Aluhnum, Or Aluminium, one of the metals of the earths never found native, but occurring in combination with other elements in 105 different species of minerals, and consequently constituting a large part of the solid crust of the earth. Among the minerals and rocks containing this metal may be mentioned the following: ruby, sapphire, corundum, emery, gibbsite, bauxite, turquoise, lapis lazuli, topaz, i cryolite, feldspar, clay, and slates. Although so abundant, it is only within a few years that the metal has been prepared in a free state, and even at the present time the manufacture is too expensive to admit of its common use in the arts. Davy, Berzelius, and Oersted at-tempted to decompose the oxide by means of the electric current, but without success. Oer-sted, who discovered the chloride, failed in his efforts to decompose this salt by metallic alkalies. It was first prepared in 1827 by Wohler, who obtained a gray metallic powder on de-! composing the chloride with potassium under: a gentle heat. In 1845 Wohler obtained it in the form of a metallic button by passing vaporized chloride of aluminum over heated potassi-urn. Its chemical and physical properties were then determined, and the subject allowed to rest till 1854, when it was a second time discovered by Deville. He heated the crude chloride of alu-minum in an upright iron cylinder, connected by a pipe with a smaller horizontal cylinder containing iron nails, which reduced any perchlo-ride of iron present to the less volatile proto-chloride, and also detained any hydrochloric acid or chloride of sulphur present.
The vapor of aluminum chloride passed next through a long wrought-iron cylinder containing three dishes holding a pound of sodium each, and heated on the lower side to dull redness. The reaction is sometimes so violent as to require a careful regulation of the heat. Metallic aluminum is formed along with the double chloride of sodium and aluminum. This mass is then heated in an iron vessel or clay crucible until it is entirely melted and the double salt begins to evaporate. When cold the chloride of sodium found on top is removed, the buttons of aluminum are washed with water, dried, and heated to redness, when they may be pressed together. The loss of aluminum by this process is very considerable. The method was afterward abandoned, and the following mixture employed: chloride of aluminum and sodium, 400 grammes; common salt, 200; tiuor spar, 200; sodium, 75 to 80. The double salt is previously fused and heated almost to redness, the common salt fused or strongly ignited, the fluor spar powdered and well dried. The double salt and common salt are broken up into a coarse powder, mixed with the fluor spar, and placed in a crucible with alternate layers of sodium, the whole being covered with a layer of common salt.
It is heated gently at first, then more strongly, until the melting point of silver is nearly but not quite reached. The mass is stirred with a clay pipe stem, and poured out on a dry slab of limestone. The aluminum is readily separated from the slag:, find should yield 25 grammes from 75 grammes of sodium. In this experiment the fluor spar should be free from silica, and the sides of the crucible be protected by a layer of alumina prepared from a paste of 4 parts ignited aluminum and 1 part aluminate of lime. The process requires some experience in order to succeed. It is much easier and simpler to employ cryolite instead of fluor spar. In 1855 II. Rose in Berlin, and Dr. Percy in England, prepared aluminum from cryolite. The pulverized mineral was mixed with half its weight of common salt, and the mixture arranged in alternate layers with sodium (2 parts sodium to 5 parts cryolite), in an earthen or iron crucible covered with a layer of pure cryolite, and the whole covered with common salt. The crucible, well covered, is heated to a bright red heat by means of a blast lamp for half an hour, then allowed to cool, and the contents removed with a chisel, at the same time tapping the crucible with a hammer.
In 1858 Gerhard invented and patented an improvement, consisting in the use of a re-verberatory furnace with two hearths, one above the other, communicating by an iron pipe. In the lower is placed the mixture of sodium with the aluminum compound, and in the upper a stratum of common salt, or of a mixture of sodium and cryolite, or of the slag from a former operation. This layer when melted is made to run into the lower furnace in quantity sufficient to cover completely the mixture contained therein, so as to protect it from the air. - Several attempts have been made, but with doubtful success, to separate aluminum from its compounds by means of the ordinary reducing agents, hydrogen and carbon. Johnson has patented the following process: Mix together sulphide of aluminum and anhydrous sulphate of aluminum, in such proportions that the oxygen present is just sufficient to convert all the sulphur into sulphurous acid (Al2 S3 + Al2 (SO4)3 = 4A1 + 6SO2). The mixture is heated in a non-oxidizing atmosphere to a red heat. Corbelli of Florence mixes the impure sulphate with 2 parts ferrocyanide of potassium and 1 1/2 of common salt, heating the whole to redness. Knowles decomposes the chloride by means of cyanide of potassium.
