,these facts do not accord with previous conclusions1 according to which no mineral should be so active as thorium or uranium4 ,to throw light on this point1 ,i prepared artificial chalcolite by the process of ,debray1 starting with the pure products4 ,the process consists in mixing a solution of uranium nitrate with a solution of copper phosphate in phosphoric acid and warming to #ej or #fj4 ,after some time1 crystals of chalcolite appear in the liquid4 ,chalcolite thus obtained possesses a perfectly normal activity1 given by its composition2 it is two and a-half times less active than uranium4 ,it therefore appeared probable that if pitchblende1 chalcolite1 and autunite possess so great a degree of activity1 these substances contain a small quantity of a strongly radio-active body1 differing from uranium and thorium and the simple bodies actually known4 ,i thought that if this were indeed the case1 ,i might hope to extract this substance from the ore by the ordinary methods of chemical analysis4 ,,chapter ,,ii4 ,,method ,,of ,,research4 ,the results of the investigation of radio-active minerals1 announced in the preceding chapter1 led ,m4 ,curie and myself to endeavour to extract a new radio-active body from pitchblende4 ,our method of procedure could only be based on radio-activity1 as we know of no other property of the hypothetical substance4 ,the following is the method pursued for a research based on radio-activity3--,the radio-activity of a compound is determined1 and a chemical decomposition of this compound is effected2 the radio-activity of all the products obtained is determined1 having regard to the proportion in which the radio-active substance is distributed among them4 ,in this way1 an indication is obtained1 which may to a certain extent be compared to that which spectrum analysis furnishes4 ,in order to obtain comparable figures1 the activity of the substances must be determined in the solid form well dried4 ,polonium1 ,radium1 ,actinium4 ,the analysis of pitchblende with the help of the method just explained1 led us to the discovery in this mineral of two strongly radio-active substances1 chemically dissimilar3--,polonium1 discovered by ourselves1 and radium1 which we discovered in conjunction with ,m4 ,bmont4 ,polonium from the analytical point of view1 is analogous to bismuth1 and separates out with the latter4 ,by one of the following methods of fractionating1 bismuth products are obtained increasingly rich in polonium3-- #a4 ,sublimation of the sulphides in vacuo2 the active sulphide is much more volatile than bismuth sulphide4 #b4 ,precipitation of solutions of the nitrate by water2 the precipitate of the basic nitrate is much more active than the salt which remains in solution4 #c4 ,precipitation by sulphuretted hydrogen of a hydrochloric acid solution1 strongly acid2 the precipitated sulphides are considerably more active than the salt which remains in solution4 ,radium is a substance which accompanies the barium obtained from pitchblende2 it resembles barium in its reactions1 and is separated from it by difference of solubility of the chlorides in water1 in dilute alcohol1 or in water acidified with hydrochloric acid4 ,we effect the separation of the chlorides of barium and radium by subjecting the mixture to fractional crystallisation1 radium chloride being less soluble than that of barium4 ,a third strongly radio-active body has been identified in pitchblende by ,m4 ,debierne1 who gave it the name of actinium4 ,actinium accompanies certain members of the iron group contained in pitchblende2 it appears in particular allied to thorium1 from which it has not yet been found possible to separate it4 ,the extraction of actinium from pitchblende is a very difficult operation1 the separations being as a rule incomplete4 ,all three of the new radio-active bodies occur in quite infinitesimal amount in pitchblende4 ,in order to obtain them in a more concentrated condition1 we were obliged to treat several tons of residue of the ore of uranium4 ,the rough treatment was carried out in the factory2 and this was followed by processes of purification and concentration4 ,we thus succeeded in extracting from thousands of kilogrms4 of crude material a few decigrammes of products which were exceedingly active as compared with the ore from which they were obtained4 ,it is obvious that this process is long1 arduous1 and costly4 ,other new radio-active bodies have been notified since the termination of our work4 ,m4 ,giesel1 on the one hand1 and ,,mm4 ,hoffmann and ,strauss on the other1 have announced the probable existence of a radio-active body similar to lead in its chemical properties4 ,at present only a few samples of this substance have been obtained4 ,radium is1 so far1 the only member of the new radio-active substances that has been isolated as the pure salt4 ,spectrum of ,radium4 ,it was of the first importance to check1 by all possible means1 the hypothesis1 underlying this work1 of new radio-active elements4 ,in the case of radium1 spectrum analysis was the means of confirming this hypothesis4 ,m4 ,demaray undertook the examination of the new radio-active bodies by the searching methods which he employs in the study of photographic spark spectra4 ,the assistance of so competent a scientist was of the greatest value to us1 and we are deeply grateful to him for having consented to take up this work4 ,the results of the spectrum analysis brought conviction to us when we were still in doubt as to the interpretation of the results of our research4 ,the first specimens of fairly active barium chloride containing radium1 examined by ,m4 ,demaray1 exhibited together with the barium lines a new line of considerable intensity and of wave-length #chadg in the ultra-violet4 ,with the more active products prepared subsequently1 ,demaray saw the line #chadg more distinctly2 at the same time other new lines appeared1 and the intensity of the new lines was comparable with that of the barium lines4 ,a further concentration furnished a product for which the new spectrum predominated1 and the three strongest barium lines1 alone visible1 merely indicated the presence of this metal as an impurity4 ,this product may be looked upon as nearly pure radium chloride4 ,finally1 by further purification1 ,i obtained an exceedingly pure chloride1 in the spectrum of which the two chief barium lines were scarcely visible4 ,the following is a list1 according to ,demaray1 of the principal radium lines for the portion of the spectrum included between #ejjj and #cejj 4 ,the intensity of each line is represented by a figure1 the strongest being marked #af3-- 4 ,intensity4 #dhbfc #aj #dgbfi #e #dfiih #c #dfiba #g #dfhcj #ad #dfdai #d #dfjjc #c #decce #i #ddcfa #h #dcdjf #ab #chadg #af #cfdif #ab ,all the lines are clear and narrow1 the three lines #chadg1 #dfhcj1 #dcdjf are strong1 and equal the most intense of those actually known4 ,two well-marked misty bands are also visible in the spectrum4 ,the first1 which is symmetrical1 extends from #dfcaj to #dfbai1 with a maximum at #dfbge4 ,the second1 which is stronger1 fades towards the ultra-violet2 it begins1 sharply defined1 at #ddfcg1 and passes through a maximum at #ddeeb2 the region of the maximum extends as far as #ddecd1 then a nebulous band1 gradually fading1 extends about as far as #dci4 ,in the least refrangible part1 not photographed in the spark spectrum1 the only significant line is #effe 7approx471 much more feeble1 however1 than #dhbfc4 ,the general aspect of the spectrum is that of the metals of the alkaline earths2 these metals are known to have well-marked line spectra with certain nebulous bands4 ,according to ,demaray1 the position of radium may be among the bodies possessing the most sensitive spectrum reaction4 ,i also have concluded from the work of concentration1 that in the first specimen examined1 which showed clearly the line #chadg1 the proportion of radium must have been very small 7perhaps about #jjb per cent74 ,nevertheless1 an activity fifty times as great as that of metallic uranium is required in order to distinguish clearly the principal radium line in the spectra photographed4 ,with a sensitive electrometer the radio-activity of a substance only #a_/ajj of that of metallic uranium can be detected4 ,it is clear that1 in order to detect the presence of radium1 the property of radio-activity is several thousand times more sensitive than the spectrum reaction4 ,bismuth containing polonium and thorium containing actinium1 both very active1 examined by ,demaray1 have so far each only yielded bismuth and thorium lines4 ,in a recent publication1 ,m4 ,giesel1 who is occupied in preparing radium1 states that radium bromide gives a carmine flame colouration4 ,the flame spectrum of radium contains two beautiful red bands1 one line in the blue-green1 and two faint lines in the violet4 ,extraction of the ,new ,radio-active ,substances4 ,the first stage of the operation consists in extracting barium with radium from the ores of uranium1 also bismuth with polonium and the rare earths containing actinium from the same4 ,these three primary products having been obtained1 the next step is in each case to endeavour to isolate the new radio-active body4 ,this second part of the treatment consists of a process of fractionation4 ,the difficulty of finding a very perfect means of separating closely allied elements is well known2 methods of fractionation are therefore quite suitable4 ,besides this1 when a mere trace of one element is mixed with another element1 no method of complete separation could be applied to the mixture1 even allowing that such a method was known2 in fact1 one would run the risk of losing the trace of the material to be separated4 ,the particular object of my work has been the isolation of radium and polonium4 ,after working for several years1 ,i have so far only succeeded in obtaining the former4 ,pitchblende is an expensive ore1 and we have given up the treatment of it in large quantities4 ,in ,europe the extraction of this ore is carried out in the mine of ,joachimsthal1 in ,bohemia4 ,the crushed ore is roasted with carbonate of soda1 and the resulting material washed1 first with warm water and then with dilute sulphuric acid4 ,the solution contains the uranium1 which gives pitchblende its value4 ,the insoluble residue is rejected4 ,this residue contains radio-active substances2 its activity is four and a-half times that of metallic uranium4 ,the ,austrian ,government1 to whom the mine belongs1 presented us with a ton of this residue for our research1 and authorised the mine to give us several tons more of the material4 ,it was not very easy to apply the methods of the laboratory to the preliminary treatment of the residue in the factory4 ,m4 ,debierne investigated this question1 and organised the treatment in the factory4 ,the most important point of his method is the conversion of the sulphates into carbonate by boiling the material with a concentrated solution of sodium carbonate4 ,this method avoids the necessity of fusing with sodium carbonate4 ,the residue chiefly contains the sulphates of lead and calcium1 silica1 alumina1 and iron oxide4 ,in addition nearly all the metals are found in greater or smaller amount 7copper1 bismuth1 zinc1 cobalt1 manganese1 nickel1 vanadium1 antimony1 thallium1 rare earths1 niobium1 tantalum1 arsenic1 barium1 c474 ,radium is found in this mixture as sulphate1 and is the least soluble sulphate in it4 ,in order to dissolve it1 it is necessary to remove the sulphuric acid as far as possible4 ,to do this1 the residue is first treated with a boiling concentrated soda solution4 ,the sulphuric acid combined with the lead1 aluminium1 and calcium passes1 for the most part1 into solution as sulphate of sodium1 which is removed by repeatedly washing with water4 ,the alkaline solution removes at the same time lead1 silicon1 and aluminium4 ,the insoluble portion is attacked by ordinary hydrochloric acid4 ,this operation completely disintegrates the material1 and dissolves most of it4 ,polonium and actinium may be obtained from this solution2 the former is precipitated by sulphuretted hydrogen1 the latter is found in the hydrates precipitated by ammonia in the solution separated from the sulphides and oxidised4 ,radium remains in the insoluble portion4 ,this portion is washed with water1 and then treated with a boiling concentrated solution of carbonate of soda4 ,this operation completes the transformation of the sulphates of barium and radium into carbonates4 ,the material is then thoroughly washed with water1 and then treated with dilute hydrochloric acid1 quite free from sulphuric acid4 ,the solution contains radium as well as polonium and actinium4 ,it is filtered and precipitated with sulphuric acid4 ,in this way the crude sulphates of barium containing radium and calcium1 of lead1 and of iron1 and of a trace of actinium are obtained4 ,the solution still contains a little actinium and polonium1 which may be separated out as in the case of the first hydrochloric acid solution4 ,from one ton of residue #aj to #bj kilogrms4 of crude sulphates are obtained1 the activity of which is from thirty to sixty times as great as that of metallic uranium4 ,they must now be purified4 ,for this purpose they are boiled with sodium carbonate and transformed into the chlorides4 ,the solution is treated with sulphuretted hydrogen1 which gives a small quantity of active sulphides containing polonium4 ,the solution is filtered1 oxidised by means of chlorine1 and precipitated with pure ammonia4 ,the precipitated hydrates and oxides are very active1 and the activity is due to actinium4 ,the filtered solution is precipitated with sodium carbonate4 ,the precipitated carbonates of the alkaline earths are washed and converted into chlorides4 ,these chlorides are evaporated to dryness1 and washed with pure concentrated hydrochloric acid4 ,calcium chloride dissolves almost entirely1 whilst the chloride of barium and radium remains insoluble4 ,thus1 from one ton of the original material about #h kilogrms4 of barium and radium chloride are obtained1 of which the activity is about sixty times that of metallic uranium4 ,the chloride is now ready for fractionation4 ,polonium4 ,as ,i said above1 by passing sulphuretted hydrogen through the various hydrochloric acid solutions obtained during the course of the process1 active sulphides are precipitated1 of which the activity is due to polonium4 ,these sulphides chiefly contain bismuth1 a little copper and lead2 the latter metal occurs in relatively small amount1 because it has been to a great extent removed by the soda solution1 and because its chloride is only slightly soluble4 ,antimony and arsenic are found among the oxides only in the minutest quantity1 their oxides having been dissolved by the soda4 ,in order to obtain the very active sulphides1 the following process was employed3--,the solutions made strongly acid with hydrochloric acid were precipitated with sulphuretted hydrogen2 the sulphides thus precipitated are very active1 and are employed for the preparation of polonium2 there remain in the solution substances not completely precipitated in presence of excess of hydrochloric acid 7bismuth1 lead1 antimony74 ,to complete the precipitation1 the solution is diluted with water1 and treated again with sulphuretted hydrogen1 which gives a second precipitate of sulphides1 much less active than the first1 and which have generally been rejected4 ,for the further purification of the sulphides1 they are washed with ammonium sulphide1 which removes the last remaining traces of antimony and arsenic4 ,they are then washed with water and ammonium nitrate1 and treated with dilute nitric acid4 ,complete solution never occurs2 there is always an insoluble residue1 more or less considerable1 which can be treated afresh if it is judged expedient4 ,the solution is reduced to a small volume and precipitated either by ammonia or by excess of water4 ,in both cases the lead and the copper remain in solution2 in the second case1 a little bismuth1 scarcely active at all1 remains also in solution4 ,the precipitate of oxides or basic nitrates is subjected to fractionation in the following manner3--,the precipitate is dissolved in nitric acid1 and water is added to the solution until a sufficient quantity of precipitate is formed2 it must be borne in mind that sometimes the precipitate does not at once appear4 ,the precipitate is separated from the supernatant liquid1 and re-dissolved in nitric acid1 after which both the liquids thus obtained are re-precipitated with water1 and treated as before4 ,the different fractions are combined according to their activity1 and concentration is carried out as far as possible4 ,in this way is obtained a very small quantity of a substance of which the activity is very high1 but which1 nevertheless1 has so far only shown bismuth lines in the spectroscope4 ,there is1 unfortunately1 little chance of obtaining the isolation of polonium by this means4 ,the method of fractionation just described presents many difficulties1 and the case is similar with other wet processes of fractionation4 ,whatever be the method employed1 compounds are readily formed which are absolutely insoluble in dilute or concentrated acids4 ,these compounds can only be re-dissolved by reducing them to the metallic state1 e4g41 by fusion with potassium cyanide4 ,considering the number of operations necessary1 this circumstance constitutes an enormous difficulty in the progress of the fractionation4 ,this obstacle is the greater because polonium1 once extracted from the pitchblende1 diminishes in activity4 ,this diminution of activity is slow1 for a specimen of bismuth nitrate containing polonium only lost half its activity in eleven months4 ,no such difficulty occurs with radium4 ,the radio-activity remains throughout an accurate gauge of the concentration2 the concentration itself presents no difficulty1 and the progress of the work from the start can be constantly checked by spectral analysis4 ,when the phenomena of induced radio-activity1 which will be discussed later on1 were made known1 it seemed obvious that polonium1 which only shows the bismuth lines and whose activity diminishes with time1 was not a new element1 but bismuth made active by the vicinity of radium in the pitchblende4 ,i am not sure that this opinion is correct4 ,in the course of my prolonged work on polonium1 ,i have noted chemical effects1 which ,i have never observed either with ordinary bismuth or with bismuth made active by radium4 ,these chemical effects are1 in the first place1 the extremely ready formation of insoluble compounds1 of which ,i have spoken above 7especially basic nitrates71 and1 in the second place1 the colour and appearance of the precipitates obtained by adding water to the nitric acid solution of bismuth containing polonium4 ,these precipitates are sometimes white1 but more generally of a more or less vivid yellow1 verging on red4 ,the absence of lines other than those of bismuth does not necessarily prove that the substance only contains bismuth1 because bodies exist whose spectrum reaction is scarcely visible4 ,it would be necessary to prepare a small quantity of bismuth containing polonium in as concentrated a condition as possible1 and to examine it chemically1 in the first place determining the atomic weight of the metal4 ,it has not yet been possible to carry out this research on account of the difficulties of a chemical nature already mentioned4 ,if polonium were proved to be a new element1 it would be no less true that it cannot exist indefinitely in a strongly radio-active condition1 at least when extracted from the ore4 ,there are therefore two aspects of the question3--,first1 whether the activity of polonium is entirely induced by the proximity of substances themselves radio-active1 in which case polonium would possess the faculty of acquiring atomic activity permanently1 a faculty which does not appear to belong to any substance whatever2 second1 whether the activity of polonium is an inherent property1 which is spontaneously destroyed under certain conditions1 and persists under certain other conditions1 such as those which exist in the ore4 ,the phenomenon of atomic activity induced by contact is still so little understood1 that we lack the ground on which to formulate any opinion on the matter4 7,,note4--,a work has recently appeared on polonium by ,m4 ,marckwald4 ,he plunges a small rod of pure bismuth into a hydrochloric acid solution of the bismuth extracted from the pitchblende residue4 ,after some time the rod becomes coated with a very active deposit1 and the solution now contains only inactive bismuth4 ,m4 ,marckwald also obtains a very active deposit by adding tin chloride to a hydrochloric acid solution of radio-active bismuth4 ,from this he concludes that the active element is allied to tellurium1 and gives it the name of radiotellurium4 ,this active substance of ,m4 ,marckwald seems identical with polonium1 from its behaviour1 and from the easily absorbed rays it emits4 ,the choice of a new name for this substance is futile in the present state of the question74 ,preparation of the ,pure ,chloride of ,radium4 ,the method by which ,i extracted pure radium chloride from barium chloride containing radium consists in first subjecting the mixture of the chlorides to fractional crystallisation in pure water1 then in water to which hydrochloric acid has been added4 ,the difference in solubility of the two chlorides is thus made use of1 that of radium being less soluble than that of barium4 ,at the beginning of the fractionation1 pure distilled water is used4 ,the chloride is dissolved1 and the solution raised to boiling-point1 and allowed to crystallise by cooling in a covered capsule4 ,beautiful crystals form at the bottom1 and the supernatant1 saturated solution is easily decanted4 ,if part of this solution be evaporated to dryness1 the chloride obtained is found to be about five times less active than that which has crystallised out4 ,the chloride is thus divided into two portions1 ,a and ,b--portion ,a being more active than portion ,b4 ,the operation is now repeated with each of the chlorides ,a and ,b1 and in each case two new portions are obtained4 ,when the crystallisation is finished1 the less active fraction of chloride ,a is added to the more active fraction of chloride ,b1 these two having approximately the same activity4 ,thus there are now three portions to undergo afresh the same treatment4 ,the number of portions is not allowed to increase indefinitely4 ,the activity of the most soluble portion diminishes as the number increases4 ,when its activity becomes inconsiderable1 it is withdrawn from the fractionation4 ,when the desired number of fractions has been obtained1 fractionation of the least soluble portion is stopped 7the richest in radium71 and it is withdrawn from the remainder4 ,a fixed number of fractions is used in the process4 ,after each series of operations1 the saturated solution arising from one fraction is added to the crystals arising from the following fraction2 but if after one of the series the most soluble fraction has been withdrawn1 then1 after the following series1 a new fraction is made from the most soluble portion1 and the crystals of the most active portion are withdrawn4 ,by the successive alteration of these two processes1 an extremely regular system of fractionation is obtained1 in which the number of fractions and the activity of each remains constant1 each being about five times as active as the subsequent one1 and in which1 on the one hand1 an almost inactive product is removed1 whilst1 on the other1 is obtained a chloride rich in radium4 ,the amount of material contained in these fractions gradually diminishes1 becoming less as the activity increases4 ,at first six fractions were used1 and the activity of the chloride obtained at the end was only #ja that of uranium4 ,when most of the inactive matter has been removed1 and the fractions have become small1 one fraction is removed from the one end1 and another is added to the other end consisting of the active chloride previously removed4 ,a chloride richer in radium than the preceding is thus obtained4 ,this system is continued until the crystals obtained are pure radium chloride4 ,if the fractionation has been thoroughly carried out1 scarcely any trace of the intermediate products remain4 ,at an advanced stage of the fractionation1 when the quantity of material in each fraction is small1 the separation by crystallisation is less efficacious1 the cooling being too rapid and the volume of the solution to be decanted too small4 ,it is then advisable to add water containing a known quantity of hydrochloric acid2 this quantity may be increased as the fractionation proceeds4 ,the advantage gained thus consists in increasing the quantity of the solution1 the solubility of the chlorides being less in water acidified with hydrochloric acid than in pure water4 ,by using water containing much acid1 excellent separations are effected1 and it is only necessary to work with three or four fractions4 ,the crystals1 which form in very acid solution1 are elongated needles1 those of barium chloride having exactly the same appearance as those of radium chloride4 ,both show double refraction4 ,crystals of barium chloride containing radium are colourless1 but when the proportion of radium becomes greater1 they have a yellow colouration after some hours1 verging on orange1 and sometimes a beautiful pink4 ,this colour disappears in solution4 ,crystals of pure radium chloride are not coloured1 so that the colouration appears to be due to the mixture of radium and barium4 ,the maximum colouration is obtained for a certain degree of radium present1 and this fact serves to check the progress of the fractionation4 ,i have sometimes noticed the formation of a deposit composed of crystals of which one part remained uncoloured1 whilst the other was coloured1 and it seems possible that the colourless crystals might be sorted out4 ,the fractional precipitation of an aqueous solution of barium chloride by alcohol also leads to the isolation of radium chloride1 which is the first to precipitate4 ,this method1 which ,i first employed1 was finally abandoned for the one just described1 which proceeds with more regularity4 ,i have1 however1 occasionally made use of precipitation by alcohol to purify radium chloride which contains traces of barium chloride4 ,the latter remains in the slightly aqueous alcoholic solution1 and can thus be removed4 ,m4 ,giesel1 who1 since the publication of our first researches1 has been preparing radio-active bodies1 recommends the separation of barium and radium by fractional crystallisation in water from a mixture of the bromides4 ,i can testify that this method is advantageous1 especially in the first stages of the fractionation4 ,determination of the ,atomic ,weight of ,radium4 ,in the course of my work ,i determined at intervals the atomic weight of the metal contained in specimens of barium chloride containing radium4 ,with each newly obtained product ,i carried the concentration as far as possible1 so as to have from #ja grm4 to #je grm4 of material containing most of the activity of the mixture4 ,from this small quantity ,i precipitated with alcohol or with hydrochloric acid some milligrams of chloride for spectral analysis4 ,thanks to his excellent method1 ,demaray only required this small quantity of material to obtain the photograph of the spark spectrum4 ,i made an atomic weight determination with the product remaining4 ,i employed the classic method of weighing as silver chloride the chlorine contained in a known weight of the anhydrous chloride4 ,as control experiment1 ,i determined the atomic weight of barium by the same method1 under the same conditions1 and with the same quantity of material1 first #je grm4 and then #ja grm4 ,the figures obtained were always between #acg and #ach4 ,i thus saw that the method gives satisfactory results1 even with a very small quantity of material4 ,the first two determinations were made with chlorides1 of which one was #bcj times and the other #fjj times as active as uranium4 ,these two experiments gave the same figure as the experiment with the pure barium chloride4 ,there was therefore no hope of finding a difference except by using a much more active product4 ,the following experiment was made with a chloride1 the activity of which was about #cejj times as great as that of uranium2 and this experiment enabled me1 for the first time1 to observe a small but distinct difference2 ,i found1 as the mean atomic weight of the metal contained in this chloride1 the number #adj1 which showed that the atomic weight of radium must be higher than that of barium4 ,by using more and more active products1 and obtaining spectra of radium of increasing intensity1 ,i found that the figures obtained rose in proportion1 as is seen in the following table 7p4 #bh74 ,the figures of column ,a must only be looked upon as a rough estimate4 ,the calculation of the activity of strongly radio-active bodies is difficult1 for many reasons which will be discussed later4 ,a4 ,m4 #cejj #adj ,spectrum of radium faint4 #dgjj #ada #gejj #adeh ,spectrum of radium strong1 but that of barium predominating4 ,order of ,magnitude1 #agch ,the two spectra of almost equal intensity4 #ajf 444 #bbe ,only a trace of barium present4 ,a represents the activity of the chloride1 that of uranium being unity2 ,m the atomic weight found4 ,at the termination of the processes described above1 ,i obtained1 in ,march1 #aijb1 #jab grm4 of radium chloride1 of which ,demaray made the spectral analysis4 ,this radium chloride1 in the opinion of ,demaray1 was fairly pure2 its spectrum1 however1 showed the three principal barium lines with considerable intensity4 ,i made four successive estimations of the chloride1 the results of which as follows3-- ,anhydrous radium chloride4 ,silver chloride4 ,m4 ,i4 #jaaej #jaacj #bbjg ,,ii4 #jaadj #jaaai #bbcj ,,iii4 #jaaace #jajhf #bbbh ,,iv4 #jajibe #jajfde #bbca ,i then re-purified this chloride1 and obtained a much purer substance1 in the spectrum of which the two strongest barium lines were very faint4 ,given the sensitiveness of the spectrum reaction of barium1 ,demaray estimated that the purified chloride contained only the merest traces of barium1 incapable of influencing the atomic weight to an appreciable extent4 ,i made three determinations with this perfectly pure radium chloride4 ,the results were as follows3-- ,anhydrous radium chloride4 ,silver chloride4 ,m4 ,i4 #jjiaib #jjhhij #bbec ,,ii4 #jjhicf #jjhfbg #bbeh ,,iii4 #jjhhci #jjhehi #bbdj ,the mean of these numbers is #bbe4 ,they were calculated in the same way as the preceding ones by considering radium as a bivalent element1 the chloride having the formula ,ra,cl#b1 and taking for silver and chlorine the values ,ag #ajgh1 ,cl #ced4 ,hence the atomic weight of radium is ,ra #bbe4 ,the weighings were made with a ,curie aperiodic balance1 perfectly regulated1 accurate to the twentieth of a milligrm4 ,this direct reading balance permits of very rapid weighing1 a condition which is essential in the case of the anhydrous chlorides of radium and barium1 which gradually absorb moisture1 in spite of the presence of desiccating substances in the balance4 ,the bodies to be weighed were placed in a platinum crucible2 this crucible had been long in use1 and its weight did not vary the tenth part of a milligrm4 during the course of one operation4 ,the hydrated chloride obtained by crystallisation was placed in the crucible and heated till converted into the anhydrous chloride4 ,when the chloride has been kept for several hours at #ajj its weight becomes constant1 and does not change even if the temperature is raised to #bjj4 ,the anhydrous chloride thus obtained constitutes1 therefore1 a perfectly definite body4 ,the following is a series of determinations on this point4 ,the chloride 7#ajj m4g47 is dried in the oven at #ee1 and placed in a desiccator over anhydrous phosphoric acid2 it then gradually loses weight1 which proves that it still contains moisture2 in the course of twelve hours the loss was #c m4g4 ,the chloride is replaced in the stove1 and the temperature raised to #ajj4 ,during this process1 the chloride lost #fc m4g4 in weight4 ,after being left three hours fifteen minutes in the oven1 it lost #be m4g4 more4 ,the temperature was maintained for forty-five minutes between #ajj and #abj1 which caused a loss of weight of #ja m4g4 ,then after being kept for thirty minutes at #abe1 the chloride showed no diminution in weight4 ,then1 however1 after thirty minutes at #aej1 it lost #ja m4g4 ,finally1 after being heated for four hours at #bjj1 it lost #jae m4g4 ,during these operations the crucible varied from #jje m4g4 ,after each determination of the atomic weight1 the radium was converted into the chloride in the following manner3--,to the solution containing the weighed radium nitrate and excess of silver nitrate was added pure hydrochloric acid2 the silver chloride was filtered off2 the solution was evaporated to dryness several times with excess of pure hydrochloric acid4 ,in this way the nitric acid is entirely removed4 ,the precipitated silver chloride was always radio-active and phosphorescent4 ,in determining the amount of silver contained in it1 ,i satisfied myself that no ponderable amount of radium had been carried down with it out of the solution4 ,the method ,i pursued was to reduce the silver chloride precipitated in the crucible by hydrogen generated from dilute hydrochloric acid and zinc2 after washing1 the crucible was weighed with the metallic silver contained in it4 ,i made another experiment which showed that the weight of radium chloride regenerated was the same as that before beginning the operation4 ,these verifications are not so reliable as direct experiments2 but they serve to indicate the absence of any significant error4 ,from its chemical properties1 radium is an element of the group of alkaline earths1 being the member next above barium4 ,from its atomic weight also1 radium takes its place in ,mendeleeff's table after barium with the alkaline earth metals1 in the row which already contains uranium and thorium4 ,characteristics of the ,radium ,salts4 ,the salts of radium1 chloride1 nitrate1 carbonate1 and sulphate1 resemble those of barium1 when freshly prepared1 but they gradually become coloured4 ,all the radium salts are luminous in the dark4 ,in their chemical properties1 the salts of radium are absolutely analogous to the corresponding salts of barium4 ,however1 radium chloride is less soluble than barium chloride2 the solubility of the nitrates in water is approximately the same4 ,the salts of radium are the source of a spontaneous and continuous evolution of heat4 ,fractionation of ,ordinary ,barium ,chloride4 ,we have endeavoured to determine whether commercial barium chloride contains small quantities of radium chloride1 which escape detection with the means of estimation at our command4 ,for this purpose we fractionated a great quantity of commercial barium chloride1 in the hope of thus concentrating the trace of radium chloride if such were present4 ,fifty kilos4 of commercial barium chloride were dissolved in water2 the solution was precipitated by hydrochloric acid free from sulphuric acid1 which yielded #bj kilos4 of the precipitated chloride4 ,this was dissolved in water and partially precipitated by hydrochloric acid1 which gave #he kilos4 of precipitated chloride4 ,this chloride was fractionated by the method used for the barium chloride containing radium2 and at the end of the process1 #aj grams of chloride were obtained1 corresponding to the least soluble part4 ,this chloride showed no radio-activity2 it therefore contained no radium2 this substance is1 consequently1 absent from the ores of barium4 ,,chapter ,,iii4 ,,radiation ,,of ,,the ,,new ,,radio-,,active ,,substances4 ,methods of ,investigation of the ,radiation4 ,in order to investigate the radiation emitted by radio-active bodies1 any one of the properties of this radiation can be utilised4 ,thus the action of the rays on photographic plates may serve1 or their property of ionisation of the air1 which renders it a conductor1 or their capacity for causing fluorescence of certain bodies4 ,henceforth1 in speaking of these different methods of working1 ,i shall use the expressions radiographic method1 electrical method1 fluoroscopic method4 ,the first two have been used from the beginning in the study of uranium rays2 the fluoroscopic method can only be applied in the case of the new bodies which are strongly radio-active1 for the feebly active bodies such as uranium and thorium produce no appreciable fluorescence4 ,the electrical method is the only one which serves for exact determinations of intensity2 the other two are specially adapted for giving qualitative results1 and only furnish rough approximations4 ,the results obtained with the three methods just considered are not strictly comparable the one with the other4 ,the sensitive plate1 the gas which is ionised1 the fluorescent screen1 are in reality receivers1 which absorb the energy of the radiation1 and transform it into another kind of energy1 chemical energy1 ionic energy1 or luminous energy4 ,each receiver absorbs a fraction of the radiation1 which depends essentially upon its nature4 ,later on1 we shall see that the radiation is complex1 that the fractions of the radiation absorbed by the different receivers may differ among themselves both quantitatively and qualitatively4 ,finally1 it is neither evident1 nor even probable1 that the energy absorbed is entirely transformed by the receiver into the form that we wish for observation2 part of this energy may be transformed into heat1 into the evolution of secondary radiations which may or may not assist in the production of the observed phenomenon1 into chemical action which differs from that under observation1 c41 and here also the effective action of the receiver1 with reference to the end we have in view1 depends essentially upon the nature of that receiver4 ,let us compare two radio-active substances1 one containing radium and the other polonium1 and which show an equal degree of activity in the condenser of ,fig4 #a4 ,if each is covered with a thin leaf of aluminium1 the second appears considerably less active than the first1 and the same is the case when they are placed under the same fluorescent screen1 if the latter is of sufficient thickness1 or is placed at a certain distance from the two radio-active bodies4 ,energy of ,radiation4 ,whatever be the method of research employed1 the energy of radiation of the new radio-active substances is always found to be considerably greater than that of uranium and thorium4 ,thus it is that1 at a short distance1 they act instantaneously upon a photographic plate1 whereas an exposure of twenty-four hours is necessary when operating with uranium and thorium4 ,a fluorescent screen is vividly illuminated by contact with the new radio-active bodies1 whilst no trace of luminosity is visible with uranium and thorium4 ,finally1 the ionising action upon air is considerably stronger in the ratio of #ajf approximately4 ,but it is1 strictly speaking1 not possible to estimate the total intensity of the radiation1 as in the case of uranium1 by the electrical method described at the beginning 7,fig4 #a74 ,with uranium1 for example1 the radiation is almost completely absorbed by the layer of air between the plates1 and the limiting current is reached at a tension of #ajj volts4 ,but the case is different for strongly radio-active bodies4 ,one portion of the radiation of radium consists of very penetrating rays1 which penetrate the condenser and the metallic plates1 and are not utilised in ionising the air between the plates4 ,further1 the limiting current cannot always be obtained for the tensions supplied2 for example1 with very active polonium the current remains proportional to the tension between #ajj and #ejj volts4 ,therefore the experimental conditions which give a simple interpretation are not realised1 and1 consequently1 the numbers obtained cannot be taken as representing the measurement of the total radiation2 they merely point to a rough approximation4 ,complex ,nature of the ,radiation4 ,the researches of various physicists 7,,mm4 ,becquerel1 ,meyer and von ,schweidler1 ,giesel1 ,villard1 ,rutherford1 ,m4 and ,mdme4 ,curie7 have proved the complex nature of the radiation of radio-active bodies4 ,it will be convenient to specify three kinds of rays1 which ,i shall denote1 according to the notation adopted by ,mr4 ,rutherford1 by the letters 1 1 4 ,i4 ,the -rays are very slightly penetrating1 and appear to constitute the principal part of the radiation4 ,these rays are characterised by the laws by which they are absorbed by matter4 ,the magnetic field acts very slightly upon them1 and they were formerly thought to be quite unaffected by the action of this field4 ,however1 in a strong magnetic field1 the -rays are slightly deflected2 the deflection is caused in the same manner as with cathode rays1 but the direction of the deflection is reversed2 it is the same as for the canal rays of the ,crookes tubes4 ,,ii4 ,the -rays are less absorbable as a whole than the preceding ones4 ,they are deflected by a magnetic field in the same manner and direction as cathode rays4 ,,iii4 ,the -rays are penetrating rays1 unaffected by the magnetic field1 and comparable to ,rntgen rays4 ,illustration3 ,,fig4 #d4 ,consider the following imaginary experiment3--,some radium1 ,r1 is placed at the bottom of a small deep cavity1 hollowed in a block of lead1 ,p 7,fig4 #d74 ,a sheaf of rays1 rectilinear and slightly expanded1 streams from the receptacle4 ,let us suppose that a strong uniform magnetic field is established in the neighbourhood of the receptacle1 normal to the plane of the figure and directed towards the back4 ,the three groups of rays1 1 1 1 will now be separated4 ,then rather faint -rays continue in their straight path without a trace of deviation4 ,the -rays are deflected in the manner of cathode rays1 and describe circular paths in the plane of the figure4 ,if the receptacle is placed on a photographic plate1 ,a ,c1 the portion1 ,b ,c1 of the plate which receives the -rays is acted upon4 ,lastly1 the -rays form a very intense shaft which is slightly deflected1 and which is soon absorbed by the air4 ,these rays describe in the plane of the figure a path of great curvature1 the direction of the deflection being the reverse of that with the -rays4 ,if the receptacle is covered with a thin sheet of aluminium 7#ja m4m4 thick71 the -rays are suppressed almost entirely1 the -rays are lessened1 and the -rays do not appear to be absorbed to any great extent4 ,action of the ,magnetic ,field4 ,we have seen that the rays emitted by radio-active bodies have many properties common to cathode rays and to ,rntgen rays4 ,cathode rays1 as well as ,rntgen rays1 ionise the air1 act on photographic plates1 cause fluorescence1 undergo no regular deflection4 ,but the cathode rays differ from ,rntgen rays in being deflected from their rectilinear path by the action of the magnetic field1 and in the transportation of charges of negative electricity4 ,the fact that the magnetic field acts upon the rays emitted by radio-active substances was discovered almost simultaneously by ,,mm4 ,giesel1 ,meyer and von ,schweidler1 and ,becquerel4 ,these physicists observed that the rays of radio-active substances are deflected by the magnetic field in the same manner and direction as the cathode rays2 their observations were in relation to the -rays4 ,m4 ,curie demonstrated that the radiation of radium comprises two groups of quite distinct rays1 of which one is readily deflected by the magnetic field 7-rays71 whilst the other seems to be unaffected by the action of this field 7- and -rays74 ,m4 ,becquerel did not find that the specimens of polonium prepared by us emitted rays of the cathode kind4 ,on the contrary1 he first noticed the effect of the magnetic field on a specimen of polonium prepared by himself4 ,none of the polonium prepared by us ever gave rise to rays of the cathode order4 ,the polonium of ,m4 ,giesel only gives rise to these rays when recently prepared1 and it is probable that the emission is due to the phenomenon of induced radio-activity of which we shall speak later4 ,the following are experiments which prove that one portion of the radiation of radium1 and one portion only1 consists of easily deflected rays 7-rays74 ,these experiments were done according to the electrical method4 ,the radio-active body ,a 7,fig4 #e7 sends forth radiations in the direction ,a ,d between the plates ,p and ,p4 ,the plate ,p is now at a potential of #ejj volts1 plate ,p is connected to an electrometer and to a quartz electric piezometer4 ,the intensity of the current passing through the air under the influence of the radiations is measured4 ,the magnetic field can be established at will perpendicular to the plane of the figure over the whole region ,e ,e ,e ,e4 ,if the rays are deflected1 even slightly1 they no longer pass between the plates1 and the current is suppressed4 ,the region of the passage of the rays is surrounded with masses of lead1 ,b1 ,b1 ,b1 and by the armatures of the electro-magnet2 when the rays are deflected1 they are absorbed by the masses of lead ,b and ,b4 ,illustration3 ,,fig4 #e4 ,the results obtained depend essentially on the distance1 ,a ,d1 of the radiating substance1 ,a1 from the condenser at ,d4 ,if the distance ,a ,d is great enough 7greater than #g c4m471 most of the radium rays 7#ij to #ajj per cent7 arriving at the condenser are deflected and suppressed for a field of #bejj units4 ,these are the -rays4 ,if the distance ,a ,d is less than #fe m4m41 a smaller part of the rays are deflected by the action of the field2 this portion is also entirely deflected by a field of #bejj units1 and the proportion of the rays suppressed is not increased by increasing the field from #bejj to #gjjj units4 ,the proportion of the rays not suppressed by the field increases with decrease of the distance1 ,a ,d1 between the radiating body and the condenser4 ,for small distances1 the rays which can be easily deflected form a very small fraction of the total radiation4 ,the penetrating rays are therefore1 for the most part1 deviable rays of the cathode order 7-rays74 ,under the experimental conditions just described1 the action of the magnetic field on the -rays could not be well observed for the fields employed4 ,the chief radiation1 