27c. RESINA, U.S.—RESIN. ROSIN. COLOPHONY. The clarified residue left after distilling off the volatile oil from turpentine. It has been asserted that Pinus palustris, the official species, contains more resin than any other German or American pine. When pure, rosin is of a clear, pellucid, amber color, but the commercial rosin is yellowish-brown, more or less dark, sometimes almost black, the color depending upon its purity and the amount of heat used in its preparation; it breaks with a shining, shallow, conchoidal fracture; odor and taste faintly terebinthinate. White rosin is an opaque variety made by incorporating it with water.
CONSTITUENTS.—Rosin is the anhydride of abietic acid, C44H62O4, into which acid it may be converted by warming with dilute alcohol. Ash, 0.05 per cent.
ACTION AND USES.—An important ingredient of ointments and plasters, and is said to have the property of preserving them from rancidity by preventing the oxidation of the fatty base.
OFFICIAL PREPARATION. Emplastrum Resinae.