JOHN H. NORTHROP 



737 



in the rates is not much greater than the experimental error. The 

 determination of the minimum was checked, however, by noting the 

 degree of liquefaction of the solutions after 90 days at 40°C. 10 

 cc. of the various solutions were brought to pH 5.0, the salt concen- 

 tration and total volume made the same in all the tubes, and the 

 tubes then immersed in a water bath at 5° for 2 hours. The degree 

 of liquefaction was then noted. The result is given in Table IX. 

 According to this determination the minimum point is about pH 

 6.5. 



Two hypotheses may be suggested to explain this anomalous in- 

 fluence of low concentrations of hydrogen and hydroxyl ions. First, 

 the velocity of hydrolysis is independent of the hydrogen ion con- 

 centration between pH 2.0 and 11 .0 (or is proportional to the product of 

 Ch X Cqh)- Second, some change takes place in the gelatin solution 



TABLE IX. 



in this range which causes the gelatin to hydrolyze very much more 

 rapidly and so compensate for the decrease in the Ch and Cjjq. 



It seems very unlikely from our knowledge of reactions in general 

 that the rate of a reaction should be quantitatively proportional to 

 the hydrogen ion concentration over a wide range and then suddenly 

 become independent of it, to become later directly proportional to 

 the hydroxyl ion concentration. 



If we assume temporarily that the rate really is proportional to the 

 hydrogen and hydroxyl ion concentration and that the discrepancy 

 between the observed rate and the rate calculated on this basis is 

 due to a change in the gelatin, we must assume that the gelatin 

 is changed to a form which is very much more rapidly hydrolyzed. 



ohscTVcd vclocilv 



The value of the expression will evidently be a mea- 



Ch + 30 CoH 



sure of this change. In Fig. 6 the logarithms of the values of 



this expression are plotted over the pH together with the titration 



