SHEET METALS 451 



supply comes from South America and Russia. It is as 

 durable as gold, as hard as iron, resembles silver in color, 

 and is extremely ductile and tenacious. It melts at 2000 F. 

 Owing to its high melting point and its resistance to the 

 action of most chemicals, no single acid will act on it. A 

 mixture of nitric and hydrochloric acid (aqua regia) will 

 dissolve it. Finely divided platinum is called platinum 

 black and has the power of absorbing gases. 



526. Properties of Antimony. Antimony is a hard metal 

 used as an alloy with tin and lead for various purposes where 

 great hardness and durability are needed. Printers' type 

 metal, which must be firm enough to bear the pressure of a 

 heavy printing press, is composed of lead and antimony. 

 Antimony is also used as a medicine, while its oxide is valu- 

 able for the purpose of coloring glass. Sometimes found in 

 the native state, its most important ore is the sulphide, 

 stibnite (Sb 2 S 3 ). The pure metal is obtained by strongly 

 heating the ore with iron filings in a crucible, or by roasting 

 the sulphide in a furnace until it is converted into the oxide 

 (Sb 2 O 4 ). It is then mixed with powdered coal and heated 

 to a redness. As a result the carbon dioxide escapes and 

 antimony remains. 



527. Bismuth. Bismuth has a reddish white metallic 

 luster, and is found as a pure metal, or in compounds as a 

 sulphide. The ore is first roasted to oxidize the arsenic and 

 sulphur, and is then mixed with carbon and iron filings and 

 melted in a crucible. The metal collects in the bottom of 

 the crucible. Bismuth is chiefly used because of its extreme 

 fusibility, as it melts at 270 F., while its alloys melt at even 

 a lower temperature. 



