Brass which is required for rolling into sheets should contain no antimony, as this metal renders the alloy very brittle, and extremely liable to crack. That which has to be turned contains inva riably a small proportion of lead, usually about 2 per cent; this addition is made when the crucible containing the fused metals is taken out of the furnace. The following is an analysis by Chaudet of a brass which is well adapted for this purpose :— Copper .. 65.8 Lead.. .. 2.15 The presence of tin was believed to be accidental. Brass required for engraving upon should always contain a little tin, in order to render it sufficiently firm.
Brass may be made either in a crucible, as in the ordinary Birmingham brass-foundries, or in a reverberatory furnace. The crucibles commonly used are circular, and made of fireclay ; they are about 1 ft. in depth, 8 in. in diameter at the top, and 6 in. at the middle, internal measurements ; they are also / in. in thickness at the top, and 2 in. at the bottom ; they contain about 84 lb.
The copper is first placed in the crucible, and the zinc is added to it bit by bit with much caution, as soon as the former metal is in a state of incipient fusion. The ingots of copper should be heated to redness before being put into the crucible. In Birmingham, the chief seat of the brass manufacture, the furnaces employed are square, their dimensions being 10 in. in the side and 24 iu. in depth. Those used in London are circular in form. The flue between the furnace and the chimney should be narrow, and should lead out from the top of the furnace ; its dimensions vary with those of the chimney, and with other conditions. Coke of the very best quality is the fuel employed. When the mixture is well fused together, the cinders are removed, and it is poured, if required for casting, into sand-moulds ; if, on the contrary, it is to be used for rolling, it is cooled in close iron ingotmoulds, previously heated, oiled, and dusted lightly over in the interior with powdered char coal. A loss of zinc invariably occurs by volatilization, which is always taken into consideration when weighing out the metal.
The following formula) show the composition of different varieties of brass:— For fine brass, an alloy of 2 parts of copper with 1 part of zinc is the correct proportion ; the metals are melted separately, poured suddenly together, and united by vigorous stirring. By slightly raising the proportion of copper, as 7 parts of copper and 3 parts of zinc, a b•ight-yellow and malleable alloy is obtained. More copper still, as 4 parts of copper and 1 part of zinc, yields a metal of darker colour than the last.
For malleable brass, good proportions are 33 parts ; zinc, 25 parts ; or, copper, 3 parts ; zinc, 2 parts. These are malleable when hot.
For button brass, an alloy of 8 parts of copper and 5 parts of zinc is commonly used by the Bir mingham makers, under the name of "platin.' An alloy paler in colour, and used for the common buttons, consists of 25 parts of copper, 20 parts of zinc, 3 parts of lead, and 2 parts of tin.
Brass for fine castings is an alloy of 62 parts of copper, 35 parts of zinc, 2 parts of lead, and 1 part of tin ; this is rather pale and brittle. An alloy used for the same purpose, and of a deep, rich colour, consists of copper, 90 parts ; zinc, 7 parts ; tin, 2 parts ; lead, 1 part.
For gilding, good proportions are: copper, 64 parts; zinc, 32 parts ; lead, 3 parts ; tin, 1 part. For soldering, an alloy of fine brass, 12 parts ; zinc, 6 parts; tin, 1 part, melted together, is most commonly.employed.
For turning, the proportions are : fine brass, 98 parts ; lead, 2 parts, both melted together ; or, copper, 65 parts ; zinc, 33 parts; lead, 2 parts.
For wire, an alloy of copper, 72 parts; zinc, 28 parte, is commonly used ; this alloy must be afterwards hardened by tempering.
Bronze.—This alloy has been known and employed since very remote ages. It was used exclusively by the ancients for making sworde and other sharp instruments, for coinage, statues, aud many other useful and ornamental purposes. It is composed of copper and tin, sometimes with the addition of a little zinc and lead. Great variations are made in the proportions of the two chief constituents, according to the nature of the application for which it is destined. For statuary, the proportions used by the Brothers Keller, the most noted bronze-founders of modern times, were e.opper, 91.40; zinc, 5.53 ; tin, 1-70 ; and lead, 1.37. The bronze coinage of this country contains 95 parts copper, 4 of tin, and 1 of zinc. The addition of a little zinc to the alloy is an advantage, but too much diminishes its tenacity ; lead is objectionable, owing to its tendency to sink after casting, thus destroying the homogeneity of the alloy. The metals should be melted rapidly to prevent loss of metal by oxidation, and the melted mass should be covered with a layer of charcoal, and kept constantly stirred. The operation is generally carried on in refractory crucibles, heated in a reverberatory furnace of suitable form. The cooling in the moulds must be as rapid as possible, in order to prevent the separation of the metals.