Acid Tungstate

The acid tungstate, 4Na2O.10WO3.23H2O, may be prepared by passing carbon dioxide for several days through an aqueous solution of normal sodium tungstate, or by gradually adding formic acid, until the action is distinctly acid, to a solution containing 100 grams of the normal tungstate in 100 c.c. of water.

The action of glacial acetic acid on a solution of sodium tungstate produces a mixture of the salts 4Na2O.10WO3.23H2O and 5Na2O.12WO3.28H2O. The salt, 4Na2O.10WO3.23H2O, forms monoclinic crystals which effloresce rapidly in dry air and have density 4.3. When heated, the salt loses 17 molecular proportions of its water of crystallisation at 100° C., the remainder only being driven off by strong ignition. It melts at 680.8° C. It is soluble in water - 19 parts of the salt dissolve in 100 parts of water at ordinary temperature - forming an acid solution.