20S

PURIFICATION.

first purifier has become completely saturated, the handle of the lower valve is turned one-fourth round and that purifier is shut off.

Fig. 68.

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W hen that purifier has been recharged, the upper valve is then turned one-fourth, andboth purifiers are again put in action. Figs. 69 and 70 show the greatest combination ofpurifiers required in any works, the several figures in each showing in respective order thedirections in which the valves are turned to produce the altered course of the gas throughall the necessary changes. In Fig. 69 all the purifiers are shown in action, and in Fig. 70the purifier on the left-hand, which iu the previous figure received the gas first, is shownas shut off to be recharged. In this manner the gas may be passed through all the puri-fiers in succession, and the lime, or oxide of iron, in each purifier becomes successivelythe foulest, and that which was the foulest becomes the cleanest.

The valves, from their conical shape and horizontal action, are said to keep very tight, topresent little friction, and to continually sweep the faces clean, sending the sweepingsthrough the passages, and thus out of the body of the valve. An oiling-passage from thetop admits oil down the centre of the diaphragm, which lubricates the valve without allow-ing the oil to come in contact with the gas.

Fig. 69.