90 



ION SERIES AND PROTEINS. 



The slight differences in the maximal height of the four curves are 

 within the limits of the accuracy of these experiments, and the same 

 or even greater variations may be observed when the same experiment 

 is repeated several times with the same acid. The maximal values of 

 osmotic pressure reached in these experiments at pH 3.5 are the same as 

 those reached with gelatin salts of any other monovalent anion, CI, 

 Br, NO3, phosphate, citrate, succinate, etc. 



S pn20 Z2 ZA 2.6 as 3.0 3.2 a4 3.6 3.8 40 42 44 4.6 46^. 



Fig. 1. The ordinates represent the number of cc. of 0.1 n acetic, mono-, di-, 

 and trichloracetic acids required to bring 1 gm. of isoelectric gelatin to the pH 

 indicated by the abscissas. Enough H2O was added to bring the gelatin-acid 

 solution to a volume of 100 cc. 



It follows from this that the conclusions which are based upon a 

 comparison of the quantities of the acid added instead of upon the 

 pH of the protein solutions cannot be correct. 



The reason why we get identical curves when we plot the osmotic 

 pressures as ordinates over the pH as abscissae seems to be as follows. 



When we add a definite small quantity of acid to 1 gm. of isoelectric 

 gelatin, melt, and bring the volume of the solution to 100 cc. by adding 

 H2O, part of the acid will combine with gelatin and part will remain 



