Preparation

For medical purposes, this salt should be prepared by heating together dilute sulphuric acid and iron wire. The iron is oxidized at the expense of the water, hydrogen escaping with effervescence; while the acid unites with the oxide to form the sulphate of the protoxide, which remains in solution. In order that there may be no admixture of the sesquioxide, which it is desirable to avoid, the iron should be in excess, and, after the resulting: solution has been poured off, a very little sulphuric acid should be added; care being taken, in the subsequent filtration, evaporation, and crystallization, to exclude atmospheric air as much as possible. This is the process of Bonsdorff, which has been adopted in the U. S. Pharmacopoeia, and affords a pure sulphate of the protoxide.

Composition

Crystallized sulphate of iron consists of one equivalent of sulphuric acid, one of protoxide of iron, and seven of water.

Properties

Obtained in the manner above described, the crystals are of a fine bluish-green colour. If quite green, they contain a considerable proportion of sesquioxide. They are inodorous, of a strongly astringent, inky or ferruginous taste, very soluble in water, and insoluble in alcohol. A moderate heat drives off their water of crystallization, and reduces them to the state of a whitish powder. By an intense heat they are decomposed, sulphurous and sulphuric acids being given off, and the red sesquioxide remaining. Prepared by the method of Bonsdorff, they undergo little change upon exposure, on account of a minute quantity of un-combined sulphuric acid contained in them; but, as ordinarily found in the shops, they effloresce in the air, and at the same time absorb oxygen, with the production of a red subsulphate of the sesquioxide. In consequence of this change, they first become quite green, and afterwards more or less covered with a whitish or reddish-brown powder; the latter colour predominating after long exposure. Their solution, which reddens litmus, is at first bluish-green, but afterwards becomes successively green, greenish-brown, and reddish, through the absorption of oxygen, and the gradual conversion of the protoxide into sesquioxide; the latter being partly deposited in the state of an insoluble subsulphate of the sesquioxide, and partly remaining in solution as the neutral sulphate of the same oxide. When the liquid has assumed a clear red colour, this change may be considered as complete, and no protoxide is left. The solution, however, may be kept in the original state, by means of iron wire, which appropriates the oxygen as fast as absorbed; and sugar has the same effect by its peculiar influence in preventing the oxidation of iron. The sulphate of iron of the shops almost invariably contains more or less of the sesquioxide.

Incompatibles. This salt is decomposed by the alkalies, the alkaline carbonates, soaps, lime-water, the soluble salts of lime, lead, and baryta, the borate and phosphate of soda, nitrate of silver, the soluble sulphurets, and ferrocyanide of potassium. When a perfectly pure sulphate of the protoxide, it is not affected by tannic acid, or the vegetable astringents; but, as kept in the shops, it always yields a black or bluish-black precipitate with these reagents, in consequence of the sesquioxide of iron contained in it. But, though it gives precipitates with the above substances, it does not follow that they are all medicinally incompatible. On the contrary, it is often given in connection with an alkaline carbonate, with a view to the production of the carbonate of the protoxide, which is a milder salt, and may be more advantageously employed when the object is to affect the general system. The officinal compound mixture of iron, and compound pills of iron, are prepared on this principle. (See page 451).

Effects on the System

Sulphate of iron is locally excitant and actively astringent. On the stomach, in moderate doses, it operates often very kindly as a tonic, and in the bowels is apt to produce constipation by its astringency. In larger quantities it becomes irritant, causing heat and uneasiness in the stomach, and, in excessive doses, nausea. vomiting, and diarrhoea, with griping pains. In great excess, it may even prove poisonous by inflaming the stomach and bowels. Orlila found two drachms to kill a dog; and Dr. Christison states that he has met with a case, in which half an ounce seemed to have proved fatal in a child. (Christison's Dispensatory.) It is no doubt capable of bringing the system under the influence of iron; but it is probably never absorbed as a sulphate; undergoing decomposition in the stomach, and forming new compounds before it is dissolved by the gastric juice. In the mean time, it exercises its excitant influence upon the mucous membrane of the stomach; and, if given freely, with a view to the impregnation of the system, it endangers unpleasant symptoms of gastric and intestinal irritation.

Therapeutic Application

From the above considerations, it may be inferred that sulphate of iron is useful as a tonic in dyspepsia, and as a joint tonic and astringent in relaxed states of the bowels attended with diarrhoea. In the defective appetite and feeble digestion of convalescence, especially when accompanied with an atonic diarrhoea, it is particularly indicated; and it may be used with hopes of benefit in passive hemorrhages from the stomach or bowels. It has often, moreover, been employed, with a view to its operation through the circulation, in anemic affections, amenorrhoea, passive hemorrhages generally, colliquative sweats, diabetes, excessive secretion from the mucous membrane of the urinary passages, leucorrhoea, and chronic catarrh with exhausting expectoration; but, for reasons stated in the preceding paragraph, it is not so well adapted for the chalybeate impregnation of the system as some of the milder preparations, and has been nearly superseded by them. It has also been used in intermittent fevers, and for the destruction of the tape-worm; but is of little real service in either of these affections.

Administration

It may be given in pill or solution. If in the former method, it should first be deprived of its water of crystallization; as, if made from the crystals, the pills would be apt to crumble from the efflorescence of the salt In this state, it is officinally directed under the name of Dried Sulphate of Iron (Ferri Sulphas Exsiccata, U.S., Br.). In solution, the salt may be given dissolved in sweetened water, in order to protect it from oxidation, or in carbonic acid water, which aids its tonic effect in dyspepsia. The dose of the crystallized sulphate is from one to five grains, of the dried from half a grain to three grains.*

The British Pharmacopoeia has a preparation denominated Granulated Sulphate of Iron (Ferri Sulphas Granulata, Br.), which differs from the crystallized simply in having been made to assume the form of a coarse powder by agitation during crystallization. It is said to have the advantage of oxidizing less readily by exposure. The dose is the same.

External Use

Sulphate of iron has been considerably used as a topical remedy. In the aggregate solid state, in powder, or in strong solution, it has been used to check the oozing of blood from hemorrhagic or wounded surfaces; in weaker solution, as a collyrium in ophthalmia, and an injection in gleet, leucorrhoea, and prolapsus ani; and, in the same form, as a wash in indolent or flabby ulcers, and cutaneous eruptions, especially in the lichenous or herpetic ring-worm of the face. The strength of the solution may vary, according to the purposes for which it is used, from one to twenty grains to the fluidounce of water; the feeblest proportion being used in ophthalmia, the strongest to arrest hemorrhage, or with a view to a powerful alterative influence on limited surfaces, as those of diseased ulcers, and patches of chronic cutaneous eruptions. Velpeau has found it the most efficacious local remedy that he has used in erysipelas, stating that it never fails to cut short the inflammation in one or two days. He uses a lotion consisting of about half an ounce of the salt dissolved in a pint of water, which is aplied by compresses, frequently wetted so as to keep the skin constantly moist. (Lond. Med. Times and Gaz., March, 1855, p. 239).

Sulphate of iron is one of the salts which has been applied to the interior of the larynx and the bronchial tubes, in the form of spray, by means of the atomizer. (See page 76.) It may be used in ulceration and chronic inflammation; and the solution may be employed of a strength varying from one to ten grains to the fluidounce of water.