148 Dr. Henry on the aeriform compounds 
From the volume of the residuary gas, it was necessary to 
deduct the amount of impurity previously ascertained to exist 
in the chlorine ; and the remainder, taken from the volume 
of mixed gases which had been operated on, showed how 
much olefiant gas had been condensed by the chlorine. When 
very narrow tubes were employed, and the column of gases 
mixed with chlorine was of considerable length, a longer 
continuance of the experiment was found necessary, and the 
gases were suffered to remain in contact during an hour or 
more. In this way it was ascertained, that olefiant gas may 
be accurately separated by chlorine from hydrogen, carbu- 
retted hydrogen, or carbonic oxide gases, or from mixtures 
of two or more of those gases, which are left quite unchanged 
in volume and in chemical properties, when light has been 
carefully excluded from the mixture. 
This property of chlorine is the foundation of a fresh ana- 
lysis, to which I have thought it expedient to submit the 
gases from coal and oil, in order to decide what aeriform fluids 
remain after the separation of that portion which is conden- 
sible by chlorine ; — whether the residue consists, as I have 
heretofore maintained, of carburetted hydrogen chiefly, with 
variable proportions of hydrogen and carbonic oxide ; or 
whether, according to the new view of the subject, it consists 
of hydrogen gas only. 
In the experiments made for this purpose, I operated gene- 
rally on from 60 to 80 cubic inches of oil gas or coal gas, 
assaying a small specimen first, as a guide to the quantity of 
chlorine which it would be necessary to employ. The volume 
of chlorine thus found to be requisite, and about half as much 
more, was passed into an air receiver standing over water, and 
