52 



THEORY OF COLLOIDAL BEHAVIOR 



the more from that ratio the higher the pH, as the theory 

 demands. 



The curves in Fig. 8 represent the values for the cubic centi- 

 meters of 0.1 N acid found in combination with 1 gm. of originally 

 isoelectric gelatin in 100 c.c. solution at different pH. The 

 results are tabulated in Table III. The table shows that 

 within the limits of accuracy of the experiments, at the same pH 

 approximately equal numbers of cubic centimeters of 0.1 N HC1 

 and 0.1 N H 2 S0 4 are in combination with 1 gm. of originally 

 isoelectric gelatin in 100 c.c. solution, while about three times as 

 many cubic centimeters of 0.1 N H 3 PO 4 are in combination. The 

 number of cubic centimeters of 0.1 N oxalic acid in combination 

 with 1 gm. of gelatin is less than twice that of HC1 as long as the 

 pH is above 3.0, while below 3.0 the combining ratio of the two 

 acids is approximately as 1:2, as the theory demands. 



TABLE III. CUBIC CENTIMETERS OF 0.1 N ACID IN COMBINATION WITH 

 1 GM. OF ORIGINALLY ISOELECTRIC GELATIN IN 100 c.c. SOLUTION 



These experiments corroborate our conclusion that acids 

 combine stoichiometrically with proteins if the hydrogen ion 

 concentration is properly taken into consideration. 



Similar experiments were made with casein prepared after the 

 method of L. L. Van Slyke and J. C. Baker, 1 who described in 



1 VAN SLYKE, L. L. and BAKER, J. C., J. Biol Chem., vol. 35, p. 127, 

 1918. 



