Barium carbonate
Barium carbonate is a carbonate of barium, also known as poisonous earth, poisonous earth, and light. It is a little toxic and is used in the production of glass and ceramics products, rodenticide. It does not dissolve in water, but because it is a carbonate, it reacts when it comes in contact with stomach acid, so barium dissolves as carbon dioxide escapes, so it should never be used as a contrast agent.