By repeated evaporation of the oxychloride with small quantities of water, a ‘metazirconium chloride’ is obtained, which dissolves in water to a colloidal solution, and on dialysis yields a colloidal solution of ‘metazirconic acid.’
The bromide, ZrBr₄, very closely resembles the chloride; when treated with water it forms the oxybromide, which separates from solution according to the conditions in various hydrated forms, of which the commonest is the octohydrate, ZrOBr₂,8H₂O. The iodide, ZrI₄, is a very reactive body, which closely resembles the preceding; it forms an oxyiodide, ZrOI₂,8H₂O.
Zirconyl chlorate, ZrO(ClO₃)₂,6H₂O, is obtained from the sulphate by double decomposition with barium chlorate; it forms very soluble colourless needles. Alkali iodates or iodic acid throw down a voluminous oxyiodate, very sparingly soluble, like the corresponding ceric and thorium salts, in water and acids.
The Sulphates.—When zirconium dioxide is dissolved in concentrated sulphuric acid, and the excess of acid removed by heating to 400°, the ‘neutral’ sulphate, Zr(SO₄)₂, remains. The compound dissolves in dilute sulphuric acid to form solutions which contain various ‘complexes’ as shown by conductivity measurements, and the behaviour towards oxalic acid. Whilst solutions of the nitrate or chloride give immediate precipitates with this reagent, solutions of the ‘sulphate’ give no precipitate, or at most a very gradual one; moreover, addition of sulphuric acid or of alkali sulphates to other zirconium salts inhibits the oxalate precipitation. These facts are explained by regarding the ‘neutral’ sulphate, Zr(SO₄)₂,4H₂O, as zirconylsulphuric acid, ZrOSO₄,H₂SO₄,3H₂O, which in solution ionises to 2H. and ZrOSO₄,SO₄´´. This conclusion is confirmed by the fact that whilst in solutions of the chloride in hydrochloric acid, zirconium goes on electrolysis to the cathode, on addition of sulphuric acid to the solution it travels to the anode. The anhydrous compound and the hydrate are extremely soluble in water, but much less readily soluble in dilute sulphuric acid. Probably in solution more complex salts are formed by further hydrolysis, for by addition of concentrated alkali sulphate solution in the cold, double salts of the formula Zr₂O₃(RSO₄)₂,8H₂O are obtained. When the solution is kept for some time at 39°-40°, a basic sulphate, 4ZrO₂,3SO₃,14H₂O, separates slowly. When concentrated solutions are boiled, a salt, 2ZrO₂,3SO₃,5H₂O, separates as a crystalline precipitate; in contact with water it slowly hydrates itself to the compound 2ZrO₂,3SO₃,14H₂O; when heated to 300°, it becomes anhydrous without further change. Various other basic, acid and complex salts have also been described.
The nitrate, Zr(NO₃)₄,5H₂O, separates from concentrated solutions of the oxide in nitric acid by evaporation over sulphuric acid and sodium hydroxide; it is believed to be a zirconylnitric acid, ZrO(NO₃)₂,2HNO₃,4H₂O by analogy with the sulphate. When its aqueous solutions are warmed, basic salts separate. Kolbe[468] has described an additive compound with antipyrine, Zr(NO₃)₄,6C₁₁H₁₂ON₂, which is soluble in water, and melts at 217°-218°.
[468] Zeitsch. anorg. Chem. 1913, 83, 143.
When phosphoric acid or a soluble phosphate is added to a solution of a zirconium salt, zirconium phosphates of doubtful composition are thrown down; by fusion methods, various double phosphates have been prepared. A hypophosphate, Zr(PO₃)₂,H₂O, has recently been obtained by Hauser and Herzfeld[469] by precipitation. The same authors have prepared a hypophosphite, which is sensitive to light. When hypophosphorous acid, H₃PO₂, is added to a solution of zirconium nitrate, a precipitate is obtained, which dissolves in excess of the acid; by addition of alcohol to the clear solution, the hypophosphite, Zr(H₂PO₂)₄,H₂O, is thrown down in colourless, highly refracting prisms, which on exposure to sunlight for a short time become deep violet, without further perceptible change.
[469] Zeitsch. anorg. Chem. 1913, 84, 92.
Zirconium carbonate has recently been obtained by Chauvenet.[470] Addition of sodium carbonate precipitates a basic orthocarbonate, ZrCO₄,ZrO₂,8H₂O, soluble in excess; when dried in vacuo, the precipitate loses water, forming the dihydrate, ZrCO₄,ZrO₂,2H₂O. When the latter compound is treated with carbon dioxide at a pressure of 30-40 atmospheres, the neutral orthocarbonate, ZrCO₄,2H₂O, is formed. When the compounds are heated, other basic salts are obtained.
[470] Bull. Soc. Chim. 1913 [iv.], 13, 454.