776 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
powdered substance, moistened with water on the back of the hand, gives no sensible 
heat. The peroxide was carefully freed from any adhering glass, or pieces in which 
the absorption was incomplete, from which it may be distinguished by the colour, 
and was preserved in stoppered bottles over sulphuric acid ; a precaution which was 
desirable, as the preparations had to be preserved for a long time without any altera- 
tion in the per-centage of oxygen. 
The peroxide of barium thus obtained is a perfectly stable body. When dry, it is 
only a very intense heat which can drive off its oxygen. It is nearly insoluble in water, 
the filtered solution giving no gas with oxide of silver, which would be the case if 
any substance were dissolved ; and when preserved from the action of the carbonic 
acid of the air, it may be long kept even in water without any sensible evolution of 
gas. When the powdered substance is even boiled with water, no gas is given off; and 
after long boiling, on examining the dried residue, I have found that the effect of 
boiling has actually been to increase the per-centage of oxygen, the baryta, of which 
a certain quantity is always present, being dissolved. These facts are contrary to the 
usual statements*, and probably this stability only belongs to a very pure substance, 
for a small quantity of the oxides of iron or of manganese would alter these reactions. 
The peculiar experiments of the reduction of the metallic oxides, as stated by 
Thenard and other chemists, are referred to the peroxide of hydrogen ; and it is on 
the peculiar instability of this body that the explanation of Liebig of these pheno- 
mena rests, the spontaneous decomposition of the peroxide being considered as ante- 
cedent to and necessary to set up the action in the other substances. I was however 
anxious to see whether the peroxides of metals themselves would not produce similar 
effects ; and on placing the peroxide of potassium (the mass which is produced by 
the action of potassium on melted nitre) in contact with moist chloride of silver in 
water, I found that the chloride was reduced, just as it might be by zinc, and oxygen 
evolved ; and the same takes place with the iodide, bromide, cyanide, nitrate and oxide 
of silver and with other metallic combinations. Water alone, as is well known, de- 
composes the peroxide of potassium ; this body therefore was in a similar unstable 
state to that supposed in the peroxide of hydrogen ; but on extending my experiments 
to the peroxide of barium itself, 1 found that all the reductions wdiich could be made 
with the peroxide of hydrogen, took place with this body also with the greatest faci- 
lity. Finely-divided platinum, silver or carbon, decompose it, but far less rapidly 
than those substances which are themselves also decomposed. I will not here discuss 
the general chemical reactions of this peroxide, but defer their consideration until I 
can treat with advantage, in a more exact manner, of the general theory of this action. 
The facts I have just mentioned gave a direction to my experiments, and instead 
of the peroxide of hydrogen, the preparation and preservation of ivhich involved 
many difficulties, and with which it was inconvenient to work, I determined to use, 
in the experiments I proposed, the peroxide of barium itself. 
* See Barium superoxyd, Handworterbuch der Chemie, vol. i. p. 667. 
