184 A I uminium. 



from the materials ; but these impurities are found only in the 

 first portions detached from the platina plate. On account of 

 the small atomic weight of aluminium, compared with that of 

 zinc, the mode of obtaining it by electrolysis is too expensive 

 for ordinary purposes. 



The properties of aluminium are very remarkable, and many 

 of them are highly important. It is white, with a bluish tinge, 

 but when its surface is quite clean, its appearance differs very 

 little from that of silver ; its splendour is not indeed quite so 

 great, but lasts much longer. A very white and beautiful, 

 though not a polished surface, may be easily given to it, by 

 plunging it for an instant into a very dilute solution of caustic 

 soda, washing it with water, and then digesting it in strong 

 nitric acid. This removes everything that can soil it, except 

 silicium if in considerable proportion. Aluminium takes a fine 

 polish, and preserves it for an indefinite period ; but to render it 

 as brilliant as possible, a mixture of stearic acid and spirits of 

 turpentine must be used, between the rotten stone and finishing 

 powder; and the polishing process must end with spirits of 

 turpentine. Its characteristic blue tint is more perceptible 

 when the surface is polished than when it is dull. It often 

 assumes a crystalline form, if cooled slowly. When pure, it 

 has not any taste. If it contains a large portion of silicium, it 

 has a slight smell of siliciuretted hydrogen; otherwise it is 

 inodorous. Hot or cold, it is as malleable as gold or silver, 

 and is reducible to as thin leaves. It differs from all other 

 malleable metals, by being deprived of malleability if alloyed 

 with any other metal. It is so ductile, that it may be drawn 

 into an extremely fine wire : but its ductility also is affected by 

 admixture. Its tenacity, and elasticity, are nearly the same as 

 those of silver. When cast, it is as hard as pure silver ; but 

 when hammered, it is as hard as soft iron. It seems to be one 

 of the best known conductors of electricity ; its conducting 

 power is eight times greater than that of iron : but this also 

 depends very much on its purity. Since metals generally con- 

 duct heat in about the same proportion as electricity, it is, as we 

 might expect, an excellent conductor of heat — probably a better 

 one than silver. It is slightly magnetic. When pure, and in 

 the form of a bar, it is remarkably sonorous : and if suspended by 

 a thread, it emits a sound like that of a glass bell : but in other 

 forms, its tones have not been found agreeable. Its specific 

 gravity is only 2*56, and when hammered 2 - 67; no other 

 metal of small density has been found malleable, tenacious, 

 sonorous, and a good conductor. Iron is nearly three times as 

 heavy, copper nearly four times, lead nearly five times, and 

 platina nearly nine times. Even though prepared to find it 

 very light, we are astonished on handling it. This property 



