Copper, a reddish metallic element. It was one of the first metals to be made into tools. After iron, it is the most useful of all metals. Copper can be drawn into wire that has great strength. It is one of the best conductors of electricity. It does not rust, but forms a greenish coating called patina when exposed to moist air. Copper mixes with zinc to form brass and with tin to make bronze, and forms other useful alloys with such metals as gold, silver, nickel, aluminum, and iron.

Copper is used in the manufacture of electrical conductors, especially in the form of wire. It is used in building construction as a roofing material and for flashings, gutters, and downspouts. Large quantities are used in making water pipes, coils, and tanks. Copper is also used as a catalyst in many chemical processes. It is made into coins, utensils, jewelry, and craft articles. Copper also has important uses in a wide range of industrial products.

The bodies of many animals, including humans, require tiny amounts of copper for proper nutrition. Nearly all ordinary foods contain some copper. The tissues of the human liver are about 0.00003 per cent copper. Physiologists do not fully understand the part copper plays in body functions.

In some animals, including arthropods and mollusks, the oxygen in the blood is not carried by hemoglobin (an iron compound), but by a copper compound called hemocyanin. The blood of these animals is bluish-green.