JOHN H. NORTHROP 739 



It must be remembered that a slight error in the pH determinations 

 causes a very large variation in the constant and that a shift of the 

 steeper portions of the titration curves of less than 0.2 pH will make 

 a difference in the value of K^ of several hundred per cent. It must 

 also be noted that the values on the figure are plotted as the logarithms 

 so that the discrepancies are larger than they appear. 



It may be pointed out that a reaction very similar to the above was 

 studied by Clibbins and Francis'^ in connection with the hydrolysis 

 of nitrosotriacetoneamine. In this case also the reaction is directly 

 proportional to the Cqh over a wide range and then becomes nearly 

 independent of it. In still more alkaline solution the velocity be- 

 comes inversely proportional to the Cqh- Clibbens and Francis con- 

 sider also that this is due to some change in the condition of the 

 substance undergoing the reaction but were unable to- account for 

 it quantitatively. Many reactions have been studied in which the 

 velocity of reaction of the ions was very different from that of the 

 free substance. Richards and StulP'' found that, in the reaction be- 

 tween oxalic acid and bromine, the divalent oxalate ion reacts very 

 much more rapidly than any of the other forms present. Stieglitz^* 

 accounted for the mechanism of the hydrolysis of the imiido-esters 

 by the hypothesis that the ester-salt hydrolyzed either more or less 

 rapidly than the free ester. Similar explanations have been proposed 

 by Acree, Goldschmidt, and others. 



It will be noted that the peculiar results obtained in the present 

 work are all in the range of acidity where the enzymes are active 

 and where the growth of microorganisms is possible. It seemed 

 possible, therefore, that the increased rate in this range might be 

 due to traces of enzymes or to the presence of bacteria or the action 

 of the various preservatives. The experiments were therefore re- 

 peated at a temperature of 65°, without the addition of preserva- 

 tives. Any traces of enzjrmes present would be inactivated very 

 rapidly at this temperature and their effect would be noticed only 

 for the first few hours at most. No such effect was noted. The 



23 Clibbens, D. A., and Francis, F., /. Chem. Soc, Tr. 1912, ci, 2358. Francis, 

 F., and Geake, F. H., Soc, J. Chem. Tr. 1913, ciii, 1722. 



24 Stieglitz, J., Am. Chem. J., 1908, xxxix, 29. 



