of Charcoal and Hydrogen. 91 
brief recapitulation, with the view merely of connecting them 
with what is to follow. 
In the first of these essays (Nicholson’s Journal, 8vo, June, 
1805), I detailed a series of experiments on the gases obtained 
by the destructive distillation of wood, peat, pit-coal, oil, wax, 
&c., from which it appeared that the fitness of those gases for 
artificial illumination was greater, as they required for combustion 
a greater proportional volume ofoxygen ; and that the gases gene- 
rated from different inflammable bodies, or from the same inflam- 
mable substance under different circumstances, are not so many 
distinct species, which under such a view of the subject would be 
almost infinite in number, but are mixtures of a few well known 
gases, chiefly of carburetted hydrogen with variable proportions 
of olefiant, simple hydrogen, sulphuretted hydrogen, carbonic 
acid, carbonic oxide, and azotic gases ; and that the elastic fluids 
obtained from coal, oil, &c. have probably, 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 certain anomalies that appear in the experi- 
ments 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 further 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 re- 
specting this species of aériform bodies. To Mr. Dalton, also, 
-we are indebted for an accurate acquaintance with carburetted 
hydrogen gas, and for much information that is valuable in assist- 
ing us to judge of the composition of mixed combustible gases, 
by the phenomena and results of firing them with oxygen +. 
In the second Memoir (Philosophical Transactions, 1808), I 
described a series of experiments on the gases obtained from se- 
veral different varieties of pit-coal, and from the same kind of 
coal under different circumstances. Various species of that mi- 
neral were found to yield aériform 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 de- 
composing any one species of coal, the gaseous fluids were ascer- 
tained not to be of uniform quality throughout the process, but 
to vary greatly at different stages; the heavier and more com- 
bustible gases coming over first, and the lighter and less com- 
bustible afterwards. By subsequent experiments on the gases ob- 
tained from coal on the large scale of manufacture, it was found 
* Nicholson’s Journal, 8vo. xi. 72. 
+ New System of Chemical Philosophy, passim, 
M 2 that 
