510
MODERN GASWORKS PRACTICE
the liquid until it (the gas) finds an outlet through the perforations in the bent plate and then.ce upwards into the space above the plate, whence it travels to the outlet chamber. The bubbles of gas in passing through, the liquor into the tube space convert the surface into a foam, thus the most thorough contact of gas and liquor is assured. In Order to preveirt the gas passing direct from the inlet to the outlet chamber the ends of the intermediate spaces are securely closed up. The perforations in the tubes are usually one-twentieth of an inch in diameter, and so placed that there are about thirty to the square inch. The washer will be found to work most effectively when the depth. of liquor is such that it rises to an inch above the top of the pear-shaped plates, in which case 3 inches of pressure is thrown.
Fig. 313.— Livesey Washek, Detail of Perforated Plates.
There are now many washers in use which are operated on the bubbling and wire-drawing principle ; and from the point of view of tar extraction effi.cien.cy the type is probably not to be excelled. Cockey’s washer is shown in. Fig. 311. It con-sists of a cast-iron vessel divided ofl by horizontal partitions into three or more cham-bers. The gas entering at the base travels upwards through a vertical pipe to the top of which is fitted a hood. The gas meets the hood and is then deflected down-wards through four openings in the horizontal plate and passes through the liquor. It then. travels past several serrated edges which are sealed in liquor, and afterwards finds its way to the next chamber. The liquor flows from the top chamber down-wards ; and the depth of the seals may be regulated as desired.
Dempster’s washer is shown in Fig. 315. It is composeet of a series of cast-iron trays placed one above the other, the trays ha ving a number of narrow openings, with raised edges. These openings are covered with. lioods having serrated edges.