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Radioactivity

Identifieur interne : 001364 ( Istex/Corpus ); précédent : 001363; suivant : 001365

Radioactivity

Auteurs : Frederick Soddy

Source :

RBID : ISTEX:58FF1D8FB1A66235438B9B697F9594B87714AC47

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DOI: 10.1039/AR9161300245

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ISTEX:58FF1D8FB1A66235438B9B697F9594B87714AC47

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<p>RA1I)IOACTIVITY.The H e t e ~ o y e r z e i t y of Cheniiccil E’lerrie7zts.IN the two years 1915 and 1916 since the last Annual Report onRadioactivity much more has been clone t o confirm the generalcorrectness of the new views, wit’h regard t o the nature of thechemical elements and the significance of the periodic law, describedin the Report for 1913. A general description of the point of viewattained niay not be out of place. F o r these new views are farmore fundamental and are far more subversive of the establishedconceptions of chemistry even than was the discovery of the spon-taneous transmutations suffered by the radio-elements. I n the firstplace, they give US the first real knowledge of what constitutes thedifference between one element and another. </p>
<p>In the second place,they show t h a t important differences may exist in certain proper-ties, notably the atomic weight and stability, of elements whichare completely identical and homogeneous, judged by all the usualcriteria depended on by the chemist. The analysis of matter intothe so-called chemical elements is indeed only a superficial analysis,and does not imply more than the superficial identity of the atomicstructure. So long as all the known methods of discrimination andidentification depended on properties conferred by the surface orouter shell of the atomic structure, the analysis appeared ultimate.Even the newer X-ray spectra, although a degree more fundamentalthan tlie older methods, are powerless t o reveal any difference what-ever, but the phenomena of radioactivity, in which the innernucleus of tlie atom alone is primarily concerned, has shown matterto be indefinitely more complex than the chemist had hithertorealised. </p>
<p>It may now be taken as proved t h a t so long as the netcharge of the nucleus of the atom is the same, the element willshow the definite chemical and pliysico-chemical character associatedwith one or other of the ninety-two places of the periodic table,quite independently of the nature and constitution of the nucleus.Moreover, both with regard to its ordinary light spectrum and itsX-ray spectrum investigated by Moseley, complete identity will be24246 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.found; but the same net charge of the nucleus may result froiiidifferent absolute numbers of positive and negative charges, inwhich case atoms with identical chemical character will show differ-ent atomic masses, the mass being primarily a function, althougli inall probability not a simple additive function, of the number ofpositive charges present. </p>
<p>If they are radioactive, they will showalso differences in the manner and the rate of their disintegrationand in the manner and rates of disintegration of their respectiveproducts. Even the same net nuclear charge and the same absolutenumber of the two opposite kinds of charges in the nucleus may beassociated with different nuclear structures, in which case themanner and rate of disintegration will reveal the difference unlessthe atom is completely stable. By f a r the greater number of therecognised chemical elements are stable, and for them the sclepossible criterion for recognising this new complexity is the atomicweight and the few physical properties, such as rate of diffusion,which depend directly on it. </p>
<p>I n the radioactive sequence ofelements t-he heterogeneity is much more easily recognised, and, ofcourse, it was first recognised in this field by the existence of theisotopic elements, that is, of elements occupying the same place i nthe periodic table, completely identical in their ordinary analyticaland physico-chemical behaviour. The expulsion in any order of ana-particle carrying two positive charges, and of two P-particles, eachcarrying one negative charge, from the nucleus, for example, leavesthe r e t nuclear charge, and with i t the whole of the chemical char-acter, identical with what i t originally was, although the atomicmass has been lowered by 4 units, by the expulsion of the a-particle.Again, when the series branches, as, f o r example, when some of theatoms expel first an a- and then a &particle, whilst the others expelfirst a P- and then an a-particle, the net nuclear charges and alsothe gross nuclear charge of the two resulting products are identical,but the inner constitution of their nuclei is different, their internalenergy, for example, is different, and therefore their atoms are notidentical. </p>
<p>This is a finer degree of isotopy-the chemical character,spectrum, and atomic mass all alike-but the atoms are not thesame, and, if the process of change proceeds further, the difference isrevealed in the manner and rate of the subsequent transfcrmation.If the atoms, on the other hand, are stable, there is no experimentalmethod of disclosing their differences. </p>
<p>That is to say, with regardto the ordinary elements, heterogeneity in what has hitherto beenregarded as homogeneous is to be sought for by the atomic mass,but homogeneity in this respect does not preclude the existence ofdifferences beyond the present methods of experiment to establish,but which would be revealed as soon as artificial transmutatioRADIOACTIVITY. 247became possible.with.The atomic weight evidence may first be dealtAtomic Weight, Density, and Spectrum of Lead.The first section of the 1914 Report dealt with the work on theatomic weight of lead from va_rious sources, radioactive and other-wise, and it was then shown that the theoretical prediction that theatomic weight, of lead derived from thorium would prove to beabout one unit higher, and that for uranium about a unit lowerthan the international value, was being borne out. </p>
<p>The first workt o be published in this field had reference to the lead derived fromCeylon thorite-not thorianite, a totally different mixed uraniumand thorium mineral often confounde)d with it, even by some of theworkers in this field. I n subsequent work, 30 kilos. of the materialwere hand-sorted into three grades, and from the 20 kilos. in thefirst grade some 80 grams of metallic lead were separated. </p>
<p>Thiswas cast in a vacuum into a cylinder and the density determined,ltogether with that of a similar weight of ordinary assay lead simi-larly purified and prepared. The values of D;O were found t o be11.3465 for the ordinary lead, in good agreement with the valuefound by Kahlbaum, Roth, and Siedler-11.3415 for lead distilledin a vacuum-and 11.376 for the thorite lead, which is 0.246 percent. greater. Both samples of lelad were then fractionally distilledin a vacuum, and the atomic weight of the t8wo middle fractionswas determined. The lead was dissolved in dilute nitric acid in aquartz receptacle#, the nitrate evaporated to dryness, and then con-verted into chloride1 by means of a current of hydrogen chloride,the temperature being gradually raised to near the fusion pointof lead chloride, and weighings taken until the weight was constant.The value so found from the ratio P b : PbCl, was, for ordinary lead,207-199, in good agreement with the most recent determinations-207.20 and 207.18.3 The value found for thorite had was 207.694,which is 0.238 per cent. </p>
<p>greater. Owing to the researches beinginterrupted by the war, only single atomic weight determinationscould be done.4It will be seen that, as is to be expected on the general view thatthe mass and constitution of the nucleus has no effect on the outerF. Soddy. Nature, 1315, 94, 615.G. P. Raxter and F. I,. Grover, J. Amcr. Ghem. Soc., 1915, 37, 1037;-4.? 1915, ii, 456.0. Honigschmid and (Mlle.) S. </p>
<p>Horovitz, Monatuh., 1915, 36, 355 ; A . ,191.5, ii, 635.These results were communicated in two lectures t o the Royal Institution,May 15 and 18, 1915 ; see Engineering, May 28, 1915, and t o Section A ofthe British Association, Birmingham, 1915 ; see Engineering, Oct. 1, 1915,but owing to their incomplete character have not yet been further published248 AXNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.electronic system of the atom, tlie atomic volumes of the two speci-mens of lead are practically the same, the specimen from thoritebeing 0.246 per cent. greater in atomic weight than ordinary leadand 0.238 per cent. more dense. The atomic volume is in each case18.26 a t 20°.An important result attained in this research was t h a t no bismuthcould be found in the whole1 20 kilos. </p>
<p>of selected mineral, whicheffectually disposes of the many speculations t h a t bismuth is oneof the ultimate products of radioactive change Thallium, however,was present in easily detectable amount. The supposed a-radiationof bismuth derived from Joachimsthal pitchblende has been defi-nitely shown to be due to admixture1 with ionium.6More extended data are now available for the case of uranium-lead. The preliminary researches of 0. Honigschmid and Mlle.Horovitz,7 which gave the figure 206.73 for the lead from Joachims-thal pitchbtende residues, were undoubtedly influenced by the leadpresent in the crude sulpliuric acid used t o treat the mineral. Thefilial value obtained f o r the lead from 20 kilos. </p>
