Dr. F. H. Thomson's Historical Notes of Copper Smelting. 331 



B — Calcination of metal A . 



B — Melting of calcined metal B, with ores of mean per centage and 

 purity. Formation of second metal. 



C — Calcination of metal B. 



D — Melting of calcined metal. 



C — With rich and pure ores. Formation of third metal. 



E — Calcination of metal D. 



C — Melting of calcined metal E, with very rich and pure ores. 

 Formation of black copper. 



D — Eefining of black copper. 



But although in reaUty so many operations are noted, the classifica- 

 tion may be reduced to five, as the repeated calcinations are purely for 

 the purpose of getting rid of arsenic and antimony by volatilization. 

 Metals, such as nickel, cobalt, &c., separate under the influence of 

 calcination and melting, by which all substances, more oxidizable than 

 copper, are by preference converted into oxides and silicates ; but in 

 order to expel all the arsenic contained in certain ores, it is necessary 

 to repeat many times the alternate calcinations and meltings of the 

 metal before obtaining black copper. 



Mr. Mitchell writes a paper in the Mining Journal for 1850, page 

 489, and at some length gives a summary, combining Le Play's, his 

 own, and Mr. Vivian's experience of the best method of smelting 

 copper ores of all classes ; and although displaying great chemical 

 knowledge, and containing much valuable information as to the difierent 

 groups, and the best methods of treating each particular class, yet it all 

 results in the same principle being carried out. 



He says that " the chief characteristic of the Welsh method is the 

 facility offered for the rapid and sure working of all the ores and copri- 

 ferous products which mining or industrial art can furnish. No other 

 process seems to possess this peculiarity, and to be so well adapted to 

 the continuous extraction of copper contained in substances unexpect- 

 edly and continually varying in per centage and chemical composition." 

 This method, considered in its minutest details, is not identical in all 

 smelting works. There exist slight variations either in manipulation or 

 in the form of apparatus, according to the skill or the pecuhar 

 ideas of the manager, the period at which the works are established, 

 the nature of the ores worked by preference, or the quality of the pro- 

 duct required. The ores thus treated in a metallurgical point of view 

 contain substances which may be divided into three groups : — 



1. Silica, the earthy oxides, and ready formed silicates, all of which, 

 after various reactions, nearly entirely pass into the slags. 



2. The sulphuretted and oxidized compounds, containing all tlic 



