1821.] of Charcoal and Hydrogen. 169 



retted hydrogen ; and that the gases evolved by heat from coal 

 and oil are in fact nothing more than mixtures of olefiant and 

 simple hydrogen gases in various proportions. 



In assuming, in the first Essay, the existence of light carbu- 

 retted hydrogen as a definite compound, characterized by its 

 requiring, for the complete combustion of each volume, two 

 volumes of oxygen, and giving one volume of carbonic acid, I 

 relied on the sole authority of Mr. Dalton ; for the gas of 

 marshes, though before known to be inflammable, had not been 

 subjected to accurate examination by any other chemist. Mr. 

 Cruickshank, indeed, speaks of it as " pure hydrocarbonate ;" * 

 but since he classes it in that respect with the gas obtained by 

 the destructive distillation of camphor, from which it differs 

 essentially in composition, it is plain that he was not correctly 

 acquainted with the properties of pure carburetted hydrogen. 

 Previously to the second set of experiments, I satisfied myself 

 by the careful analysis of a specimen of the gas from stagnant 

 water, for which I was indebted to Mr. Dalton, that it really has 

 the properties which have been ascribed to it by him as charac- 

 teristic ; and in 1807 I found precisely the same characters in 

 the fire-damp of coal-mines.f Dr. Thomson, also, from experi- 

 ments in 181 \,X on the gas from stagnant water, and Sir Hum- 

 phry Davy,§ from the analysis of the fire-damp in 1815, drew the 

 same conclusions. It is in the power, indeed, of every chemist 

 to investigate for himself the properties and composition of car- 

 buretted hydrogen gas, since it may easily be procured in consi- 

 derable quantity, by stirring the bottom of almost any stagnant 

 pool, especially if composed of clay. During the last summer, 

 I obtained it from a source of this kind, which afforded it in such 

 abundance, that several gallons might have been collected in a 

 few minutes. This gas 1 submitted to repeated and most care- 

 ful examination. It contained one-twentieth its volume of 

 carbonic acid, but no sulphuretted hydrogen whatever, and no 

 proportion of oxygen gas that could be discovered by attentively 

 testing- it with nitrous gas. The results of its combustion with 

 oxygen gas, effected in a Volta's eudiometer in the usual manner, 

 showed that it was contaminated with 1-loth its volume of azotic 

 gas. Apart, however, from this, the pure portion, in a great 

 number of trials, required, as nearly as can be expected in expe- 

 riments of this sort, two volumes of oxygen for combustion, 

 and gave one volume of carbonic acid. Its specific gravity, 

 taken on quantities procured at three several times, varied only 

 from -582 to *586, the mean of which is -584 ; and this, allowing 

 for 1-loth of azotic gas of specific gravity -972, gives '556 for 

 the specific gravity of pure carburetted hydrogen gas, a num- 

 ber which coincides almost exactly with that found by Dr. 



NichoUon's Journal, 4 to. vol. v. p. 6. -f- Ibid. 8vo. xix. 149. 



£ Memoirs of the Wemcrian Society, i. 506. \ Phil. Trans. 1816, p. 5. 



