Magnesium Perchlorate, Mg(ClO₄)₂

Magnesium Perchlorate, Mg(CIO₄)₂, occurs in deliquescent needles which were said to be very soluble in either water or alcohol. It is prepared by dissolving magnesia in aqueous perchloric acid, and has been described as a hexa-aquo-salt with the formula [Mg(H₂O)₆] (ClO₄)₂.

The hexahydrate has been obtained by drying over the anhydrous perchlorate. It melts between 145° C. and 147° C., and the crystallised salt does not deliquesce though the fused material does. It becomes the trihydrate when kept over phosphorus pentoxide at 20°-25° C., and anhydrous when heated in dry air up to 250° C. The anhydrous salt hisses in water, and compares favourably with phosphorus pentoxide as a drying agent. The trihydrate is less efficient than the anhydrous at temperatures above 0° C. The densities of the three salts, at 25°/4° C. and corrected to a vacuum, are respectively 1.970, 2.044, and 2.60.