Potassium ferri-disulphite, K₃Fe(SO₃)₂SO₄

Potassium ferri-disulphite, K₃Fe(SO₃)₂SO₄, results when a solution of potassium ferro-heptanitroso sulphide is digested at 4° C. with sodium hydrogen sulphite for about a month. It yields lustrous, dark yellow leaflets which are practically insoluble in cold water, but in boiling water are decomposed, yielding ferric hydroxide and a soluble ferric salt.