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Barium Sulfate
CAS number [7727-43-7]	ATC code V08BA01
Chemical formula	BaSO4
Molar mass	233.43 g/mol
Specific gravity	4.5
Bioavailability	negligible orally
Melting point	1580°C
Density	4.5 g/cm3
Solubility in water	0.00115 g/L (18°C)
Solubility Product in water	1.08×10-10 (25°C)
RTECS number	CR060000 tlh;lhlllllltl#rh0

Barium sulfate (or barium sulphate) is a white crystalline solid with the chemical formula BaSO₄. It is poorly soluble in water and other traditional solvents but is soluble in concentrated sulfuric acid. The mineral barite is composed largely of barium sulfate and is a common ore of barium.

Barium sulfate is frequently used clinically as a radiocontrast agent for X-ray imaging and other diagnostic procedures. It is most often used in imaging of the GI tract during what is colloquially known as a 'Barium meal'.

It is administered, orally or by enema, as a suspension of fine particles in an aqueous solution (often with sweetening agents added). Although barium is a heavy metal, and its water-soluble compounds are often highly toxic, the extremely low solubility of barium sulfate protects the patient from absorbing harmful amounts of the metal. Barium sulfate is also readily removed from the body, unlike Thorotrast, which it replaced. Due to its relatively high atomic number (Z = 56) of barium, its compounds absorb X-rays more strongly than compounds derived from lighter nuclei.

Barium sulfate mixtures are used as white pigment for paints. The combination of barium sulfate and zinc sulfide (ZnS) is called lithopone. Barium sulfate itself is called blanc fixe. It replaced white lead due to the latter's toxicity.

Barium sulfate is also used as a high temperature oxidizer in certain pyrotechnic formulas, as bariums compounds emit a green colored light when burned. Barium nitrate is more common in green pyrotechnic formulas, as it contains an oxidizer while still producing green colored light.

Barium sulfate is used as a filler in plastics and as a component of oil well drilling fluid to increase the density.

It is used in brake linings, acoustic foams and powder coatings

Barium sulfate is also used during the procedure of the soil pH test. In this test it is used so that it precipitates out any particles (usually clay particles) which would otherwise 'cloud' solution preventing one from seeing the colour of the pH indicator i.e. the result of the test.

It is used in root canal filling.

In colorimetry barium sulphate is used as a near-perfect diffuser when measuring light sources.

Barium sulfate is reduced to barium sulfide by carbon. The accidental discovery of this conversion many centuries ago led to the discovery of the first synthetic phosphor (Hollman and Wiberg, 2001). The sulfide, unlike the sulfate, is water soluble.

• Holleman, A. F. and Wiberg, E. (2001) Inorganic Chemistry, San Diego, CA : Academic Press, ISBN 0-12-352651-5