CHAPTER IV 



USEFUL METALS (GROUP I) 



LEAD AND MERCURY 



Properties. Lead, symbol Pb, is a soft, bluish- white metal. 

 Its freshly cut surface has a bright metallic luster. The metal 

 upon exposure quickly becomes coated with a film of the 

 oxide. Lead, unlike the other metals, is sufficiently soft to be 

 scratched with the thumb-nail. It even leaves a lead gray 

 streak upon paper. Lead is fashioned into foil or wire by rolling 

 and pressing. It is readily soluble in nitric acid but the other 

 mineral acids are without special solvent effect upon the metal 

 at ordinary temperatures. Its specific gravity is 11.3. Its 

 melting-point 327 C. Its atomic weight 207.10. 



Ores of Lead. Native lead occurs in small quantities in many 

 localities both in the United States and in foreign countries. It 

 is always of secondary origin, the product of reduction from other 

 lead minerals through volcanic action. 



Galenite, PbS, 86.6 per cent, of lead. 



Anglesite, PbS0 4 , 68.3 per cent, of lead. A white or gray 

 sulphate. 



Cerussite, PbCOs, 77.5 per cent, of lead. A white or pink 

 carbonate. 



Pyromorphite, 3Pb 3 (P04)2,PbCl2. Often in small hexagonal 

 crystals. 



Cotunnite, PbCh, 74.5 per cent, of lead. 



Massicot, PbO, 92.8 per cent, of lead. A buff powder. 



Minium, PbaO 4 , 90.6 per cent, of lead. A vivid red powder. 



Plattnerite, Pb02, 86.6 per cent, of lead. An iron black oxide. 



Crocoite, PbCrO 4 , 65 per cent, of lead. 



Wulfenite, PbMoO 4 , 57 per cent, of lead. 



Stolzite, PbWO 4 , 44.9 per cent, of lead. 



Galenite is by far the most important ore of lead. It crystallizes 

 in the isometric system in perfect cubes and regular octahedrons. 

 It also occurs massive and granular. Silver sulphide, Ag 2 S, 



110 



