454 APPLIED SCIENCE 



exceedingly tough, dense, and close-grained metal. It will 

 resist vibratory and sudden stresses and shocks, and will 

 not rust or corrode in the presence of air or sea water. 



533. Gun-Metal. Gun-metal is an alloy of copper and 

 tin, with sometimes a small proportion of zinc. It is a harder 

 metal than either of its constituents and has a greater den- 

 sity. It is more fusible and less likely to corrode than copper. 

 When a casting of gun-metal rapidly cools or chills, the 

 density, strength, and toughness of the metal are increased 

 because the composition becomes more uniform. For heavy 

 bearings hardness is considered of greater importance than 

 strength. A hard gun-metal consists of 79% copper and 

 21% tin. 



The general effect of tin in an alloy is to increase its hard- 

 ness, and whiten its color. Zinc in small quantities with 

 copper increases fusibility without reducing hardness; in 

 large quantities it prevents forging when hot, but increases 

 malleability when cold. Common bronze mixes better when 

 a small quantity of zinc has been added. 



534. Nickel. Nickel is a hard, white metal, more nearly 

 resembling silver than tin and is used because of its luster 

 and permanence. Dilute sulphuric and hydrochloric acid 

 affect it only slightly, but nitric acid will dissolve it readily. 

 It will neither rust nor corrode in the presence of air, even 

 though the air be moist. Nickel forms valuable alloys and 

 is used extensively for nickel-plating. 



535. Bronzing. Bronzing is an attempt to produce the 

 effect of bronze on other metals or substances. A solution 

 Of sal ammoniac ancj salt of sorrel in vinegar is used for 



