132 THEORIES AS TO ACTION OF 



solution, and that the substratum possesses a higher solubility in 

 the particles of the ultra-microscopic emulsion, or by surface tension 

 is attracted in increased concentration to the surface of the particles. 

 In either case a portion of the system is obtained in a state 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 heterogensous systems studied by 

 Bodenstein, Bredig, Goldschmidt, Findlay, and 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-ethyl amine and ethyl iodide 

 was tested in eight different organic solvents and found to be 

 different in all of them, the extreme variation between acetophenon 

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

 no less than 720 times. 



Accordingly, if we may regard the colloidal enzyme and the 

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

 distinct phases in which the substratum to be acted upon possesses 

 different reaction velocities, arid also different solubilities, a scheme 

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

 tion in such cases. 



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

 it is not necessary that the catalyst should be colloidal provided 

 that the substratum is in such a case colloidal. 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, 



