LEAD AND TIN 503 



be used for hard water, but not for rain water. In presence of air, 

 acids (even feeble vegetable acids) interact with the metal, which is 

 therefore unsuitable for kitchen utensils. 



Uses of Lead. The metal is rolled into sheets, which are used 

 for lining tanks. Lead pipes are made by pressing the metal, 

 while hot, through dies. Their pliability, and the ease with which 

 they can be cut and soldered, fits them for use in plumbing and for 

 covering electric cables. 



JCype metal, containing 20 per cent of antimony, is harder than 

 lead, and expands on solidifying. Small shot (p. 340) contain 0.5 

 per cent of arsenic. Solder (lead, tin 1 : 1) remains melted at a 

 lower temperature than pure lead (m.-p. 326) and so can be 

 applied to a lead joint without danger of melting the lead itself. 



. Lead monoxide PbO is made by oxidizing melted 

 lead in a current of air. At low temperatures a buff colored 

 powder, massicot, is obtained. When the oxide is allowed to melt, 

 it solidifies to a reddish-yellow, scaley mass litharge. The 

 Qxide is predominantly basic, absorbing carbon dioxide from the 

 ah- and, with acids, giving salts. It is used in makirip; glass. and 

 finfl.Tflftla. Stone and glass can be cemented with a mixture of 

 massicot and glycerine. 



Minium or red lead Pb 3 C>4 is a bright-red powder formed by 

 oxidizing the monoxide in air at 470 to 480 : 



6PbO + Oj <= 2Pb 3 4 . 



Rp^ lead is used in making flint pfasfi a,H ^ p^'pl 



Lead dioxide PbOo. is a brown powder, made by treating red 

 lead with diluted nitric acid. 



Paints. A paint usually contains three ingredients: 1. The 

 oil, which hardens (" dries ") to a tough resin, being oxidized by 

 the air, and adheres firmly to the surface being painted. 



