182 Aluminium. 



water : and the globules, covered up in a porcelain crucible 

 either with mixed chlorides of aluminium and sodium, or with 

 common salt, are fused together by a strong heat. 



This process answers still better on the large scale ; but, 

 instead of the porcelain tube and boat, two cast-iron cylinders 

 connected by a smaller tube of iron are employed. The an- 

 terior cylinder contains the chloride of aluminium ; the posterior, 

 sodium in a tray; and the iron tube, kept at a temperature 

 of from 400° to 500° Fahr, scraps of iron to separate any of 

 that metal which may rise with the vapour of chloride of 

 aluminium, by changing it from volatile per to fixed proto- 

 chloride. 



CErsted, who was the first to form chloride of aluminium, is 

 said to have obtained that metal, by heating the chloride with 

 an amalgam of potassium, rich in the latter, and driving off 

 the mercury from the resulting amalgam of aluminium, by 

 heat. 



Aluminium may also be procured from Cryolite, a mineral 

 which exists abundantly in Greenland, though it is found only 

 in small quantities elsewhere. It is a double fluoride of alumi- 

 nium and sodium : and may be produced artificially, by adding 

 hydrofluoric acid in excess to calcined aluminium and carbonate 

 of soda, so as to produce 



Fluorine 54*5 



Aluminium 13'0 



Sodium 32-5 



100-0 



then evaporating, and fusing the result. Both the native and 

 factitious cryolite give aluminium with sodium, and with the 

 galvanic current. The latter, with a mere mixture of aluminium, 

 and fluoride of sodium, would afford only sodium and fluorine. It 

 occurred to Rose that, on account of the deliquescence and 

 volatility of the chlorides of the alkaline metals, and the neces- 

 sity, when they are employed, of preventing any access of 

 atmospheric air, it would be better, in the reduction of alumi- 

 nium, to use a fluoride of that metal combined with an alkaline 

 fluoride ; and he proposed to use cryolite, but was deterred by 

 its scarcity at that period. To obtain aluminum in this way, 

 finely powdered cryolite and sodium are placed alternately 

 in layers, in cast-iron crucibles, the whole being covered with 

 a good thickness of chloride of potassium as a flux. The cru- 

 cible is then carefully closed with a porcelain cover, and raised 

 to a red heat for half an hour. After Avhich, the calcined matter 

 having been softened with water, it is broken down in a por- 

 celain mortar. The larger globules of aluminium are easily 



