cements, sorel's - Cements, Sorel's cements, sorel's - There are two different cements which go by the name of Sorel's: namely, the "oxychloride of zinc" and the "magnesia" cement.
Oxychloride of Zinc. - A solution of chloride of zinc is prepared by dissolving zinc in hydrochloric acid, so that some metallic zinc always remains undissolved. The solution is filtered and concentrated until it has the sp. gr. 1.800. Commercial oxide of zinc is mixed with water containing 2 per cent, of nitric acid to a stiff paste, which, after being dried, is heated in crucibles to a white heat, after which it is reduced to an impalpable powder. The object of this baking is to reduce the oxide to as small a bulk as possible, in which condition it has more binding power. The powder must be kept from contact with the air, to prevent access of moisture and carbonic acid gas. On bringing together the oxide and solution of chloride of zinc, the whole solidifies in a few minutes to a very hard mass. If it is desired to retard the hardening, the zinc solution may be diluted to about 1.500-1.600 sp. gr., and the oxide of zinc may be mixed with 2 to 3 per cent, of borax or chloride of ammonium.
Magnesia. - This was originally prepared from magnesite (chiefly native carbonate of magnesium), by making a paste with powdered magnesite, 10 to 20 per cent, of hydrochloric acid, and a sufficient quantity of water, forming the mass into bricks, then burning them at a strong heat, and _ finally grinding them. This yields a very hard, bright-coloured cement, which bears large dilution with sand, but is not entirely waterproof. Since the immense saline deposits at Stassfurt have been worked, this cement is prepared from kieserite (a native hydrated sulphate of magnesium), many thousand tons of which are annually obtained. Kieserite is mixed with calcium hydrate, in the proportion of two molecules of the former to one of the latter, with addition of water; the mass is formed into bricks or cakes, dried, and "burnt," and powdered. The powdered mass when moistened solidifies to a marble-like mass, which does not, however, permanently resist moisture, and is best used only in the interior of buildings.
The following composition forms an excellent material for moulding or for uniting stone, etc. Mix commercial zinc white with ½ its bulk of fine sand, adding a solution of chloride of zinc of 1.26 sp. gr., and rub the whole thoroughly together in a mortar. The mixture must be applied at once, as it hardens very quickly.