238 THEOKIES AS TO ACTION OF 



higher local concentration than in the absence of the catalyst, 

 and accordingly the reaction will proceed more rapidly in this 

 portion of the system. If now the relative solubilities of the 

 substratum and products of reaction in the colloidal catalyst 

 portion and the remainder of the solution are such as to give 

 sufficient rapidity of diffusion, of the substratum into, and of the 

 products of reaction out of, the colloidal particles, then the reaction 

 as a whole will be hastened by the condensation within or upon the 

 colloidal particles. 



This view as to the mode of action of colloidal catalysts has 

 in recent times been prominently put forward, and the chemical 

 kinetics of reactions in such heterogeneous systems studied by 

 Bodenstein, Bredig, Goldschmidt, Findlay, von Ernst, and 

 others. 



It has been shown by Menschutkin that the nature of the solvent 

 exercises an enormous influence upon the velocity of the reaction, 

 so that the same reaction running at the same temperature but 

 in different media may occur at excessively different rates. Thus 

 the velocity of reaction between tri-ethylainine and ethyl iodide 

 was tested in eight different organic solvents and found to be 

 different in all of them, the extreme variation between acetophenone 

 in which it was greatest, and hexane in which it was least, being 

 no less than 720 times. 



Accordingly, if we may regard the colloidal enzyme and the 

 solution in which it is present as a heterogeneous system with two 

 distinct phases in which the substratum to be acted upon possesses 

 different reaction velocities, and also different solubilities, a scheme 

 is at hand by which the catalytic reaction can receive an explana- 

 tion in such cases. 



It may here be pointed out, as an extension of such a theory, 

 that it is not necessary that the catalyst should be colloidal pro- 

 vided that the substratum is in such a case a colloid. All that is 

 necessary is that there shall be a heterogeneous system with two 

 phases present, in one of which the velocity can be increased by 

 the presence of the catalyst. Thus in the case of a colloidal solution, 

 such as starch, undergoing catalysis by a non- colloidal catalyst, 

 such as dilute acid, the starch particles may be regarded as a phase 

 to which the hydrogen ions are attracted and become concentrated, 

 and in which they increase the velocity of reaction, the products 

 of reaction then rapidly diffusing out, through the large surface 



