BRASS, in Chemistry and Manufacture", an alloy of copper and zinc. This name, however, has not been exclusively applied to the alloy of these metals; for the gun-metal, which has been also called brass, is an alloy of copper with tin. The same alloy, with more tin, is used in machinery, and is preferred to the alloy of copper and zinc, on account of its greater hardness.
It appears from the analysis of the braes of the ancients, that it was an alloy of copper and tin. A small portion of tin gives to copper great hardness, and renders it capable of bearing much greater re sistance. A larger portion of tin gives increased hardness, but is less fitted to bear a straining resist ance, on account of its brittleness. Its elasticity is very great, which fits it for bells. In this state it is called bell-metal ; with a still greater pro portion of tin, it forms an alloy employed for the mirrors of reflecting telescopes. The alloy of cop per with tin is easily distinguished from that with zinc from the agreeable colour of the latter, which varies with the proportions of the metals. Pinch beck has the least proportion of sine. Common brass has more zinc, kind the gold-coloured alloy called Prince's metal, contains a still greater propor tion of zinc. Au alloy of copper with a very large proportion of zinc is used for the common white metal buttons.
These various alloys of copper with tin and zinc forming the different kinds of brass, are to be con sidered as chemical compounds, and, of course, go verned by the same laws of definite proportions which belong to the more conspicuous compounds.
On these principles, which cannot be doubted, we have an unerring rule for uniting these and other metals in the best proportions, the weights of their stoma being previously known. See the irticle Aromic THRORY in this Supplement.
The weight of the atom of copper being 8, tin 7.35, and zinc 4 ; the following table will exhibit the pro portions of the various alloys, expressed in atoms, and their proportions by weight, the third column pointing out the colour and character of the result ing compound. CZ and T are to represent the atoms of the metals respectiv'ely.
Hitherto the proportions of these alloys have de pended upon the caprice of workmen, obtained by numerous trials ; and what confirms the law of de‘ finite proportions, is proved by the necessity of ad hering to such fixed proportions, ascertained by trials. By attending to the stages of composition
pointed out in the above table, the most striking and proper compounds will be produced, without the trouble of trying. Any proportions intermediate will, doubtless, be marked by defective colour irre gular crystallization, or imperfect malleability, in such as are expected to be so.
Although the most direct way of forming these different kinds of brass is by immediately combining the metals one of them, which is most properly celled brass, was manufactured long be fore zinc, one of its component parts, was known in its metallic form. The ore of the latter metal was cemented with sheets of copper, charcoal being present. The zinc was formed and united with the copper, without becoming visible in a distinct form. The same method is still practised for making brass, which we are about to describe.
The materials used in making brass are, copper in small rounded masses produced by passing the melt ed metal through an appropriate vessel into water, in which state it is called shot copper, and calamine, an ore of zinc. This latter substance is a carbonate of zinc, often containing some oxyd of iron, which gives it a reddish appearance. As it is chiefly fnund with lead, the lumps frequently contain more or leas paella, which requires to be separated by the 'lame means employed for purifying lead ore. The cala ague is first reduced te,powder, and the lead is then sepal:sued by washing. When the calamine is sepa rated, reduced to powder, and sifted, it is heated upon the hearth of a reverberatory furnace. This 4Veht do* valatila patter, which is principally water and carbonic acid. What remains is principally oxyd of zinc, abounding with some earthy matter, and probably much carbonic acid, which is not all expelled ,by the heat. The calamine thus prepared, charcoal powder, and copper, are the materials to be operated upon. The proportion in which they are mixed together, are equal weights of copper and prepared calamine, and their weight of pow dered charcoal.