apparently undergoing no deflection1 observed at a short distance from the radiating source1 consisted of -rays2 the undeflected radiation observed at a greater distance consisted of -rays4 ,if an absorbing lamina 7aluminium or black paper7 is placed in the path of the bundle of rays1 those which pass through are nearly all deflected by the field in such a way that1 with the aid of the screen and the magnetic field1 almost all the radiation is suppressed in the condenser1 the remainder being due to the -rays1 the proportion of which is small4 ,the -rays are absorbed by the screen4 ,an aluminium plate of #a_/ajj m4m4 thickness is sufficient for the suppression of almost all the rays not readily deflected when the substance is far enough from the condenser2 for smaller distances 7#cd m4m4 and #ea m4m47 two pieces of this aluminium foil are necessary to give the same result4 ,similar determinations were made with four substances containing radium 7chlorides or carbonates7 of very different activity2 analogous results were obtained4 ,it may be remarked that1 in all cases1 the penetrating rays deflected by the magnet 7-rays7 form only a small fraction of the total radiation2 they influence but slightly the determinations in which the whole radiation is made use of to produce conductivity of the air4 ,the radiation emitted by polonium may be studied by the electrical method4 ,when the distance1 ,a ,d1 of the polonium from the condenser is varied1 no current is observed at first while the distance is fairly great2 on nearing the polonium1 the radiation suddenly becomes manifest with great intensity2 the current then increases uniformly whilst approaching the polonium1 but the magnetic field produces no appreciable effect under these conditions4 ,the radiation of polonium is apparently limited in space1 and does not pass into the air beyond a kind of sheath surrounding the substance to a thickness of several centimetres4 ,the interpretation of the experiments ,i have just described must be accompanied by some important general reservations4 ,in speaking of the proportion of the rays deflected by the magnet1 ,i refer only to that portion of the radiation capable of causing a current in the condenser4 ,in employing the fluorescent action of the ,becquerel rays1 or their action on photographic plates1 the proportion would probably be different--a measure of intensity having1 as a rule1 no meaning except for the method of measurement adopted4 ,the rays of polonium are -rays4 ,in the experiments just described1 ,i observed no action of the magnetic field upon them1 but the experimental conditions were such that a slight deflection would pass unnoticed4 ,the experiments made by the radiographic method confirmed the preceding results4 ,taking radium as the source of radiation1 and receiving the impression on a plate parallel to the primitive shaft and normal to the field1 a very clear print is obtained of two shafts separated by the action of the field1 the one deflected1 the other not deflected4 ,the -rays constitute the deflected beam2 the -rays1 being very slightly deflected1 are not to be distinguished from the undeflected bundle of the -rays4 ,deflected -,rays4 ,the experiments of ,m4 ,giesel and ,,mm4 ,meyer and von ,schweidler showed that the radiation of the radio-active bodies is1 in part at least1 deflected by a magnetic field1 and that this deflection resembles that of the cathode rays4 ,m4 ,becquerel investigated the action of the field on the rays by the radiographic method4 ,the experimental arrangement was that of ,fig4 #d4 ,the radium was placed in the lead receptacle1 ,p1 and this receptacle was placed on the sensitive face of a photographic plate1 ,a ,c1 covered with black paper4 ,the whole was placed between the poles of an electro-magnet1 the magnetic field being normal to the plane of the figure4 ,if the field is directed to the back of this plane1 the part ,b ,c of the plate is acted upon by rays which1 after having described circular paths1 return to the plate and strike it at a right angle4 ,these rays are -rays4 ,m4 ,becquerel has demonstrated that the impression consists of a wide diffused band1 a continuous spectrum indeed1 showing that the sheaf of deviable rays emitted by the source is formed of an infinite number of radiations unequally deflected4 ,if the gelatin of the plate be covered with different absorbent screens 7paper1 glass1 metals71 one portion of the spectrum is suppressed1 and it is found that the rays most deflected by the magnetic field--otherwise those which have the smallest radius of curvature--are the most completely absorbed4 ,with each screen1 the impression on the plate begins at a certain distance from the source of radiation1 this distance being proportional to the absorptive power of the screen4 ,charge of the ,deflected ,rays4 ,the cathode rays are1 as shown by ,m4 ,perrin1 charged with negative electricity4 ,further1 according to the experiments of ,m4 ,perrin and ,m4 ,lenard1 they are capable of carrying their charge through the metallic envelopes connected to earth and through isolating screens4 ,at every point where the cathode rays are absorbed1 there is a continuous evolution of negative electricity4 ,we have proved that the same is the case for the deflected -rays of radium4 ,the deviable -rays of radium are charged with negative electricity4 7,,note4--,let the radio-active substance be placed on one of the plates of a condenser1 this plate being connected to earth2 the second plate is connected to an electrometer1 it receives and absorbs the rays emitted by the substance4 ,if the rays are charged1 a continuous flow of electricity into the electrometer should be observed4 ,in this experiment1 carried out in air1 we were not able to detect a charge accompanying the rays1 but such an experiment is not delicate4 ,the air between the plates being caused by the rays to conduct1 the electrometer is no longer isolated1 and can only respond to charges if these be sufficiently strong4 ,in order that the -rays may not interfere with the experiment1 they may be suppressed by covering the source of radiation with a thin metallic screen4 ,we repeated this experiment1 without more success1 by causing the rays to pass through the interior of a ,faraday cylinder in connection with the electrometer74 ,according to the preceding experiments1 it was evident that the charge of the rays of the radiating body employed was a weak one4 ,in order to fix a feeble evolution of electricity upon the conductor which absorbs the rays1 this conductor should be completely insulated2 this is effected by screening it from the air1 either by placing it in a tube with a very perfect vacuum1 or by surrounding it with a good solid dielectric4 ,we employed the latter arrangement4 ,illustration3 ,,fig4 #f4 ,a conducting disc1 ,m ,m 7,fig4 #f71 is connected by the wire1 t1 to the electrometer2 the disc and wire are completely enveloped by the insulating substance i i i i2 the whole is again surrounded with the metallic covering1 ,e ,e ,e ,e1 which is in electric connection with the earth4 ,the insulator1 p p1 and the metallic envelope are very thin upon one of the faces of the disc4 ,this face is exposed to the radiation of the barium and radium salt1 ,r1 placed outside in a lead receptacle4 ,the rays emitted by the radium penetrate the metallic envelope and the insulating lamina1 p p1 and are absorbed by the metallic disc1 ,m ,m4 ,the latter then becomes the source of a continuous evolution of negative electricity1 as determined by the electrometer1 and is measured by means of a quartz piezometer4 ,the current thus created is very weak4 ,with very active barium-radium chloride1 forming a layer of #be sq4 c4m4 in area1 and of #jb c4m4 in thickness1 a current of magnitude #aj-aa ampres is obtained1 the rays utilised having traversed1 before being absorbed by the disc ,m ,m1 a thickness of aluminium of #jja m4m41 and a thickness of ebonite of #jc m4m4 ,we used successively lead1 copper1 and zinc for the disc ,m ,m1 ebonite and paraffin for the insulator2 the results obtained were the same4 ,the current diminishes with increasing distance from the source of radiation1 ,r1 also when a less active product is used4 ,we obtained the same results again when the disc ,m ,m is replaced by a ,faraday cylinder filled with air1 and covered outside with insulating material4 ,the opening of the cylinder1 closed by the thin insulating plate1 p p1 was opposite the radiating source4 ,illustration3 ,,fig4 #g4 ,finally1 we made the inverse experiment1 which was to place the lead receptacle with the radium in the centre of the insulating material and in connection with the electrometer 7,fig4 #g71 the whole being surrounded with the metallic covering connected to earth4 ,under these conditions1 it is evident from the electrometer that the radium has a positive charge equal in magnitude to the negative charge of the former experiment4 ,the radium rays penetrate the thin dielectric plate1 p p1 and leave the conductor inside carrying with them negative electricity4 ,the -rays of radium do not interfere in these experiments1 being almost completely absorbed by a very thin layer of matter4 ,the method just described is not suitable for the study of the charge of the rays of polonium1 these rays very slightly penetrating4 ,we observed no indication of any charge in the case of polonium1 which gives rise to -rays only2 but1 for the reason just given1 no conclusion can be drawn from this4 ,thus1 in the case of the deflected -rays of radium1 as in the case of cathode rays1 the rays carry a charge of electricity4 ,but1 hitherto1 the existence of electric charges uncombined with matter has been unknown4 ,in the study of the emission of the -rays of radium1 we are therefore led to make use of the theory which is in vogue for the study of cathode rays4 ,in this ballistic theory1 formulated by ,sir ,william ,crookes1 since developed and completed by ,prof4 ,j4 ,j4 ,thomson1 the cathode rays consist of extremely minute particles1 which are hurled from the cathode with great velocity1 and which are charged with negative electricity4 ,we might similarly conceive that radium sends into space negatively electrified particles4 ,a specimen of radium1 enclosed in a solid thin perfectly insulated envelope1 should become spontaneously charged to a very high potential4 ,by the ballistic hypothesis the potential would increase until the potential difference of the surrounding conductors became sufficient to hinder the ejection of the electrified particles and to cause their return to the source of radiation4 ,we have performed an experiment on these lines4 ,a specimen of very active radium was enclosed for some time in a glass vessel4 ,in order to open the vessel1 we made a trace on the glass with a glass cutter4 ,whilst so doing1 we clearly heard the report of a spark1 and upon examining the vessel with a magnifying glass1 we observed that the glass had been pierced by a spark at the spot where it had been weakened by the scratch4 ,the phenomenon produced is comparable to the rupture of the glass of an overcharged ,leyden jar4 ,the same phenomenon occurred with another glass4 ,further1 at the moment of the passing of the spark1 ,m4 ,curie1 who was holding the glass1 felt the electric shock of discharge in his fingers4 ,certain kinds of glass have good insulating properties4 ,if the radium is enclosed in a sealed glass vessel1 well insulated1 it is to be expected that1 at a given moment1 the vessel will be spontaneously perforated4 ,radium is the first example of a body which is spontaneously charged with electricity4 ,action of the ,electric ,field upon the ,deflected -,rays of ,radium4 ,the -rays of radium1 being analogous to the cathode rays1 should be deflected by an electric field in a manner similar to the latter2 i4e41 as would a particle of matter negatively charged and hurled into space with a great velocity4 ,the existence of such a deflection has been demonstrated both by ,m4 ,dorn and ,m4 ,becquerel4 ,let us consider the case of a ray which traverses the space situated between the two plates of a condenser4 ,suppose the direction of the ray parallel to the plates3 when an electric field is established between the latter1 the ray is subjected to the action of this uniform field along its whole path in the condenser l4 ,by reason of this action the ray is deflected towards the positive plate and describes the arc of a parabola2 on leaving the field1 it continues its path in a straight line1 following the tangent to the arc of the parabola at the point of exit4 ,the ray can be received on a photographic plate perpendicular to its original direction4 ,observations are taken of the impression produced on the plate when the field is zero1 and when it has a known value1 and from that is deduced the value of the deflection1 1 which is the distance of the points in which the new direction of the ray and its original direction meet a common plane perpendicular to the original direction4 ,if h is the distance of this plane from the condenser1 i4e41 at the edge of the field1 we have1 by a simple calculation1-- e,fl 7l_/#b h7 ---------------------------------------- --2 mv#b m being the mass of the moving particles1 e its charge1 v its velocity1 and ,f the strength of the field4 ,the experiments of ,m4 ,becquerel enable him to assign a value approaching to 4 ,relation of the ,charge to the ,mass for a ,particle ,negatively ,charged ,emitted by ,radium4 ,when a material particle having a mass m and a negative charge e1 is projected with a velocity v into a uniform magnetic field perpendicular to its initial velocity1 this particle describes1 in a plane normal to the field and passing through its initial velocity1 an arc of a circle of radius 1 so that--,h being the strength of the field--we have the relation-- m ,h ------ v4 e ,if1 for the same ray1 the deflection1 1 and the radius of curvature1 1 be measured in a magnetic field1 values could be found from these two experiments for the ratio e_/m and for the velocity1 v4 ,the experiments of ,m4 ,becquerel threw the first light upon this subject4 ,they gave for the ratio e_/m a value approximately equal to #ajg absolute electro-magnetic units1 and for v a magnitude of #af #ajaj4 ,these values are of the same order of magnitude as those of the cathode rays4 ,accurate experiments have been made on the same subject by ,m4 ,kaufmann4 ,this physicist subjected a narrow beam of radium rays to the simultaneous action of an electric field and a magnetic field1 the two fields being uniform and having a similar direction1 normal to the original direction of the beam4 ,the impression produced on a plate normal to the primitive beam and placed beyond the limits of the field with reference to the source1 has the form of a curve1 each point of which corresponds to one of the original beam4 ,the most penetrating and least deflected rays are at the same time those with the greatest velocity4 ,it follows from the experiments of ,m4 ,kaufmann1 that for the radium rays1 of which the velocity is considerably greater than that of the cathode rays1 the ratio e_/m decreases1 while the velocity increases4 ,according to the researches of ,j4 ,j4 ,thomson and ,townsend1 we may assume that the moving particle1 which constitutes the ray1 possesses a charge1 e1 equal to that carried by an atom of hydrogen during electrolysis1 this charge being the same for all the rays4 ,we are therefore led to the conclusion that the mass of the particle1 m1 increases with increase of velocity4 ,these theoretical considerations lead to the idea that the inertia of the particle is due to its state of charge during motion1 the velocity of an electric charge in motion being incapable of modification without expenditure of energy4 ,to state it otherwise1 the inertia of the particle is of electro-magnetic origin1 and the mass of the particle is--in part at least--a virtual mass or an electro-magnetic mass4 ,m4 ,abraham goes further1 and assumes that the mass of the particle is entirely an electro-magnetic mass4 ,if1 according to this hypothesis1 the value of this mass1 m1 be calculated for a known velocity1 v1 we find that m approaches infinity when v approaches the velocity of light1 and that m approaches a constant value when the velocity1 v1 is much less than that of light4 ,the experiments of ,m4 ,kaufmann are in agreement with the results of this theory1 the importance of which is great because it foreshadows the possibility of establishing mechanical bases upon the dynamical of little particles of matter charged in a state of motion4 ,these are the figures obtained by ,m4 ,kaufmann for e_/m and v4 e_/m vc4m4_/sec4 ,electro-magnetic units4 #ahfe #ajg #jg #ajaj;,for cathode rays 7,simon74 #aca #ajg #bcf #ajaj;,for radium rays 7,kaufmann74 #aag #ajg #bdh #ajaj #jig #ajg #bei #ajaj #jgg #ajg #bgb #ajaj #jfc #ajg #bhc #ajaj ,m4 ,kaufmann concludes1 from comparison of his experiments with the theory1 that the limiting value of the ratio e_/m for radium rays of relatively small velocity would be the same as the value e_/m for cathode rays4 ,the most complete experiments of ,m4 ,kaufmann were made with a minute quantity of pure radium chloride1 with which we provided him4 ,according to ,m4 ,kaufmann's experiments1 certain -rays of radium possess a velocity very near to that of light4 ,these rapid rays seem to possess great penetrating capacity towards matter4 ,action of the ,magnetic ,field upon the -,rays4 ,in a recent work1 ,mr4 ,rutherford announced that1 in a powerful electric or magnetic field1 the -rays of radium are slightly deflected1 in the manner of particles positively electrified and possessing great velocity4 ,mr4 ,rutherford concludes from his experiments that the velocity of the -rays is of the order of magnitude #be #aji;c4m4_/sec4 and that the ratio e_/m for these rays is of the order of magnitude #f #ajc1 which is #ajd times as great as for the deflected -rays4 ,we shall see later that these conclusions of ,mr4 ,rutherford are in agreement with the properties already known of the -radiation1 and that they account1 in part at least1 for the law of absorption of this radiation4 ,the experiments of ,mr4 ,rutherford have been confirmed by ,m4 ,becquerel4 ,m4 ,becquerel has further demonstrated that polonium rays behave in a magnetic field like the -rays of radium1 and that1 for the same field1 they seem to have the same curvature as the latter4 ,it also appears from ,m4 ,becquerel's experiments that the -rays do not form a magnetic spectrum1 but act rather like a homogeneous radiation1 all the rays being equally deflected4 ,action of the ,magnetic ,field on the ,rays of other ,radio-active ,substances4 ,we have just seen that radium gives off -rays comparable to the tube rays1 -rays comparable to cathode rays1 and -rays which are penetrating and not deflected4 ,polonium gives off -rays only4 ,amongst the other radio-active substances1 actinium seems to behave like radium1 but the study of its radiation has not yet advanced so far as in the case of radium4 ,as regards the faintly radio-active bodies1 we know to-day that uranium and thorium give rise to -rays as well as -rays 7,becquerel1 ,rutherford74 ,proportion of -,rays in the ,radiation of ,radium4 ,as ,i have already mentioned1 the proportion of -rays increases with increase of distance from the source of radiation4 ,these rays never occur alone1 and for great distances the presence of -rays is always discernible4 ,the presence of very penetrating1 undeflected rays in the radiation of radium was first observed by ,m4 ,villard4 ,these rays constitute only a small portion of the radiation measured by the electrical method1 and their presence escaped our notice in our first experiments1 so that we believed falsely that the radiation at great distances contained only rays capable of deflection4 ,the following are the numerical results obtained with experiments made by the electrical method with an apparatus similar to that of ,fig4 #e4 ,the radium was only separated from the condenser by the surrounding air4 ,i shall indicate by the letter d the distance from the source of radiation to the condenser4 ,the numbers of the second line represent the current subsisting when the magnetic field is acting1 supposing the current obtained with no field equal to #ajj for each distance4 ,these numbers may be considered as giving the percentage of the total - and -rays1 the deflection of the -rays having been scarcely observable with the conditions employed4 ,at great distances there are no -rays1 and the undeflected radiation is therefore of the kind only4 ,experiments made at short distances3-- d1 in centimetres #cd #ea #fj #fe ,percentage of undeflected rays #gd #ef #cc #aa ,experiments made at long distances with a product considerably more active than that which was used for the preceding series3-- d1 in centimetres #ad #cj #ec #hj #ih ,percentage of undeflected rays #ab #ad #ag #ad #af d #abd #aeg ,percentage of undeflected rays #ad #aa ,it is thus evident that after a certain distance the proportion of undeflected rays in the radiation is approximately constant4 ,these rays probably all belong to the species4 ,the following is another series of experiments in which the radium was enclosed in a very narrow glass tube1 placed below the condenser and parallel to the plates4 ,the rays emitted traversed a certain thickness of glass and air before entering the condenser3-- d1 in centimetres #be #cc #da #ei #ge #if #aac ,percentage rays not deflected #cc #cc #ba #af #ad #aj #i d #aci #agb ,percentage rays not deflected #i #aj ,as in the preceding experiments1 the number of the second line approximate to a constant value1 when the distance d increases1 but the limit is reached for smaller distances than in the preceding series1 because the -rays have been more completely absorbed by the glass than the - and -rays4 ,the following experiment shows that a thin sheet of aluminium 7#jja m4m4 thick7 absorbs principally -rays4 ,the product being placed #e c4m4 from the condenser1 the proportion of rays other than 1 when the magnetic field is acting1 is about #ga per cent4 ,when the same substance is covered with the sheet of aluminium1 the distance remaining the same1 the radiation transmitted is found to be almost totally deflected by the magnetic field1 the -rays having been absorbed by the aluminium4 ,the same result is obtained when paper is used as the absorbing screen4 ,the greatest part of the radiation of radium consists of -rays1 which are probably emitted principally by the superficial layer of the radiating matter4 ,when the thickness of the layer of radiating matter is varied1 the intensity of the current increases with this thickness2 the increase is not proportional to the thickness for the whole of the radiation2 it is1 moreover1 more considerable for the -rays than for the -rays1 so that the proportion of -rays increases with the thickness of the active layer4 ,the source of radiation being placed at a distance of #e c4m4 from the condenser1 it is found that for a thickness equal to #jd m4m4 of the active layer1 the total radiation is given by the number #bh1 and the proportion of the -rays is #bi per cent4 ,by making the layer #b m4m4 thick1 i4e41 five times as thick1 a total radiation equal to #ajb1 and a