Normal Antimony Sulphate, Sb₂(SO₄)₃

Normal Antimony Sulphate, Sb₂(SO₄)₃, may be obtained by crystallisation from a hot solution of antimony trioxide in concentrated sulphuric acid, or by the action of concentrated sulphuric acid upon antimony trisulphide or antimony sulphide ore. It crystallises in thin, four-sided prisms, density 3.6246. It is stable in dry air, but deliquesces in moist air. It is decomposed by water, forming a variety of basic compounds. It absorbs dry hydrogen chloride, and may perhaps form a complex chlorosulphate. It forms double salts, of the general formula SbM'(SO₄)₂, with the sulphates of the alkali metals, the alkaline earth metals and silver.

Many basic sulphates of antimony have been described, among them being the compounds 7Sb₂O₃.SO₃; 7Sb₂O₃.2SO₃; 2Sb₂O₃.SO₃; (SbO)₂SO₄; 3Sb₂O₃.5SO₃; Sb₂O₃.2SO₃. They are obtained by the decomposition of normal antimony sulphate by water. Basic sulphates have also been obtained by fusing either antimony or antimony trisulphide with potassium hydrogen sulphate.

By the action of fuming sulphuric acid on antimony trioxide, an acid sulphate, Sb₂O₃.4SO₃, has been obtained in the form of small, brilliant, granular crystals, readily decomposed by water.

By adding a hydrochloric acid solution of antimony trioxide to one containing a mixture of sodium thiosulphate and the chloride of an alkali or alkaline earth metal, several metallic antimony thiosulphates, or stibiothiosulphates, have been obtained. The mixture is maintained at a temperature of about 3° C. These salts, with the exception of those of sodium, calcium and strontium, may be crystallised out by the addition of alcohol.