EXPLANATION OF PLATES. PLATE I. THIS plate represents a connected view of the principal appartus employed in the process of making and purifying Coal Gas. (A,) exhibits the fire-places, or furnaces, by which the Retorts that contain the coal for distillation are heated to a red heat to produce the gas; and (1, 1, 1,) shew the Retorts as they are arranged and set in the frame, or oven, of brickwork. The mouths of two of them are closed with their lids, which are screwed up, and fitted air-tight; but the others are left open. As the gas is disengaged, it ascends through the upright pipes (2, 2) that are connected, near the top, with some short pipes,-called dip-pipes,-to pass into the Hydraulic Main. (B,) shews the Hydraulic Main more than half filled with water, with the ends of the dip-pipes immersed in the water* a little below its surface, so that the gas and vapours may be forced to pass through the water to be condensed, in order to separate the tar and ammonia; and the gas, ascending to the upper part of the Hydraulic Main, passes along the pipe (3) to the large Condenser. * To render the description more intelligible, the representation in the plate shews a part of the cylinder as if it were broken off, in order to point out the height of the water, and the pipes dipping into it. B (C,) exhibits a section of the Condenser, which consists of a great number of pipes, inclosed in a large square or circular cistern, and completely surrounded with cold water. In its passage through this vessel, the gas becomes so much cooled as to occasion the condensible products mixed with it, to be deposited, and the tar sinks to the lower part of the Condenser (4); but the gas passes through the pipe (5) into the Purifying Machine. (D,) shews a section of the Tar Cistern, which receives the tar as it accumulates, and forms a connexion with the Condenser by means of a syphon pipe. (E,) represents a section of the Purifying Machine, which is formed of a large iron cylinder, divided into three compartments, to contain a mixture of lime and water. Each of these chambers has a small cylinder (6, 7, 8) fixed in it, and quite closed at the top, but the bottom has a broad spreading rim, or flanche, which sinks several inches into the lime and water, and occasions the gas to diffuse itself in the mixture. By means of revolving paddles, or agitators, (9,) fixed to a spindle that passes through the centre of the machine, and is connected with a horizontal bevil-wheel to give it motion, the mixture of lime and water is kept constantly stirred, in order that the gas may be effectually exposed to the chemical action of the lime, which purifies it; and when purified, it passes through the pipe (10, 10) into the Gaso meter. (F,) exhibits a section of the Gasometer, which is the reservoir where the gas is collected and preserved to afford the supply as it may be required. This machine consists of two vessels: the lower (11, 11) is a large tank or cistern, the greater part of which is sunk or fixed in the ground, and it is filled with water :-the upper is another large vessel, which is made rather less in its diameter, and it is also inverted |