Chromium Molybdates

Simple molybdates of chromium, or Chromium Molybdates, have not been prepared, but a series of complex salts, analogous to those of aluminium, of the type 3R^•₂O.Cr₂O₃.12MoO₃.aq., may be prepared by the action of chromic hydroxide on solutions of acid molybdates, or by boiling together solutions of chromic salts and paramolybdates and allowing to crystallise. The ammonium salt, 3(NH₄)₂O.Cr₂O₃.12MoO₃.20H₂O (or 26H₂O), and the potassium salt, 3K₂O.Cr₂O₃.12MoO₃.20H₂O, form rose-coloured crystals which are soluble in water, and whose solutions give precipitates with barium, bismuth, caesium, lead, mercurous, rubidium, and silver salts. All these insoluble compounds contain the complex Cr₂O₃.12MoO₃, which appears to possess considerable stability. The free chromimolybdic acid 3H₂O.Cr₂O₃.12MoO₃.aq. is obtained by decomposing the mercurous salt with hydrochloric acid. Two barium salts, of composition 4BaO.Cr₂O₃.12MoO₃. 15H₂O and 5BaO.Cr₂O₃.12MoO₃.16H₂O, have been described.