BRASS, an alloy consisting mainly if not exclusively of copper and zinc; in its older use the term was applied rather to alloys of copper and tin, now known as bronze (q.v.).
The brass of the Bible was probably bronze, and so also was much of the brass of later times, until the distinction between zinc and tin became clearly recognized. It is quite likely that from very early times brass was made accidentally, owing to the admix ture of zinc ores with those of copper, but was not recognized as distinct from bronze. The Latin word aes signifies either pure cop per or bronze, not brass, but the Romans comprehended a brass compound of copper and zinc under the name of orichalcum or aurichalcum, into which, according to Pliny, copper was converted by the aid of cadmic (a mineral of zinc). One of the earliest examples of Roman brass is a coin of date 20 B.C. containing 17.3% of zinc. There was considerable production of brass in the Low Countries commencing about A.D. 300, and it became an im portant article of commerce. There are ecclesiastical brasses, or "lattens," still to be seen in many churches, particularly in East Anglia. The word latten is a corruption of the French word laiton; and till about 155o latten was always imported from Flanders and Germany. One of the earliest lattens in England is at Stoke d'Abernon and commemorates Sir John Daubernon (c. 1277). The composition of these lattens is approximately 66% of copper, 1-3% of tin, up to 7% of lead, and the remainder of zinc.
There is good evidence of the manufacture of brass in England in the 16th century, for Queen Elizabeth by patent granted to William Humfrey and Christopher Schutz the exclusive right of working calamine and making brass. This right subsequently devolved upon a body called "The Governors, Assistants and So cieties of the City of London of and for the Mineral and Battery Works," which continued to exercise its functions down to the year 1710. The word "battery" refers to the process of hammer ing brass into sheets, which was the normal method in England for some 200 years ; but by the latter half of the 18th century this method began to be superseded by the rolling-mill, and it is now obsolete. Till 185o brass was still being made by the calamine process, in which copper shot were heated with calamine and charcoal. The resulting partially-brassed shot were then melted, mixed and cast. This process, however, had been going out of favour since 1781, when James Emerson patented the production of brass from copper and zinc metals, which is the method now in use.
Copper and zinc will alloy in all proportions, but there are several distinct series, known technically as "solid solutions," which are distinguished by the letters of the Greek alphabet, the alpha brass having the greatest percentage of copper and being the sole constituent of all wrought brasses containing over 64% of copper. It is to this constituent that brass owes its malleability and general usefulness. The beta mixture contains less copper and is of a much harder nature, and as this constituent increases the brass becomes less amenable to cold work, though it can be easily worked hot. The other solid solutions contain less and less copper.
The unworkable brasses are known as the white brasses and are not of great industrial importance. The 5o% mixture is much used in a crushed or granulated form for purposes of brazing, and those with lower percentages of copper can be cast and used for sliding parts, since though brittle they offer considerable resistance to frictional abrasion. They also form the basis of certain alloys used for die-casting, a form of casting which has come into much prominence since the war.
The malleable brasses may be further divided into the cold working and the hot working alloys. The dividing line is not pre cisely drawn, but commercially it is not usual to work alloys of less than 62% copper cold since an excessive amount of annealing would be needed. Hot working above 62% copper is attended with considerable difficulty on account of the very brittle nature of these alloys when just below red heat, and it does not give the fine structure of the metal and the smooth surface which is ob tained with cold work.
The most widely used of the brasses are those of 70% copper and from 62 to 66% copper. The former, which is known as cart ridge metal and is the most suitable for extreme amounts of work, has mechanical properties, in the cast state, of 15 to 16 tons per sq.in. and 6o% elongation; when cold worked, of 3o-4o tons and 10% .elongation or less; when cold worked and annealed, of 21 tons and up to 7o% elongation. The general mechanical proper ties of brass are very varied; indeed it is this wide range which makes brass such an important alloy. By variation of the compo sition, or by the amount of cold work put upon the metal, or by the degree of annealing, a tensile strength of from 15 to 45 tons per sq. in., an elongation of from 3% to 70%, and a hardness of from 6o to 150 Brinell can be obtained with all the intermediate degrees. It is readily drawn into fine wire, rolled into strips as thin as •oo 'in , drawn into tubes and extruded as rods or sections.
There is a series of alloys which are commonly classed as brasses since brass is their foundation, but they contain other metals also. (See also ALLOYS; COPPER; ZINC.) BIBLIOGRAPHY.-W. T. Brannt, Metallic Alloys (2nd ed. 1896) ; H. Bibliography.-W. T. Brannt, Metallic Alloys (2nd ed. 1896) ; H. Le Chatelier, Contribution a l'etude des Alliages (1901) ; W. Gowland, "Copper and its Alloys in Early Times" (Journ. Inst. Metals, vol. vii., 1912) and The Metallurgy of the Non-Ferrous Metals (3rd ed. 1921) ; E. F. Law, Alloys (2nd ed. 1914) ; Sir W. Roberts-Austin, An Intro duction to the Study of Metallurgy (6th ed. 1914) ; G. H. Gulliver, Metallic Alloys (4th ed. 1921) ; L. Aitchison and W. R. Barclay, Engi neering Non-Ferrous Metals and Alloys (1923) ; Institute of Metals, Journals (passim) . (S. P.)