218 Rev. J. Barlow, [March 14, 



nium from alumina, it has effectually aided in obtaining that metal. 

 Not only was it the first source of potassium and sodium, substances 

 indispensable to the production of aluminium, but in the subsequent 

 preparation of those bodies, the philosophy of the pile has rendered 

 essential service to chemists. Faraday has shown that electrical 

 power is identical with chemical power. This being admitted, 

 whatever the one power can effect, tlie other may be expected to 

 accomplish. This consideration sanctions, if it does not suggest, 

 the processes by which Gay Lussac and Tht^nard, and Mitscherlich, 

 and Brunner, and Donny and Mareska,* and ultimately Deville, 

 have obtained potassium and sodium (the latter metal especially,) 

 by direct chemical reaction ; by a process so productive, that the 

 melted sodium actually runs out in a continued stream, as in com- 

 mon distillation, from the iron retort, into a receptacle placed to 

 receive it-l 



The powerful deoxidizing effect of the alkaline metals has been 

 proved by its effecting not only the decomposition of carbonic 

 acid gas, but also by the reduction of calcium, barium, and of 

 silicium, a substance to which the attention of the audience was 

 especially directed. 



Clay had already been designated as a silicate of alumina : in 

 fact, three-fourths by weight of a portion of pure clay are silica. 

 Of this silica one half is oxygen, the other half silicium, a substance 

 altogether new in its properties ; it is not affected by water or by 

 air, and it can be kept in either ; it has no lustre, or any other 

 resemblance to a metal ; it is analogous to carbon. 



Now it is important to notice, that it was not from silica (the 

 oxide), but from the fluoride and chloride of silicium that Berzelius 

 obtained this substance. This fact perhaps instigated Wohler's 

 successful attempt to decompose the chloride of aluminium (a 

 fusible and volatile substance,) by the vapour of potassium, which 

 has no effect on the oxide of aluminium. But the production of 

 the chloride of aluminium demands a concentration of chemical 

 power. The hydrated chloride, resulting from the solution of 

 alumina in hydrochloric acid, on being evaporated, decomposes 

 the last portions of the mother-liquor, and the operation ends by 

 the reproduction of alumina. This difiiculty was surmounted by 

 CErsted : he caused the affinity of oxygen for carbon and of 

 aluminium for chlorine to act simultaneously, and under the most 

 favourable circumstances, by chlorine gas being led over an intimate 

 mixture of alumina and charcoal heated to redness in a porcelain 



* Recherches sur I'extraction du Potassium, par M.M. J. Mareska et F. 

 Donny, An. de Chem. Ser. 3, torn. xxxv. p. 147. 



t Recherches sur les Metaux, &c., An. de Chem., Ser. 3, tom. xliii. p. 19. 

 M. Deville fused and cast above half a pint of sodium in a large ingot-mould 

 to illustrate this part of the discourse. The present retail price of sodium, in 

 London, is 4«. the ounce. 



