248 ELECTROCHEMISTRY 



involving the minimal combining capacity of proteins, such as 

 casein, which are insoluble in the free condition. 



4. The Solubility and Minimal Combining Capacity of 

 Casein and of Serum Globulin in Solutions of Bases. — We have 

 seen that the relation between 61, the concentration of a KOH- 

 solution in which casein is dissolved, and X, the depression of 

 its conductivity which is caused by the casein, are connected 

 by the relation 



X X 10^ = 26,880 61 - ^^^^ bi"- 28.98 C; 



putting X equal to zero we obtain 



61 = 0.00114 C or 0.05536 C. 



Considering, for the present, only the smaller value of 61, we 

 see that when X = 0, that is, when the change in the conduc- 

 tivity of an alkaline solution which is brought about by dissolving 

 a given percentage of casein is zero, then the proportion of alkali 

 to casein is such that one gram of casein is combined with 

 11.4 X 10~^ equivalents of alkali. This is precisely the combining 

 capacity of casein at "saturation^' of the base with casein, that is, 

 when the base has dissolved the maximum amount of casein which 

 it will dissolve. 



The exact coincidence of the two numerical values, especially 

 when we consider that the above is computed by least squares 

 from a number of determinations which are apparently not 

 connected with estimates of the solubility of casein, is surprising, 

 and leaves no room for doubt that the magnitude of the two 

 quantities is determined by identical factors. This result is 

 probably to be interpreted as follows: The conductivity (= Xi) 

 of the solution of base to which casein is added is /ibi, where 

 n is the equivalent molecular conductivity of the base and 61 

 the equivalent concentration of the base. The conductivity 

 (= x) of the solution containing casein is fib + 96.43 (u + v) z, 

 where b is the equivalent concentration of the unneutralized 

 base, u +, v is the sum of the equivalent mobilities of the ions 

 and z is the equivalent concentration of protein ions. Assuming 

 that at the concentrations employed the casein salt is tolerably 

 completely dissociated z = pm, where m is the equivalent con- 

 centration of base neutralized by the protein and p the number 



