MR. GROVE ON THE DECOMPOSITION OF WATER BY HEAT. 
7 
detail. The effect, did not take place with perfectly dry gas over mercury, and I 
thence was led to attribute it to some combination with aqueous vapour ; the in- 
crease turned out to be occasioned by the formation of carbonic acid. By agitation 
with caustic potash or lime water the gas was reduced to exactly its original bulk, 
but it was now found to be mixed with a volume of hydrogen equal to the volume 
of carbonic acid by which it had been increased ; it was thus perfectly clear that 
half a volume or one equivalent of oxygen derived from the vapour of the water, had 
combined with one volume or equivalent of carbonic oxide, and formed one volume 
or equivalent of carbonic acid, leaving in place of the carbonic oxide with which it 
had combined, the one volume or equivalent of hydrogen with which it had been 
originally associated. 
Comparing the last experiment, viz. that of mixed carbonic acid and hydrogen with 
this, I was naturally struck with the curious reversal of affinities under circumstances 
so nearly similar ; in the one case, hydrogen taking oxygen from carbonic acid to 
form water and leaving carbonic oxide ; in the other, carbonic oxide taking oxygen 
from water to form carbonic acid and leaving hydrogen. 
I thought much upon this experiment ; it appeared to me ultimately that the ignited 
platinum had no specific effect in producing either composition or decomposition of 
water, but that it simply rendered the chemical equilibrium unstable, and that the 
gases then restored themselves to a stable equilibrium according to the circumstances 
in which they were placed with regard to surrounding affinities ; that if the state of 
mixed oxygen and hydrogen gas were, at a certain temperature, more stable than 
that of water, ignited platinum would decompose water as it does ammonia. 
This is a very crude expression of my ideas, but we have no language for such 
anticipatory notions, and I must adapt existing terms as well as I am able. 
It now appeared to me that it was possible to effect the decomposition of water by 
ignited platinum; that, supposing the atmosphere of steam in the immediate vicinity 
of ignited platinum were decomposed, or the affinities of its constituents loosened, if 
there were any means of suddenly removing this atmosphere I might get the mixed 
gases ; or secondly, if, as appeared by the last two experiments, quantity had any 
influence, that it might be possible so to divide the mixed gases by a quantity of a 
neutral ingredient as to obtain them by subsequent separation (or as it were filtration) 
from the neutral substance. Both these ideas were realized. 
To effect the first object, after, as usual in such circumstances, much groping in 
the dark, I cemented a loop of platinum wire in the end of a tube retort similar to 
fig. 3, and covered it with asbestos, ramming this down so as to form a plug at the 
closed extremity of the tube, the platinum wire being in the centre. My object was, 
by igniting the platinum wire, to drain the water out of the asbestos, and the ignited 
wire being then in an atmosphere of steam, I hoped the water would by capillary 
attraction keep constantly oozing down to the platinum wire as the steam or decom- 
posed water ascended. The experiment did not succeed ; the water established a 
