94 On the aériform Compounds 
acid at 46°5 grains, and the charcoal in 100 grains of that acid 
at 27°3 grains) of 
Grains. Grains. - Grains. 
Charcoal), «4 12:69 (0.0 ..-74'S7. 0000100 
Hydrogen .. 4°26 .... 25°13 .... 33°41 
16:95 100. 133-41 
And olefiant gas (giving twice its volume of oxygen by com- 
bustion, and weighing 29°64 grains for 100 cubical inches*) 
must be vonstituted of 
Grains. Grains. Grains, 
NATO, | fl LOTS ve an GUO @ hae ke 
Fiydropent 45 Se aa at BAPOL, a neh OLN 
29°64 100: 116°71 
And as 16:7.is to 100, so very nearly is 1 to 6, which last 
number is the weight of the atom of charcoal, as deduced from 
the constitution of elefiant gas. It is true, that this determina- 
tion a little exceeds that which is derived from the composition 
of carbonic acid (viz. 5°65), the atom of oxygen being taken at 
7°5. But if 8 be the true number for oxygen, which now seems 
to be most probable both from experiment and analogy, we shall 
then find an exact coincidence between the relative weight of the 
atom of charcoal, as deduced from olefiant gas, and as deter- 
mined from carbonic acid. Perhaps the true specific gravity of 
hydrogen gas, on which depend the relative weights of the atoms 
of hydrogen and oxygen, may be fully as correctly ascertained 
from the composition of carburetted hydrogen, as by direct at- 
tempts to weigh so light a fluid. Now, as the hydrogen in 100 
cubic inches of hydro-carburet weighs only 4°26 grains, and is 
equivalent to 200 cubic inches of hydrogen gas, we have 2°13 
grains for the weight of 100 cubic inches of hydrogen gas, from 
which may be deduced ‘0698 for its specific gravity, that of air 
being 1. And if the specific gravity of oxygen gas be 1-111, it 
will be found that the two volumes of hydrogen, required to sa- 
turate one volume of oxygen gas, have as nearly as possible the 
relative weight of | to 8. 
Were any additional argument necessary to establish the exist- 
ence 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 
* I adopt this result of Dr. Thomson from its near coincidence with that 
of an experiment of my own, on the specific gravity of olefiant gas, published 
in the Phil. Trans. 1808, p. 2933 
having 
