Thallous acid sulphate, Tl₃H(SO₄)₂

The acid sulphate, Tl₃H(SO₄)₂, crystallises when a solution of thallous sulphate with ten equivalents of sulphuric acid is concentrated. The crystals are trigonal (a:c = 1:3.717). Another modification probably exists, since the salt is isodimorphous with the corresponding potassium salt.