By calcination:—(Brown-red colcothar, Crocus, Indian red, Rouge, Jewellers’ r.; Ferri oxydum rubrum, L.)—Calcine ferrous sulphate until the water of crystallisation is expelled, then roast it with a strong fire until acid vapours cease to rise; cool, wash the residuum with water until the latter ceases to affect litmus, and dry it.
Ferrous sulphate, 100 parts; common salt, 42 parts; calcine, wash well with water, dry, and levigate the residuum. This process yields a cheap and beautiful product, which is frequently sold for the ferri sesquioxydum; but it is less soluble, and therefore unfitted for a substitute for that preparation.
By precipitation;—Ferri sesquioxydum—B. P., Ferri oxydum rubrum—Ph. E. L. By precipitating a solution of ferric sulphate or chloride with ammonia, in excess, and washing, drying, and igniting in the resulting hydrate. Pure; anhydrous.
Ferrous sulphate, 4 lbs.; sodium carbonate, 4 lbs. 2 oz.; dissolve each separately in water, 3 galls.; mix the solution whilst hot, set the mixture aside, that the precipitate may subside, and subsequently wash and dry it as before. Contains water, and a trace of alkali.
Ferric hydrate, Ferri peroxydum hydratum—(Ph. D., Ferrugo—Ph. E.)—a. (Ph. E.) Ferrous sulphate, 4 oz.; sulphuric acid, 31⁄2 fl. dr.; water, 1 quart; mix, dissolve, boil, and gradually add of nitric acid, 9 fl. dr.; stirring well and boiling for a minute or two after each addition, until the liquor yields a yellowish-brown precipitate with ammonia; it must then be filtered and precipitated with liquor of ammonia (fort.), 31⁄2 fl. oz.; rapidly added and well mixed in; collect the precipitate, wash it well with water, drain it on a
calico filter, and dry it at a heat not exceeding 180° Fahr. When intended as an antidote for arsenic it should not be dried, but kept in the moist or gelatinous state.
Ferric peroxide, moist (B. P.) Syn. Ferri peroxidum humidum. Prep. Mix solution of persulphate of iron (B. P.), 4 fl. oz., with 1 pint of distilled water, and add it gradually to 33 fl. oz. of solution of soda (B. P.), stirring constantly and briskly. Let them stand for two hours, stirring occasionally; then put on a calico filter, and when the liquid has drained away, wash the precipitate with distilled water till what passes through ceases to give a precipitate with chloride of barium. Lastly, enclose the precipitate without drying it in a stoppered bottle, or other vessel, from which evaporation cannot take place.
Dry hydrate of peroxide of iron (B. P.). Ferri peroxidum hydratum. Dry the moist peroxide, 1 lb., at a temperature not exceeding 212° Fahr., till it ceases to lose weight. Reduce to a fine powder.—Dose, 5 to 30 grains.
Prop. Ferric oxide, prepared by precipitation (1, c), is an impalpable powder, of a brownish-red colour, odourless, insoluble in water, freely soluble in acids, and possessing a slightly styptic taste, especially when recently prepared. When exposed to heat its colour is brightened, its sp. gr. increased, and it is rendered less easily soluble in acids. The oxide prepared by calcination is darker and brighter coloured, less soluble, and quite tasteless. It has either a scarlet or purplish cast, according to the heat to which it has been exposed. The finest Indian red, or crocus, usually undergoes a second calcination, in which it is exposed to a very intense heat. It is then known as ‘purple brown.’ The best jeweller’s rouge is prepared by calcining the precipitated oxide until it becomes scarlet.
The hydrate is of a yellowish-brown colour, and though it can be dried without decomposition, it requires to be kept in a moist state. It is best preserved in a well-stoppered bottle, filled with recently distilled or boiled water.