1 kg aluminum chloride hydrate was dissolved in 2 kg water and reacted with a solution of 1.2 kg sodium hydroxide in 2.5 kg water, under constant stirring. The resultant sodium aluminate solution was cooled to about 20°C and, with thorough stirring, it was reacted with 3.5 kg of a magnesium sulfate solution produced by dissolving 1 kg of magnesium sulfate anhydride in 2.5 kg water. The magnesium sulfate solution was introduced in a plurality of thin jets through several shower heads to avoid localized differences of concentration as much as possible. After all the magnesium sulfate was added, stirring was continued for about ? hour.
A colorless, colloidal precipitate was formed and stirred thoroughly for about
15 minutes, whereupon it was filtered by suction. The raw product thus
obtained was washed with water until it contained only about 0.5% watersoluble salts. After drying for 12 hours in a vacuum apparatus at 60°C and
under a pressure of 12 mm Hg, the product had the form of hard pieces. The
pieces were comminuted to powder in a ball mill and the powder was passed
through a sieve (3,600 meshes per cm2). The small residue on the sieve was
again pulverized and passed through the same sieve. The yield was 870 g, or
99% of theoretical, calculated on the assumed formula
[Mg(OH)]4[(HO)4Al(OH)(HO)Al(OH)4] · 2H2O with a molecular weight of 425.
