Valency of tlie Radio elements. 395 



The total number N A of anions migrating is 



and since N a =Nk we get 



d±_ RT(U-V) cfc 



^T-ne[c(U + V) + 7fU' + V)] das' 



Hence the total number of cations migrating is 



_ U^ <h ( 2V + (U'4-V) 7 /c \ 



1Nk_ n (iAU + V + (U 7 + V) 7 | C j J 



and the total number of anions migrating is 



YRT dc ( 2 U + ( IP + U) 7 /g \ 

 ^a"" 7i rf«VU + V + (U' + V)7/c/; 



The diffusion constant of the cation D' in excess of the 

 union is 



N K It 



■-It- 



I ax 



From equation (1) the usual diffusion coefficient D is 



2UV dc 

 V + V d£' 



and therefore we get 



o 



/ ^U' + v 



D ~ . , U'+,V : 



and for the case <y= co , D' U + V 



GO 



For the particular case of RaClo diffusing in an excess o£ 

 hydrochloric acid, we have 



U =1-036 u . 10~ 5 = 0-00059, 

 V =1-036 v . 10" 5 = 0-00068, 

 U' = 1-036 wM0" 5 =0-00329 ; 



where u, v, and u' are the absolute mobilities of the ions of 

 radium, chlorine, and hydrogen, respectively. 



