Metallic iron in the form of fine, bright, and non-elastic wire.

Iron forms ferrous salts in which it is bivalent, e.g. FeCl2 or FeS04, and ferric, in which it is either trivalent or quadrivalent. Ferric chloride may be regarded as FeCl3 or as Fe2Cl6, in which each of two atoms of quadrivalent iron have one affinity saturated by union with each other, and the other three by chlorine, Cl3=Fe - Fe = Cl3.

General Sources. - It is found native in the metallic state, and also as oxide, sulphide, chloride, carbonate, phosphate, sulphate, and arseniate. It is obtained from its ores by smelting with coke and clay or limestone.

General Reactions. - These are shown in the accompanying table. The reactions most generally mentioned in the pharmacopoeias are those with ferrocyanide and ferricyanide of potassium. It is to be remembered that a preparation of iron containing it in both the ferrous and ferric condition, or which, by its decomposition, yields iron in these two states, gives a precipitate with both of these reagents. The arseniate of iron, B.P., phosphate of iron, and the citrate of iron and quinine are examples of this.

General Reactions Of Iron Salts

Reagent

Ferrous Salts

Ferric Salts

Hydrogen sulphide .

No precipitate

White precipitate of sulphur (the ferric are reduced to ferrous).

Ammonium sulphide

Black precipitate

Black precipitate.

Caustic alkalis and ammonia

Nearly white precipitates of ferrous hydrate rapidly becoming green and then brown

Foxy-red precipitates of ferric hydrate.

Carbonates of ditto .

Whitish precipitate of ferrous carbonate which changes like the hydrate

Foxy-red precipitates. Carbonic acid escapes.

Potassium ferro-cyanide

Nearly white precipitate becoming blue on exposure

Deep blue precipitate (Prussian blue).1

Potassium ferri-cyanide

Deep blue precipitate

No precipitate. Dark coloration.

Tincture of galls

Intense black.

General Impurities. - Zinc, copper, and fixed alkalis may be present in its salts. Ferrous salts may be present as impurities in ferric and vice versa.

Tests.- The test used for the chloride in the U.S.P. is as follows : - If the iron be completely precipitated from a solution of the salt by an excess of water of ammonia the filtrate should not yield either a white precipitate (absence of zinc) or a dark-coloured precipitate with hydrosulphuric acid (absence of copper), nor should it leave a fixed residue on evaporation and gentle ignition.

The absence of ferrous salts as impurities in ferric is ascertained by the solution giving no precipitate with ferricyanide of potassium.

The absence of ferric salts as an impurity in ferrous is ascertained by the precipitate with ferrocyanide of potassium not being blue at first, but nearly white, and only becoming blue on exposure.

General Preparation Of Salts Of Iron

Prepared from

By

Ferrous Sulphate (p. 741)

Iron

Dissolving in sulphuric acid.

Dried Sulphate (p. 741)

Ferrous sulphate

Heating to drive off water of crystallisation.

Granulated Sulphate, B.P., Precipitated, U.S.P. (p. 741)

Ditto

Pouring an aqueous solution into spirit.

Carbonate (Saccha-rated) (p. 742)

Ditto .

Decomposing (by ammonium carbonate, B.P.), (by sodium bi-car-bonate, U.S.P.), and mixing with sugar.

Do. (Mistura Ferri Composita) (p. 742)

Ditto .

Decomposing by potassium carbonate and mixing with myrrh, etc.

1 With the tartrate of iron and ammonium (U.S.P.) no colour or precipitate is produced unless the solution is acidulated with hydrochloric acid.

General Preparation Of Salts Of Iron - Continued

Prepared from

By

Ferric Sulphate, B.P. (P. 742)

Ferrous sulphate

Adding sulphuric acid and oxidising by heating with nitric acid. (6FeSO4 + 3H2O4 + 2HNO3 = 3Fe2(SO4)3 + 4H2O + N2O2.)

Ferric Tersulphate, U.S.P. (p. 742)

Ferric Subsulphate, U.S.P. (p. 743)

Ditto, using too little sulphuric acid to form tersulphate.

