234 CHEMISTEY. 



GEOUP III. ALUMINIUM (ETC.). GEOUP IV. MAGNESIUM 

 AND ZINC. 



325. Aluminium. This metal, the base of the oxide alu- 

 mina, though it was unknown until a few years ago, is al- 

 ready used for a variety of purposes. It is a white metal, 

 resembling silver in color and hardness, as well as in its 

 power of resisting the action of air and water, but differ- 

 ing from it greatly in weight, silver being four times as 

 heavy. It is admirably fitted for ornamental purposes, and 

 has already been so employed to a considerable extent. It 

 is very sonorous, and therefore will make good bells. The 

 French government at one time used it for helmets and 

 cuirasses, for which it is well fitted, as it is both light and 

 strong. Formerly this metal was very costly, but in the 

 year 1854 M. Deville, who had charge of the private lab- 

 oratory of the Emperor of France, discovered a process by 

 which it can be obtained in large quantities, and at com- 

 paratively low price. And as silver is four times as heavy, 

 articles can be made of this beautiful metal for less than 

 the cost of silver. 



326. Aluminium Oxide, or Alumina, A1 2 O 3 . This earth is 

 the essential ingredient of all clays, and is present more or 

 less in all fertile soils and in many of the slaty rocks. The 

 metal of which this is an oxide is therefore quite abun- 

 dant, and widely diffused in the earth, though it is never 

 found in its metallic state, but is always in combination 

 with other substances. Alumina appears in some beauti- 

 ful forms. The sapphire, which in some of its varieties is, 

 next to the diamond, the most costly of gems, is pure alu- 

 mina crystallized. Blue is the true sapphire color. * When 

 this gem has other colors it receives other names : when 

 red, Oriental niby ; when yellow, Oriental topaz ; when vio- 

 let, Oriental amethyst; and when green, Oriental emerald. 



