610 



COLLOrOAL BEHAVIOR OF EDESTIN 



It will be observed that the agreement between the observed and 

 calculated values for the p.d, is within the experimental error, and 

 that the experiment includes that range of pH where the values did 

 not agree well in the case of the solutions without buffer. The curve 

 in Fig. 6 is of a different shape from that in Fig. 5 because the depress- 

 ing action of the anion of the salt has more effect in the less acid solu- 

 tions, since the concentration of the anion furnished by the acid is 

 originally less in such solutions. The existence of a difference in pH 

 in such buffered solutions and the agreement between the observed 



CO 



o 



> 



a 



0^ 



pH 3.2 3.4 3.6 3.8 4.0 4.2 44 4.6 4.8 



Fig. 6. Effect of pH on p. d. observed and calculated for 1 per cent edestin 

 acetate in m /lOO sodium acetate. 



and calculated values for the p.d. constitute a striking proof of the 

 validity of Donnan's theory. This experiment, therefore, supple- 

 ments the results in Tables VI and VII by proving that Donnan's 

 theory applies to solutions of edestin in acid in the region near the 

 isoelectric point as well as in more acid solutions. 



A further consequence of Donnan's theory, as applied by Loeb to 

 amphoteric colloids, is that the pH inside should become less than the 

 pH outside on the alkaline side of the isoelectric point of the protein ; 

 i.e., the p.d. should be opposite in sign to that found on the acid side. 

 This was tested by working with solutions of edestin in NaOH. It 



