Silver Tungstates

The normal salt, Ag₂WO₄, is produced as a fine yellow precipitate when a solution of sodium tungstate is treated with silver nitrate; it is slightly soluble in water and, on heating, turns dark purple and melts. A tungstate containing excess of silver and called "argentous" tungstate has been shown to be a mixture of the normal salt and metallic silver. An ammoniotungstate, Ag₂WO₄.4NH₃, is formed when ammonia is added to a solution of a silver salt, or when the dry silver salt is saturated with ammonia gas; in the former case, tabular crystals are obtained on evaporation; in the latter, a white bulky powder remains. It is soluble in water, but the solution decomposes. On heating, the substance loses all its ammonia at 60° C.

Silver Paratungstate, 5Ag₂O.12WO₃.28H₂O, is obtained as a whitish-yellow crystalline precipitate on adding a solution of a silver salt to a solution of sodium paratungstate. After drying at 60° C. it contains 8H₂O. It melts at a red heat, and on cooling solidifies to a white lustrous crystalline mass.