Tar. - An empyreumatic oleoresin obtained by the destructive distillation of the wood of Pinus palustris, Miller, and of other species of Pinus (nat. ord. Coniferae).

Habitat

United States.

Characters

Thick, viscid, semi-fluid, blackish-brown, heavier than water, transparent in thin layers, becoming granular and opaque with age; odor empyreumatic, terebinthinate; taste sharp, empyreumatic.

Solubility

Slightly, in water; soluble in Alcohol, fixed and volatile oils, and solution of Potassium or Sodium Hydrate. On distillation it gives off an empyreumatic oil (oil of tar), which is official {see below), and pyroligneous acid. What remains behind is pitch. This is black, solid, melting in boiling water.

Composition

Tar is a very complex substance. The chief constituents are - (1) Oil of Turpentine (see p. 515). (2) Creosote {see p. 334). (3) Phenols {see p. 324). (4) Pyrocatechin, or Catechol, C6H6O2 (which see). (5) Acetic Acid. (6) Acetone. (7) Xylol. (8) Toluol. (9) Methylic Alcohol. (10) Resins.

Dose, 1/4 to 1 dr.; 1. to 4. gm., in the form of pill.

Preparations

1. Syrupus Picis Liquidae. - Syrup of Tar. Tar, 75; Water, 150; Boiling Distilled Water, 400; Sugar, 800; Glycerin, 100; Distilled Water to 1000. By solution, decantation and filtration.

Dose, 1 to 4 fl. dr.; 4. to 15. c.c.

2. Unguentum Picis Liquidae. - Tar Ointment. Tar, 500; Yellow Wax, 125; Lard, 375.

Oleum Picis Liquidae. Oil Of Tar

A volatile oil distilled from Tar.

Characters

An almost colorless liquid when freshly distilled, but soon acquiring a dark, reddish-brown color, and having a strong, tarry odor and taste. Sp. gr., about 0.970.

Solubility

Readily in Alcohol.

Action Of Tar

External

Tar has precisely the same action as oil of turpentine, but it is not so powerful, therefore the vascular dilatation rarely proceeds to the stage of vesication; but pustules may result if the tar is rubbed in.

Internal

It is very liable to upset digestion; in large doses it causes epigastric pain, vomiting, severe headache, dark urine, and other symptoms of carbolic acid poisoning (see p. 332). Some of its constituents are excreted by mucous membranes, especially the bronchial, on which it acts as a disinfectant, stimulating expectorant.

Therapeutics Of Tar

External

Tar ointment, which is sometimes rather hard, and may be softened by half the wax with almond oil, is often applied as a stimulant to chronic skin diseases, such as psoriasis and chronic eczema. Because of its mildly anaesthetic action, it is sometime? useful in pruritus.

Wood tar is the only official form of tar, but coal tar is often used in medicine. The prepared form of it is made by simply heating and stirring coal tar at 120o F. 48o C. for an hour. Liquor Picis Carbonis not official is a favorite preparation for many skin diseases. It may be made thus: Dissolve resin soap, 1 (see below) in alcohol, 8; add prepared coal tar, 4; digest at 125o F. 51o C for two days, allow it to cool, then decant and filter. An ointment of 3 parts of lard with 1 of this solution may be made. Liquor Carbonis Detergens not official is an alcoholic solution of ordinary coal tar. It is used externally in skin diseases, diluted in 20 parts of water.

Internal

Coal tar is rarely prescribed for internal use. Wood tar is only given as an expectorant, and it is very valuable for chronic bronchitis. It may be prescribed as a pill or as the syrup, or as Vinum Picis not official (a saturated solution of wood tar in sherry, dose 1 to 4 fl. dr. 4. to 15. c.c.), or as the French preparation, Eau de Goudron. Tar water is made by stirring wood tar with water 1 to 4 for fifteen minutes and decanting. The dose is a pint 480. c.c. daily. It may be used externally as a wash. The syrup with syrup of wild cherry (see p. 462) and apomorphine hydrochlorate 1/20 gr.; .003 gm., forms an excellent cough mixture.