Copper seems to have been one of the few metals known to barbarous peoples. It is found pure, and in combination. Specimens obtained from the Lake Superior region, in mines worked by the mound builders,[10] have led some to believe that they possessed the art of hardening copper. Malachite is a carbonate of copper, of a beautiful mottled green color, and is made into elegant ornaments. Some magnificent specimens were in the Russian exhibit at the Philadelphia Exposition. It is found in great perfection in the Ural mountains. Tin is obtained from its binoxide (SnO₂). It was known to the ancients. Some historians claim that the Phœnicians procured it long before the time of Christ, from the mines of Cornwall, England. Until recently our country has seemed to be destitute of this valuable metal. Reports now indicate that Dakota is destined to supply this deficiency. It is a handsome metal, but little affected by oxygen, and capable of being rolled into thin sheets. Zinc is found in two different ores: red oxide (ZnO) and zinc blende (ZnS), from which it can be separated by smelting, in much the same manner as we obtain iron. Lead constitutes the fifth of the common metals which are preëminently useful. It is found in the sulphide of lead (PbS), the sulphide being expelled by roasting the ore. It forms numerous compounds, some of which are of great value. For example, lead carbonate (PbCO₃), the white lead which furnishes the most valuable ingredient of all paints. NOBLE METALS. These are so called because they retain their brilliancy and are not easily affected by other substances. Three of them are specially important: gold, silver and platinum. Gold is mentioned in the second chapter of Genesis: “and the gold of that land is good.” Although constituting an inconsiderable part of the earth, it is much more widely distributed than many suppose, but often exists in such small quantities that its production is not profitable.