COPPER AND MERCURY 511 



with sand in a converter. Here the rest of the iron is oxidized and 

 eliminated as silicate in the slag, and the sulphur escapes as S0 2 . 

 The slag and metallic copper are poured separately. The latter 

 gives off some dissolved sulphur dioxide in bubbles as it solidifies 

 and, from its appearance, is named blister copper. Finally, since 

 the copper now contains dissolved cuprous oxide Cu 2 0^ the blister 

 copper is melted and " poled," by stirring with green wood, 

 gases (hydrocarbons, etc., p. 435) given off by the heated wood 

 reduce the oxide to copper. If the copper is to be refined electro- 

 lytically (p. 485), it is then cast in plates 3 feet square and f inch 

 thick. 



The old methods of concentrating copper sulphide ores 

 by simple washing left large amounts of copper in the rejected 

 gangue. Recent flotation processes prevent this loss. The ore 

 is finely ground and beaten up with water containing a small 



/quantity of oil. The particles of copper sulphide become wetted 

 by the oil, the particles of gangue are preferentially wetted by the 

 water. When air is forced through the pulp, the copper sulphide 

 particles float with the froth to the top and are scraped off, while 

 the gangue sinks to the bottom. Sixty million tons of ore per 

 year are now treated by this method. 



Properties. Copper has a characteristic bright yellow-pink 

 luster, quickly darkened by oxidation. It is second only to silver 

 in electrical conductivity and to iron in tenacity. It is third in order 

 of malleability. It melts at 1057. 



In moist air copper acquires a green coating of basic carbonate, 

 which protects the metal. It is not affected by dilute hydro- 

 chloric or sulphuric acids, when air is excluded. Hot concentrated 

 sulphuric acid gives cupric sulphate and sulphur dioxide (p. 271), 

 and nitric acid gives cupric nitrate and oxides of nitrogen (p. 310). 



Uses. Pure copper is used for electric wires and cables. 

 Traces of other metals greatly reduce the conductivity. Kettles, 





