2. ALU'MINA, noun An earth or earthy substance, which has been considered to be elementary, and called pure clay; but recently, chimical experiments have given reason to believe it to be a metallic oxyd, to the base of which has been given the name aluminum. This metallic base however has not been obtained in such a state as to make its properties susceptible of examination. Alumina is destitute of taste and smell. When moistened with water, it forms a cohesive and ductile mass, susceptible of being kneaded into regular forms.
The metallic base of alumina. This metal is white, but with a bluishtinge, and is remarkable for its resistance to oxidation, and for its lightness, having a specific gravity of about 2.6. Atomic weight 27.08. Symbol Al.
ALUMINIUM, a metallic substance, first separated from the chloride by Wöhler in 1828. It remained a laboratory product until Deville, about 1858, succeeded in improving the mode of production, so as to render the operations capable of management on the manufacturing scale. The process consists in heating to a red heat a mixture of the double chloride of aluminium and sodium, or the double fluoride of aluminium and sodium (cryolite), with the metal sodium. A vigorous action takes place, chloride of sodium being formed and the metal aluminium separated. On the large scale the reduction is effected by throwing a mixture of 10 parts of the double chloride, 5 parts of cryolite, and 2 parts of sodium on the hearth of a reverberatory furnace. Immediately after the action, the fused metal and slag, consisting of common salt and fluoride of aluminium, are run out, and a new quantity of the previous mixture introduced. The various patents that have been secured with reference to this manufacture have all regard to the saving of the metal sodium. The metal aluminium may be separated from the double chloride by electrolysis. For this purpose the fused salt has the electric current from ten cells of a battery passed through it, carbon poles being used. The metal appears at the negative pole in large globules, which may be collected and melted together under a layer of fused salt....
Aluminium is a white metal resembling silver in appearance. It is very malleable and ductile, and may be beaten and rolled into thin sheets, or drawn into fine wire. By hammering in the cold it becomes as hard as soft iron, but may be softened again by fusion. Being highly sonorous, it has been used for making bells. It is very light, being only 2½ times heavier than water, and is thus four times lighter than silver. After fusion it has a specific gravity of 2 ∙ 56; by hammering this may be increased to 2 ∙ 67. It melts at a red heat, and is non-volatile at very high temperatures. The metal conducts heat and electricity as well as silver. Aluminium does not oxidise in air, even at a red heat, has no action on water at ordinary temperatures, and is not acted upon by sulphuretted hydrogen or sulphide of ammonium, and thus preserves its lustre where silver would be tarnished and blackened. It is not attacked by nitric acid, even when concentrated, and is not soluble in dilute sulphuric acid, but is readily soluble in dilute or concentrated hydrochloric acid with evolution of hydrogen. Solutions of caustic potash or soda dissolve the metal with great ease, forming aluminate of potash or soda, and giving off hydrogen. Aluminium forms alloys with most metals. The copper alloy called aluminium-bronze is the most important because of its colour, hardness, and malleability, and is largely used for articles of jewellery, for mounting sextants and other astronomical instruments, and for making balance beams.
9th ed. Encyclopædia Britannica, vol. 1, p. 647 [494 words — estimated reading time: 3 minutes]
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