772 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
1818 , no new fact of the slightest importance has been added to its history. The 
properties however of which I speak, can all be observed with the solution of the 
peroxide of barium, in hydrochloric or acetic acid, which can be readily prepared. 
The properties of this solution are different according- as it is alkaline or acid. The 
alkaline solution is of an unstable nature; even at ordinary temperatures it continu- 
ally loses oxygen, and on heating undergoes rapid decomposition. The acid solution 
is more permanent, may be long kept without sensible alteration, and may even be 
heated to the boiling-point with no evident evolution of gas. Either solution, how- 
ever, is violently decomposed when certain substances (among which finely divided 
carbon or platinum are very effective) are thrown into it. In these cases the peroxide 
is decomposed, while the carbon and platinum remain, as far as we know, unaltered. 
There are however other bodies which cause this decomposition with perhaps greater 
energy, and themselves undergo a chemical change of the most surprising nature; 
these bodies are all those metallic oxides which can readily be reduced, — the oxides 
of gold, and silver and mercury, and the peroxides of lead, manganese, nickel and 
other similar substances. These bodies decompose the solution, as does platinum or 
carbon, while the substances themselves also, during the decomposition, lose oxygen, 
and are reduced either to a metal or to a lowei- degree of oxidation. The solution, 
whether acid or alkaline, is ever decomposed by these bodies ; but the facility with 
which the substance itself is reduced, and in some cases whether this reduction takes 
place at all, depends upon the neutral or acid condition of the solution, and varies 
with the particular substance taken in a way on which it is not now necessary to 
dwell. The decomposition caused by platinum and carbon, however strange, is not 
quite without parallel. But the simultaneous reduction of the peroxide of hydrogen 
and the oxide of silver is a solitary fact, by the side of which chemists have been able 
to place scarcely an analogous much less a similar instance. Yet eminent chemists 
have offered an explanation of these phenomena, and if these are adequate, further in- 
quiry is unnecessary. I shall not criticise the absolute or the relative value of these 
explanations ; but they add so much to the interest of the question, so clearly show 
the difficulties under which chemical theory has laboured in dealing with these facts, 
and also, as I believe, how inadequate it has proved to meet them, that I shall briefly 
mention the most remarkable. 
The following quotation gives the impression made by these facts upon Thenard, 
who first discovered them : — 
“Quelle est la cause des phenomenes que nous venons d’exposer? Voila main- 
tenant ce qu’il s’agit de rechei-cher. Pour cela qu’il nous soit permis de rappeler ceux 
que presentent foxide d’argent et fargent avec le nitrate oxigene neutre du potasse. 
L’argent tres divise degage rapidement foxigene de ce sel ; il ne s’altere point, et le 
nitrate oxigene devient nitrate neutre. 
“ L’oxide d’argent degage plus rapidement encore que fargent foxigene du nitrate 
oxigene ; lui-meme est decompose, il se reduit, fargent se precipite tout entier, et fon 
