Copper when pure is of a red color, exceedingly malleable and ductile. When rolled, hammered, or worked into sheets, it is used to a great extent for roofing and sheathing vessels, and for making cylindrical pipes and copper wire. When hammered or worked in the cold, copper becomes brittle, but its toughness is restored by heating it to 500° F. When heated to redness it can be drawn apart and forged, but if overheated it becomes coated with black oxide of copper. In the ingot or cast condition it contains much oxide and therefore is not so strong as when it is rolled out into sheets.
* See page 171.