METALS AND SOME OF THEIR COMPOUNDS 261 



in the manufacture of aluminium by heating it with the anhy- 

 drous chloride of that metal, but the extension of facilities for 

 electrolytic methods, together with the dangers and uncertain- 

 ties of the sodium process led to its abandonment. 



ALUMINIUM 



Aluminium is probably the most abundant metallic element 

 in the earth, as in the form of the oxide, alumina A1 2 3 , it is 

 the chief constituent of many crystalline rocks and of all clays. 

 The metal was first isolated in the form of powder by Wohler, 

 but it was not until about 1845 that it was obtained in a compact 

 state and on a manufacturing scale by Deville. Aluminium is 

 distinguished by its low density, which is only about 2-7 times 

 that of water, and therefore about one-third the weight of iron. 

 It is a good conductor of electricity, though inferior to copper. 

 It forms a very valuable alloy with copper, which is known as 

 aluminium bronze. This was manufactured by the Cowles pro- 

 cess before the difficulties in the reduction of pure aluminium 

 had been overcome. To obtain the bronze a mixture of corun- 

 dum (alumina) with charcoal and granulated copper is heated 

 in an electric furnace. The carbon takes the oxygen of the 

 alumina, while the copper unites with the aluminium and forms 

 a fusible alloy to which larger quantities of copper can afterwards 

 be added if required. This alloy has nearly the colour of gold, 

 while it has great strength and elasticity. 



Aluminium has been manufactured for many years by sub- 

 mitting to electrolysis alumina (prepared bauxite) dissolved in 

 fused cryolite, the double fluoride of aluminium and sodium. 

 The operation is carried out in an iron pot lined with carbon 

 which forms the cathode. The current is introduced by means 

 of thick carbon rods forming the anode which dips into the mix- 

 ture. The metal sinks to the bottom and is tapped off at inter- 

 vals, while carbonic oxide gas escapes. In proportion as the 

 metal is removed the supply of alumina is kept up by adding it 

 to the molten mixture. 



In the production of aluminium, as in so many other cases, the 

 source of power is the energy of falling water, and factories have 

 been established in connection with many of the great water- 

 falls of the world, such as Niagara, the Falls of the Rhine at 

 Schaffhausen, and in our own country at Kinlochleven in 

 Argyllshire. The bauxite consumed in the production of the 



