Lead — (Anglo-Saxon lead), Pb (L. plumbum); atomic weight 207.2; atomic number 82; melting point 327.502°C; boiling point 1740°C; specific gravity 11.35 (20°C); valence 2 or 4. Long known, mentioned in Exodus, the alchemists believed lead to be the oldest metal and associated it with the planet Saturn. Native lead occurs in nature, but it is rare. Lead is obtained chiefly from galena (PbS) by a roasting process. Anglesite (PbSO4), cerussite (PbCO3), and minim (Pb3O4) are other common lead minerals.
Lead is a bluish-white metal of bright luster, is very soft, highly malleable, ductile, and a poor conductor of electricity. It is very resistant to corrosion; lead pipes bearing the insignia of Roman emperors, used as drains from the baths, are still in service. It is used in containers for corrosive liquids (such as in sulfuric acid chambers) and may be toughened by the addition of a small percentage of antimony or other metals.
Natural lead is a mixture of four stable isotopes: Pb204 (1.48%), Pb206 (23.6%), Pb207 (22.6%), and Pb208 (52.3%). Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements: Pb206 for the uranium series; Pb207 for the actinium series; and Pb208 for the thorium series. Seventeen other isotopes of lead, all of which are radioactive, are recognized. Its alloys include solder, type metal, and various antifriction metals.
Great quantities of lead, both as the metal and as the dioxide, are used in storage batteries. Much metal also goes into cable covering, plumbing, ammunition, and in the manufacture of lead tetraethyl, used as an antiknock compound in gasoline. The metal is very effective as a sound absorber, is used as a radiation shield around x-ray equipment and nuclear reactors, and is used to absorb vibration.
White lead, the basic carbonate, sublimed white lead (PbSO4), chrome yellow (PbCrO4), red lead (Pb3O4), and other lead compounds were used extensively in paints; in recent years the use of lead in paints has been drastically curtailed to eliminate or reduce health hazards. Lead oxide is used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. The nitrate and the acetate are soluble salts. Lead salts such as lead arsenate have been used as insecticides, but their use in recent years has been practically eliminated in favor of less harmful organic compounds.
Care must be used in handling lead as it is a cumulative poison. Environmental concern with lead poisoning has resulted in a national program to reduce the concentration of lead in gasoline.