Origin. - Native calcium carbonate, freed from most impurities by elutriation.

Description and Properties. - A white, amorphous powder, often molded into conical drops, odorless and tasteless, permanent in the air. Almost insoluble in water; insoluble in alcohol; soluble in diluted acetic, hydrochloric, or nitric acid, with copious effervescence, but without leaving more than a trifling residue.

Dose. - 5-60 grains (0.3-4.0 Gm.) [15 grains (1 Gm.), U. S. P.].

Official Preparations

Hydrargyrum cum Creta - Hydrargyri cum Creta - Mercury with Chalk. Dose, 2-10 grains (0.12-0.6 Gm.) [4 grains (0.25 Gm.), U. S. P.]. (Described under Hydrargyrttm.)

Pulvis Cretae Compositus - Pulvoris Cretae Compositi - Compound Chalk Powder. - Dose, 20-60 grains (1.3-4.0 Gm.) [30 grains (2 Gm.), U. S. P.].