<p>of selected purestJoachimsthal pitchblende, extracted by the use of pure reagents,was 206.405. The lead from the crystallised uranium ore, examinedby Marckwald, from an old primary formation in Morogoro,German East Africa, gave the value 206.046. Almost the samevalue, 206.063, was obtained for the lead from broggerite from&loos, Norway, which contains 79 per cent. of U,O,, 4.5 per cent.of Tho,, and 9.5 per cent. of PbO. Ordinary lead in controlexperiments gave the value 207.180. The arc and spark spectra ofall these specimens of lead showed absolute identity.*I n another and more detailed examination with a grating, of thearc spectra of ordinary lead and of lead from Joachimsthal pitch-blende, complete identity was also found.9 I n the case of two ofthe lines, x 3500 and x 4100, the difference of wave-length must havebeen less than 0.03 if.U., whilst a more accurate comparison ofh 4058 by a Fabry and Perot &don showed t h a t the difference inwave-length could not exceed 0.003 A.U. </p>
<p>This is against the theoryof Professor Hicks t h a t the magnitude of the atomic weight entersexactly into the series relationships of spectra.10Further important results on the atomic weight of lead fromAnn. Report, 1914, 286.6 L. Meitner, Physiknl. Zeitsch., 1915, 16, 4 ; A . , 1915: ii, 126.Ann. Report, 1814, 269.0. Hiinigschmid and (Mlle.) S. Horovitz, Monafsh., 1915, 36, 353 ; -4.,T. R. Merton, Proc. Ro?y. SOC., 1915, [A], 91, 19s; A . . 1915, ii, 119.1915, ii, 635.lo ,412n. </p>
<p>Report, 1913, 265RADIOAGTIV ITY. 249various uranium minerals have been obtained a t Harvard, and exam-ination has also been made of the density.llLead from the Olary ores, S. Australia, described as Australiancarnotite, and known t o be derived partly from admixed galena,was found t o have a density, a t ZOO, of 11.288 and atomic weight206.34. That from a carefully selected specimen of Norwegiancleveite had a density, a t ZOO, of 11.273 and atomic weight 206.085.For ordinary lead the values 11.337 and 207.18 were found. I n allcases the density is proportional t o the atomic weight, and the valueof the atomic volume is constant a t 18.28, which is practically thesame as t h a t found for thorite lead, 18.26, although the two are notstrictly comparable. Other atomic weights determined were thoseof the lead from &4merican carnotite, 207*004, and from Norwegianbroggerite, 206*122.Thus a t the present time varieties of lead are known varyingfrom 207.7 to 206.05 in atomic weight and from 11.376 to 11.273in density, and in all cases so far examined the atomic volume8 isconstant. </p>
<p>The spectra of the different varieties appear to be abso-lutely identical, the one difference in the intensity of the unimpor-t a n t line, 4760.1, noticed in the first sample of thorite leadexamined not having been recorded by other observers.Period, A t o w i c TT'eight, aiid Spectrum of loiiium.Possibly the finest achievement of the period under review hasbeen the comparison in Vienna of the atomic weight and spectrumof thorium with that of the thorium separated by von Welsbachfroin 30 tons of Joachimsthal pitchblende and known t o contain aconsiderable, if indefinite, proportion of the isotope, ionium. </p>
<p>Theseexperiments bear out an estimate of the period of ionium recentlyobtained from the1 experiments on tlie growth of radium from puri-fied uranium preparations, which have been in progress for thelast thirteen years, and these results may first be given.12 Thesepreparations showed for tlie first time) beyond doubt t h a t radiumwas being produced from carefully purified uranium, and t h a t therate of production was proceeding as nearly as could be seen pro-portionally to the square of the lapse of time from purification, astheory demands if ionium is the only long-lived element betweenuranium and radium. </p>
<p>Thus for a preparation containing 3 kilos.of uranium (element) the growth after three years from purifica-l1 T. W. Richards and C. Wadsmorth, J . Anzer. Chern. A ~ O C . , 1916, 38, 221,l 2 Compare Ann. Report, 1912, 320 ; F. Soddy and(Miss) A. F. R. Hitchins,1658, 2613 ; A., ii, 251, 566.Phil. Mag., 1915, [vi], 30, 209 ; A., 1915, ii, 7?6250 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.tion was 2 x 10-l1 gram of radium, and after six years from puri-fication, 8 x 10-l1 gram of radium. This gives for the period ofaverage life of ionium almost exactly 100,000 years. Any ioniuminitially present would make the estimate1 of the period too low,and it was concluded t h a t 100,000 years might be accepted as aminimum estimate, not far from the real period. </p>
<p>Thus there mustbe a t least forty times as much ionium as radium by weight inuranium minerals, t h a t is, a t least 12.3 grams of ionium per 1000kilos. of uranium. The amount of thorium and its isotope, ionium,separated by Welsbach from about 30 tons of Joachimsthal pitch-blende was so small and so intensely radioactive t h a t the questionas to its atomic weight became of the utmost interest. F o r theatomic weight of ionium, calculated from the recent value found foruranium, 238'18,13 by subtracting eight for the two a-particlesexpelled, must be 230.18, and calculated from that of radium, 226.0,by adding four for the a-particle still t o be expelled is 230.0. </p>
<p>Themean of these is 230.09, whereas the international value for theatomic weight of thorium is 232.4. The first step was a carefulrevision by new methods of the atomic weight of thorium by theanalysis of thorium bromide,l* analogous to tlie method t h a t hadbeen used f o r uranium. The operations were more difficult, butthe method gave very satisfactory results, and, as in the case ofuranium, a lower value than the1 international figure was obtained,namely, 232.12. The ionium--thorium preparation referred to,treated in an identical manner, gave' the value 231.51, which isnearly 0.6 unit lower. A careful comparison of the spectra of thetwo preparations used in the determinations showed complete iden-tity and complete absence of impurities, thus confirming the earlierconclusion as to the identity of the spectra of these two isotopes.15Ionium and thorium thus furnish the second example' of twoelements differing in atomic weight, b u t spectroscopically and chemi-cally identical. </p>
<p>Assuming a mean 230.06 as the true value of theatomic weight of ionium, it has been calculated thatl in the ionium-thorium preparation with atomic weight 231.51 there must bepresent 29.5 per cent. by weight of ionium and 70.5 per cent. of13 Ann. Report, 1014, 272. Further determinat,ions have since been madeof the atomic weight of the uranium separated from Morogoro pitchblende.From the Pb : U ratio, this is some 3.2 times more ancient than the Joachims-thal pitchblende and is practically a pure compound, whereas that fromJoachimsthal contains most, of the known elements. </p>
<p>The result found, 238.16,agrees within the limit of error with tho value 238.18 previously found for theuranium from Joachimsthal. (0. Honigschmicl and [Mlle.] S. Horovitz,d4onntsh., 1916, 37, 185 ; A . , ii, 484).l4 0. Honigschmid and (Mllc.) 8. Horovitz, Monatsh., 1916, 37, 305, 335 ;A., ii, 510. Ann. Report, 1912, 321RADIOACTIVITP. 25 1thorium. On this assumption, the life-period of ionium was foundby comparing the a-radiation from a drop of the solution cvapor-ated over a large area with that from a similar known quantityof radium. The life-period so found was 58.1 times that of radium.Tliis is, 145,000 years for the period of average life, or 100,000years for the period of half change,lG and confirms in a satisfactorymanner the period estimated directly from the rate of growth ofradium from pure uranium compounds.I n consequence, it may be calculated that, per 1 gram of radium(element) in Joachimsthal pitchblende, there are 58 grams ofionium and 139 grams of thorium, a total weight of thorium iso-topes of 157 grams. </p>
<p>But for the excessively minute proportion ofthorium in this particular mineral, the difference in atomic weightand the identity of spectra of thorium and ionium could not havebeen est.ablished. It follows also that the radium which consti-tutes the1 international radium standard a t Paris and the Viennasub-standards contains so minute a proportion of the isotope, meso-thorium, that the a- and y-radiations of these standards can onlybe affected to the extent of a few thousandths per cent., a quantityfar below the limit of accuracy of radioactive measurements.The Definition of the Atom and the Element.The foregoing account contains most of the important new factshaving reference to the existence of isotopic elements, but a largenumber of r&um& and theoretical papers have appeared, dealingwith the new conceptions and the progress made in our knowledgeof the nature of matter generally. First, however, may be men-tioned a thoughtful pap’er on the changes in chemical nomenclaturenecessitated by the widening of our outlook.17 The subject is treatedhistorically, and the gradual evolution of the meaning attached tothe terms element and atom traced from the time of Boyle. </p>
<p>Dalton’satomic theory and Boyle’s conception of elements together led tothe point of view that there are as many kinds of absolutely similaratoms as elements, a view that is now no longer true. Panethrecommends retaining the idea of elements previously held andspeaking of all the isotopes of one element, o r of a mixture ofthem, still as one element. The light and X-ray spectra wouldthus still remain the distinguishing criteria of a chemical element,which would be defined as a substance that cannot be decomposedinto anything simpler by any chemical process. Two elementswould be denoted by the same name if, once mixed, they cannotbe separated by any chemical process. Atoms, on the other hand,R. </p>
