ELECTROLYTIC DISSOCIATION 65 



represents the fraction decomposed, and the total number 

 of molecules, counting each ion as such, exceeds the 

 normal amount in the ratio 



I : (T a) + 2 a I : I + or, 

 so that we have 



i = i+a= I+ 

 Moo 



Comparing a special case directly with de Vries' experi- 

 ments in which urea was chosen as normal substance, we 

 find for the concentrations mentioned the following results 

 (plasmolysis p, no plasmolysis n, intermediate state np) : 



Normality Urea Nitre 



= 0-285 0-3 0-315 0-33 0-345 



n n np p p 



N = 0-16 0-17 0-18 0-19 0-20 



n n np p p 



so that 0-315 normal urea is isotonic with 018 normal 

 nitre. Accordingly for a 018 normal nitre solution 



0*315 



' = -StlF = '** 



By the conductivity we get, interpolating for the same 

 solution, 



jui = 99-7, so that i i+ = 14- ^^ = 1-81. 



Moo 1 '22, 



The agreement is here satisfactory. Unfortunately it has 

 not in all cases remained equally so on application of the 

 more exact procedure of the freezing point. 



It would be very desirable to form a collection of results 

 obtained by the freezing-point method, to serve as a test 

 of Arrhenius' law by comparison with the collection of data 

 011 conductivity 1 . 



Under these circumstances it seems desirable to choose 

 Ostwald's ' law of dilution ' as a second characteristic, and 

 divide electrolytes into two groups according as they follow 

 it or not. 



1 Das Leiti-ermogen der Elektrolyte, inslesondere der Losungen, Kohlrausch and 

 Holbom. Leipzig, 1898. 



E 



