170 Dr. Henri/ on the Aeriform Compounds [Sept. 



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 hydrogen gas as a true chemical 

 compound, characterized by perfect uniformity of properties and 

 composition. At the temperature of 60° Fahrenheit, and under 

 30 inches pressure, 100 cubical inches must weigh 16*95 grains, 

 and be composed (taking the weight of 100 cubic inches of car- 

 bonic acid at 46*5 grs. and the charcoal in 100 grs. of that acid 

 at 27-3 grs.) of 



Grains. Grains. Grains. 



Charcoal . . 12-69 .... 74-87 .... 100-00 

 Hydrogen.. 4-26 ....25-13 33-41 



16-95 100-00 133-41 



And olefiant gas (giving twice its volume of carbonic acid by 

 combustion, and weighing 29-64 grs. for 100 cubical inchest) 

 must be constituted of 



Grains. Grains. Grains. 



Charcoal .. 25-38 .... 85-63 .... 100-00 

 Hydrogen.. 4-26 14-37 .... 16-71 



29-64 100-00 116-71 



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 olefiant 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 

 attempts to weigh so light a fluid. Now, as the hydrogen in 100 

 cubic inches of hydrocarburet weighs only 4*26 grs. and is equi- 

 valent to 200 cubic inches of hydrogen gas, we have 2-13 grs. 

 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 saturate one 



* Annals of Philosophy, xvi. 25S. 



+ I adopt this result of Dr. Thomson from its near coincidence with that of an expe- 

 riment of my own, on the specific gravity of olefiant gas, published in the Phil. Trans. 

 1808, p. 293. 



