AMPHOTERIC COLLOIDS. 



III. Chemical Basis of the Intluence of Acid upon the Physical 

 Properties of Gelatin. 



By JACQUES LOEB. 



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



(Received for publication, November 27, 1918.) 



/. 



Many of the authors who have worked on the physical chemistry of 

 proteins, Hke Hardy, Pauli, Michaelis, Robertson,^ and others, have 

 pointed out that the different properties of proteins, e.g. swelling, 

 viscosity, are affected by electrolytes in a parallel way, a fact which 

 suggests that these variations are due to the same variable. The 

 nature of this variable is not known and the majority of authors 

 believe it to be connected with the colloidal character of the proteins, 

 while others are inclined to assume a purely chemical or stoichiome- 

 trical relation. The reason for this doubt lies in the fact stated 

 appropriately by Pauli^ in discussing the influence of acid and alkali 

 upon the osmotic pressure of gelatin. 



Pauli and Handowski have pointed out that in these experiments too the 

 essential feature is the formation of ionic protein. But a satisfactory explana- 

 tion of this increase is still lacking, because we have no measurements of the 

 molecular concentrations with the aid of other methods, which prove that we are 

 dealing with a true osmotic pressure in the sense of van't Hoflf. 



Pauli assumes that the ionized protein undergoes a stronger "hy- 

 dratation" than non-ionized protein and that this hydratation ex- 

 plains the swelling of gelatin, as well as the apparent osmotic pressure, 

 the latter being only a phenomenon similar to swelling. 



^ The reader is referred for the literature on the subject to Robertson, T. B., 

 The physical chemistry of the proteins, New York, 1918. 

 ^ PauH, W., Fortschr. naturwiss. Forschung, 1912, iv, 245. 



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