118 Experiments on the Gas from Coal. 



In the same essay I maintained an opinion which, on the most 

 mature consideration, 1 see no reason to change; that the great 

 variety of gases evolved by the destructive distillation of inflam- 

 mable substances, do not constitute so many distinct species, but 

 are mixtures of a few, the nature and properties of which were 

 before ascertained. It will contribute to render what follows 

 more intelligible, if a brief account be given of those gases of 

 known composition, the mixtures of which, in various propor- 

 tions, compose, according to this view, all the observed varieties ; 

 and I shall make their comparison under a form best adapted to 

 illustrate their practical application. 



1. Hydrogen 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 sulphuric acid, it contains impurities which 

 give it a disagreeable smell ; but well purified hydrogen has lit- 

 tle if any odour. It burns with a pale and feelDle flame, not at 

 all suited to artificial illumination. 



Product of its combustion, 

 grains. • grains. 



The cubic foot weighs about 40 

 Consumes half a cubic foot 

 of oxygen . . . . 300 



.•MO Water .. ..340 



2. Carburettkd hydrogen has been shown to constitute the 

 gas of marshes and the fire-damp of coal-mines. In these na- 

 tural forms, it is contaminated with a small proportion of car- 

 bonic acid, and a larger one of azotic gas, but appears to be free 

 from all other impurities. It is proved to be a definite compound 

 of hydrogen and charcoal without any oxvgen. It is lighter than 

 common air, in the proportion of aliout 600 to 1000; it has very 

 little odour ; and burns with a flame greatly surpassing that of 

 hydrogen in density and illuminating power. 



Products, 

 oz. dr.* oz. dr. 



A cubic foot weighs 12 1 cubic foot of carb. acid I 13 

 Consumes 2 cubic 



feet of oxygen 2 1 Water 1 9 



3 6 3 6 



3. Carbonic oxide is rather lighter than common air. It con- 

 tains no hydrogen, and is purely a compound of charcoal and oxy- 

 gen, the latter being in just half the proportion which is required 

 to constitute carbonic acid. It burns with a feeble blue light. 



* The avoirdupois ounce of 437^ grains, or 16 drachms, is to be under- 

 stood. 



