Ferri Sesquioxydum. Lond. Sesquioxide of Iron

"Take of sulphate of iron, four pounds; carbonate of soda, four pounds two ounces; boiling water, six gallons. Dissolve separately the sulphate of iron and the carbonate of soda in three gallons of the water; then mix together the solutions, and set the mixture aside, that the powder may subside; then pour off the supernatant fluid; wash the precipitate in water, and dry it.

Carbonas Ferri Praecipitatus, Edin. Precipitated Carbonate of Iron. Carbonas Ferri, Dub. Carbonate of Iron.

"Take of sulphate of iron, four ounces (twenty-five parts, Dub.); subcarbonate of soda, five ounces (twenty-six parts,

1 Chalybs pracparatus e aceto, et sine aceto, P. L. 1720. Chalybis rubigo praeparata, P. L. 1745. Ferri rubigo, P. L. 1787. Ferri subcarbonas, P. L. 1829.

Dub.); water, ten pounds (eight parts, Dub.). Dissolve the sulphate in the water; then add the subcarbonate previously dissolved in the water, and mix them together. Let the carbonate of iron, which is precipitated, be washed with tepid water, and afterwards dried."

Subcarbonas Ferri Praeparatus, Edin. Prepared Sub-carbonate of Iron.

"Let purified filings of iron be frequently moistened with water, till they fall into rust, which is to be rubbed to powder."

Ferri Rubigo, Dub. Rust of Iron.

"Take of iron-wire, any quantity. Cut it into small pieces, which are to be exposed to the air and frequently moistened with water, until they be converted into rust; let this be rubbed in an iron mortar, and by pouring water on it, wash over the finest part of the powder, which is to be dried."

Syn. Carbonate de Fer (F.), Kohlensaures eisin Rost(G.), Ossido Carbonato di Ferro (I.), Sudud ul hedeed (drab.), Eerumboo Lohayka zung(Duk.), Man-dura (Sans.), Kith (Hind.), Zafran ahun (Pers.), Tuppoo (Tarn.).

This preparation was originally intended to be a protocar-bonate of iron; but even when the sulphate employed is a protosulphate, it contains more sesquioxide of iron than pro-tocarbonate : thence its present name. By mixing the solutions together, a double decomposition is effected; the sulphuric acid of the sulphate of iron combines with the soda, while the iron attracts the disengaged carbonic acid of the carbonate of soda; and thence the products are an insoluble protocarbonate of iron, and a soluble sulphate of soda, which are easily separated by washing and filtration. When first precipitated, the protocarbonate of iron has a whitish colour, and is at a minimum of oxidizement; but while drying, it attracts oxygen rapidly from the atmosphere, parts with the carbonic acid, and is converted into the sesquioxide. I have ' found that the precipitate combines with the largest proportion of carbonic acid when the solutions are mixed at a temperature of 150° of Fahrenheit. Filtration is necessary for separating it, the decantation of the clear fluid being very difficult, owing to the lightness of the precipitate.

The great solubility of the sulphate of soda renders much subsequent washing unnecessary; and the precipitate, after being washed in distilled tepid water, should be dried in the paper on which it is filtered, by a heat not exceeding 200°.

Qualities.-Precipitated sesquioxide of iron is inodorous, has a slightly styptic taste, and is of a chocolate-brown colour. It is insoluble in water, but acids dissolve it with slight effervescence, disengaging the small portion of carbonic acid which it contains in the gaseous form. It is decomposed by heat, and converted into the peroxide of the metal. In my experiments, ten grains of the dried sesquioxide, prepared with protosulphate of iron, and effloresced carbonate of soda, lost 2.3 grains when dissolved in hydrochloric acid; and the same quantity prepared with the crystallised alkali, and dried with great care, lost 1.4; so that, prepared in the former method it contained 23 per cent. of carbonic acid, and in the latter 14 per cent. Mr. Phillips says, he has found that it contains

15 per cent. when prepared with the greatest care, which indicates its composition to be carbonate of iron 40, sesquioxide of iron 60, in 100 parts1; but it rarely contains so much of the carbonate. The composition of the carbonate is 1 eq. protoxide of iron =36 + 1 of carbonic acid =22.12, making the equivalent 58.12; that of the sesquioxide is

2 eq. of iron = 56+3 of oxygen=24, making the equivalent =80.

Medical properties and uses.-This preparation is a useful tonic: it has been prescribed with great advantage in tic douloureux, chorea, and other affections of the nervous system. Its medical powers have been ascribed to the carbonate of iron which it contains. One great objection to its use is the large dose required in tic douloureux; on which account I generally administer the carbonate of iron the moment it is formed, by decomposing grs. vi. of the sulphate, in solution, with a scruple of bicarbonate of soda. The dose is from grs. iv. to grs. xxx. given three times a day, combined with myrrh, or aromatics. But in tic douloureux it is given to the extent of four drachms or more for a dose.

Officinal preparations. - Tartarum Ferri, D. Tinctura Ferri Sesqui-chloridi, L.