and the Black Oxide of Iron at a white heat. 187 



absolute amount accordingly of disunion of the elements of 

 M'ater occasioned is very small. 



If allowance, however, be made for the apparent difference 

 in extent of effect which heat shows in uniting and in dis- 

 uniting the elements of water, the phaenomena otherwise 

 seem referable solely to the intensity of the temperature to 

 which hydrogen and oxygen are exposed. The opposite pro- 

 cesses might go on simultaneously, union or disunion being 

 determined simply by the different temperatures to which 

 different portions of the gases were raised. At least it seems 

 not improbable that if a mixture of steam and of hydrogen 

 and oxygen were exposed to electric discharge, decomposition 

 of the steam and combination of the hydrogen and oxygen 

 might be effected by the same spark, provided the volume of 

 steam were not large. In the track of the spark decompo- 

 sition would occur, so long as a white heat prevailed. When 

 the temperature fell, combination would happen where the 

 spark had passed, if it had not already commenced in the 

 neighbourhood of its direct route. Similar remarks apply 

 mutatis mutandis to the action of a hot platinum wire on a mix- 

 ture of steam with oxygen and hydrogen. 



It may be objected to this view, that Mr. Grove decora- 

 poses steam in his eudiometer, and obtains a permanent bub- 

 ble of gas, consisting of hydrogen and oxygen. The bubble 

 however obtained in this way is very small, and could not 

 probably be greatly increased. Mr. Grove has not mentioned 

 how large a volume of hydrogen and oxygen he could obtain 

 in the same eudiometer, by alternately boiling the water till 

 the steam produced caused the liquid to fall below the wire, 

 and allowing the steam to condense till the water rose above 

 the metal. But I venture to say that no large volume of per- 

 manent gas could be procured by this process if the same 

 eudiometer were employed many times successively. The 

 combining action of the wire might not take effect on the 

 hydrogen and oxygen when their quantity was small, and 

 they were diluted through a large volume of steam, for in 

 virtue of the law of diffusion, the molecules of hydrogen and 

 oxygen would be separated from each other by molecules of 

 water-vapour; but when the latter diminished in bulk, it 

 seems impossible to doubt that kindUng of the gases would 

 occur. 



Mr. Grovels experiments then do not appear to prove that 

 heat of the same intensity is able in the same circumstances 

 to form water and to decompose it. When therefore it is 

 stated that water can be produced by the processes that dis- 

 unite its elements, the word ^process ^ can only be understood 

 to signify that the general arrangement in both cases is the 



