of charcoal and hydrogen. 143 
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. 
Dalton, 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 char- 
coal 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 
vertically into three parts, we have the original substances ; 
and separating it horizontally, we obtain the two new com- 
pounds. 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 carbu- 
retted 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 com- 
bustible gases. This is a part of the subject that was first 
investigated, though with a different view, by Mr. Cruick- 
