BRASS, in Chemistry and Manufactures, an alloy of copper and zinc. This name, however, has not been exclusively applied to the alloy of these metals; for the gunmetal, 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 brass 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 resistance. A larger portion of tin gives increased hardness, but is less fitted to bear a straining resistance, on account of its brittleness. Its elasticity is very great, which fits it for bells. In this state it is called bell-metal; and with a still greater proportion of tin it forms an alloy employed for the mirrors of reflecting telescopes. The alloy of copper with tin is easily distinguished from that with zinc, from the agreeable colour of the latter, which varies with the proportions of the metals. Pinchbeck has the least proportion of zinc. Common brass has more zinc, and the gold-coloured alloy called prince’s metal contains a still greater proportion of zinc. An alloy of copper with a very large proportion of zinc is used for the common white metal buttons.

i The various alloys of copper with tin and zinc forming the different kinds of brass, are to be considered as chemical compounds, and, of course, governed by the same laws of definite proportions which obtain in 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 atoms being previously known.

The weight of the atom of copper being 8, tin 7∙35, and zinc 4, the following tables exhibit the proportions of the various alloys, expressed in atoms, and their proportions by weight, the third column pointing out the colour and character of the resulting compound. CZ and T are to represent the atoms of the metals respectively.
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Hitherto the proportions of these alloys have depended upon the practice of workmen, guided by numerous trials; but what confirms the law of definite proportions, is the necessity of adhering to fixed proportions, ascertained by trial. By attending to the proportions pointed out in the above tables, the most striking and proper compounds will be produced, without the trouble of trying. Any intermediate proportions will, doubtless, be marked by defective colour, irregular crystallization, or imperfect malleability.

Although the most direct way of forming these different kinds of brass is by immediately combining the metals together, one of them, which is most properly called brass, was manufactured long before ziric, one of its component parts, was known in its metallic form. The ore of the [7:5:186]latter metal was cemented with sheets of copper, charcoal being present; and the zinc was united with the copper, without becoming visible in a distinct form. The same method is still practised for making brass.

The materials used in making brass are copper in small round masses, produced by passing the melted 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 oxide of iron, which gives it a reddish appearance. As it is chiefly found in combination with lead, the lumps frequently contain more or less gallena, which requires to be separated by the same means as those employed for purifying lead ore. The calamine is first reduced to powder, and the lead is then separated by washing. When the calamine is separated, reduced to powder, and sifted, it is heated upon the hearth of a reverberatory furnace. This expels the volatile matter, which is principally water and carbonic acid. What remains is principally oxide 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 proportions in which they are mixed together are equal weights of copper and prepared calamine, and ⅛th their weight of powdered charcoal.

This mixture, intimately blended, is compressed into a crucible of the form of fig. 3, Plate CXXVII. One of these crucibles holds about 100 lbs. of brass when the process is finished; but as this consists of the pure copper and zinc, the pot, when charged, will contain of copper 66 ’ 3 lbs., of calamine 63 lbs., and of charcoal powder 13 lbs. When the crucible is filled, the contents should be covered with a mixture of clay sand and horse-dung, in order to defend the metals and charcoal from the action of the air. When this covering is strictly attended to, less charcoal powder may be employed, and a larger dose of the other ingredients may be put in its place; but it is generally the most defective part of the process.

Fig. 1, Plate CXXVII., is a plan of the furnace. The part AB is taken at the level EF, showing the opening into the furnace on the ground floor at a and b; while c and d are horizontal flues leading to the chimney f which may be cut off from the same by the dampers seen in the dark part of the fluc. CD, in the same figure, is a plan on the level GH, where the pots rest upon the cast-iron plate on the bottom x, y.

Fig. 2 is an elevation and section of the same furnace. AB shows a front view of the pyramidal chimney, and the archway opening into it. CD is a section of the same, through the middle of the fire-place 11. R,P,Q, is a vaulted passage going across the building, and open at both ends for the admission of air, which passes through the openings in the arch, into the fires. The bottom of the furnace is not a common grate, but a thick plate of castmetal, perforated with holes for the air to pass through; one hole being between each pot, as they are seen arranged in fig. 1, at I, I, and also in the section at x, y. When the pots are put upon the plate, the fire is not placed immediately upon them, as it would not only injure them, but displace the covering. To prevent this, the pots are first covered by some dried heath or common brambles, which defend them for a time, when the fuel is thrown in. By the time the brambles are consumed the coal will have coked upon the pots, and thus act as a defence for the rest of the process. The fire is kept up from twelve to twenty hours at the Cheudle brass-works in Staffordshire, from which these drawings were taken. They cast twice in the twenty-four hours.

