190 Drs.Christison and Turner [SfiPT. 



Article VI. 



On the Comparative Advantages of Oil and Coal Gas. By 

 Robert Christison, MD. FRSE. and Edward Turner, MD. 

 FRSE.* 



The question of the relative advantages of oil and coal gas 

 resolves itself into two : the first regards their relative economy ; 

 the second their comparative utility. 



1. Before we can determine their relative economy, it is requi- 

 site to settle their average quality. Taking their specific 

 gravity as the ground of comparison, we apprehend that, in 

 small towns, where the cannel coal can be had at a low price, 

 coal gas companies may be able to manufacture a gas of the 

 density of 700. In larger cities, such as Glasgow and Edinburgh, 

 where coal of every kind is dearer, and the cannel coal cannot 

 easily be procured in sufficient quantity, the average specific 

 gravity of the gas will not exceed 600. And in such a town as 

 London, where the cannel coal can scarcely be procured at all, 

 the average specific gravity will not exceed 450. 



The average specific gravity of oil gas should eventually be 

 the same every where. It is difficult to ascertain what the 

 average is at present, as made by large establishments; but 

 there is no substantial cause why it should fall short of 920. We 

 have assigned strong reasons, however, for believing that it must 

 be soon improved considerably. This improvement indeed may 

 be no great gain ; for the question will then occur, whether it 

 can be effected without diminishing the quantity of gas in the 

 same proportion with its increase in quahty. It is generally 

 supposed, that an improvement in the Quality of oil gas is neces- 

 sarily attended by a loss in quantity ; but, so far as can be dis- 

 covered, this idea rests on experiments performed by operatives 

 only, whose authority we are satisfied, from repeated observa- 

 tion, can by no means be relied on. If charcoal is left in the 

 retorts at the end of each charge, it is clear that the gas may be 

 improved by the addition of all this charcoal, without any dimi- 

 nution in quantity ; for, if it be added to the fight carburetted 

 hydrogen, which gives little light, so as to convert it into the 

 olefiant gas, which is powerfully illuminating, the change, it is 

 well krtown, will take place without any alteration in volume. 

 On the other hand, if good oil gas be exposed to a high tem- 

 perature, it is partly decomposed, and deposits some of its 

 charcoal. Part of the olefiant gas becomes light carburetted 

 hydrogen, and without any increase in volume ; for the volume 

 is not increased unless it is resolved into charcoal and hydrogen. 



♦ From the Edinburgh Philosophical Journal. 



