Potassium Octamolybdate, K₂Mo₈O₂₅.13H₂O

Potassium Octamolybdate, Potassium Hydrogen Tetramolybdate, K₂Mo₈O₂₅.13H₂O or K₃H₇[H₂(Mo₂O₇)₆]15H₂O, has been prepared by allowing to crystallise a solution of trimolybdate to which molybdic anhydride has been added until a precipitate begins to form; by double decomposition of hot solutions of ammonium tetramolybdate and potassium sulphate; or by saturating a solution of the tetramolybdate with sulphur dioxide. The salt is decomposed by water.