262 CHEMICAL DISCOVERY AND INVENTION 



metal is obtained chiefly from the South of France, and in 1907 

 amounted to 260,000 tons. The total world output of metal in 

 1909 was estimated at 30,000 tons. 



Aluminium is valuable not only for its lightness but on account 

 of its peculiar behaviour toward acids and alkalis. It dissolves 

 rapidly in diluted hydrochloric acid, but is very slowly attacked 

 by sulphuric or nitric acids, and still less by vegetable acids. 

 On the other hand it is dissolved by alkaline solutions with 

 evolution of hydrogen. Hence aluminium is used in a variety 

 of ways for making cooking utensils and in the storage of a great 

 variety of foodstuffs, but it is important to remember that 

 saucepans or pots of aluminium must not be cleaned with the 

 assistance of soda. 



Aluminium melts below a red heat, and when heated quickly 

 in the air it becomes covered with a white film of oxide which 

 prevents rapid oxidation. A thin piece of aluminium foil in a 

 bottleful of oxygen gas if touched with a red-hot wire disappears 

 instantly with an extremely brilliant flash, leaving the white 

 oxide behind. The combination of aluminium with oxygen is 

 attended by the evolution of a larger amount of heat than is 

 disengaged by the combustion of an equivalent quantity of any 

 other metal. The consequence is that a mixture of aluminium 

 powder with the oxide of another metal when heated at a single 

 point enters into a violent chemical reaction, at the end of which 

 the aluminium is converted into oxide while the other metal is 

 found in the metallic state. The action is so violent in some 

 cases, copper oxide for example, that a kind of explosion occurs 

 and part of the metal is volatilised. A mixture of aluminium with 

 various oxides has been turned to account for the isolation of 

 some metals not previously known or obtainable with difficulty. 

 The metal chromium, for example, is obtainable in this way, in 

 a state of purity, also manganese, which had previously been 

 known only in combination with carbon or with iron. 



An ingenious application of this property of aluminium is 

 found in the " thermit " process. A mixture of ferric oxide 

 with aluminium powder is placed in a crucible with a removable 

 bottom, and a fuse placed in the top of the mass being ignited 

 the whole mass becomes incandescent, and in a few minutes a 

 layer of molten iron sinks to the bottom of the pot and can be 

 run off into a mould. The method is applied to the repair of 

 broken castings, or to joining the ends of tramway rails without 



