3S0 Bolt wood — Ionium, a New Radio-active Element. 



of the thorium by hydrogen peroxide, sodium thiosulphate, 

 meta-nitro-benzoic acid or fumaric acid. From its position 

 with respect to radium it can be safely assumed that the atomic 

 weight of ionium is probably not far from 230, and the atomic 

 weight of thorium, 232*5, would bring these two elements into 

 close proximity in the periodic table. 



By observations of the growth of radium in purified salts 

 of thorium obtained from monazite by commercial methods, 

 Halm* has demonstrated that ionium is also contained in these 

 compounds. 



General Discussion of Results. 



It appears highly probable from the data now available that, 

 in the earlier experiments of Debierne, the material which he 

 described under the name of "actinium"' consisted in reality 

 of a mixture of ionium with the element first definitely iden- 

 tified and described by Giesel under the name of " emanium." 

 Debierne's statement, quoted in the introduction, that he had 

 used in his experiments only preparations which had retained 

 a constant activity for a certain time, while not very explicit, 

 would at least appear to exclude the possibility that the incor- 

 rect chemical properties which he attributed to what is now 

 known as actinium can be explained by any other assumption.. 

 That Giesel's preparations of the " emanating substance " have 

 in one case, at least, contained appreciable amounts of ionium, 

 is evident from the results obtained by Rutherford on the 

 growth of radium in a specimen of this material. 



The anomalous behavior of the thorium separated from 

 uranium minerals by Hofmann and Zerban can also be explained 

 without difficulty. In those cases where a permanent high 

 activity was shown by the thorium it was probably due to a 

 relatively high proportion of ionium in the preparation. 

 When the freshly separated thorium contained radio-actinium, 

 the activity at first rose and later fell with the time ; when 

 actinium itself was present the activity rose only. It is prob- 

 able that the radio-active measurements were not sufficiently 

 sensitive to detect the activity of thorium and its products 

 when not accompanied by other active substances, so that when 

 thorium was separated from minerals containing but a small 

 proportion of uranium it was erroneously assumed to be 

 inactive. 



The existence of ionium also has a bearing on the conclusion 

 readied by Hahnf that thorium itself on disintegrating emits 

 an a radiation. Hahn has published as yet no quantitative 

 data in regard to this matter, but measurements which I have 



*Ber. d. cheni. Ges., xl, 4415, 1907. 

 f Ibid., xl, 3304, 1907. 



