Iron di-arsenide, FeAs₂

Iron di-arsenide, FeAs₂, occurs as the mineral lolingite, and may be prepared artificially by heating iron in arsenic vapour at 430° to 618° C. Hilpert and Dieckmann recommend heating finely powdered iron and arsenic in a bomb tube to c. 700° C. On treatment with dilute acid the pure di-arsenide is obtained as a silver-grey powder, of density 7.38. Insoluble in hydrochloric acid, both dilute and concentrated, it is slowly oxidised by nitric acid, yielding arsenic acid. Heated with concentrated sulphuric acid, sulphur dioxide is evolved. When heated in air it burns, yielding arsenious oxide and ferric oxide. It is nonmagnetic.