1823.] Dr. Henry*s Chemistry, 141 



olefiant gas, much less carburetted hydrogen, and instead of 

 these, a large proportion of hydrogen and carbonic oxide, both 

 of which afford very little light by their combustion. 



" It is scarcely possible to assign the quantity of gas, which 

 ought to be obtained from a given weight of coal, but it may be 

 considered as an approach to a general average to state, that 

 112 lbs. of good coal are capable of giving from 450 to 500 

 cubic feet of gas of such quality, that half a cubic foot per hour 

 is equivalent to a mould candle of six to the pound, burning 

 during the same space of time. 



^^ Oil Gas. — In Nicholson's Journal for 1805, I have given an 

 account of some experiments on the gas obtained by the destruc- 

 tive distillation of spermaceti oil, which showed that of all the 

 artificial gases, this, next to olefiant gas, consumes most oxygen,, 

 and is the best adapted to afford light. Since that time, an appa- 

 ratus has been invented by Messrs. Taylor, of London, which 

 has greatly facihtated the preparation of oil gas on a large scale, 

 and this gas is now much used as a source of artificial fight. 

 The process consists in letting whale oil (the purity of which is 

 not essential, since very inferior oil answers the purpose) fall by 

 drops into an iron cylinder placed horizontally in a furnace, and 

 ignited to a cherry redness. From each wine gallon of oil, 

 about 1 00 cubic feet of gas may with care be obtained, of the 

 specific gravity of more than -900, containing upwards of 40 per 

 cent, of gas condensible by chlorine, and of which 100 volumes 

 consume 260 volumes of oxygen, and yield 158 of carbonic acid. 

 But of gas from Wigan cannel, when the whole product is min- 

 gled together, 100 measures do not saturate more than. 155 of 

 oxygen, and give 88 measures of carbonic acid. Oil gas, there- 

 fore, from this document, may be inferred to contain, in a given 

 volume, twice the quantity of combustible matter that is present 

 in the average of gas from cannel coal; and its illuminating 

 power will be as 2 to 1. The experiments of Mr. Brande led 

 him to conclude, that to produce the fight of ten wax candles 

 for one hour, there will be required 



2600 cubical inches of olefiant gas. 



4875 oil gas. 



13120 coal gas. 



" But it seems probable that the coal gas, employed in these 

 experiments, was below the general standard, and that it is a 

 fair average to consider 1 volume of oil gas as equivalent to 2 

 or at most 2^ volumes of gas from coal of good quality. This 

 estimate agrees with the experience of the late Mr. Creighton, 

 of Glasgow, author of the excellent article ' Gas Lights,' in the 

 Supplement now publishing to the Encyclcp. Britan. Oil gas 

 he considers as superior, in an equal volume, to good average 

 coal gas^ in the proportion of only 2 to 1 ; and he has given the 



