CHAPTER XI 
ORES OF ALUMINIUM INCLUDING BAUXITE 
ALuMiNTUM—USES AND SEPARATION—Aluminium Al; at. 
wt, 27:1; sp. gr, 26; melting-point, 1210° F.; tensile 
strength about 17 tons per square inch; electrical conduc. 
tivity about 614 per cent. that of copper) is the commonest 
metal in the crust of the earth, and in the whole earth is less 
abundant only than iron. Its many useful properties will 
doubtless render it second only to iron in service to man. 
Owing to its strong affinity for oxygen it always occurs in 
nature as compounds, and its separation as a metal has been 
achieved with difficulty. It has a beautiful silvery white 
colour and does not tarnish. It is light and can be drawn out 
into thin sheets and wire. It resists corrosion by organic 
products, so that it can be safely used for the cooking and 
preservation of food. Its electric conductivity is so high in 
proportion to its weight that it may provide the cheapest 
electric cables. Its great affinity for oxygen renders it a 
powerful reducing agent, and owing to the high heat (5500° 
F.) generated by the oxidation of fine aluminium powder 
it is used for welding, as a violent explosive, and as an 
incendiary material. It unites with other metals in many 
alloys invaluable from their combined lightness and strength. 
Aluminium was isolated in small globules in 1845, and its 
production was begun in 1854 by St. Claire de Ville ; but it 
was first prepared on a commercial scale in 1885, and its 
production was increased by the electrolytic processes of 
Héroult (1886) and Hall (1892); it was obtained by the 
fusion of cryolite, the double fluoride of sodium and alumin- 
ium mined from a vein in gneiss in Greenland. The em- 
ployment of aluminium on a great scale only became possible 
after the Bayer process enabled it to be extracted electrically 
[Zn