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._ _SIR_, _Enclosed are the result of a series of experiments made under my direction with a view of ascertaining the relative value of the different modes of working cast-iron cylindrical retorts, from which you will perceive that it is more economical to work eight hours charges, as the workmen call it, that is to say, to suffer the distillatory process to go on for eight hours, when nearly two bushels of coal are contained in each retort, than to discontinue the operation at the end of six hours._ _I am with respect, Sir, Yours, &c. T. S. PECKSTON._ _To Mr. F. Accum, Compton Street, Soho._ _Process A._