Barium carbonate (Ba CO3), also known as witherite, is a chemical compound used in rat poison, bricks, ceramic glazes and cement.1  1 Witherite.t is the chief source of barium salts and is mined in considerable amounts in Northumberland. It is used for the preparation of rat poison, in the manufacture of glass and porcelain, and formerly for refining sugar. It is also used for controlling the chromate to sulfate ratio in chromium electroplating baths.