Barium is the chemical element with atomic number 56 and chemical symbol Ba. Barium is a soft, silvery-white alkaline earth metal. Barium oxide (BaO) was isolated in 1774 by Carl Wilhelm Scheele, but it wasn't until 1808 when Sir Humphrey Davy was able to isolate the pure element barium. One common application of barium sulfate is as a X-ray contrast agent for viewing the digestive tract. Barium is also used in making green fireworks.

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