Apparatus requisite for preparing Coal Gas in a state fitted for the purposes of When pit-coal is made to undergo destructive dis•, tillation in a close vessel or retort, the products will, in general, be found to consist of the following sub stances ; though, from the varying nature of the coal, they do not all exist in every species, some of them at least but very sparingly : Coke or Charcoal.
Tar and oil, two or three varieties.
Water.
Ammonia; partly as hydrosulphuret, and partly as subcarbonate.
Carbureted hydrogen gas.
Olefiant gas.
Sulphureted hydrogen gas, besides portions of carbonic acid, of hydrogen gas, and common air ; and also azotic gas, especially towards the end of the process.
The construction and management of the retort will naturally come first under consideration ; and in tracing the progress of the liquid and gaseous pro ducts, the condensing, collecting, and disposal of the latter come next to be treated of. The purification of the mixed gases, after they are separated from the tar and other liquids, forms an important subject of inquiry; and subsequent to which, the preservation of the purified gas in proper receptacles will be treat ed of. Its distribution to places where lights are re quired will then follow; and, lastly, a view of some facts relative to its combustion under different cir cumstances will enmnlete this nart of the sithieet.
Of the Retort.
The retort first employed by Mr Murdock was made of cast-iron, and of a cylindrical form. See Plate LXXXI. fig. 1, where it is represented, as in serted into a common portable furnace ; a, the retort ; 6, its cover made air-tight by luting ; c, the tube or branch-pipe to convey away the gas and other pro ducts. This retort, being about two-thirds filled with coal, was submitted to the action of the fire; and, on its acquiring a red-heat, the decomposition of the coal commenced; the tar, oil, and gaseous products escaping through the tube c, and the charcoal or coke remaining behind in the retort.
It is obvious, that this form of retort is inconve nient, as regards the removal of the coke at the ter mination of each process, and, to remedy such in convenience, a different construction was adopted, and which we saw in use as early as the year 1802. Of this a representation is given in fig. 2; a a, the retort, consisting of a cylindrical vessel placed horizontally, with a door or cover b, to charge and discharge it of its contents, and branch pipe c to convey away the products of distillation ; d the grate ; the flues were so constructed that the flame surround ed the retort and afterwards made its escape at the chimney e. Retorts on this construction, from twelve
' to twenty inches diameter, and from diree to seven feet in length, were found to answer tolerably well, and could be charged and discharged with facility.
Figures 3 and 4 represent the other varieties which we observed in use in the years 1804 and 1805. The peculiarity of these consists in their having each two openings or doors b and f, the first to admit the coal, and the other to allow of the discharge of the char coal ; a, d, c, refer to the same parts as in fig. 2. These retorts are necessarily more costly than those having only one opening, and they were, on the whole, found more troublesome to manage and keep in or der.
Fig. 5 is a representation of one of the retorts first used at the works of Messrs Philips and Lee, which differs little from fig. 1, except in magnitude, being made to contain about 16 cwt. of coal, while the other would hold only about the same number of pounds. The grate, flues, and chimney, and general construc tion, require no particular explanation, the letters referring to the same parts as in 6g. 2. In order to facilitate the discharge of the cokes, an iron cage e, figured separate in the plate, formed somewhat like a grappler, was let down into the retort previ ous to its being charged with coal ; and when the process of distillation was completed, the grappler was lifted out by means of a small crane, carrying the mass of charcoal along with it. Another grappler being then introduced, a fresh charge of coal was thrown in, and the process of distillation carried on with very little interruption. The quantity of gas produced from each cwt. of good common coal, ob tained in the neighbourhood of Manchester, was from 330 to 360 cubic feet, when these retorts were em ployed, each yielding it at the rate of 160 cubic feet per hour on an average. The quantity of gas, how ever, varied considerably with the temperature at which the process was carried on ; and the rate at which it was produced diminished greatly after the expiration of a few hours from the commencement of the distillation.