$12 Mr. A. B. Wood on the 



It will be noticed that no Th D is volatilized till a tempe- 

 rature of about 520° C. is reached. At this point, however, 

 the percentage removed increases rapidly with small increases 

 of temperature, and at a temperature of about 700° 0. prac- 

 tically the whole of the Th D has been volatilized. The curve 

 bears a strong resemblance to that obtained by Barratt and 

 Wood * in the case of ThB. It is also interesting to note 

 that the temperature of volatilization obtained in the present 

 experiments agrees very well with the temperature obtained 

 by them in the case where the Th D was present in equilibrium 

 with Th B and C. 



(ii.) ThD dissolved in pure concentrated Nitric Acid. 



In this case the Th D obtained by recoil was dissolved in a 

 drop of nitric acid and rapidly dried. With a little practice 

 this could be done fairly quickly without serious loss due to 

 decay or volatilization in drying. When the foil was per- 

 fectly dry its activity was measured, the heating and sub- 

 sequent measurement of activity being the same as that 

 described above. The temperature of volatilization of Th D 

 treated with nitric acid was found to be exactly the same as 

 that of Th D undissolved in acid, and the curve of volatili- 

 sation is identical in both cases. Apparently, when treated 

 with nitric acid and heated, Th D is in the same condition as 

 when untreated with acid, i. e. either Th D is insoluble in 

 nitric acid or it at once forms an oxide when heated 

 afterwards. A few simple experiments proved that ThD 

 was quite soluble in nitric acid, so that the second alternative 

 seems to be the correct one. 



(iii.) Tk D dissolved in pure concentrated Hydrochloric Acid. 



In these experiments hydrochloric acid was used instead of 

 nitric acid, and the previous procedure repeated. The curve 

 of volatilization is shown in fig. 2 (B). The most noticeable 

 feature in this case is the low temperature of volatilization, 

 viz. about 270° C. Another important point is the striking- 

 resemblance between the two curves A and B, showing that 

 volatilization proceeds on similar lines in each case. The 

 low temperature of volatilization gives further support to the 

 view originally advanced by Schrader t that definite chemical 

 compounds of these infinitesimally small quantities of sub- 

 stance are formed, the chlorides in every case being much 

 more volatile than the untreated substance. 



* Loc. cit. 



t Schrader, loc. cit. 



