Within the last few years a remarkable increase in the output of the copper mines of the world has been recorded. This is due mainly to the demand for copper on account of the great strides in electrical achievements during recent years. Yet there is no doubt that the world's supply is wholly adequate to meet demands on it for a long period to come. The high conductivity of copper renders it especially useful for conveying electric currents and its most important use at present is in electricity. However, it is also a common convenience in many arts. Its alloys are numerous, bronze and brass being the most common. Bronze is an alloy of copper and tin and brass of copper and zinc. The manufacturer of bronze bells finds opportunity for an interesting study of the alloy used in his product. The varying tones of bells are due to the different percentages of copper and tin used in the bell metal.
In locality and mode of occurrence lead is somewhat closely allied with copper, and the ores of lead and zinc are almost invariably associated. Hence a description of lead naturally follows that of copper and may also be understood as typical, so far as occurrence and mining methods are concerned, for that of zinc.
Lead occurs in nature chiefly in the forms of the sulphide, galenite or galena, the sulphate, anglesite and the carbonate, cerussite. Galena is lead-gray, quite soft, and frequently occurs in a coarsely crystalline condition, the crystals often being cubical. The luster is metallic, hence a superficial examination of a specimen might result in mistaking the mineral for the copper ore, chalcopyrite, already described. The streak will serve to identify any specimen, however, it being a lead-gray of much lighter shade than that of chalcocite. Anglesite and cerussite are far less abundant than galena. The former varies from white through gray to yellow and has a resinous luster. Cerussite is white or gray, resembling anglesite, and has a brilliant, vitreous luster. Both minerals, like galena, are soft and easily scratched with a knife.
The ores of lead are widely distributed throughout the United States and it is difficult to assign boundaries to special districts. Galena occurs in small quantities—too small for profitable working—throughout the Appalachian region, and is found in paying quantities in what is known as the Missouri lead district. In the Colorado and other western mines the ore is found in silver-bearing veins. Were it not for the presence of silver in those veins the production of lead from them would probably practically cease, as the anglesite, the principal lead ore of the veins, does not occur in amount to pay for working the mines for that product alone.
White lead, used in paints, is the most important use of the metal. Painters prefer the product to zinc-white chiefly because it is much more opaque and possesses a much greater covering power. Much lead is made into pipes for conveying water. Pure lead is not used for the making of shot, but instead an alloy of lead and arsenic. Unlike pure lead, the alloy assumes a spherical form when dropped through the air. "Shot towers" are constructed to make use of this property in the manufacture of shot. The demands for lead have not been increased by recent extraordinary development of any of the arts employing the metal, hence the world's output of lead during the past decade has had a normal increase. For the year 1897 the total production of lead was 725,200 metric tons.
[2] The common short ton is 2,000 pounds; the long ton contains 2,240 pounds; the metric ton equals 2,204 pounds. It will be noted that statistics of the production of different metals frequently employ different tons as units.
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| CHICAGO: A. W. MUMFORD, PUBLISHER. | ORES. Full size. | COPYRIGHT 1900, BY NATURE STUDY PUB. CO., CHICAGO. |
| Chalcopyrite | Anglesite | |
| Cerussite coating Galenite | Native Copper | |
| Galenite | Chalcocite | |
