Calcium carbonate, obtained by precipitating a solution of a salt of calcium by a soluble carbonate, collecting and washing the precipitate and drying.

Properties : Precipitated calcium carbonate is a fine white powder without odor or taste. It is practically insoluble in water, but dissolves to a considerable extent in water containing carbon dioxid. It is decomposed by acids, forming a salt of calcium and giving off carbon dioxid with effervescence.

Action and Uses : Calcium carbonate neutralizes the acid of the gastric juice, chlorid of calcium being formed and absorbed to some extent. If the stomach contains no acid it may escape solution and absorption. When absorbed the action is that of the soluble salts of calcium, which will be described under Calcium Chlorid.

Calcium carbonate is used chiefly as an antacid. For this purpose it is used as the base of many tooth-powders. It is given in the form of powder as an antacid in acid gastritis, hyperchlorhydria and gastric ulcer. In prescribing it for such affections its power to check diarrhea and the astringent power with which it is credited should be born" in mind. It is especially appropriate to cases in which there is hyperacidity with accompanying diarrhea and in diarrhea with acid fermentation. It may be used in skin-diseases as a dusting-powder to neutralize acid secretions and to protect the skin.

Calcium carbonate is the appropriate antidote to oxalic acid as it neutralizes the acid with the formation of the insoluble oxalate of calcium. It is also a suitable antidote to other corrosive acids and has the advantage that an excess can be given without doing harm.

Dosage: From 1 to 3 gm. or irom 15 to 45 grains. The fine powder can be given to adults in teaspoonful doses as no harm is to be feared from moderate excess. One gram will neutralize 0.730 gm. of absolute HC1 or approximately the amount of free HC1 in 500 c.c, or 1 pint of stomach contents having 40 degrees of free acidity.