Drs. Christison and Turner an Oil and Coal Gas. 209 



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 two will be nearly the same in price. This state- 

 ment is, of course, drawn from our own experiments on their 

 illuminating power, coupled with the well-known computations 

 of Accum, Peckston, Ricardo, and others, regarding their re- 

 lative 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 quality 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 the artificial illumination of colours, and not liable to give 

 the human 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 in 

 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 of an exceedingly offensive nature, like that of sul- 

 phuretted hydrogen. In Edinburgh coal gas we have ge- 

 nerally observed the empyreuma alone; but frequently the 

 other is perceptible also, and sometimes it prevails to an in- 

 sufferable degree. 



The most serious objection to coal gas arises from the pre- 

 sence of impurities. These are, a black matter like tar, and 

 compounds of sulphur, — all derived from the coal itself, and 

 therefore necessarily present originally in every description of 

 coal gas. Without purification, therefore, coal gas could 

 scarcely be used at all; and it becomes a question of impor- 

 tance to determine whether or not the noxious ingredients may 

 be wholly removed from it. The greater part of the tar is de- 

 posited at the works in the proper vessels, but a minute por- 

 tion does commonly pass over with the gas. It tends to clog 

 the apertures of the burner, and of course soils substances 

 upon which it is deposited. In common shops, where a free 

 current of air is preserved, the effect is hardly noticed; but 



Vol. 66. No. 329. Sept. 1825. 2 P we 



