Synonym. Ferri Oxidum Nigrum. Edin.

Prep. By dissolving two parts of sulphate of iron in water acidulated with sulphuric acid, and boiling this mixture with a little nitric acid, until on the sudden disengagement of ruddy vapours the liquid passes from a dark to a red colour; a solution of one part of sulphate of iron is then added, and subsequently a solution of soda: the whole boiled for a few minutes, the precipitate collected on a calico filter, washed and dried without heat in a confined portion of air over a capsule containing sulphuric acid.

In this process two parts of the sulphate of the protoxide are converted into a persalt by boiling with nitric acid, and to these one part of the solution of protoxide is added; so that on the addition of soda a mixture of peroxide and protoxide of iron is precipitated.

Prop. & Comp. Peroxide of iron (Fe2 O3), with about 9 per cent. of the protoxide (Fe O), and 22 of water. It is a brownish-black powder, without taste, strongly magnetic, dissolves without effervescence in hydrochloric acid diluted with half its bulk of water, and this solution gives blue precipitates with the ferrocy-anide, and the ferridcyanide of potassium. Twenty grains, moistened with nitric acid, and calcined at a low red heat, leave 15.8 grains of the peroxide of iron; the same quantity dissolved in hydrochloric acid continues to give a blue precipitate with the ferridcyanide of potassium, until 8.3 measures of the volumetric solution of bichromate of potash have been added, indicating about 1.4 grains of protoxide.

Therapeutics. It may be used for the same purposes as reduced iron; it is a cheaper preparation, but probably much less effectual.

Dose. 3 gr. to 5 gr., or more.