1. Symbol Ba A soft, silvery-white or yellowish-white alkaline-earth metal, used to deoxidize copper and to absorb trace gases in vacuum tubes, and used in various alloys. Atomic number 56; atomic weight 137.33; melting point 727°C; boiling point 1,897°C; specific gravity 3.62; valence 2. See Periodic Table.

2. A radiopaque solution containing barium sulfate that is used to visualize the gastrointestinal tract on x-rays.