Chemistry and Physics. 79 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Parent- Substance of Radium. — Hahn has given an 

 account of the views that have been brought forward in regard 

 to the origin of radium, together with some of his own recent 

 observations. As soon as its rate of decay was observed, it was 

 necessary to suppose that radium is being formed from something 

 else, for the solid crust of the earth is so very old that even if the 

 whole earth had been originally composed of this substance it 

 would long since have disappeared. After some time it was 

 established that radium was produced by the much more slowly 

 decaying element uranium, but it was shown also that there must 

 be one or more intermediate products between the two. It was 

 observed by Boltwood in 1906 that an actinium solution showed 

 an undoubted increase in radium, and he believed that actinium 

 must be the direct mother substance, but Rutherford soon showed 

 that it was not actinium, but some unknown substance present 

 with the actinium. Boltwood has since found that the hypothet- 

 ical element follows the reactions of thorium, and gives peculiar 

 a-rays, and he has named the new element ionium. Hahn now 

 states that he also has found in another way that the direct parent 

 of radium follows the chemical reactions of thorium, and may 

 thus be obtained from uranium minerals. He has found, in fact, 

 that old preparations of thorium salts from monazite contain 

 considerable amounts of radium, while newer preparations from 

 the same source contain much less, and he has succeeded in 

 showing an increase, in the course of a few months, in individual 

 samples of these thorium salts. In an indirect way Hahn has 

 calculated the period of decay of radium from the results of his 

 experiments with the monazite product, and has obtained 3250, 

 2840, and 2630 years as the result. These figures correspond as 

 closely as could be expected with Rutherford's calculation, 2600 

 years, and are entirely at variance with the results recently ob- 

 tained by Cameron and Ramsay, 163 years. — Berichte, xi, 4415. 



h. l. w. 



2. The Reduction of Arsenic Trisulphide and Pentasidphide 

 to Disulphide. — It was noticed by Eheenfeld that in a certain 

 qualitative test for arsenic a red precipitate was obtained, when 

 a stannous salt was present, in the place of the usual yellow pre- 

 cipitate of sulphide of arsenic. This led him to examine the 

 action of stannous chloride in the presence of strong hot hydro- 

 chloric acid upon the two sulphides of arsenic, and he found that 

 both were thus readily and completely converted into the red 

 disulphide : 



As 2 S 3 + SnCI s + 2HC1 = As„S 2 + SnCl 4 + H 2 S 

 As 2 S 5 + 3SnCl 2 + 6HC1 3 = As 2 S 2 + 3SnCl 4 + 3H 3 S 



