Barium Manganate

Barium Manganate is used as a colouring matter under the name of Cassels' green, manganese green, or Rosensthiel's green. The composition depends on the method of preparation. Insoluble hexagonal plates of 3BaO.2MnO₃ are formed by heating a mixture of barium oxide and nitrate with manganese oxide, or barium peroxide with manganese dioxide, or carbonate, or by the action of hydrogen peroxide on the permanganate.

An impure manganate of formula BaMnO₄, containing no water of crystallisation, is obtained by precipitating barium chloride with potassium manganate. It is also formed by heating pure manganese dioxide with potassium chlorate and barium hydroxide, or by heating the manganite above 1500° C.

By heating a mixture of permanganate and barium hydroxide the compound, Ba₃Mn₂O₈.H₂O, which does not lose its water at red heat, is formed.