Mr. Grove on the Decomposition of Water by Heat. 27 



third of its original volume, in the greater number of instances 

 to one-fifth : this increase depended upon the intensity of ig- 

 nition, which it was very difficult to maintain at its maximum 

 on account of the frequent fusions of the platinum wires. 



Here again I had a long research and many erroneous 

 guesses, which I need not 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 increase 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 vo- 

 lume or equivalent of hydrogen with which it had been origi- 

 nally 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 car- 

 bonic acid to form water and leaving carbonic oxide ; in the 

 other, carbonic oxide taking oxygen from water to form car- 

 bonic acid and leaving hydrogen. 



1 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 de- 

 compose 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 



