11-Tungsto-arsenates

These are completely analogous to the 11-tungstophosphates. The barium salt, 7BaO.As₂O₅.22WO₃.54H₂O or Ba₇[As(OH)(W₂O₇)₅]-W₂O₇-[(W₂O₇)₅(OH)As].53H₂O, is obtained by adding a 5 per cent, solution of ammonium carbonate to a suspension of the ammonium 12-tungsto-arsenate in boiling water until a clear solution results, when, on adding barium chloride, the salt crystallises in double pyramids isomorphous with the corresponding phosphate. Other salts of the series may be obtained from the barium salt by double decomposition.