370 Boltwood — Ionium, a New Radio-active Element. 



an excess of sodium thiosulphate, was precipitated in solutions 

 of the neutral nitrate with hydrogen peroxide, and the hydrox- 

 ide suspended in water was treated with hydrofluoric acid. 

 The material obtained after this series of operations was to 

 all appearances and chemical tests pure thorium hydroxide, 

 but it still possessed a high activity out of all proportion to 

 the actual amount of thorium present. The possibility of the 

 presence of a new and previously unidentified radio-active 

 substance naturally suggested itself, but in the absence of more 

 convincing evidence the agreement with the chemical behavior 

 of " actinium " as given by Debierne appeared to offer an 

 insurmountable objection to such a conclusion. The numerous 

 radio-active changes which had already been shown to exist in 

 the actinium series were suggestive of the possibility of fur- 

 ther complicated relations of a similar nature. The problem 

 was therefore temporarily abandoned. In a paper on the 

 radio-activity of thorium minerals and salts,* in discussing the 

 results obtained by Hofmann and Zerban, it was stated that : — 

 " This element (actinium) invariably accompanies the thorium, 

 and in the thorium separated from minerals containing much 

 uranium and little thorium the activity due to the actinium 

 may be much greater than the activity due to the thorium 

 present." 



Later Experiments. 



The definite and constant proportion which has been shownf 

 to exist between the quantities of uranium and radium in 

 minerals could be satisfactorily explained only by the assump- 

 tion that radium was a disintegration product of uranium. 

 On the other hand, attempts to observe the growth of radium 

 in solutions of purified uranium salts had given results;}: which 

 demonstrated that radium was not directly formed from ura- 

 nium at anything like the rate which was to be expected from 

 the value for the life of radium as calculated by Rutherford. 

 The discrepancy could be accounted for if an intermediate, 

 slowly changing product intervened between uranium and 

 radium, but the existence of such a product had not yet been 

 established. In the search for this product my attention was 

 again directed to the active substances separated with the rare 

 earths from uranium minerals, as the anomalies already men- 

 tioned had been observed in these preparations, and as, more- 

 over, my earlier experiments had shown that practically all of 

 the permanent activity, other than that due to uranium, radium 

 and polonium, was associated with this material. 



* This Journal, xxi. 424, 1906. 



f Boltwood, Phil. Mag., ix, 003, 1905. 



% This Journal, xx, 239, 1905. 