Ferric Oxide (p. 743)

Ferric sulphate . .

Mixing with magnesia and water, U.S.P.

Mixing with water and solution of soda, B.P.

Ferric Oxide (Hy-drated, U.S.P.) (p. 743)

Ditto . . .

By precipitating with ammonia, washing and making into a paste with water, U.S.P.

Ferric Oxide (Hy-drated,B.P.)(p.744)

Ditto . . .

Pouring the diluted solution into solution of soda, B.P.; and drying below 212°.

Reduced Iron (p. 744)

Ferric oxide . .

Passing hydrogen over it while heated (Fe2O3 + 6H = Fe2 + 3H2O).

Ferric Chloride (p. 745)

Iron . . .

Dissolving in hydrochloric acid and oxidising by nitric acid. (3Fe2 + 12HC1 = 6FeCL + 12H 6FeCl2 + 6HC1 + 2HNO3 = 3Fe2Cl6 + 4H2O + N2O2.)

Ferric Nitrate (p. 747)

Iron . . .

Dissolving in nitric acid (Fe2 + 8HNO3 = Fe2(NO3)6 + 4H2O + N2O2).

Ferric Oxychloride (Dialysed Iron) B.P. (p. 746)

Ferric chloride .

Precipitating ferric oxide by ammonia, dissolving it in solution of perchloride, and dialysing the solution until it is tasteless.

Ferric Acetate (Solution of), B. and U.S.P. (p. 744)

Ferric sulphate .

Precipitating ferric oxide by ammonia, washing, and dissolving in glacial acetic acid, and diluting to the necessary strength.

Ferric Citrate.U.S.P. (p. 748)

Ditto (Tersulphate)

Precipitating oxide by ammonia, washing and dissolving in citric acid. This forms the Liquor Ferri Citratis, U.S.P. Ferri Ci-tras is prepared by evaporation of the Liquor under 60° C.

Tartrate of iron and potassium, U.S.P.

(FerrumTartaratum, B.P.) (p. 747)

Persulphate . .

Precipitating ferric oxide by ammonia, washing and mixing with acid tartrate of potassium.

Tartrate of iron and ammonium, U.S.P. (P. 747)

Ditto . .

Ditto, using tartaric acid and tartrate of ammonium in place of acid tartrate of potassium.

Citrate of iron and ammonium, B. and U.S.P. (p. 748)

Ditto . . .

Ditto, using citric acid and ammonia.

Citrate of iron and quinine, B. and U.S.P. (p. 749)

Ditto and sulphate of quinine

Precipitating ferric oxide and quinine by ammonia and dissolving it in citric acid.

Citrate of iron and strychnine, U.S.P. (p. 749)

Ferric sulphate and strychnine

Precipitating ferric oxide by ammonia and dissolving it along with strychnine in citric acid.

Sulphate of iron and ammonium, U.S.P. (p. 749)

Ferric sulphate and ammonium sulphate

Heating them together.

General Preparation Of Salts Of Iron - Continued

Prepared from

By

Ferrous Lactate, U.S.P. (p. 750)

Iron.

Dissolving in lactid acid.

Ferrous Oxalate, U.S.P. (p. 750)

Ferrous sulphate

Precipitating a solution with oxalic acid (ferrous oxalate is very slightly soluble).

Ferrous Iodide, B.P. (Syrup of) (p. 750)

Iron.

Heating with iodine and water (the completion of the process is recognised by the brown colour of the iodine disappearing and the froth becoming white) and then adding syrup.

Ferrous Iodide (Pill of), B.P. (p. 750)

Ditto

Same as syrup, but mixing with sugar and powdered liquorice root instead of with syrup.

Ferrous Bromide (Syrup of) U.S.P. (p. 751)

Ditto

Same as syrup of iodide, using bromine instead of iodine.

