USEFUL METALS 225 



agency <! mineral springs. The action which brought about tin- 

 precipitation was doubtless metasomatic and dependent upon the 

 limestone. 



According to Thomas and MacAlister m< tusomatic bauxite 

 deposits occur in the Puy de D6me district of Central F ranee. 

 and in the northern part of Ireland in association with l.a-altie 

 rocks from which they were evidently derived. 



Geological Horizon. The ores of aluminum are not confined 

 to the rocks of any particular age. Corundum and emery are 

 more abundant in the older geological formations as the pre- 

 Cambrian, Cambrian and Ordovician. The bauxite deposits of 

 Arkansas are in part as late as the Tertiary. 



Methods of Extraction. Aluminum was isolated for the first 

 time in 1827 by Wohler by means of the effect of potassium upon 

 the anhydrous chloride. Commercially it has been obtained in 

 large quantities by the ignition of cryolite with sodium or potas- 

 sium. Two processes have been used to produce commercial 

 aluminum: The chemical process, and the electrolytic process. 



(1) In the chemical process the chloride of the metal is fused 

 with the double fluoride, cryolite, in the presence of metallic 

 sodium or potassium when elemental aluminum results from the 

 reducing action of the sodium or potassium. It has been pro- 

 duced commercially without the aid of an alkali from a mixture 

 of clay, cryolite, bauxite, with carbon and carbon disulphide. 



(2) In the electrolytic process a mixture of corundum, cryolite 

 and bauxite have been subjected to the intense heat of an electric 

 furnace. A carbon-lined crucible has served as the cathode and 

 a bundle of carbon rods as the anode. The metallic aluminum 

 collects at the bottom of the crucible. 



Uses of Aluminum. Aluminum is used in many forms in the 

 minor as well as the grosser industries, in articles useful, or 

 luxurious. It is used in the manufacture of keys, visiting cards, 

 pocket calenders, thimbles, brushes, combs, letter cases, cigar 

 cases, cigarette cases, for which the metal is highly valued on 

 account of its extreme lightness. 



It is used in the manufacture of opera glasses, spectacle-. 

 knives, watches, and many articles of adornment. It finds a 

 use in household utensils such as cups, saucers, plates, chafing 

 dishes, tea urns, etc. It is used in individual communion sets, also 

 in the manufacture of a large number of toys. It is utilized in 

 the alums in medicine. It is used in the springs in shoes. Alum- 



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