E—_ 0 iii — oe 
4 
Experiments on the Gas from Coal. 393 
riety of gases, evolved by the destructive dis- 
tillation of inflammable substances, do not 
constitute so many distinct species, but are 
_ mixtures of a few, the nature and properties 
of which were before ascertained. Tt will 
contribute to render what follows more in- 
telligible, if a brief account be given of those 
gases of known composition, the mixtures 
of which, in various proportions, compose, 
according to this view, all the observed va- 
rieties ; and I shall’ make their comparison 
under 4 form best adapted to illustrate their 
practical application. 
1. HyproGeEn Gas. This is the lightest 
of all known gases, its specific gravity, 
that of atmospheric air being taken at 1000, 
being about 73. As ordinarily procured, by 
the solution of iron or zinc in diluted sulphu- 
ric acid, it contains impurities -whichi give it 
a disagreeable smell; but well purified hy- 
drogen has little if any odour. It burns 
with a pale and feeble flame, not at all suited 
to artificial iumination, 
Product of its combustion. 
grains grains 
The cubic foot weighs ‘outs 
Consumes half a cubic 
foot of oxygen......... 300 
340 Water...... 340 
VOL. ILI. pdd 
