1 58 Dr. Henry on the aeriform compounds 
oxygen , and from 2^ to 3 volumes of carbonic acid for each 
volume of the condensible gas. 
On comparing also the specific gravity of the gases from 
coal and oil, as ascertained by experiment, with that which 
ought to result from mixtures of the residue left by chlorine, 
with such a proportion of olefiant gas as is deducible 
from analysis, I have invariably found, that the real specific 
gravity has considerably exceeded the estimated. For in- 
stance, the London oil gas was composed of 38 volumes of a 
gas condensible by chlorine, and 6 2 volumes of mixed gases 
not characterized by that property, and having the specific 
gravity .606. But 6 2 volumes of gas of specific gravity .606, 
mixed with 38 volumes of olefiant gas of specific gravity 
.970, should give a mixture of the specific gravity .754, instead 
of .906, which was the actual specific gravity of the entire 
oil gas. It will be found on calculation that the 38 volumes 
of gas, in order to make up the real specific gravity of the 
oil gas, must have had the specific gravity of 1.4 very nearly. 
This is the highest number that is deducible from my experi- 
ments for the specific gravity of that portion of oil gas or coal 
gas, which is condensed by the action of chlorine. In other 
instances, it varied from that number down to 1.2, but in 
every case its weight surpassed that of common air. 
It is evident from these facts that the aeriform ingredient 
of oil gas and coal gas, which is reducible to a liquid form by 
chlorine, is not identical with the olefiant gas obtained by the 
action of sulphuric acid on alcohol, but considerably exceeds 
that gas in specific gravity and combustibility. Two views 
may be taken of its nature ; for it may either be a gas sui 
generis 3 hitherto unknown, and constituted of hydrogen and 
