THEORIES OF COLLOIDAL BEHAVIOR 



115 



since swelling might be directly due to the existence of this water 

 jacket, and viscosity should also increase with the mass of water 

 surrounding each particle. If an acid, e.g., HC1, is added to 

 isoelectric gelatin, the latter will be transformed into gelatin 

 chloride which, being a salt, is strongly dissociated. The more 

 acid is added the more gelatin is transformed into gelatin chloride. 

 We have shown in Chap. V that the curves for osmotic pres- 

 sure, swelling, and viscosity reach a maximum at a pH varying 

 between 3.5 and 2.8, and that they then drop. Pauli assumes 

 that the drop is due to a repression of the degree of electrolytic 

 dissociation of the gelatin chloride (or any protein-acid salt) 

 through the addition of more acid on account of the common 

 anion. It should, however, be mentioned that Pauli 1 and 

 Manabe and Matula 2 state that the maximum of the curves 

 occurs not at pH between 3.5 or pH 2.8, but at pH 2.1 or 2.0. 

 Table X shows that the pH for the maximal values of the 

 physical properties of gelatin, crystalline egg albumin, and 

 casein solutions is considerably higher than 2.1. In fact at a 

 pH of 2.1 the osmotic pressure of gelatin chloride and albumin 

 chloride solutions is half way down between that at the maxi- 

 mum (pH 3.4) and at the minimum (the isoelectric point, 

 pH 4.7). 



TABLE X 



The assumption that the maximum lies at pH 2.1, therefore, 

 does not agree with the observations made on the physical 

 behavior of the three proteins mentioned in Table X. It might 

 be true for the viscosity of solutions of blood albumin, on which 



1 PAULI, W., " Kolloidchemie der Eiweisskorper," Dresden and Leipsic, 

 1920. 



2 MANABE, K. and MATULA, J., Biochem. Z., vol. 53, p. 369, 1913. 