proportion of -rays equal to #de per cent are obtained4 ,the total radiation which exists at this distance has therefore been increased in the ratio of #cf1 and the -radiation has become five times as strong4 ,the preceding experiments were made by the electrical method4 ,when the radiographic method is used1 certain results seem to be in contradiction with what precedes4 ,in the experiments of ,m4 ,villard1 a beam of radium rays1 subjected to the action of the magnetic field1 was received on to a pile of photographic plates4 ,the undeflected and penetrating -beam passed through all the plates1 leaving its trace on each4 ,the deflected -beam produced an impression on the first plate only4 ,this beam appeared therefore to contain no rays of great penetration4 ,on the contrary1 in our experiments a beam which is propagated in the air contains at the greatest distances accessible to observation about #i_/aj of -rays1 and the same is the case when the source of radiation is enclosed in a little sealed glass vessel4 ,in ,m4 ,villard's experiments1 these deflected and penetrating -rays did not affect the photographic plates beyond the first1 because they are to a great extent diffused in all directions by the first solid obstacle encountered1 and no longer form a beam4 ,in our experiments the rays given off by radium and transmitted through the glass of the vessel were also probably scattered by the glass1 but the vessel being very small would itself act as a source of -rays at its surface1 and we were able to follow the course of the latter to a great distance from the vessel4 ,the cathode rays of ,crookes tubes can only traverse very thin screens 7aluminium screens of #jja m4m4 thickness74 ,a beam of rays striking the screen normally is scattered in all directions2 but the diffusion becomes less with diminishing thickness of the screen1 and for very thin screens the emerging beam is practically the prolongation of the incident beam4 ,the deflected -rays of radium behave in a similar manner1 but the transmitted beam experiences1 for the same thickness of screen1 a much slighter modification4 ,according to the experiments of ,m4 ,becquerel1 the very readily deflected -rays of radium 7those with a relatively small velocity7 are powerfully scattered by an aluminium screen of thickness #ja m4m42 but the penetrating and less deflected rays 7rays of the cathode kind of great velocity7 pass through this screen without being sensibly diffused1 whatever be the inclination of the screen to the direction of the beam4 ,the -rays of great velocity penetrate without diffusion a much greater thickness of paraffin 7several centimetres71 and in this the curvature of the beam produced by the magnetic field can be traced4 ,the thicker the screen1 and the more absorbent the material of which it is composed1 the greater is the modification of the deflected primitive beam1 because1 with increasing thickness of screen1 diffusion occurs progressively among fresh groups of rays of increasing penetration4 ,the -rays of radium experience a diffusion in passing through the air1 which is very marked for readily deflected rays1 but which is much slighter than that produced by equal thicknesses of solid substances4 ,for this reason1 the -rays traverse long distances in the air4 ,penetrating ,power of the ,radiation of ,radio-active ,bodies4 ,since the beginning of the researches on radio-active bodies1 investigations of the absorption produced by different screens upon the rays given off by these bodies have been carried on4 ,in a previous paper on this subject ,i gave figures 7quoted at the beginning of this work7 representing the penetrating power of uranium and thorium rays4 ,mr4 ,rutherford has made a special study of the radiation of uranium1 and proved it to be heterogeneous4 ,mr4 ,owens has arrived at the same results for thorium rays4 ,when the discovery of strongly radio-active bodies immediately followed upon this1 the penetrating power of their rays was also studied by various physicists 7,becquerel1 ,meyer and von ,schweidler1 ,curie1 ,rutherford74 ,the first observations brought to light the complexity of the radiation1 which seems to be a general phenomenon1 and common to the radio-active bodies4 ,in them we have sources which give rise to a variety of radiations1 each of which has a power of penetration proper to itself4 ,radio-active bodies emit rays which are propagated both in the air and in vacuo4 ,the propagation is rectilinear2 this fact is proved by the distinctness and shape of the shadows formed by interposing bodies opaque to the radiation between the source and the sensitive plate or fluorescent screen which serves as receiver1 the source being of small magnitude in comparison with its distance from the receiver4 ,various experiments demonstrating the rectilinear propagation of uranium1 radium1 and polonium rays have been made by ,m4 ,becquerel4 ,it is interesting to know the distance that rays can travel in air4 ,we have found that radium emits rays which can be detected in the air at a distance of several metres from the source4 ,in certain of our electrical determinations1 the action of the source upon the air of the condenser made itself felt at a distance of between #b and #c metres4 ,we have also obtained fluorescent effects and radiographic impressions at similar distances4 ,the experiments are not easily carried out1 except with very intense radio-active sources1 because1 independently of the absorption by the air1 the action upon a given receiver varies inversely as the square of the distance from a source of small dimensions4 ,this radiation1 which travels a long distance in the case of radium1 comprises rays of the cathode kind and rays which are undeflected2 however1 the deflected rays predominate1 according to the results of the experiments already mentioned4 ,the greater part of the radiation 7-rays7 is1 on the contrary1 limited in air to a distance of about #g c4m4 from the source4 ,i made several experiments with radium enclosed in a little glass vessel4 ,the rays emerging from the vessel1 after traversing a certain space of air1 were received in a condenser1 which served to measure their ionising capacity by the usual electrical method4 ,the distance1 d1 from the source to the condenser was varied1 and the current of saturation1 i1 obtained in the condenser was measured4 ,the following are the results of one of the series of determinations3-- d1 c4m4 i4 i d#b #aj-c4 #aj #abg #ac #bj #ch #ae #cj #agd #af #dj #aje #ag #ej #fi #ag #fj #dg #ag #gj #ch #ai #ajj #afe #ag ,after a certain distance1 the intensity of radiation varies inversely as the square of the distance from the condenser4 ,the radiation of polonium is only propagated in air to a distance of a few centimetres 7#d to #f c4m47 from the source of radiation4 ,in the case of the absorption of radiations by solid screens1 we find another fundamental difference between radium and polonium4 ,radium emits rays capable of penetrating great thicknesses of solid matter1 e4g41 several centimetres of lead or of glass4 ,the rays which have passed through a great thickness of a solid body are extremely penetrating1 and it is practically impossible to absorb them entirely by any material whatever4 ,but these rays form only a small fraction of the total radiation1 the greater part of which is absorbed by a slight thickness of solid matter4 ,polonium emits rays which are readily absorbed1 and which can only pass through extremely thin screens4 ,the following are figures showing the absorption produced by an aluminium lamina of thickness #jja m4m4 ,this lamina was placed above and almost in contact with the substance4 ,the direct radiation and that transmitted by the aluminium were measured by the electrical method 7apparatus of ,fig4 #a72 the current of saturation was practically obtained in every case4 ,i have represented the activity of the radiating body by a1 that of uranium being unity4 a4 ,fraction of radiation transmitted4 ,chloride of barium and radium #eg #jcb ,bromide of barium and radium #dc #jcj ,chloride of barium and radium #abjj #jcj ,sulphate of barium and radium #ejjj #jbi ,sulphate of barium and radium #aj1jjj #jcb ,metallic bismuth and polonium #jbb ,compounds of uranium #jbj ,compounds of thorium in a thin layer #jch ,we see that radium compounds of different nature and activity give very similar results1 as ,i have already pointed out in the case of uranium and thorium compounds at the beginning of this work4 ,we see also that1 taking into account the whole of the radiation1 and with a given absorbent screen1 the different radio-active bodies can be arranged in the following decreasing order of penetrating power3--,thorium1 radium1 polonium1 uranium4 ,these results are similar to those which have been published by ,mr4 ,rutherford4 ,mr4 ,rutherford also finds that the order is the same when air is the absorbent substance4 ,but it is probable that this order has no absolute value1 and would not be maintained independently of the nature and thickness of the screen4 ,experiment shows1 indeed1 that the law of absorption is very different for polonium and radium1 and that1 for the latter1 the absorption of the rays of each of the three groups must be considered separately4 ,polonium is particularly well adapted to the study of -rays1 because the specimens which we possess emit no other kind of rays4 ,i made a preliminary series of experiments with extremely active recently prepared specimens of polonium4 ,i found the absorbability of the rays to increase with increase of thickness of the matter traversed4 ,this singular law of absorption is contrary to that known for other kinds of radiation4 ,i employed for this research our apparatus for the determination of electrical conductivity arranged in the following manner3-- ,the two plates of a condenser1 ,p ,p and ,p ,p 7,fig #h71 are horizontally disposed in a metallic box1 ,b ,b ,b ,b1 connected to earth4 ,the active body1 ,a1 placed in a thick metallic box1 ,c ,c ,c ,c1 connected with the plate ,p ,p1 acts upon the air of the condenser across a metallic sheet1 ,t2 the rays which pass through the sheet are alone utilised for producing the current1 the electric field being limited by the sheet4 ,the distance1 ,a ,t1 of the active body from the sheet may be varied4 ,the field between the plates is established by means of a battery4 ,by placing in ,a upon the active body different screens1 and by adjusting the distance ,a ,t1 the absorption of rays which travel long or short distances in the air may be determined4 ,illustration3 ,,fig4 #h4 ,the following are the results obtained with polonium3-- ,for a certain value of the distance ,a ,t 7#d c4m4 and more71 no current passes2 the rays do not penetrate the condenser4 ,when the distance ,a ,t is diminished1 the appearance of the rays in the condenser is manifested somewhat suddenly1 a weak current changing to one of considerable strength for a slight diminution of distance2 the current then increases regularly as the active body continues to approach the sheet ,t4 ,when the active body is covered with a sheet of aluminium #a_/ajj m4m4 thick1 the absorption produced by the lamina becomes greater1 the greater the distance ,a ,t4 ,if a second similar lamina of aluminium be placed upon the first1 each absorbs a fraction of the radiation it receives1 and this fraction is greater for the second lamina than for the first4 ,in the following table ,i have represented in the first line the distances in centimetres between the polonium and the sheet ,t2 in the second line the percentage of the rays transmitted by a sheet of aluminium2 in the third line the percentage of the rays transmitted by two sheets of the same aluminium3-- ,distance ,a ,t #ce #be #ai #ade #je ,percentage of rays transmitted by one lamina #j #j #e #aj #be ,percentage of rays transmitted by two lamin #j #j #j #j #jg ,in these experiments the distance of the plates1 ,p and ,p1 was #c c4m4 ,we see that the interposition of the aluminium screen diminishes the intensity of the radiation to a greater degree at further distances than at nearer distances4 ,this effect is still more marked than the preceding figures seem to indicate4 ,for a distance of #je c4m4 #be per cent represents the mean penetration for all the rays which pass beyond this distance4 ,if1 for example1 only those rays between #je c4m4 and #a c4m4 be comprehended1 the penetration would be greater4 ,and if the plate ,p be placed at a distance of #je c4m4 from ,p the fraction of the radiation transmitted by the aluminium lamina 7for ,a ,t #je c4m47 is #dg per cent1 and through two lamin it is #e per cent of the original radiation4 ,i have recently performed a second series of experiments with these same specimens of polonium1 the activity of which was considerably diminished1 the interval of time between the two series of experiments being three years4 ,in the former experiments1 polonium nitrite was used2 in the latter1 the polonium was in the state of metallic particles obtained by fusing the nitrite with potassium cyanide4 ,i found that the radiation of polonium had preserved its essential characteristics1 and ,i discovered new results4 ,the following1 for different values of the distance ,a ,t1 are the fractions of the radiation transmitted by a screen composed of four superposed very thin leaves of beaten aluminium4 ,distance ,a ,t1 in centimetres #j #ae #bf ,percentage of rays transmitted by the screen #gf #ff #ci ,i also found that the fraction of the radiation absorbed by a given screen increases with the thickness of the material already traversed by the radiation1 but this only occurs after the distance ,a ,t has reached a certain value4 ,when this distance is zero 7the polonium being in contact with the sheet1 either outside or inside the condenser71 it is observed that with several similar superposed screens1 each absorbs the same fraction of the radiation it receives2 otherwise expressed1 the intensity of the radiation diminishes therefore according to an exponential law as a function of the thickness of the material traversed1 as in the case of homogeneous radiation transmitted by the lamina without changing its nature4 ,the following numerical results are given with reference to these experiments3-- ,for a distance ,a ,t equal to #ae c4m4 a thin aluminium screen transmits the fraction #jea of the radiation it receives when acting alone1 and the fraction #jcd of the radiation it receives when it is preceded by another similar screen4 ,on the contrary1 for a distance ,a ,t equal to zero1 the same screen transmits in both the cases considered the same fraction of the radiation it receives1 and this fraction is equal to #jga2 it is therefore greater than in the preceding case4 ,the following numbers indicate for a distance ,a ,t equal to #j and for a succession of thin superposed screens1 the ratio of the radiation transmitted to the radiation received for each screen3-- ,series of nine very thin copper ,series of seven very thin aluminium leaves4 leaves4 #jgb #j4fi #jgh #j4id #jge #j4ie #jgg #j4ia #jgj #j4ib #jgg #j4ic #jfi #j4id #jgi #jfh ,taking into account the difficulties of the manipulation of very thin screens and of the superposition of screens in contact1 the numbers of each column may be looked upon as constant2 the first number only of the aluminium column indicates a greater absorption than that indicated by the following numbers4 ,the -rays of radium behave similarly to the rays of polonium4 ,these rays may be investigated almost isolated by deflecting to one side the -rays with the magnetic field2 the -rays seem of slight importance in comparison with the -rays4 ,the operation can only be carried on at some distance from the source of radiation4 ,the following are the results of an experiment of this kind4 ,the fraction of the radiation transmitted by a lamina of aluminium #jja m4m4 thick is measured2 this screen was placed always in the same position1 above and at a little distance from the source of radiation4 ,with the apparatus of ,fig4 #e1 the current produced in the condenser for different values of the distance ,a ,d is observed1 both with and without the screen3-- ,distance ,a ,d #fj #ea #cd ,percentage of rays transmitted by the aluminium #c #g #bd ,the rays which travel furthest in the air are those most absorbed by the aluminium4 ,there is therefore a great similarity between the absorbable -rays of radium and the rays of polonium4 ,the deflected -rays and the undeflected penetrating -rays are1 on the contrary1 of a different nature4 ,the experiments1 notably of ,,mm4 ,meyer and von ,schweidler1 clearly show that1 considering the radiation of radium as a whole1 the penetrating power of this radiation increases with the thickness of the material traversed1 as is the case of ,rntgen rays4 ,in these experiments the -rays produce scarcely any effect1 being for the most part suppressed by very thin absorbent screens4 ,those which penetrate are1 on the one hand1 -rays more or less scattered2 on the other hand1 -rays1 which appear similar to ,rntgen rays4 ,the following are the results of some of my experiments on the subject3-- ,the radium is enclosed in a glass vessel4 ,the rays1 which emerge from the vessel1 traverse #cj c4m4 of air1 and are received upon a series of glass plates1 each of thickness #ac m4m42 the first plate transmits #di per cent of the radiation it receives1 the second transmits #hd per cent of the radiation it receives1 the third transmits #he per cent of the radiation it receives4 ,in another series of experiments the radium was enclosed in a glass vessel placed #aj c4m4 from the condenser which received the rays4 ,a series of similar screens of lead each #jaae m4m4 thick were placed on the vessel4 ,the ratio of the radiation transmitted to the radiation received is given for each of the successive screens by the following numbers3-- #jdj #jfj #jgb #jgi #jhi #jib #jid #jid #jig ,for a series of four screens of lead1 each of which was #ae m4m4 thick1 the ratio of the radiation transmitted to the radiation received was given for the successive screens by the following numbers3-- #jji #jgh #jhd #jhb ,the results of these experiments show that when the thickness of the lead traversed increases from #ja m4m4 to #f m4m41 the penetrating power of the radiation increases4 ,i found that1 under the experimental conditions mentioned1 a screen of lead #ah c4m4 thick transmits #b per cent of the radiation it receives2 a screen of lead #ec c4m4 thick transmits #jd per cent of the radiation it receives4 ,i also found that the radiation transmitted by a thickness of lead of #ae m4m4 consists largely of rays capable of deflection 7cathode order74 ,the latter are therefore capable of traversing not only great distances in the air1 but also considerable thicknesses of very absorbent solids1 such as lead4 ,in investigating with the apparatus of ,fig4 #b the absorption exercised by an aluminium screen #jja m4m4 thick upon the total radiation of radium1 the screen being always placed at the same distance from the radiating body1 and the condenser being placed at a variable distance1 ,a ,d1 the results obtained are the sum of those due to the three groups of the radiation4 ,at a long distance the penetrating rays predominate1 and the absorption is slight2 at a short distance the -rays predominate1 and the absorption becomes less with nearer approach to the substance2 for an intermediate distance the absorption passes through a maximum and the penetration through a minimum4 ,distance ,a ,d #ga #fe #fj #ea #cd ,percentage of rays transmitted by aluminium #ia #hb #eh #da #dh ,certain experiments made in connection with absorption always demonstrate a certain similarity between the -rays and the -rays4 ,thus it was that ,m4 ,becquerel discovered that the absorbent action of a solid screen upon the -rays increases with the distance of the screen from the source1 such that if the rays are subjected to a magnetic field1 as in ,fig4 #d1 a screen placed in contact with the source of radiation allows a larger portion of the magnetic spectrum to be in evidence than does the same screen placed upon the photographic plate4 ,this variation of the absorbent effect of the screen with the distance of the screen from the source is similar to that which occurs with the -rays2 this has been verified by ,,mm4 ,meyer and von ,schweidler1 who operated by means of the fluoroscopic method2 ,m4 ,curie and ,i observed the same fact when working by the electrical method4 ,however1 when the radium is enclosed in a glass tube and placed at a distance from the condenser1 which is itself enclosed in a thin aluminium box1 it becomes a matter of indifference whether the screen be placed against the source or against the condenser2 the current obtained is the same in both cases4 ,the investigation of the -rays led me to the reflection that these rays behave like projectiles having a certain initial velocity1 and which lose their force on encountering obstacles4 ,these rays1 moreover1 travel by rectilinear propagation1 as has been shown by ,m4 ,becquerel in the following experiment3--,polonium emitting rays was placed in a very narrow straight cavity hollowed in a sheet of cardboard4 ,thus a linear source of radiation was produced4 ,a copper wire1 #ae m4m4 in diameter1 was placed parallel and opposite to the source at a distance of #di m4m4 ,beyond was placed a parallel photographic plate at a distance of #hfe m4m4 ,after an exposure of ten minutes1 the geometric shadow of the wire was perfectly reproduced1 with a narrow penumbra corresponding to the size of the source4 ,the same experiment succeeded equally well when a double leaf of beaten aluminium was placed against the wire1 through which the rays must pass4 ,there are therefore rays capable of giving perfect geometric shadows4 ,the experiment with the aluminium shows that these rays are not scattered in traversing the screen1 and that this screen does not give rise to any noticeable extent to secondary rays similar to the secondary rays of the ,rntgen rays4 ,the experiments of ,mr4 ,rutherford show that the projectiles which constitute the -rays are deflected by a magnetic field1 as if they were positively charged4 ,the deflection in a magnetic field becomes less as the product mv_/e becomes greater2 m being the mass of the particle1 v its velocity1 and e its charge4 ,the cathode rays of radium are but slightly deflected1 because their velocity is enormous2 they are1 on the other hand1 very penetrating1 because each particle has a very small mass together with a great velocity4 ,but particles which1 with an equal charge and a less velocity1 have a greater mass1 would be also only slightly influenced by the action of the field1 and would give rise to very absorbable rays4 ,from the results of ,mr4 ,rutherford's experiments1 this seems to take place in the case of the -rays4 ,the penetrating -rays appear to be of quite another nature and similar to ,rntgen rays4 ,we have now seen how complex a phenomenon is the radiation of radio-active bodies4 ,the difficulties of investigation are increased by the question as to whether the radiation undergoes a merely selective absorption on the part of the material1 or whether a more or less radical transformation4 ,little is so far known with regard to