DECOMPOSITION OF WATER BY HEAT. 315 



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 car- 

 bonic 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 in- 

 fluence, 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 realised. 



To effect the first object, after, as usual in such circum- 

 stances, 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 



