Of all the alloys of one metal with another, none are more useful than those of copper with zinc, forming the different varieties of brass. This alloy appears to have been in use at a very early period, if the Latin word aes is correctly translated brass instead of copper; for Lucretius observes, Et prior erat ceris quam ferri cognitus usus - "The use of brass was known before that of iron." Pliny speaks of its use soon after Rome was founded, and states that Numa, the successor of Romulus, formed the workers of it into a kind of community. It is also certain that before zinc was ever obtained as a distinct metal, its alloy with copper was in use, the zinc ores being reduced in process of making the alloy by the charcoal mixed with them; when thus formed, the metallic zinc is absorbed in the copper placed in the crucible, without once appearing in its own form. Brass continued to be manufactured in this manner till the year 1781, when James Emerson obtained a patent for making it by direct fusion of its metallic elements. His method, which is still employed, is to melt the metallic zinc and introduce the copper in thin slips. "When enough is added to render the alloy difficult of fusion, the heat is increased and the additional copper required is introduced in a melted state.
Another process is to melt the copper first and introduce the zinc with iron tongs; but at the present time brass is usually made by placing the copper and zinc in alternate layers in fire-clay or graphite crucibles, and smelting them under a thick layer of charcoal. When the fusion is complete the alloy is cast into granite moulds luted with clay. Owing to the uncertain quantity of zinc which escapes in consequence of the high melting point of copper, which is above 2,200° F. (Daniel, 2,548°), while that of zinc is only about 770°, it is difficult to exactly preserve the proportions of the two metals. Old brass is often used, which also complicates the estimation of the relative quantities of the constituents. From these causes the exact composition is never known except from analysis. The best proportions to make fine brass are two equivalents of copper, 31.7 x 2 = 63.4, and one equivalent of zinc, 32.5; or in 100 parts, 66.11 of copper to 33.89 of zinc. The usual practice is to mix two parts of copper, by weight, with one of zinc. The quality of brass, in regard to its ductility, malleability, and tenacity, varies much according to the proportions of its ingredients.
In certain proportions it is more ductile at ordinary temperatures than pure copper, but it is generally brittle at a red heat. The most ductile of all the alloys of copper and zinc are those containing 84.5 per cent, of copper and 15.5 of zinc, called tombac, and brass which contains 71.5 per cent, of copper and 28.5 of zinc; but in this latter proportion it is not malleable while hot, and articles made of it must be cast. An alloy prepared of 60 parts of copper and 40 of zinc has a fine close-grained fracture and greater density than common brass, and when hot can be rolled into thin sheets. This is known as Muntz's metal, a patent having been obtained for it by Mr. G. B. Muntz of Birmingham in 1832. It has to a great extent superseded copper for sheathing ships, and possesses the advantages of keeping the bottoms cleaner and of being less expensive. The addition of one or two per cent, of lead to brass improves its quality for being worked with tools, but impairs its toughness by diminishing its adhesiveness. Bath metal, Prince's metal, tombac, pinchbeck, Mannheim gold, and other alloys resembling inferior jeweller's gold, contain 80 per cent, or more of copper; and on account of the expensiveness of tin, have been much used as substitutes for bronze.
Oreide is the name given by Meurier and Valient of Paris to an alloy of golden brilliancy. It is prepared by fusing 100 parts of copper, by weight, and adding 6 parts of magnesia, 3.6 parts of sal ammoniac, 1.8 part of quicklime, and 9 parts of crude tartar gradually, and stirring for about half an hour. Seventeen parts of zinc are then added, and after stirring, the crucible is covered and kept hot for about 35 minutes. It is then uncovered, and the alloy carefully skimmed and cast into a metal or moist sand mould. It has a fine grain, is malleable, takes a brilliant polish, and may have its complexion restored by acidulated water. Corinthian brass was an alloy of gold, silver, and copper. In the following table of the composition of various alloys of copper and zinc used in the arts, taken from Watts's "Dictionary of Chemistry," it will be observed that some specimens contain small portions of tin and lead, in some cases enough of the former to approach the character of bronze:
Brass from Augsburg........
" " Romilly........
Coin of Titus Claudius......
" Nero, A. D. CO......
" Titus, A. D. 79.....
Antique bracelet, Naumburg........
Antique chain, Ronneburg..
Statue of Louis XIV.......
" Louis XV.........
If copper sheets are exposed at a red heat to the vapors of zinc, they are completely penetrated by them and converted to brass. Lyons gold lace is made by thus exposing copper rods to the vapor of zinc until the surface is converted to brass, and then drawing them out into wire. If a copper coin is placed in a crucible above a mixture of zinc oxide and charcoal, and heated, it will become brass without obliteration of the device. - Brass is much used for the bearings of machinery, for making the reeds of wind musical instruments, for those parts of machinery where iron would be objectionable or where ornamentation is desired, for various kinds of tubing, for tacks, bolts, and screws, and for optical and other instruments of like construction. - Brass solder is usually composed of two parts of brass to one of zinc, but the proportions may be made according to the desired degree of fusibility, which property is almost in exact proportion to that of the zinc used. (See Brazing).