Brass Founding. 37 Brass Founding.—The moulds used in the casting of brass require no new description, the only difference in this class of work being the manner in which the metal is melted. As the castings required are much smaller than those we have recently been describing, the brass is made directly in crucibles of some,impermeable material, black-lead being the best. The melting furnaqe is-shewn in Fig. 50, and usually there are several of these side by side and separately connected with the chimney. The top of .the furnace is only a little above the floor level, and in brass foundries it is customary to have the part of the shop near the furnace entirely reserved for casting purposes; the casting and moulding shops being entirely divided by a wall in the best establishments. The principal difficulty in the making of brass is that of the different fusing points of the two metals used—Copper and Zinc. Thus, copper melts at 1996° F., while the melting point of zinc is as low as 773° F. The copper is first melted, and the zinc is only introduced a short time before casting, by means of tongs, pushing it down in small pieces under the melted copper. It should flare up on doing this, which is a sign that the heat is quick enough. If it is left in too long, much of the zinc will be lost by evaporation.* * See also Appendix I., p. 747.