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326                    METALLURGY OF CAST IRON.
to prevent the fuel from dropping into it and stopping its blast passage. Good kindling is used up to within, say, 12 inches of the top. On this, coke broken to about double egg size, is then placed. The coke is poked down as the fire burns until there is a solid bed of live coals up to within 15 inches of the top. If the metal to be fused is of a light character, or easily melted, it is then charged at this height; but if it is heavy or hard to liquefy, then the bed of live fuel should extend up to about 12 inches from the top, as shown by the pigs at X. As this cupola has ample tuyere area evenly divided, it can be worked with a mild or strong blast, as may be desired. The tap holes at D D are left open so as to permit the metal to flow out as fast as it melts, thus allowing a record to be made of the'metal's first and last appearance. Of course, should the cupola be used simply for the purpose of melting to get metal to pour a casting, it could then be stopped and tapped the same as any cupola used in ordinary practice. If the cupola is employed for testing the comparative fusibility of metals, it may often require about six men to operate it  one for timekeeper, one to charge on fuel evenly and press it down so as to preserve a solid fire until the iron is about half down, one at each tap hole to keep it open that the rnetal may flow freely, and then, if the metal is to be caught into moulds, two men on each side to take away the filled moulds and replace empty ones. If the cupola is only to be used to obtain metal to pour a small casting, or to record the time of fusing by letting the metal down into a ladle or " pig " as it comes out, then two men are sufficient to operate it; In. charging any metal for a comparative test, care must be exercised to have theations of others, down to that most readily fused.the bottoms. Our Mj)pnrheii.sion as to loss of iron through slai;" was	r> ">'	I I   O/..