ALUMINIUM 129 



not contain the impurities referred to as so prejudicial, or contains them in such a 

 form as to admit of their easy separation. This material is Bauxite, so called from 

 the name of the locality -where it is found in France. The Bauxite is ground and 

 mixed with the ordinary soda-ash of commerce, and then heated in a furnace. The 

 soda combines "with the alumina, and the aluminate of soda so formed is separated 

 from the insoluble portions viz., peroxide of iron, silico-aluminato of soda, &c. by 

 lixiviation. Muriatic acid or carbonic acid is then added to the solution, which 

 throws down pure alumina. The remainder of the process is precisely that which is 

 described by Mons. St. Clairo Deville. The alumina is mixed with common salt and 

 charcoal, made into balls the size of an orange, and dried. These balls are placed in 

 vertical earthen retorts, kept at a red heat, and through the heated contents chlorine 

 gas is passed. The elements of the earth, xinder the joint influence of carbon and 

 chlorine at that temperature, are separated, the carbon taking the oxygen and 

 the chlorine the aluminium. The latter substance accompanied by chloride of sodium 

 (common salt) sublimes over, and is collected as a double chloride of aluminium and 

 sodium. Sodium, : being required to effect the decomposition of this compound, is 

 thus prepared. In small iron retorts kept at as high a temperature as iron can bear, 

 a mixture of soda (carbonate of soda) and carbonaceous matter with a little ground 

 chalk is placed. The metallic base of the alkali distils over, and is collected in coal 

 oil. A portion of the double chloride of aluminium and sodium, and the metallic 

 sodium, along with fluxes, is exposed to a full red heat in a reverberating furnace. 

 The sodium seizes the chlorine combined with the aluminium, and thus liberates the 

 latter metal, which falls to the bottom of the fixed mass. Aluminium is used in 

 sufficient quantity to keep the only work in England viz., that at Washington 

 pretty actively employed. As a substance for works of art, when whitened by means 

 of hydrofluoric and phosphoric acid, it appears well adapted, as it runs into the most 

 complicated patterns, and has the advantage of preserving its colour, from the 

 absence of all tendency to unite with sulphur, or to become affected by sulphuretted 

 hydrogen, as happens with silver.' Aluminium has been used in the manufacture 

 of weights and scale-beams for chemists, and for opera- and field-glasses, for which 

 purposes it is exceedingly valuable, by reason of its lightness and its not being 

 liable to tarnish. A greatly increased activity has boon given to the manufacture of 

 aluminium by its use in the manufacture of aluminium-bronze a compound of 

 exceeding beauty, so much like gold that it can scarcely be distinguished from that 

 precious metal. 



Properties. The metal is white, but with a bluish tinge, and even when pure has 

 a lustre far inferior to silver. 



Specific gravity, 2'56, and when hammered, 2'67. 



Conducts electricity eight times better than iron, and is feebly magnetic. It is 

 highly sonorous. 



Its fusing-point is between the melting-points of zinc and silver. 



By electrolysis it is obtained in forms which Deville believes to bo regular octa- 

 hedra ; but Eose, who has also occasionally obtained aluminium in a crystalline state 

 (from cryolite), denies that they belong to the regular system. 



When pure, it is unoxidised even in moist air ; but most of the commercial spe- 

 cimens (probably from impurities present in the metal) become covered with a bluish- 

 grey tarnish. 



It is unaffected by cold or boiling water ; even steam at a red heat is but slowly 

 decomposed by it. 



It is not acted upon by cold nitric acid, and only very slowly dissolved even by the 

 boiling acid ; scarcely attacked by dilute sulphuric acid, but readily dissolved by 

 hydrochloric acid, with evolution of hydrogen. 



Sulphuretted hydrogen and sulphides have no action upon it ; and it is not even 

 attacked by fused hydrated alkalis. Professor Wheatstone ' has shown that in the 

 voltaic series, aluminium, although having so small an atomic number, and so low a 

 specific gravity, is more electro-negative than zinc; but it is positive to cadmium, tin, 

 lead, iron, copper, and platinum. 



Impurities in Aluminium. Many of the discrepancies in the properties of alumi- 

 nium, as obtained by different experimenters, are due to the impurities which are 

 present in it. 



If the naphtha be not carefully removed from the sodium, the aluminium is liablo 

 to contain carbon. 



Frequently, in preparing aluminium, by the action of the chloride on sodium, by 

 Deville's original process, copper boats have been used for holding the sodium ; in 

 this case the metal becomes contaminated, not only with copper, but also with any 



1 Phil. Map. x. 143. 

 Vol. I. K 



