270 ALLOYS OF COPPER AND TIN. COPPER-continued. 1 oz. 13 oz. 1 oz. Modern Copper and Tin Alloys. Soft gun-metal, that bears drifting, or stretching from a perforation. A little harder, fit for mathematical instruments; or 12 copper and 1 very pure grain tin. Still harder, fit for wheels to be cut with teeth. 1 to 2 oz. Brass ordnance, or 8 to 12 per cent. tin; but the general proportion is one ninth part of tin. Hard bearings for machinery. Very hard bearings for machinery. By Muschenbroëk's Tables it appears that the proportion 1 tin and 6 copper is the most tenacious alloy; it is too brittle for general use, and contains 24 oz. to the pound of copper. See p. 289. For some other alloys used in machinery, see Alloys of Copper, Zinc, Tin and Lead, p. 272. oz. Soft musical bells. 3 oz. Chinese gongs and cymbals, or 20 per cent. tin. (Ure, fol. 191.) oz. House bells. 4 4 oz. Large bells. 5 oz. Largest bells. 7 to 84 oz. Speculum metal. Sometimes one ounce of brass is added to each pound as the means of introducing a trifling quantity of zinc, at other times small proportions of silver are added; the employment of arsenic was strongly advocated by the Rev. John Edwards. Lord Oxmantown, now the Earl of Ross, says, "tin and copper, the materials employed by NEWTON in the first reflecting telescope, are preferable to any other with which I am acquainted; the best proportions being four atoms of copper to one of tin (TURNER'S numbers); in fact, 126-4 parts of copper to 58.9 of tin.”—Trans. Royal Soc., 1840, p. 504. The object agreed upon by all experimentalists appears to be the exact saturation of the copper with the tin, and the proportionate quantities differ very materially, (in this and all other alloys,) according to the respective degrees of purity of the metals: for the most perfect alloys of this group, Swedish copper, and grain tin, should be used. Mr. Ross says, "When the alloy is perfect, it should be white, glassy, and flaky. When the copper is in excess, it imparts a red tint easily detected; when the tin is in excess, the fracture is granulated and also less white." His practice is to pour the melted tin into the fluid copper when it is at the lowest temperature that a mixture by stirring can be effected, then to pour the mixture into an ingot and to complete the combination by remelting in the most gradual manner, by putting the metal into the furnace as soon almost as the fire is lighted: trial is made of a little piece taken from the pot prior to pouring. See Dr. Edward's Paper on Speculums, published in the Nautical Almanack, 1787, reprinted in Gill's Technological Repository, vol. i. p. 240, and 264. See likewise Lord Oxmantown's Paper, Trans. Royal Society, 1840, pp. 503-527. ALLOYS OF COPPER AND LEAD. 271 COPPER-continued. 32 oz. of tin to one pound of copper, make the alloy called by the pewterers "temper," which is added in small quantities to tin, for some kinds of pewter, called "tin and temper," in which the copper is frequently much less than 2 oz. 4 oz. 6 oz. 7 oz. 8 oz. 1 per cent. See PEWTER, 284, and mixing the same, 310. REMARKS ON THE ALLOYS OF COPPER AND TIN ONLY. These metals seem to mix in all proportions. The addition of tin continually increases the fusibility, although when it is added cold it is apt to make the copper pasty, or even to set it in a solid lump in the crucible. The red colour of the copper is not greatly impaired in those proportions used by the engineer, namely, up to about 24 ounces to the pound; it becomes greyish white at 6, the limit suitable for bells, and quite white at about 8, the speculum metal; after this, the alloy becomes of a bluish cast. The tin alloy is scarcely malleable at 2 ounces, and soon becomes very hard, brittle, and sonorous; and when it has ceased to serve for producing sound, it is employed for reflecting light. The tough tenacious character of copper under the tools rapidly gives way; alloys of 1 cut easily, 2 assume about the maximum hardness without being crystalline; after this they yield to the file by crumbling in fragments rather than by ordinary abrasion in shreds, until the tin very greatly predominates as in the pewters, when the alloys become the more flexible, soft, malleable, and ductile, the less copper they contain. ALLOYS OF COPPER AND LEAD ONLY. Note.