Boltwood — Ionium, a New Radio-active Element. 369 



were not practicable because of the very limited amount of 

 material available, but over three years later the substance 

 was again tested and found to have apparently lost none of its 

 original activity. The material was again obtained in hydro- 

 chloric acid solution and the active substance was found to be 

 precipitated by treatment with an excess of sodium thiosul- 

 phate. This close agreement with the properties of " actin- 

 ium " given in Debierne's papers appeared to remove all doubt 

 as to the identity of the active substance. 



In the winter of 1903-1904 I made a rather systematic 

 investigation of the constituents of a number of radio-active 

 minerals, in the course of which I frequently observed that 

 the rare earths freshly separated from certain primary urani- 

 nites, and other similar minerals containing uranium and thor- 

 ium, always had associated with them a highly radio-active 

 substance. It was further noted that when a solution of the 

 chlorides of the earths was treated with an excess of sodium 

 thiosulphate, the active substance was almost entirely precipi- 

 tated with the thorium. The material remaining in the filtrate 

 was essentially inactive when first prepared, but gained in 

 activity slowly, until at the end of several months it was nearly 

 as active as the thorium precipitate from which it had been 

 separated. The activity of the thorium preparation remained 

 nearly constant during the same period. It was also found 

 that if a little thorium salt were added to the solution of a 

 mineral initially free from thorium (for example, carnotite) 

 and the thorium afterwards separated in the usual manner, an 

 active substance was obtained with, the thorium which appeared 

 to be identical with that obtained in the other cases. If, 

 instead of a thorium salt, a solution of rare earths from cerite 

 was added to the solution of the uranium mineral and these 

 earths were again separated, a highly active body was found 

 to have been removed with them. 



It was at first supposed that these results could be explained 

 on the assumption that the active material which was found 

 to accompany the thorium was Debierne's "actinium," while 

 that which accompanied the other rare earths was Giesel's 

 " emanium," a supposition which was somewhat supported by 

 the fact that the production of a short-lived emanation could 

 be detected in the earths in all cases and in the thorium only 

 occasionally. But even this hypothesis did not appear to be 

 defensible in the face of Debierne's emphatic assertions as to 

 the identity of "emanium" and "actinium." 



A number of unsuccessful attempts were then made to eifect 

 a separation of the thorium from the more strongly active 

 substance which was associated with it. The thorium w r as 

 repeatedly precipitated in dilute hydrochloric acid solution by 



