18 
MR. GROVE ON THE DECOMPOSITION OF WATER BY HEAT. 
nicely-balanced compound affinities, it may change the chemical arrangement of the 
constituents of a compound, hut I do not know of any case in which a powerful 
chemical affinity can be overcome by catalytic action ; to effect this we require some 
natural force of greater intensity than that to be overcome. We might as well say 
that the platinum electrodes of a voltaic battery decompose water, as to say that 
platinum decomposes it in the case in question ; there, the force of electricity acts 
only by means of matter, and matter of a peculiar description ; its action also is only 
perceptible at the surface of this matter. I seek to use the expression in my title 
with reference to heat in a similar sense to that in which we use similar terms with 
reference to electricity, i. e. to regard heat as the immediate dynamic force which 
overcomes the affinity ; thus, as we say when employing the voltaic battery, that we 
decompose water by electricity, so here we should say that we decompose it by heat. 
If it be said that heat so weakens or antagonizes the affinity of the elements of 
water as to enable catalytic action to separate them, this amounts to the same theory, 
as heat is then regarded as the antagonizing force, and in this case the action, both 
thermic and catalytic, is the reverse of the normal action. I have thought it de- 
sirable shortly to discuss this question as likely to lead to further investigation, 
though I have been somewhat embarrassed by the want of definite meaning in the 
term catalysis ; I must plead guilty to have frequently used the term, but notwith- 
standing, or perhaps on account of, its convenience, it has I fear had an injurious 
effect on scientific perspicuity. 
The following experiments were made to ascertain whether platinum was the only 
substance by which the effect could be produced. A knob or button of the native 
alloy of iridium and osmium of the size of a small pea was formed by the voltaic 
battery ; to this was attached by fusion another smaller knob of the same metal one- 
fourth the size of the former, and to this smaller one was attached a stout platinum 
wire ; the object of the second knob was both to prevent the fusion of the platinum 
wire and also to avoid the possibility of any surface of platinum being exposed to the 
recipient tube or alloyed with the metal to be heated. The preparation of this simple 
instrument was very troublesome, but when made it answered the purpose well; the 
larger button could be fully ignited to an intense glow, while on account of the 
narrow neck which united them, the smaller was barely red-hot, and the platinum wire 
not perceptibly ignited. An experiment having been made with this metallic button 
and prepared water, similar to that previously made with platinum, gas was given 
off which averaged 03 of mixed gas ; the residue was nitrogen mixed with varying 
small quantities of oxygen. The effect, upon the whole, was decidedly inferior to 
that of the platinum. Indeed as platinum is the most dense and unalterable of all 
known substances, it would be likely, upon any received theory of heat, to produce 
the greatest effects. 
I tried palladium in the same manner; the gas yielded was hydrogen with small 
quantities of oxygen, and the water was stained with the oxide o the metal. 
