Aluminium. 183 



separated mechanically ; the smaller, by dissolving away the 

 mass in which they are imbedded, with nitric acid, without 

 heat. The globules are fused, as before, under the mixed 

 chlorides, or common salt ; without this, the slight coating of 

 oxide on their surface would prevent their union. When com- 

 mon salt alone is used, a higher temperature is required. The 

 aluminium obtained from cryolite almost always contains silicium, 

 and even iron : and the product is not abundant, since 10 of 

 cryolite and 4 of sodium give only 05 of aluminium. Rose 

 attempted also to procure aluminium, by placing the mixed 

 chloride of aluminium and sodium, in alternate layers with 

 sodium ; but the results were not satisfactory. 



Bunsen proved, in 1854, that aluminium may be obtained 

 by means of the galvanic battery, in the same way as mag- 

 nesium. But, as chloride of aluminium cannot be used for the 

 purpose, since, instead of fusing, it volatilizes, he employed the 

 double chloride of aluminium and sodium, which is not volatile 

 except at a higher temperature than the fusing point of alumi- 

 nium. The apparatus also must be somewhat different from that 

 used in reducing magnesium. For the electrolysis, two parts 

 chloride of aluminium, and one part common salt dried and 

 pulverized, are mixed in a porcelain capsule, and heated to 

 about 390° Fahr.; after a while the mixture becomes a clear 

 liquid. 



The apparatus, in which the decomposition is to be effected, 

 consists of a glazed porcelain crucible, placed in another of earth ; 

 the latter is closed with a cover having one opening, at the side, 

 sufficient to allow a thick plate of platina to pass down through 

 it for the negative electrode, and another in the centre, to ad- 

 mit a porous vessel, which has been well dried, and in which 

 is placed the positive electrode — a piece of gas-retort graphite. 

 Both the crucible and the porous vessel — which is of less depth, 

 are filled to the same height with the melted double chlo- 

 ride : and the latter is kept hot, but not sufficiently so to melt 

 the aluminium. A battery of about five circles is connected 

 with the electrodes ; and the aluminium and common salt, which 

 will be deposited on the platina plate, is occasionally removed. 

 Chlorine and a little chloride of aluminium will separate in the 

 porous vessel, unless prevented by a small quantity of common 

 salt, thrown into it now and then, in a dry pulverulent state. 

 The mixture which has been detached from the platina plate, 

 is melted in a porcelain crucible protected by another of earth ; 

 the fused mass is dissolved in water, and the particles of metal 

 obtained from it, are melted several times under the double 

 chloride of aluminium and sodium. 



The battery does not give so pure a metal as the sodium 

 process, which removes the silicium, sulphur, — and even the iron, 



