Next in importance to white lead is the use of lead in the form of lead oxides, litharge (Pb0) and red lead Both litharge and red lead are used in very large amounts in the manufacture of lead storage battery plates. The plates consist of antimonial lead grids filled with paste which is made by moistening litharge and red lead with sulphuric acid. Red lead is also an important paint pigment and red lead paint is the standard protective ing for iron and steel. Red lead and litharge are used in pottery glazes and litharge is extensively used in the refining of petroleum, in compounding rubber, in the manufacture of insecticides, in the making of certain colours, particularly chrome yellow and chrome green and for innumerable other purposes. Litharge and red lead are made by oxidizing metallic lead in a furnace at high tem perature.
Large amounts of metallic lead in the form of sheet, pipe and plumbers' supplies are used in the construction of buildings, chemical apparatus and water mains and for many other purposes. Lead alloyed with tin in the form of solder is used in large tonnage and many industries could not be carried on in their present form without solder of this kind. Lead alloyed with antimony, tin and copper is used extensively in anti-friction metals for lining the bearings of moving machinery. There are many other uses for lead, such as in cable coverings for telephone wires, ammunition, caulking metal, foil, type metals, linings for X-ray apparatus and others too numerous to mention.
Lead was one of the first metals known to mankind. It has been a great aid in the development of civilization and to-day the value of lead is so great that this metal has become practically indispensable in our modern industrial fabric.
in 1937, has been the largest producer. Australia and Mexico have been next in importance, each with a production of about 200,000 tons per annum; Canada, with an annual production of about 17 5,00o tons, was the fourth largest in 1937. The Mexican output has increased rapidly during the last few years, and prior to 1920 the Mexican production was much less than that from Australia and Spain. Lead is obtained from some of the other countries of the world but in much smaller amounts than from the four leading producers, which together furnish about two thirds of the entire production of the world.
The largest lead producing district of the world is in the United States in the south-eastern part of the State of Missouri. The lead in this district is found in the form of galena disseminated through horizontal bedded limestone. The deposits vary from about 30o ft. to Boo ft. in thickness and are many hundreds of acres in extent. The second largest producing locality is the Broken Hill district in Australia, and the third in size is the large district in Central Spain in the vicinity of the towns of Penarroya and Linares. In both the Australian and Spanish districts, the lead occurs in the form of galena in true vein deposits.
Because of the nature of the ore deposits, nearly all lead mining is done with shafts, tunnels and adits which are required to reach the ore bodies at considerable depth. In some mines, the ore as recovered is sufficiently rich to be smelted directly into metallic lead, but the ore from most of the mines contains so much waste mineral that a preliminary milling treatment is required to me chanically remove the waste rock and concentrate the galena in fairly pure form. (R. L. HT. ; X.)