Volatility of Thorium D. 815 



the active deposit. It also accounts for the low temperature 

 of volatilization of Th D in that case, when compared with 

 the temperature of volatilization of the Th D obtained by recoil 

 from the active deposit dissolved in hydrochloric acid. 



Summary and Conclusions. 



1. The temperatures of volatilization of Th D obtained 

 under varying circumstances have been determined. 



Temperature of volatilization of Th D untreated with acid 



= 520° C. 



,, „ „ „ treated with nitric acid 



= 520° C. 



„ „ „ „ „ hydrochloric acid 



= 270° C. 



2. The results support the views of Schrader, Russell, 

 Barratt and Wood, on the formation of definite chemical 

 compounds of the active deposits of the various radio-active 

 substances. 



3. Th D recoils from Th C in the atomic form, whatever 

 the form of the parent ThC(freeor combined with acids). 

 Evidence has been obtained, in the case of Th D recoiling 

 from thorium active deposit dissolved in hydrochloric acid, 

 that a portion of the recoiling atoms recombine with the 

 free chlorine which is liberated on disintegration of molecules 

 of Th chloride. 



Note on the Relative /3 Activities of Th C and Th D. 



The foregoing experiments have shown that Th D is com- 

 pletely volatilized at temperatures above 700° 0. Recently 

 Barratt and Wood * have found that the temperature of 

 volatilization of Th C is about 780° O. Consequently, 

 when the active deposit is heated to temperatures above 

 700° C. the Th D is completely separated from the Th C, and 

 by heating the active deposit to a suitably high temperature 

 it is possible to remove practically the whole of the Th B also, 

 thus leaving Th C almost " pure/'' The method of volatili- 

 zation has proved a simple and efficient means of obtaining 

 Th C free from Th D. Methods used by other experimenters t 

 have depended on the difference of electrochemical behaviour 



* Loc. cit. 



t Von Lerch, Wien. Ber. cxiv. ii. a (1905) ; von Hevesv, Phil. Mag. 

 p. 628, April 1912. 



