Dithallous hydrogen arsenate, Tl₂HAsO₄

Dithallous hydrogen arsenate, Tl₂HAsO₄, is obtained by neutralising a boiling solution of arsenic acid with thallous carbonate and cooling the solution. It forms long, transparent needles, readily soluble in water. When strongly heated it gives off water, and then decomposes, leaving a black residue of thallic oxide (Lamy).