VARIOUS METALS. 397 



COPPER, ALLOYS OF COPPER, "ALUMINIUM, TIN 

 LEAD, ZINC. 



212. Next to iron and its alloys, the most important 

 metal in the arts at the present time is undoubtedly copper, 

 either in its commercially-pure form or alloyed with other 

 metals. Its chief advantages are its softness and mallea- 

 bility, its high heat-conducting properties, its non-corro- 

 dibility, and its high electrical conductivity. The tensile 

 strength of copper is considerable, varying from six tons in 

 castings to 16 tons per square inch for unannealed rolled 

 bars. Copper and its alloys are annealed by heating to 

 redness and cooling suddenly in water. 



Alloyed with zinc, copper yields the useful metal 

 yellow brass, which has a low tensile strength, and is only 

 used for ornamental work, where strength is not required ; 

 and "Muntz metal," having a tensile strength of about 

 25 tons. 



The group of bronzes consist of copper alloyed with 

 tin and a little zinc, and give a tensile strength of from 

 10 to 27 tons, according to the mixture and manner 

 of manufacture. 



A small percentage (3 to 8) of aluminium added to 

 bronze produces a metal of considerable ductility and 

 very high tensile strength, this latter being from 25 to 

 40 tons per square inch. 



The most striking characteristic of copper and its 

 alloys from the point of view of the load-strain diagrams 

 is the almost complete absence of a sudden yield point, such 

 as is found in the irons, and the low elastic limit. Typical 

 strain diagrams are shown in Figs. 190 and 191. 



o o 



Aluminium is now produced fairly cheaply in the 

 form of rolled bars, drawn rods, wire, sheet rnetal, angles, 

 tees, and beams, as well as ingot metal for castings, the 

 price being now between Is. and 2s. Gd. per pound. 



In the form of rods or bars, aluminium has a tensile 

 strength of about 10 tons per square inch, accompanied 

 by a fair amount of ductility. 



The load-strain diagram for aluminium has the same 

 peculiarity as iron at high temperature, it being found 

 that the deformations take place in jumps, with the result 

 of producing a stepped curve. (See Figs. 192 and 193.) 



