1 37 
Dr. Henry on the aeriform compounds , &c. 
portions of olefiant, simple hydrogen, sulphuretted hydro- 
gen, carbonic acid, carbonic oxide, and azotic gases; and 
that the elastic fluids obtained from coal, oil. See. have pro- 
bably, in addition to these, an inflammable vapour diffused 
through them when recent, which is not removed by passing 
them through water. * In the same paper I explained cer- 
tain anomalies that appear in the experiments of the late Mr. 
Cruickshank, of Woolwich, which are not at all chargeable 
as errors upon that excellent chemist, and could only be 
elucidated by farther investigation of the gases to which they 
relate. Of his labours it would be unjust, indeed, to speak 
in any terms but those of approbation, for they may fairly 
be considered as the foundation of most that is now known 
respecting this species of aeriform bodies. To Mr. Dalton, 
also, we are indebted for an accurate acquaintance with car- 
buretted hydrogen gas, and for much information that is 
valuable in assisting us to judge of the composition of mixed 
combustible gases, by the phenomena and results of firing 
them with oxygen.-f* 
In the second Memoir (Philosophical Transactions, 1808), 
I described a series of experiments on the gases obtained from 
several different varieties of pit-coal, and from the same kind 
of coal under different circumstances. Various species of 
that mineral were found to yield aeriform products, differing 
greatly in specific gravity, combustibility, and illuminating 
power ; the cannel coal of Wigan, in Lancashire, being best 
adapted to the purpose, and the stone-coal of South Wales 
the least so. In decomposing any one species of coal, the 
* Nicholson’s Journal, 8vo. XI. 72. 
f New System of Chemical Philosop y ,pastim. 
MDCCCXXI. T 
