204 ELECTROCHEMISTRY 



itself speaks very strongly in favor of the view that the protein 

 compounds which are formed do not yield, by electrolytic disso- 

 ciation, the corresponding acid anions. They, moreover, find 

 that the combining capacity of deaminized gelatin is hardly 

 inferior to that of normal gelatin. 



The electrometric method of measuring the combining capaci- 

 ties of proteins for acids and bases has also been employed by 

 D'Agostino and Quaghariello (2), Rohonyi (61), Manabe and 

 Matula (38), Blasel and Matula (4), Ringer (52) and Schmidt 

 (63) (64). 



2. The Combining Capacity of Casein for Bases and of Ovo- 

 mucoid for HCl at Absolute Neutrality. — A number of investi- 

 gators have shown (66) (34) (71), by direct titration to neutrality 

 to litmus, that the combining capacity of casein at absolute 

 neutrality is constant, that is, independent of the total dilu- 

 tion of the system. The potentiometric determinations, cited in 

 the above tables, enable us to confirm these observations. It 

 will be recollected that the OH' concentration in the solutions 

 containing casein was determined by measuring the potential 

 between two hydrogen electrodes, the one dipped in a solution 

 containing a given concentration of casein, the other in an ex- 

 actly similar solution to which no casein had been added. Plot- 

 ting a curve in which the reaction of the solutions containing 

 no casein form the abscissse and the potentials between the two 

 solutions the ordinates, the reactions {= x) oi the solution to which 

 the given concentration of casein had to be added in order to 

 procure an exactly neutral solution * is given by the intersection 

 of this curve with the curve defined by the formula: 



y = 0.4107 - 0.0601 logio x. . 



The points of intersection of these curves may be found, with 

 suflScient approach to accuracy, in the following way: The values 

 of y in the above curve corresponding to x (alkalinity of the 

 solution containing no casein) = 0.0025; 0.005; 0.0075; 0.010; 

 0.015 and 0.020 are computed and these points are marked upon 

 accurately ruled "squared paper" and joined by straight lines. 

 Experimental values of w lying upon each side of its value at 

 neutrality, in each solution, are then also marked off upon the 



* Taking the H+ concentration at absolute neutrality at 30 degrees as 

 1.47 X 10^; cf. Kohlrauch and Heydweiller (33). 



