Calcium Octamolybdate, CaMo₈O₂₅.18H₂O

Calcium Octamolybdate, CaMo₈O₂₅.18H₂O, or Ca₃H₁₄[H₂(Mo₂O₇)₆]₂.22H₂O, separates in prismatic crystals when a solution of the normal molybdate in hydrochloric acid (containing 1 molecule CaMoO₄ to 1.75 molecule HCl) is allowed to evaporate. The crystals dissolve readily in hot water. On heating, water is given up, and the residue fuses. An octamolybdate, of composition CaMo₈O₂₅.17H₂O, separates as an amorphous powder when aqueous solutions containing calcium chloride and sodium tetramolybdate in equivalent proportions are mixed. The precipitate is only slightly soluble in hot water. A dodecamolybdate, CaMo₁₂O₃₇.23H₂O, has also been described.