relttimg to Gas Illumination." 43 



Let us now, from the supposed constitution of oil gas and coal 

 gas, take a view of their actual composition ; and we shall find 

 that, instead of their relative values being as 4 to 1, in reality 

 they will seldom be even as 2 to I *. And for this evident reason, 

 that oil gas is seldom or ever (as we have been presuming) free 

 from light carburetted hydrogen, and likewise that the gas from 

 coal is never free from olefiant gas. In proportion, therefore, as 

 these two gases are made, by a good or bad method, to approxi- 

 mate, in tlie same proportion will their relative values approxi- 

 mate. It is therefore evident, that those individuals or towns that 

 shall l)e led Ijy this mis-statement to erect gas-holders, or to lav 

 pipes for oil gas in the reduced ratio to those of coal gas of 1 

 to 4, will to their inevitable disappointment soon discover the 

 error ; and it will be found that the proportion stated as Mr. De 

 Ville's, of 5 to 9, is the nearest the truth. 



With regard to the composition of oil gas. Dr. Henry states in 

 his paper lately read before the Manchester Society, that in his 

 experiments upon the decomposition of oil, he always obtained a 

 mixture of the two gases; but that M. Berthollet had succeeded in 

 obtaining from oil [query, animal or vegetable] pure olefiant gas. 

 From this it is evident, that on the same fortuitous circumstances 

 of temperature, pressure, and extent of heated surfaces, as mainly 

 depends the generating of olefiant gas from oil as from coal. If 

 further proof were wanting as to the scientific principle, as well 

 as to the benefit resulting from the passing of crude gas (either 



to be far short of being so in comparison with ours. For he says that 

 " 3500 cubic feet of gas was collected from 1 120 pounds of cannel coal ; and 

 3000 cubic feet from the same quantity of the Clitton coal." Either of these 

 products is far, very far short of Brande's experiments (or of the every day's 

 practice about us). In some experiments at the Royal Institution he obtained 

 26 cubic feet from four pounds of coal. This shows how much depends on 

 the method of carbonization, and leads one to suspect, that the gas on 

 which Dr. H. made his experiments was not generated on the now gene- 

 rally adopted principle, of applying the coal in thin strata, in either semi- 

 circular or elliptical retorts, (to say nothing of the still further improve- 

 ment of the heated medium before condensation,) and that the retorts be 

 charged every four or five hours, as recommended by Mr. Peckston in his 

 excellent book upon Gas Lighting ; and not every twelve hours, as seems to 

 have boen the case in Dr. Henry's experiments. We, in our small esta- 

 blishment, greatly prefer four hours charges; finding thereby we have more 

 light and less tar from a given weight of coal. Though our coal is rich in 

 bitumen, the tar produced seldom exceeds one-fourth of the condensible 

 fluids. 



* See Brande's Manual of Chemistry, page 1.56. We are there informed 

 (speaking of oil gas) that " from two to three cubic feet may be regarded 

 as equivalent to five or six of coal gas." This was published in April; yet 

 in July wc are gravely informed that one of oil gas is equivalent to four of 

 coal gas ! ! 



^ oil 



