732 PROCEEDINGS OF THE AMERICAN ACADEMY. 



velocity we have been studying, and that it is the reaction which is cata- 

 lyzed by the presence of the silver. In fact silver is known to catalyze 

 many gaseous reactions. 



The above line of reasoning would apply equally to other reactions in 

 which oxygen is evolved. Let us consider two cases as different from 

 this one as possible, namely, the decomposition of hydrogen peroxide 

 and of potassium chlorate. Both of these reactions may be accelerated 

 by catalyzers ; the catalysis of the latter by manganese dioxide, and of the 

 former by manganese dioxide, platinum, and other substances, are familiar 

 to all chemists. If in these cases also we assume that the union of two 

 atoms of oxygen is the reaction, the slowness of which retards the de- 

 composition, then this reaction is catalyzed by platinum and by manga- 

 nese dioxide. These substances, therefore, if our assumptions are correct, 

 ought to aid the decomposition of silver oxide as silver does. We have, 

 therefore, the means of testing our suppositions by direct experiment. 



Two tubes, each containing 5 grams of silver oxide, and one contain- 

 ing besides .25 gram pure platinum black, were put into the thermostat 

 simultaneously. The one containing platinum began to give off oxygen 

 at once. At the end of two hours it was evolving 1 c.c. in twelve sec- 

 onds, and the other tube 1 c.c. in ten minutes. 



A similar experiment was tried with another preparation of silver 

 oxide, in which case the silver oxide containing platinum was entirely 

 decomposed in twenty-four hours and the other not until after three days. 

 In a similar experiment manganese dioxide, which had been previously 

 heated to redness, was used in place of the platinum, and showed also 

 marked catalyzing power. 



These results speak strongly in favor of the truth of the assumptions 

 that we have made. It is true that catalysis of silver oxide and hydrogen 

 peroxide by platinum may be specifically different, but let us consider a 

 few of the reactions, where oxygen is a factor or a product, which are cata- 

 lyzed by platinum: the combustion of gases such as hydrogen, methane, 

 ammonia, vapor of methyl alcohol ; the decomposition of oxidizing agents 

 such as hydrogen peroxide ; the electrochemical solution of oxygen at the 

 cathode and its separation at the anode. Certainly there seems to be 

 ground for believing that in all these cases, while several reactions occur 

 together, an important and in many cases the only factor in determining 

 the speed of the whole reaction is the speed in one direction or the other 

 of the intermediate reaction, 20 = Oo, and that this reaction is catalyzed 

 by platinum and by a number of other substances, as well of course in 

 one direction as in the other. 