Arseniate of Iron, B.P. (p. 751)

Ferrous sulphate, arseniate of sodium, and acetate of sodium

Mixing a solution of arseniate and acetate of sodium with one of ferrous sulphate. If arseniate of sodium alone were used, free sulphuric acid would be formed, which would react on the arseniate. 3FeSO4 + 2Na2HAsO4 = Fe3As2O8 + 2Na2SO4 + H2SO4. To avoid this acetate of sodium is added. The sulphuric acid combines with the sodium and sets free acetic acid, which has no action on the arseniate of iron. 3FeSO4 + 2Na,HAsO4 + 2NaC2H3O2 = Fe3As2O8 + 3Na2SO4 + 2HC2H3O2.

Phosphate of Iron, B. and U.S.P. (p. 751)

Ferrous sulphate, phosphate of sodium, and acetate of sodium

The same process as in the preparation of arseniate. The reactions are similar. 3FeSO4 + 2Na2HPO4 + 2NaC2H3O2 = Fe3 P2O8 + 3Na2SO4 + 2HC2H3O2.

Pyrophosphate of Iron, U.S.P. (p. 752)

Citrate of iron.

Decomposing solution by solution of sodium pyrophosphate.

Hypophosphite of Iron, U.S.P. (p. 752)

Ferrous sulphate

Decomposing by hypophosphite of calcium when ferrous hypophosphite is precipitated, but on evaporation becomes ferric.

Valerianate of Iron, U.S.P. (p. 752)

Ferric sulphate

Decomposing by valerianate of sodium.

General Action of Iron Salts. - Iron differs from most of the other heavy metals in forming a normal constituent of the animal body, so that it may be regarded as a food as well as a medicine. It forms an important constituent of the haemoglobin in the blood. This acts as the oxygen-carrier to the tissues, and, therefore, the tissue-oxidation and the functional activity of the organs depend more or less upon the amount of iron present in the body. According to Preyer, in a healthy woman the minimum amount of iron in 100 grammes of blood is .048 gramme, of haemoglobin 11.57 grammes; the maximum, .057 gramme and 13.69 grammes of iron and haemoglobin respectively. In a healthy man, in 100 grammes the proportion is .0508 gramme of iron (minimum), .063 (maximum), 12.09 grammes haemoglobin (minimum), and 15.07 grammes (maximum).1 Both per- and proto-salts of iron form compounds with albumen, but they differ in their properties. The ferrous salts give a yellow colour with albuminous solutions, but do not precipitate them, the albuminous compound being, apparently, usually soluble. Diluted ferric salts, on the contrary, precipitate albumen slowly, and concentrated solutions precipitate it rapidly. The precipitate is soluble in dilute acids and in gastric juice.

When applied to the skin neither ferrous nor ferric salts have any action, as they do not dissolve the epidermis nor pass through it in any appreciable quantity. When applied to a denuded surface, or to a mucous membrane they combine with albumen. The ferrous salts have but a slight astringent action, whereas the ferric salts coagulate the albumen on the surface and also blood. They are thus powerful astringents and styptics. In the mouth they all have an inky taste, and as they are liable to form black sulphides with sulphuretted hydrogen, which is not unfrequently present in the breath, they are apt to discolour the teeth or tongue. In the stomach they have an astringent and irritant action, that of the ferric being more powerful than that of the ferrous salts. In the intestine they have a somewhat similar action; meeting here, as they often do, with sulphuretted hydrogen they become converted, in great part, into sulphides, and, passing out in the stools, give to them an inky black colour which sometimes alarms patients. In small doses they usually have an astringent action, and tend to cause constipation. Larger doses, on the other hand, seem to stimulate peristalsis, and increase the number of stools, and sometimes even small doses will cause diarrhoea in some individuals. After absorption into the blood they are found to increase, not only the number of the blood-corpuscles, but the percentage of haemoglobin contained in them, and may also cause a little free iron to be present in the serum. By thus increasing oxidation in the tissues they increase the functional activity of the various organs. The effect of ferrous and ferric salts added to the blood is very different, ferric salts producing a firm coagu-lum, whereas the ferrous salts tend rather to diminish the coagulability of the blood.

Iron has an action on the nervous system which varies according to the dose and mode of administration. When injected subcutaneously in frogs, iron salts cause slight excitement and then paralysis of the central nervous system. In the later stages of poisoning the irritability of the voluntary muscles is diminished,