Talc

TALC, Talcum (Ph. VII), a natural magnesium silicate, consisting mainly of the acid magnesium silicate Mg₃H₂(SiO₃)₄ with impurities of aluminum silicates and other substances. Obtained by pulverizing the natural mineral (Ural). T. is a white, greasy-feeling powder, insoluble in water, organic solvents, and diluted mineral acids. When calcined, it loses water. For medical purposes, T. must be free from iron salts and substances soluble in water or alcohol; the T. powder must be the finest (sieve M/50). Widely used as an adsorbent powder, differing from organic powders (starch, lycopodium) in its stability, inability to serve as a nutrient medium for microbes, and low cost. In tablets, it is used as a lubricating (sliding) agent; also in massage. When taken internally, it burdens the mucous membranes (by adsorption); sometimes prescribed as a base for powders with calomel. T. used for medical purposes should be sterilized (at 160-170°) to avoid infection of wounds, bedsores, and chafes, to which it is applied.