Prep. By drying the hydrated peroxide of iron, and reducing it to powder.

Prop. & Comp. A dark-brown powder, insoluble in water, but soluble in hydrochloric acid; diluted with half its volume of water, it forms a solution which gives a copious blue precipitate with ferrocyanide of potassium. The solution should give no precipitate with chloride of barium or with the ferridcyanide of potassium. Composition (Fe2 O3). It is often calcined to improve its colour, but this process injures it by diminishing the solubility.

Off. Prep. Emplastrum Ferri. Plaster of Iron. (Peroxide of iron, in fine powder, one ounce; Burgundy pitch, two ounces; litharge plaster, eight ounces).

Therapeutics. It is a non-irritating preparation of iron, and is useful when it is desirable to continue the use of iron for a long time, or to give it in large doses; it has been much administered in tic douloureux and other neuralgic affections. As an external application its value is very questionable.

Dose. 10 gr. to 60 gr., or more, in treacle or honey.

[Ferri sub carbonas, U. S. Made by precipitating a solution of the sulphate of iron with the carbonate of soda. In drying nearly all the carbonate is changed into peroxide. The effects and the dose are the same as in the preceding preparation.]