Prep. Made by precipitating a mixed solution of arseniate of soda (four parts) and acetate of soda (three parts) by a solution (of nine parts) of sulphate of iron; collecting and washing the precipitate. It should be dried by squeezing it in folds of linen in a screw-press, and afterwards exposing it on porous bricks in a warm-air chamber, whose temperature should not exceed 100°.

Prop. & Comp. Arseniate of iron is a tasteless amorphous powder, of a green colour, insoluble in water, but readily soluble in hydrochloric acid. It consists of arseniate of iron (3 Fe O, AsO5) partially oxidated. Its solution gives a precipitate both with ferro-and ferrideyanide of potassium. A small quantity boiled with an excess of caustic soda and filtered, gives, when exactly neutralized by nitric acid, a brick-red precipitate on the addition of a solution of nitrate of silver (arseniate of silver). The solution in hydrochloric acid when diluted gives no precipitate with chloride of barium (absence of sulphate).

Twenty grains, dissolved in excess of hydrochloric acid diluted with water, continue to give a blue precipitate with the ferrid-cyanide of potassium, until at least 17 measures of the volumetric solution of bichromate of potash have been added, corresponding to 2.8 grains of protoxide of iron. In this quantitative test, the protoxide of iron is converted into the peroxide, by the action of the bichromate of potash, and the solution ceases to strike a blue colour with the ferrideyanide of potassium when this conversion is complete. One equivalent of bichromate of potash is capable of converting 6 equivalents of iron from the state of a protosalt to that of a persalt. One hundred measures of the volumetric solution contain 1/10 of an equivalent in grains of the bichromate, and are capable therefore of converting 1/10 of 6 equivalents of iron from protoxide to peroxide.

Therapeutics. Arseniate of iron possesses the therapeutic properties of arsenic and iron, and is useful in the treatment of certain skin diseases occurring in anaemic states of the system.

Dose. 1/10 to 1/8 gr.