SULPHATE OF MAGNESIA.

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caustic lime and water, all the magnesian sulphate would be decomposed,and the liquor being filtered, to separate the precipitated magnesia andsulphate of lime, yields, on evaporation, sulphate of soda. If shaken inthe cold with carbonate of baryta, a solution of carbonate of soda wouldbe obtained, easily recognized by its alkaline properties. 100 grains ofpure sulphate of magnesia, dissolved in water, and mixed with a boilingsolution of carbonate of soda, yields 34 grains of subcarbonate of mag-nesia when dried. If sulphate of soda were present, the precipitatewould weigh less. (Phillips, Transl. of Pharm.)

Physiological Effects. —Sulphate of magnesia is a mild and per-fectly safe antiphlogistic purgative, which promotes the secretion as wellas the peristaltic motion of the alimentary canal. It is very similar inits operation to sulphate of soda, than which it is less likely to nauseate,or otherwise disorder the digestive functions, while it acts somewhatmore speedily on the bowels. It does not occasion nausea and griping,like some of the vegetable purgatives, nor has it any tendency to createfebrile disorder or inflammatory symptoms ; but, on the other hand, hasa refrigerant influence: hence it is commonly termed a cooling purgative.In small doses, largely diluted with aqueous fluids, it slightly promotesthe action of other emunctories: thus, if the skin be kept cool, andmoderate exercise be conjoined, it acts as a diuretic ; whereas if the skinbe wann, it operates as a diaphoretic.

Uses. —On account of the mildness and safety of its operation, itsready solubility, and its cheapness, sulphate of magnesia is by far themost commonly employed purgative, both by the public and the profes-sion. The only objection to its use is its bitter and unpleasant taste. Tostate all the cases in which it is administered, would be to enumerate nearlythe whole catalogue of known diseases. It must, therefore, be sufficient tomention, that it is excellently well adapted as a purgative for febrileand inflammatory diseases, obstinate constipation, ileus, lead colic, evenincarcerated hernia, narcotic poisoning, &c. It may be used as an anti-dote in poisoning by the salts of lead and baryta.

Administration. —As a purgative it is usually administered in dosesof from half an ounce to an ounce and a half; but if dissolved in a largequantity of water, a smaller dose will suffice. Thus, two drachms inhalf a pint or more of water, taken in the morning fasting, will actspeedily, sufficiently, and mildly, in ordinary cases ; and in delicatefemales, a drachm, or even less, in the above quantity of water, willusually produce the desired effect. Some carminative or aromatic (aspeppermint water or tincture of ginger) is frequently conjoined to obviateflatulency. In febrile and inflammatory diseases, the solution may beacidulated with dilute sulphuric acid with great advantage; or the sul-phate may be dissolved in the compound infusion of roses. It is fre-quently used as an adjunct to the compound infusion of senna, whosepurgative effect it promotes, but whose griping tendency it is said tocheck. In dyspeptic cases, accompanied with constipation, it is con-joined with bitter infusions (as of quassia, gentian, calumba, &c.). As apurgative enema, an ounce or more of it may be added to the ordinaryglyster.

The bitter purging saline waters (vide p. 174), as those of Seidlitz,Epsom, Beulah, Kilbum, and the Cheltenham pure saline, owe theirpurgative property principally to sulphate of magnesia,