-The marginal numbers denote the ounces of lead added to each pound of copper. A red-coloured and ductile alloy. Less red and ductile; neither of these is so much used as the following, as the object is to employ as much lead as possible. Ordinary pot-metal, called dry pot-metal, as this quantity of lead will be taken up without separating on cooling; this is brittle when warmed. This alloy is rather short, or disposed to break. Inferior pot-metal, called wet-pot metal, as the lead partly oozes out in cooling, especially when the new metals are mixed; it is therefore always usual to fill the crucible in part with old metal, and to add new for the remainder. This alloy is very brittle when slightly warmed. More lead can scarcely be used as it separates on cooling. REMARKS ON THE ALLOYS OF COPPER AND LEAD ONLY. These metals mix in all proportions until the lead amounts to nearly half, after this they separate in cooling. The addition of lead greatly increases the fusibility. The red colour of the copper is soon deadened by the lead; at about 4 ounces to the pound the work has a bluish leaden hue when first turned, but changes in an hour or so to a dull gun-metal character. 272 ALLOYS OF COPPER, ZINC, TIN, LEAD, ETC. COPPER-continued. When the lead does not exceed about 4 oz. the mixture is tolerably malleable, but with more lead it soon becomes very brittle and rotten: the alloy is greatly inferior to gun-metal, and is principally used on account of the cheapness of the metal, and the facility with which it is turned and filed, &c. ALLOYS OF COPPER, ZINC, TIN, AND LEAD, &c. This group refers principally to gun-metal alloys, to which more or less zinc is added by many engineers; the quantity of tin in each pound of the alloy, which is expressed by the marginal numbers, principally determines the hardness. Keller's statues at Versailles are found as the mean of four analyses, to consist of 1 to 2 oz. tin to 1 lb. copper used for bronze medals, or 8 to 15 per cent. tin, with the addition of 2 parts in each 100 of zinc, to improve the colour. (Ure.) The modern so-called bronze medals of our Mint are of pure copper, and are afterwards bronzed superficially. 1 oz. tin zinc to 16 oz. copper. Pumps and works requiring great tenacity. 1 oz. tin 2 oz. brass 16 1 2 21 For wheels to be cut into teeth. } F 16 دو دو دو For nuts of coarse threads, and bearings. The engineer who uses these five alloys recommends melting the copper alone, the small quantity of brass is then melted in another crucible, and the tin in a ladle; the two latter are added to the copper when it has been removed from the furnace, the whole are stirred together and poured into the moulds without being run into ingots. The real quantity of tin to each pound of copper is about one-eighth oz. less than the numbers stated, owing to the addition of the brass, which increases the proportion of copper. 1 oz. tin, 17 oz. zinc, to 1 lb. copper. This alloy, which is a tough, yellow, brassy, gun-metal, is used for general purposes by a celebrated engineer; it is made by mixing 1 lb. tin, 14 lb. zinc, and 10 lbs. of copper; the alloy is first run into ingots. 2 oz. tin, oz. of zinc, to 1 lb. copper, used for bearings to sustain great weights. 2 oz. tin, 2 oz. zinc, to 1 lb. copper, were mixed by the late Sir F. Chantrey, and a razor was made from the alloy; it proved nearly as hard as tempered steel, and exceedingly destructive to new files, and none others would touch it. (Wilkinson.) 1 oz. tin, 2 oz. zinc, 16 oz. brass. oz. tin, 1 oz. zinc, 16 oz. brass. Best hard white metal for buttons. AND REMARKS ON THE SAME. GOLD. COPPER-continued. 273 10 lbs. tin, 6 lbs. copper, 4 lbs. brass constitute white solder. The copper and brass are first melted together, the tin is added, and the whole is stirred and poured through birch twigs into water to granulate it; it is afterwards dr and pulverized cold in an iron pestle and mortar: this white solder was introduced as a substitute for silver solder in making gilt buttons. Another button solder consists of 10 parts copper, 8 of brass, and 12 of spelter or zinc. REMARKS ON ALLOYS OF COPPER, ZINC, TIN, AND LEAD, &c. ORDINARY YELLOW BRASS, (copper and zinc,) is rendered very sensibly harder, so as not to require hammering, by a small addition of tin, say or oz. to the lb. On the other hand, by the addition of tooz. of lead, it becomes more malleable and casts more sharply. Brass becomes a little whiter for the tin, and redder for the lead. The addition of nickel to copper and zinc constitutes the German silver. See NICKEL, p. 279. GUN METAL, (copper and tin,) very commonly receives a small addition of zinc; this makes the alloy mix better, and to lean to the character of brass by increasing the malleability without materially reducing the hardness. The standard measures for the Exchequer were made of a tough alloy of this kind. The zinc, which is sometimes added in the form of brass, also improves the colour of the