<p>Mcyer, Monatsh., 1916, 37, 347, A., ii, 511.F. Paneth, Zezksch. physikal. Chem., 1916, 91, 171 ; A . , ii, 2402.52 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.would be defined as the particles of matter, unchanged by chemicalanalysis, which represent the limit of chemical decomposition.Elements made up of the same kind of atoms would be defined as((pure,� and those comprising different kinds of isotopic atoms as((mixed.� It must be confessed, when one tries to carry out theselogical rules into practice, difficulties must arise. Thus radium andmesothorium are the same element, and must have the same name,and similarly with ioniuin and thorium. The facts will make, it isto be feareld, as much havoc among these new rules as it hasalready done among the old. </p>
<p>The whole trouble arises from thefact t h a t the words atom and element imply the idea of ultimateconstituents, and we know now that our analysis of matter cannever be ultimate.Theories of A toniic Structure.Physicctl Properties of Isotopes.-After the discovery of thedifference of density between tlie different varieties of lead, thegeneral question as to the physical and chemical properties ofisotopes received theloretical attention. Lindemannl8 concludedthat if the atomic volumes of isotopes were the same, their elasticconstants, vapour pressure, and melting points should differ, and hepredicted that the le’ad from thorite should melt 1 * 5 O above themelting point of ordinary lead, a prediction which, like manyothers, it lias not yet been found possible to test. </p>
<p>He regards theforces of attraction and relpulsion between the atoms, the inter-action of which results in tlie solid state, as originating in tlienucleus. Apparently these conclusions are opposed to those drawnby Bohr.lg Another examination from the point of view ofBolir’s theory has been made by Fajans,20 who concludes that a tabsolute zero tlie atomic volumes of isotopes should be identical, butshould difTer progressively as the temperature rises, the differenceamounting to less than 1 / 10,000tli part a t the ordinary temperaturefor the isotopes of lead. The specific heats should, however, bedifferent, the greatest difference amounting in the case of the leadisotopes to 0.75 per cent. </p>
<p>It is clear t h a t the further examinationof the physical properties of the isotopes of lead will prove a verysearching means of testing some of the) newer pliysico-chemicaltheories of the solid state.A tom BiriZdiug.-A series of papers has been published giving aP. A. Lindemann, Naewe, 1916, 95, 7.l9 British Association Meeting, 1915. Discussion in Section A. See2o I<. Fajans, Arbeiten cius r l e ? ~ Geheit rlcr Physik, Afrith. Cl~emie, 623 ;A’ngineeriny, Oct. 1 , 1915.-4., ii, 400RADIOACTIVITY. 253comprehensive survey of much of the modern work and its detailedbearing on chemical problems.21 The possible existence of isotopesmay account for some of the largar departures of the atomic weightsfrom whole numbers, such as those of magnesium and chlorine. </p>
<p>Onthe modern theory, however, t h a t mass is wholly due to electro-magnetic inertia, it is not t o be expected t h a t the mass of an atomshould be the exact sum of the separate masses of its constituentsub-atoms, although the deviations on this account are probablyquite small. The problem of mutual electromagnetic mass, as it iscalled, has also been considered by other workers.22 Indeed, in1910, Silberstein solveid the problem rigorously for the two physi-cally important cases, either when the electric charges are entirelyseparated or when one is entirely within the other. His expres-sions, which are contained in the reference cited, make the differ-ence between the masses of the separate components and that ofthe complex a relatively simply function of the radii of the electriccharges and of their distance apart. </p>
<p>Most important informationas to these atomic dimensions could be immediately obtained if theatomic weights of the various products of a disintegration seriescould be determined to the very high degree of accuracy required.Nicholson, with an approximate solution, has already concluded,from such data as were available for thorite lead, that the meandistance apart of the a-particles in a thorium atom is of the sameorder as the radius of the electron.The mean departure from whole numbers, in terms of hydrogenas unity, of the atomic weights of the first twenty-seven elements,excluding hydrogen, is nearly a constant percentage, 0.77. Foroxygen, it is exactly this, and therefore the approximation t o wholenumbers of the atomic weights of these elements, on the basis ofoxygen as 16, is very close. </p>
<p>The chance of this being accidental iscalculated a t one in fifteen million. This 0.77 per cent. is regardedas the packing effect, or loss of mass when the hydrogen nuclei arepacked together to form a heavy atom. As an illustration merely,of no practical application, it is calculated t h a t a positive andnegative electron would lose 0.77 per cent. of their separate massesif caused t o approach to a distance apart four hundred times theradius of the positive electron. From nickel onward no tendencyto approximate to whole numbers seems t o exist, for the mean21 W. D. Harkins and E. </p>
<p>D. Wilson, J . Arner. Chem. SOC., 1915, 37, 1367,1383, 1396* ; 1916, 38, 169 ; A., 1915, ii, 543, 544, 544* ; 1916, ii, 241 ;Phil. Mag., 1915, [vi], 80, 723, A., 1915, ii, 814. The paper asterisked is asummary of modern work, especially valuable in its interpretation of Nichol-son’s theories.22 L. Silberstein, Phil. &lay., 1015, [vi], 30, 370; J. W. Kicholson, ibid.,6 5 9 ; Proc. Physical SOC., London, 1915, 27, 2 1 7 ; A . , 1915, ii, 404254 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.departure from integers for the thirteen best determined atomicweights between nickel and barium is 0.25 unit, as it should be 011a purely chance distribution.I n common with van der Broek,23 the helium nucleus is picturedas built up out of four hydrogen nuclei and two negative nuclearelectrons. </p>
<p>The authors regard nearly all the (‘ packing effect� t ooccur in the formation of these helium nuclei, the aggregation ofthese into more complex atoms not producing any noticeable changeof mass. Along these lines, the constituent helium nuclei beingregarded as much more stable than the complexes formed out ofthem, is to be sought the explanation of why helium and nothydrogen is expelled in the disintegration of radio-atoms. Vander Broek, suggests the further aggregation, within the complexatoms, of four helium nuclei and two nuclear negative electrons,this complex being the oxygen nucleus. He ascribes radio-activity to the disintegration of these with successive expulsion offour a- and two &particles, a common sequence in the radioactiveseries. </p>
<p>This represents a change of 16 units of atomic mass for6 of atomic number, and this, he points out, is the average for allthe elements between magnesium and thorium, which differ by 208units of mass and 78 units of atomic number, that is, as 16 isto 6.Periodic Law.-The fifth paper of the series deals with theperiodic law and its representation by helical models. Many usefuldata, relative especially to the physical properties of the elements,are here collected together. The authors are alive to the essentialchanges of outlook effected by the recent advances on the repre-sentation of the Periodic Law, but their model offers little ofnovelty or advantage over earlier efforts, although discussed inmuch greater detail. </p>
<p>I n one important point they seem to be atfault. They divide the Periodic Table into three cycles of 42, 6?,and 82 elements, and each cycle into two periods each of 8, 18,32 elements respectively, the last part of the last very long periodof 32 elements being missing, and they argue that this representsa numerical expression of some function appertaining t o atomicstructure; but the series from the emanation to uranium runs likethat from krypton to molybdenum, and not like that from xenon totungsten, wherein the rare earths are interpolated.24 Although thelast very long period is incomplete, i t runs far enough t o makethis division of the table into cycles of 42, 62, 8 2 elements fanciful.Again, the eighth group is still only accommodated in their model23 A. </p>
<p>van der Broek, Physika7. Zcitsch., 1916, 17, 260 ; Nature, 1916, 97,24 Soddy, “ Chemistry of the Radio-Elements,� Part 11, p. 11, 1014.479 ; A . , ii, 465RADIOACTIVITY. 255on the old supposition that “ a catastrophe of some sort seems totake place here,� whereas these elements with their gradual changeof properties are as significant and marked a feature of the PeriodicLaw as is the intensely abrupt change of properties that occurs oneither side of the zero group.Stellar Elements.-Fraunhofer’s discovery of the dark lines ofthe solar spectrum, the discovery of helium, and the theory of theevolution of the heavy elements from the lighter ones that hasbeen advanced by Lockyer as a consequence of the study of thelife-history of the stars, have made chemists familiar with thefruitful bearing of astronomical observations on their own science.From such sources, aided by mathematical reasoning applied to anew theory of atomic structure, Nicholson has formed some tenta-tive conclusions of great interest to chemists 25He regards the terrestrial elements as differing in character andatomic structure from the elements coronium2 nebulium, andothers, the existeiice of which, like that of helium, has beeninferred from unidentified lines in the solar corona and in nebuh.These lines appear to him to originate from earlier and simplerevolutionary forms of matter from which the terrestrial elementshave developed. </p>
