The first step in making brass is to plunge slips of copper into melted zinc till an alloy of somewhat difficult fusion be formed, to raise the heat, and add the remaining proportion of the copper.
The brass of the first fusion is broken to pieces, and melted with a fresh quantity of zinc, to obtain the finished brass. Each melting takes about 8 or 9 hours. The metal is now cast into plates, about 40 inches long by 26 inches broad, and from one third to one half inch thick. The moulds are, in this case also, slabs of granite mounted in an iron frame. Granite appears to be preferred to every thing else as a mould, because it preserves the heat long, and by the asperities of its surface, it keeps hold of the clay lute applied to secure the joinings.
The cast plates are most usually rolled into sheets. For this purpose they are cut into ribands of various breadths, commonly about 61⁄2 inches. The cylinders of the brass rolling-press are generally 46 inches long, and 18 inches in diameter. The ribands are first of all passed cold through the cylinders; but the brass soon becomes too hard to laminate. It is then annealed in a furnace, and, after cooling, is passed afresh through a rolling press. After paring off the chipped edges, the sheets are laminated two at a time: and if they are to be made very thin, even eight plates are passed through together. The brass in these operations must be annealed 7 or 8 times before the sheet arrives at the required thinness. These successive heatings are very expensive; and hence they have led the manufacturers to try various plans of economy. The annealing furnaces are of two forms according to the size of the sheets of brass. The smaller are about 12 feet long, with a fire place at each end, and about 13 inches wide. The arch of the furnace has a cylindrical shape, whose axis is parallel to its small side. The hearth is horizontal, and is made of bricks set on edge. In the front of the furnace there is a large door, which is raised by a lever, or chain, and counterweight, and slides in a frame between two cheeks of cast iron. This furnace has, in general, no chimney, except a vent slightly raised above the door, to prevent the workmen being incommoded by the smoke. Sometimes the arch is perforated with a number of holes. The sheets of brass are placed above each other, but separated by parings, to allow the hot air to circulate among them, the lowest sheet resting upon two bars of cast iron placed lengthwise.
The large furnaces are usually 32 feet long, by 61⁄2 feet wide, in the body, and 3 feet at the hearth. A grate, 13 inches broad, extends along each side of the hearth, through its whole length, and is divided from it by a small wall, 2 or 3 inches high. The vault of the furnace has a small curvature, and is pierced with 6 or 8 openings, which allow the smoke to pass off into a low bell-chimney above. At each end of the furnace there is a cast-iron door, which slides up and down in an iron frame, and is poised by a counterweight. On the hearth there is a kind of railway, composed of two iron bars, on the grooves of which the carriage moves with its loads of sheets of brass.
These sheets, being often 24 feet long, could not be easily moved in and out of the furnace; but as brass laminates well in the cold state, they are all introduced and moved out together. With this view, an iron carriage is framed with four bars, which rest on four wheels. Upon this carriage, of a length nearly equal to that of the furnace, the sheets are laid, with brass parings between them. The carriage is then raised by a crane to a level with the furnace, and entered upon the grooved bars which lie upon the hearth. That no heat may be lost, two carriages are provided, the one being ready to put in as the other is taken out; the furnace is meanwhile uniformly kept hot. This method, however convenient for moving the sheets in and out, wastes a good deal of fuel in heating the iron carriage.
The principal places in which brass is manufactured on the great scale in England, are Bristol, Birmingham, and Holywell, in North Wales.
The French writers affirm, that a brass, containing 2 per cent. of lead, works more freely in the turning lathe, but does not hammer so well as the mere alloy of copper and zinc.
At the brass manufactory of Hegermühl, upon the Finon canal near Potsdam, the following are the materials of one charge; 41 pounds of old brass, 55 pounds refined copper (gahrkupfer) granulated; and 24 pounds of zinc. This mixture, weighing 120 pounds, is distributed into four crucibles, and fused in a wind furnace with pitcoal fuel. The waste varies from 21⁄2 to 4 pounds upon the whole.