alloy, both in the recent and bronzed states. Lead in small quantity improves the ductility of gun-metal, but at the expense of its hardness and colour; it is seldom added. Nickel has been proposed as an addition to gun metal by Mr. Donkin, and antimony by Dr. Ure. POT METAL (Copper and lead) is improved by the addition of tin, and the three metals will mix in almost any proportions: when the tin predominates, the alloy so much the more nearly approaches the condition of gun metal. Zinc may be added to pot-metal in very small quantity, but when the zinc becomes a considerable amount, the copper takes up the zinc, forming a kind of brass, and leaves the lead at liberty, and which in great measure separates in cooling. Zinc and lead are also very indisposed to mix alone, although a little arsenic assists their union by "killing" the lead as in shot-metal. Antimony also facilitates the combination of pot-metal: 7 lead, 1 antimony, and 16 copper, mixed perfectly well the first fusion, and the alloy was decidedly harder than 4 lead and 16 copper; and apparently better metal. "Lead and antimony, though in small quantity, have a remarkable effect in diminishing the elasticity and sonorousness of the copper alloys." GOLD is of a deep and peculiar yellow colour. It melts at a bright red heat, equivalent, according to Daniell, to 2016o of Fahrenheit's scale, and when in fusion appears of a brilliant greenish colour. Its specific gravity is 19.3. It is so malleable that it may be extended into leaves which do not exceed one two hundred and eighty-two thousandth of an inch in thickness, or a single grain may be extended over 56 square inches of surface. This exten 274 GOLD-continued. USES OF FINE GOLD. GOLD ALLOYS. sibility of the metal is well illustrated by gilt buttons, 144 of which are gilt by 5 grains of gold, and less than even half that quantity is adequate to giving them a very thin coating. It is also so ductile that a grain may be drawn out into 500 feet of wire. The pure acids have no action upon gold. (Brande, 972.) GOLD in the pure or fine state is not employed in bulk for many purposes in the arts, as it is then too soft to be durable. The gold leaf used by dentists for stopping decayed teeth is perhaps as nearly pure as the metal can be obtained: it contains about 6 grains of alloy in the pound troy, or the one-thousandth part. Each superficial inch of this gold leaf weighs of a grain, and is 42 times as thick as that used for gilding. The wire for gold lace prepared by the refiners for gold-lace manufacturers, requires equally fine gold, as when alloyed it does not so well retain its brilliancy. The gold in the proportion of about 100 grains to the lb. troy of silver, or of 140 grains for double-gilt wire, is beaten into sheets as thin as paper; it is then burnished upon a stout red-hot silver bar, the surface of which has been scraped perfectly clean. When extended by drawing, the gold still bearing the same relation as to quantity, namely, the 57th part of the weight, becomes of only one-third the thickness of ordinary gold-leaf used for gilding. In water-gilding, fine gold is amalgamated with mercury and washed over the gilding metal, (copper and tin,) the mercury attaches itself to the metal, and when evaporated by heat it leaves the gold behind in the dead or frosted state: it is brightened with the burnisher. (See Technological Repository, vol. ii. p. 361-1828. By the electrotype process a still thinner covering of pure gold may be deposited on silver, steel, and other metals. Mr. Dent has introduced this method of protecting the steel pendulum springs, &c., of marine chronometers and other time-pieces from rust.-See Note, p. 252. Fine gold is also used for soldering chemical vessels made of platinum. GOLD ALLOYS. Gold-leaf for gilding contains from 3 to 12 grs. of alloy to the oz., but generally 6 grs. The gold used by some dentists, for plates, &c. is nearly pure, but contains about 6 grains of copper in the oz. troy, or one 80th part; thers use gold containing upwards of one-third of alloy, the copper is then very injurious. With copper, gold forms a ductile alloy of a deeper colour, harder and more fusible than pure gold : this alloy, in the proportion of 11 of gold to 1 of copper, constitutes standard gold; its density is 17.157, being a little below the mean, so that the metals slightly expand on combining. One troy pound of this alloy is coined into 4628 sovereigns, or 20 troy pounds into 934 sovereigns and a half. The pound was formerly coined into 44 guineas and a half. The standard gold of France consists of 9 parts of gold and 1 of copper. (Brande, 979.) |