<p>It is significant that there seems to be no roomin the Periodic Table, as we now understand it, for any of thesestellar elements. Nicholson’s model atom is of the Rutherfordtype, in which the electrons revolve in orbits round a centralpositive nucleus, but in his calculations, unlike Bohr, he does notdepart from the classical mechanics or introduce the quantumhypothesis. </p>
<p>The energy of the spectrum is not derived frominternal atomic energy, but from external sources, and on thispoint there can scarcely be any reasonable doubt that he is correct.I n spite of its great initial successes in calculating correctly themagnitude of the Rydberg constant, and in correctly ascribing thePickering series of lines t o helium rather than to hydrogen, Bohr’stheory does not seem to have been generally so successful. I n theNicholson atom, the vibrations from which the spectral linesoriginate are perpendicular to the plane of the ring of revolvingelectrons. The strongest and first class of vibrations are due t othe entire ring vibrating as a whole, keeping parallel to its posi-tion when not in vibration. </p>
<p>In the second class of vibrations, thering vibrates in halves, that is, there are two nodes and two creststravelling round the ring. In general, there are as many classesof vibrations possible as there are electrons in the ring, although25 Nicholson’s earlier theories were fully discussed in the Annual ReportThe present account is derived mainly from the third paper for 1911, 269.in the series referred to, by Harkins and MTilson256 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.the higher classes are probably too feeble to detect. For thenebulium atom Nicholson postulates a nucleus of four positivecharges. The chief line attributed to this element is h=5006*9,and if this constitutes what has been termed the first class, thecalculated wave-length of the second class should be 4367.0, whichcorresponds with the strong observed line h=4363.4. </p>
<p>The nextshould be 4352.9, and it was only after its wave-length had beencalculated that a line 4352.3 was photographed at the LickObservatory. A search of older photographs showed its existenceon plates taken several years before, but it had escaped observa-tion owing to its feebleness. Again, two lines formerly attributedt o nebulium could not be obtained from the structure of the atompostulated, and these, simultaneously with this result, were shownby Wolf, of Heidelberg, to originate in a different part of thenebula from the rest.Similarly for model atoms of 2, 3, 5, and 6 charges, by assumingone line to be due to the first. </p>
<p>class of vibration, the wave-lengthsof the other classes of vibrations have been calculated and corre-spondence found with observed lines. Thus twenty-one out of thetwenty-seven lines of the solar corona have been accounted for bythe vibrations of a model atom of five charges. The atomic weightsof these stellar elements can only be very indirectly and unsatis-factorily inferred, but the values given are 0;082 multiplied by thesquare of the nuclear charge. </p>
<p>Thus protohydrogen is 0.082,nebulium 1.3, protofluorine or coronium 2.1.This work thus suggests the existence of types of matteraltogether unknown upon the earth, and for which no place existsin the Periodic Table. The difference between the two kinds isprobably t o be sought in the constitution of the nucleus of theatom. We know from the expulsion of &particles and the exist-ence of isotopes that negative electrons do form an integral partof the nucleus of the radioactive atoms, and that the nuclearcharge or atomic number is the difference between the number ofpositive and negative electrons. Nicholson’s idea seems to be thatthis is true of all terrestrial elements, including hydrogen, andthat it constitutes the difference between these elements and thestellar elements. On this view, then, the hydrogen nucleus is nota single positive electron, but a combination of several with anumber of negative electrons one less. </p>
<p>This in turn involves asimpler ultimate unit of atomic structure than hydrogen, but isnot necessarily inconsistent with the conception of nuclei, ofhelium, and of hydrogen as penultimate nuclear constituents of themore complex atoms known on the earth.Cause of Atomic Disintegration.--For the first time, an attempRADIOACTIVITY. 257has been niade to frame a theory of the process resulting in atomicdisintegration.26 Hitherto the barrier has been the exponentiallaw of change, which is the law of pure chance, that out of adefinite number, Q, of atoms a definite fraction, AQ, break up inthe unit of time, independent of every consideration whatever.On this theory, the cause of instability is that N separate particlesin the atomic nucleus should all pass some critical position in theshort time 7, 7 being the time taken f o r a strain (regarded as asound-wave) to traverse the nucleus. </p>
<p>An analogy is given whichhelps to make the theory intelligible. A number of smallimpulses applied to a pendulum will result in a maximum displace-ment if all are applied while the pendulum is moving in one direc-tion. The constant A, then, appears as the probability ofLT particles being all in the critical region in the short interval 7.This is (rv)N, where v is the frequency or number of times theparticle passes the critical region per second. </p>
<p>It is shown thatN is 1.5 B, where B is the constant of the Geiger-Nuttall relationbetween A and the range R of the a-particle expelled, namely,logh =n + 13 log R . N is equal to 80, which, as the atomic numberis between 80 and 90, indicates that nearly all the free positiveparticles in the nucleus must conspire t o effect its disintegration.The radius of the nucleus, evaluated on this theory from theconstant A , agrees with that found by Rutherford for the goldnucleus.High- f re p z L e n c y S y e c t rct of t h e Ele rti r: 11 t s.As previously pointed 0 ~ t , 2 7 the discovery of the regular reflec-tion of X-rays from crystal surfaces has been the experimentalmeans of two distinct advances, the elucidation of crystallinestructure and the determination of the wave-length of the X-rays,the latter only falling within the province of this Report. </p>
<p>It wasby this means, some six months ak'ter the elucidation of the natureof a- and &changes had proved that the consecutive places a t theend of the Periodic Table correspond with unit difference of atomiccharge, that Moseley was able to extend the conception towardsthe beginning of the table as far as aluminium, and to call theroll of the elements, which confirmed in so striking a manner theaccumulated labours of chemists since the time of Robert Boyle.Numerous extensions and confirmations of this fundamental workfall to be recorded.I n a long series of papers,2* the L-series of spectra, for which26 F. </p>
<p>A. Lindemann, Phil. Mug., 1915, [vil, 30, 5 6 0 ; A.. 1915, ii, 720.27 Ann. Report, 1913, 273.REP.-VOL. XIII. KCompare a!so A4. Debierne, Ann. Phpique, 1916, [is], 4, 323 ; A., ii, 168.&I. Siegbahn and E Friman, PAysikuZ. Zeitsch., 1916, 17, 17 ; PhiE. May.258 ANNUAL REPORTS ON THE PROGRESS O F CHEMISTRY.Moseley observed five line groups and measured three,Zg has beenmuch extended. Fourteen groups of lines are now recognised inthe L-series, and the elements examined have been extended asfar as zinc in one direction to uranium in the other.30 Indeed,very few of the elements now have not had their atomic numberdirectly determined by measurement of the frequency of one ormore of the lines in one or more of the various series. Animproved vacuum spectrograph has enabled the L-series t o befollowed down t o wave-length 12-35 A ., whereas the greatest wave-length hitherto measured was 8.4 ;\. </p>
<p>Only for three lines (al,a2, and p 2 ) is the linear relation between atomic number andsquare root of the oscillation frequency exact. For the othersthe curves are slightly convex to the atomic number axis. Theatomic number of uranium, the last element, is, as previously pre-sumed, 92, thorium being 90, bismuth 83, lead 82, thallium 81,mercury 80, and gold 79, while it is claimed that the values 84and 85 for polonium and radium have been experimentally estab-lished. With regard to lead, an interesting table is given31 com-paring twelve lines of its L-series spectrum with fifteen lines ofthe soft y-ray spectrum of its isotope, radium-B, as given byRutherford and Aiidrade.3' Ten of the lines are nearly identicalin wave-length, thus confirming still further the identity of theX-ray spsctra of isotopes. Tellurium and iodine have the atomicnumbers 52 and 53 respectively, as the periodic law requires. </p>
<p>I nthe K-series, four lines have been measured for the elementschromium to germanium, and, in the most recent work, investiga-tion has been pushed as far as sodium, with results in full accordwith Moseley's work. Lastly, a new series, the M-series, comprisingsix or seven rays, softer than the L-series, but very similar incharacter to this and to the I<-series, has been found, and thewave-length measured for the elements uranium to gold. </p>
<p>Thisseries also obeys the linear relation over the range studied. Thusthe X-ray spectra are losing their pristine simplicity, but thetheoretical interpretation of the various series should still be child'splay t o the mathematician in comparison with that of light spectra.The atomic numbers of the rare earths do not differ from thosepreviousIy given.33 Numbers 61 and 72 are still vacant, but the1916, [v;], 31, 403 ; &4., ii, 167 ; Physikal. Zeitsch., 1916, 17, 48, 61 ; A . ,ii, 205, 277 ; M. Siegbahn and W. Stenstrom, ibid., 1916,17, 318 ; A . , ii, 509 ;M.Siegbahn, Ber. Deut. physikal. Ges., 1916, 18, 39, 150, 278 ; A., ii, 462,462, 463 ; also Ann. Physik., 1916, [iv], 49, 611, 616 ; A., ii, 362 ; Phil. </p>
