Magnesium Vanadates

MgO.2V₂O₅.8H₂O is obtained as a sparingly soluble yellow salt, decomposed by hot water with separation of vanadic acid, by interaction between ammonium divanadate and magnesium chloride. Red and brown varieties of 3MgO.5V₂O₅.28H₂O were prepared by treating the product of the action of amorphous vanadic acid on magnesia alba and water with acetic acid. This dimorphous salt crystallises in the triclinic system. Manasse obtained it by diluting the concentrated solution of the normal vanadate, MgO.V₂O₅.6H₂O, with acetic acid. Small, radiating, colourless prismatic crystals of the normal salt were obtained by boiling vanadic acid with magnesia alba and water, evaporating and crystallising. A yellowish-red crystalline crust of 4MgO.6V₂O₅.19H₂O settles out of a hot solution containing potassium divanadate and excess of magnesium sulphate. It loses its water at 200° C.