658 Ratio between Uranium and Radium in Minerals. 



these of Mile. Gleditsch that the ratio for thorianite is 

 20 per cent, higher than for pitchblende. It is interesting 

 to notice that investigations published subsequently to 

 Mile. Gleditsch's work (Marckwald, Ber. Chem. Ges. 1910, 

 xliii. p. 3420 ; Soddy, Trans. Chem. Soc. 1911, xcix. 

 p. 72) show that in separating the radium she must 

 also have separated the mesothorium quantitatively from 

 the thorianite, though this does not account for her 

 results. 



We are inclined to ascribe the undoubtedly high value 

 obtained for " Th I " to contamination with radium before it 

 came into our hands. All the other specimens were samples 

 of large quantities purchased direct from the importers, but 

 '• Th I " was obtained from a retail dealer who handles radium 

 preparations and sells spinthariscopes. We attach no im- 

 portance to the high result for the single specimen of 

 German East-African pitchblende, as the same doubt arises. 

 It came to us through Mr. Russell from Prof. Marckwald's 

 laboratory, where chemical work on radium has long been 

 carried on. 



With regard to the autunites, all of which came from 

 various mines in Portugal, the values range from that of 

 "A D," which has 74 per cent, of the equilibrium amount, to 

 that of "A S," which has only 24 per cent, and is the lowest 

 yet recorded, that described by Mr. Russell (Nature, Aug. 25, 

 1910) from Autun, Prance, having 27 per cent. It is inter- 

 esting to note that both these specimens "AD" and "AS" 

 were from the same property (compare Ann. Reports, 

 Chem. Soc. 1910, vii. p. 264). The pilbarite is also low 

 (64 per cent.;, but the mineral, described as probably a 

 hydrous pseudomorph of an anhydrous parent mineral, is 

 evidently much altered. 



The main point at issue, that possibly the life-period of 

 ionium is sufficiently extended to cause the equilibrium ratio 

 of radium to uranium to be less in a geologically recent 

 mineral like Joachimsthal pitchblende than in an ancient 

 mineral like thorianite, although no doubt still an open one, 

 certainly receives no support from these measurements. 



Physical Chemical Laboratory, 



University of Glasgow. 



March 22nd, 1911. 



