Sodium ferric sulphide, Na₂Fe₂S₄

Sodium ferric sulphide, Na₂S.Fe₂S₃, or Na₂Fe₂S₄, may be obtained in a similar manner to the potassium salt, or by heating four parts of sodium thio-sulphate with one of iron. As obtained in this way, sodium ferric sulphide forms dark green acicular crystals, which gradually disintegrate upon exposure to air, becoming voluminous, and finally a brownish black powder.

When heated, sodium ferric sulphide is converted into oxide. With concentrated hydrochloric acid it yields hydrogen sulphide, free sulphur being deposited. It is insoluble in water; but, when boiled with an aqueous solution of potassium cyanide, it yields potassium ferrocyanide.

Sodium ferric sulphide occurs in the "black ash" liquors formed in the Leblanc Soda Process, and a convenient wet method of producing it in the laboratory consists in adding a solution of a ferric salt to excess of sodium sulphide solution. It also results when excess of sodium poly sulphide acts on a solution of a ferrous salt.

The constitution assigned by Schneider is: -