of alumina and carbon pressed together, having the conducting wire leading through their whole length in order to lessen the resistance as much as possible. The metal is obtained as a granular powder mixed with NaCl. Where possible, vessels of chalk or magnesia should be used, since aluminium takes up silicon from siliceous crucibles and becomes brittle." There have been some improvements made in the form of apparatus over those used by Bunsen and Deville, designed to produce the metal on a commercial scale. The best one is that patented in Germany by Richard Grätzel.* He uses meltingpots of porcelain, alumina, or aluminium, which serve also as negative electrodes. A number of these are placed in one furnace. The following section shows the arrangement (Fig. 16). The positive electrode K can be made of a mixture of anhydrous alumina and carbon pressed into shape and ignited. A mixture of alumina and gas-tar answers very well; or it can even be made of gastar and gas-retort carbon. During the operation little pieces of carbon fall from it and would contaminate the bath, but are kept from doing so by the mantle G. This isolating vessel G is perforated around the lower part at g, so that the chlorine gas liberated at K may escape through the tube O', while reducing gases can be brought into the cruci * D. R. Pat. No. 26,962. ble by the tube 0. To lessen the electrical resistance and to renew the bath of chloride or fluoride, bars of carbon, alumina, or magnesia are placed inside the isolating mantle G. This process is now being worked on a large scale in Germany, being also used for producing magnesium. There are works at Bremen and Hamburg. M. Duvivier states that by passing an electric *The Chemist, Aug. 1854. current from eighty Bunsen cells through a small piece of laminated disthene between two carbon points, the disthene melted entirely in two or three minutes, the elements which composed it were partly disunited by the power of the electric current, and some aluminium freed from its oxygen. Several globules of the metal separated, one of which was as white and as hard as silver. Kagensbusch,* of Leeds, makes the singular proposition to melt clay with fluxes, then add zinc or a like metal, pass an electric current through the fused mass, isolating an alloy of aluminium and the metal, from which the foreign metal may be removed by distillation, sublimation, or cupella tion. Gaudint reduces aluminium by a process to which he applies the somewhat doubtful title of economic. He melts together equal parts of cryolite and NaCl, and traverses the fused mass by an electric current. Fluorine is evolved at the positive pole, while aluminium accumulates at the negative. Thus far we have given the methods based on electrolyzing fused salts. These seem to be the operations best suited to throwing down aluminium in mass. The electrolysis of aqueous solutions seems so far to have succeeded only in depositing very thin films of metal. We will now give the * Eng. Pat. 1872, No. 4811. various methods proposed for electrolyzing aluminium in the wet way. Messrs. Thomas and Tilly* coat metals with aluminium and its alloys by using, for depositing the pure metal, a solution of freshly precipitated alumina dissolved in boiling water containing potassium cyanide, or a solution of freshly calcined alum in aqueous potassium cyanide; also from several other liquids. Their patent covers the deposition of the alloys of aluminium with silver, tin, copper, iron, silver and copper, silver and tin, etc. etc. M. Corbelli, of Florence,† deposits aluminium by electrolyzing a mixture of rock alum or sulphate of alumina with CaCl2 or NaCl, in aqueous solution, the anode being mercury placed at the bottom of the solution and connected to the battery by an iron wire coated with insulating material and dipping its uncovered end into the mercury. The zine cathode is immersed in the solution. Alu minium is deposited on the zinc, and the chlorine which is liberated at the anode unites with the mercury, forming calomel. J. B. Thompsont reports that he has for over two years been depositing aluminium on iron, steel, and other metals, and also depositing aluminium * Eng. Pat., 1855, No. 2756. bronze.of various tints, but declines to state his process. J. A. Jeancon has patented a process for depositing aluminium from an aqueous solution of a double salt of aluminium and potassium of specific gravity 1.161; or from any solution of an aluminium salt, such as sulphate, nitrate, cyanide, etc., concentrated to 20° B. at 50° F. He uses a battery of four pairs of Smec's or three Bunsen's cells, with elements arranged for intensity, and electrolyses the solutions at 140° F. The first solution will decompose without an aluminium anode, but the others require such an anode on the negative pole. The solution must be acidulated slightly with acid corresponding to the salt used, the temperature being kept at 140° F. constantly. M. A. Bertrand states that he deposited aluminium on a plate of copper from a solution of double chloride of aluminium and ammonia, by using a strong current, and the deposit was capable of receiving a brilliant polish. C. Winklert states that he has spent much time and tried all methods so far proposed, and comes to the conclusion that aluminium cannot be deposited by electro-deposition in the wet way. Annual Record of Science and Industry, 1875. + Chem. News, xxxiv. 227. Journal of the Chem. Soc., x. 1134. |