THEORIES OF COLLOIDAL BEHAVIOR 119 



exclude the assumption of a high degree of hydration of protein 

 ions. 



The theory of adsorption is used to explain the precipitation of 

 colloids by low concentrations of salts. The experiments de- 

 scribed in the second, third, and fourth chapters of this book flatly 

 contradict the assumption of such an adsorption when the con- 

 centration of salts is low. 



The adsorption theory, the aggregate theory, and the hydration 

 theory cannot explain the features of colloidal behavior enu- 

 merated at the beginning of this chapter. 



As long as chemists continue to believe in the applicability 

 of the adsorption formula to the behavior of proteins, no scientific 

 theory of colloidal behavior will be possible. We intend to show 

 in the second part of the book that such a theory can be given on 

 the basis of the stoichiometrical proof that proteins form true 

 salts with acids and alkalies, and that these salts lead to the 

 formation of protein ions. Colloidal behavior is due to the fact 

 that these protein ions cannot diffuse through many membranes 

 which are permeable to the majority of crystalloidal ions, or that 

 protein ions form solid gels in which cohesive forces prevent their 

 diffusion, while such gels are permeable to crystalloidal ions. The 

 theory of the equilibrium conditions resulting from this difference 

 in the diffusibility of the two opposite ions of an electrolyte was 

 developed by Donnan. These equilibrium conditions give rise 

 to forces, such as P.D., osmotic pressure, etc., which are the only 

 cause of colloidal behavior. It will be shown that Donnan's 

 theory gives not only a qualitative but a quantitative and 

 mathematical explanation of colloidal behavior. 



