4i8 



NATURE 



[July 19, 1917 



thorium-I were non-separable by chemical processes, 

 and had a chemical character not merely like, but 

 identical. It followed that some of the common 

 elements might similarly be mixtures of chemically 

 identical elements. In the cases cited the non-separable 

 pairs differ in atomic weight from two to four units. 

 Hence the lack of any regular numerical relationships 

 between the atomic weights would, on this view, fol- 

 low naturally (Trans. Chem, Soc, 191 1, vol. xcix., 

 p. 72). This idea was elaborated in the Chemical 

 Society's Annual Report on Radio-activity for 1910, 

 in the concluding section summing up the position at 

 that time. This was, I think, the beginning of the 

 conception of different elements, identical chemically, 

 which later came to be termed "isotopes," though it 

 is sometimes attributed to K. Fajans, whose valuable 

 contributions to radio-activity had not at that date 

 commenced, and whose first contribution to this sub- 

 ject did not appear until 1913. 



In the six or seven years that have elapsed the view 

 has received complete vindication. Really three dis- 

 tinct lines of advance converged to a common conclu- 

 sion, and, so far as is possible, these may be dis- 

 entangled. First there has been the exact chemical 

 characterisation from the new point of view of every 

 one of the members of the three disintegration series 

 with lives over one minute. Secondly came the 

 sweeping generalisations in the interpretation of the 

 periodic law. Lastly there has been the first begin- 

 nings of our experimental knowledge of atomic struc- 

 ture, which got beyond the electronic constituents and 

 at the material atom itself. 



In pursuance of the first, Alexander Fleck, at my 

 request, commenced a careful systematic study of the 

 chemical character of all the radio-elements known, 

 of which our knowledge was lacking or imperfect, to 

 see which were, and which were not, separable from 

 known chemical elements. Seldom can the results of 

 so much long and laborious chemical work be ex- 

 pressed in so few words. Every one that it was pos- 

 sible to examine was found to be chemically identical 

 either with some common element or with another of 

 the new radio-elements. Of the more important char- 

 acterisations, mesothorium-II was found to be non- 

 separable from actinium, radium-A from polonium, 

 the three B-members and radium-D from lead, the 

 three C-members and radium-E from bismuth, acti- 

 nium-D and thorium-D from thallium. These results 

 naturally took some time to complete, and became 

 known fairly widely to others working in the subject 

 before they were published, through A. S. Russell, an 

 old student, who was then carrying on his investiga- 

 tions in radio-activity in Manchester. Their interpre- 

 tation constitutes the second line of advance. 



Before that is considered, it may first be said that 

 every case of chemical non-separability put forward 

 has stood the test of time, and all the many skilled 

 workers who have pitted their chemical skill against 

 Nature in this quest have merely confirmed it. The 

 evidence at the present day is too numerous and 

 detailed to recount. It comes from sources, such as 

 in the technical extraction of mesothorium from 

 monazite, where one process, is repeated a nearly end- 

 less number of times ; from trials of a very great 

 variety of methods, as, for example, in the investiga- 

 tions on radium-D and lead by Paneth and von 

 Hevesy; it is drawn from totally new methods, as in 

 the beautiful proof by the same authors of the electro- 

 chemical identity of these two isotopes; it is at the 

 basis of the use of radio-active elements as indicators 

 for studying the properties of a common element iso- 

 topic with them, at concentrations too feeble to be other- 

 wise dealt with ; and from large numbers of isolated 

 observations, as well as prolonged systematic re- 

 searches. One of the finest examples of the latter kind 

 NO. 2490, VOL. 99I 



of work, the Austrian researches on ionium, will be 

 dealt with later. The most recent, which appeared 

 last April, is by T. W. Richards and N. F. Hall, 

 who subjected lead from Australian carnotite, contain- 

 ing therefore radium-D, to more than a thousand 

 fractional crystallisations in the form of chloride with- 

 out appreciably altering the atomic weight or the /3 

 activity. So that it may be safely stated that no one 

 who has ever really tested this conclusion now doubts 

 it, and, after all, they alone, have a right to an 

 opinion. 



This statement of the non-separability by chemical 

 methods of pairs or groups of elements suffers per- 

 haps from being in a negative form. It looks too 

 much like a mere negative result, a failure, but in 

 reality it is one of the most sweeping positive general- 

 isations that could be made. Ionium, we say, is non- 

 separable from thorium, but every chemist knows 

 thorium is readily separated from every other known 

 element. Hence one now knows every detail of the 

 chemistry of the vast majority of these new radio- 

 elements by proxy, even when their life is to be 

 measured in minutes or seconds, as cornpletely as if 

 they were obtainable, like thorium is, by the ton. The 

 difference it makes can only be appreciated by those 

 who have lived through earlier days, when, in some 

 cases, dealing with the separation of radio-constituents 

 from complex minerals, after every chemical separa- 

 tion one took the separated parts to the electroscope 

 to find out where the desired constituent was. 



As the evidence accumulated that we had to deal 

 here with something new and fundamental, the ques- 

 tion naturally arose whether the spectrum of isotopes 

 would be the same. The spectrum is known, like the 

 chemical character, to be an electronic rather than 

 mass phenomenon, and it was to be expected that the 

 identity should extend to the spectrum. The question 

 has been tested very thoroughly, by A. S. Russell and 

 R. Rossi in this country, and by the Austrian workers 

 at the Radium Institut of Vienna, for ionium and 

 thorium, and by numerous workers for the different iso- 

 topes of lead. No certain difference has been found, 

 and it may be concluded that the spectra of isotopes 

 are identical. This identity probably extends to the 

 X-ray spectra, Rutherford and Andrade having shown 

 that the spectrum of the y-rays of radium-B is iden- 

 tical with the X-ray spectrum of its isotope lead. 

 {To he continued.) 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



The Merthyr Education Committee has accepted 

 with thanks an offer from Mr. H. Seymour Berry to 

 equip a technical mining and engineering institute at 

 a cost of io,oooL. in commemoration of the part his 

 late father, ex-Alderman J. M. Berry, had taken in the 

 public life of the town. 



The trustees of the Beit Fellowships for Scientific 

 Research, which were founded and endowed four years 

 ago by Mr. Otto Beit in order to promote the advance- 

 ment of science by means of research, have recently 

 elected Mr. Leslie Hartshorn to a fellowship. Mr./ 

 Hartshorn will carry out his research in the Imperial] 

 College at South Kensington. 



A CON'FERENCE ou new ideals in education is to he] 

 held at Bedford College, Regent's Park, London, on 

 August 14-21. The inaugural address will be de- 

 livered by the President of the Board of Education, 

 Mr. H. A. L. Fisher, on August 15 at 10 a.m. 

 Among the subjects and speakers we notice the fol- 

 lowing : On August 15, Mr Frank Roscoe, on the 

 mind of youth ; on August 16, Prof. Bompas Smith, 

 on problems of the urban continuation school ; on 



