Dr Fyfe on the Comparative Value of Oil and Coal Gas. 178 
of the gas gives warning of its escape ; so that one of its proper- 
ties considered offensive actually proves a valuable safeguard. 
Of the Nature of the Gaseous Fluid emitted by the decomposi- 
tion ef Oil and Coal. 
The gaseous matter, given off from coal and oil, now known 
by the name of coal and oil gas, contains nearly the same ingre- 
dients, but in different proportions. Dr Henry has shown, that 
they are mixtures of hydrogen, carbonic oxide, carburet ted hydro- 
gen and olefiant gas, with occasionally a little nitrogen ; and in 
addition to these, coal-gas, before it is subjected to the process 
of purification, always contains ammonia, carbonic acid and sul- 
phuretted hydrogen, but from which it is, or at least ought to 
be, freed before it is sent into the gas-holder, so that both gases, 
when exposed for sale, contain the same ingredients, but in dif- 
ferent proportions. There is also given off*, during the decom- 
position of coal and oil, an essential oil, which seems to be held 
in solution, in a state of vapour, in the gas, and w hich is the cause 
of the smell, and, as some suppose, adds to the illuminating 
power. 
Dr Henry, in his paper in the Annals of Philosophy for Sep- 
tember 1821, has given the component parts of different samples 
of gas. The coal-gas was prepared from Wigan Canal, at the 
manufactory of Messrs Phillips and Lee, and collected from an 
opening in a pipe between the retort and the tar-pit, generally 
about half an hour after the commencement of the distillation, 
except in the instance of the gas No. 4., which was taken five 
hours, and No. 5., ten hours from that period ; the carbonic acid 
and sulphuretted hydrogen being removed by washing it with 
solution of potassa. 
Spec. Grav. 
Gas Condensible by Chlorine. 
Gas, No. 1. 
650 
13 per cent. 
2. 
620 
12 
3. 
630 
12 
4. 
500 
7 
5r 
345 
0 
