Page:The American Cyclopædia (1879) Volume I.djvu/391

 ALUMINUM 367 glass and soap. The pure anhydrous alumina is prepared by the calcination of the hyd rated oxide obtained as above described, or by expos- ing ammonia alum to a lively red heat. A peculiar modification of alumina is obtained, according to Walter Crum, by long-continued boiling of acetate of alumina; the acetic acid is liberated, and there remains a hydrated oxide soluble in water. A second modification of soluble alumina was discovered by Professor Graham, which can be obtained by the dialytic decomposition of a solution of hydrate of alu- mina in chloride of aluminum ; it has proper- ties differing from either of the other forms. Properties of alumina. When pure it is a white, light powder, devoid of taste and odor, infusi- ble excepting before the oxyhydrogen blow- pipe, when it constitutes a viscous fluid that can be drawn in strings like melted quartz, and on cooling yields a crystalline mass sufficiently hard to scratch and cut glass. Calcined alumi- na is absolutely insoluble in water, but if it has not been heated to redness it combines with a certain portion of water with disengagement of heat. Hydrated alumina is white when moist, but becomes translucent by desiccation, and sometimes yellow if it has been precipitated in the presence of organic matter. Its affinity for coloring matter is so great that it readily absorbs the organic dyes from solutions, and has extensive application as a mordant, as a clarifying agent, and in the manufacture of lakes. The hydrate of alumina after calcina- tion is soluble only with difficulty in acids, but readily soluble when freshly precipitated. The hydrates, prepared according to the methods of Crum and Graham, are soluble in water and possess characteristic properties. Several of the metallic oxides, as soda and potash, if fused in a silver crucible with alumina, combine with it and form aluminates. The minerals corun- j dum, sapphire, and ruby have been made arti- ficially by Deville and Caron, by heating the fluoride of aluminum in a carbon crucible, underneath which is suspended a platinum capsule containing boracic acid ; at an elevated temperature the fluorine reacts on the boracic acid and yields a fluoride of boron and a crystalline metallic oxide. By adding variable quantities of sesquioxide of chromium, good imitations of the ruby, sapphire, and corundum can be obtained ; and it is said that Bonsdorf has made the mineral gibbsite by exposing a solution of aluminate of potash to the action of an atmosphere of carbonic acid. When metallic aluminum is heated to redness in the air or in oxygen gas, it burns brightly and is converted into alumina, 53 - 3 parts of the metal taking up 46'69 parts of oxygen to form the pure earth. The compound thus produced is inferred to be sesquioxide because it is isomor- phous with the sesquioxides of iron and chro- mium, and is capable of replacing these oxides in combination in any proportion. ALUMINUM, or Aluminium, one of the metals of the earths never found native, but occurring in combination with other elements in 195 dif- ferent 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, 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 alka- lies. 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 vapor- ized chloride of aluminum over heated potassi- um. 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 con- taining 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 1 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 re- quire 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 ; fluor 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 lime- stone. The aluminum is readily separated