1821.] of Charcoal and Hydrogen. 171 



volume of oxygen gas, have as nearly as possible the relative 

 weight of 1 to 8. 



Were any additional argument necessary to establish the 

 existence of carburetted hydrogen as a distinct species, it might 

 be derived from the action of water on that gas, which, besides 

 being absorbable in a constant proportion, admits of being 

 expelled again by the application of heat, not otherwise changed 

 than in having acquired a small quantity of those gases which 

 are always present in water, and of which it is impossible to 

 deprive it even by long continued boiling. 



The process, by which carburetted hydrogen gas is evolved 

 in natural operations, is no doubt the decomposition of water, 

 and admits of being explained on the atomic theory of Mr. Dal- 

 ton, by supposing two atoms of charcoal to act at once on two 

 atoms of water. One atom of charcoal attracts the two atoms 

 of hydrogen, forming carburetted hydrogen gas, and the other 

 atom of charcoal unites with two atoms of oxygen, constituting 

 carbonic acid. This is illustrated by the annexed 

 figure, in which two atoms of charcoal, C, C, are 

 represented as interposed between two atoms of 

 water, each consisting of an atom of hydrogen and 

 an atom of oxygen. Dividing the diagram verti- 

 cally into three parts, we have the original substances ; and 

 separating it horizontally, we obtain the two new compounds. 

 This theoretical view of the subject is confirmed by the fact, 

 that the carburetted hydrogen, formed at the bottom of stagnant 

 pools, is never accompanied by carbonic oxide, but always by 

 carbonic acid, the full quantity of which is prevented from 

 appearing, in consequence of the absorption of a great part of 

 it by the mass of water, under which the changes are taking 

 place. 



Being provided with such an abundant supply of carburetted 

 hydrogen, I availed myself of it to examine the mutual action of 

 that gas and chlorine on each other, principally with a view to 

 ascertain how far reliance may be placed on the latter as an 

 instrument in the analysis of mixed combustible gases. This is 

 a part of the subject that was first investigated, though with a 

 different view, by Mr. Cruickshank.* He observed that a mix- 

 ture of chlorine with hydrogen, carburetted hydrogen, or 

 carbonic oxide in certain proportions, kept in a bottle entirely 

 filled with the mixture, and furnished with an air-tight stopper, 

 did not exhibit any immediate action, but that in 24 hours, on 

 withdrawing the stopper, the fluid immediately rushed in, and 

 filled most of the space originally occupied by the gases. But 

 he was not aware of the influence of light on these changes, 

 which was discovered about the same time by Gay-Lussacf and 



• NicbolnonV Journal, 4 to. v. 202. 

 t Mem. de laSoc. d'«\rcucil, it. 349. 



