Dithallous hydrogen phosphate, Tl₂HPO₄

Dithallous hydrogen phosphate, Tl₂HPO₄.H₂O, may be prepared by neutralising a boiling solution of phosphoric acid with thallous carbonate, evaporating the liquid to a syrup, and allowing it to crystallise. The crystals are orthorhombic (a:b:c = 0.934:1:0.657) and isomorphous with sodium dihydrogen phosphate, NaH₂PO₄.H₂O. The anhydrous salt has a density of 1.779.