Magnesium Arsenites

Magnesium orthoarsenile, Mg₃(AsO₃)₂, is obtained as a white precipitate, easily soluble in water and dilute acids, by adding to a solution of magnesium chloride in 50 per cent, alcohol a solution of potassium orthoarsenite made just neutral with acetic acid. The pyroarsenile, Mg₂As₂O₅.4H₂O, is produced by double decomposition between barium pyroarsenite and magnesium sulphate. It is a white, granular, hygroscopic, amorphous powder, soluble in dilute acids and water, which readily darkens on heating. Bloxam obtained a pyroarsenite by precipitating magnesium sulphate with ammonium arsenite and heating the precipitate.