ADVANTAGES OF GAS. 57 



to undertake the arrangement of such machinery, upon the correct working 

 of which must depend its success ; and those who suffer themselves thus to be 

 imposed upon will only find out their error when it is too late to rectify it. 



The manufacture of gas is one of those processes which appear perfectly 

 simple and straight-forward at first sight, and this may in some measure 

 account for the errors of such men as I have just noticed. It is true that the 

 operations do appear exceedingly plain ; but there are few that require more 

 scientific judgement, system, and strict care. The retorts, for instance, must 

 be set in such a manner as to be heated sufficiently with the smallest quantity 

 of fuel, and without the liability of being made too hot : they must be carefully 

 watched, lest the incrustration of carbon in the interior accumulate more 

 than is absolutely unavoidable, and lest they burn out before the time calcu- 

 lated. These particulars can only be learned by practice ; they will vary with 

 every different quality of coal, and be affected by the size and shape of the 

 distillatory vessel itself. It also requires much experience to determine the 

 most O3conomical arrangements for the condensers, purifiers, etc., and to re- 

 gulate the quantity of gas to the demand. But, above all, the proper distri- 

 bution of the street-mains requires the most skill, which, in the section 

 treating upon this subject, I shall endeavour to point out. 



The supplying of light to the street or parish lamps alone, can never be 

 undertaken with ceconomy in any district ; the most beneficial application 

 being in those situations where a quantity of light is wanted in a small space. 

 Where the light is required to be more diffused, the profit is less, owing to 

 the greater extent of services and fittings. 



It is hardly necessary to remark, in the present advanced state of the art, 

 that the use of coal-gas for the purposes of artificial light is more ceconomical 

 than that obtained from either wick-lamps or candles. To those, however, 

 unacquainted with the actual saving, I may observe that 6000 cubic feet of 

 coal-gas of the specific gravity '400, when supplied with a sufficient volume of 

 oxygen for its complete combustion, is equal to the light from 2400 candles, 

 eight in the pound ; or 1000 cubic feet will give as much light as 50 Ibs. of 

 candles, eight in the pound, for the same length of time. 



One thousand cubic feet of gas costs 8*. ; in some places it is higher, there- 

 fore we will say 12s. : 50 Ibs. of candles at 6\d. costs 27s. Id., making a dif- 

 ference in favour of the coal-gas of 15s. Id. ; and when we consider, in addi- 

 tion to this, its greater convenience, cleanliness and safety, we may wonder 



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