JOHN H. NORTHROP 



721 



ture would have on the pH. In order to determine the value of this 

 temperature effect a series of gelatin solutions containing 2 per 

 cent gelatin and having a pH of from 0.0 to 14.0 was made up. The 

 pH was adjusted by varying amounts of HCl, NaOH, Na2C03, and 

 sodium citrate. The total salt content of all the solutions was between 

 0.02 and 0.05 N. The pH of these solutions was then determined 

 at 25° and at 37°C. (The electrodes regulated at 37°C. were put 

 at the author's disposal by Dr. Glenn E. Cullen). The results are 

 summarized in Table II. The Cqh was calculated by the formula 

 Ch Coh = Kw (or pH + pOH = Log Kw). The value of AV at 25° 

 was taken as 1 X IQ-i^ and at 40° as 2.8 X10-". It was found 

 that the hydrogen ion concentration was independent of the tem- 



TABLE II. 

 Efect of Temperature on pH of Gelatin Solution. 



perature from pH 0.0 to pH 8.8, and that the (calculated) hydroxyl 

 ion concentration was independent of the temperature from pH 11 

 to pH 14. Between pH 8.8 and 11.0 the concentrations of both 

 hydrogen and hydroxyl ions increased with the temperature. In all 

 the other experiments therefore the hydrogen ion concentration was 

 assumed to remain the same at 25° and 40°C. on the acid side of 

 pH 8.5, and the hydroxyl ion concentration was assumed to remain 

 constant on the alkaline side of pH 11.0. The experiments which 

 fell between pH 8.8 and 11.0 were measured at 37°C. 



The Course of the Reaction. — It has been known for a long time that 

 proteins may be hydrolyzed to the amino-acids by prolonged heating 

 with acids or alkali. The kinetics of the reaction, however, have 

 received little or no attention. Since it was desired to compare the 



