Potassium ferri-sulphite

Potassium ferri-sulphite, KFe(S03)S04, is prepared by the action of potassium hydrogen sulphite upon ferric ammonium alum. It crystallises in slender needles, which are sparingly soluble in cold water. With hot water, ferrous and potassium sulphates pass into solution, leaving an insoluble yellow residue. 

Potassium ferri-disulphite, K3Fe(S03)2S04, 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. 

Sodium ferri-disulphite, Na3Fe(S03)2S04.6H20, may be prepared by digesting a solution of sodium ferro-heptanitroso sulphide with sodium hydrogen sulphite for several days. It crystallises in flat, yellow prisms, and closely resembles the corresponding potassium salt. 

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