COPPER. 255 



The oxide of iron thus removed, is derived from the 

 sulphuret of iron, which is a usual constituent of cop- 

 per ores. 



634. Both of the above processes of 



State further 



particulars of roasting and heating with charcoal, and 

 epro sand, must be several times repeated 



before pure metallic copper is obtained. It is to be 

 remarked that the formation of a slag, which shall 

 remove this iron, depends on the fact that its oxide is 

 by no means so easily reduced as copper. Being once 

 brought into the state of oxide, it remains in this con- 

 dition and unites with the silicic acid of the sand. 



635. ACTION OF HEAT AND AIR. Copper 

 What is the , .,..,. 



effect of heat is readily oxidized m the air, at a high 

 temperature. Its oxidation may be ob- 

 served, by holding a copper coin in the flame of a spirit 

 lamp, as described in the section on Flame. The iri- 

 descent hues observed in the experiment, are owing to 

 the varying depth of oxide on different portions of 

 the coin. By long continuation of the process, the 

 whole surface is converted into black oxide. If it be 

 sooner suspended, and the coin plunged into cold 

 water, a coating of red oxide containing less oxygen 

 is obtained. 



636. USES OF COPPER. Copper is used 



Mention some . . . , . 



of the uses of ior a variety of purposes, for which iron 

 copper. would be less suitable, on account of its 



rapid oxidation. Its employment in sheathing ships, is 

 an example. It is also a constituent of various alloys, 

 to be hereafter described. Among these, all gold and 

 silver coins, and the metal of gold and silver plate, are 

 included. 



