774 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
case, is a problem which remained to us, and which, in the case of one at least of 
these experiments, it was my hope to solve. 
Hitherto, in the breaking up of the oxide of silver and the peroxide of hydrogen, 
no chemical fact has been recognised but the simultaneous decomposition of two 
chemical substances. This is that fact for which it has been so difficult to account. 
Were it, for example, a hydride of silver which was thus decomposed and water 
formed and not simply oxygen, the experiment would have attracted no attention. 
On the view I have given, the formation of the oxygen itself is as truly a chemical 
synthesis as the formation of water, and may be substituted for it in a chemical 
change. This supplies an explanation of these facts at once adequate and simple; 
the oxide of silver in this experiment being reduced by the oxygen of the peroxide 
of hydrogen, just as in other cases it might be by hydrogen ; the formation of 
the silver from the particles of which it is composed being the corresponding fact 
in the decomposition of the oxide of silver to the formation of water in the peroxide, 
so that we may represent the change thus : — 
HO O O Agi Agi=H0+0,+ Ag. 
V ) 
No one can be more sensible than I am of the wide interval which exists between 
such a mode of representing a chemical change and an ascertained fact. The very 
form in which I have just expressed the decomposition involves an important assump- 
tion, an assumption indeed on which, in my opinion, the whole question rests. If it 
be true that these bodies are thus decomposed in definite and equivalent proportions, 
and that the simultaneous decomposition of the bodies proceeds according to this law, 
it is impossible to deny the chemical relation of these changes and the mutual che- 
mical action of the substances ; and, on the other hand, if the formation of this oxygen 
is to be regarded as a true chemical synthesis, this synthesis must follow the universal 
law of the formation of chemical substances, and the masses must combine in definite 
and equivalent proportions. It is only the apparent absence of this relation between 
the decomposing bodies which removes fermentation from ordinary chemical changes, 
and causes its chemical nature to be denied; and in that parallel which Liebig 
draws between these decompositions and fermentation, it is tacitly assumed that in 
this case also, as well as in the case of fermentation, no such relation exists. The 
following words of Liebig, from tiie paper I have already referred to, clearly show 
this point: — “^A certain quantity of ferment is required to cause fermentation in a 
portion of sugar ; its action however is no action of mass, but is entirely limited to its 
presence up to that moment when the last atom of sugar is decomposed. It is there- 
fore no peculiar body, no substance or matter which effects decomposition, but these 
are the carriers of an activity* which extends itself over the sphere of the decomposing 
body.” 
* “Trager einer Thatigheit.” Liebig’s Anualen, vol. xxx, p. 279. 
