708 



DONNAN EQUILIBRIUM AND OSMOTIC PRESSURE 



values which the neglect of the protein value in the calculated curves 

 postulates. 



Procter assumes in his theory of swelling that the protein particles 

 do not participate in the osmotic pressure inside the gel, and the 

 writer is willing to admit that the same assumption may be neces- 

 sary for the osmotic pressure of the protein solutions. The fact 

 that the maximal observed osmotic pressure of gelatin solutions agrees 

 with the maximal pressure calculated, without regard to the possible 

 osmotic pressure caused by the protein ions, seems to agree with 

 Procter's view. In this case, we should have to say that the curves 

 for the observed values coincide with the curves for the calculated 

 values if the latter curves are moved to the right, parallel with 

 themselves. 



pH L6 1.8 ZO 22 2A Z<6 26 30 3.2 3.4 3.6 3.8 4.0 42 4.4 



Fig. 6. Comparison of curves for observed and calculated values of osmotic 

 pressure of solutions of 1 per cent crystalline egg albumin sulfate. 



VI. The Depressing Influence of Neutral Salts on the Osmotic Pressure 

 of a Gelatin Chloride Solution. 



The question arises whether the membrane equilibrium could also 

 be responsible for the depressing influence of salts on the osmotic 

 pressure of protein solutions of a given pH and concentration of 

 originally isoelectric protein. Although Donnan has shown that 

 such a result is to be expected from his theory, the theory does not 

 include all the facts in the case of gelatin chloride solutions. If on 

 one side of the membrane there be a solution of NaCl, on the other 

 side a colloidal salt NaR, where R is the colloidal ion, the real osmotic 

 pressure {P^ of the colloidal solution NaR can, according to Donnan, 



