32 Dr. Ileitry's Experiments on the Gas from Coal. [Jan. 



Article VI. 



Experiments on the Gas from Coal, chiefly icitli a View to its 

 F tactical Application. By VV^illiam Henry, M.D. F.R.S. &c. 



{Concluded from vol. xiv. p. 344.) 



On the Purification of Coal Gas. 



Th e chief impurities mingled with the gas from coal, which. 

 it is desirable and practicable to remove before applying it to use, 

 are carbonic acid and sulphuretted hydrogen gases. The 

 former is of little importance ; but the latter imparts to the coal 

 gas, when unburned, a very offensive smell, resembling that of 

 bilge water, or the washings of a gun-barrel, and the inconve- 

 nient property of tarnishing silver plate ; and during combustion 

 gives rise to the same suffocating fumes (sulphurous acid) which 

 are produced by the burning of a brimstone match. The most 

 obvious method of absorbing both the carbonic acid and the 

 sulphuretted hydrogen is to bring the 'recent gas into contact 

 with quicklime ; and the cheapness of that substance, and faci- 

 lity of applying it, led me, several years ago, to propose it for 

 the purpose.* It has since, I believe, been suggested that the 

 sulphuretted hydrogen may be removed by chlorme ; but a suffi- 

 cient objection to this agent is, that it would also separate the 

 most valuable part of the product, the defiant gas. The trans- 

 mission of the gas through ignited tubes has also been proposed; 

 but it is a well-knov.n property of both the varieties of carburet- 

 ted hydrogen, that they deposit charcoal, when strongly heated ; 

 and M. Berthollet has shown that the amount of this effect is 

 proportionate to the increase of temperature.'!' Some persons 

 practically engaged in lighting with gas have, to my knowledge, 

 been led, by the increase of the quantity of gas which is obtained 

 by passing it through red-hot tubes, to imagine that an advan- 

 tage is thus gained ; and they have not been aware that the gas, 

 when thus treated, sustains a much more than proportional loss 

 of illuminating power. 



The quantity of quicklime required for the absorption of a 

 cubic foot of carbonic acid, or of the same volume of sulphuretted 

 hydrogen gas, will be found on calculation not to exceed 1050 

 grains, or about 2i ounces avoirdupois. A volume of coal gas 

 containing a cubic foot of each of those impurities will require,, 

 therefore, at least five ounces of lime applied in the best possible 

 manner. But it is never found in practice that the whole of any 

 gas, when sparingly diff'used through another, can be taken out 

 entirely, without using much more of the appropriate agent than,, 

 from its known powers of saturation, might have been deemed 

 equivalent to the effect. The proportion employed by Mr. Lee 



• Phil. Trans. 1808, p. 303. + Memoires dc la Soc. d'Arcueil, iii. 154. 



