Aluminum Elements,
Alloys and Symbols

• Cryolite, Na₃AlF₆. 
• Bauxite, Al₂O(OH₄)
• Corundum, Al₂O₃. 
• The Feldspars, KAlSi₃O₈,NaAlSi₃O, CaAl₂Si₂O₃, etc.
• Gibbosite, Al(OH)3. kaolin, H₄Al₂Si2O₉.

Aluminum is the most common of all the metals. Unlike other metals, however, its occurrence, with the exception of the fluorides, is restricted to minerals containing oxygen. It is most abundantly found in the rocks-making silicates, in the majority of which it is as essential constituent. It also occurs in large amount in the clays. The minerals which can be used as ores of the metal are, however, few in numbers, the only one at present of importance being bauxite. The enormous amounts of aluminum contained in the various silicates are not yet available because of the difficulty and expense of extraction.

Bauxite is produced in the United States chiefly from Arkansas, Alabama, Georgia and Tennessee. The deposits in Arkansas are found in Pulaski and Saline counties. They have an average thickness of 10 to 15 feet. In one district the beds lie directly upon a body of kaolin, which in turn rests upon a syenite rocks-mass and it is probable that Alabama-Georgia district extends from Jacksonville, Alabama, to Cartersville, Georgia. The ore occurs as pockets or lenses in a clay which has bee derives by weathering processes form a dolomite limestone. The bauxite is either pisolitic or clay-like in structure.

Cryolite, imported from Greenland, has been used as an ore of aluminum and at present in used as a flux in the electrolytic process by which most of the metal is obtained.

The usual process at present by which aluminum is extracted from the bauxite ores is briefly as follows: the ore is heated to low redness with sodium carbonate forming sodium aluminate. This compound is leached out by water and by passing CO2 gas into the solution the aluminum is precipitated as the hydroxide. The latter on being heated is converted into the oxide of the metal. The pure metal is prepared from this oxide by an electrolytic process which takes place in a bath of fused cryolite. The tank in which the reaction takes places is lined with carbon and forms the cathode, while graphite rods suspended in the bath serve as the anode. The metal collects in the bottom of the tank.

  Aluminum is valuable because of its low density and because it is not easily oxidized or corroded. It is a good electrical conductor and to some extent is replacing copper used for that purpose. It is used in many alloys, particularly with zinc, copper and nickel. Duraluminum is the trade name of the most important alloy. It is used in small amounts in casting steel in order to take up any oxygen in the melt and also to porosity in the metal. Aluminum and iron oxide are mixed in a finely divided state to form the material known as thermite. When this mixture is ignited the heated of the combustion of the aluminum is so great that it can be used in welding iron and steel. Sheets and tubes and casting of aluminum are used wherever a light weight metals is desired, for instance in the manufacture of certain parts of automobiles. Aluminum is used in the manufacture of cooking utensils, as a substitute for lithographic stones and zinc plates, as powder in the manufacture of metallic paints, etc. It is used also in the form of salts, chiefly alum and aluminum sulfate, to harden paper, in the purification of water, as mordant in dyeing, in baking powders, in medicine, etc.