42 



THEORY OF COLLOIDAL BEHAVIOR 



since, in the latter, part of the H ions of the free HC1 added 



+ 



becomes part of the complex gelatin cation, gelatin-NH 3 . The 

 figures in Table I then prove that a strong acid, like HC1, com- 

 bines with the protein according to Werner's ideas. 



TABLE I 



It was found that whenever the same amount of acid was added 

 to the same amount, e.g., 1 gm., of originally isoelectric gelatin, 

 making up the volume to 100 c.c., the pH of the solution was 

 always the same ; so that we can say how much Cl is in combina- 

 tion with the protein if we know the pH of the gelatin chloride 

 solution. The lower the pH, the more chloride enters into com- 

 bination with the protein, until finally, all the protein is trans- 

 formed into protein chloride. 



It seems that when an acid, e.g., HC1, is added to isoelectric 

 gelatin (or any other isoelectric protein), an equilibrium is 

 established between free HC1, protein chloride, and non-ionogenic 

 (or isoelectric) protein; when alkali is added to isoelectric gelatin, 

 an equilibrium is established between metal proteinate, non- 

 ionized protein, and free alkali (above pH 4.7). Similar results 

 had been obtained by S0rensen. 1 



1 S0RENSEN, S. P. L., Studies on proteins : Compt. rend. trav. Lab. Carlsberg, 

 vol. 12, Copenhagen, 1915-17. 



