Sulphate of magnesium 1, olive oil 1, starch mucilage 15.

Action. - Sulphate of magnesium to saturation precipitates lobulins.

In moderate doses it causes a copious secretion from the itestinal mucous membrane, and acts as a purgative. It does ot stimulate the muscular coat of the bowels much; it thus causes little griping. As it does not accelerate peristaltic action, a part of the fluid poured out into the intestine may be reabsorbed as it passes slowly along. It is therefore usual when we wish to produce free purgation to combine the salt with some purgative which will stimulate the muscular coat of the' bowel, such as senna or cascara sagrada. When given alone it is apt to produce much flatulent distension of the abdomen and rumbling, and a carminative is therefore often given along with it. Its objectionable bitter taste may be covered by dissolving it in acid infusion of roses and adding spirit of chloroform. It may be employed as a purgative enema. When absorbed into the blood it acts as a diuretic if the skin be kept cool, and as a diaphoretic if the skin be kept warm or moderate exercise be taken. It is absorbed more readily when given in small quantities, but a little is also taken up when purgative doses are employed, and it is therefore a useful purgative in febrile states.

Uses. - Sulphate of magnesium is one of the most common and useful saline purgatives. For its mode of action and uses, vide pp. 391-394. On account of its great solubility it may be used in very concentrated solution to remove dropsy (p. 394) when less soluble salts cannot. Repeated small doses are very serviceable in biliousness.

U.S.P. Magnesii Carbonas. Carbonate of Magnesium. (MgCO3)4Mg(HO)2.4H2O; 484. This corresponds to the two kinds mentioned in the B.P.

B.P. Magnesii Carbonas. Carbonate of Magnesium. (MgCO3)3Mg(HO)2.4H2O.

B.P. Magnesii Carbonas Levis. Light Carbonate of Magnesium. (MgCO3)3Mg(HO)2.4H2O.

Both the light and heavy carbonates of magnesium have the same chemical composition, and differ only in their weight.

Properties. - A white granular powder almost tasteless.

Preparation. - Both are prepared by precipitating a solution of sulphate of magnesium by a solution of carbonate of sodium; removing the resulting sulphate of sodium, washing the carbonate, and drying it at a temperature not exceeding that of boiling water so as not to decompose it.

In preparing the heavy carbonate, concentrated boiling solutions are used, the mixture evaporated to dryness, and the sulphate of sodium removed by subsequent digestion with water. In preparing the light carbonate, dilute solutions are employed: they are mixed cold; boiled for fifteen minutes; and the sulphate of sodium separated by filtration.

Reactions. - It is recognised as a carbonate by dissolving with effervescence in hydrochloric acid, and the magnesium is detected by the appropriate tests in the resulting solution (p. 658). The two carbonates are distinguished by their weight.

Action. - When swallowed, carbonate of magnesium will have a less stimulating effect upon the mucous membrane than potash or soda, as it is nearly insoluble; but on this very account it is to be preferred to them for neutralising acid in the stomach after meals, inasmuch as it will only neutralise the excess of acid without rendering the fluids alkaline. In the intestine it acts as a laxative, and is partly excreted in the faeces and partly converted into magnesium salts which are absorbed and pass out in the urine.

Uses. - As an antacid and laxative, especially in children; in heartburn, in dyspepsia, and vomiting during pregnancy; and in cases where it is desirable to render the urine alkaline, as in gouty persons, where potash and soda disagree.

Dose. - As an antacid, 5 to 20 grains; as a laxative, 10 to 60 grains. It may be conveniently given in milk.

Officinal Preparations

B.P.

Dose.

liquor Magnesii Carbonatis, as antacid,

1-4 fl. dr.; as laxative, 1-2 fl. oz.

„ „ Citratis, as laxative,....

5-10 fl. oz.

U.S.P.

Mistura Magnesii et Asafoetidas...........................

fl. oz.