16 



THE NATURE OF THE CATALYTIC ACTION. 



At first sight the explanation of the catal^^tic action of the silver 

 would seem to be like that which is sometimes offered for the 

 development of a photographic j^late, namely, that the silver as it 

 is produced becomes supersaturated and finally reaches such a 

 concentration as to stop the reaction except where silver is already 

 present upon which it may deposit. If this explanation is correct 

 the phenomenon we are studying closel}'' resembles the simple 

 process of crystallization from a supersaturated solution. In fact, 

 I may point out that every case of such crystallization is a case of 

 autocatalysis, and that here also the reaction velocity rises and 

 falls as the crystallization continues — rises as the surface of the 

 crystal increases, falls as the degree of supersaturation decreases. 



Striking as the analogy is, it must be borne in mind that in this 

 case we are dealing with the action of one solid upon another, and 

 the great regularity of the reaction seems hard to reconcile with all 

 the other facts known concerning reactions in solid phases. 



As a result of other studies I have been inclined to entertain an 

 entirely different explanation of the phenomenon. In the course 

 of researches, some of which will shortly be published, I have been 

 led to believe in the great importance to chemistry of the two follow- 

 ing reactions: 



2H%H, 



20 %0, 



These two reactions have frequently been discussed in connection 

 with the theory of the nascent state, l)ut little attention seems to 

 have been paid to the immense importance of the velocity of these 

 reactions in a large number of processes, such as the union of 

 ox3"gen and hydrogen, combustions in general, reduction by 

 hydrogen, spontaneous decomposition of oxydizing and reducing 

 agents, and especially in the phenomenon of galvanic polarization. 

 Here, however, this larger proljlem concerns us only as it offers a 

 possible explanation of the autocatalysis of silver oxide. When 

 we consider the probable mechanism of the decomposition it 

 is evident that instead of the one reaction 2Ag20 = 4 Ag + 0^ we 

 may write with at least equal probability the two reactions 

 Ag^O = 2Ag + and 20 = 0,. If in fact the decomposition takes 

 place in these two stages the important question is, Which is the 



