Valency of the Radio-elements. 589 



dissociation similar to that obtained by v. Ende from a con- 

 sideration of the influence of the addition of salt on the 

 solubility of lead chloride. 



For the diffusion constant of thorium B mixed with lead 

 chloride the following values were obtained : — 



Dl6°-2« Dl8°« 



L «267 1>05 ™ 



IL 2^280 i' 02 1,()7 



IV - TO279 1*01 i' 06 



L iTOSS I'M 1-08 



IL iW^2l • °- 98 i' 05 



IV - « 1-01 1-09 



Mean value for D i8 o is 1*07 sq. cm. per day. 



In this experiment thorium B chloride (Th B Cl 2 ) and 

 lead chloride were mixed, and had therefore the same degree 

 of dissociation, and they showed, within the limits of ex- 

 perimental error, the same coefficient of diffusion. Further, 

 the velocity with which a 1/5000 N lead chloride and 

 1/100 N hydrochloric acid solution containing thorium B 

 diffused into a 1/10,000 N hydrochloric acid solution was 

 determined. The quantity of lead here was so small that a 

 gravimetric estimation could not be carried out, and the 

 diffusion constant was only ascertained by comparing! the 

 activities of single layers ; the results were 



Di6o-2. -Dl8°« 



L rs&a> °' 67 °- 70 



IL m!&m °' 64 °- 67 



IV - im&m ' C3 ' 66 



Mean value for D i8 o is # 68 sq. cm. per day. 



At this concentration, therefore, thorium B measured in 

 lead chloride is almost completely dissociated, and pos- 

 sesses a diffusion constant characteristic of doubly charged 

 ions. 



Phil. Mag. S. 6. Vol. 27. No. 160. April 1914. 2 R 



