Exhibits a perspective view of a gas-light apparatus,[40] for lighting factories, or small districts of houses. It consists of the following parts: which may be considered separately. [40] This apparatus was erected by Mr. CLEGG, and is now in action at Mr. ACKERMAN’s establishment, in this metropolis. FIG. 1. The _Retort Furnace_, for distilling the coals. It is built of brick-work. The bricks which are exposed to the immediate action of the fire, are _Welch tumps_, or fire-bricks; they are bedded in clay, or Windsor loam. FIG. 2. The _Tar Cistern_, to collect the coal-tar, and other condensible products obtained during the distillation of the coals. It is a cast-iron hollow cylinder, closed at the top with a cast-iron cover, which has a very small hole to allow the air to escape as the liquid enters into the vessel. FIG. 3. The _Lime Machine_, for purifying the crude coal-gas, and to render it fit for use. The construction of this machine will be explained in plate VII. It is put together of cast-iron plates. FIG. 4. The _Gasometer_, for collecting and preserving the purified gas, and for distributing and applying it as occasion may require. It consists of two principal parts--namely, a large interior vessel closed at the top and open at the bottom, made of sheet iron, designed to contain the gas, and an outer cistern or vessel, of rather greater capacity, constructed of cast-iron plates, in which the former vessel is suspended. The latter contains the water by which the gas is confined. The interior vessel which contains the gas is suspended by chains hung over wheels or pullies, to which weights are attached, so as to be just sufficient to balance the weight of the gasometer, all but a small difference, and allowing its slow descent in the manner which is found as nearly adapted as can be to the proper supply of the lamps. The weight of the chains must be equal to the specific gravity of the material of which the gasometer is composed, so as to compensate accurately for the quantity of water which the gasometer displaces, or what is the same, it must be equal to the loss of weight which the gasometer sustains, when immersed in the water; and the counterpoise weight must be equal (or nearly so) to the absolute weight of the gasometer. The action of these different parts of the apparatus will be obvious from the following explanation: