| When ammonia is added in large excess to a solution of 12-tungstosilicic acid, and the mixture boiled and continually shaken, an ammonium salt is formed, which crystallises in orthorhombic prisms and corresponds in composition to the formula (NH4)8[SiO(W2O7)5].8H2O. The crystals are readily soluble in water, and on evaporation the solution yields an amorphous glass which is supposed to be the free acid. The same amorphous substance is obtained on shaking out with acid and ether according to Drechsel's method. On neutralisation by means of bases, well-defined products are not obtained and the character of the amorphous glass appears doubtful. By the action of potassium carbonate on the tetrabasic potassium 12-tungstosilicate, a well-crystallised salt, of composition K7[Si(OH)(W2O7)5].11H2O, is obtained. A corresponding guanidinium salt has also been prepared. |