WORLD'S SUPPLY OF COPPER 257 



use of copper in recent years is due to the fact that it is, 

 next to silver, the best conductor of electricity. 



But copper has many other uses. It is employed in 

 the manufacture of tubular boilers, for the sheathing of ships, 

 for electrotypes, in coinage and in many otlier ways too numer- 

 ous to mention. It is valuable also for use in the form of 

 alloys with other metals, its principal alloys being brass, 

 bronze, bell metal, speculum metal, aluminum bronze and 

 German silver. 



In combination with oxygen, copper forms four oxides, 

 quadroxide or sub-oxide; cuprus oxide, hemioxide or prot- 

 oxide; cupric oxide or monoxide; and peroxide. Cuprus and 

 cupric oxide are the most important of the four. Cuprus 

 oxide, which is found native as cuprite or red copper ore, is 

 used in the production of ruby glass. Cupric oxide is found 

 native as tenorite or black copper ore, and is used in making 

 green and blue glass and as a pigment. 



Of the copper salts the most important is cupric sulphate 

 or blue vitriol. It may be prepared by dissolving metallic 

 copper or its oxides in sulphuric acid. It is used extensively 

 in calico printing, in dyeing, in the preparation of pigments 

 and for the preservation of timber and in agriculture. Many 

 other compounds are extensivel}' used in pigments. 



In the extraction of crude copper from its ore three 

 methods are employed. They are known as the wet, dry, 

 and electro-metallurgical methods. W^ere the wet method 

 is employed the copper produced is called black or blistered 

 copper. It contains a number of foreign substances which 

 must be removed before it can be used. It is refined either 

 by the dry or electrolytic methods. The most important ores 

 of copper are the sulphuretted compounds. Next in order 

 come the oxides, carbonates and silicates of copper, as well as 

 native copper, containing impurities. All these ores when 

 sufficiently rich are treated by smelting or by the dry method. 

 Only when ores are so poor in copper that no other method 

 can be used profitably is the wet process used. 



The dry methods of copper smelting are several. They 



include blast furnace smelting, known also as the German 

 Vol. &-n 



