This section is from the "A Handbook of Useful Drugs" book, by State Medical Examining and Licensing Boards.
A mixture of magnesium carbonate and magnesium hydroxid, approximately (MgCO3)4.Mg(OH)2.5H2O.
Properties : Magnesium carbonate is a light, white, friable mass, or a bulky, white powder, without odor, and having a slightly earthy taste. It is practically insoluble in water and in alcohol, but soluble with effervescence in dilute acids.
Incompatibilities : It is incompatible with acids which form salts of magnesium.
Action and Uses: Magnesium carbonate when taken internally neutralizes the acids in the stomach. It may be used in cases of hyperacidity or acid gastritis, but it is sometimes objectionable on account of the carbon dioxid gas evolved. The salt formed is laxative. If magnesium carbonate passes the stomach without neutralization, it may escape solution in the intestines and not act as a laxative. Large doses sometimes produce an accumulation of the insoluble carbonate and may lead to intestinal obstruction. Magnesium carbonate is largely used as a dusting powder in intertrigo and in similar conditions, and as a cosmetic.
Dosage: 3 gm. or 45 grains.