Copper is used by the builder chiefly for slate nails and bell wires, sometimes for rain-water pipes and gutters, for covering roofs, for lightning-conductors, and for dowels; also for bolts and fastenings in positions where iron would be corroded or oxidised. Moreover, it forms most useful alloys with other metals.
It is frequently found in the metallic slate, and is also obtained from copper pyrites, grey and red copper ores, from copper glance, and other ores, by roasting, calcining, refining, and melting them with certain fluxes and oxidising agents.
In tenacity it is inferior to wrought iron, but is superior to all other metals. The tensile strength of copper wire is about 16 tons per square inch, that of cast copper being 81/2 tons. It is not so ductile as wrought iron, and cannot therefore be drawn into such fine wires.
It can be worked either cold or hot - in the latter case it is easily oxidised - but it cannot be welded.
Copper oxidises very slowly in air, being covered with a film of carbonate, commonly called verdigris.1 The appearance of this film is well known to all; it forms a protective coating which preserves the surface of the copper from further oxidation.
Sheet Copper. - The most useful form for the builder in which copper is sold, is in sheets measuring about 4 feet by 2 feet (in Scotland 4 feet by 3 feet 6 inches), and described according to their thickness (by the Birmingham Wire Gauge), and their weight per foot superficial, or their weight per sheet.
The gauges of the sheets vary from No. 1 to 30 W.G. The weights of a few of the most useful thicknesses are given in the Table below : -