586 LEAD. 



SECTION VIII. 



LEAD. 

 Eg. 1294.5 or 103.73; Pb (plumbum). 



Lead was one of the earliest known of the metals. A consi- 

 derable number of its compounds are found in nature, but the 

 sulphuret, or galena, is the only one which is important as an 

 ore of lead. The reduction of the metal is effected by heating 

 with exposure to air (or roasting) the sulphuret, by which much 

 of the sulphur is burned and escapes as sulphurous acid, and 

 a fusible mixture of oxide of lead and sulphate of lead is pro- 

 duced. A fresh portion of the ore is added, which reacts upon 

 the oxide of lead, the sulphur and oxygen forming sulphurous 

 acid, and the lead of both oxide and sulphuret being consequently 

 reduced. Lime also is added, which decomposes the sulphate of 

 lead, and exposes the oxide to be reduced by the fuel or by 

 sulphuret. 



Lead has a bluish grey colour and strong metallic lustre, is 

 very malleable, and so soft, when it has not been cooled rapidly, 

 as to produce a metallic streak upon paper. Its density is 

 11.445, and is not increased by hammering. Its tenacity is less 

 than that of any other ductile metal. The melting point of 

 lead is 612; on solidifying, this metal shrinks considerably, 

 so that bullets cast in a mould are never quite round. Lead, 

 like most other metals, assumes the octohedral form on cry- 

 stallizing. Lead is one of the less oxidable metals, at least, 

 when massive ; its surface soon tarnishes, and is covered with a 

 grey pellicle, which appears to defend the metal from farther 

 change. Rain or soft water cannot be preserved with safety in 

 leaden cisterns, owing to the rapid formation of a white hydrated 

 oxide at that line where the metal is exposed to both air and 

 water ; the oxide formed is soluble in pure water, and highly 

 poisonous. But a minute trace of any sulphate or chloride in 

 the water, which spring and well water usually contain, arrests 

 the corrosion of the lead, by converting the oxide of lead into 

 an insoluble salt, and prevents the contamination of the water, 

 (Dr. Christisori's Treatise on Poisons). Lead is not directly 

 attacked by hydrochloric and sulphuric acids, at the usual tern- 



