The quantity of gas to be supplied each night, was 50,000 cubic feet.
In order to produce this quantity, thirty cylindrical retorts, each containing two bushels of Newcastle coal, were put in action. The temperature at which the retorts were worked, was a bright cherry redness, at which they produced at the rate of ten thousand cubic feet of gas, from a chaldron of Newcastle coal.
To work the retorts, three workmen by day and three by night, were required.
The retorts were charged three times every twenty-four hours. The first total expence of erecting the retorts, was £. 23 each, and it was found, that when worked night and day, they could not, with the utmost care, be made to continue fit for use for more than from five to six months; hence, a double set of the original number of retorts was requisite each year.
The whole annual operation pursued on this plan stood as follows:
| Cost of sixty retorts, thirty at work and thirty to spare, with brick-work foundation, iron cokehearth, perpendicular pipe connected with hydraulic main, see P, fig. 2, [plate IV.], at £ 23. each. | £. 1380 | 0 | 0 | |||
| Six workmen, three during day-time, and three at night, at £ 1. 6s. each the week | 405 | 12 | 0 | |||
| Coals, 1825 chaldron, requisite for producing the gas, at £ 2. 8s. the chaldron | 4380 | 0 | 0 | |||
| Wear and tear of grate bars, fire-shovels, tongs and rackers | 42 | 0 | 0 | |||
| 4561⁄4 chaldron of Coal for fuel, £. 2 1s. the chaldron | £. 935 | 6 | 3 | |||
| Total expence, | £. 7142 | 18 | 3 | |||
| Subtract the market price of saleableCoke[25] produced by the process, viz. 1825 chaldron,at £ 1. 3s. the chaldron | £. 2098 | 15 | 0 | |||
| 4561⁄4 chaldron of small Coke or Breeze, at ten shillings the chaldron | 228 | 2 | 6 | |||
| 2326 | 17 | 6 | ||||
| There remains | £. 4816 | 0 | 9 | |||
for the annual expence of maintaining the apparatus on this construction.
[25] The tar and ammoniacal liquor afforded by the process, not being always saleable articles, are omitted to be charged in the estimates.
Process II.
The next experiment made was, to ascertain the contrary practice of operating, namely the mode of working the retorts, on the principle which holds out, that it is more economical to be satisfied with a less quantity of gas than what the coal is capable of furnishing, because by so doing the retorts become less deteriorated and remain for a longer time in a state fit for use.