Catalytic Phcmomena with Allotropy. 249 



by the word " Allotropj'," and in what follows it will be 

 attempted to refer a number of catalytic phaenomena to allo- 

 tropic conditions. 



I must first of all adduce, as a most remarkable fact, that the 

 greatest number and the most striking actions of contact are to 

 be observed in oxygen compounds, of which peroxide of hydrogen 

 affords the most instructive example. 



A series of simple substances, as, for instance, platinum, gold, 

 iridium, silver, carbon, &c., without materially taking part in 

 the decomposition, decompose this compound into water and 

 common oxygen gas. Other catalysing substances of a com- 

 pound nature, in decomposing the peroxide of hydrogen, suffer 

 themselves a decomposition, as, for instance, the oxides of the 

 previously-mentioned metals, which, as is well known, are com- 

 pletely reduced; or a number of metallic peroxides which lose pai't 

 of their oxygen, as, for instance, the puce oxide of lead, the black 

 oxide of manganese, &c. 



Since their discovery by Thenard, these phfenomena of decom- 

 position have justly excited much attention, on account of their 

 unusual character, and they have been the chief means of direct- 

 ing the theoretical chemist to the investigation of catalytic phfe- 

 nomena. The catalysis of peroxide of hydrogen may therefore 

 be considered as a fundamental phfenomenon with just as much 

 reason, as we look upon the electrolysis of water as the type of 

 all electro-chemical decompositions. 



Now, if it were possible to make out the ultimate cause of the 

 catalytic decomposition of peroxide of hydrogen, we might also 

 be able to understand that of the catalysis of othei", at any rate 

 of oxygen compounds; — in the same manner as the correct 

 explanation of the electrolysis of water necessarily leads also 

 to the explanation of the electrolytic decomposition of all oxygen 

 compounds, of potash, of oxide of lead, &c. 



For this reason, therefore, I will select the peroxide of hy- 

 drogen as the subject on which to make the attempt to esta- 

 blish the views on the relation of catalysis to allotropy, which 

 I have in past years incidentally brought forward on various 

 occasions. 



So long as that fact was still unknown, the establishment of 

 which 1 hold to be the greatest discovery which has been made 

 in modern times in the field of chemistry, the fact, namely, that 

 simple bodies are capable of existing in very different conditions, 

 not only in respect of their chemical, but of their physical rela- 

 tions, so long there could be no hope of obtaining an insight 

 into the ultimate reason of catalysis, because, in my opinion, 

 the direct cause of this phsenomenon is to be sought in allotropic 

 relations. 



