of charcoal and hydrogen. 141 
gives *556 for the specific gravity of pure carburetted hy- 
drogen gas, a number which coincides almost exactly with 
that found by Dr. Thomson.* Since, therefore, the same 
results have been obtained from the examination of gases 
similarly collected at distant times and places, there appears 
to me no reason for refusing to consider carburetted hydro- 
gen gas as a true chemical compound, characterized by per- 
fect uniformity of properties and composition. At the tem- 
perature of 6o° Fahrenheit, and under 30 inches pressure, 
100 cubical inches must weigh 16*95 grains, and be com- 
posed (taking the weight of 100 cubic inches of carbonic 
acid at 46*5 grains, and the charcoal in 100 grains of that 
acid at 27*3 grains) of 
Grains. Grains. Grains. 
Charcoal . . 12*69 .... 74*87 . ... 100 
Hydrogen . . 4*26 .... 25*13 .... 33*41 
16*95 100. 1334 1 
And olefiant gas (giving twice its volume of oxygen by 
combustion, and weighing 29*64 grains for 100 cubical in- 
ches-f) must be constituted of 
Grains. Grains. Grains. 
Charcoal . . 25*38 .... 85.63 .... 100 
Hydrogen . . 4*26 .... 14.37 .... 16*71 
C rn» iM ■ ■ 1 -1 .a ■ ■ «i i n 
29*64 IOO. Il6*7l 
And as 16*7 is to 100, so very nearly is 1 to 6, which 
* Annals of Philosophy, Vol. XVI. p. 252. 
+ 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. 293. 
