Origin

This was known so early as the middle of the sixteenth century. It is prepared by acting upon metallic zinc with dilute sulphuric acid. The metal is oxidized at the expense of the water, the liberated hydrogen escapes, and the oxide of zinc formed unites with the acid, to produce the sulphate, which is then obtained by evaporation and crystallization.

Composition

The crystallized salt, which should always be selected for use, consists of one equivalent of sulphuric acid, one of oxide of zinc. and seven of water. On exposure, it partially effloresces, and loses much of its water.

Properties

The crystals are small, slender, transparent, four-sided prisms, and in mass very closely resemble those of Epsom salt, for which they have sometimes been mistaken. They are inodorous, of a styptic, metallic, disagreeable taste, very soluble in water cold or hot, and insoluble in alcohol. By heat they are dissolved in their own water of crystallization, which gradually escapes, leaving the salt in the form of a white opaque powder. By an intense heat they are decomposed.

Incompatibles. Sulphate of zinc is decomposed, with insoluble precipitates, by the alkalies and alkaline earths and their carbonates, by the soluble salts of lead, of lime or calcium, and of baryta or barium, by sulphuretted hydrogen and the soluble sulphurets, and by astringent vegetable infusions through their tannic acid.

Effects on the System

These are such as have been described in the general remarks on zinc, and do not require to be repeated particularly here. It is sufficient to state that this is the most astringent of the salts of zinc, and one of the most energetic in its effects on the system, whether medicinal or poisonous. It has been frequently taken, by mistake for sulphate of magnesia, in doses of an ounce or more, and sometimes, though very rarely, with fatal results. Happily, the powerful emetic properties of the salt usually cause the whole of it to be rejected, before it has had the opportunity to produce a caustic effect upon the coats of the stomach. In a case of the kind which fell under my knowledge, one of the severest symptoms was a feeling of excessive constriction of the mouth, throat, and oesophagus; but the patient, who was a young woman, recovered without any serious consequences. Generally, along with incessant vomiting and retching, there is violent gastric and intestinal pain; and, in the fatal cases, there have been observed, in addition, purging, anxiety, restlessness, great prostration, and ultimately convulsions. The treatment required in such cases has been already stated.

Therapeutic Application

As an emetic, sulphate of zinc will be considered particularly with the class of emetics. First, I shall treat of its internal, and afterwards of its external use.

1. For its direct effects on the alimentary canal, the salt has been used in dyspepsia, diarrhoea, dysentery, and colica pictonum. As a gentle tonic, in very small doses, it is sometimes beneficial in simple indigestion; but it is seldom used in that affection. To diarrhoea it is adapted by its strong astringency; but it is too irritant for the disease in its acute form, unless associated with great intestinal relaxation. It is to chronic diarrhoea that it is best adapted, and especially to those cases in which there may be a suspicion of ulcers in the small intestines. In these cases, associated with opium in small doses, it is sometimes very useful, though less effective, I think, than the corresponding salt of copper. In acute dysentery it should not be used by the mouth, except, sometimes, in the very advanced stages; but it may at any time be tried in the chronic form of the disease, when the tongue remains moist, and the ordinary measures have been employed in vain. There is a condition of dysentery in which it may often be used with very great benefit, I allude to cases in which the rectum is the part mainly affected, whether the case be subacute or chronic. In instances of the latter kind, the patient will often suffer long with the most harassing tenesmus; and though, from the want of constitutional sympathy, his general health may suffer less than when the higher portions of the large intestines are inflamed or ulcerated, yet the local distress and inconvenience are so great that life is rendered burdensome. The remedy should here be used by injection. so as to bring it into direct contact with the ulcerated surface. I have been for many years in the habit of resorting to this measure in the class of cases mentioned; and, though the disease may have been of several months'duration, and, in one instance which I remember, had continued a year, they have speedily begun to improve, and generally marched on steadily to convalescence. I usually direct from four to eight fluidouncee of water, holding two grains of the sulphate in solution for each fluid-ounce, with the addition of thirty or forty drops of laudanum, to be thrown up the bowel twice a day. With the use of the salt in colica pictonum I have no experience; and I should not be disposed to rely on it, while medicines known to be efficient are at command.

2. In reference to its tonic effects upon the system generally, and on the nervous centres more especially, the medicine has been given in most of the chronic nervous diseases to which the metallic tonics are thought to be peculiarly applicable. Epilepsy, hysteria, hooping-cough, and asthma are among these complaints; but the one in which it has the highest reputation, and in which experience has shown it to be most efficacious is chorea, or St. Vitus's dance. It is certainly among the remedies which I have found most effectual in that complaint, especially when used in connection with occasional purging. Upon the same principle, it will sometimes succeed in interrupting the paroxysms of intermittent fever, though probably less efficacious in this affection than sulphate of copper, and incomparably less so than sulphate of quinia, or the arsenical preparations. It is asserted to have proved useful in obstinate chronic gleet and leucorrhoea; and Dr. Christison, in his Dispensatory, states that, in the dose of from three to six grains twice or thrice daily, he had frequently been successful with it in such cases. It would appear to operate by something more than a mere astringency. It may possibly exert an alterative influence over the mucous membranes, and thus prove useful also in chronic bronchitis with profuse expectoration, in which it has been recommended.

Administration

The dose, to begin with, is one or two grains, twice or three times a day, which may be gradually increased, if requisite, as the stomach is found to tolerate it without inconvenience. Dr. Babing-ton has increased to thirty-six grains three times a day; but this can rarely be necessary; and it is probable that all that the medicine can effect may be obtained from much smaller quantities. It may be given in pill or solution.