<p>Mag.,1916, [vi], 32, 39 ; A., ii, 405.30 E. Friman, Phil. Mug., 1916, [vi], 32, 4 9 7 ; A . , ii, 689.31 Phil. Mag., 1916, [vi], 32, 49.32 Ann. Report, 1914, 275. 33 Ibid., 28028 Aim. Report, 1914, 278RADIOACTIVITY. 259others have all been measured except No. 69, ascribed to thulium.Urbain3.1 states t h a t celtium has not yet been discovered by thismethod, t h a t there is only one thulium, one erbium, and twoytterbiums-neoytterbium and luteciurn. It is to be hoped thatagreement will now be reached as to the names of these elements,as several of them, having been discovered independently, havealiases. A number of other papers on this subject have alsoappeared.35The rays from the Coolidge X-ray tube with a tungsten anti-cathode have been subjected to an interesting examination t odetermine the maximum frequency of the X-rays emitted underdifferent constant voItages.35 The hope previously expressed,37 thatthis tube would enable X-rays as penetrating as the ?-rays ofradium to be artificially generated, has now been definitely dis-pelled. </p>
<p>The penetrating power and frequency of the X-raysreaches a maximum a t 143,000 volts, and does not sensibly increasebeyond this when the voltage is raised to 1'70,000 volts. Theminimum value of the absorption coefficient, p(cm.) -I, Al, is 0.39,as compared with 0.115 for the penetrating y-rays of radium-C.For lead the value is 23, as compared with 0.5 for radium-C, and3 mm. of lead afford practically complete protection against themost penetrating X-rays that the Coolidge tube can produce. </p>
<p>Thelimiting frequency is probably determined by the highest frequencythat exists in the atom, i n this case, of tungsten. It is anticipatedt h a t by the use of a uranium anti-cathode, a limiting penetratingpower of p =0'23, instead of 0.39, in aluminium could be attained.Plaiick's quantum theory appears to hold for the relations betweenfrequency, v, and voltage, E, for small voltages, but for highervoltages, instead of Izv=E, the relation assumes the formhv=E-cE2, where c is a constant. This formula does not holdbeyond the maximum frequency given by E=1/(2c). The voltagerequired t o excite the most penetrating radiation is about twicewhat is t o be expected on the quantum theory, and the eficiencya t high voltage is only about 1/500th. If one-half of the energyof each contributing electron appears as radiation, this indicatest h a t only one in some two hundred electrons contribute t o theradiation. </p>
<p>I n this work there was no evidence that the radiationfrom the tube could be analysed into definite characteristic radia-34 Obituary notice of H. G. J. Moseley, Proc. Roy. Soc., 1916, [A], 93,xsvii.35 1. Malmar, PhiZ. M n g . , 1914, [vi], 28, 787 ; A . , 1915, ii, 2 ; 32. dr, Broglie,Compt. rend., 1916, 163, 57 ; A., ii, 509 ; J. Barnes, Phil. Alag., 1916, [ \ T i ] ,30, 3 6 8 ; A., 1915, ii, 658.3G Sir E. Rutherford, J. Barnes, and H. Richardson, ibid., 339, 361.37 A m . Report, 1314, 277.K 260 ANNUAL REPORTS ON THE PROGRESS OF CIIEMISTRY.tions, although the initial potential, 10,300 volts, a t which X-raysbegan to be generated corresponds well with t h a t required t oexcite the L-characteristic of tungsten, and the most penetratingrays correspond with the shortest wave-length component of itsI<-characteristic radiation. </p>
<p>On the other hand, de Broglie hasfound it possible with a Coolidge tube to follow the absorptionband of an element a t least as far as bismuth, and considers thathis results put beyond doubt the presence of radiation far morepenetrating than the X-radiation of its tungsten anti-cathode.a-, 0-, and y-Radiutio,is.a-Rays.-Hitherto, the fastest known a-rays have been those ofthorium-C', with a range of 8.16 cm. in air a t N.T.P. A smallnumber of bright scintillations, undoubtedly due to a-rays, froma strong preparation of the active deposit of thorium, were observedon a zinc sulphide screen after the passage of the a-rays throughthe equivalent of 10.7 cm. </p>
<p>of air a t N.T.P.39 Further investigationsdisclosed t h a t two new sets of a-rays were probably present, one-third of range 9.7 cm. and two-thirds of range 10.7 cm. in air a tX.Y.P. The division is just the same as for the ordinary a-raysof thorium-C, which gives two sets of different range, one-thirdwith range 4.55 and two-thirds with range 8.16 cin. These newa-rays certainly come from the active deposit of thorium, for theydecay a t the same rate as the other a-rays, but it is not yetdefinitely proved t h a t they come from thorium-C. </p>
<p>It is suggestedthat the a-particles of 9.7 cm. range accompany those of 4.55 cm.range, and those of 10.7 cm. range accompany those of 8.16 cm.range. For each a-particle in the two new sets, 10,000 in the twoold sets are emitted. The Geiger-Nuttall relation indicates thatthe period of average life of the atoms yielding these two new setsof a-rays must be 10-13 and second respectively, and theirvelocities are estimated to be 2.18 and 2.26 ( x 1 0 9 cm. per sec.).A new determination of the velocities of the other two sets ofa-rays from thorium-C gave 1-714 and 2.060 ( x 1 0 9 cm. per sec.),and this indicates t h a t the range of the slower a-particle shouldbe about 4.70 cm. instead of 4.55 a t iV.T.P.40 A determinationof the velocity of the a-particle from radium-A gave 1.69 ( x 109 cm.per sec.), in good agreement with that calculated from the range.41It has now been definitely shown e that the emission of 8-rays from39 Sir E. </p>
<p>Rutherford a,nd A. 13. Wood, Phil. Maq., 1916, [vi], 31, 379 ; A . ,i j , 282.4 0 A. R. Wood, i b i d . , 1915, [vi], 30, 703; A . , 1915, ii, 814.42 J. McLennan and C. C,. Found, ibid., 30, 491 ; A . , 1915, ii, 712. Coin.N. Tunstall and W. Rfakower, ibid., 29, 259 ; A . , 1915, ii, 80.pare Ann. Report, 1912. 301RADlOACTIVITY. 2G 1metals bombarded with a-rays is, like the photoelectric effect,dependent on a surface gas film, and in the complete absence ofthis no emission occurs.Several microphotographic investigations of the tracks ofa-particles in photographic films have been made,43 and the hope isexpressed that with a suitable plate (Wratten and Wainwright'slantern plate being alone found suitable) all the phenomenahitherto studied by the scintillation method can be more con-veniently studied by this means. </p>
<p>Certainly such a method wouldhave many advantages. The halos obtained when an active needlepoint is made to touch a photographic plate have under the micro-scope many of the characteristics of the pleochroic halos. Themethod has been used to investigate the straggling of a-particlestowards the end of the range, with results much closer in accordwith a theoretical formula, calculated by Bohr, than earliermeasurements by other methods,Twoattempts have been made, by Wilson's method, to photograph thetracks of the H-particles known to be produced in the passage ofa-rays through hydrogen. </p>
<p>The first45 was not attended withsuccess. I n a large number of beautiful photographs of a-raytracks in hydrogen, no evidence whatever of the production ofH-particles was obtained. I n the second,*R the separation of thepath of the a-particle, a t the point of its collision with thehydrogen nucleus, into two distinct paths, corresponding with therecoiling H-particle and the deflected a-particle respectively, wasclearly shown, and the number observed were in satisfactory agree-ment with the Rutherf ord-Darwin formula.On the other hand, Mar~den,~7 who first observed these 11-par-ticlea, in attempting a quantitative verification, by counting thescintillations they produce, in an apparatus similar to t h a t used t ostudy the scattering of a-particles, observed effects several timesgreater than the formula leads to. </p>
<p>It was then found t h a t thea-ray tube and emanation alone were emitting N-particles, withoutany layer of paraffin-wax, which was put on as a convenient formof hydrogen atoms. The source of these is doubtful, as i t seemsunlikely that there was sufficient hydrogen in the glass tube, or anyH-P'crrticZcs.44-This subject is in rather a confused state.43 S. Kinoshita and H. Tkeuti. Phil. Mag., 1915, [vi], 29, 420 ; R. R. Sahni,ibid., 836 ; H. Ilieuti, ibid., 32, 129; W. Makower, ibid., 222.41 Ann. Report, 1914, 274.45 J. C. Mc1,ennaii and H. </p>
<p>V. Xercer, Phil. -?tug., 1915, [vi], 30, 676.4G D. Rose, Physikal. Zeitsch., 1916, 17, 388 ; A.. ii, 547. Unfortunately,the ahstract only is available to the writer, who has not seen tho actualphotographs.47 E. Marsden and W. C . Lantsberry, Phil. Mag., 1915, [vi], 30, 240262 ANNUAL REPORTS ON THE PROGRESS OF C‘HEMISTHT.condensed water filni present, to produce them, and the suspicionis crested t h a t they are emitted by the radioactive atoms them-selves. This seems to contradict the results of tlie special researchmade for radiant particles, differing either in mass or charge fromthe a-particles, in the rays from the radium emanation,@ but in thelatter it is stated t h a t the nuinber is certainly less than 1 in 10,000a-particles, and possibly the two statements are not inconsistent.P-Rnys.-Two sets of P-rays, of velocity 0.51 and 0.47 times t h a tof light, hitherto attributed to thorium-5, have been shown t o bedue t o radio-tlioriuin, which in this respect is now analogous t oradio-actiniurn.49 The paper contains useful information on thedeposition of filnis of thorium-X and radio-thorium on short, finewires. </p>
