Medical properties and uses.-Metallic iron exerts no action on the living system, unless it meets with acid in the stomach, -in which case it becomes tonic. Iron filings, therefore, are not adapted for all the cases in which chalybeate remedies prove useful; and are chiefly suited to those cases of dyspepsia, hysteria, chlorosis, and general debility, which are accompanied with acidity in the first passages. When iron is oxidized by the assistance of watery fluids, hydrogen gas is evolved: hence, when the filings are rendered active in the stomach, foetid eructations are produced, and the faeces are coloured black; which are evident symptoms of the medicine having taken effect As an anthelmintic, iron filings may operate mechanically, and dislodge worms; but even in worm cases, the oxidizement of it in the stomach renders it more useful. Iron filings reduce the salts of copper to metal, hence they are administered in cases of poisoning by these salts. They are employed as anthelmintics in ascarides, the oxyuris vermicularis.

Sydenham preferred iron filings to the salts of iron, in hysteria and hypochondriasis; but modern practitioners have not followed him in this respect.

Iron wire is useful for pharmaceutical preparations, on account of the purity of the iron from which it is made : as the softest and purest iron only can be drawn.

The filings are given in the form of powder combined with some aromatic, or made into an electuary with honey, or in pills in combination with myrrh, ammoniacum, assafoetida, or some bitter extract. The dose may be from grs. v. to 3 ss.

Officinal preparations.-Ferri Limatura purificata, E. Oxidum Ferri Nigrum purificatum, E. D. Subcarbonas Ferri prceparatus, E. Rubigo Ferri, D. Ferri Sulphas, L. E. D. Ferrum tartari-zatum, L. Tartras Potassae et Ferri, E. Tartarum Ferri, D. Tinctura Acetatis Ferri, D. Liquor Ferri alkalini, L. Vinum Ferri, L. D. Sulphuretum Ferri, E.

2. Percyanide of Iron.

Officinal. Ferri Percyanidum, Lond. Ferri Cyanuretum, Dub. Prussian Blue. Syn. Hydrocyanate de Fer, Prussiate de Fer, Bleu de Prusse (F.).

This salt was originally the production of accident. In 1710, Dippel, a celebrated German chymist, furnished a colour-maker of Berlin, named Diesbach, with a quantity of vegetable alkali prepared from blood, with which he intended to prepare a lake, by precipitating cochineal, alum, and sulphate of iron, with potassa; but instead of the lake, a beautiful blue was produced. This pigment was continued to be formed in the same manner; but it was not till twenty years afterwards that the method of preparing it was made public, and the preparation named Berlin or Prussian blue. It is now prepared by calcining 100 parts of the carbonate of potassa of commerce with 25 parts of animal charcoal made from blood: horn and other animal matters are next added, and again 25 parts of animal charcoal. This mixture is continued in the furnace, and constantly stirred until only a blue flame is given out; it is then taken from the fire, and thrown into water, in which, after brisk stirring, it is left at rest. In twenty-four hours the fluid is decanted, evaporated, and crystallized.

To a solution of the hydrochlorate of the tritoxide of iron a solution of the above salt is added, as long as a precipitate is thrown down : the supernatant fluid is then decanted off; and the precipitate, well washed with boiling water, and dried, is Prussian blue. It may be more readily prepared by adding a solution of ferrocyanide of potassium to a solution of sulphate of peroxide of iron, acidulated with sulphuric acid. After the subsidence of the precipitate, the supernatant fluid is to be drawn off, and cold water, acidulated with sulphuric acid, added; and this repeated several times. The precipitate is then to be washed with pure water, and dried.

By the above process, the calcination of the alkali with the blood and bones azotizes it; and hydrocyanic acid is formed: the union of the hydrocyanic acid with the oxide of iron forms the Prussian blue, or a ferro-sesquicyanide of iron.

Qualities.-Prussian blue is of a rich deep blue colour, insipid, inodorous, and much heavier than water, in which it is insoluble. If exposed to the air it partly loses its blue colour, and becomes greenish: but again changes to blue when placed in contact with deoxygenizing substances. When submitted to a very strong heat, it is decomposed, giving out some pure water, then a small quantity of hydrocyanate of ammonia, carbonate of ammonia, and a residue, which, when calcined in a current of air, is oxide of iron.

Medical properties and uses. - Prussian blue has been occasionally used as a medicine. Dr. Zollikoffer, an American physician, gave it successfully in agues and remittent fevers, in doses of one grain, repeated several times a day. He gives it during the paroxysm, and affirms that it does not disagree with the most irritable stomachs. Dr. Bridges, another American physician, recommends it in neuralgia. The dose for an adult is gr. iv. three times a day. Dr. Kir-choff prescribed it with advantage in epilepsy, in doses of gr. j. increased to grs. iij. As an external application, an ointment, formed with gj. to j. of cetaceous ointment, is used in cases of cancerous ulceration. It is admitted into the Pharmacopoeia chiefly for preparing bicyanide of mercury and hydrocyanic acid.

Officinal preparations. - Hydrargyri Bicyanidum, L. Cyanure-turn Hydrargyri, D, Acidum Hydrocyanicum dilutum, L. Acidum Prussicum, D.

3. Oxidized Iron.

Officinal. Ferrum; squamae Oxidi, Dub. The Scales of the

Oxide of Iron.

Syn. Bluettes de Fer (F.), Eissenoxyd (G.), Scaglio di Ferro (I.), Escamas de Hierro (S.).

These scales are detached by the hammer of the smith from the surface of iron heated to redness in the forge, and hammered on the anvil.

Qualities.-They are inodorous and insipid, attracted by the magnet, sp. gr. 3.5, brittle, and reducible by trituration to a powder, which is of a dull, greyish black colour. They consist of both protoxide and peroxide: the proportion in the outer layer being one equivalent of the peroxide and four equivalents of the protoxide : the inner consists of one equivalent of the peroxide and six equivalents of the protoxide. This mixed oxide is soluble in acids, without producing hydrogen gas.

• Medical properties and uses.-These scales are used in the same cases and in the same manner as the filings, and are preferable; for, as they do not produce hydrogen gas when dissolving in the stomach, their use is unaccompanied by the distension and flatulence which the filings often occasion.