JOHN H. NORTHROP 741 



unless some means are provided such as buffer solutions for keeping 

 it constant. The same is true for the hydroxyl ion concentration. 

 According to the classical definition, therefore, the reaction is not 

 catalytic since some of the catalyst combines with the products of 

 the reaction and so would effect the final equilibrium. It seems 

 probable that this is always true to some extent and that as was 

 emphasized by Stieglitz, a "catalytic" reaction is merely the limiting 

 case of an ordinary reaction in which the products of the reaction 

 dissociate more or less completely liberating more or less of one of the 

 original substances (cf. also Lewis^^ and Falk-''). If the dissociation 

 is complete no change could be detected in the concentration of one 

 of the reacting substances and the reaction would be monomolecu- 

 lar in regard to the other. If there were no dissociation the reaction 

 would, of course, be bimolecular. The present reaction is inter- 

 mediate between the two. It is exactly analogous in this respect 

 to the hydrolysis of gelatin by pepsin. 



SUMMARY. 



1. The hydrolysis of gelatin at a constant hydrogen ion concen- 

 tration follows the course of a monomolecular reaction for about 

 one-third of the reaction. 



2. If the hydrogen ion concentration is not kept constant the 

 amount of hydrolysis in certain ranges of acidity is proportional 

 to the square root of the time (Schiitz's rule). 



3. The velocity of hydrolysis in strongly acid solution (pH less 

 than 2.0) is directly proportional to the hydrogen ion concentration 

 as determined by the hydrogen electrode i.e., the "activity;" it is 

 not proportional to the hydrogen ion concentration as determined 

 by the conductivity ratio. 



4. The addition of neutral salts increases the velocity of hydrolysis 

 and the hydrogen ion concentration (as determined by the hydrogen 

 electrode) to approximately the same extent. 



^^ Lewis, W. C, McC, A system of physical chemistry, 2nd ed., London, 

 New York, Bombay, Calcutta, Madras, 1918-19, i, 416. 



^'^Falk, K. G., The chemistry of enzyme actions, American Chemical Society 

 Monograph Series, New York, 1921, 33. 



