28. Pix liquida.—Tar.

SOURCE.—An empyreumatic oleoresin obtained by the destructive distillation of the wood of Pinus palustris Miller, and of other species of Pinus. The pine logs are cut into billets, and built up into a stack and covered with earth, as in making charcoal. Slow combustion is started through an opening in the top of the stack, and the resinous matter, as it melts out and collects in a cavity in the center, is drawn off into barrels.

DESCRIPTION.—A resinous, black semiliquid, of an empyreumatic, terebinthinate odor, and a sharp, bitterish, empyreumatic taste. Acid in reaction. Partly soluble in water.

Birch tar, Dagget, or Oleum Rusci, from Betula alba Linné, has an odor similar to that of Russian leather.

CONSTITUENTS.—Tar is a very complex substance, varying with the kind of wood, amount of resins present therein, and the care exercised in its preparation, the chief constituents being an empyreumatic volatile oil, pyrocatechin, acetone, xylol, toluol, cresols (creosote), guaiacol, phenol, etc. The acid reaction which characterizes tar is due to acetic acid, obtained in an impure state as pyroligneous acid by distillation. In the retort is left behind the ordinary solid and fusible pitch of commerce.

ACTION AND USES.—Stimulant, irritant, insecticide, similar to, but less irritant than, the turpentines. Dose: 8 to 60 gr. (0.6 to 4 Gm.). The syrup is much used in pulmonary affections.

Syrupus Picis Liquidae (0.5 per cent) Dose: 1 to 4 fl. dr. (4 to 15 mils)
Unguentum Picis Liquidae (50 per cent.).

28a. OLEUM PICIS LIQUIDAE RECTIFICATUM.—OIL OF TAR. A volatile oil distilled from tar, the residue left being common pitch, pix nigra. A nearly colorless liquid when first distilled, but soon acquires a dark, reddishbrown color; it has the characteristic odor and taste of tar, which depends upon it for its medicinal properties. Dose: 1 to 5 drops (0.065 to 0.3 mil), in capsules or emulsion.

A Manual of Organic Materia Medica and Pharmacognosy, 1917, was written by Lucius E. Sayre, B.S. Ph. M.