336 Dr. Henrys Experiments on the Gas from Coal. [Nov, 



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

 most mature consideration, I see no reason to change ; that the 

 great variety of gases evolved by the destructive distillation 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. 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 

 proportions, 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 "little if 

 any odour. It burns with a pale and feeble 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 



340 Water.... 340 



2. Carbnretted Hydrogen has been shown to constitute the 

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

 natural 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 oxygen. It is lighter than 

 common air, in the proportion of about 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. . . : J2 1 cubic foot of carb. acid 1 : 13 

 Consumes 2 cubic feet of 



oxvgen 2:10 Water 1 : 09 



3 : 06 3 : 06 



3. Carbonic Oxide is rather lighter than common air. It 

 contains no hydrogen, and is purely a compound of charcoal and 

 oxygen, 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£ gr. or 16 drams, is to be understood. 



