AT THE MOMENT OF CHEMICAL CHANGE. 
769 
hydrogen) are to one another in the same polar relation, and fulfill the same part in 
the change as the two equivalents of the hydrogen itself in the decomposition of the 
hydruret. 
3. When a solution of bichromate of potash is poured into a strong and acid solu- 
tion of the peroxide of barium in hydrochloric or nitric acid, a violent effervescence 
and escape of oxygen takes place ; apart, these solutions are perfectly stable ; bring 
them together, they are both decomposed ; the chromic acid passes into chloride of 
chrome, the peroxide of hydrogen into water, and the oxygen formed is due to the 
simultaneous decomposition of both bodies, thus — 
3ClH-f 2Cr Og-f 3H02=Cr2 CI3-I-6HO+3O2. 
I certainly regard the oxygen itself, in this experiment, as the true reducing agent, and 
I believe that the chromic acid is decomposed by the oxygen of the peroxide of hydro- 
gen, according to the same law of decomposition, and for the very same reason, as 
it would be by hydrogen itself if a piece of zinc were thrown into the acid solution, 
this reason being the polarity of the particle induced by chemical change. In this 
experiment is brought before us, in a very forcible manner, the very slight difference 
which truly separates the phenomena of oxidation and reduction, which are usually 
regarded as so distinct. In speaking of the formation of sulphuric acid, I have said 
that the oxidation of sulphurous acid by nitric acid is to be attributed to a polar 
condition of the oxygen liberated from the nitric acid, which polar condition is in- 
duced by the formation of hyponitric acid within the system of which it forms a part. 
Now the formation of water in the peroxide of hydrogen is a fact precisely similar 
to the formation of the hyponitric acid in the nitric acid, and it might reasonably 
be anticipated that this oxygen would have a similar oxidizing power. This is in 
truth the case ; for when the temperature is low, the solutions dilute, and the experi- 
ment carefully managed, no gas is given off, but a deep blue solution is formed, 
containing perhaps, as stated by Barueswil*, who first examined this reaction, a 
higher oxide of chrome. This solution however rapidly decomposes, oxygen is 
evolved, the blue colour disappears, and the final result is the same as if the com- 
pound had never been formed. When manganate of potash, peroxide of manganese 
and various other substances are substituted for the chromate of potash in this expe- 
riment, a similar decomposition takes place, but without any signs of the intermediate 
stage of oxidation. Under other circumstances the oxidation and reduction may be 
separated. Thus, when peroxide of barium is thrown into an acid solution of the 
prussiate of potash, the prussiate is oxidized and the red prussiate is formed. When, 
on the other hand, the same experiment is made with the alkaline or neutral solu- 
tion of the red prussiate, oxygen gas is given off in abundance from the peroxide of 
barium as well as from the red prussiate, and the latter passes into prussiate. On 
adding to this solution an acid solution of perchloride of iron, care being taken that 
TMDCCCL. 
* Annales de Chimie, vol. xx. p. 364, 
5 F 
