paratungstate

— PARATUNGSTATES. A number of acid tungstates have been isolated, the composition of which is expressed by one of the formulæ 3RO.7WO₃ or 5RO.12WO₃. The former formula was given by Lotz (A. 91, 49) and Scheibler (J. pr. 83, 273) ; the latter formula by Laurent (A. Ch. [3] 21, 54) and Marignac (A. Ch. [3] 69, 5). The two formulæ represent salts of almost identical composition, and no way has been found of deciding which formula is the better (cf. Knorre, J. pr. [2] 27, 83). The acid tungstates of this series are more easily formed and crystallise better than the other acid salts ; they are generally called paratungstates, following the suggestion made by Marignac. The alkali paratungstates are obtained by saturating hot alkali solutions with WO₃ and crystallising ; most of the other paratungstates are prepared by ppn. [precipitation] from solutions of the alkali salts. […] If the simpler (3:7) formula is adopted, the paratungstates are represented as 3Rᴵ₂O.7WO₃, 3RᴵᴵO.7WO₃, and Rᴵᴵᴵ₂O₃.7WO₃, i.e. as salts of the hypothetical acid H₁₀W₁₂O₄₁ […] ; if the less simple formula (5:12) is adopted, the paratungstates of monovalent and divalent metals are regarded as […]