this question4 ,if the radiation of radium be regarded as containing rays both of the cathode and ,rntgen species1 it might be expected to undergo transformations in traversing screens4 ,it is known3--,firstly1 that cathode rays emerging from a ,crookes tube through an aluminium window are greatly scattered by the aluminium2 and1 further1 that the passage through the screen entails a diminution of the velocity of the rays4 ,in this way1 cathode rays with a velocity equal to #ad #ajaj c4m4 lose #aj per cent of their velocity in passing through #jja m4m4 of aluminium4 ,secondly1 cathode rays on striking an obstacle give rise to the production of ,rntgen rays4 ,thirdly1 ,rntgen rays1 on striking a solid obstacle1 give rise to the production of secondary rays1 which partly consist of cathode rays4 ,the existence1 by analogy1 of all these preceding phenomena may therefore be predicted for the rays of radio-active substances4 ,in investigating the transmission of polonium rays through a screen of aluminium1 ,m4 ,becquerel observed neither the production of secondary rays nor any transformation into cathode rays4 ,i endeavoured to demonstrate a transformation of the rays of polonium by using the method of interchangeable screens4 ,two superposed screens1 ,e#a and ,e#b1 being traversed by the rays1 the order in which they are traversed should be immaterial if the passage through the screens does not transform the rays2 if1 on the contrary1 each screen transforms the rays during transmission1 the order of the screens is of moment4 ,if1 for example1 the rays are transformed into more absorbable rays in passing through lead1 and no such effect is produced by aluminium1 then the system lead-aluminium will be more opaque than the system aluminium-lead2 this takes place with ,rntgen rays4 ,my experiments show that this phenomenon is produced with the rays of polonium4 ,the apparatus employed was that of ,fig4 #h4 ,the polonium was placed in the box1 ,c ,c ,c ,c1 and the absorbing screens1 of necessity very thin1 were placed upon the metallic sheet ,t4 ,screens employed4 ,thickness4 ,current observed4 ,m4m4 ,aluminium #jja #agi ,brass #jjje ,brass #jjje #fg ,aluminium #jja ,aluminium #jja #aej ,tin #jjje ,tin #jjje #abe ,aluminium #jja ,tin #jjje #aci ,brass #jjje ,brass #jjje #dd ,tin #jjje ,the results obtained prove that the radiation is modified in passing through a solid screen4 ,this conclusion accords with the experiments in which1 of two similar superposed metallic screens1 the first is less absorbent than the second4 ,from this it is probable that the transforming action of a screen increases with the distance of the screen from the source4 ,this fact has not been verified1 and the nature of the transformation has not been studied in detail4 ,i repeated the same experiments with a very active salt of radium2 the result was negative4 ,i only observed insignificant variations in the intensity of the radiation transmitted with interchange of the order of the screens4 ,the following systems of screens were experimented with3-- ,aluminium1 thickness #jee m4m4 ,aluminium1 thickness #jee m4m4 ,aluminium1 thickness #jee m4m4 ,aluminium1 thickness #ajg m4m4 ,aluminium1 thickness #jee m4m4 ,aluminium1 thickness #ajg m4m4 ,aluminium1 thickness #jae m4m4 ,aluminium1 thickness #jae m4m4 ,aluminium1 thickness #jae m4m4 ,platinum1 thickness #jja m4m4 ,lead1 thickness #ja m4m4 ,tin1 thickness #jjje m4m4 ,copper1 thickness #jje m4m4 ,brass1 thickness #jjje m4m4 ,brass1 thickness #jjje m4m4 ,platinum1 thickness #jja m4m4 ,zinc1 thickness #jje m4m4 ,lead1 thickness #ja m4m4 ,the system lead-aluminium was slightly more opaque than the system aluminium-lead1 but the difference was not great4 ,thus1 ,i was unable to discover an appreciable transformation of the rays of radium4 ,however1 in various radiographic experiments1 ,m4 ,becquerel observed very intense effects due to scattered or secondary rays1 emitted by solid screens which received radium rays4 ,lead seemed to be the most active substance in this respect4 ,ionising ,action of ,radium ,rays on ,insulating ,liquids4 ,m4 ,curie has pointed out that radium rays and ,rntgen rays act upon liquid dielectrics as upon air1 imparting to them a certain electrical conductivity4 ,the experiment was carried out in the following manner 7,fig4 #i73-- ,the experimental liquid is placed in a metal vessel1 ,c ,d ,e ,f1 into which a thin copper tube1 ,a ,b1 is plunged2 these two pieces of metal serve as electrodes4 ,the outer vessel is maintained at a known potential1 by means of a battery of small accumulators1 one pole of which is connected to earth4 ,the tube1 ,a ,b1 is connected to the electrometer4 ,when a current traverses the liquid the electrometer is kept at zero by means of a quartz electrical piezometer1 which gives the strength of the current4 ,the copper tube1 ,m ,n ,m ,n1 connected to earth1 serves as a guard tube1 preventing the passage of the current through the air4 ,a bulb containing the radium-barium salt may be placed at the bottom of the tube1 ,a ,b2 the rays act on the liquid after having penetrated the glass of the bulb and the sides of the metal tube4 ,the radium may also be allowed to act by placing the bulb beneath the side1 ,d ,e4 ,in working with ,rntgen rays the course of the rays is through side ,d ,e4 ,the increase of conductivity by the action of the radium rays or the ,rntgen rays seems to be produced in the case of all liquid dielectrics2 but in order to determine this increase1 the conductivity of the liquid itself must be so slight as not to mask the effect of the rays4 ,m4 ,curie obtained results of the same order of magnitude with both radium rays and ,rntgen rays4 ,when investigating with the same apparatus the conductivity of air or of another gas under the action of the ,becquerel rays1 the intensity of the current obtained is found to be proportional to the difference of potential between the electrodes1 as long as the latter does not exceed a few volts2 but at higher tensions1 the intensity of the current increases less and less rapidly1 and the saturation current is practically attained for a tension of #ajj volts4 ,liquids examined with the same apparatus and the same radio-active body behave differently2 the intensity of the current is proportional to the tension when the latter varies between #j and #dej volts1 and when the distance between the electrodes does not exceed #f m4m4 ,illustration3 ,,fig4 #i4 ,the figures of the following table multiplied by #aj-aa give the conductivity in megohms per c4c43-- ,carbon bisulphide #bj ,petroleum ether #ae ,amylene #ad ,benzine #d ,liquid air #ac ,vaseline oil #af ,we may1 however1 assume that liquids and gases behave similarly1 but that1 in the case of liquids1 the current remains proportional to the tension up to a much higher limit than in the case of gases4 ,it therefore seemed probable that the limit of proportionality could be lowered by using a much more feeble radiation1 and this idea was verified by experiment4 ,the radio-active body employed was #aej times less active than that which had served for the previous experiments4 ,for tensions of #ej1 #ajj1 #bjj1 #djj volts1 the intensities of the current were represented respectively by the numbers #aji1 #ahe1 #bee1 #cce4 ,the proportionality was no longer maintained1 but the current showed great variation when the difference of potential was doubled4 ,some of the liquids examined are nearly perfect insulators when maintained at a constant temperature and when screened from the action of the rays4 ,such are liquid air1 petroleum ether1 vaseline oil1 and amylene4 ,it is therefore very easy to study the effect of the rays4 ,vaseline oil is much less sensitive to the action of the rays than is petroleum ether4 ,this fact may have some relation to the difference in volatility which exists between these two hydrocarbons4 ,liquid air1 which has boiled for some time in the experimental vessel1 is more sensitive to the action of the rays than that newly poured in2 the conductivity produced by the rays is one-fourth as great again in the former case4 ,m4 ,curie has investigated the action of the rays upon amylene and upon petroleum ether at temperatures of #aj and -#ag4 ,the conductivity due to the radiation diminishes by one-tenth of its value only1 in passing from #aj to -#ag4 ,in the experiments in which the temperature of the liquid is varied1 the temperature of the radium may be either that of the surrounding atmosphere or that of the liquid2 the same result is obtained in both cases4 ,this leads to the conclusion that the radiation of radium does not vary with the temperature1 and remains unaltered even at the temperature of liquid air4 ,this fact has been verified directly by measurements4 ,various ,effects and ,applications of the ,ionising ,action of the ,rays ,emitted by ,radio-active ,substances4 ,the rays of the new radio-active substances have a strongly ionising action upon air4 ,by the action of radium the condensation of supersaturated water vapour can be easily induced1 just as happens by the action of cathode rays and ,rntgen rays4 ,under the influence of the rays emitted by the new radio-active substances1 the distance of discharge between two metallic conductors for a given difference of potential is increased2 to put it otherwise1 the passage of the spark is facilitated by these rays4 ,in causing conductivity1 by the action of radio-active bodies1 in the air in the neighbourhood of two metallic conductors1 one of which is connected to earth and the other to a well-insulated electrometer1 the electrometer is seen to be permanently deflected1 which gives a measure of the electromotive force of the battery formed by the air and the two metals 7electromotive force of contact of the two metals1 when they are separated by air74 ,this method of measurement was employed by ,lord ,kelvin and his students1 the radiating body being uranium2 a similar method had been previously employed by ,m4 ,perrin1 who was using the ionising action of ,rntgen rays4 ,radio-active bodies may be employed in the study of atmospheric electricity4 ,the active substance is enclosed in a little box of thin aluminium fixed at the extremity of a metal wire connected with the electrometer4 ,the air is made to conduct in the neighbourhood of the end of the wire1 and the latter adopts the potential of the surrounding air4 ,radium thus replaces1 with advantage1 the flames or the apparatus of running water of ,lord ,kelvin1 till now in general use for the investigation of atmospheric electricity4 ,fluorescent and ,luminous ,effects4 ,the rays emitted by the new radio-active bodies cause fluorescence of certain substances4 ,m4 ,curie and myself first discovered this phenomenon when causing polonium to act upon a layer of barium platinocyanide through aluminium foil4 ,the same experiment succeeds yet more easily with barium containing radium4 ,when the substance is strongly radio-active the fluorescence produced is very beautiful4 ,a large number of bodies are capable of becoming phosphorescent or fluorescent by the action of the ,becquerel rays4 ,m4 ,becquerel studied the effect upon the uranium salts1 the diamond1 c4 ,m4 ,bary has demonstrated that the salts of the metals of the alkalis and alkaline earths1 which are all fluorescent under the action of luminous rays and ,rntgen rays1 are also fluorescent under the action of the rays of radium4 ,paper1 cotton1 glass1 c41 are all caused to fluoresce in the neighbourhood of radium4 ,among the different kinds of glass1 ,thuringian glass is specially luminous4 ,metals do not seem to become luminous4 ,barium platinocyanide is most conveniently used when the radiation of the radio-active bodies is to be investigated by the fluoroscopic method4 ,the effect of the radium rays may be followed at distances greater than #b m4 ,phosphorescent zinc sulphide is made extremely luminous1 but this body has the inconvenient property of preserving its luminosity for some time after the action of the rays has ceased4 ,the fluorescence produced by radium may be observed when the fluorescent screen is separated from the radium by absorbent screens4 ,we were able to observe the illumination of a screen of barium platinocyanide across the human body4 ,however1 the action is incomparably greater when the screen is placed immediately in contact with the radium1 being separated from it by no solid screen at all4 ,all the groups of rays appear capable of producing fluorescence4 ,in order to observe the action of polonium1 the substance must be placed close to the fluorescent screen1 without the intervention of a solid screen1 unless the latter be extremely thin4 ,the luminosity of fluorescent substances exposed to the action of radio-active bodies diminishes with time4 ,at the same time the fluorescent substance undergoes a transformation4 ,the following are examples3-- ,radium rays transform barium platinocyanide into a brown1 less luminous variety 7an action similar to that produced by ,rntgen rays1 and described by ,m4 ,villard74 ,uranium sulphate and potassium sulphate are similarly altered4 ,the changed barium platinocyanide is partially regenerated by the action of light4 ,if the radium be placed beneath a layer of barium platinocyanide spread on paper1 the platinocyanide becomes luminous2 if the system be kept in the dark1 the platinocyanide becomes changed1 and its luminosity diminishes considerably4 ,but if the whole be exposed to light1 the platinocyanide is partially regenerated1 and if the whole is replaced in darkness the luminosity reappears with vigour4 ,by means of a fluorescent body and a radio-active body1 we have therefore obtained a system which acts as a phosphorescent body capable of long duration of phosphorescence4 ,glass made fluorescent by the action of radium becomes coloured brown or violet4 ,at the same time its fluorescence diminishes4 ,if the glass thus changed be warmed1 it is decolorised1 and when this occurs the glass becomes luminous4 ,the glass has now regained its fluorescent property in the same degree as before the transformation4 ,zinc sulphide1 which has been exposed for a sufficient length of time to the action of radium1 gradually becomes used up1 and loses its phosphorescent property1 whether under the action of radium or that of light4 ,the diamond becomes phosphorescent under the action of radium1 and may thus be distinguished from paste imitations1 which have only a very faint luminosity4 ,all the barium-radium compounds are spontaneously luminous4 ,the dry anhydrous halogen salts emit a particularly intense light4 ,this illumination cannot be seen in broad daylight1 but it is easily visible in the twilight or by gas-light4 ,the light emitted may be strong enough to read by in the dark4 ,the light emitted emanates from the entire body of the product1 whilst in the case of a common phosphorescent body1 the light emanates specially from the portion of the surface illuminated4 ,radium products lose much of their luminosity in damp air1 but they regain it on drying 7,giesel74 ,there is apparently conservation of luminosity4 ,after many years no sensible modification is produced in the luminosity of feebly active products1 kept in the dark in sealed tubes4 ,in the case of very active and very luminous radium-barium chloride1 the light changes colour after several months2 it becomes more violet and loses in intensity2 at the same time the product undergoes transformations2 on re-dissolving the salt in water and drying it afresh1 the original luminosity is restored4 ,solutions of barium-radium salts1 which contain a large proportion of radium1 are equally luminous2 this fact may be observed by placing the solution in a platinum capsule1 which not being itself luminous permits of the faint luminosity of the solution being seen4 ,when a solution of a barium-radium salt contains crystals deposited in it1 these crystals are luminous at the bottom of the solution1 and much more so than the solution itself1 so that they alone appear luminous4 ,m4 ,giesel has made a preparation of barium-radium platinocyanide4 ,when this salt is newly crystallised1 it has the appearance of ordinary barium platinocyanide and is very luminous4 ,but gradually the salt becomes spontaneously coloured1 taking a brown tint1 the crystals at the same time becoming dichroic4 ,in this state the salt is much less luminous1 although its radio-activity is increased4 ,the radium platinocyanide1 prepared by ,m4 ,giesel1 changes still more rapidly4 ,radium compounds are the first example of self-luminous bodies4 ,evolution of ,heat by the ,salts of ,radium4 ,,mm4 ,curie and ,laborde have recently discovered that the salts of radium are the source of a spontaneous and continuous evolution of heat4 ,this evolution has the effect of keeping the salts of radium at a temperature higher than that of their surroundings2 an excess of temperature of #ae has been observed4 ,this excess of temperature is dependent upon the thermal insulation of the body4 ,,mm4 ,curie and ,laborde have determined the amount of heat produced in the case of radium4 ,they found that the output is of the order of magnitude of #ajj calories per grm4 of radium per hour4 ,one grm4-atom 7#bbe grm47 of radium give rise in one hour to #bb1ejj cal41 a quantity of heat comparable to that produced by the combustion of #a grm4-atom 7#a grm47 of hydrogen4 ,so great an evolution of heat can be explained by no ordinary chemical reaction1 more particularly as the condition of the radium remains unaffected for years4 ,the evolution of heat might be attributed to a slow transformation of the radium atom4 ,if this were the case1 we should be led to conclude that the quantities of energy generated during the formation and transformation of the atoms are considerable1 and that they exceed all that is so far known4 ,chemical ,effects produced by the ,new ,radio-active ,bodies4 ,colourations4--,the radiations of strongly radio-active bodies are capable of causing certain chemical reactions4 ,the rays emitted by radium products exercise colouring actions upon glass and porcelain4 ,the colouration of glass1 generally brown or violet1 is very deep2 it is produced in the body of the glass1 and remains after removal of the radium4 ,all glasses become coloured after a longer or a shorter interval of time1 and the presence of lead is not essential4 ,this fact may be compared to that recently observed of the colouration of the glass of vacuum tubes1 after having been long in use for the production of ,rntgen rays4 ,m4 ,giesel has demonstrated that the crystallised halogen salts of the alkali metals become coloured under the influence of radium1 as under the action of cathode rays4 ,m4 ,giesel points out that similar colourations are obtained when the salts of the alkalis are exposed to sodium vapour4 ,i investigated the colouration of a collection of glasses of known composition1 kindly lent me for the occasion by ,m4 ,le ,chatelier4 ,i observed no great variety in the colouration4 ,it is generally brown1 violet1 yellow1 or grey4 ,it appears to be associated with the presence of the alkali metals4 ,with the pure crystallised alkali salts more varied and more vivid colours are obtained2 the salt1 originally white1 becomes blue1 green1 yellow1 brown1 c4 ,m4 ,becquerel has discovered that yellow phosphorus is transformed into the red variety by the action of radium4 ,paper is changed and coloured by the action of radium4 ,it becomes brittle1 scorched1 and1 finally1 resembles a colander perforated with holes4 ,under some circumstances there is a production of ozone in the neighbourhood of very active compounds4 ,rays emerging from a sealed jar containing radium do not produce ozone in the air they pass through4 ,on the contrary1 a strong odour of ozone is detected when the jar is opened4 ,in a general way1 ozone is produced in the air when the latter is in direct contact with the radium4 ,communication by a channel1 even if extremely narrow1 suffices2 it appears as if the production of ozone is associated with the propagation of induced radio-activity1 of which we shall speak later4 ,radium compounds appear to change with lapse of time1 doubtless under the action of their own radiation4 ,it was seen above that crystals of barium-radium chloride1 which are colourless when formed1 become gradually coloured first yellow or orange1 then pink2 this colouration disappears in solution4 ,barium-radium chloride generates oxygen compounds of chlorine2 the bromide those of bromine4 ,these slow changes generally manifest themselves some time after the preparation of the solid product1 which at the same time changes in form and colour1 becoming yellow or violet4 ,the light emitted also becomes more violet4 ,a solution of a radium salt evolves hydrogen 7,giesel74 ,pure radium salts seem to undergo the same changes as those containing barium4 ,however1 crystals of the chloride1 deposited in acid solution1 do not become sensibly coloured after some time has elapsed1 whereas crystals of barium-radium chloride1 rich in radium1 become deeply coloured4 ,production of ,thermo-luminosity4--,certain bodies1 such as fluorite1 become luminous when heated2 they are thermo-luminescent4 ,their luminosity disappears after some time1 but the capacity of becoming luminous afresh through heat is restored to them by the action of a spark1 and also by the action of radium4 ,radium can thus restore to these bodies their thermo-luminescent property4 ,fluorite when heated undergoes a change1 which is accompanied by the emission of light4 ,if the fluorite is afterwards subjected to the action of radium1 an inverse change occurs1 which is also accompanied by an emission of light4 ,an absolutely similar phenomenon occurs when glass is exposed to radium rays4 ,here also a change is produced in the glass while luminous from the effect of the radium rays2 this change shows itself in the colouration which appears and gradually increases4 ,if the glass is afterwards heated1 the inverse change takes place1 the colour disappears1 and this phenomenon is accompanied by production of light4 ,it appears very probable that we have here a change of a chemical nature1 and the production of light is associated with this change4 ,this phenomenon may be general4 ,it might be that the production of fluorescence by the action of radium and the luminosity of radium compounds is of necessity associated with some chemical or physical change in the substance emitting the light4 ,radiographs4--,the radiographic action of the new radio-active bodies is very marked4 ,however1 the method of operating should be very different with polonium and radium4 ,polonium acts only at very short distances1 and its action is considerably weakened by solid screens2 it is practically annihilated by means of a screen of slight thickness 7#a m4m4 of glass74 ,radium acts at considerably greater distances4 ,the radiographic action of radium rays may be observed at more than #b m4 distance in air1 even when the active product is enclosed in a glass vessel4 ,the rays acting under these conditions belong to the - and -groups4 ,owing to the differences in transparency of different materials to the rays1 radiographs of different objects may be obtained1 as in the case of ,rntgen rays4 ,metals are1 as a rule1 opaque1 with the