Strontium Orthoarsenates

By fusing sodium arsenate with strontium oxide and alkali chlorides, tristrontium arsenate in long colourless orthorhombic prisms is obtained, provided the proportion of arsenate is not below 12 per cent, of the mixture when chlorinated products are formed. It is soluble in dilute acids but not affected by boiling water. It may also be prepared by adding strontium hydroxide solution to arsenic acid and washing the precipitate to neutrality.

Compounds with strontium halides corresponding to apatite and wagnerite have been prepared.

Distrontium orthoarsenate, SrHAsO₄, is obtained as a crystalline precipitate from hot solutions of disodium arsenate and strontium chloride. When dried at 100° C. it has the formula SraH₂(AsO₄)₂.3H₂O. It is soluble in acetic acid and crystallises out in leaflets as SrHAsO₄.H₂O, strontium haidingerite, of density 3.606 at 15° C. The anhydrous salt, strontium arsenomonetite, forms triclinic prisms of density 4.035.

Several double arsenates with the alkalies are formed, SrNaAsO₄, SrKAsO₄, SrNaAsO₄.18H₂O, SrNaAsO₄.H₂O, and 9H₂O.