98 



THEORY OF COLLOIDAL BEHAVIOR 



properties of proteins can also be shown for the influence of 

 alkalies. Thus, the addition of KOH to Na gelatinate of pH 12.0 

 depresses the viscosity in the same way as the addition of KC1 

 (Fig. 32) ; while the addition of little KOH to Na gelatinate of 

 pH 4.8 to 8.0 increases the viscosity, and the addition of KC1 to 

 Na gelatinate always depresses the viscosity. The depressing 

 effect of salts on the viscosity of solutions of metal gelatinate is 



1 



ft.JdL 1L JtLliJl JHL 11 M ^^ 



u 6192409620451024512 256 1Z8 64 32 16 



Concentration 



FIG. 32. The depressing effect of KOH and KC1 on Na gelatinate of pH 12.0 

 is practically the same. 



due to the cation of the salt added, that of bivalent cations 

 being greater than that of monovalent cations, while the valency 

 of the anion has no effect. 



We have already stated that the addition of neutral salt to 

 isoelectric gelatin leaves the viscosity and osmotic pressure of the 

 solution practically unchanged. This fact is of great importance 

 for the theory of colloids. 



The depressing effect of neutral salts on the physical prop- 

 erties of proteins is, therefore, the same phenomenon as the 

 drop in the curves of these properties when too much acid or too 

 much alkali has been added. It is due to the fact that in all 