<p>The two sets of &rays emitted by radium-D, velocities 0.39and 0.37,sO have been the subject of an interesting examination.Hitherto, on account of their feeble penetrating power, which is lessthan t h a t of the a-rays, they have only been detected photographi-cally by means of their magnetic spectrum. After an extremelycareful purification from radium-3, which gives penetrating &rays,and radium-F, which gives a-rays, radium-D was found t o be givingP-rays capable of detection by the electroscope, which were reducedin intensity t o 10 per cent. of the initial value by 0.0035 mm. </p>
<p>ofaluminium. The absorption-coefficient is 5500 (cm.) -1 Al, whichagrees almost exactly with the value, 5067, f o r cathode rays of36 per cent. light velocity, as measured by Becker. The experimeiitsfavoured the view t h a t tlie absorption of &rays is primarily dueto tlie completed stoppage of the individual particles in singleencounters with atoms, rather than to the gradual wearing down ofthe velocity of the whole beam, alternatives that have previouslybeen fully discussed.51 With regard to the absorption of homo-geneous 8-rays in aluminium, the absorption curve is nearly linearand the rays have a definite “range,� varying from 0.025 cm. </p>
<p>f o rrays of Hp=1930, velocity 0.75, t o 0.5 cm. f o r rays of Hp=11,500,velocity 0.99 times t h a t of light. This is due t o the chance balanc-ing of tlie scattering and the diminution of velocity, for in paper,where the scattering is smaller, the absorption curve is concave, andin platinum, where it is large, convex to the origin.52y-Bnys.-Experiments on the excitation of y-rays by P-raj s inplates of iron, nickel, copper, and zinc showed t h a t the y-raysexcited were similar in abso~rption-coeffic:ent t o Earkla’s charecter-4 5 Ann. Report, 1914, 27k.4 9 0. Baeyer, 0. Hahn, aiid L. Meitner, PhysikctZ. Zeitsch., 1915, 16, G ; &4.,50 Ann. </p>
<p>Report, 1911, 2 7 8 ; L. Meitner, ibid., 272; -4., 1915, ii, 663.51 -4nn. Report, 1007, 315. ‘‘ R. W. Varder, Phil. M u g . , 1915, [vi], 29, 725 ; A , , 1915, ii, 4011915, ii, 127RADIOACTIVITY. 263istic secondary S-radiations froin these metals, and, in silver andtin, with Barkla's K-radiations of these meta1~.~3 The absorption ofthe y-rays of radium-B and -C in lead shows no such anomaly, dueto the atomic numbers of these elements and of lead being similar,as might have been expected from Barkla's work on the absorptionof X-rays. Eiglity-five per cent. of the ionisation due to radium4is from the well-known penetrating rays, ~ ~ 0 . 5 (cm.)-I, Pb, and15 per cent. to rays of apparently exactly the same character as they-rays of radium-B. </p>
<p>The latter comprises three types, with p inlead, 1.5, 6.0, and 46 respectively contributing 12, 26, and 46 percent. of the total ionisation.5'Rcrdioactive Recoil.Once thel charge carried by the a-particle was a debated problem.55Was it intrinsic, or was it simply the result of its encounter withtlie first atom in its way? It was very certain that an atom travel-ling a t such a speed would be ionised itself, even if initially un-charged. After many researches, it was finally decided that, sofar as experimental tests could show, the charge was intrinsic, andnow we know t h a t it is the loss of tliese two charges from thenucleus in an a-ray cliaiige which is the cause of- the shift of twoplaces in the Periodic Table. </p>
<p>Exactly the same question has nowbeen asked of the recoiling particle,5G which ordinarily carries asingle positive cliarge,57 a i d here also tlie tlieoretical importance oftlie question is considerable.5e The recoil of radium-D fromradium-6' was clioseii, and here it was a t once found that in a suffi-ciently good vacuum the recoiling particle is uncharged. It gainsits charge by collisions with the molecules of the gas in its path.I n a vacuum a t a pressure measured by the Knudsen absolutemanometer to be 0.6 dyne per cm.2 (4.5 x lo-' mni. of mercury)-six hundred times, i t may be remarked, t h a t measured by theMcLeod gauge-no charge was carried by the recoiling atoms. Asthe pressure rose, the charge acquired increased and, a t sufficientlyhigh pressure, equalled t h a t carried by the a-particles, showingthat the radium-D atom can acquire multivalent charges. </p>
<p>Sincea t atmospheric pressure a univalent charge is carried, it is clearthat, as in the case of the canal-rays, successive recombinaticns and53 (Miss) J. Szmidt, Phil. Mag., 1915, [vil, 30, 220 ; A4,, 1915, ii, 721.54 H. Richardson, PYOC. R o ~ . SOP., 1915, [A], 91, 396; A . , 1915, ii, 401.55 Ann. Report, 1904, 256 ; 1905, 302 ; 1906, 344 ; 1907, 315.66 L. Wertenstein, Comnpt. rend., 1915, 161, 896 ; A., ii, 69.57 Ann. Report, 1910, 272 ; H. P. Walmsley and W. Makowor, Phil. Mag.,5 5 Ann. Report, 1913, 281.1915, [vi], 29, 253264 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.ionisations occur along the path. </p>
<p>It would not be safe to generalisefrom the case of radium-]), for it is produced in the excessivelyquick change of radium-C':, which itself, a t the moment of itsdisruption, may still carry a positive charge acquired a t its birth,10-11 second earlier, by the expulsion of a P-ray from radium-C'.This might lead t o the expectation t h a t in other cases the recoil-atom will be found negatively charged. The research opens outa whole series of questions as to the conservation of electric chargesduring radio-active changes, and further results will be awaitedwith interest.Attempts have been made t o detect a photographic action bothof radium-G recoiling from polonium,sg and of radium-]) fromradium-C,Go using Schumann plates in which the amount of gelatinin the film was reduced t o a minimum. </p>
<p>No photographic and nophosphorescent effect on zinc sulphide could be detected in the firstcase, but, in the second, a weak photographic effect, attributed tothe recoil atoms, was obtained. A line in the magnetic deflectionexperiment was found nearly midway between that due to thedeflected and undeflected a-particles of radium-C, and it was con-cluded t h a t the atoms of radium-]) are projected with a singlepositive charge, as is the case with radium-]) recoiling fromradium-A. The experiments were done in a vacuum, but it is clear,from Wertenstein's results, already noted, t h a t the charge carriedby the recoiling atom of radium-11 varies with the pressure ofthe gas.A method of determining the ratio of the " ranges " of the recoil-ing atoms of radium-B and -D respectively from the efficiency ofthe recoil of the latter from a plate on which radium-A had beendeposited indicated a greater difference in their ranges than inthose of the corresponding a-particles of radium-;l and radium-6'respectively which accompany these recoiling atoms.61Chemical L4 ctioizs of t h e Radicttioiis.-The spontaneous reactionbetween hydrogen arsenide and oxygen is accelerated by P- andy-rays, and, instead of the arsenic being liberated as such, it isoxidised to arsenious acid, 2AsH3 + 30, = 2€13As03.62 The velocityof the esterification of acetic acid is scarcely increased by the actionof the radium rays, but' ethyl acetate is decomposed by the pene-trating rays, primarily with the formation of an acid and an uii-saturated hydrocarbon. </p>
<p>The oxidation of acetone t o acetic acid by5 9 A. B. Wood and ,4. T. Steven, Proc. Physical Soc., London, 3915, 27.6" A. B. Wood and W. Rfakower, Phil May.. 1915, [vi], 30, 811 ; A., ii, 6.62 H. Rerltleben and G. Lockcmatin, Zeitsch. anol-9. Chein., 1915, 92, 145 ;189 ; A . , 1915, ii, 403.W. Maltower, ibid., 1916, [Ti], 32, 226; A . , ii, 547.A . , ii, 209RADIOACTIVITY. 265radium rays is detectable, but, as is usually the case, is very slightcompared with similar action brought about by ultra-violet light.63An investigation of the union of hydrogen and chlorine, under theinfluence of a-particles from radium emanation, showed t h a t thereaction is of the first order, is not affected by the hydrogen chlorideformed, and is retarded by oxygen a t all stages proportionally tothe oxygen concentration. </p>
<p>As regards the kinetics of the combina-tion, the reaction showed complete parallelism to the photochemicalreac tion.G4I n a series of experiments on colloidal solutions, the penetratingrays of radium were found to precipitate electropositive, but notelectronegative, colloids. Native, well dialysed albumin is changedand finally coagulated by the rays, which produce also a loweringof the coagulation temperature and increased precipitability byalcohol. Salts exercise a protective action.65i1-e IJI TT'ork o I L t h e Rtrrlio el P ttl P 11 f c.A number of more extended accounts of collected investigations,previously published in brief, have appeared dealing with (1) theradio-active decomposition of water ; (2) the production of heliumfrom radio-active substances ; (3) the atomic weight of the radio-active emanations; and (4) the deposition of the active deposit ofradium.66Thorium.-The life-period of thorium has been determined as1.77 x 1010 years for the period of half-change, 2.56 x 1010 years forthe period of average life, from the ionisation of films of thoriumoxide of vanishing thickness.67Rndi7cnz.-The life of radium has been redetermined by Bolt-wood's method,G* by separating the whole of the ionium in auranium mineral and determining the rate of growth of radiumfrom it in terms of the equilibrium amount present in the mineraLG0Carefully selected specimens of uraninite (N. </p>
