200 



ELECTROCHEMISTRY 



The relation between m, the amount of alkali neutralized by the 

 casein, and 61, the alkalinity of the solution in which the casein 

 was dissolved, is shown graphically, for all of the concentrations 

 of casein employed, in the accompanying figure : 



0.05 



0.04 



0.03 



0.02 



0.01 



b, 



0.01 



0.02 



0.03 



0.04 



0.05 



The ordinates = m = the concentration of KOH neutralized 



by 0.5%, 1%, 1.5%, 2.0% and 3% casein. 



The abscissae = 6 : = the concentration of the KOH solution 



in which the casein was dissolved. 



It will be understood, of course, that the curves only represent 

 this relation for the alkalinities of the original solutions in excess 

 of that necessary to dissolve all of the casein. For an ordinary 

 acid, forming only one salt with the base, which did not undergo 

 hydrolytic dissociation, the curve would, of course, be a straight 

 line parallel with the horizontal axis. It will be seen that as the 

 proportion of base to casein declines, the combining capacity of 

 the casein tends to become directly proportional to the concen- 

 tration of the base, but that as the proportion of base to casein 

 (and the excess of unneutralized base) becomes large, the com- 

 bining capacity of the casein tends towards constancy, i.e., in 

 comparatively strongly alkaline solutions the behavior of casein 

 approximates more and more to that of an ordinary acid. 



These results are to be interpreted as follows: When just 

 enough alkali (= 11.4 X 10~ 5 equivalents per gram, Cf. Chap. V) 



