Synonym. - Ferrum Arseniatum.
Present name. - Triferric Diarseniate. Fe32AsO4.
The method of preparing this is given in the British Pharmacopoeia as follows: -
Sulphate of Iron ....
Arseniate of Soda, dried at 300° . .
Acetate of Soda ....
Boiling Distilled Water.. . . .
Dissolve the Arseniate and Acetate of Soda in 2 pints, and the Sulphate of Iron in 3 pints of the water, mix the two solutions, collect the white precipitate which forms on a calico filter, and wash until the washings cease to be affected by a dilute solution of Chloride of Barium. Squeeze the washed precipitate between folds of strong linen in a screw press, and dry it on porous bricks in a warm air-chamber whose temperature shall not exceed 100°.
Characters and Tests. - A tasteless amorphous powder of a green colour, insoluble in water, but readily dissolved by Hydrochloric Acid, This solution gives a copious light blue precipitate with the yellow Prussiate of Potash, and a still more abundant one of a deeper colour with the red Prussiate of Potash. 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 solution of Nitrate of Silver, The solution in Hydrochloric Acid when diluted gives no precipitate with Chloride of Barium. 20 grains dissolved in an excess of Hydrochloric Acid diluted with water continue to give a blue precipitate with the red Prussiate of Potash, until at least 170 grain measures of the volumetric solution of Bichromate of Potash have been added.
Preparation. - Trituration.