exception of aluminium1 which is very transparent4 ,there is no noteworthy difference of transparency between flesh and bone4 ,the operation may be carried on at a great distance and with a source of very small dimensions2 and very delicate radiographs are thus produced4 ,the beauty of the radiograph is enhanced by deflecting to one side the -rays1 by means of a magnetic field1 and utilising only the -rays4 ,the -rays1 in traversing the object to be radiographed1 undergo a certain amount of diffusion1 and thus cause a slight fog4 ,in suppressing them1 a longer time of exposure is necessary1 but better results are obtained4 ,the radiograph of an object1 such as a purse1 requires one day with a radiating source composed of several centigrams of a radium salt1 enclosed in a glass vessel1 and placed at a distance of #a m4 from the sensitive plate1 in front of which the object is placed4 ,if the source is at a distance of #bj c4m4 from the plate1 the same result is obtained in one hour4 ,in the immediate vicinity of the source of radiation1 a sensitive plate is instantaneously acted upon4 ,physiological ,effects4 ,radium rays exert an action upon the epidermis4 ,this has been observed by ,m4 ,walkhoff and confirmed by ,m4 ,giesel1 since also by ,,mm4 ,becquerel and ,curie4 ,if a celluloid or thin indiarubber capsule containing a very active salt of radium be placed upon the skin1 and be left thus for some time1 a redness is produced upon the skin1 either immediately or at the end of some time1 which is longer in proportion as the action is weaker2 this red spot appears in the place which has been exposed to the action2 the local change in the skin appears and acts like a burn4 ,in certain cases a blister is formed4 ,if the exposure was of long duration1 an ulceration is produced which is long in healing4 ,in one experiment1 ,m4 ,curie caused a relatively weak radio-active product to act upon his arm for ten hours4 ,the redness appeared immediately1 and later a wound was caused which took four months to heal4 ,the epidermis was locally destroyed1 and formed again slowly and with difficulty1 leaving a very marked scar4 ,a radium burn with half-an-hour's exposure appeared after fifteen days1 formed a blister and healed in fifteen days4 ,another burn1 caused by an exposure of only eight minutes1 occasioned a red spot which appeared two months after1 its effect being quite insignificant4 ,the action of radium upon the skin can take place across metal screens1 but with weakened effect4 ,the action of radium upon the skin has been investigated by ,dr4 ,daulos1 at the ,hospital of ,st4 ,louis1 as a process of treating certain affections of the skin1 similar to the treatment with the ,rntgen rays or the ultra-violet rays4 ,in this respect radium gives encouraging results2 the epidermis partially destroyed by the action of the radium is renewed in a healthy condition4 ,the action of radium is more penetrating than that of light1 and its use is easier than that of light or of ,rntgen rays4 ,the study of the conditions of application is of necessity rather lengthy1 because the effect of the application does not at once appear4 ,m4 ,giesel has observed the action of radium upon plant leaves4 ,the leaves thus treated turn yellow and wither away4 ,m4 ,giesel has also discovered the action of radium rays upon the eye4 ,if a radio-active substance be placed in the dark in the vicinity of the closed eye or of the temple1 a sensation of light fills the eye4 ,this phenomenon has been studied by ,,mm4 ,himstedt and ,nagel4 ,these physicists have demonstrated that the centre of the eye is rendered fluorescent by the action of radium1 and this explains the sensation of light experienced4 ,blind people whose retina is intact are sensitive to the action of radium1 whilst those whose retina is diseased do not experience any sensation of luminosity4 ,radium rays either arrest or hinder the development of colonies of microbes1 but this action is not very intense4 ,m4 ,danysz has recently demonstrated the ready action of radium upon the marrow and brain4 ,after one hour's exposure paralysis of the animals experimented upon occurred1 and the latter usually died in a few days4 ,influence of ,temperature upon ,radiation4 ,there is so far but little information regarding the manner of variation of the radiation of radio-active bodies with temperature4 ,we know1 however1 that radiation subsists at low temperatures4 ,m4 ,curie placed a glass tube containing barium-radium chloride in liquid air4 ,the luminosity of the radio-active body persisted under these conditions4 ,at the moment1 indeed1 of removing the tube from the cold bath1 it appears more luminous than at the ordinary temperature4 ,at the temperature of liquid air radium continues to cause fluorescence in the sulphates of uranium and potassium4 ,m4 ,curie has verified1 by electrical determinations1 that the radiation1 measured at a certain distance from the source1 possesses the same intensity whether the radium be at the temperature of the atmosphere or of liquid air4 ,in these experiments the radium was placed at the bottom of a tube closed at one end4 ,the rays emerged from the tube at the open end1 traversed a certain space in the air1 and were received into a condenser4 ,the action of the rays upon the air of the condenser was determined both on leaving the tube in the air and on surrounding it to a certain height with liquid air4 ,the same result was obtained in both cases4 ,the radio-activity of radium persists at high temperatures4 ,barium-radium chloride after being fused 7towards #hjj7 is radio-active and luminous4 ,however1 prolonged heating at a high temperature has the effect of temporarily lowering the radio-activity of the body4 ,this decrease is very considerable2 it may constitute #ge per cent of the total radiation4 ,the decrease is less in proportion for the absorbable rays than for the penetrating rays1 which are to some extent suppressed by heating4 ,in time the radiation of the product regains the intensity and composition that it possessed before heating2 this occurs after the lapse of about two months from the occasion of heating4 ,,chapter ,,iv4 ,,communication ,,of ,,radio-,,activity ,,to ,,substances ,,initially ,,inactive4 ,during the course of our researches on radio-active substances ,m4 ,curie and ,i have observed that every substance which remains for some time in the vicinity of a radium salt becomes itself radio-active4 ,in our first publication on this subject1 we confined ourselves to proving that the radio-activity thus acquired by substances initially inactive is not due to the transference of radio-active particles to the surface of these substances4 ,this is proved beyond dispute by all the experiments which will be here described1 and by the laws according to which the radio-activity excited in naturally inactive bodies disappears when the latter are removed from the influence of radium4 ,we have given the name of induced radio-activity to the new phenomenon thus discovered4 ,in the same publication1 we indicated the essential characteristics of induced radio-activity4 ,we excited screens of different substances by placing them in the neighbourhood of solid radium salts1 and we investigated the radio-activity of these screens by the electrical method4 ,we observed the following facts3-- #a4 ,the activity of a screen exposed to the action of radium increases with the time of exposure1 approaching to a definite limit according to an asymptotic law4 #b4 ,the activity of a screen which has been excited by the action of radium1 and which is afterwards withdrawn from its action1 disappears in a few days4 ,this induced activity approaches zero as a function of the time1 following an asymptotic law4 #c4 ,other things being equal1 the radio-activity induced by the same radium product upon different screens is independent of the nature of the screen4 ,glass1 paper1 metals1 all acquire the same degree of activity4 #d4 ,the radio-activity induced in one screen by differing radium products has a limiting value which rises with the increased activity of the product4 ,shortly afterwards1 ,mr4 ,rutherford published a research1 which showed that compounds of thorium are capable of producing the phenomenon of induced radio-activity4 ,mr4 ,rutherford discovered for this phenomenon the same laws as those just enunciated1 besides this additional important fact1 that bodies charged with negative electricity become more active than others4 ,mr4 ,rutherford also observed that air passed over thorium oxide preserves a notable conductivity for about ten minutes4 ,air in this condition communicates induced radio-activity to inactive substances1 especially to those negatively charged4 ,mr4 ,rutherford explains his experiences by the supposition that compounds of thorium1 particularly the oxide1 give rise to a radio-active emanation capable of being carried by air currents and charged with positive electricity4 ,this emanation would be the origin of induced radio-activity4 ,m4 ,dorn has repeated1 with salts of barium containing radium1 the experiments of ,mr4 ,rutherford with thorium oxide4 ,m4 ,debierne has shown that actinium causes1 to a marked degree1 induced activity of bodies placed in its vicinity4 ,as in the case of thorium1 there is a considerable carriage of activity by air currents4 ,induced radio-activity has various aspects1 and irregular results are obtained when the activity of a substance in the neighbourhood of radium is excited in free air4 ,,mm4 ,curie and ,debierne have observed1 however1 that the phenomenon is quite regular when operating in a closed vessel2 they therefore investigated induced activity in a closed space4 ,activity ,induced in an ,enclosed ,space4 ,the active material is placed in a little glass jar1 a1 open at ,o 7,fig4 #aa71 in the centre of a closed space4 ,several plates1 ,a1 ,b1 ,c1 ,d1 ,e1 placed in the enclosure become radio-active after one day's exposure4 ,the activity is the same whatever be the nature of the plate1 for equal dimensions 7lead1 copper1 aluminium1 glass1 ebonite1 wax1 cardboard1 paraffin74 ,the activity of one face of one of the plates is greater in proportion to the amount of free space about this face4 ,if the preceding experiment be repeated with the jar1 a1 completely closed1 no activity is induced4 ,the radiation of radium does not directly affect the production of induced radio-activity4 ,for this reason1 in the preceding experiment the plate ,d1 screened from the radiation by a lead plate of thickness1 ,p ,p1 is made as active as ,b and ,e4 ,radio-activity is transmitted by the air by degrees from the radiating body to the body to be excited4 ,it can even be transmitted to a distance by very narrow capillary tubes4 ,induced radio-activity is both more intense and more regular if the solid radium salt be replaced by an aqueous solution of the same4 ,liquids are capable of acquiring induced radio-activity4 ,for example1 pure water may be rendered active by placing it with a solution of a radium salt within an enclosure4 ,illustration3 ,,fig4 #aa ,certain substances become luminous when placed in an active enclosure 7phosphorescent and fluorescent bodies1 glass1 paper1 cotton1 water1 salt solutions74 ,phosphorescent zinc sulphide is particularly brilliant under the circumstances4 ,the radio-activity of these luminous bodies is1 however1 the same as that of a piece of a metal or other body which is excited under the same conditions without becoming luminous4 ,whatever be the substance made active in a closed vessel1 this substance acquires an activity which increases with length of time until it attains a limiting value1 always the same1 for the same material and the same experimental arrangement4 ,the limit of induced radio-activity is independent of the nature and pressure of the gas inside the active enclosure 7air1 hydrogen1 carbonic acid74 ,the limit of induced radio-activity for the same enclosure depends only on the quantity of radium present in the state of solution1 and is apparently proportional to it4 ,part played by ,gases in the ,phenomena of ,induced ,radio-activity4 ,emanation4--,the gases present in an enclosure containing a solid salt or a solution of a salt of radium are radio-active4 ,this radio-activity persists when the gas is drawn off with a tube and collected in a test-tube4 ,the sides of the test-tube become themselves radio-active1 and the glass of the test-tube is luminous in the dark4 ,the activity and luminosity of the test-tube finally completely disappear1 but very gradually1 and a month afterwards radio-activity may still be detected4 ,since the beginning of our researches1 ,m4 ,curie and ,i have1 by heating pitchblende1 extracted a strongly radio-active gas1 but1 as in the preceding experiment1 the activity of this gas finally completely vanished4 ,we could discern no new ray in the spectrum of this gas2 this was therefore not a case of a new radio-active gas1 and we understood later that it was the phenomenon of induced radio-activity4 ,thus1 for thorium1 radium1 and actinium induced radio-activity is progressively propagated through the gases1 from the radiating body to the walls of the enclosure containing it1 and the exciting principle is carried away with the gas itself1 when the latter is extracted from the enclosure4 ,when the radio-activity of radium compounds is measured by the electrical method by means of the apparatus of ,fig4 #a1 the air between the plates is itself radio-active2 however1 on passing a current of air between the plates1 there is no observable lowering of the intensity of the current1 which proves that the radio-activity distributed in the space between the plates is of little account in comparison with that of the radium itself in the solid state4 ,it is quite otherwise with thorium4 ,the irregularities which ,i observed in determining the radio-activity of the thorium compounds arose from the fact that at this point ,i was working with a condenser open to the air2 the least air current caused a considerable change in the intensity of the current1 because the radio-activity dispersed in the space in the vicinity of the thorium is considerable as compared with the radio-activity of the substance4 ,this effect is still more marked in the case of actinium4 ,a very active compound of actinium appears much less active when a current of air is passed over the substance4 ,the radio-active energy is therefore contained in the gas in a special form4 ,mr4 ,rutherford suggests that radio-active bodies generate an emanation or gaseous material which carries the radio-activity4 ,in the opinion of ,m4 ,curie and myself1 the generation of a gas by radium is a supposition which is not so far justified4 ,we consider the emanation as radio-active energy stored up in the gas in a form hitherto unknown4 ,dissipation in ,free ,air of the ,induced ,activity of ,solid ,bodies4 ,a solid body1 which has been excited by radium in an enclosed space for a sufficient length of time1 and which has then been removed from the enclosure1 parts with its activity in free air according to an exponential law1 which is the same for all bodies represented by the following formula3-- ,i ,i#j7;ae-t_/#a - 7a - #a7;e-t_/#b74 ,i#j being the initial intensity of the radiation at the moment of withdrawing the plate from the enclosure2 ,i1 the intensity after time1 t2 a is a numerical coefficient1 a #dbj2 #a and #b are time constants1 #a #bdbj secs41 #b #ahfj secs4 ,after two or three hours this law becomes practically a simple exponential1 and the effect of the second exponential upon the value of ,i is negligible4 ,the law of dissipation is therefore such that the intensity of radiation becomes diminished to one-half its value in twenty-eight minutes4 ,this final law may be considered as characteristic for the dissipation in an unconfined air space of the activity induced in solid bodies by radium4 ,solid bodies excited by actinium lose their activity in the open air1 according to an exponential law similar to the preceding1 the dissipation being1 however1 rather slower4 ,solid bodies1 made active by thorium1 lose their activity much more slowly2 the intensity of the radiation is reduced to one-half in eleven hours4 ,dissipation of ,activity in a ,confined ,space4 ,velocity of ,destruction of the ,emanation4 ,an enclosure1 made active by radium and then removed from its influence1 loses its activity by a law which is much less rapid than that of dissipation in the open air4 ,the experiment may be carried out with a glass tube1 rendered active internally by placing it for some time in contact with a solution of a salt of radium4 ,the tube is then sealed in the flame1 and the intensity of radiation emitted by the walls of the tube is measured while the dissipation takes place4 ,the law of dissipation is an exponential law4 ,it is given very accurately by the formula4 ,i ,i#j;et_/4 ,i#j initial intensity of radiation4 ,i intensity of radiation at time1 t4 a time constant1 #digj #aje secs4 ,the intensity of the radiation is reduced to one-half in four days4 ,this law of dissipation is absolutely invariable whatever be the experimental conditions 7dimensions of enclosure1 nature of the walls1 nature of the gas within the enclosure1 duration of action1 c474 ,the law of dissipation remains the same for any temperature between -#ahj and #dej4 ,the law is therefore altogether characteristic4 ,in these experiments it is the radio-active energy accumulated in the gas that maintains the activity of the walls4 ,if the gas be withdrawn and a vacuum caused in the enclosure1 we have found that dissipation of activity at once occurs in the rapid method2 the intensity of radiation being reduced to one-half in twenty-eight minutes4 ,the same result is obtained when ordinary air is substituted for the active air in the enclosure4 ,the law of dissipation with reduction of intensity of radiation to one-half in four days1 is therefore characteristic of the disappearance of radio-active energy accumulated in the gas4 ,by making use of the expression adopted by ,mr4 ,rutherford1 the emanation from radium may be said to disappear spontaneously as a function of the time1 with reduction to one-half in four days4 ,the emanation from thorium is of another kind1 and disappears much more rapidly4 ,the intensity of radiation diminishes to one-half in about one minute ten seconds4 ,the emanation from actinium disappears still more rapidly2 reduction to one-half takes place in a few seconds4 ,variation of ,activity of ,liquids rendered ,active and of ,radium ,solutions4 ,any liquid whatever becomes radio-active when placed in an active confined space4 ,on being removed and left freely exposed to the air1 the liquid rapidly loses its activity1 imparting it to the gas and solid bodies surrounding it4 ,if a liquid thus made active be placed in a closed flask1 it loses its activity much more slowly2 the latter being reduced in intensity to one-half in four days1 just as would a gas under similar circumstances4 ,this fact may be explained by assuming that the radio-active energy is stored in liquids in exactly the same form as in gases 7in the form of an emanation74 ,a solution of a radium salt behaves in a somewhat similar manner4 ,at first1 it is a remarkable fact that the solution of a radium salt placed for some time in a confined space is no more active than pure water placed in a vessel in the same enclosure1 when the equilibrium of activity is established4 ,if the radium solution be removed from the enclosure and left standing in the air in a wide-necked vessel1 the activity spreads itself into space1 and the solution becomes nearly inactive1 though still containing radium4 ,if this solution be now enclosed in a stoppered flask1 it gradually regains1 in about a fortnight1 a maximum of activity1 which may be considerable4 ,on the other hand1 a liquid made active1 but not containing radium1 does not regain its activity in a closed flask after having been exposed to the atmosphere4 ,theory of ,radio-activity4 ,the following is1 according to ,,mm4 ,curie and ,debierne1 a very general theory which allows of the co-ordination of the results of the investigation of induced radio-activity1 which results ,i have just stated1 and which constitute facts apart from any hypothesis4 ,it may be said that each atom of radium acts as a constant and continuous source of energy1 without actually defining the origin of this energy4 ,the radio-active energy which accumulates in the radium tends to become dissipated in two different ways3--7#a7 ,by radiation 7rays both charged and uncharged with electricity72 7#b7 by conduction1 i4e41 by gradual transmission to surrounding bodies in a medium of gases and liquids 7production of an emanation and transformation into induced radio-activity74 ,the loss of radio-active energy1 both by radiation and by conduction1 increases with the amount of energy accumulated in the radio-active body4 ,the system is necessarily in equilibrium when the double loss of which ,i have just made mention compensates the constant gain due to the action of radium4 ,this manner of regarding the subject is similar to that in use for calorific phenomena4 ,if in the interior of any body there is1 owing to any cause1 a continuous and constant evolution of heat1 the heat accumulates in the body and the temperature rises until the loss of heat by radiation and conduction is in equilibrium with the constant gain of heat4 ,in general1 except under certain special circumstances1 the activity is not propagated through solid bodies4 ,when a solution is kept in a sealed tube1 the loss by radiation alone takes place1 and the radiating activity of the solution is of a higher degree4 ,if1 on the contrary1 the solution stands in an open vessel1 the loss of activity by conduction becomes considerable1 and when the state of equilibrium is attained1 the radiating activity of the solution is very feeble4 ,the radiating activity of a solid radium salt left exposed to the air does not sensibly diminish1 because the propagation of activity by conduction not taking place through solid bodies1 it is a very thin superficial layer only that produces induced radio-activity4 ,the solution1 however1 of the same salt produces much more intense phenomena of induced radio-activity4 ,with a solid salt the radio-active energy accumulates in the salt1 and is dissipated chiefly by radiation4 ,on the other hand1 when the salt has been for several days in aqueous solution1 the radio-active energy is divided between the salt and the water1 and if separated by distillation the water carries with it a large portion of the activity1 and the solid salt is much less active 7ten or fifteen times7 than before solution4 ,afterwards the solid salt gradually regains its original activity4 ,the preceding theory may be yet further defined by supposing the radio-activity of radium itself to be produced through the medium of the radio-active energy emitted in the form of an emanation4 ,each atom of radium may be considered as a constant and continuous source of emanation4 ,at the same moment that this form of energy is produced1 it undergoes a progressive transformation into radio-active energy of the ,becquerel radiation4 ,the velocity of this transformation is proportional to the quantity