Prep. Made by precipitating a solution of persulphate of iron with soda, collecting the precipitate on a calico filter, and preserving it, without drying, in a well-covered vessel. [In the U. S. P., ammonia is used to precipitate the iron and the washed precipitate is kept under water.]

Prop. & Comp. Hydrated peroxide of iron (2 Fe2 O 3 HO), with a variable amount of uncombined water. It is a pasty mass of reddish-brown colour, dissolving readily in hydrochloric acid, giving a copious blue precipitate with ferrocyanide of potassium. It is free from grittiness, and leaves on calcination about 12 per cent. of peroxide of iron.

Therapeutics. The hydrated peroxide is not given internally to produce the general effects of iron on the system, but has been used as an antidote in cases of arsenical poisoning. It is capable of converting arsenious acid, the form in which the poison is usually taken, into an insoluble arseniate of iron (2 Fe2 O3 + As O8=4 Fe O + As O5).