12-Tungsto-arsenates

Only the ammonium salt, (NH₄)₃H₄[As(W₂O₇)₆].4H₂O, has been prepared. It separates as a white crystalline precipitate when a solution containing normal sodium tungstate (8 molecules) and arsenic acid (1 molecule) is acidified with hydrochloric acid, treated with solid ammonium chloride, and boiled. The free acid is unstable and undergoes hydrolysis in solution.