This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
The large number of officinal iron compounds may be with advantage considered in the following order: - The preparations of the metal itself and its oxides; the astringent preparations; and those which are not at all, or not markedly, astringent.
Metallic iron is introduced in the form of soft or wrought iron wire, or nails free from rust, and also combined with some oxide, as ferrum re-dactum.
By passing a stream of hydrogen at red heat over the hydrated peroxide - Fe2O3H1O + H6 = 4H1O + Fe2. At the same time, by incomplete reduction, some magnetic oxide is formed - 3Fe2O3 + H1 = 2Fe8O4 + H1O.
Pure reduced iron is an impalpable grayish-black powder, strongly magnetic, and showing metallic streaks on firm pressure. The oxide can be separated from the metal, and its amount ascertained by digestion with iodine and iodide of potassium, which dissolves the metal alone; of this, it should contain at least 50 per cent.; a little sulphide is sometimes present, and is liable to cause disagreeable eructation.
Black oxide - containing about 20 per cent. of water.
This being a mixture of proto- and peroxide, is prepared by adding a mixed solution of proto- and persulphate of iron to an excess of soda; the precipitate is washed and dried at a moderate temperature (120°), for at a greater heat it would absorb oxygen.
A brownish-black powder, tasteless, strongly magnetic, and soluble in acids without effervescence: bubbles of hydrogen would show the presence of metallic iron.
By pouring solution of persulphate of iron into excess of soda, and washing away the sodium sulphate: a similar precipitate would be thrown down by potash or ammonia.
A pasty mass, reddish-brown in color, and containing water, both combined and uncombined, to the amount of nearly 90 per cent.: it is the only iron preparation used in the moist state: it dissolves readily in cold dilute hydrochloric acid.
1 "Reduced" iron means the metal minutely divided by chemical process as distinguished from simple filings or powder (mechanical division); the percentage of metal in this form is often small (Pharmaceutical Journal, August, 1875).
By drying the moist peroxide last described at a temperature of 212°, and reducing to powder.
A tasteless powder, distinguished from the magnetic oxide by its dark-brown color, and its being non-magnetic.
(The astringent preparations of iron are mainly those which are formed by direct solution of the metal in the strong mineral acids, and include the chloride, nitrate, and sulphate.)
By dissolving iron wire in an excess of hydrochloric acid (by which a ferrous chloride is obtained), and treating this with nitric acid to peroxidation - thus
Fe + 2HCl = FeCl2 + H1. 6FeCl2 + 2HNO3 + 6HC1 = 3Fe2Cl6 + 2NO + 4H1O.
Sufficient distilled water is added to give a sp. gr. of 1.44. The per-salt could not be formed by the first-mentioned acid alone, because the nascent hydrogen which is set free, reduces ferric salts to the ferrous state.
The liquid is at first black from the combination of some nitric oxide (NO) with ferrous salt, but on heating the mixture the gas is expelled, and an orange-brown solution remains: it generally contains some free acid, and has a very strong styptic taste.
Liquor et Tinctura Ferri Perchloridi (v. p. 180).
By dissolving iron wire in nitric acid, and diluting to the proper strength, and a sp. gr. of 1.107. It is a clear solution of reddish-brown color, acid and astringent.
By boiling a solution of the proto-sulphate with some additional sulphuric and some nitric acid. A dense solution of reddish-brown color; very astringent.
The proto-sulphate of iron is the salt from which the greater number of the other compounds are prepared. Three forms of it are officinal- ferri sulphas (green vitriol), ferri sulphas exsiccata, and ferri sulphas granulata.
By dissolving iron wire in dilute sulphuric acid, and crystallizing.
The sulphate occurs in oblique rhombic prisms, of greenish-blue color and very styptic taste, soluble in water, insoluble in spirit. Exposed to air, it absorbs oxygen and turns brown from formation of ferric sulphate: if the crystals be rich green in color, some ferric oxide is present, but if nearly free from any ferric salt, the precipitate with yellow prussiate of potash will be nearly white. The crystals effloresce slightly in dry air; at 238° F. they lose most of their water of crystallization, and at 400° only one atom of water is retained, and the salt becomes a yellowish-gray powder.
Ferri Sulphas Exsiccata - Dried Sulphate of Iron (FeSO4H1O). This does not alter on exposure, and is not gritty: 3 gr. are equal to 5 gr. of the crystallized salt.
By filtering a boiling solution of ordinary sulphate into cold rectified spirit, constantly stirring.
Occurs in small green granules which are stable, and if carefully dried retain their properties many years.