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stood by the term "alloys." For example, one per cent of zinc in copper will make it hard and red-short, but 20 per cent of zinc alloyed with 80 per cent copper will produce an exceedingly malleable alloy. Alloys of copper will be considered as those alloys in which copper is the principal constituent, and not those in which copper plays a subordinate part. Thus standard silver and standard gold contain copper, and these are not termed copper alloys, but silver and gold alloys respectively. The chief alloys of copper are: brass, bronze, and German silver, and these are the alloys most extensively used in the various industries.

BRASS

§ 23. The term brass will be used in this work to signify all alloys of which copper and zinc are the essential and chief constituents; but it is generally limited in the industrial arts to those alloys which are decidedly yellow, or have the yellowish tint characteristic of common brass. Alloys of zinc and copper are known in commerce by a variety of names, and indeed, great confusion has been introduced by the multiplication of empirical names to represent one and the same substance. This is doubtless owing to the ignorance that formerly prevailed, when every mixture was jealously guarded as a great secret, and fanciful names given to hide the real composition. Moreover, some alloys have been handed down to us from very early times, and their names corrupted so as to have different appellations in different localities. Dr. Percy mentions "that the terms tombac, prince's metal, similor, and Mannheim gold are used by some authors to designate alloys consisting of about 85 per cent copper and 15 per cent zinc ; whereas, according to others, prince's metal and Mannheim gold are synonymous, and are composed of 75 per cent copper and 25 per cent zinc; according to another author, similor consists of about 711 per cent copper and 28 per cent zinc; and Mannheim gold

of 80 per cent copper and 20 per cent zinc; and again, according to another author, similor and Mannheim gold are synonymous, and are applied to alloys of copper containing from 10 to 12 per cent zinc and from 6 to 8 per cent tin."1

That brass was known to the ancients is beyond dispute, but its direct preparation from copper and zinc is an invention of more modern times. Mines containing the ores from which yellow metal was produced were highly esteemed, and much regret was expressed when the ores were exhausted, In process of time it was observed that a certain ore (probably calamine ZnCO), when smelted in contact with copper, produced a metal of a yellow colour, and this process long continued to be used for making brass, without it becoming known what metal the ore contained, and what imparted the change of properties to the copper. The preparation of brass, by direct mixing of the two metals, copper and zinc, was probably practised soon after the metal zinc was first isolated. In 1743 it is stated that zinc works were established at Bristol, and in 1758 a patent was granted to Mr. Champion of Bristol for making "spelter" and brass, but the brass was still made by the indirect process from calamine ZnCO, or calcined blende ZnO. Hutton states that the brass industry was introduced into Birmingham about 1740 A.D. by the family of Turner, and that the chief supply of the metal was derived from the Macclesfield, Cheadle, and Bristol companies.

Commercial brass never consists entirely of copper and zinc, since whatever impurities exist in the separate metals will also be found in the alloy, though probably in smaller quantity, the most common of these being lead, tin, iron, and arsenic. It often happens that some of these are purposely added, to produce a given effect in the alloys. The colour of brass shows great variations, according to the proportions of the constituents, ranging from the red of copper at one end, to the bluish-white of zinc at the other. But the change

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from red to white is not so uniform as a casual observer might suppose. Thus alloys containing 94 to 99 per cent copper are red, with only a faint yellow tint; with 87 to 93 per cent copper, the colour is reddish-yellow; from 79 to 86 per cent copper, a yellowish-red tint prevails; below this, down to 74 per cent copper, the alloys are yellow, with a content of 67 per cent copper, a reddish-yellow tint is obtained; with 60 to 66 per cent copper the colour is a full yellow; with 59 per cent copper, a reddish colour is obtained; with 52 per cent copper the colour is nearly goldenyellow; with a less quantity of copper than the above, the colour of the zinc begins to overpower the red colour of the copper, the alloys becoming more lead-like in appearance as the proportion of zinc increases.

