590 Dr. Gr. Hevesy on the Diffusion and 



An experiment, carried out under exactly similar conditions 

 as the last hut with the complete absence of lead chloride, 

 gave an identical value for the diffusion constant as 

 follows : — 



Di 6 °. Dl8°. 



L 2Wm 0>67 °- 70 



IL 'srSsB 0>66 O' 69 



0-57 

 IV * 2-24x0-408 °' 63 °' 66 



Mean value for D 18 ° is 0'68 sq. cm. per day. 



The diffusion constant of completely dissociated (thorium B) 

 chloride gives, therefore, the value 2 for its valency, in com- 

 plete agreement with Fleck's result* from the chemical 

 evidence that thorium B is non-separable from lead. The 

 former value of 1 found by the author is not that of thorium 

 B ions, but that of the complex (Th B) Cl 2 ions which were 

 predominant in a partially dissociated solution of thorium B. 



The Diffusion of Radium JE. 



In order to avoid convection currents it is necessary that 

 the specific gravity of the liquid in successive layers should 

 vary somewhat. Even in the last experiment disturbances 

 due to these currents were met with to some extent, but in 

 the case of radium E these difficulties are multiplied. In 

 order to obtain complete dissociation, diffusion must take 

 place in dilute acid solution. To obtain a difference in the 

 specific gravities of the two layers — the one containing 

 radium E and the other free from that substance — an addi- 

 tion of 5 per cent, of ethyl alcohol was made to the latter. 

 This addition did not influence the degree of dissociation f 

 of radium E, but decreased its mobility slightly, and thus 

 also its velocity of diffusion. In order to deduce the value 

 of the diffusion velocity from the value thus obtained, 

 one can either add a correction of 13 per cent, which 

 follows from the determination of Arrheniust, or one can 

 determine the diffusion velocity of radium D — the value of 

 which for water has been determined in the same alcoholic 

 solution as the radium E. This latter proceeding permits 

 the elimination of any other effects of the addition of the 

 alcohol. The diffusion constants which were obtained by 



* Fleck, he. cit. ; F. Paneth and Gr. Hevesy, Wiener Ber. p. 122 

 (1913). 



t Sv. Arrhenius, Zeit. phys. Chem. x. p. 51 (1892). 

 X Arrhenius, he. tit. 



