26 THEORY OF COLLOIDAL BEHAVIOR 



seems a complete proof for the correctness of Donnan's theory of 

 membrane equilibrium, and also a further proof for the correctness 

 of the purely chemical conception of the combination of proteins 

 with acids and alkalies. For unless the proteins form true ioniz- 

 able salts with acids and alkalies they cannot fulfill the require- 

 ments of the Donnan equilibrium. 



It was, however, possible to go a step further, inasmuch as 

 these membrane potentials showed the typical colloidal charac- 

 teristics noticed in connection with viscosity, swelling, and 

 osmotic pressure, namely, the potential difference across the mem- 

 brane was depressed by the addition of neutral salts, was increased 

 by the addition of little acid to isoelectric protein, and depressed 

 by the addition of more acid; the depressing effect was in both 

 cases due to the ion with the opposite sign of charge to that of the 

 protein ion, and finally the depressing influence increased rapidly 

 with the valency of the active ion while the other characteristics 

 of the ion aside from sign and valency had no effect. In this 

 case there was not the slightest doubt that the effects were exclu- 

 sively the result of the Donnan equilibrium since they could be 

 mathematically predicted and calculated from the equilibrium 

 formula. 



The writer was able to show, in addition, that the analogous 

 behavior of the osmotic pressure and viscosity of protein solutions 

 could be explained and calculated on the basis of Donnan's 

 theory. 



It, therefore, turns out that two laws of classical chemistry 

 suffice to explain colloidal behavior quantitatively and mathe- 

 matically, and these two laws are the stoichiometrical law and 

 Donnan's theory of membrane equilibria. The proof for this 

 statement is the purpose of this volume. 



