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II. Supplementary Paper on certain Phenomena of Voltaic Ignition , and the Decom- 
position of Water into its Constituent Gases by Heat. By W. R. Grove, Esq. 
Received November 26, — Read November 26, 1846. 
In selecting the above title, I endeavoured to give as clear an enunciation of the 
phenomena to be described in the paper as was consistent with the brevity usual in 
a title. 
An exception has, however, been taken to it, that as the effects of decomposition 
are produced by ignited platinum, the phenomena may result from that obscure 
mode of action called catalysis. That I did not intend to exclude from consideration 
any possible action of the substance employed, will be evident from the paper itself, 
in which I have called attention to the general production of catalytic effects by 
solid bodies. 
Whatever value or novelty there may be in the facts I have communicated, is the 
same whether they be regarded as resulting from catalytic or from thermic actions. 
If the action be catalytic, it is one absolutely the reverse of that usually produced by 
platinum, and therefore just as much at variance with received experience as decom- 
position of water by heat would be ; the effect of platinum, like that of heat, on the 
elements of water having been hitherto known only as combining them. With regard 
to any theoretic views I may have advanced, I by no means attach the same import- 
ance to them as I do to the facts themselves, though I consider it necessary for the 
collation of facts, and desirable for the progress of science, that an author pretending 
to communicate new results should give with them the impressions which led to their 
discovery, and the inferences which he regards as immediately deducible from them. 
No expression can be given to facts which does not involve some theory, and ad- 
mitting the difficulty (perhaps insuperable) of correctly enunciating new phenomena, 
and the probability of future discoveries entirely changing our views regarding them, 
I cannot at present see that the title of my paper could be altered without being 
open to greater objections. I am of this opinion, not so mhch because other bodies 
than platinum will produce the effect, as I shall presently show, nor from the fact 
that the electrical spark will decompose aqueous vapour, though these are arguments 
in its favour; but from the following considerations. The catalytic action of plati- 
num will induce or enable combination to take place where there is already a strong 
affinity or tendency to combine, as with mixed oxygen and hydrogen gases ; it will 
also induce decomposition where the affinities are extremely weak, or in a state of 
unstable equilibrium, as in Thenard’s peroxide of hydrogen ; again, where there are 
MDCCCXLVII. D 
