326 SMITH'S INTERMEDIATE CHEMISTRY 



the rest lead. The alloy is also harder than lead, and is less 

 quickly deformed by handling and by use in the printing press. 



Babbitt's metal (Sb 3, Zn 69, As 4, Pb 5, Sn 19), and other 

 anti-friction alloys, used in lining bearings, contain antimony 

 along with zinc, copper, and other metals. Molten mixtures of 

 metals (alloys), when solidifying, do not always form a homogene- 

 ous, solid mass. In an anti-friction alloy, what is wanted is a 

 mass, in general soft, but containing hard particles. The latter 

 bear most of the pressure, yet, as the alloy wears, they are pressed 

 into the softer matrix so that a smooth surface is always presented. 

 An alloy which has the opposite composition, that is, which gives 

 a hard mass containing softer particles, develops heat by friction 

 rnuclnaaeire rapidly. 



BISMUTH Bi 



As the Atomic weight increases, the members of this family 

 become more like metallic elements in their chemical properties. 

 Thus bismuth is a true metallic element. Its oxides are basic, 

 and its compounds give positive ions Bi ++ + and include salts like 

 the carbonate, sulphate, chloride, and phosphate. 



Metallic Bismuth. The metal occurs free in nature. It is 

 a brittle metal, with a pink metallic luster. It melts at 270 and 

 vaporizes at a high temperature. It does not tarnish. It is 

 used in preparing alloys with very low melting-points. Thus 

 Wood's metal contains bismuth (m.-p. 270) 4 parts, lead (m.-p. 

 326) 2 parts, tin (m.-p. 233) 1 part, and cadmium (m.-p. 320) 

 1 part. As is the case with other solutions, the melting-point is 

 lower than that of any of the components, namely 60. Alloys of 

 this class are used as plugs in sprinkler systems and stops to hold 

 steel fire-doors open. When, in consequence of a fire, the tem- 

 perature rises, the alloy melts, the water exits are opened and the 

 fire-doors swing shut. Safety plugs in steam boilers, made of a 

 similar, but less fusible alloy, melt when, as the result of failure 



