AT THE MOMENT OF CHEMICAL CHANGE. 
803 
increases with the temperature. By increasing the mass of the oxide or chloride, on 
the other hand, the velocity of the chemical action is relatively increased ; in this case 
therefore we have a great reduction. Again, a substance in a fine state of division 
is decomposed more rapidly than one which is dense and compact ; here, therefore, 
and in other similar differences, is the cause of the different results given by different 
preparations of the peroxide*. 
By the words contact and chemical, I mean to express no theory, and am indeed 
drawing but a momentary distinction between facts, for I cannot believe that the 
one of these portions of oxygen is formed according to one law and the other in a 
different manner, that the one fact is a chemical synthesis and the other not. The 
only difference between them I believe to be, that in the case of the action I have 
called chemical, the peroxide of barium decomposes peroxide of lead, or oxide of 
silver, or the like ; and in the contact action one particle of peroxide of barium decom- 
poses another particle of the same substance, the platinum, silver oxide or other 
body causing that chemical relation between the particles which renders the decom- 
position possible. The important question as to the nature of that definite relation 
which these experiments indicate between the contact action and the chemical action, 
I reserve for future inquiry. 
I have made various experiments to ascertain whether the same kind of reduction 
could be effected by means of other metallic peroxides, such, for example, as the per- 
oxide of lead or manganese, as with the peroxide of barium and potassium, but with- 
out success. I believe this to admit of a very rational explanation, and that this re- 
ducing power is a result of the peculiar chemical nature of the alkaline metals and 
their compounds ; in short, of what is usually termed their powerful chemical affini- 
ties and position on the electro-chemical scale, to which indeed we may distinctly 
trace it. This relation may be expressed in various ways, but which mean essentially 
one and the same thing. If, for example, in the last experiment we express the change 
which takes place thus — 
-l_ — -|_ — -I — 
Ba O O O H I=BaI-f O2+HO, 
V ) 
it follows, from the view I have given of the mutual relation of these particles, and the 
interdependence of these chemical changes, that we cannot substitute for the barium 
a metal which stands in a different chemical relation to the particles between which 
it is placed without altering the relation of all the other particles of the system, so 
that if the chemical difference on which combination depends does not exist between 
the metal and the iodine, neither can it exist between the particles of the oxygen. In 
this way the fact, at first sight very anomalous, admits of a very simple explanation, 
* I by no means wish to exclude from these a real chemical dilFerence in their nature, which the behaviour 
of certain analogous bodies leads me to suspect. 
5 K 2 