of the emanation accumulated4 ,when a radium solution is placed within an enclosure1 the emanation is able to expand into the enclosure and to spread out over the walls4 ,here it is1 therefore1 that it is transformed into a radiation1 the solution giving off but few ,becquerel rays2 the radiation is1 in some sort1 externalised4 ,on the other hand1 with solid radium1 the emanation not being able to escape readily1 accumulates1 and is transformed into the ,becquerel radiation on the spot2 this radiation therefore acquires a higher value4 ,if this theory of radio-activity were general1 we should have to say that all radio-active bodies give rise to an emanation4 ,now this emission has been confirmed in the case of radium1 thorium1 and actinium2 with the latter in particular the emission is enormous1 even in the solid state4 ,uranium and polonium do not seem to emit any emanation1 though they generate ,becquerel rays4 ,these bodies produce no induced radio-activity in an enclosed space1 as do the radio-active bodies mentioned before4 ,this fact is not in absolute contradiction to the preceding theory4 ,if uranium and polonium were to emit emanations which become destroyed with very great rapidity1 it would be very difficult to observe the carriage of such emanations by the air and the effects of induced radio-activity produced by them upon neighbouring bodies4 ,such a hypothesis is not improbable1 since the times required for certain quantities of the emanations of radium and thorium to diminish to one-half are in the proportion of #ejjj to #a4 ,we shall see1 moreover1 that1 under certain conditions1 uranium can excite induced activity4 ,another ,form of ,induced ,radio-activity4 ,according to the law of dissipation in the open air of the activity induced by radium in solid bodies1 the activity after one day is almost imperceptible4 ,certain bodies1 however1 form exceptions2 such are celluloid1 paraffin1 caoutchouc1 c4 ,when these bodies have been acted upon to a sufficient degree1 they lose their activity more slowly than the law can account for1 and it is often fifteen or twenty days before the activity becomes imperceptible4 ,these bodies appear to have the property of becoming charged with radio-active energy in the form of an emanation2 they afterwards lose it gradually1 causing induced radio-activity in the vicinity4 ,induced ,radio-activity with ,slow ,dissipation4 ,there is yet another form of induced radio-activity1 which appears to be produced in all bodies which have been kept for months in an active enclosure4 ,when these bodies are removed from the enclosure their activity at first diminishes to a very low value according to the ordinary law 7diminution to one-half in half-an-hour72 but when the activity has fallen to about #a_/bj1jjj of the initial value1 it diminishes no further1 or at least it is dissipated very slowly1 sometimes even increasing in amount4 ,we have sheets of copper1 aluminium1 and glass which still retain a residual activity after six months4 ,these phenomena of induced radio-activity appear to be of a different kind from the ordinary ones1 and show a much slower process of evolution4 ,a considerable time is also necessary both for the production and dissipation of this form of induced radio-activity4 ,radio-activity ,induced upon ,substances in ,solution with ,radium4 ,when a radio-active ore containing radium is treated1 with the object of extracting the radium1 chemical separations are effected1 after which the radio-activity is confined entirely to one of the products4 ,in this way active products1 which may be several hundred times as active as uranium1 are separated from totally inactive products1 such as copper1 antimony1 arsenic1 c4 ,certain other bodies 7iron1 lead7 were never separated in an entirely inactive state4 ,as these active bodies are concentrated1 the case is no longer the same2 each chemical separation no longer furnishes absolutely inactive products2 all the resulting products of a separation are active in varying degrees4 ,after the discovery of induced radio-activity1 ,m4 ,giesel was the first to attempt to excite activity in ordinary inactive bismuth by keeping it in solution with very active radium4 ,he thus obtained radio-active bismuth1 and from this he concluded that the polonium extracted from pitchblende was probably bismuth made active by the vicinity of the radium contained in the pitchblende4 ,i have also prepared active bismuth by keeping bismuth in solution with a very active radium salt4 ,the difficulties of this experiment consist in the extreme precautions which must be taken to remove all traces of radium from the solution4 ,if we realise what an infinitesimal quantity of radium suffices to produce very considerable radio-activity in #a grm4 of material1 it is difficult to believe in the possibility of sufficiently washing and purifying the active product4 ,each purification causes a diminution of activity of the product1 whether this be due to removal of traces of radium or that the induced radio-activity is1 under these circumstances1 not proof against chemical reactions4 ,the results ,i obtained appear1 however1 to establish with certainty the fact that the activity is produced and persists after the radium is removed4 ,on fractionating the nitrate of my active bismuth by precipitation with water from the nitric acid solution1 ,i found that after careful purifying it fractionated like polonium1 the most active portion being precipitated first4 ,if the purification is not complete the opposite occurs1 showing that traces of radium still remain4 ,i thus obtained active bismuth which from the manner of fractionation showed great purity and which was #bjjj times as active as uranium4 ,this bismuth diminishes in activity with lapse of time4 ,but another portion of the same product1 prepared with the same precautions1 and fractionating in the same manner1 preserves its activity without diminution for actually a period of about three years4 ,this activity is #aej times as great as that of uranium4 ,i have also prepared active lead and silver by leaving them in solution with radium4 ,generally induced radio-activity obtained in this way scarcely lessens with lapse of time1 but it does not as a rule withstand many successive chemical changes of the active body4 ,m4 ,debierne made active barium by placing it in solution with actinium4 ,this barium remains active after several chemical reactions1 its activity being therefore a somewhat stable atomic property4 ,active barium chloride fractionates like barium-radium chloride1 the more active portions being the least soluble in water and dilute hydrochloric acid4 ,the dry chloride is spontaneously luminous3 its ,becquerel radiation is similar to that of barium-radium chloride4 ,m4 ,debierne has prepared an active barium chloride #ajjj times as active as uranium4 ,this barium1 however1 had not acquired all the characteristics of radium1 for it showed none of the strongest radium lines in the spectroscope4 ,further1 its activity diminished on standing1 and after three weeks it had become one-third of its original value4 ,there is a wide field for research upon the radio-activity induced in substances in solution with active bodies4 ,it appears that1 according to the conditions of experiment1 more or less stable forms of induced atomic radio-activity may be obtained4 ,the radio-activity induced under these circumstances is perhaps identical with that form1 which dissipates slowly1 obtained by prolonged exposure at a distance in an active enclosure4 ,we have reason to enquire to what degree induced radio-activity affects the chemical nature of the atom1 and if it is able to modify the chemical properties of the latter1 either temporarily or permanently4 ,the chemical investigation of bodies excited at a distance is rendered difficult by the fact that the induced activity is limited to a very thin superficial layer1 and that1 consequently1 only a very small proportion of the material has been affected4 ,induced radio-activity also results from leaving certain substances in solution with uranium4 ,the experiment succeeded in the case of barium4 ,if1 as was done by ,m4 ,debierne1 sulphuric acid be added to a solution containing uranium and barium1 the precipitate of barium sulphate acquires radio-activity1 and1 at the same time1 the uranium salt loses part of its activity4 ,m4 ,becquerel found1 after repeating this experiment several times1 that almost inactive uranium was obtained4 ,this might lead to the opinion that a radio-active body differing from uranium had been separated from the latter1 its presence producing radio-activity in uranium4 ,this1 however1 is not the case1 for after some months the uranium regains its original activity2 the precipitated barium sulphate1 on the contrary1 loses what it acquired4 ,a similar phenomenon is observed with thorium4 ,mr4 ,rutherford precipitated a solution of a salt of thorium with ammonia2 he separated off the solution and evaporated it to dryness4 ,he thus obtained a small very active residue1 and the precipitated thorium was observed to be less active than before4 ,this active residue1 to which ,mr4 ,rutherford gives the name of thorium ,x1 loses its activity after a time1 whilst the thorium regains its original activity4 ,it appears1 then1 that concerning induced radio-activity all bodies do not behave in a similar manner1 and that certain of them are much more readily excited than others4 ,dissemination of ,radio-active ,particles and ,induced ,radio-activity of the ,laboratory4 ,in making investigations of strongly radio-active bodies1 particular precautions must be observed for obtaining delicate determinations4 ,the different objects used in the chemical laboratory and those used for physical experiments soon acquire radio-activity1 and act upon photographic plates through black paper4 ,dust particles1 the air of the room1 clothing1 all become radio-active4 ,the air of the room becomes a conductor4 ,in our laboratory the evil has become acute1 and we no longer have any apparatus properly insulated4 ,special precautions must therefore be taken to avoid as much as possible the dissemination of active dust particles1 and to avoid also the phenomena of induced activity4 ,the objects employed in chemistry should never be brought into the room where physical research is carried on1 and as far as possible should be avoided any unnecessary keeping of active substances in this room4 ,before beginning our researches we were in the habit1 in the case of electrical experiments1 of making a connection between the different parts of the apparatus by insulated metallic wires1 protected by metal cylinders connected to earth1 which screened the wires from all outside electrical forces4 ,in the investigation of radio-active bodies this arrangement is quite defective2 the air being a conductor there is incomplete insulation between the thread and the cylinder1 and the inevitable electromotive force of contact between the thread and the cylinder tends to produce a current through the air1 and to cause a deflection of the electrometer4 ,we now screen all the wires from the air by placing them inside cylinders filled with paraffin or other insulating material4 ,it would also be advantageous in these investigations to make use of carefully enclosed electrometers4 ,activity ,induced ,outside the ,influence of ,radio-active ,substances4 ,attempts were made to produce induced radio-activity outside the action of radio-active bodies4 ,m4 ,villard subjected to the action of the cathode rays a piece of bismuth placed as anticathode in a ,crookes tube2 the bismuth was thus rendered active to a very slight degree1 for it required an exposure of eight days to obtain a photographic impression4 ,mr4 ,mac,lennan has exposed different salts to the action of cathode rays1 afterwards warming them slightly4 ,the salts then acquired the property of neutralising bodies positively charged4 ,studies of this kind are of great interest4 ,if1 by using known physical agents1 it were possible to create a considerable radio-activity in bodies originally inactive1 we might hope thence to discover the cause of the spontaneous radio-activity of certain substances4 ,variations of ,activity of ,radio-active ,bodies4 ,effects of ,solution4 ,the activity of polonium1 as ,i have said above1 diminishes with time4 ,this diminution is slow1 and does not take place at the same rate with different specimens4 ,a sample of bismuth-polonium nitrate lost half its activity in eleven months1 and #ie per cent in thirty-three months4 ,other specimens have evidenced similar diminution4 ,a specimen of metallic bismuth containing polonium was prepared from the nitrite1 its activity after preparation being #ajj1jjj times that of uranium4 ,the metal is now only a body of medium radio-activity 7#bjjj times that of uranium74 ,its radio-activity is determined at intervals4 ,in six months it has lost #fg per cent of its activity4 ,the loss of activity does not seem to be facilitated by chemical action4 ,in rapid chemical changes no considerable loss of activity has in general taken place4 ,in contrast to that which occurs with polonium1 radium salts possess a permanent radio-activity which evidences no appreciable diminution after many years4 ,a freshly prepared radium salt in the solid state does not at first possess an activity of constant strength4 ,its activity increases from the time of preparation until it attains a practically constant limiting value after about one month4 ,the opposite is the case for a solution4 ,when freshly prepared the solution is very active1 but when left exposed to the air it rapidly loses activity1 and finally reaches a limiting activity which may be considerably less than the original4 ,these variations of activity were first observed by ,m4 ,giesel4 ,they are easily accounted for by the emanation theory4 ,the diminution of the activity of the solution corresponds to the loss of the emanation which escapes into space2 this diminution is much less when the solution is contained in a sealed tube4 ,a solution which has lost its activity in air recovers a greater activity in a sealed tube4 ,the time of increase of the activity of the salt which1 after solution1 has been recently obtained in the solid state1 is that during which the emanation is being newly stored in the solid radium4 ,the following are some experiments on this subject3-- ,a solution of barium-radium chloride left exposed to the air for two days becomes #cjj times less active4 ,a solution is enclosed in a stoppered vessel2 the vessel is opened1 the solution poured into a dish1 and the activity determined3-- ,activity immediately determined #fg ,activity after two hours #bj ,activity after two days #jbe ,a solution of barium-radium chloride1 which has been kept open to the air1 is enclosed in a sealed glass tube1 and the radiation of this tube determined4 ,the following results were observed3-- ,activity determined immediately #bg ,activity determined after #b days #fa ,activity determined after #c days #gj ,activity determined after #d days #ha ,activity determined after #g days #ajj ,activity determined after #aa days #ajj ,the initial activity of a solid salt after preparation is feeble in proportion as the time of solution was long4 ,a greater proportion of activity is then transmitted to the solvent4 ,the following figures give the initial activity with a chloride whose limiting activity is #hjj1 and which was kept for a given time in solution2 the salt was afterwards dried1 and its activity immediately determined3-- ,limiting activity #hjj ,initial activity after solution and immediate evaporation #ddj ,initial activity after the salt has remained dissolved #e days #abj ,initial activity after the salt has remained dissolved #ah days #acj ,initial activity after the salt has remained dissolved #cb days #aad ,during this experiment the dissolved salt was placed in a vessel merely covered with a watch-glass4 ,i made with the same salt two solutions which ,i kept in sealed tubes for thirteen months2 one of these solutions was eight times the strength of the other3-- ,initial activity of the salt in concentrated solution after evaporation #bjj ,initial activity of the salt in dilute solution after evaporation #ajj ,the loss of activity of the salt is therefore greater when the amount of solvent is greater1 the radio-active energy transmitted to the liquid having a greater volume of liquid to saturate and a greater space to fill4 ,the two specimens of the same salt1 which thus had a different initial activity1 further increased in activity at very different rates at first2 at the end of one day they had the same activity1 and the increase of activity now continued in the same manner for both till the limit was reached4 ,when the solution is dilute the loss of activity by the salt is very rapid1 as is shown by the following experiments3--,three equal portions of the same radium salt are dissolved in equal quantities of water4 ,the first solution 7a7 is allowed to stand in contact with the air for one hour1 and is then evaporated4 ,the second solution 7b7 has a current of air passed through it for one hour1 and is then evaporated4 ,the third solution 7c7 is left exposed to the air for thirteen days1 and then evaporated to dryness4 ,the initial activity of each of the three salts is3-- ,for portion a #adeb ,for portion b #adaf ,for portion c #ajbf ,the limiting activity of the same salt is about #dgj4 ,we thus see that the greatest part of the effect was produced at the end of one hour4 ,further1 the air current bubbling through solution b for one hour produced little effect4 ,the proportion of salt in solution was about #je per cent4 ,radio-active energy in the form of an emanation is propagated with difficulty from solid radium in air2 it experiences the same resistance to propagation from solid radium in a liquid4 ,when radium sulphate is shaken with water for a whole day1 its activity after the operation is practically the same as that of a portion of the same sulphate left exposed to air4 ,on placing the radium salt in a vacuum1 all the emanation capable of displacement is withdrawn4 ,however1 the radio-activity of a radium chloride kept in vacuo for six days was not sensibly affected by the operation4 ,this experiment shows that the radio-activity of the salt is principally due to the radio-active energy generated within the particles1 and which is unaffected by the vacuum4 ,the loss of activity that radium undergoes when in solution is relatively greater for the penetrating rays than for the absorbable rays4 ,the following are examples of this3-- ,a radium chloride which had reached its limit of activity1 #dgj1 was dissolved and left in solution for one hour2 it was then evaporated1 and its initial radio-activity determined by the electrical method4 ,the total initial radiation was found to be equal to the fraction #jc of the total limiting radiation4 ,if the determination of the intensity of radiation be made by covering the active body with an aluminium screen #jja m4m4 thick1 the initial radiation which traverses this screen is found to be only the fraction #jag of the limiting radiation traversing the same screen4 ,when the salt has been thirteen days in solution1 the total initial radiation is found to be the fraction #jbb of the total limiting radiation1 and is #jac of the limiting radiation after traversing #jja m4m4 of aluminium4 ,in the two cases the ratio of the initial radiation after solution to the limiting radiation is #ag times as great for the total radiation as for the radiation which has traversed #jja m4m4 of aluminium4 ,it must further be mentioned that on evaporating the product after solution1 it is impossible to avoid a certain period of time during which the product is in an intermediate condition1 neither entirely solid nor entirely liquid4 ,neither can one avoid warming the product to remove the water quickly4 ,for these two reasons it is scarcely possible to determine the true initial activity of the product passing from solution to the solid state4 ,in the experiments just quoted1 equal quantities of the active bodies were dissolved in the same quantity of water1 and the solutions were then evaporated to dryness under conditions as identical as possible1 and without heating above #abj or #acj4 ,i investigated the law according to which the activity of a solid radium salt increases1 from the moment in which the salt is obtained dry after solution to the moment in which it reaches its limit of activity4 ,in the tables which follow1 the intensity of radiation1 ,i1 is represented as a function of the time1 the limiting intensity being supposed equal to #ajj1 and the time being reckoned from the moment at which the product was dried4 ,table ,i4 7,fig4 #ab1 ,curve ,i47 refers to the total radiation4 ,table ,,ii4 7,fig4 #ab1 ,curve ,,ii47 refers only to the penetrating rays 7rays which have traversed #c c4m4 of air and #jja m4m4 of aluminium74 ,,table ,i4 ,,table ,,ii4 ,time4 ,i4 ,time4 ,i4 ,days4 ,days4 #j #ba #j #ac #a #be #a #ai #c #dd #c #dc #e #fj #f #fj #aj #gh #ae #gj #ai #ic #bc #hf #cc #ajj #df #id #fg #ajj ,illustration3 ,,fig4 #ab4 ,i made several other series of determinations of the same kind1 but they do not absolutely agree with one another1 although the general character of the curves obtained remains the same4 ,it is difficult to obtain very regular results4 ,it may1 however1 be remarked that the acquisition of activity requires more than one month for its production1 and that the most penetrating rays are the most deeply affected by solution4 ,the initial intensity of the radiation which is able to traverse #c c4m4 of air and #jja m4m4 of aluminium is only #a per cent of the limiting intensity1 whilst the initial intensity of the total radiation is #ba per cent of the total limiting radiation4 ,a radium salt which has been dissolved and recently evaporated to dryness possesses the same power of causing induced activity 7and1 consequently1 of allowing the escape of an emanation71 as a specimen of the same salt which1 after having been prepared in the solid state1 has remained in this condition long enough to have attained its limiting radio-activity4 ,the radiant activity of these two products is1 however1 quite different2 the former is1 for example1 five times less active than the latter4 ,variations of the ,activity of ,radium ,salts on ,heating4 ,when a radium compound is heated1 it gives off an emanation and loses activity4 ,the more intense and the more prolonged the heating1 the greater is the loss of activity4 ,thus1 on heating a radium salt for one hour to #acj1 it loses #aj per cent of its total radiation2 on the other hand1 heating for ten minutes to #djj produces no apparent effect4 ,heating to redness for several hours destroys #gg per cent of the total radiation4 ,the loss of activity on heating is more considerable for the penetrating than for the absorbable rays4 ,thus1 heating for several hours destroys about #gg per cent of the total radiation1 but the same amount of heating destroys nearly the whole 7#ii per cent7 of the radiation that traverses #c c4m4 of air and #jja m4m4 of aluminium4 ,if barium-radium chloride be kept fused for several hours 7towards #hjj7 #ih per cent of the radiation