The supreme importance of the alloys in the arts is apparent when it is considered that very little of the vast quantities of metal used in civilized life is the pure metal. Steel is an alloy of pure iron and carbon, and other metals are added in alloy to produce the higher grades of steel — chrome steel, manganese steel, nickel steel, tungsten steel, vanadium steel, etc.; cast iron is an alloy of pure iron with carbon, sulphur and phosphorus; commercial tin is an alloy of pure tin and lead; commer cial gold and silver are alloys of these precious metals with others to add the required hard ness to withstand wear; the brasses are alloys of copper and zinc; the bronzes are alloys of copper and tin, with other metals added; etc. Although many of these alloys have been long known, yet newer and often valuable com binations of the same metals are daily discovered, which are better adapted than the older ones for the new uses which practical engineering and processes demand.
A beautiful and useful alloy of gold 78 and aluminum 22, carrying a rich purple shade, is now employed in the manufacture of jewelry, which formerly consisted of a gold, silver and copper combination. An alloy of silver 25 and aluminum 75 furnishes a metal adapted for the manufacture of fine instruments, electrical ap paratus, dentists' tools, etc. It makes delicate castings and takes on a fine polish. The com binations with copper are more important.
Aluminum Bronze is a combination of cop per 89 or 90, with aluminum 11 or 10 per cent. Although hard, it can be readily soldered. It can be rolled into thin sheets, worked with the hammer and stamped into form. Its color re sembles that of American gold coin, and it is susceptible of high polish. With copper 95 and aluminum 5 the combination resembles pure gold very closely.
Boron Bronze.— Into a fused admixture of fluorspar and vitrified boric anhydride, aluminum is introduced, when reduction takes place and this result when combined with a copper admixture in the proportions of the pre pared aluminum 5 to 10 and copper 95 to 90 per cent renders an alloy denser, more durable and less brittle than aluminum bronze; and fur nishes more uniform and delicate castings. The aluminum-copper alloys with 90 to 93 aluminum and 10 to 7 copper yield a metal of great ten sile strength, largely employed in the manu facture of automobile and aeroplane parts.
Aluminum Brass is an alloy with an elastic limit up to nearly 15 tons to the square inch, the aluminum imparting to the brass greater fluidity in casting and additional tensile strength. For these reasons it is extensively used for electrical purposes. A small propor tion of aluminum with cast iron, wrought iron or steel has resulted in alloys of commercial value. From 1 to 2 per cent aluminum to cast ings of iron will cause the metal to flow more leisurely and take on a closer grain. In steel castings the proportion of aluminum commonly used is minute, about 1/50th to 1/30th of 1 per cent, although for certain steel castings this has been advantageously increased to 1 and even 2 per cent of aluminum. The latter adds
tensile strength and homegeneity to the alloy, gives it a smoother surface and lessens its liability to oxidation. An alloy of aluminum 70 and zinc 30 has been found useful in casting frames for sewing machines and like small manufactures. A combination of aluminum 80, zinc 15, tin 2, copper 2, and % each of man ganese and iron is an alloy in which the alu minum is hardened and the product becomes applicable to many useful manufactures.
Aluminum Zinc, composed of zinc 90 to 95 and aluminum 10 to 5, is used in the galvan izing bath and treated the same way as pure zinc, except that no sal-ammoniac is used for clearing out the oxide, the aluminum being sufficiently effective.
This name is given to those alloys which are sufficiently plastic under the pressures to which they are sub jected in bearings to mold themselves to the shape of the shaft which they support and still hard enough to stay in place. This property of fitting to the shaft is of course approxi mate, for in fact the shaft and its bearings are always separated by a thin film of oil. These anti-friction metals are generally alloys of tin with tin-antimony and tin-copper; or they may be of lead compounded with tin antimony or of lead and tin so compounded. The first of these anti-friction alloys was the famous Babbitt metal, now almost wholly superseded by more effective combinations. See ANTI-Flucriox Murats.
Coinage The coinage of gold and silver dollars and multiples or fractions thereof, as first authorized by the act of Congress passed 2 April 1792, provided that the gold dollar should contain 27 grains of gold 9163i fine. The amount of fine gold in the dollar was there fore 244 grains. The silver dollar was ordered to contain 416 grains of silver, 892.4 fine, or 37124 grains of fine silver. By the act of 28 June 1834 the gold dollar was reduced to the weight of 25.8 grains, 900 fine, or 23.22 grains finegold. No change was made in either the weight or alloy of the silver dollar. By the act of 18 Jan. 1837 the alloy, but not the fine contents, of the silver dollar was changed. It was thenceforth to contain 412% grains of silver, 900 fine, or 371% grains of fine silver; practically the same contents of fine silver as before. No further change was made in the gold dollar. The alloy of both gold and silver coins has always been of copper, although a minute quantity of silver has at times been introduced into the gold coin alloy, rather to improve the color of the coins, than from any design to increase their bullion value. By the act of 21 Feb. 1853 important reductions were made in the weight and fineness and therefore in the alloy of the subsidiary coins; a subject that belongs less to alloys than to coins. The current five-cent coins, or °nickels,* are an alloy of 75 per cent copper and 25 per cent nickel. The °copper cent* is an alloy of copper, 95 per cent and zinc and tin, 5 per cent.