This section is from the book "Cassell's Cyclopaedia Of Mechanics", by Paul N. Hasluck. Also available from Amazon: Cassell's Cyclopaedia Of Mechanics.
Lead (symbol Pb, melting point 612° F., specific gravity 111) is a bluish grey metal which is lustrous when freshly cut. Being very malleable, ductile, and tough, it is used largely in many of the crafts. It is devoid of elasticity, very soft, and can be cold-welded by pressure. Lead is not affected by most acids, but moisture and nitric acid rapidly oxidise it. If it is slowly cooled from its melting point, it crystallises into octahedrons. Sheet-lead is of two kinds, cast and rolled, the latter being known as milled; and it is jointed, when occasion requires, in one of two ways, soldering or burning. Lead is easily fused, and enters into the composition of many useful alloys, some of which are solders. Lead occurs in the form of ore, and generally as sulphide of lead, known commercially as galena. This has a metallic lustre, and often is in crystallised cubes, always containing silver. Less important lead ores are cerusite, a dirty white substance, containing, besides lead, carbon and oxygen; pyromorphite, a green, yellow, or brown ore containing, besides lead, phosphorus, carbon, oxygen, and chlorine; mimetesite, which is similar to pyromorphite, but contains arsenic in the place of phosphorus; and anglesite, a white or grey ore composed of lead, sulphur, and oxygen.
In the reduction of the principal ore - galena - it is first picked, then broken and washed, most of the mechanical impurities being removed. The ore then is partially roasted or calcined for two hours in a reverberatory furnace, some of the ore becoming lead oxide and the rest becoming lead sulphate; some of the sulphur in the ore helps to form sulphurous acid, which escapes as gas. On raising the heat of the furnace, the oxide, sulphate, and unaltered sulphide react mutually, and form sulphurous acid and metallic lead; lime is thrown into the furnace during the latter stages of the process, at the end of which the molten lead is run off and the slag is removed.