726 



ACTIVITY COEFFICIENT OF THE HYDROGEN ION 



tion. The velocity will therefore be considered as the increase ex- 

 pressed as per cent of the original titration divided by the elapsed 

 time in days. The resulting figure is the per cent increase in the 

 original titration per day, assuming that the amount of unhydrolyzed 

 gelatin remains approximately unchanged. In most of the experi- 

 ments determinations were made at several different times and the 

 velocities so obtained were averaged. In all cases the experiment 



380 



^ 340 



(0 



g 



300 

 260 

 220 



i: 180 



iS 



140 



100 



25 



3.0 35 4.0 



05 1.0 1.5 2.0 



YTdays 



Fig. 4. Comparison of the course of reaction with constant and with varying 

 hydrogen ion concentrations. 



was continued until the original titration had increased at least 

 50 per cent and in all, except a few between pH 5.0 and 7.0, until 

 the titration value had increased over 200 per cent. 



Concentration of Gelatin. — Since the reaction approximates that of 

 a monomolecular, the velocity when expressed as percentage change 

 should be independent of the gelatin concentration. Table III con- 

 tains the result of an experiment in which the gelatin concentration 

 was varied from 10 to 1.25 per cent; it shows that the velocity is 

 independent of the concentration for the early stages of the hydrolysis. 