Copper and zinc may be united in all proportions, forming homogeneous alloys; and the combination is usually attended with evolution of heat. Certain varieties of brass are exceedingly malleable and ductile, and these properties, combined with the variety of shades of colour obtained by suitable mixing, and the moderate cost, render copper-zinc alloys most valuable for ornamental purposes. Brass possesses all the necessary advantages as a constructive material for works of art, and with the aid of transparent varnishes, termed lacquers, which have been brought to great perfection, it resists the action of the atmosphere remarkably well. The malleability of brass varies with the composition, with the temperature, and with the presence of foreign metals, which are sometimes in minute quantities. Some varieties are only malleable when rolled hot, others can be rolled at any temperature. Alloys containing up to 35 per cent zinc can be drawn into wire, but those containing 15 to 20 per cent of zinc are the most ductile. The alloy known as Dutch metal, which is an alloy of copper and zinc, containing more copper than ordinary brass, is an example of the great malleability of certain kinds of brass. The thickness of the leaves of Dutch metal is said not to exceed 2300 of an

inch.

Brass is harder than copper, and therefore better adapted to resist wear and tear. It acts well under the influence of a percussive force, as in the process of stamping, provided it is suitably annealed at proper intervals, in order to counteract the effects of local hardening, due to the compression of the particles into what may be termed unnatural positions. During the ordinary process of annealing the metal becomes coated with a scale of oxide, by union with the oxygen of the air, which oxide requires to be removed at each stage. This is done by dipping the metal in aquafortis, or dilute sulphuric acid, then scouring with sand if necessary, and finally well rinsing in water.

The melting point of brass is less than the mean of the melting points of its constituents, and this moderate melting point is of the utmost importance in the case of remelting, for casting or other purposes. The melting point of zinc is very much below that of copper, and when an alloy of these metals is strongly heated, the zinc volatilises, while the copper remains for the most part fixed, so that the loss of zinc will be considerable if the temperature is raised too high, and the operation of melting unduly prolonged; moreover, the affinity of zinc for oxygen is far greater than that of copper, and if air is freely admitted a considerable portion of the zinc will be oxidised, so that the metal should be excluded from the air as much as possible, by covering it with a layer of charcoal, or other substance, which has no chemical action upon the metal. The easy fusibility of brass, and its fluidity when melted, render it valuable for casting, as it is capable of receiving very fine impressions from the mould. Cast brass is generally more or less crystalline, which is very pronounced in the brittle varieties.

The formation of copper-zinc alloys is generally attended with contraction, which attains its maximum in the alloys Cu, Zn, and CuZn2, containing 39.2 and 32.6 per cent of copper respectively. These alloys are brittle, and exhibit none of the characteristic properties of the constituent metals. The density of brass is increased by mechanical

treatment, but this effect is partly annulled by sudden, and still more by slow cooling.1

In mixing brass for casting, old copper from wornout articles, scrap brass, etc., are frequently used, and as these often contain injurious ingredients, which modify the properties of the alloy, great care should be exercised in the selection. For some kinds of casting this is not important, but when the metal is required for rolling into sheet, or drawing into wire, or for making the best kinds of brass tubing, the use of impure metal is often fatal, entailing a considerable amount of expense on account of waste, and much annoyance to those concerned. The most common impurities, as already stated, are lead, tin, iron, and arsenic, all of which harden the metal and tend to make it brittle. For brass intended for filing and turning, 1 to 2 per cent of lead is added, in order to prevent the unpleasant fouling of the tools in working. Brass containing lead should be very thoroughly mixed before pouring, and the cast metal should be cooled as quickly as is expedient, otherwise the lead separates out in the lower portion of the casting, producing unsightly spots. A little tin is often an advantage in brass; it renders the metal more easily fusible, less brittle, somewhat sounder, and enables it to take a better polish. A little iron considerably increases the hardness of brass, lightens the colour, and such metal is more easily tarnished by the atmosphere than brass free from iron.

When an ingot of ordinary brass is broken while hot, its fracture is coarsely fibrous, but when broken while cold, it should be finely granular. When the fracture of a cast ingot of certain metals is fibrous, the directions of the fibres will be at right angles to the cooling surface. In the case of a sphere, the fibres will have the direction of radii; and in the case of a square, two diagonals will be plainly visible on the transverse fracture, formed by the points of junction of the internal extremities of the fibres.2 Mr. F. H. Storer 3 Riche, Ann. Chim. Phys. (4), xxx.

2 Percy's Metallurgy, p. 608.

3 Mem. of Amer. Acad. 1860 (8), p. 35.

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