Conditions of Molecular Action. 371 



soon cease to exist as such, and would lose its catalytic property, 

 it becomes obvious that catalytes must be chemically indifferent 

 to the substances they act upon. And not only is this the 

 case in fact, but we find that all the substances which have the 

 greatest catalytic energy display chemical indifference, not alone 

 towards those substances which they affect, but also towards or- 

 dinary chemical reagents. 



Thus, among metalloids, charcoal is at once the most energetic 

 in molecular actions and the least attracted chemically ; pounded 

 glass and sand, compounds of silica, also rank high amongst ca- 

 talytes. Among metals, only those placed at the highest point 

 of the scale, as least subject to the action of oxygen (the 

 most powerful chemical agent) — metals like platinum — these 

 alone act catalytically, without change of chemical constitution. 

 This fact is very clearly shown by some experiments made in the 

 year 1834, by Dr. Charles Henry and my father, "on the 

 Action of Metals in determining gaseous combination"*. They 

 proved that the oxidizable metals, such as copper, cobalt, nickel, 

 lead, iron, silver, even when in a state of minute subdivision 

 (produced by reducing their oxides by hydrogen), did not them- 

 selves act catalytically, but in every case their oxides possessed 

 the power of determining the union of oxygen and hydrogen. 



The oxides whose power of assisting the combination of oxygen 

 with various substances has been best observed are lime, alumina, 

 binoxide of manganese, sesquioxide of iron, sesquioxide of chro- 

 mium, sesquioxide of nickel, protoxide and sesquioxide of cobalt, 

 protoxide of cadmium, hydrated sesquioxide of uranium, prot- 

 oxide of copper, red oxide of lead, protoxide and binoxide of tin, 

 tungstic acid, and oxide of silver. And amongst these it is in- 

 teresting to mark that Mr. Eyre Ashby, who has most carefully 

 studied this subject, observes that it is not those oxides which 

 have an excess of oxygen, nor yet those which most readily part 

 with it, whose influence is most felt, but "it is the sesquioxides 

 which have the strongest tendency to produce and maintain the 

 catalytic glow, and which do produce it in every case in which 

 they are not decomposed by the heat necessary to begin the 

 operation/'' 



In relation to this condition of molecular action, it is worthy 

 of notice that ferments, the most remarkable substances in the 

 organic kingdom for their catalytic power, belong universally 

 to the class of colloid bodies, one of whose chief characteristics is 

 that of "chemical indifference "j\ 



* A paper on the subject was read before the Literary and Philosophical 

 Society by Dr. Henry, and published in the London and Edinburgh Phi- 

 losophical Magazine and Journal of Science for May 1835. 



f Even during those fermentations in which certain changes are pro- 



2B2 



