TREATMENT OF ORES. 239 



reducing it, by means of a crushing machine, to a state of 

 impalpable powder, for the success of a good chloruretting 

 almost solely depends on the state of extreme division of the 

 ore. The substances used for chloruretting by the wet method 

 are the sodium chloride, the sulphate of copper, or the sulphate 

 of peroxide of iron, in proportions dependent on the composition 

 of the ore and its percentage of silver. (The quantities re- 

 quired are approximately one-tenth in sodium chloride and one- 

 twentieth in sulphate of the weight of the ore.) 



The silver ore can also be chloruretted by previously mixing 

 it with sodic chloride and gradually pouring 3 kilogrammes of 

 nitric acid on 100 kilogrammes of the mixture. 



The silver ores composed of double sulphides and of mul- 

 tiple combinations can only be chloruretted by the dry method, 

 that is, by roasting, with addition of sodic chloride and often of 

 pyrites. After the ore has been pulverised and mixed with the 

 sea-salt and pyrites, the roasting is effected in a reverberatory 

 furnace, stirring it constantly with a poker, so as to multiply 

 the points of contact with air. The object of the roasting is to 

 get rid of the sulphur, the arsenic, the selenium, and the 

 antimony. A portion of the sulphur escapes in the state of 

 sulphurous acid, and the other is transformed into sulphuric 

 acid, which combines with the bases and forms sulphates. 

 These sulphates react on the sodic chloride ; there is forma- 

 tion of sodic sulphate and liberation of chlorine, which combines 

 with silver. 



Copper in. ores is found in either a metallic state or in a 

 state of oxide or chloride, of sulphide or carbonate, &c. ; in the 

 majority of cases its sulphide is combined with iron sulphide, 

 and constitutes the cuprous pyrite ; when combined with other 

 sulphides it constitutes some multiple sulphides, the treatment 

 of which by the dry method offers some difficulties. It is those 

 combinations which are submitted to the roasting. When the 

 copper is in a metallic state it is separated from the gangue by 

 means of lixiviation ; if it is in the state of oxide or carbonate, 

 it must be combined with sulphuric acid ; if it is in the state 

 of simple, double, or multiple sulphide, it must be roasted with 

 great care, so as not to produce any oxide. When the cuprous 