<p>Carolina), cleveite(Norway), and broggerite (Norway) were used. The ionium wasseparated by addition and separation of thorium, several separationsbeing carried out, and the last kept distinct for a blank test, toG3 A. Kailan, Monatsh,. 1914, 35, 859; A . , 1915, ii, 663.64 H. R. Taylor, J . Amer. Ckem. Soc., 1915, 37. 2 4 ; A . , 1915, ii, 80.G,5 A. Fcrnau and W. Pauli, Biockem. Zeitsch., 1915, 70, 426 ; A . , 1915,i , 722.66 A. Dsbierne ( 1 ) Ann. physiybe, 1914, [ixJ, 2, 97 ; A . , 1915, ii, 126 ; (2)ibid., 425, 478 ; A., 1915, ii, 132, 725, 726 ; (3) ibid., 1915, [ixl, 3, 18, 62;A . , 1915, ii, 302, 303 ; (4) ibid., 1915, [ixl, 4, 408 ; A., 1915, ii, 667.6 i R. Heimann, Monatsh., 1914, 35. </p>
<p>1533 ; A . , 1915, ii, 665.6 8 Ann. Report, 2909, 263.69 (Mlle.) E. Gleditsch, -4mer. J . Sci., 1916, [iv!, 41, 112; A . , ii, 168266 ANNUBL REPORTS ON THE PROGRESS OF CHEMISTRY.make sure all ionium had been removed. The two most satisfactoryexperiments gave the period of half-change as 1660 years, in goodagreement with Rutherford's value, 1690 years, obtained by count-ing the a-particles expelled per second from a known weight ofradium. The value for the period of average life is 2347 years,somewhat less than the value, 2500 years, usually taken.Polonium.-Some indirect evidence has been obtained of theexistence of a volatile hydride of polonium, in the course of experi-ments on the range of the a-particles in hydrogen, in which agradual increase in the ionisation current a t a given distance withthe lapse of time was observed.70 Being in the sixth family ofelements, it is to be expected t h a t it should form a volatile com-pound with hydrogen dissociating a t the ordinary temperature.The Emanations.-A lengthy series of experiments has beencarried out on the volatility of the thorium and radium emanationsto see if these two isotopes, once mixed, could be separated by con-densation a t low temperature.71 A large number of puzzling pheno-mena were encountered, and the results obtained varied widelyfrom experiment to experiment. </p>
<p>Owing to this, and the greatdifference in the periods of average life, and, consequently, in theconcentration of the two emanations, no definite conclusions couldbe reached on the main question, which remains unanswered. </p>
<p>I nthe course of the investigation, two maxima were observed incertain cases in the condensation curve of radium emanation, onea t - 7 5 O and the other a t - 1 6 1 O . This may be connected withthe well-known phenomenon that, when a tube containing emana-tion is immersed in liquid air, the condensation, as shown by theluminous ring on the tube, occurs always a short distance abovethe level of the surface of the liquid air.The Branching Poiti t of t h e Thorizcm Series.72-The supposedseparation of the two sets of thorium-C atoms, which give a-rays ofrange 5.7 and 8.16 cm. respectively, has not been confirmed. Thetwo stages in the volatilisation, 35 per cent. being volatilised belowand 65 per cent. </p>
<p>above 900°, has been confirmed, but it has beenshown t h a t the isotope radium4 shows in every respect a com-pletely identical behaviour. This a t once rules out the explanationthat the 35 per cent. of the thorium-C atoms which give short-range a-rays had been separated from the 65 per cent. which givea-rays of long range, because in this case, although radium-C dis-integrates dually also, all but an infinitesimal fraction of the atomsio R. W. Lawson, Monatsh., 1915, 36. 846 ; A . , ii, 121.72 -4nn Report, 1914, 287; S. JJoriit, Ph,ysikal. Zeitsch., 1916,17, 6 ; Monatsh.,A. Fleck, Phil. Mac/., 1916, [vi], 29, 337 ; A . , 1915, ii, 131.1916, 37, 1 7 3 ; A . , ii, 169, 465RADIOACTIVITY. 267follow one of the two modes. </p>
<p>These C-members are isotopic withbismuth, and it is probable that, like bismuth, they form severaloxides stable within different limits of temperature, which accountsfor the discontinuity in the volatilisation curve.Adsorptiou of the Radbelenien ts.The definite chemical characterisation of all the known radio-elements raises the problem as to how it' is they show such definitebehaviour in so dilute a solution, and are precipitated, along withother precipitates, a t ionic concentrations far below the solubilityproduct. Several papers have been published on this subject.73M7here the substance carrying down the radio-element is isotopicwith it, absorption, of course, can play no special part, for theratio of t h s concentrations of the two isotopes in both the solidand liquid phases must be the same, and the ratio of the quantityprecipitated to the quantity left in solution also the same for each.Where, however, the two substances are not isotopic, but merelyanalogous, the radio-element is carried down by the precipitate ifunder the same conditions it would be precipitated if present insufficient concentration. The various workers agree on the con-clusion that the negative ion governs the precipitation. </p>
<p>Adsorp-tion is favoured if the adsorbent has an electronegative constituent,the compound of which with the radio-element is insoluble.Similarly, the addition of an acid containing such an electronegativeconstituent favours the adsorption. Adsorption in these cases isquite in keeping with the chemical character, whereas in the caseof some of the adsorbents firstl used, such as charcoal, entirelydifferent considerations may apply. An exhaustive study of theadsorption of uranum-X, by the last-mentioned substance hasshown that the action of the isotope, thorium, in preventing theadsorption, discovered by Ritzel, is shown also by a large numberof substances-zirconium salts, benzoic acid, strychnine nitrate,and basic dyes.74 It was found that a solution of thorium nitratewhich has been shaken with charcoal produced afterwards a muchsmaller effect in preventing the adsorption of uranium-X1 by char-coal. </p>
<p>Similarly, uranium-X1, freshly produced from uranyl nitratet h a t has been shaken with charcoal, is more readily adsorbed bycharcoal. </p>
<p>The authors assume the existence of small quantitiesof still undiscovered radio-elements in thorium and uranyl nitrateswhich are the cause of the effect, and are removed when shaken73 I<. Horovitz and F. Paneth, Zeitsch. physikal. C'hem.. 1915, 89. 513 ;&4., 1915, ii, 215 ; F. Pnneth, Physikal. Zeitsch., 1914, 15, 924 ; A . , 1915, ii,2 0 5 ; K. Fajans and F. Richter, B e y . , 1915, 48. 700; A . , 1915, ii, 406.n H. Freundlich and H. Kaempfer, Zeitsch. physikal. Chein., 1915, 90,681 ; A . , ii, 70268 ANNUAL REPORTS Oh’ THE PROGRESS OF CHEMISTRY.with charcoal. Thorium nitrate, unlike the other substancesinhibiting the adsorption, is eRective if added to the charcoal afteri t has adsorbed uranium-X1, causing the latter to redissolve. Itwas recognised long ago’s that, if thorium nitrate did not preventthe adsorption of the isotope uranium-S1, this means would beavailable for separating two isotopes, assuming, of course, that thethorium nitrate itself was not, equally with uranium-S,, adsorbedby the charcoal. </p>
<p>The fact that other substances have the sameeffect as thorium in no way affects this coiiclusion, but the diminu-tion of the effect of thorium nitrate by shaking the solution withcharcoal requires an explanation if these authors’ somewhat sweep-ing assumptions of undiscovered radio-elements is not accepted.Perhaps, t o hazard a suggestion, the thorium nitrate itself is moreeasily absorbed by charcoal after its solution has been shaken withcharcoal, which naturally would make it less effective in preventingadsorption of uranium-X,.The method of adsorbing radium by colloidal silicic acid, with aview to the subsequent volatilisation of the latter by hydrogenfluoride, has been found unsatisfactory in practice, being verysensitive t o the presence of acids and t o variations in the characterof the silicic acid gel.76 Manganese dioxide hydrate, preparedeither by reducing a permanganate with methyl alcohol or withmanganese chloride, has been found suitable, and here it is to benoted the action is chemical, depending on the formation of aradium manganite. </p>
<p>An enrichment of the radium from bariummay be effected by partial de-adsorption by the electric current,but the best method is to treat the dioxide hydrate with aluininiunchloride solution (15 grams of crystallised salt per litre), whichreplaces more radium than barium in the manganite. </p>
<p>It isdoubtful from the figures given whether the process is so simpleand effective as Mme. Curie’s original method of fractionallycrystallising the chlorides.T e c J w z icnl T1-m t I ~ L e I I t of R cr tl ioci c t i f 6 M(i t e 1.ictl.7.The same authors recommend for the reduction of crude radiumresidues, consisting mainly of lead and alkaline-earth sulphates, tosulphides soluble in acids, a mixture of calcium hydride andcalcium carbide, the latter moderating the violent action of theformer.77 A proportion of one to three suffices for rich residues,75 Ann. Report, 1910, 276.T G Ibid., 1911, 292 ; E. </p>
<p>Ehler and W. Bender, Zeytscli. nngezc. Chem.. 191,5?7 7 Compare -4~2n. Report, 1913, 377 ; E. EhIer and W. Bender, Zeitsch.28, 35, 41 ; A . , 1913? ii, 659; 1915, ii, 129.anorg. Chejn., 1914, S$, 25.5; A , , 1915, ii, 404RADIOACTlVITY. 260but more hydride must be added for the poorer varieties. Forthe separation and concentration of radium and its isotopes frombarium, the fractional precipitation of barium hydroxide from itssolution by addition of an alkali hydroxide has been patented.78Ionium and actinium have been recovered, from the crudesulphates of the Olary ores, from the filtrate from which thealkaline earths have been separated by sulphuric acid.79C'ctrnotite.-The report of the Bureau of Mines, Washington,Bulletin 104, Mineral Technology 12, dated November, 1915, onthe extraction and recovery of radium, uranium, and vanadiumfrom carnotite, contains an interesting account of the steps takenin America to nationalise the extraction of radium. </p>
