Thallous hydrogen sulphate, TlHSO₄

Thallous hydrogen sulphate, TlHSO₄, is obtained when thallous sulphate is dissolved in sulphuric acid and brought to constant weight at 220° to 240°. It may be also crystallised from a solution of thallous sulphate in moderately concentrated sulphuric acid, and exists in a monoclinic and an orthorhombic (?) form; while another modification would appear to exist, since the salt is isotrimorphous with potassium hydrogen sulphate.