This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
The mild antacid and laxative action of magnesia, and its slight taste, render it a very suitable remedy for the acidity of stomach which so readily occurs in children; it is valuable both when constipation is present, and when unwholesome food has caused irritative diarrhoea (marked by red furred tongue, and greenish, sour, and liquid motions): 2 to 10 gr. of the carbonate may be given thrice daily, its antacid action only being desired, and its purgative effect avoided, unless with the first dose. On several occasions I have known 4 gr. severely purge an infant at the breast. When the attack is clearly traceable to unsuitable food, "Gregory's powder," containing rhubarb and ginger, with the magnesia, is a popular and very useful combination.