BARIUM

Barium is somewhat more abundant than strontium, occurring in nature largely as barytes, or heavy spar (BaSO₄), and witherite (BaCO₃). Like strontium, it closely resembles calcium both in the properties of the metal and in the compounds which it forms.

Oxides of barium. Barium oxide (BaO) can be obtained by strongly heating the nitrate:

Ba(NO₃)₂ = BaO + 2NO₂ + O.

Heated to a low red heat in the air, the oxide combines with oxygen, forming the peroxide (BaO₂). If the temperature is raised still higher, or the pressure is reduced, oxygen is given off and the oxide is once more formed. The reaction

BaO₂ <--> BaO + O

is reversible and has been used as a means of separating oxygen from the air. Treated with acids, barium peroxide yields hydrogen peroxide:

BaO₂ + 2HCl = BaCl₂ + H₂O₂.

Barium chloride (BaCl₂·2H₂O). Barium chloride is a white well-crystallized substance which is easily prepared from the native carbonate. It is largely used in the laboratory as a reagent to detect the presence of sulphuric acid or soluble sulphates.

Barium sulphate (barytes) (BaSO₄). Barium sulphate occurs in nature in the form of heavy white crystals. It is precipitated as a crystalline powder when a barium salt is added to a solution of a sulphate or sulphuric acid:

BaCl₂ + H₂SO₄ = BaSO₄ + 2HCl.

This precipitate is used, as are also the finely ground native sulphate and carbonate, as a pigment in paints. On account of its low cost it is sometimes used as an adulterant of white lead, which is also a heavy white substance.

Barium compounds color the flame green, and the nitrate (Ba(NO₃)₂) is used in the manufacture of green lights. Soluble barium compounds are poisonous.