230 /Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE, 



I. Chemistry and Phystcs. 



1 . Mesothorium. — The existence of this radio-active element as 

 one of the products of thorium was established in 1907 by Hahn, 

 who showed that its half decomposition period was about 5% 

 years, and that it was separated from thorium in the commercial 

 extraction of the latter from its ores. Later, Hahn was able to 

 find this substance in the residues from the extraction just men- 

 tioned, and he showed that it is not directly transformed into 

 radiothorium, but that there is an intermediate product with a 

 half-period of 6-2 hours, which he called mesothorium II. Hahn 

 has recently been able to concentrate this last substance to such 

 an extent that the i-adio-activity of the product is several times 

 greater than that of pure radium salts. 



W. Marckwald has now made some interesting observations 

 in regard to these substances, for it appears that nothing has been 

 published concerning the chemical properties of mesothorium I. 

 He had occasion to examine a "radium preparation" which had 

 been manufactured from the residues of uranium and thorium 

 ores. This preparation, consisting chiefly of barium chloride, 

 gave a y-ray radiation corresponding to more than 1 per cent of 

 radium chloride, but the radium emanation obtained from it 

 corresponded to only about 0"2 per cent of radium. A further 

 study of the product showed that about 80 per cent of the y-radi- 

 ation came from mesothorium II, for when an aqueous solution of 

 the salt was treated with a trace of ferric chloride and made 

 ammoniacal the mesothorium II was precipitated with the ferric 

 hydroxide. The precipitate gave a strong y-radiation, while the 

 barium chloride recovered from the nitrate by evaporation had 

 lost almost the whole of this radiation. However, while the pre- 

 cipitate lost its activity at the rate of one-half in about 6 hours, 

 the salt regained the greater part of its activity within a day. 

 The precipitate by ammonia must have contained also the 

 radiothorium produced by the mesothorium, and in fact this was 

 found to be the case, as the precipitate gave the a-rays of the 

 thorium emanation after the disappearance of the mesothorium II. 

 Mesothorium is evidently entirely analogous to radium in its 

 chemical behavior, for Marckwald has been unable to find any 

 means of separating the two. This is interesting in connection 

 with the fact that no chemical method is known for separating 

 the four elements, thorium, radiothorium, ionium and uranium X, 

 and it appears that radium and mesothorium form a similar group, 

 which possibly may contain other members also. It is evident 

 that radium preparations are liable to be contaminated with meso- 

 thorium, and since radium has a period of existence about 300 

 times as long as the other, this contamination is of much import- 



