1820.] Specific Gravity of Gases. 253 



carburetted hvdrogen gas. One volume of this gas lequii es for 

 complete combustion two volumes of oxygen gas, and there 

 remains after the explosion exactly one volume of carbonic acid 

 o-as. Now one half of the oxygen must have gone to the forma- 

 tion of carbonic acid ; the remaining volume of oxygen must 

 have combined with hydrogen, and formed water, and it must 

 have combined with a quantity of hydrogen which, ifit had been 

 in the gaseous state, would have amounted to two volumes. 

 Carbonic acid gas contains exactly its own volume of vapour of 

 carbon. It is' obvious from this that a volume of carburetted 

 hydrogen gas is composed of 



1 volume vapour of carbon"? ^on^gi^ge^i j^to one volume. 



2 volumes hydrogen gas . . 3 



Consequently its specific gravity must be equal to twice the 

 specific gravity of hydrogen gas + the specific gravity of 

 carbon vapour. 



Sp. gr. of hydrogen = 0-0694 and 0-0694 x 2 = 0-1388 

 carbon ..= 0-4166 0-416(i 



carburetted hydrogen = 0-5555 



It is clear from this (if our data be accurate) that the specific 

 gravity of pure carburetted hydrogen gas is 0-5555. Now this 

 differs less than --oV o^h part from the result of my experiments 

 made in 1810 — a degree of precision as near as can be expected 

 in experiments of this nature. The latter experiments were less 

 accurate, because the gas examined was much purer than what 

 I employed the first time ; and though not absolutely pure, too 

 much so to enable us to detect with certainty the proportion of 

 common air which it contained. 



We see from what has been stated that carburetted hydrogen 

 is a ternary compound,, consisting of two atoms of hydrogen 

 united to oiie atom of carbon. Hence the weight of an integrant 

 particle of it is I'OOO, or the same as that of oxygen ; for 



2 atoms hydrogen = 0-25 



1 atom carbon = 0-75 



1-00 



= an atom of carburetted hydrogen. 



If we make the specific gravity of oxygen gas unity, then the 

 specific gravity of carburetted hydrogen gas will become 0-5 and 

 0-5 X 2= 1-000; so that the weight of the atom of carburetted 

 hydrogen is just double its specific gravity. In this respect it 

 agrees with olefiant gas, and with the other gases enumerated in 

 the preceding part of this paper. 



Carburetted hydrogen gas differs fiom olefiant gas merely in 



