TREATMENT OF ORES. 237 



the cost of fuel and labour were not covered by the gold and 

 silver obtained as sub-products, the pure coppers obtained from 

 native copper would probably be used for telegraphic purposes, 

 and those obtained by the ordinary metallurgic processes would 

 be used for general purposes. The preparation of certain 

 simple bodies is also one of the interesting branches of electro- 

 metallurgy. 



BUNSEN'S PROCESS. Bunsen was the first who succeeded in 

 rapidly preparing in comparatively large quantities the mag- 

 nesium, the barium, the aluminium, and the calcium by means 

 of electricity. He acted on some chlorides of these metals, 

 either by dissolving them in water so as to obtain a concentrated 

 solution, of which he raised the temperature at the same time 

 that he submitted them to the decomposing action of the electric 

 current, or in melting them in an anhydrous state in a porcelain 

 crucible highly heated, and using as electrodes some well 

 reduced coke carbon.* 



For magnesium, for instance, Bunsen used well dried 

 chloride of magnesium and placed it in a varnished porcelain 

 crucible internally divided by means of a porous porcelain 

 partition which did not reach the bottom; the porcelain 

 cover was provided with two holes for the introduction of the 

 conductors. As soon as the chloride reached a state of fusion, 

 he sent through it a current of 15 to 20 volts, and the decom- 

 position immediately took place: the chlorine going to the 

 positive pole, and the magnesium to the negative. As the 

 metal is not so dense as the chloride, the operator took care to 

 retain it in the liquid by means of oblique grooves cut in the 

 carbon electrode on which it was deposited ; the magnesium 

 would without this precaution have risen to the surface of the 

 bath and been burned. 



Bunsen prepared aluminium in the same manner, operating 

 on a double chloride of ammonium and sodium (the chloride of 

 aluminium does not melt, but vaporises at a low temperature). 



M. Sainte-Claire Deville has perfected this latter process. 

 To this effect he prepared the solution to be decomposed by 

 mixing in a porcelain cup heated to about 200 C. 2 parts of 

 * De La Rive, vol. iii. pp. 511 and following. 



