Barium sulfate is used in radiology to provide contrast in X-ray photography. Internal tissues such as the digestive system and kidneys allow the passage of X-rays to varying extents. But when filled with a substance that blocks the X-rays, they can be made opaque and show up as white. The barium meal, a harmless paste that passes through and out of the intestines unchanged, can be swallowed (1) or injected into the rectum (2). When swallowed, it outlines in turn the esophagus, the stomach, and the small intestine (A). Ulcers, tumors, and alterations of function can be seen. Similarly, the colon or large bowel can be photographed (B).
Barium (Ba) is a soft, silvery-white metallic element that readily tarnishes in air. It is one of the alkaline earth metals. It was discovered by Humphry Davy in 1808 and occurs chiefly as barite (barium sulfate, BaSO4) and as witherite (barium carbonate, BaCO3).
The compounds of barium resemble those of calcium but are poisonous. They are used in the manufacture of paints, glass, rodent poison, and fireworks, and as drying agents. Barium sulfate is swallowed to allow X-ray examination of the stomach and intestines because barium atoms are opaque to X-rays; this is called a "barium meal." The most common isotope is barium-138 (71.66 percent).
|relative atomic mass||137.34|
|melting point||725°C (1,337°F)|
|boiling point||1,640°C (2,984°F)|