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One light, equal in intensity (by comparison of shadows) tothat of a tallow candle six in the pound, consumes about half ofa cubic foot of gas per hour. * A pound of these candles, oneburning at a time, lasts 40 hours, and costs, say one shilling.
On an average, each pound of good coal produces three cubicfeet of gas :—hence a foot of gas is nearly equal to an ounce ofcandle; f or 20 feet (to burn 40 hours) require 7 lib. of bestcoal, which, at 8d. per cwt., is one halfpenny.
But this disparity of 24 to 1, is by no means so great in prac-tice as at first sight it may appear to be, as the interest of theoutlaid money, tear and wear, attendance, &c. is very great.—This will best be seen on the large scale, by the following calcu-lations, founded on minutes taken at two of the Gas Light esta-blishments in the vicinity of Glasgow .
Dh.
To 1000 lights, each equal in intensity to a candlesix in the pound, and burning ten hours each, willconsume 5000 cubic feet of gas; this will require1066 lib., or 15 cwt. of good coal, at 8d. p. cwt.To the same quantity of common coal for outside ofretort at 6d.—( N. B. Dross is sometimes used fortliis purpose, but, requiring a great current of air,it is more dangerous for the retorts)
To attendance, 2 men keeping the retorts going nightand day, as, when allowed to cool overnight, theyare long before they become effective in the morn-ing.— (iV. B. The watchman of the work some-times officiates during the night; but where retortsare numerous, continual going is not absolutely ne-cessary ).
To one day’s interest of sum sunk in buildings, re-torts, gazometer, pipes, cocks, incidents, and lay-ing, say 30s. each light, 1500/.—(iV. B. In someCases the outlay exceeds, in others it is less thanthis, a good deal depending on local circumstancesand economical arrangements) ...To one day’s tear and wear, including new retorts,fire bricks, building, incidents, repairs, &c. 10 percent, on outlay ------
L.O 10 0
0 7 6
0 5 0
0 i 20 8 i
L.l 15
* The (circular) aperture through which that gas passes, with a modernpressure, is nearly the 32nd part of an inch in diameter.
| 9419 ounces of tallow make one cubic foot.