<p>I n an experi-mental plant, from which 4.25 grams of radium (element) wereextracted, the cost worked out a t 37.6 dollars per milligram, ofwhich 20.71 dollars was the cost of the extraction and the rest thecost of ore. This is on the basis that the uranium and vanadiumwere not recovered. Actually they were recovered, and it isexpected will more than pay the cost of recovery. Full detailsare given of the factory operations and methods employed, andthe report would be invaluable to anyone wishing to start extract-ing radium technically.A method which seems promising, previously used in the estima-tion of radium by the emanation method,80 has been applied tothe extraction of radium from carnotite.81 Boiling a low-gradeore with 96 per cent. </p>
<p>sulphuric acid removed 95 per cent., 78 percent. sulphuric acid 92 per cent., and 35 per cent. sulphuric acid42 per cent. of the contained radium, the latter strength sufficingto remove the vanadium and uranium effectively. I n actual workwith 10 kilogram lots, 18 kilos. of acid, 60° Baum6, containing78 per cent. of acid, were heated t o 190°, and the ore addedgradually, with stirring, heating being continued for fifteenminutes a t least until the temperature reached 220O. The mixturewas filtered on a " Filtros '' medium, washed with two lots of freshhot acid, and the filtrate run into eight times its volume of hotwater and well stirred. </p>
<p>The radium is precipitated with thebarium as sulphate, and in this one operation its concentration isincreased more than 230 times. Several per cent. of the radiumsettles out from the turbid filtrate obtained by washing the residue7 8 H. N. McCoy, U.S. Pat., 1103E,OO, J . SOC. Chem. Ind., 1914, 33, 919;7 9 S. Radcliff, J . Roy. SOC. New 80zith Wales, 1914, 48, 408; A . , 1915,R o -4m. Report, 1911, 294.A . , 1915, ii, 3 .ii, 665.TT. Srhliiurlt, J . Physicnl Chern., 1916, 20, 485 ; A , , ii, 430270 ANNUAL REPORTS ON THE PROGRESS O F CHEMISTRY.on the filter with water. An actual recovery of 85 t o 95 percent. of the radium is recorded in four experiments.A careful investigation of various methods of treating carnoti te,noteworthy because all the radio-constituents were traced by a-raymeasurements, showed a recovery of 90 per cent. </p>
<p>of the uraniuniand of the radium, 50 per cent. of the polonium, 61 per cent. ofthe ionium, and 52 per cent. of the actinium.82 The treatmentinvolved boiling the ore (1) with sodium carbonate to remove theuranium, which separated in a pure form as sodium uranylcarbonate on concentrating the filtered solution ; (2) with hydro-chloric acid, which removed most of the radium; ( 3 ) with nitricacid, some 8 to 10 per cent. more of the radium being obtained;(4) with moderately concentrated sulphuric acid, which removedthe ionium. </p>
<p>I t is interesting that the ionium was not removedin the first three treatments. The residue, which was reduced inweight to one-half t h a t of the mineral, still contained 4.2 per cent.of the initial radium. The carnotite used was not pure, but con-tained much of its vanadium in a very difficultly attacked form,probably as the silicate, roscoelite. Only part of the vanadiumwas recovered even by heating the ore in dry hydrogen chloride,when the volatile oxychloride distils away. This method is statedto remove the whole of the vanadium from the crude sodiumuranate obtained as a by-product from cariiotite.83 Other methodsof effecting the latter separation are (1) the heating of a paste ofthe uranate and ammonium chloride with water; (2) solution ofthe uranate in the minimum of dilute acid and boiling, when thevanadium and 13 per cent. </p>
<p>of the uranium are precipitated.Mndapacczr Mitz emT.y.-The districts of Antsirabe and Betafo,Central Madagascar, 100 miles S.W. of Tananarive, is stated t o beextraordinarily rich in minerals containing some 20 per cent. ofuranium along with columbium, tantalum, and titanium. Thecomplete analyses of four, blomstrandite, betafite, samiresite,ampangabeite, by Lacroix, show 18.1, 26.6, 21.2, and 19.4 per cent.of UO, respectively, and also in the second 1.3 and the fourth2.5 per cent. of thorium oxide.8' I n a new examination of pyro-morphite from various sources by radioactive methods,sS the surf aceconcentration of the radium is denied, and the mineral is statedt o be homogeneous as regards its radium content. </p>
<p>It is regardedas a young formation, in which radium, deposited a t the time of83 H. 31. Plum, J . r1?)29T. Che7n. SOC , 1315, 37, 1797 : L4., 1915, ii, 666.83 H. 13. Rarker and R. Schlundt, J . POC. C'hcm. Ind., 1916, 35, 176 ; -4.,84 T. P. Waites, J . Chem. Met. Min. SOC. S. A4.frica, March, 191C, p. 187.85 M. Bamberger and G. Weissenbtrger. Monntsh., 1915, 36, 169 ; A.,i, 189.1915, ii, 506 ; compare Ann. Reports, 1909, 260 ; 1910, 264R AD1 0 ACT I\' I TY. 271its formation from the water in which it was formed, has not yethad time to decay.A r ti fic ial Tra 11 smut a tio n .In aseries of electric discharge experiments in hydrogen with differentsized coils, different types of interrupters, various sized and shapedtubes, with palladium, platinum, and aluminium electrodes, noproduction of helium or neon was observed,8$ which confirms theview previously taken in these Reports that these gases are notobtained when due precautions against contamination are taken.Uranium oxide subjected t o cathode rays lost oxygen t o someextent, but there was no evidence t h a t the compound had beenrendered more radioactive. </p>
<p>Bismuth, similarly treated, was notrendered active, and although it showed subsequently a spectro-scopic trace of thallium, this was present also in the untreatedmeta1.87 Lastly, attempts made to influence the velocity of radio-active transformation by a-rays were unsuccessful, uranium oxideand mesothorium preparations being exposed t o the bombardmentof the a-rays from the radium emanation without any change intheir radioactivity, as subsequently measured, being produced.**The results to be recorded in this field are all negative.iQa t ural R udioa c t i L' it y .A radioactive determination of the thorium content of 86 acid,48 intermediate, and 56 basic rocks gave mean values of 2.1, 1.5,and 0.5 ( x 10-5 gram per gram), with a general mean of 1-4.89Analyses of the ochre deposited by a strongly radioactive Tyrdlspring showed a concentration of radium several times greater thanthat in the rock from which the water issues, which was a graphite-quartzite containing zircon and about 0.1 per cent. of t h o r i ~ n i . </p>
<p>~ ~A connexion between fertility of the soil and radioactive contentwas found in the case of thirteen typical Minnesota soils, thosericher in radioactive constituents being without exception the morefertile.91A comprehensive survey of the radioactivity of 400 Swedishspring waters showed a relatively high radium content, the most86 A. C. G. Egerton, Proc. Roy. SOC., 1915, [A], 91, 280; A., 1915, ii, 132.87 W. P. Jorissen and J . -4. Vollgraff, Zeit.sch. physikal. Chem., 1914, 89,151 ; 1915, 90, 557; A., 1915, ii, 134 ; 1916, ii, 71 ; also A., 1915, ii, 664.J. Danysz and L. Wertcnstein, Gompt. rend., 1915, 161, 784 ; A., ii, 69.J. H. J. Poole, Phil. May., 1915, [vi], 29, 483 ; A . , 1915, ii, 207.G. Weissenherger, C'e?z.fr. Min., 1914, 481 ; A . , 1915, ii, 305.91 J. C. Sanderson, Amer. J. Sci., 1915, [iv!, 39, 391 ; A . , 1915, ii, 306272 ANNUAL REPORTS ON THE PROGRESS O F CHEMISTRY.radioactive-up to 172 Mache units-being those from deepborings in the acid rocks-granites and syenites.91 Two springs,the first in Bloomington, Indiana, and the second a t Tuwa, Kaira,Bombay, in which the emanation content varied with the seasonalvariation of the flow of the spring, showed precisely oppositebehaviour. I n the first case the emanation content increased, andin the second case decreased as the flow of the spring increased,suggesting in the latter case a constant supply of total emanationall the year round, independent of flow, and in the former a supplyderived from the surrounding soil and depending on the rate ofpercolation of the water, less decay en route taking place the morerapid the percolation and greater the rainfall.93Obit L l c r T y .I n conclusion, it is fitting to recall the great losses the sciencehas suffered in the period under review by the deaths of €1. G. J.Moseley, in his twenty-eighth year, in the fighting a t Suvla Bay,Gallipoli, the youngest investigator, surely, to have won so securea place in the history of science, and of Sir William Ramsay, who,pre-eminent in chemical science before the discovery of radio-activity, devoted the last ten or twelve years of his vigorous andcrowded life more and more exclusively t o the young science he didso much to advance.FREDERICK SODDY.s3 N. Sahlhom, Srkiv Kern. Min. Geol., 1916, 6, No. 3, 1 ; A . , i i , 208.g3 R. R. Ramsay, Phil. Mag., 1915, [vi], 30, 815 ; A., ii, 6 ; A. Steichen,ihid., 31, 401 ; 9., ii, 28-1.ADDENDUM TO FOOTNOTE 4, PAGE 247.An interesting and important confirmation has just' been receivedthrough Dr. Lawson, who is interned in Vienna and allowed towork in the Radium Institut under Professor Stefan Meyer. Thewriter sent Dr. Lawson the first fraction of the above distilled thoritelead, and he now reports (January 31st, 1917) that ProfessorHonigschmid has made four determinations of its atomic weightby the silver method, the mean result found being 207.77 k0.014,in excellent agreement with the value 207.74 calculated from therelative density of the specimen as found by the writer.F. 8</p>
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