In the United States the richest ores are found chiefly in the Western States, the car boniferous limestone bearing both hard and soft ores, which contain silver chloride and cerussite. The output of smelting works in Colorado, Idaho, Missouri, Montana, Utah, etc., figures largely in the industrial statistics of the country. (See LEAD INDUSTRY, AMERICAN). At the present time the main supply of lead is obtained from the Rocky Mountain regions, where the ores are argentiferous — as to some extent all galena is — and the lead-silver mines in some of the States mentioned have produced much wealth for their owners. Conde lead is imported into the United States from British Columbia and Mexico. Other minerals associ ated with galena are anglesite or sulphate of lead, lanarkite, which is a basic sulphate, pyro morphite, or phosphato-chloride of lead, and bournonite, consisting of the sulphides of lead, copper and antimony. Galena is very heavy and usually can be easily separated from most of the lighter • minerals with which it is associated. The heavier minerals, such as barytes, pyrites and blende, are not, so easily or completely sepa rated. In Great Britain the ore is crushed to pass through about a half-inch sieve and is dressed to contain over 76 per cent of lead. In other countries the concentration is not so high and sometimes no dressing is resorted to. This is specially the case in districts where the blast furnace is used for smelting, since finely divided material is unsuited for the blast-furnace.
Metallurgy.- Galena is the principal' lead ore employed for the purposes which metallurgy (q.v.) now so widely subserves. The next im portant ores, the sulphate and the carbonate, are seldom treated except in combination with oth ers. The three main processes are the air-re duction, the roasting and carbon reduction and the iron or precipitation reduction processes. Galena when taken from the mine is broken up into small pieces or reduced to powder, and the impurities, in so far as these can be removed mechanically, separated by machines. If the dressed galena is nearly as it often is, the smelting operation is simple. The processes of lead-smelting galena being the ore which have grown up in various parts of the world, are strikingly similar in principle, though differing much in detail. Since. 1913 -flotation has been extensively resorted to for the con centration of lead ores. It is estimated that in 1915 its process recovered not less than 50,000 tons of metal formerly lost in fines and slimes. In the United States lead is smelted in rever beratory furnaces made of brick, or in water jacketed. blast-furnaces. The blast-furnace is always preferable to the reverberatory where it can be used, and has now become almost uni yersal for lead-smelting.
Production.- The latest, complete figure; available for the world's production of lead are those of 1913; the outreak of the Euro pean War in 1914 demoralized the mining in dustries of all European countries. The world's total of lead produced in 1913 was 1,270,458 tons. Of this, the United States
produced 411,878 tons-32.4 per cent of the whole, The output of the other lead-mining countries was as follows: Spain, 223,767. tons; Germany, 199,627 tons; Australia, 127,867 tons; Mexico, 68,343 tons; Belgium, 55,997 tons; Great Britain, 33,620 tons.; France, 30,864 tons; Austria-Hungary, 26,565 tons; Italy,•23,920 tons; Greece, 20,282 tons; Canada, 18,849 tons; Tur key in Asia, 15,322 tons..
The output of lead in the United States for 1915 was 550,055 short tons, valued at $51,705, 000. Of the Missouri produced 195,634 tons; Idaho, 160,680 tons; Utah, 106,105 tons; Colorado, 32,352 Nevada, 7,664 tons; Arizona, 6,953 tons; California, 5,606 tons; Montana, 4,853 tons; Oklahoma, 4,346 tons; Wisconsin, 2,632 tons; and Kansas, 1,320 tons. The lead produced by Missouri, Montana, Oklahoma, Wisconsin and Kansas is non-argen tiferous,' or what is known as soft lead.* In 1915 the United States imported 76,757 tons of lead of which 47,123 tons carne from Mexico, 2,710 tons from South America and 1,150 tons from Canada. In the same year the lead exports of the United 'States included 26,547 tons to Canada; 13,445 .tons to Japan; 11.549 tons to Russia; and 10,663 tons to Great Britain. The output of lead in the United States in 1916 is placed at 552,228 short tons; in 1917, 640,000 short tons.
Lead Oxides.- Five oxides of lead are known, namely, the suboxide (Pb,O), the monoxide (PbO), the sesquioxide (Pb30,), the red oxide (PbaO.), and the peroxide or dioxide (PbO,). Of these, however, only three-the monoxide, the red oxide and the dioxide - are of any importance. Lead monoxide (PbO), lith arge, or massicot, is largely used in the arts, and is made by heating molten lead in a shal low reverberatory furnace with free access of air, the litharge as it forms being pushed to one side so as to expose a fresh surface of the metal. The mass thus obtained is ground and separated from intermixed lead. It is then the buff-colored powder known as ground litharge or massicot. When the oxidation takes place above the melting point of the oxide, as in cupellation, the litharge on solidification breaks up into orange-colored scales and is then known as "flake litharge Litharge melts at about 600° C. to a clear liquid, and at higher tem eratures volatilizes. Lead oxide is a powerful ase and dissolves in acids forming salts, At igh temperatures it combines readily with silica, forming fusible silicates, and therefore has a very corrosive action on crucibles or firebricks which contain silica. An electrolytic process of making red lead and litharge from galena Is used at Niagara Falls. When lith arge is heated to dull redness with free access of air, oxygen is taken up and the red oxide red lead is formed. It is manufac tured by roasting ground litharge with free access of air for about 24 hours; the opera tion being carried on till the required tint is obtained on cooling. It is used as a pigment and in the manufacture of flint glass and enamels.