Valency of the Radioelements. 403 



present has decayed to 1/1000 of its original amount. It is 

 much more difficult to prepare pure ThC than it is the cor- 

 responding products of the other two series. Perfectly pure 

 ThC cannot be obtained by von Lerch's method of depositing 

 it on nickel, nor by the author's method *, which consists in 

 depositing it on silver from a neutral solution of a silver 

 salt. Prepared by these methods the ThC was found to 

 contain 1 to 5 per cent, of the equilibrium amount of ThB. 

 Since ThB decavs to half value in 10 v 6 hours, and ThC in 

 1 hour, at the end of 10*6 nours one half of the disturbing 

 ThB is present with only 1/1000 of the ThC. It is thus 

 impossible to determine the diffusion constant of the Th C 

 prepared in this way. The author has shown in a previous 

 paper * that the ratio of the amounts of Th B and Th C 

 deposited on a metal plate from a solution is a function of 

 the potential difference metal/solution, and that the more 

 electronegative the latter is, the purer is the ThC deposited. 

 We succeeded in depositing very pure ThC by the following 

 method. A solution of NiCl 2 was added to the active HC1 

 solution, and in it was immersed a plate of nickel which had 

 been previously rendered passive by polarizing it in a solution 

 of caustic soda. After the plate was removed from the solution, 

 the ThC deposited on it was found to be very pure, the amount 

 of ThB present with it being only from '006 to *02 per cent. 

 The diffusion experiment occupied 0*313 days. The con- 

 centration of ThC in layer I was '00418 of that of the 

 original solution, and in layer II *056. Since, however, a 

 portion of the ThC did not diffuse as ThC but resulted from 

 the ThB diffusing wjth it, it was found, that in spite of the 

 very great purity of the ThC used, a not inconsiderable 

 correction had to be applied. When this was done the values 

 of the concentrations given above become '0035 and '048 

 respectively. The following are the results obtained: — 



0-119 

 313x0-66- 

 0-119 

 0-314 x 0-680 



dj 4 o. 2 = „ ,„!:!:_ =o-58 



Dgo. 2 = _,"_,_ =0-56 



-p.1 U'liy 0-K7 



Vu °- 0== 0-282 x 0^24 ~ U 

 n 11 Q' 11 9 —0-58 



The mean value Di 8 °=0-625 sq. cm. per day. 



The valency of ThC is therefore 2. 



* Phil. Mag. vol. xxiii. p. 628 (1912). 



