Sodium Tritungstate /Sodium Tetratungstate

Sodium tritungstate, Na2O.3WO3.4H2O, is prepared, according to Lefort, by gradually adding a concentrated solution of the ditungstate to a boiling 50 per cent, solution of acetic acid. On cooling, a white precipitate results which dissolves in water, and the solution on evaporation yields long prismatic crystals. The existence of a tritungstate is denied by Kantschew.

Sodium tetratungstate, Na2O.4WO3, is obtained by the complete dehydration of sodium metatungstate, and is sometimes called "anhydrous sodium metatungstate." As will be seen, however, water is essential to the constitution of metatungstates. The salt may be obtained by heating the paratungstate and treating the residue with water. It is insoluble in water, but on prolonged heating with water at 120° C. it is converted into the metatungstate.