The volume of gas which a given quantity of whale-oil yields has been variously stated, at from 80 to 110 cubic feet per gallon, and the quality of the oil, and mode of distillation, may partly account for the difference. We have not been able to ob tain more than 95 to 98 ; but as some waste took place, in the portion which was volatilized not being wholly condensed and collected, it is probable that 100 may be taken as the number of cubic feet which one wine gallon of good whale-oil will produce.
Gas from Coal Tar.
Attempts have been made to decompose coal tar in order to obtain the gaseous products ; and this may be effected without much difficulty, by an apparatus nearly similar to that used for decomposing oil, and by other means. But it does not appear from the ex periments which have been made, that the gas pro-. duced is well fitted for the purposes of illumination ; probably from a great quantity of pure hydrogen being mixed with the carbureted hydrogen gas form ed; or, if Mr Brande's theory of the nonexistence of the latter gas be correct (Annals of Philosophy, December 1819), because the olefiant gas occurs in extremely minute quantities, compared with the quantity generated during the distillation of coal.
When atmospheric air is mixed with about one eighth part of its bulk of coal gas, and set on fire, it explodes ; and, if in a confined situation, may do serious mischief. Accidents have occurred from these explosions, which originate in ignorance, mis chief, or carelessness. The offensive odour emitted both by oil and coal gases unburnt, is a very suffi cient warning of their escape; and the propriety of having every part of a gas apparatus perfectly tight, and free from leaks, is a matter of importance, not only as regarding safety and the prevention of this nuisance, but also the actual waste and loss of a va luable commodity. A leak from a hole one-twentieth of an inch diameter would, under the usual pres sure, in the course of one year, waste coal has to the value of L.10 and upwards ; and, supposing it to be emitting gas into a chimber of ten feet cube, it would require from two to three days to render the air of it explosive, and this only on the supposi tion that the apartment was nearly air-tight. Any ordinary escape of gas into a room, having a door, window, and fire-place, where a circulation of air is constantly going on, could never cause an explosion, though explosions have occurred, from its getting, in the first instance, into confined adjoining places, as closets, cup-boards, arched vaults, or the like. In
these situations, when the smell of gas is perceived, ventilation should be resorted to, by opening the doors, &c. and lights should be kept away from them, until the smell ceases to be offensive.
Economy of Gas-Lights.
We now come to.treat of the expence of light ob tained from coal and oil gases, and their comparative cost, compared with that from oil and tallow, as commonly consumed in lamps and candles. The fluctuations of price to which these commodities are liable, and the varying expence in different places of buildings, and other things required in forming a gas-work, must, of course, render any statement of comparison that can be given inappli cable to the forming of any other than a very general result.
The expence of such an apparatus, as is represent ed in Plate LXXXIV. may be taken as follows : Twenty-one retorts, with all their appendages, tar. vault, condensing and purifying apparatus, and buildings, belonging to the same, L. 5,500 Two gasometers, with their cisterns, and all apparatus, and buildings, 5,200 The cost of the main pipes, with their stop valves, water-receivers, &c. for distribut ing the gas, must depend entirely upon circumstances which cannot be consider ed here. In lighting towns, the amount has, in some cases, equalled, or some what exceeded that of the rest of the apparatus. Say then, 10,800 Total expence, - L. 21,000 This apparatus will be capable of supplying about 50,000 cubic feet of gas daily, using sixteen or seventeen of the retorts ; the remainder being kept as a reserve in case of accidents to the others from cracks, burning, or wearing out. And though such a consumption of gas should be necessary in the depth of winter, yet it will be found, that, upon an average for the year, a daily supply of about half the quantity will suffice in the way in which it is generally consumed in lighting towns. This apps ' ratus may, therefore, be considered as capable of giving 25,000 cubic feet of gas each day in the year.