Volatility of Thorium D. 813 



Case II. 



(i.) ThD recoiling from Active Deposit which had previously 

 been treated with Hydrochloric Acid, 



It was considered o£ interest to investigate by direct 

 experiment whether or not Th D recoils from a compound 

 cf Th G "free," or as a similar compound of ThD. For 

 example, does Th D recoil from " Th G chloride " in the form 

 of " Th D chloride " or in the form of " pure Th D " ? 



Thorium active deposit on a clean platinum foil was dissolved 

 in pure concentrated hydrochloric acid and dried carefully. 

 A second platinum plate was exposed as negative electrode 

 to this active deposit for 20 minutes, and the activity of the 

 Th D thus obtained measured as before. The subsequent 

 process of heating and measurement of activity were carried 

 out as described in the previous experiments. It was found 

 that Th D collected in this way has the same temperature of 

 volatilization as untreated Th D, i. e. 520° C. This would 

 appear at first to prove conclusively that Th D recoils as the 

 " atom of Th D " and not as the " chloride/'' otherwise the 

 temperature of volatilization would have been in the neigh- 

 bourhood of 270° G. It must be noticed, however, that a 

 series of experiments like the one just described extends over 

 an interval of several hours, and in that time a large pro- 

 portion of the "ThC chloride" originally in the active 

 deposit will have been replaced by Th G growing from 

 " Th B chloride." 



This new Th G may or may not be in the form of " chloride. " 

 To overcome this difficulty it became necessary to repeat the 

 experiments, this time using Th G free from Th B. 



(ii.) ThD recoiling from Th C (obtained from a Solution 

 of Active Deposit in Hydrochloric Acid by von Lerclis 

 Method) . 



An active layer of Th G chloride was deposited on a highly 

 polished nickel plate by immersing it for some time in a hot 

 solution of thorium active deposit in hydrochloric acid. 

 This nickel plate, after being carefully dried, then served as 

 a source of Th D, which was collected by recoil on a platinum 

 foil and treated as in the previous experiments. The results 

 in this case also were in good agreement with those obtained 

 in I. (i.) and II. (i.), i. e. the temperature of volatilization of 

 the product obtained by recoil from Th G chloride is approxi- 

 mately 520° G., giving further support to the view that Th D 



