MAGNESIA, MEDICAL PROPERTIES OF. Oxide of mag nesium, termed also, from the mode of procuring it, calcined magnesia, or magnesia usta, is an alkaline earth possessing the usual qualities of alkalies in their habitudes with acids, and likewise the peculiar property of exciting generally purgative action of the intestines. This last mentioned power gives it a distinctive character among alkaline remedies, as it can be employed not merely to counteract acidity, but also to remove the exciting cause when that consists in the presence of crude or undigested acid-yielding materials in the stomach. Its action as a purgative seems mainly to depend upon its meeting with acids in the stomach, and so formiug soluble salts. -When these are not present the magnesia remains undissolved, and if used repeatedly may accumu late in the intestines, and, becoming agglutinated by the mucous secretions, give rise to much uneasiness. Hence some other aperient should from time to time be given. [ANTACIDS.] When however acidity exists, either along with constipation or diarrhoea, more particularly in children, from the milk disagreeing, or from a diet unsuited to their delicate organs of digestion being forced upon them, magnesia is a very proper medicine, especially as it appears to possess a specific power of diminishing gastrointestinal irritation. (Hufeland, quoted in Pereira's ' Materia Medics.') It is generally expedient to add rhubarb to it, and combine it with some carminative. In such a state of combination it is peculiarly useful in what is termed diarrhoea crapulosa, arising from too great a mixture or too large a quantity of food.
Where it is determined to use magnesia, and sufficient acid does not exist in the stomach to ensure the formation of a soluble salt, a little lemon-juice may be added to it. The subcarbonate of magnesia has nearly the same action as the calcined magnesia, but when it meets with acids in the stomach effervescence takes place, accompanied with a disengagement of carbonic acid gas, which in some cases is bacon venient, in other instances extremely beneficial. In some almost uncontrollable irritations of the stomach, where food and medicines are alike rejected, subcarbonate of magnesia will be retained, and, by allaying the irritability, allow other remedies to be subsequently employed. Both the subcarbonate and the calcined magnesia are much used to correct heartburn, and to check the lithic acid diathesis ; but their employment requires much judgment and attention [ANTACIDS ; ANTALKALIES], as persisting too long in the employment of this or any alkaline preparation brings on a phosphatic condition.
Sulphate of Magnesia, or Epsom salts, in the ordinary form, as met with in the shops, are small acicular crystals. This renders them liable to be confounded with those of oxalic acid ; to avoid which the sulphate may be dissolved, and by recrystallisation they are obtained in large four-sided prisms,- or four-sided pyramids. The taste of sulphate of magnesia is bitter and very unpleasant ; but this is very much lessened by large dilution in water, which at the same time increases the purgative action of the salt, or by adding magnesia, or by giving it in compound infusion of roses and adding a few drops of dilute sulphuric acid, which augments the refrigerating property of the medicine. The addition of a little common salt to a solution of sul phate of magnesia increases its cathartic powers.
No saline medicine is so extensively employed as the sulphate of magnesia as a purgative ; it is more rarely used as a diuretic or diaphoretic. Its action as a purgative is in general mild and certain, causing a considerable evacuation of the serous secretions of the intestines, and so producing a cooling or lowering effect. At the com mencement of most inflammatory complaints and of fevers its employ ment is most beneficial. Its utility is often much increased by adding to the solution a very minute portion of tartarised antimony, so as to form the emetico-cathartic solution, which is found very serviceable in the fevers of India, and in those of the summer and autumn of European countries.
Small doses of sulphate of magnesia in bitter infusions are valuable in the treatment of dyspepsia accompanied with constipation. Many of the saline mineral waters resorted to for the cure of indigestion are chiefly indebted to the sulphate of magnesia for their purgative properties.
Sulphate of magnesia is a convenient antidote in cases of poisoning by the salts of lead or baryta. The saccharate of magnesia is an eligible form of exhibiting magnesia to children.
3Iagnesian limestone is sometimes employed for building, and is a very durable stone : it is however one of the most deleterious stones for masons to hew, as the gritty particles very speedily occasion disorders of the lungs, followed by early death. The mouth and nostrils of the workman should therefore always be defended by wearing a gauze mask.