Brass.

Brass. In ancient history, biblical and profane, frequent allusions are made to the employment of brass in the construction of musical instruments, vessels, implements, ornaments, and even gates; but as no mention is made of its mode of manufacture, or even of its composition, it is doubtful if the brass of the ancients, with the exception of some made by the Romans, was composed of copper and zinc. Dr Percy (Metalurgy of Copper, Murray, 1861) concludes, from the analysis of some of their coins, that the ancient Romans were well acquainted with the art of preparing brass, in the sense of an alloy of copper and zinc. However this may be, it was bronze, and to some extent iron, not ordinary brass, that was all but universally used by them for metal objects other than those made of gold and silver. Zinc does not appear to have been known as a separate metal in Europe till the 16th century; but no doubt one or more of its ores might have been employed by the Romans along with copper to prepare brass.

The term brass is commonly understood to mean an alloy of copper and zinc of a more or less yellow colour. Bronze (q.v.), on the other hand, means an alloy of copper and tin. But there is now a tendency to make brass a generic term, so as to include bronze as well as alloys of copper and lead. In this way, under one general name, there would be a zinc, a tin, and a lead group of alloys. For the tin group, see BRONZE.

A tough brass for engine-work can be made of copper 6¾, tin 1, and zinc 1; and another kind for very heavy bearings of copper 6½, tin 1, and zinc ¼ (Spretson).

As a rule, brass is easily fusible and also very malleable and ductile. Therefore it can be readily cast into moulds, rolled into sheets, hammered or stamped into various shapes, and drawn into wire. It is likewise of a pleasing colour. Brass is harder, and so stands wear better than copper, resists atmospheric influences as well, and is cheaper than that metal. These valuable properties render it next in importance to iron and steel in the metallurgical arts. The malleability of brass, however, varies with its composition, with the temperature, and with the presence, even in minute quantities, of foreign metals. Some kinds are malleable only while cold, others only while hot, and there are varieties wanting in this property at any temperature. All kinds become brittle if heated well up to their fusing-point.

Brass is more tenacious than any of the common metals except iron, steel, and copper. But if subjected to a continuous tension for some length of time, it undergoes, in many cases at least, a molecular change, and loses its tenacity. It is therefore not quite safe to hang pictures with heavy frames or weights of any kind on brass chains or wire. The surface of this metal, if not protected by lacquer, soon tarnishes and becomes black.

The old process of making brass by mixing small bits of copper with powdered zinc ore, and heating the mixture in pots in a furnace, is now almost obsolete. The modern way of preparing it is by mixing metallic zinc directly with copper in crucibles or in a reverberatory or cupola furnace. There is least waste with crucibles. The copper is first melted, and the zinc then added in a hot state, care being required to prevent much loss by the latter volatilising. When other metals are added they are also heated first.

From the crucibles the molten brass is either poured into moulds to form ingots for remelting, or more commonly into ordinary sand moulds prepared from patterns (see FOUNDING). Brass takes a sharp impression when cast in a mould. Plates or slabs for rolling into sheets are cast between two marble blocks thinly lined with loam, the sides and ends being made up with sand. These are reduced by 'breaking-down rollers,' and afterwards by other rollers, till they become of the required thickness. As is the case with tube and wire drawing, these sheets are annealed at intervals during the process of rolling. See ANNEALING.

Ordinary drawn brass tubes are soldered longitudinally, but the tubes for locomotive boilers are formed by drawing out a solid cylinder of brass. This was looked upon as a great feat, when the process, after many trials, first succeeded in 1838.

The industries which either wholly or partially depend upon brass for their raw material, so to speak, are so numerous and so varied, that even the more important of them would form a considerable list. Birmingham is the headquarters of these industries. See ALLOY, METALLURGY, METAL-WORK, WIRE; and works on brass-founding by Larkin (1866), and Graham (1887).