An apparatus for the production of the gas from coal having been prepared by Mr. Murdoch, for the very extensive cotton manufactory of Messrs. Philips and Lee, at Manchester, which is now illuminated by means of this alone upon a very large scale, this instance was selected as the best for estimating the expense of employing the gas lights.
The quantity of light there employed was asccrtained by comparison of the shadows to be equal to that of about 2500 mould candles of six in the pound, each of which consumes about four tenths of an ounce of tallow per hour.
The coal is distilled in large iron retorts, and the gas conveyed by pipes of iron to large reservoirs or gasometers, where it is Washed and purified before it is conveyed to the mill. The main pipes branch of into a variety of ramifications (the aggregate length of which amounts to several miles), the several branches diminishing in diameter in proportion as the quantity of gas to be passed through them becomes less.
The burners where the gas is consumed communicate with the main by short pipes, furnished each with a cock to regulate the admission of: gas. These burners are of two kinds: one is on the principle of the Argand lamp, and the other has a conical termination with three holes, one at its point, and the other two placed laterally about one thirn'eth of an inch in diameter. The former, of which there are 271, are each equal to four candles; and the latter amount- ing to 633. are each equal to 2% candles ; so that the total amount is, as above stated, about equal to 2500 candles.
For the hourly supply of these burners, 1250 cubic feet of gas are necessary; and since the lights are used for about two hours, the daily consumption of gas is 2500 cubic feet.
For the production of this quantity of gas, seven hundred weight of cannel coal is employed, which, notwithstanding its high price, is found to be the most economical, on account of the superior quality and quantity of the gas it yields. The number of working days being 313, the annual consumption of cannel coal is 110 tons, of which the cost is 1251. But these 110 tons yield 70 tons of coke, the value of which is 931., leaving a difference of 321., to which must be added 201. for the value of 40 tons of good common coal employed for heating the retorts.
But by far the greatest part of the cost of employing this species of light consists in interest of capital employed in furnishing the apparatus, and in repairing the wear and tear, which are stated together by Mr. Lee at about 550l. per annum, making a total annual expenditure of 600l. instead of 2000l., which would be required to produce an equal quantity of light from 2500 candles burning together, at 18. per pound.
