68 



THEORY OF COLLOIDAL BEHAVIOR 



One per cent solutions of originally isoelectric protein were 

 made, each solution containing a certain amount of an acid or of 

 alkali to give it a definite pH. In each case the collodion bag 



^0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 42 4.4 4.6 



FIG. 14. Influence of pH and valency of anion on osmotic pressure of solu- 

 tions of different gelatin-acid salts. The osmotic pressure is a minimum at the 

 isoelectric point, pH 4.7, rises with the addition of acid until pH is 3.4, and 

 then drops .upon the addition of more acid. The curves for gelatin chloride and 

 gelatin phosphate are identical. 



containing the gelatin solution was dipped, as described, into a 

 beaker containing 350 c.c. of water of originally the same pH as 

 that of the protein solution used. On account of the Donnan 

 equilibrium this equality of pH in the inside and outside solu- 