Bunsen in 1854 obtained aluminum by electrolysis of the fused chloride of aluminum and sodium in a red-hot crucible, ten elements of a Bunsen battery being required. Messrs. Bell Brothers of England commenced producing aluminum a few years since from the ammonia alum of commerce, but afterward employed a native hydrated oxide known as the mineral bauxite. (See Alumina.) The bauxite, having first been reduced to fine powder by grinding under an edge-stone, is mixed with a quantity of soda slightly more than is necessary to form aluminate of soda with the alumina of the mineral, and heated in a reverberato-ry furnace. The aluminate of soda thus produced is afterward decomposed, and furnishes the alumina for farther decomposition by means of chlorine and sodium as above described. The electro-galvanic deposition of aluminum, although frequently attempted, does not appear to have been successfully accomplished. - Properties of aluminum. Aluminum is a bluish white metal, without odor or taste, nearly as malleable as gold and silver; density of the fused metal 2.50, of the hammered 2.67; melting point between that of silver and zinc; nearly as good a conductor of electricity as silver; does not oxidize in the air, even at a strong red heat; does not decompose water excepting at a white heat; is not blackened by sulphuretted hydrogen.
It is not attacked by nitric acid, either dilute or concentrated, at ordinary temperatures, and very slowly even at the boiling heat; neither is it acted upon by sulphuric acid diluted to the degree at which that acid dissolves zinc; but hydrochloric acid, either dilute or concentrated, dissolves it easily even at low temperatures, with evolution of hydrogen. Caustic soda and potash readily dissolve it, forming aluminates of those bases. Ammonia acts but slightly on it. Professor Wurtz of New York prepares an amalgam of aluminum by heating thin foil on mercury in a glass tube so drawn out that the foil cannot swim on the mercury. This amalgam is more readily decomposed in the air and in water than sodium amalgam. Aluminum is a powerful reducing agent for solutions of chlorides, and in the preparation of the rare elements boron and silicon. An alloy of aluminum with silver, called third silver (tiers-argent), composed of one third silver and two thirds aluminum, is chiefly employed for forks, spoons, and tea service, and is harder than silver and more easily engraved. Another alloy, called miuargent, is composed of 100 parts copper, 70 parts nickel, 5 parts antimony, and 2 parts aluminum.
The beautiful tone of the metal has suggested its use in the manufacture of bells, and a successful application of it for this purpose has been made. Mixed with copper in the proportion of 10 parts of aluminum and 90 of copper, it forms a beautiful alloy known as aluminum bronze, now frequently employed for the manufacture of watch cases, watch chains, imitation jewelry, sheathing for stairs, and bearings of machinery. The alloy of aluminum with iron is crystalline and of no value in the arts. Experiments made in 18(35 at the United States mint on alloys of aluminum for coins were not sufficiently successful to induce the government to adopt them. The difficulty encountered in soldering and welding aluminum, and the high cost of its production, have seriously interfered with its extensive application in the arts. It can hardly be said to have fulfilled all the expectations that were raised at the time of the revival in its manufacture introduced in 1855 by Deville. - Salts of aluminum. These are very numerous, many of them extensively employed in the arts. Alum and the oxide alumina are separately described. The chloride, Al2Cl6, can be prepared by passing dry chlorine gas through a heated mixture of alumina and charcoal.
It is a volatile compound, and is used as above described in the manufacture of the metal aluminum. The hydrated chloride of alumina is easily prepared by dissolving aluminum in hydrochloric acid. It is sold in commerce, under the name of ehloralum, as a disinfectant and antiseptic, and is also recommended for salting paper in photography. Sulphate of aluminum is known in a crude state as alum cake, and is prepared on a large scale by roasting aluminous shales as described under Alum. It can be prepared in a small way by dissolving the hydrate of alumina in sulphuric acid. Acetate of aluminum is prepared by precipitating ace-tade of lead with sulphate of aluminum or with a solution of alum. It is extensively used as a mordant in calico printing, especially in producing madder reds, whence it is called "red liquor."