Origin, Description, and Properties given under Alkalies. Dose. - 1/4-2 drams (1.0-8.0 Gm.) [45 grains (3 Gm.), U. S. P.].

Physiological Action. - Both magnesia and magnesium carbonate are mild antacid laxatives, requiring the presence of an acid in the stomach and bowels to render them active. Occasionally, when there is marked acidity of the stomach, magnesium carbonate occasions flatulence.

When taken in large amounts or for a long time magnesia tends to accumulate in the intestines. This untoward effect may be prevented by administering lemonade with the drug, the acid of which increases the solubility of the magnesia.

Therapeutics. - Magnesium carbonate as a protective powder is an effective agent in the treatment of dermatitis of the external auditory passage. The drug is a valuable antidote to counteract the effects of phosphorus-poisoning in the throat.

Both magnesia and magnesium carbonate are mild alkalies, and may be used for the same purposes as the alkalies. They are serviceable antidotes to poisoning from mineral and oxalic acids and many mineral salts. They are pleasant laxatives, being extensively employed for children.