The normal salt, Li2WO4, is formed in solution when a suspension of tungstic anhydride in water is boiled with lithium carbonate, or when tungstic anhydride is added to fused lithium carbonate and the resulting mass extracted with water; on evaporation, short, thick, oblique rhombic prisms separate, which readily dissolve in water yielding an alkaline solution. Lithium ditung- state is described by Anthon, but its existence is doubtful.
Lithium paratungstate, 5Li2O.12WO3.33H2O or 3Li2O.7WO3.19H2O, is prepared by adding tungstic acid to a solution of lithium carbonate until the mixture is neutral to litmus, and allowing the product to evaporate slowly over sulphuric acid. It crystallises in orthorhombic tables or prisms, which are stable in air and are more soluble in water than the corresponding sodium and potassium salts. When heated to a high temperature in a current of hydrogen it is reduced to tungsten dioxide.
Lithium tetratungstate, Li2O.4WO3, remains as needle-shaped crystals after well washing with water the mass obtained by fusing together lithium carbonate (5 molecules) and tungstic anhydride (12 molecules). |