Calcium Arsenites

The orthoarsenite, Ca₃As₂O₆, is obtained as a white amorphous powder by the precipitation of dilute calcium chloride solution with potassium orthoarsenite. The product is dried at 100° C. It may also be formed by the precipitation of lime-water with boiling aqueous arsenious acid. It is soluble in acids, but not readily in water. At red heat it is decomposed with volatilisation of arsenic.

The pyroarsenite, Ca₂As₂O₅, is a white powder obtained by slowly precipitating a solution of arsenious acid with excess of lime-water, and by heating the precipitate to 105° C. A monohydrate has also been described.

Calcium metarsenite, CaAs₂O₄, is an amorphous white powder, anhydrous at 100° C., obtained by the precipitation of calcium chloride by ammonium arsenite in ammoniacal solution.

A salt of composition Ca₃As₄O₉.3H₂O, which may be regarded as consisting of one molecule of pyro- combined with one molecule of metarsenite, has been mentioned.