GAS (COAL) MANUFACTURE OF. The separation and purification of the volatile elastic fluids from pit coal, which have the property of giving out light when burned. They are various coin pounds of carbon and hydrogen, accom panied by hydrogen and carbonic oxide in large quantity.
The application of the gases produced during the destructive distillation of pit coal to the purposes of illumination is a very modern invention. But the germ of it may be traced back above 100 years ; for the first mention of the production of a permanently elastic and inflammable gas from coal occurs in the Philosophwal Transactions for 1739, in which there is a paper by the Rev. Dr. Clayton, describing a method of filling bladders with what lie calls the spirit of coal, obtained by distilling coal in a retort in the open fire. He says, " I filled a good many bladders therewith, and might have filled an inconceivable number more ,• for the spirit continued to rise for several hours, and filled the blad ders almost as fast as a man could have blown them with his mouth, and yet the quantity of coals distilled was inconsidera ble. I kept this spirit in the bladders a considerable time, and endeavored several ways to condense it, but in vain ; and when I had a mind to divert strangers or friends, I have frequently taken one of of these bladders and pricked a hole therein with a pin, and compressing gently the bladder near the flame of a candle till it once took fire, it would then continue flaming till all the spirit was com pressed out of the bladder ; which was the more surprising, because no one could discern any difference in the ap pearance between these bladders and those which arc filled with common air." Dr. Clayton seems also to have observed those curious phenomena which have lately excited so much attention under the terms esormose and endosmose • for he goes on to say that he found " that this spirit must be kept in good thick blad ders, as in those of the ox or the like ; for if I filled calves' bladders therewith, it would lose its inflammability in twenty four hours, though the bladders become not relaxed at all." Dr. Hales (in his Vegetable Stakes) and Dr. Watson (in his Chemical Essays) have each alluded to the properties of the gas from coal ; but it was not until the end of the last century that the practicability of substituting coal gas for other inflam mables, as a means of lighting streets and buildings, became an object of attention. The idea of applying coal gas to eco nomical purposes seems first to have oc curred in 1792 to Mr. William Murdoch, then residing at Redruth, in Cornwall. His apparatus consisted of an iron retort, with tinned , copper and iron tubes, through which the gas was conducted to a considerable distance ; and there, as well as at the intermediate points, was burned through apertures of varied forms and dimensions ; he also washed the gas with water, and used other means for its purification. In 1798 Mr. Murdoch con structed a larger and improved apparatus for the purpose of lighting Boulton and Watt's celebrated manufactory at Soho, near Birmingham, which, on the occasion of the peace in 1802, was publicly illumi nated by the same means.
In all extensive and well conducted es . tablishments, the processes for the man ufacture of gas are similar and uniform in the various stages. A great extent of ground is occupied with the retort house, purifying chambers, and space for the large gasometers. The arrangements are similar in all. They are, with slight exceptions, which we need not heed here, as follows :—Each side of the retort house has a succession of arched recesses, each eight or ten feet high, six or seven wide, and about as many in depth. These recesses, when bricked or otherwise closed in front, form ovens or furnaces, in which fuel is burnt on a grate at the lower part. Five, six, eight, or more ob long iron vessels, each holding from two to three bushels of coals, are ranged ho rizontally in this oven, from front to back, so that the heat, flame, and smoke from the surface may play around them, and make them red-hot. The outer end of these vessels, which are the retorts, are left opened or closed as occasion may re quire ; an iron door, connected with a screw, being accurately fitted to each re tort. The retorts are semi-cylindrical in shape, with the flat side placed lower most. The average height of the retorts is perhaps about five feet from the ground ; under them is a fireplace, through which the fuel is introduced by which they are heated ; and under this again is a 'kind of ash-pit or shallow vessel into which the lime water is poured for the purpose of evaporation. The operation then con sists in this :—The empty retorts are first brought to a red heat ; then charge of coals' is introduced ; then the cover is screwed on the end, and made air-tight by a cement of clay and lime. Thus the retorts remain for about five hours, dur ing which the fireplace is opened every hour for the renewal of the fuel with which the retorts are heated ; and at the end of this time all the gaseous and vaporizable matters having left the coal, and passed up from each retort by a pipe into the hydraulic main,' the drawing of the retorts' commences. The retort cover is loosened by turning a screw ; a slight explosion takes place when com munication with the atmosphere is open ed; the cover is removed.• by the sooty and almost fire-proof hands of the men, and the coke is drawn out by means of rakes eight or ten feet long. A kind of box, made entirely of iron, and placed upon wheels, is wheeled beneath the fropt of the retorts, and into it a portion of the fiery contents of each retort is drawn. The box is wheeled away, and in a few minutes volumes of steam are ascending profusely from it, the result of a plentiful supply of water, which is thrown on it for the sake of speedy cool ing. The remainder of the coke is then drawn out on the iron floor of the building, and, after being partially cool ed by water, is removed out into the open air.