(Science: chemical) The pentahydrate sulfate salt of copper. It is a powerful emetic and used orally as an antidote to phosphorus poisoning. Topical application of a 1 per cent solution is used in the treatment of phosphorus burns of the skin. It is also used as a catalyst with iron in the treatment of iron-deficiency anaemia. In 1:1,000,000 concentration it is used to prevent growth of algae in ponds, reservoirs, and swimming pools.