USEFUL METALS _'_>; 



Tin- specific heat of aluminum melts the snow as it falls upon 

 the win-, therefore the wires do not stretch and break under 

 the burden of the snow like copper wire The electrical 

 conductivity of aluminum is double that of copper per pound, 

 therefore it has a superior advantage for electrical purposes 

 wherever the wires are subject to severe storms. 



The general post-office authorities of England have intro- 

 duced aluminum into their long-distance communications. Tin- 

 large increase in the domestic consumption of the metal is largely 

 due to the use of aluminum for electrical conductors, and tin- 

 ease with which it replaces zinc in brass. The electric lines in 

 Chicago have in part substituted aluminum wires for copper 

 and these are giving perfect satisfaction. 



Among the newer uses of aluminum is that for the production 

 of intense heat by the combustion of the metal in the form of 

 the powder called thermit, which is the base of three important 

 branches of metallurgy. It is used in the manufacture of a 

 special explosive called amonal. It is used in the rubber in- 

 dustry for making lasts and boot trees upon which rubber boots 

 and shoes are manufactured. It is used as a substitute for 

 wood in making bobbins for spinning and revolving machinery 

 used in the manufacture of silk fiber. It is used as a substitute 

 for glass and many forms of earthern ware, in carboys employed 

 for the transportation of nitric acid, as a substitute for zhu- in 

 the linings of cisterns and other receptacles for storing water. 



Aluminum alloys readily with other metals both common and 

 rare, and furnishes many useful alloys. The number of these 

 light alloys now upon the market is large. The metal itself is so 

 soft when produced by electrolytic methods that some hardening 

 element is very desirable. Silicon possesses this factor whether 

 present accidentally or added intentionally. If more than 2 per 

 cent, silicon is present it impairs the malleability of aluminum 

 but does not diminish its value in castings. Aluminum bronze 

 containing 10 per cent, or less of aluminum is largely used in 

 the arts. It is commercially used as aluminum gold. As it 

 contains no tin it is not, strictly speaking, a bronze. Bronze 

 with 5 per cent, aluminum closely resembles pure gold. With 

 10 per cent, aluminum the alloy is a little darker than 22 carat 

 gold. With a larger percentage of aluminum the alloy whitens 

 With more than 15 per cent, aluminum the alloy becomes white. 



Many of the aluminum alloys have a tensile strength ranging 



