The same heat as we have seen from the preceding table, [p. 79], which is necessary during the first hour of the operation, for the evolution of one hundred and fifteen cubic feet of gas, is required in the eighth hour for the production of no more than forty-two cubic feet, being a decrease in effect of nearly two-thirds.

When larger retorts are employed for decomposing coal in masses, from five to ten inches in thickness, the loss of heat is in a much greater ratio.

In the hope of remedying in some measure the evils thus distinctly ascertained to arise from the undue thickness of the masses of coal subjected to the distillatory process, there have not been wanting manufacturers who have had recourse to experiments on a large scale, to ascertain with certainty whether they might not be gainers by suffering the distillatory process, when the retorts are charged with two bushels of coal, to proceed only for the space of six hours, instead of eight. But the result of these experiments, as will be presently explained, has shown satisfactorily that it is more profitable to keep up the distillatory process for a period of eight hours, with the retorts fully charged, than to abridge the operation by terminating it at the end of six hours.

Others again, have imagined, that it would be more economical to decompose a less quantity of coal at once, or to decrease the thickness of the stratum of coal in the cylindrical, or in any of the before named retorts; but then again, serious difficulties occur in the practice. The more frequent charging of the retorts and luting on the covers,[16] which such a mode of operating require, occasions a prodigious waste of fuel, time and labour. A greater number of retorts and more workmen must likewise be employed, in order to produce the requisite quantity of gas daily, which the manufacturer is called upon to supply; more space of ground is required, and more dead capital must be sunk in the establishment. The more frequent and sudden alterations of temperature which the retorts necessarily suffer, by the more frequent introduction of cold coal, renders them extremely liable to become injured; and it is almost impossible to maintain a number of retorts thus worked, at an uniform temperature.

[16] When the cover is ground on, air-tight, the cost of the retort is much increased.

From various statements, which I have been favoured with, in confirmation of my own observations on the best method of working cylindrical retorts, it may suffice to lay before the reader the result of a series of operations instituted by one of the largest and best conducted establishments in this country; the public-spirited and indefatigable directors of which have done more in the way of extensive, costly, varied and long continued experiments, to improve the new art of lighting with gas, than any other similar body in the kingdom; and without whose exertions the gas light illumination would never have reached the state of perfection it has attained.

Report on a course of Experiments made to ascertain the comparative Economy[17] of manufacturing every week, 857,667 cubic feet of gas, by means of Cylindrical Retorts variously worked.

[17] The cost of materials and price of labour in this estimate, as well as in all subsequent statements, is given such as they actually were, at the time, when the experiments to which they refer were made.

Gas Light and Coke Company’s Works,
Westminster Station.

February 8th, 1819.