Aluminum is not affected by organic acidk and resists well cold sulphuric and nitric hut dissolves speedily in hydrochloric acid. The alkalis readily decompose it. As compared with other metals, for a given gauge of plate one ton of aluminum is equal in area to 27 tons of tin, 2.:.: tons of iron, 3.33 tons of copper and 4.22 tons of lead. One pound of sheet aluminum of any thickness will cover 3% times the area covered by a sheet of bras; of the same thickness. Compared with copper, aluminum sheets are 25 to 50 per cent cheaper for the same area, 66 per cent lighter and in many cases much more durable.
Alloys.— Aluminum forms alloys with all the common metals except lead. The alloys which have been found more or le” useful have been combinations of aluminum with copper, chromium, tungsten, titanium. molybdenum, zinc, bismuth, nickel, cadmium. magnesium, manganese, tin or antimony,— all of these alloys being distinctly harder than pure aluminum. A small percentage of man ganese adds ductility to these alloys without reducing their strength. The copper-aluminum alloys, containing 10 to 11 per cent of aluminum. are known as aluminum-bronze. These alloys are not corroded by sea water, making them of special value for marine fittings. (See When aluminum is alloyed with 7 to 10 per cent of copper, a tough metal results; it is especially useful in automobile parts and other construction forms which. are subjected to sud den and severe shocks. The zinc-aluminum alloys yield a metal eminently adapted for forging, being tough and flowing well under dies. Some of the zinc-aluminum alloys are but little heavier .than pure aluminum, are as rigid as bronze, and machine as readily as They are very extensively used in making mo tor casings for automobiles and aircraft. With iron, aluminum combines in all proportions, hut the alloys of most value are those with very small percentages of aluminum. This is true especially of steel, to which the usual addition of aluminum is from two ounces to 12 ounces per ton. In this quantity the alu minum is essentially a deoxidizer, and while increasing the steel in tensile strength, its chief effect is to produce smoother and more homo geneous ingots. With cast iron the addition of aluminum is from one to two pounds per ton, lessening the tendency to chill, causing it to flow smoothly and giving it a closer grain. In wrought iron, aluminum increases the tensile strength 30 per cent and renders the iron more fluid at 2200° F. than at 3500° without it. With 2 to 10 per cent of magnesium, aluminum forms an alloy lighter even than its normal weight. This alloy goes by the name of mag nalium and is equal in strength and workabil ity to good brass. With 1 to 15 per cent of tin a series of strong and rigid alloys is produced, suitable for heavy castings. Aluminum-tungs ten and aluminum-nickel make good rolling metal for sheet forms. Alloys of aluminum with 3 to 4 per cent of copper or with 2 to 5 per cent of nickel are also very largely used for rolling into sheets. All brass is improved by the addition of small percentages of alumi num, a 2-per cent addition doubling its tenacity. Aluminum has the effect generally of lowering the melting point of the alloy. Added to gold in the proportion of 1 per cent, the resulting alloy is known as "green gold.D Five per cent of aluminum will quench the color of the gold, yielding a white metal. With silicon aluminum
combines in all proportions, but these alloys arc brittle and are not permanent. With plati num and cadmium it forms fusible metals (q.v.). An alloy consisting of 96 parts alumi num, three parts copper and one part of mag nesium is known commercially as Muralumin." It has been used extensively in making shells, helmets, grenades and camp equipment during the European War.
Welding and Plating.— The great difficulty of soldering aluminum has been overcome by the process of autogenous welding and thus the making of tanks and vessels of the largest sizes has become practicable. In this welding process the sheets of aluminum are lapped, and a pure aluminum wire laid between, with a flux, generally a mixture of fluorides of the alkalis. The heat used may be the oxy-hydrogen flame, the oxyacetylene torch or even the air-acety lene flame. Aluminum is successfully plated with other metals by first plating it with zinc upon which the other metals are then 'deposited in an electrolytic bath.
Uses.— The uses of aluminum are almost without number. More than 250 articles are made from the pure metal and nearly as many more from its alloys, and the list is continually being extended. Among them are aeroplane parts, automobile parts and bodies, blades for fans, buttons, camp equipment, chains, cooking utensils, dental plates, foil for wrapping food products and confectionery, gas and oil stoves, hair and hat pins, horseshoes, frames for mirrors and pictures, penholders, army pon toons, optical goods, scientific instruments, stoves and stove pipe, telephone fixtures, tele scope tubes, trunks and traveling cases and vacuum cleaners. In the arts aluminum has replaced other metals, notably in the brewing industry. The great fermentation vats are now made of aluminum instead of copper, as the former has no deleterious effect upon the growth of yeast, as has the former. In varnish making also, the use of aluminum kettles affords a paler varnish from the same gums, or a varnish of the same color from darker gums. The resistance of aluminum to stearic and oleic acids makes it of the greatest value in soap making. In sugar refineries the copper piping is now lined with aluminum instead of tin as formerly. In iron and steel founding powdered aluminum is used to keep up the heat of molten metal, which it does by uniting with the oxides with great energy. This prop erty of powdered aluminum is the basis of the action of thermit. (See ALumixo-ni ER M ICS ) . The powdered metal is used also in the manu facture of the explosive "ammonal.)) Mixed with ammonium nitrate in varying proportions it forms a series of safe explosives which can not be fired without a detonator, but range in power from common black powder to nitro glycerine. These explosives are of particular value in mining, as the resulting gases are .entirely harmless, being nitrogen, oxygen and steam. Powdered aluminum is used extensively in the painters' trade as a foundation for bronze powders, in which it excels all other metals. In electrical transmission cables it has found a new utility, the cables being drawn on a ste..1 core, which renders them strong enough to stand the weight of long suspensions as well as the force of the wind and the weight of ice storms.