DONNAN EQUILIBRIUM AND THE PHYSICAL PROPERTIES 



OF PROTEINS. 



III. Viscosity. 



By JACQUES LOEB. 

 {From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, May 20, 1921.) 



/. Volume of Solute and Viscosity. 



The viscosity of freshly prepared gelatin solutions is affected in 

 a similar way by the pH as are the electromotive forces, the osmotic 

 pressure, and the swelling. We have been able to show that the in- 

 fluence of the pH on the e.m.f. can be accounted for quantita.tively 

 on the basis of the Donnan equilibrium,^ and that with the excep- 

 tion of one or two minor deviations the same is true for the osmotic 

 pressure." Procter and Wilson's theory of swelling is also based on 

 Donnan's theory of membrane equilibrium.^ Fig. 1 is the expres- 

 sion of the influence of the pH on the viscosity of 0.5, 1, and 2 per 

 cent freshly prepared gelatin chloride solutions at a temperature 

 of 24°C. The abscissa are the pH of the gelatin solution, while 

 the ordinates are the relative viscosities of the gelatin solutions com- 

 pared with that of water at the temperature of the experiment. 



These curves are modified if the viscosity of the gelatin solution 

 is not measured immediately, but only after the solution has been 

 standing for some time. In this case the curve changes inasmuch 

 as the viscosity rises everywhere but the more rapidly, the nearer 

 the pH is to that of the isoelectric point. In this case the curves 

 representing the influence of pH on the viscosity of gelatin solution 

 no longer resemble the. curves representing the influence of the pH 



^Loeb, J., J. Gen. Physiol., 1920-21, iii, 577, 667. 



2 Loeb, J., /. Ge7i. Physiol., 1920-21, iu, 691. 



3 Procter, H. R., /. Chem. Soc, 1914, cv, 313. Procter, H. R., and Wilson, 

 J. A., /. Chem. Soc, 1916, cix, 307. 



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