576 



AMPHOTERIC COLLOIDS. V 



for swelling for gelatin oxalate, and chloride, which are also approxi- 

 mately identical.^ The fact that the curves for viscosity and swell- 

 ing are similar to those for osmotic pressure has been pointed out so 

 often in previous papers that we need not dwell further on this 

 point. 



300 

 Z75 



250 

 225 

 200 

 175 

 150 

 125 

 100 



75 



50 



25 







pH 25 27 29 3,1 33 35 37 39 41 43 45 47 



Citric diCid • 

 Acetic acid o 



Fig. 8. Showing identity of influence of citric and acetic acids upon osmotic 

 pressure of gelatin solution for the same pH. Curves in Fig. 8 are identical with 

 those in Fig. 7. 



^ The close proximity of the effects of different acids does not harmonize with 

 the contention of the colloid chemists who report a typical difference in the 

 effects of the acids according to the nature of the anion. This is an error due 

 to the fact that they failed to determine the pFI of their solutions and to com- 

 pare the behavior of gelatin solutions of the same pH, comparing instead the 

 effects of equimolecular concentrations of different acids, without making any 

 of the necessary corrections discussed in this paper. 



