IMS^ m Oil md Coal G^<. 191 



Hence a bad gas may be made from oil, wHctislfall riot exceed 

 in quantity the good gas of Taylor and Martineau. And, in 

 point of fact, we have several times found, when the retorts were 

 choked with charcoal, and the specific gravity of the gas was 

 only 660, that the quantity fell short of 100 cubic feet per gallon, 

 which is said to be about the average produce when the gas is 

 good. When oil gas has a specific gravity of 910, charcoal is 

 still found in the retorts. It may therefore be improved by the 

 addition of all this charcoal, and still retain its volume. Besides 

 it may be possible to improve it by the addition of charcoal from 

 other sources. Hence, while we at present assign to oil gas 

 the average specific gravity of 920, we cannot help anticipating 

 a considerable improvement, and positive gain. 



From what has been said of the average quaUty of coal gas in 

 different quarters of the kingdom, it is clear that the question of 

 its economy, compared with oil gas, can be only answered rela-^ 

 lively. In Edinburgh and Glasgow, where coal is moderately 

 cheap, and coal gas of good quality, oil gas must be somewhat 

 dearer ; in London, where the coal is dear, and the gas bad, oil 

 gas should be positively cheaper ; and in other places the twd 

 will be nearly the same in price. This statement is, of course, 

 drawn from our own experiments on their illuminating power, 

 coupled with the well-known computations of Accum, Peck- 

 ston, Ricardo, and others, regarding their relative cost. 



The second element in the question of their relative advan- 

 tages, is their comparative utility. It is certain that whatever 

 difference may exist between them in this respect must be in 

 favour of oil gas. 



In the first place, the quahty of the light is superior. It is 

 whiter, and has a peculiar sparkling appearance, superior to that 

 of coal gas. It is therefore a more beautiful light, fitter for th6 

 artificial illumination of colours, and not liable to give the hunlan 

 countenance that unpleasant sallow appearance which every one 

 has observed to be caused by coal gas. 



An objection has been urged to the employment of gas ill 

 general, that it has a disagreeable odour. This objection does 

 not apply at all, unless the gas is unconsumed ; for neither oil 

 nor even coal gas, so far at least as our observation goes, emits 

 any odour, if properly burnt. But if they escape, and mix with 

 the air, their presence is then readily detected by the smell. 

 The odour of oil gas is purely empyreumatic, but quite distinct ; 

 we have possessed occasional specimens, which had a faint 

 smell, but we never found it altogether inodorous. The best oil 

 gas appears to have the least smell. The odour of coal gas is 

 of a mixed kind, being in part empyreumatic like oil gas, and 

 partly <)f an exceedingly offensive nature, like that of sulphuret- 

 ted hydrogen. In Edinburgh coal gas we have generally 



