[ 164 ] 



XXX. Experiments on the Gas from Coal, chiefly with a vieiv 

 to its practical Application. By Wh.liam H ExN'ry, iV/.D." 

 F.R.S. &c. 



[Concluded from p. 126.] 



On the Purification of Coal Gas. 



1 HE chief impurities mingled with the gas from coal, which it 

 is clesiral)le 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 inconvenient pro- 

 pertv of tarnishing silver plate ; and during combustion, gives rise 

 to the same suffocating fumes (sulphurous acid) which are pro- 

 duced by the burning of a brimstone match. The most obvious 

 method of absorbing both the carbonic acid and the sulphuretted 

 hvdrogen, is to bring the recent gas into contact with quicklime; 

 and the cheapness of that substance, and facility of applying it, 

 led me, several years ago, to propose it for the purpose*. It 

 has since, 1 believe, been suggested that the sulphuretted hydro- 

 gen may be removed by chlorine ; but a sufficient objection to 

 this agent is, that it would also separate the most valuable part 

 of the product, the olefiant gas. The transmission of the gas 

 through ignited tubes has also been proposed ; but it is a well 

 known property of both the varieties of carburetted hydrogen, 

 that they deposit charcoal when strongly heated; and M. Ber- 

 thollet has shown that the amount of this effect is proportionate 

 to the increase of temperature f. Some persons practically en- 

 gaged 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 advantage is thus 

 gained ; and thev have not been aware that the gas, when thus 

 treated, sustains a much more than proportional loss of illumi- 

 nating power. 



The quantity of quicklime required for the absorption of a cu- 

 bic 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 2\ ounces avoird. A volume of coal gas con- 

 taining a cubic foot of each of those impurities will require, there- 

 fore, at least 5 ounces of lime applied in the best possible man- 

 ner. But it is never found in practice that the whole of any gas, 

 when sparingly diffused through another, can be taken out en- 

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



» Phil. Trans. 1808, page 303. 



\ Mimoiresde laSoc. (TArateil, iii. 154. 



from 



