240 ELECTROLYSIS. 



pyrite is roasted in a sustained but not too intense heat, the 

 sulphide of iron which is reduced at a lower temperature 

 changes into a state of peroxide, whereas the sulphate of 

 copper is to be found in almost its totality in a state of 

 anhydrous sulphate of copper in the roasted mass. When the 

 ores contain oxide or carbonate of copper, iron pyrites must 

 be added. In localities where sulphuric acid can be easily 

 procured the cuprous ores composed of oxide or carbonate 

 are directly transformed into sulphates. 



As to lead, it should be sulphated by either the dry or the 

 wet method. Plumbic sulphide requires less heat than galena, 

 because it is fusible and volatile. 



When galena is roasted, sulphurous acid is liberated, the 

 lead is oxidised, and plumbic sulphate is formed. The sul- 

 phatation of galena is obtained by the wet method by making 

 the sulphate of copper in solution react on the plumbic sulphide 

 at the ordinary temperature by the intermediary of salt 

 water. 



All that relates to this first part of the operation is minutely 

 described in M. Becquerel's work; it is the most important 

 part, and that which is generally neglected now. It is for- 

 gotten that in an electrolytic operation the bath is the essential 

 part, and it is particularly sought to economise the motive 

 power. The result is nearly always a complete failure, whereas 

 Becquerel has succeeded in rendering the electro-chemical 

 operation a perfectly industrial one. His processes, truly, 

 are expensive, but they actually exist, whereas the modern 

 methods are very economical on paper, but cannot be realised 

 in practice. 



Silver, copper, and lead ores being chloruretted or sul- 

 phated, and the dissolutions of the metallic compounds being 

 made in salt water for silver and lead, and in water for copper, 

 these three metals can be obtained in a metallic state by the 

 use of an electrical action arising from a simple bath or from 

 an external source. For the electro-chemical treatment proper, 

 Becquerel used voltaic couples composed of zinc, iron, or lead 

 associated with copper bands, to tin plates, or to pieces of 

 carbon placed in immediate contact with the metallic solution, 



