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368 ALUMINUM from the slag, and should yield 25 grammes ' from 75 grammes of sodinrn. In this experi- j ment 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 lirne. 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 earth- en 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, j 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 anhy- drous sulphate of aluminum, in such propor- tions that the oxygen present is just sufficient to convert all the sulphur into sulphurous acid (Al a S, + Al, (SO), = 4A1 + 6SO a ). The mixture is heated in a non-oxidizing atmos- phere to a red heat. Corbelli of Florence mixes the impure sulphate with 2 parts ferrocyanide of potassium and H of com- mon salt, heating the whole to redness. Knowles decomposes the chloride by means of cyanide of potassium. Bunsen in 1 854 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 baux- ite, having first been reduced to fine powder by grinding under an edge-stone, is mixed with a quantity of soda slightly more than is neces- sary to form aluminate of soda with the alumi- na of the mineral, and heated in a reverberato- ry furnace. The aluminate of soda thus pro- duced is afterward decomposed, and furnishes the alumina for further decomposition by means of chlorine and sodium as above de- scribed. The electro-galvanic deposition of aluminum, although frequently attempted, does not appear to have been successfully accomplish- ed. 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 ex- cepting at a white heat ; is not blackened by sulphuretted hydrogen. It is not attacked by nitric acid, either dilute or concentrated, at or- dinary 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 easi- ly 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 power- ful 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), com- posed 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 minargent, 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 employ- ed 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 1865 at the United States mint on alloys of alumi- num 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 ap- plication 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 manu- facture 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 de-