Titanium Sesquisulphate, Ti₂(SO₄)₃

According to Glatzel the octahydrate Ti₂(SO₄)₃.8H₂O is obtained by dissolving the metal in dilute sulphuric acid, and evaporating the solution. A violet solution, is said to be formed which on being concentrated becomes blue and deposits tufted crystals. According to Stahler and Wirthwein, however, the sesquisulphate is not formed in this way; but when a concentrated solution of the trichloride is repeatedly evaporated at 60° C. with dilute sulphuric acid in a vacuum, a crystalline precipitate of titanium sesquisulphate sulphuric acid is formed, which, after washing with acetic acid and ether, has the composition 3Ti₂(SO₄)₃.H₂SO₄.25H₂O. The same product is obtained as a violet crystalline powder when titanic sulphate dissolved in 50 per cent, sulphuric acid is reduced electrolytically for five or six hours. The anhydrous sesquisulphate, Ti₂(SO₄)₃, is separated as a green, crystalline powder, insoluble in water, alcohol, ether, or concentrated sulphuric acid, by the repeated evaporation of a dilute sulphuric acid solution of titanium sesquisulphate sulphuric acid in absence of air. Titanium sesquisulphate closely resembles the corresponding vanadium sulphate, V₂(SO₄)₃, in properties, and in the compounds it forms with sulphuric acid and other sulphates; it is decomposed by heat into SO₂, SO₃, and TiO₂.