capable of traversing #jc m4m4 of aluminium is destroyed4 ,the penetrating rays may be considered as no longer in existence after intense and prolonged heating4 ,when a radium salt has lost part of its activity by heating1 the diminution is not lasting2 the activity of the salt is spontaneously regenerated at the ordinary temperature1 and approaches a certain limiting value4 ,i have observed the curious fact that this limit is higher than the limiting activity of the salt before being heated--this1 at least1 is the case with the chloride4 ,i give examples of this3--,a specimen of barium-radium chloride which1 after having been prepared in the solid state1 has long since attained its limiting activity1 possesses a total radiation represented by the number #dgj1 and a radiation capable of traversing #jja m4m4 of aluminium1 represented by the number #aeg4 ,this1 specimen is heated to redness for several hours4 ,two months after the heating it attains its limit of activity with a total radiation equal to #fij1 and a radiation through #jja m4m4 of aluminium1 equal to #bbg4 ,the total radiation and the radiation transmitted by aluminium are therefore increased respectively in the ratios #fij_/dgj and #bbg_/aef4 ,these two ratios are practically equal to one another1 and are equivalent to #ade4 ,a specimen of radium-barium chloride which1 after having been prepared in the solid state1 has attained a limiting activity of #fb1 is maintained in a state of fusion for some hours2 the fused product is then powdered4 ,the product regains a new limiting activity equal to #adj1 which is twice as great as that to which it was able to attain when prepared in the solid state without having been sensibly heated during evaporation4 ,i have investigated the law of increase of activity of radium compounds after heating4 ,the following are the results of two series of determinations3--,the figures of ,table ,i4 and ,,ii4 represent the intensity of the radiation 7,i7 as a function of time1 the limiting intensity being supposed equal to #ajj1 and the time being reckoned from the close of the heating4 ,table ,i4 7,fig4 #ac1 ,curve ,i47 refers to the total radiation of a specimen of barium-radium chloride4 ,table ,,ii4 7,fig4 #ac1 ,curve ,,ii47 relates to the penetrating radiation of a specimen of barium-radium sulphate1 the intensity of the radiation which traversed #c c4m4 of air and #jja m4m4 of aluminium having been determined4 ,the two products were subjected to a bright red heat for seven hours4 ,,table ,i4 ,,table ,,ii4 ,time4 ,i4 ,time4 ,i4 ,days4 ,days4 #j #afb #j #jh #jf #bed #jg #ac #a #bgd #a #ah #b #ch #ai #bfd #c #dfc #f #dfb #d #ed #aj #eee #f #fge #ad #fd #aj #hd #ah #gah #bd #ie #bg #ha #eg #ajj #cf #ia #ej #iee #eg #ii #hd #ajj ,i made several other series of determinations1 but the results did not agree well4 ,the effect of heating does not persist when the heated radium compound is dissolved4 ,of two specimens of the same radium compound of activity #ahjj1 one was strongly heated and its activity thereby reduced to #fgj4 ,the two portions being now dissolved and left in solution for twenty hours1 their initial activities in the solid state were #dfj for the not heated portion and #dbj for the heated one2 the difference between the two portions was therefore not considerable4 ,but if the two products do not remain for a sufficient length of time in solution--if1 for example1 they are evaporated to dryness1 immediately after solution--the not heated product is much more active than the heated one2 a certain time is necessary in the dissolved state for the effects of heating to disappear4 ,a product of activity #cbjj was heated1 and its activity thereby reduced to #ajcj4 ,this product and a similar portion which had not been heated were simultaneously dissolved1 and the two then immediately evaporated to dryness4 ,the initial activity was #adej for the not heated portion1 and #gfj for the heated one4 ,illustration3 ,,fig4 #ac4 ,in the case of solid radium salts the capacity for exciting induced radio-activity is largely affected by heating4 ,during heating radium compounds give off a larger amount of emanation than at the ordinary temperature2 but on being cooled to the ordinary temperature1 not only is their radio-activity much less than before heating1 but their capacity for inducing activity is much diminished4 ,during the time that follows the heating1 the radio-activity of the product increases1 and may even exceed the original value4 ,the induction capacity is also partially re-established2 however1 after prolonged heating to redness1 this capacity is almost entirely destroyed without spontaneous re-appearance afterwards4 ,the induction capacity may be restored to the radium salt by dissolving it in water1 and drying it in the oven at a temperature of #abj4 ,this seems to have the effect of leaving the salt in a peculiar physical condition1 in which the emanation is given off with much less facility than is the case with the same solid product not heated to a high temperature1 and it follows naturally that the salt attains a higher limit of activity than that which it possessed before heating4 ,to transform the salts into the physical condition proper to it before heating1 it suffices to dissolve it and to evaporate it to dryness without heating it above #aej4 ,the following are numerical examples of the above3-- ,i represent by a the limit of induced activity produced in a closed vessel upon a plate of copper by a specimen of barium-radium carbonate of activity #afjj4 ,suppose a #ajj for the not heated product4 ,we find-- #a day after heating a #cc #d days after heating a #ga #aj days after heating a #ae #bj days after heating a #ae #cg days after heating a #ae ,the radio-activity of the product had diminished #ij per cent by heating1 but one month afterwards the original value was regained4 ,the following is an experiment of the same kind made with a barium-radium chloride of activity #cjjj4 ,the induction capacity is determined in the same manner as before4 ,for the product not heated a #ajj4 ,induction capacity of the product after being heated to redness for three hours3-- #b days after heating #bc #e days after heating #gj #aa days after heating #hb #ah days after heating #hb ,induction capacity of the unheated substance which has been dissolved and then dried at #aej #ib ,induction capacity of the heated substance which has been dissolved and then dried at #aej #aje ,theory of ,interpretation of the ,causes of ,variations of ,activity of ,radium ,salts after ,solution and after ,heating4 ,the facts previously indicated may be in part explained by the theory according to which the energy of radium is produced in the form of an emanation1 which is then transformed into the energy of radiation4 ,when a radium salt is dissolved1 the emanation produced by it spreads beyond the solution1 and causes radio-activity outside the source from which it proceeds2 when the solution is evaporated1 the solid salt obtained is but slightly active1 because it contains only a small amount of emanation4 ,gradually the emanation is accumulated in the salt1 the activity of which rises to a limiting value1 which is reached when the production of the emanation by the radium compensates the loss by external emission and by local transformation into ,becquerel rays4 ,when a radium salt is heated1 the external emission of the emanation is greatly increased1 and the phenomena of induced radio-activity are more intense than when the salt is at the ordinary temperature4 ,but when the salt returns to the ordinary temperature it is exhausted1 as is the case after being dissolved1 and contains but a small amount of emanation1 its activity having become greatly reduced4 ,gradually the emanation accumulates afresh in the solid salt1 and the radiation increases4 ,it may be said that radium gives rise to a constant generation of any emanation--part of which escapes to the exterior1 the remainder being transformed in the radium itself into ,becquerel rays4 ,when radium is raised to a red heat1 it loses the greater part of its capacity to cause the induction of activity2 otherwise stated1 the evolution of the emanation is lessened4 ,consequently1 the proportion of the emanation utilised in the radium itself should be greater1 and the substance attains a higher limit of radio-activity4 ,we will endeavour to establish theoretically the law of rise of activity of a solid radium salt which has been dissolved or has been heated4 ,we will assume that the intensity of radiation of radium is1 at each instant1 proportional to the quantity of emanation1 q1 present in the radium4 ,we know that the emanation is spontaneously destroyed according to a law such that1 at each instant-- q q#j;e-t_/ 4 4 4 4 4 4 4 4 4 #a1 q#j being the amount of the emanation at the moment of starting the observation1 and the time constant1 equal to #dig #aje secs4 ,now let be the evolution of the emanation by radium1 a quantity which ,i will assume constant4 ,let us consider what would occur if no emanation were escaping to the exterior4 ,the emanation generated would then be completely utilised by the radium for the production of the radiation4 ,we have from ,formula #a-- dq_/dt -7q#j_/7;e-t_/ -q_/2 and consequently1 in the state of equilibrium1 the radium would contain a certain quantity of emanation1 ,q1 such that-- ,q_/ 4 4 4 4 4 #b1 and the radiation of the radium would then be proportional to ,q4 ,let us suppose the radium placed in the circumstances under which it gives off the emanation to the exterior2 this is obtained by dissolving the radium compound or by heating it4 ,the equilibrium will be disturbed1 and the activity of the radium diminished4 ,but as soon as the cause of the loss of emanation has been abolished 7the body being restored to the solid state or the heating having ceased71 the emanation is accumulated afresh in the radium and we have a period during which the evolution1 1 surpasses the velocity of destruction1 q_/4 ,we then have-- dq_/dt - q_/ 7,q - q7_/1 from which-- 7d_/dt77,q - q7 -7,q - q7_/1 ,q - q 7,q - q#j7;e-t_/ #c1 q#j being the amount of emanation present in the radium at time t #j4 ,according to ,formula #c1 the excess of the quantity of emanation1 ,q1 contained by the radium in a state of equilibrium above the quantity1 q1 contained at a given moment1 decreases as a function of the time according to an exponential law1 which is also the law of the spontaneous disappearance of the emanation4 ,the radiation of radium being proportional to the amount of emanation1 the excess of the intensity of the limiting radiation above the actual intensity should decrease as a function of the time by the same law2 the excess should thus diminish to one-half in about four days4 ,the preceding theory is incomplete1 since the loss of emanation to the exterior has been neglected4 ,it is also difficult to determine the manner in which this acts as a function of the time4 ,in comparing the results of experiment with those of this incomplete theory1 there is found to be no satisfactory agreement2 the conviction is1 however1 retained that the theory in question is partially true4 ,the law by which the excess of limiting activity above the actual activity diminishes to one-half in four days represents approximately the course of the renewal of activity after heating for ten days4 ,in the case of the renewal of activity after solution1 the same law appears to hold approximately for a certain period of time1 which begins two or three days after evaporation to dryness and continues for ten or fifteen days4 ,the phenomena are otherwise complex2 the theory sketched out does not explain the reason of the suppression of the penetrating rays in greater proportion than the absorbable rays4 ,,nature ,,and ,,cause ,,of ,,the ,,phenomena ,,of ,,radio-,,activity4 ,from the beginning of research upon the radio-active bodies1 and when the properties of these bodies were yet hardly known1 the spontaneity of their radiation presented itself as a problem having the greatest interest for physicists4 ,to-day we have advanced considerably in the understanding of radio-active bodies1 and are able to isolate one of very great power1 viz41 radium4 ,with the object of making use of the remarkable properties of radium1 a profound investigation of the rays emitted by radio-active bodies is indispensable2 the various groups of rays under investigation present points of similarity with the groups of rays existing in ,crookes tubes3 cathode rays1 ,rntgen rays1 canal rays4 ,the same groups of rays are found in the secondary radiation produced by ,rntgen rays1 and in the radiation of bodies which have acquired radio-activity by induction4 ,but if the nature of the radiation is actually better known1 the cause of this spontaneous radiation remains a mystery1 and the phenomena always presents itself to us as a profound and wonderful enigma4 ,the spontaneously radio-active bodies1 and in the first place radium1 are sources of energy4 ,the evolution of energy1 to which they give rise1 is manifested by ,becquerel radiation1 by chemical and luminous effects1 and by the continuous generation of heat4 ,the question often arises as to whether energy is created within the radio-active bodies themselves1 or whether it is borrowed by them from external sources4 ,no one of the numerous hypotheses arising from these two points of view has yet received experimental confirmation4 ,the radio-active energy may be assumed to have been initially accumulated and then gradually dissipated1 as happens in the case of long continued phosphorescence4 ,we imagine the evolution of radio-active energy to correspond to a transformation of the nature of the atom of the active body2 the fact of the continuous generation of heat by radium speaks in favour of this hypothesis4 ,the transformation may be assumed to be accompanied by a loss of weight and by an emission of material particles constituting the radiation4 ,the source of energy may yet be sought in the energy of gravitation4 ,finally1 we may imagine that space is constantly traversed by radiations yet unknown1 which are arrested in their course by radio-active bodies and transformed into radio-active energy4 ,many reasons are adduced for and against these different views1 and most often attempts at experimental verifications of the conclusions drawn from these hypotheses have given negative results4 ,the radio-active energy of uranium and radium apparently neither becomes exhausted nor varies appreciably with lapse of time4 ,demaray examined spectroscopically a specimen of pure radium chloride after a five months' interval1 and observed no change in the spectrum4 ,the principal barium line1 which was visible in the spectrum indicating the presence of a trace of barium1 had not increased in intensity during the interval1 showing therefore that there was no transformation of radium into barium to an appreciable extent4 ,the variations of weight announced by ,m4 ,heydweiller in radium compounds cannot yet be looked upon as established facts4 ,elster and ,geitel found that the radio-activity of uranium is not affected at the bottom of a mine-shaft #hej m4 deep2 a layer of earth of this thickness would therefore not affect the hypothetical primary radiation which would be excited by the radio-activity of uranium4 ,we have determined the radio-activity of uranium at midday and at midnight1 thinking that if the hypothetical primary radiation had its origin in the sun it would be partly absorbed in traversing the earth4 ,the experiment showed no difference in the two determinations4 ,conclusions4 ,i will define1 in conclusion1 the part ,i have personally taken in the researches upon radio-active bodies4 ,i have investigated the radio-activity of uranium compounds4 ,i have examined other bodies for the existence of radio-activity1 and found the property to be possessed by thorium compounds4 ,i have made clear the atomic character of the radio-activity of the compounds of uranium and thorium4 ,i have conducted a research upon radio-active substances other than uranium and thorium4 ,to this end ,i investigated a large number of substances by an accurate electrometric method1 and ,i discovered that certain minerals possess activity which is not to be accounted for by their content of uranium and thorium4 ,from this ,i concluded that these minerals must contain a radio-active body different from uranium and thorium1 and more strongly radio-active than the latter metals4 ,in conjunction with ,m4 ,curie1 and subsequently with ,,mm4 ,curie and ,bmont1 ,i was able to extract from pitchblende two strongly radio-active bodies--polonium and radium4 ,i have been continuously engaged upon the chemical examination and preparation of these substances4 ,i effected the fractionations necessary to the concentration of radium1 and ,i succeeded in isolating pure radium chloride4 ,concurrently with this work1 ,i made several atomic weight determinations with a very small quantity of material1 and was finally able to determine the atomic weight of radium with a very fair degree of accuracy4 ,the work has proved that radium is a new chemical element4 ,thus the new method of investigating new chemical elements1 established by ,m4 ,curie and myself1 based upon radio-activity1 is fully justified4 ,i have investigated the law of absorption of polonium rays1 and of the absorbable rays of radium1 and have demonstrated that this law of absorption is peculiar and different from the known laws of other radiations4 ,i have investigated the variation of activity of radium salts1 the effect of solution and of heating1 and the renewal of activity with time1 after solution or after heating4 ,in conjunction with ,m4 ,curie1 ,i have examined different effects produced by the new radio-active substances 7electric1 photographic1 fluorescent1 luminous colourations1 c474 ,in conjunction with ,m4 ,curie1 ,i have established the fact that radium gives rise to rays charged with negative electricity4 ,our researches upon the new radio-active bodies have given rise to a scientific movement1 and have been the starting-point of numerous researches in connection with new radio-active substances1 and with the investigation of the radiation of the known radio-active bodies4 ---------------------------------------- -------------------------------- ,,radium ,,and ,,other ,,radio-,,active ,,elements4 ,a ,popular account of ,radium and other ,radio-active ,elements treated experimentally4 ,including a number of ,radium ,photographs and other ,illustrations4 ,by ,,leonard ,a4 ,,levy and ,,herbert ,g4 ,,willis4 ,,price #bs4 #f;d4 net2 post free #bs4 #i;d4 ,,contents4 ,,introduction4--,chap4 ,i4 ,the ,discovery of ,radium2 its ,extraction4--,chap4 ,,ii4 ,the ,radium ,emanation4--,chap4 ,,iii4 ,physical ,effects 7,electrical and ,magnetic74--,chap4 ,,iv4 ,physical ,effects 7continued74--,chap4 ,v4 ,chemical ,effects4--,chap4 ,,vi4 ,actions on ,animal ,life and ,living ,tissues4--,chap4 ,,vii4 ,other ,radio-active ,elements4--,appendix4--,experimental ,apparatus4 ,,percival ,,marshall ,,co41 #bf-bi1 ,,poppin',s ,,court1 ,,fleet ,,street1 ,,london1 ,e4,c4 99 99 99 99 99 ,,radium ,,spinthariscopes4 ,,as ,,designed ,,by ,,sir ,,william ,,crookes1 ,f4,r4,s41 ,for ,demonstrating the ,radio-activity of ,radium4 ,,kunzite4 ,,the ,,new ,,mineral4 ,responding in a high degree to the ,emanations from ,radium4 ,,zinc ,,sulphide ,,screens4 ,,calcium ,,sulphide--,phosphorescent4 ,,zinc ,,sulphide--,phosphorescent4 ,,pitchblende--,specimens4 ,write for particulars to ,,john ,j4 ,,griffin ,,sons1 ,ltd41 #bj1 #bb1 #bd1 #bf1 ,,sardinia ,,street1 ,,london1 ,w4,c4 ---------------------------------------- -------------------------------- ,,radium ,,applicators ,its employment in ,therapeutics and for scientific research4 7,mac,leod7 ,surface1 each #gs4 #f;d4 ,throat1 #a #as4 ,,barium ,,platinocyanide ,,screens1 per sq4 inch1 #i;d4 ,,calcium ,,sulphide1 luminous1 per lb41 #h_/- ,,kunzite1 per ,gm41 #a_/- ,,polonium1 ,,on ,,bismuth ,,copper ,,discs1 each #be_/- ,,pitchblende1 specimens1 each1 per oz41 #b_/f4 ,,uranium ,,nitrate1 oz41 #a_/-4 ,,thorium ,,hydroxide1 oz41 #d_/-2 lb41 #dh_/-4 ,,thorium ,,hydroxide ,,pads1 each #aj_/f4 ,,willemite1 ,natural ,specimens1 #b_/- each4 ,,willemite1 ,artificial ,specimens1 #a_/- each4 ,,zinc ,,sulphide1 ,active1 ,gm4 #a_/f4 ,,zinc ,,sulphide ,,screens1 #aj #aj centimetres1 each #g_/f4 ,illustration ,special ,quotations for ,quantity4 ,,chemicals ,,and ,,apparatus for ,scientific ,research4 7,write for ,price ,list47 ,,spinthariscopes showing the ,scintillations of ,radium1 #ba_/- ,illustration ,w4 ,,martindale1 ,manufacturing ,chemist1 #aj ,,new ,,cavendish ,,street1 ,w4 ,telegraphic ,address3 8,martindale1 ,chemist1 ,london40 ,telephone3 #agig ,paddington4 99 99 99 99 99 ,,radium ,,on ,,sale ,,and ,,let ,,on ,,hire4--,write for ,terms4 ,the following can be had by return of post4 ,pitchblende1 direct from ,joachimsthal1 very radio-active1 from #a_/- to #cj_/- per piece4 ,itacolomite1 or flexible sandstone1 #aj_/- to #be_/- per piece 7very rare74 ,kunzite1 #a_/- per gramme4 ,selected1 clear1 #b_/- ,sparteite 7see ,,nature1 #ca #c_/jd1 fol4 #ebc71 #b_/- and upwards4 ,chlorophane1 #b_/- and upwards4 ,barium ,platino ,cyanide in large ,crystals in course of manufacture4 7,,orders ,,booked74 ,zinc ,sulphide4 ,phosphorescing a beautiful ,green1 #b_/f per tube4 ,zinc ,sulphide4 ,phosphorescing a beautiful ,yellow1 #b_/f per tube4 ,calcium ,sulphide ,phosphorescing a beautiful ,violet1 #a_/- per tube4 ,radio-active ,residue from which ,radium is made2 very scarce1 #b_/- tube4 ,polonium ,sulphide1 in tubes of one gramme1 #ba_/- ,polonium on ,bismuth ,rod or ,disc1 #be_/- ,polonium on ,copper ,rod or ,disc1 #be_/- ,radio-active ,screens 7,willemite71 #f;d4 per sq4 inch4 ,plat4 ,bar4 ,cyan ,screen41 #i;d4 sq4 inch ,radio-active ,screens 7,zinc ,sulph471 #aj #aj cm4 #g_/f4 99 99 99 99 99 ,professional ,men1 ,universities1 ,schools1 c41 allowed special terms4 99 99 99 99 99 ,our newly invented ,thorium ,inhalers may be had on hire4 99 99 99 99 99 ,,armbrecht1 ,,nelson ,,co41 #ga #gc1 ,duke ,street1 ,grosvenor ,square1 ,london1 ,w4 ,telephone3 ,,gerrard #didb4 99 99 99 99 99 ,n4,b4--,we have to-day received a consignment of the ,new ,zealand ,vegetable ,caterpillar2 it is from #b to #c inches long1 with a stem showing fructification growing out of its head4 ,scientific name of the insect is ,hepialus virescens2 the name of the fungus is ,sphaeria ,robertsiana4 ,specimens may be had from #aj_/f to #ba_/-1 according to quality and size4 ,,terms ,,cash ,,with ,,order4 ,goods may be returned if not approved of1 when money will be refunded4 ---------------------------------------- -------------------------------- ,,transcriber',s ,,notes #a4 ,silently corrected typographical errors and variations in spelling4 #b4 ,anachronistic1 non-standard1 and uncertain spellings retained as printed4 #c4 ,enclosed italics font in underscores4 #d4 ,enclosed bold font in equals4 #e4 ,superscripts are denoted by a caret before a single superscript character or a series of superscripted characters enclosed in curly braces1 e4g4 ,mr4 or ,mister4 #f4 ,subscripts are denoted by an underscore before a series of subscripted characters enclosed in curly braces1 e4g4 ,h#b,o4