558 COLLOIDAL BEHAVIOR OF PROTEENS 



has been able to show that the conductivity measurements of protein 

 solutions contradict Pauli's ionization theory. 



The solution of the problem seems to lie in a field altogether 

 foreign to the speculations current in colloid chemistry, namely in the 

 Donnan equilibrium, which exists when a membrane separates two 

 solutions, one of an electrolyte for the ions of which the membrane 

 is permeable, and one of an electrolyte for one ion of which the 

 membrane is not permeable.^ It is immaterial whether the latter 

 ion is a colloid or a crystalloid; it is only necessary that it cannot 

 diffuse through the membrane. When a collodion membrane sepa- 

 rates a gelatin or albumin chloride solution of pH 3.3 from an aqueous 

 solution of HCl of originally the same pH (but without gelatin), the 

 pH is no longer the same on both sides of the membrane at the time 

 of equilibrium but is lower on the outside than in the gelatin solution. 

 The Donnan equilibrium demands in this case that acid be given off 

 from the gelatin chloride solution to the outside aqueous solution 

 (containing no gelatin). The writer has found that, e.g. a 1 per cent 

 gelatin chloride solution of pH 3.5 is in equilibrium with an aqueous 

 HCl solution of about pH 3.0.^ 



n. 



Gelatin chloride solutions containing 1 gm. of originally isoelectric 

 gelatin in 100 cc. solution and having a pH of 3.5 were made up in H2O 

 and in different concentrations of NaNOa varying from m/4,096 to 

 m/32 NaNOa, all of pH of 3.5. These solutions were put into collodion 

 bags connected with a manometer to measure the final osmotic pres- 

 sure of the solution. The collodion bags were put into HCl solution 

 of pH 3.0 made up in water and different concentrations of NaNOs, 

 the pH of the NaNOa solutions being also 3.0. These outside solu- 

 tions contained no gelatin. The collodion bags were put into these 

 aqueous solutions free from gelatin in such a way that the concentra- 

 tion of the NaNOs solution inside the collodion bag was always the 



* Donnan, F. G., Z. Ekktrochcm., 1911, xvii, 572. Donnan, F. G., and Harris, 

 A. B., J. Chem. Soc, 1911, xcix, 1554. Donnan, F. G., and Garner, W. E., 

 /. Chem. Soc, 1919, cxv, 1313. 



^ Loeb, J., /. Gen. Physiol, 1920-21, iii, 247. 



