Barium Octamolybdate, BaMo₈O₂₅.18H₂O

Barium Octamolybdate, BaMo₈O₂₅.18H₂O, or Barium Hydrogen Tetramolybdate, Ba₃H₁₄[H₂(Mo₂O₇)₆]₂.44H₂O, may be prepared by double decomposition of barium chloride and concentrated sodium octamolybdate solution; by the action of barium carbonate on a hot solution of molybdic acid dihydrate and evaporation of the resulting liquid; or by treating an aqueous suspension of barium molybdate with hydrochloric acid and allowing the solution to crystallise at room temperature. The salt crystallises in lustrous prisms which are only slightly soluble in cold water, and with warm water yield the tetramolybdate. On heating, the octamolybdate decomposes with loss of water. The compound BaMo₈O₂₅.15H₂O has been obtained as a white amorphous powder, soluble in hot and cold water, by treating a solution of ammonium tetramolybdate with barium chloride.