Copper oxide is an inorganic substance with the chemical formula Cuo. It is a black oxide of copper, slightly amphoteric and slightly hygroscopic. It is insoluble in water and soluble in acid. It can decompose oxygen under high temperature. Hydrogen or carbon monoxide can be reduced to copper at high temperature. Copper oxide is heated in air and releases oxygen at about 1050 ℃ to reduce to cuprous oxide. If in the gas stream of hydrogen or carbon monoxide, it is easy to be reduced to metal copper even below 250 ℃. Although copper oxide is insoluble in water, it can be dissolved in aqueous alkali metal hydroxide solution. It is used as colorant in glass, enamel and ceramic industry, anti Zou agent in paint and polishing agent for optical glass. It is used in the manufacture of dyes, organic catalyst supports and copper compounds. It is also used in rayon manufacturing industry and as a desulfurizer for grease. It is used as the raw material for manufacturing other copper salts and artificial gemstones.