Certain metals and alloys, such as brass, copper, lead, tin, zinc, tinned iron (tin-plate), aluminum, and thin sheet iron, possess strength, durability, lightness, and a clean, smooth surface. Most of these metals, particularly copper and tin, possess the property of malleability in a marked degree and can, as a result, be hammered into various shapes without being fractured. Sheet metals are made by passing metal bars through heavy rollers until the desired thickness is obtained.
Copper, the most useful of metals next to iron, is found in all parts of the world, but principally in the states of Montana, Arizona, and Michigan. It occurs in both the free and the combined forms. The combined compounds are the oxide (Cu20) and the sulphide (Cu2S). Copper is not affected by water or by oxygen at any temperature, which accounts for its being found frequently in the free state.