

CHAPTER XLII 

 LEAD AND TIN 



LEAD and tin are the best-known metallic members of the fam- 

 ily to which the non-metals silicon and carbon also belong. In 

 their compounds they are bivalent or quadrivalent. 



LEAD Pb 



Metallurgy of Lead. The chief ore of lead is galenite PbS. 

 The ore, if rich, is roasted in a reverberatory furnace (Fig. 112, p. 

 489) until a part has been converted into the oxide PbO and sul- 

 phate PbS04. The air is then shut off, and the temperature 

 raised, so that these products may oxidize the remaining galenite: 



PbS + 2PbO - 3Pb + S0 2 f 

 PbS + PbS0 4 -> 2Pb + 2S0 2 T 



The melted lead flows out. 



Ores poorer in lead are sometimes reduced by heating with 

 scrap iron, or with a mixture of iron ore and coke. 



The lead usually contains silver and some gold, which are re- 

 covered by Parke's process (see silver, p. 519). 



Properties of Lead. Lead is a soft malleable metal, with a 

 bluish-white or grey luster when freshly cut. It is quickly, but 

 only superficially, oxidized by the air. It acts very slowly upon 

 hydrochloric acid, but not upon sulphuric acid (see p. 268) . With 

 nitric acid it gives lead nitrate Pb(N0 3 )2 and oxides of nitrogen. 

 Soft water, in presence of air, dissolves it in appreciable amounts 

 as hydroxide Pb(OH) 2 , and carbonic acid assists the process. 

 Hard water, however, produces a skin of carbonate and sulphate 

 (insoluble) which protects the surface. Hence, lead pipes may 



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