barium

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barium (symbol Ba) Metallic element of the alkaline-earth group, discovered in 1808 by the English chemist Sir Humphry Davy. It is a soft, silvery-white metal whose chief sources are heavy spar (barium sulphate) and witherite (barium carbonate). Barium compounds are used as rodent poison, pigments for paints and as drying agents. Barium sulphate (BaSO4) is swallowed to allow X-ray examination of the stomach and intestines because barium atoms are opaque to X-rays. Properties: at.no. 56; r.a.m. 137.34; r.d. 3.51; m.p. 725°C (1337°F); b.p. 1640°C (2984°F); most common isotope Ba138 (71.66%).

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