236 THEORY OF COLLOIDAL BEHAVIOR 



exists probably also in the case of solutions of casein salts. 

 Solutions of Na caseinate are less opaque than those of casein 

 chloride (of the same concentration of originally isoelectric 

 casein) which indicates that the Na caseinate solution contains 

 more isolated casein ions and fewer submicroscopic solid particles 

 than the solution of casein chloride. 



The writer had already shown in a preceding chapter that the 

 maximal viscosity of a 1 per cent solution of casein chloride is 

 higher than the viscosity of solutions of Na caseinate of equal 

 concentration of originally isoelectric casein, while the osmotic 

 pressures of solutions of the two salts show exactly the reverse 

 relation, the maximal osmotic pressure of a 1 per cent solution 

 of Na caseinate being almost 700 mm. H^O while the maximal 

 osmotic pressure of a 1 per cent solution of casein chloride is 

 only about 200 mm. 



The solutions of crystalline egg albumin seem to consist (at 

 ordinary temperature and at not too high a concentration of 

 albumin and of the hydrogen ions) exclusively or almost exclu- 

 sively of isolated molecules or ions. Since the latter cannot 

 diffuse through a collodion membrane they give rise to a Donnan 

 equilibrium across the membrane and hence only the osmotic 

 pressure of solutions of salts of crystalline egg albumin is influ- 

 enced by electrolytes in the way demanded, while the viscosity 

 shows such an influence only to a negligible degree. 



2. It should be possible to give a more striking confirmation 

 of the reciprocal relation between the viscosity and the osmotic 

 pressure if we replace in a gelatin solution part of the dissolved 

 gelatin by equal weight of powdered gelatin. Such a substitu- 

 tion should increase the viscosity and diminish the osmotic 

 pressure of the solution. 



Figure 70 shows that the osmotic pressure of a 1 per cent solu- 

 tion of originally isoelectric gelatin diminishes the more the more 

 we replace the dissolved gelatin by small granules of powdered 

 gelatin. The ordinates of the upper curve represent the values 

 of the osmotic pressure of a 1 per cent solution of originally 

 isoelectric gelatin at different pH, the pH serving as abscissae of 

 the curves. The acid used was HC1, and the curve is the usual 

 one. At the beginning of the experiment the gelatin solution was 

 rapidly heated to a temperature of 45C. and rapidly cooled to 