After the refuse is skimmed off, the melted brass is cast into ingots if sold for melting over again, and into plates if intended to be rolled into sheets or made into wire. The plates are cast between large blocks of Cornwall stone. The lower stone is fixed, and the face made even and smooth, by filling up the recesses of the rough stone with fine sand. The upper stone is similarly prepared, and is suspended, over the fixed one. The height and breadth of the place to receive the metal is limited by iron bars laid on the lower stone. The upper stone is then let down upon the bars. The lower stone is a little longer than the upper one, and projects to the front. Being a little higher in that part, it forms a lip or mouthpiece for receiving the metal. The flat sides of the cast plate are therefore bounded by the surface of the stones, and the edges of these by the bars above mentioned. The ingot moulds are recesses in blocks of cast-iron, open on one side.

The most certain and correct method of forming brass and the other compounds expressed in the table above given, is by immediately uniting the metals in given weights. It should, however, be observed, that it will he found difficult to introduce zinc into melted copper. The best way of uniting it with copper, in the first instance, is to introduce the copper in thin slips into the melted zinc, till the alloy requires a considerable heat to fuse it, and then to unite this alloy with the melted copper.

Corinthian Brass, famous in antiquity, is a mixture of gold, silver, and copper. Lucius Mummius having sacked and burnt the city of Corinth, 146 years before Christ, it is said this metal was formed from the immense quantities of gold, silver, and copper, with which that city abounded, having been melted and run together by the violence of the conflagration.

Brass, in the glass trade. Thrice calcined brass is a preparation employed by glassmen to give many very beautiful colours to their work. The manner of preparing it is this: Having placed thin plates of brass on tiles on the leet of the furnace, near the occhis, let it stand to be calcined there for four days, and it will become a black powder sticking together in lumps. Pulverize this, sift it fine, and recalcine it during four or five days more; at the end of which time it will not stick together, but remain a loose powder of a russet colour. This is to be calcined a third time in the same manner; but great care must be taken in the third calcination that it be neither overdone nor underdone. The way to be certain when it is right, is, to try it several times in glass while melting. If it causes the glass, when well purified, to swell, boil, and rise, it is properly calcined; if not, it requires longer time. This, according to the different proportions in which it is used, produces a sea-green, an emerald-green, or a turquoise colour.

Brass, by long calcination alone, and without any mixture, affords a fine blue or green colour for glass; but there is a method of calcining it also with powdered brimstone, so as to make it afford a red, a yellow, or a chalcedony colour, according to the quantity and other variations in the using of it. This method of calcination is the following: Cut thin plates of brass into small pieces with shears, and lay them stratum super stratum, with alternate beds of powdered sulphur, in a crucible ’, calcine this for twenty-four hours in a strong fire, then powder and sift the whole, and finally expose the powder upon tiles for twelve davs to a reverberating furnace, at the end of which time powder it fine and keep it for use. The glass-makers have also a method of precuring a red powder from brass by a more simple calcination, which serves for many colours. The method of preparing it is this: They put small and thin plates of brass into the arches of the glass furnaces, and leave them there till they are sufficiently calcined, [7:5:187]which the heat in that place, not being sufficient to melt them, doos in great perfection. The calcined matter, powdered, is of a dusky red, and requires no further preparation.

BRASS-Colour, one prepared by the braziers and colourmen to imitate brass. There are two sorts of it, the red brass or bronze, and the yellow or gilt brass. The latter is made only of copper-fiīings, the smallest and brightest that can be found; with the former it is usual to mix some red ochre, finely pulverized; and both are used with varnish. In order to make a fine brass that will not take any rust or verdigris, it must be dried with a chafing-dish of coals as soon as it is applied. The finest brass-colour is made of powdered brass imported from Germany, diluted into a varnish, which is prepared and used after the following manner: The varnish is composed of one pound four ounces of spirits of wine, two ounces of gum-lae, and two ounces of sandarae; these two last drugs being pulverized separately, and afterwards put to dissolve in spirit of wine, and care being taken to fill the bottle but half full. The varnish being made, mix a quantity of it with the pulverized brass, and apply it with a small brush to that which it is intended to brass over. But too much must not be mixed at once, because the varnish being very apt to dry, it would not be possible to employ it all soon enough. It is therefore better to make the mixture at several times. In this manner are brassed over figures of plaster, which look almost as well as if they were of cast brass.

Brass Leaf is made of copper, beaten into very thin plates, and afterwards rendered yellow. The German artists, particularly those of Nuremberg and Augsburg, are said to possess the best method of giving to these thin plates of copper a fine yellow colour like gold, by simply exposing them to the fumes of zinc, without any real mixture of it with the metal. These plates are cut into little pieces, and then beaten out fine like leaves of gold; after which they are put into books of coarse paper and sold at a low price for the vulgar kinds of gilding. The parings or shreds of these very thin yellow leaves, being well ground on a marble plate, are rcduced to a powder similar to gold, which serves to cover, by means of gum-water or some other glutinous fluid, the surface of various mouldings or pieces of curious workmanship, giving them the appearance of real bronze, and even of fine gold, at a very trifling expense, because the gold colour of this metallie powder may be easily raised and improved by stirring it in a wide earthen bason over a slow fire.