Pix Liquida (U. S. P.)—Tar.

Preparations: Tar Water - Tar Ointment - Plasma of Tar - Compound Tar Plaster - Oil of Tar - Syrup of Tar - Glycerite of Tar - Alkaline Solution of Tar - Wine of Tar
Related entry: Oleum Pini Sylvestris.—Fir-Leaf Oil - Resina (U. S. P.)—Resin - Oleum Terebinthinae (U. S. P.)—Oil of Turpentine - Oleum Terebinthinae Rectificatum (U. S. P.)—Rectified Oil of Turpentine - Terebinthina Canadensis (U. S. P.)—Canada Turpentine - Terebinthina (U. S. P.)—Turpentins

"An empyreumatic oleoresin obtained by the destructive distillation of the wood of Pinus palustris, Miller, and of other species of Pinus (Nat. Ord.—Coniferae)—(U. S. P.).
SYNONYM: Resina empyreumatica liquida.

Source and Preparation.—The trees generally employed in producing tar are, besides the above-named Pinus palustris, Miller, the American species, Pinus rigida, Miller, Pinus Taeda, Linné;and also the European species, Pinus sylvestris, Linné;and Larix sibirica, Ledebour (see Terebinthina). Tar is made in several northern countries of Europe (e. g., Stockholm tar), and in the United States, especially in North Carolina and Virginia, from the waste of pine or fir timber; it is usually prepared by making a conical cavity in the earth, communicating at the bottom with a reservoir. Logs or billets of wood are then placed, so as not only to fill the cavity, but to form a conical pile over it, which is covered with turf or earth, and kindled at the top. The admission of air is so regulated, that the wood burns from above downward, with a slow and smothered combustion. The wood itself is reduced to charcoal, and the smoke and vapors formed are obliged to descend into the excavation in the ground, where they are condensed, and pass along with the liquefied matters into the receivers. This mixture is termed tar, Pix liquida. By long boiling or distillation in retorts, tar is deprived of its volatile ingredients (Oil of Tar; see Oleum Picis Liquidae), and converted into pitch, Resina nigra, or Pix nigra.

Description and Chemical Composition.—The U. S. P. describes tar as "thick, viscid, semifluid, blackish-brown, heavier than water, transparent in thin layers, becoming granular and opaque with age; odor empyreumatic, terebintbinate; taste sharp, empyreumatic. Tar is slightly soluble in water, soluble in alcohol, fixed or volatile oils, and solution of potassium or sodium hydrate. Water agitated with tar acquires a pale yellowish-brown color and an acid reaction, yields with ferric chloride T.S. a transient green color, and is colored brownish-red by an equal volume of calcium hydrate T.S."—(U. S. P.). Upon prolonged standing, tar becomes granular from the deposition of pyrocatechin. Tar is a very complex substance and varies in composition according to the method of preparation and the kind of wood employed. The tar from leaf-trees, e. g., the beech, is rich in phenols (see Creosotum) while pine-wood tar contains more resinous matters. Pine-wood tar also differs from beech-wood tar in being miscible with melted lard. Coal tar differs from wood tar principally in containing more basic substances, such as aniline and quinoline, while wood, upon dry distillation, yields more acid products, e. g., pyroligneous acid. (For constituents of wood tar, see Arctic Acid and Creosotum.)

Action, Medical Uses, and Dosage.—Tar is stimulant, diuretic and diaphoretic. It has been advantageously used in chronic coughs, chronic bronchial and laryngeal affections; the inhalation of its vapor acts as a stimulant and irritant to the bronchial mucous membrane, promoting its secretion, but is seldom used. It is chiefly used externally as a local application to some cutaneous affections, as porrigo, tinea capitis, lepra, psoriasis, prurigo, eczema, and herpes circinatus. Excellent results sometimes follow its employment in suppurating burns, excoriations, furuncles, cracked nipples, and piles. Oakum, a dressing sometimes impregnated with tar forms a good antiseptic absorbent for pus-bathed surfaces, and also to obstinate ulcers. It is an excellent antipruritic and that is its specific use. A tar-water has been recommended in cough and bronchial affections, and to prevent the reproduction of boils. It is prepared as follows: To ½ gallon of boiling water, add 1 pint of tar and 1 pint of honey; stir the mixture, and when cold strain off the liquid. It is stimulant and diuretic, and may be taken 3 or 4 times a day, in doses of a wineglassful. It will also be found beneficial as a wash in some forms of cutaneous disease. B. J. Crew recommends the following: Rub 2 drachms of oil of tar with 40 grains of carbonate of magnesium, add a portion of 14 ounces of water, mix well, and then add the balance, filter, and add simple syrup, 2 ounces. The dose is a small wineglassful, 3 times a day (Amer. Jour. Pharm., Vol. XXVII, p. 13). (See also Aqua Picis.) M. Adrian gives the following formula for a glycerinated tar, which has the consistence of an ointment, and the advantage of being soluble in water, and of not adhering to the skin: Take of tar, 15 parts; glycerin, 15 parts; water, 30 parts. Mix. The French employ emulsions, syrups, wine, and concentrated alkaline solutions of tar, which, however, have not been introduced into the medical practice of this country. Internally the dose of tar is from 30 to 60 grains, 3 or 4 times a day, or even oftener, but it is commonly used in the form of tar-water, 1 pint of which may be taken in a day.

Specific Indications and Uses.—Locally to itching surfaces.

Related Product.—PIX NAVALIS, Pix nigra, Resina nigra, Pix solida, Resina pini empyreumatica; Pitch, or Black pitch. This substance is obtained by evaporating or distilling off the more volatile constituents of wood tar; in the second case, oil of tar (see Oleum Picis Liquidae) distills over and pitch remains as residue. It is a black, firm substance, having a faint, tarry odor, a brilliant fracture, softening by the warmth of the hand, melting in boiling water. It is soluble in alcohol, and in alkaline solutions, and consists of empyreumatic resin and colophony (rosin).

Pix nigra has been used internally in ichthyosis, and certain obstinate diseases of the skin; its dose is from 10 to 60 grains, and may be made into pills with flour or other farinaceous substance. Pereira says it may be taken to a great extent, not only without injury, but with advantage to the general health. In piles it has been used with great advantage in the form of the following ointment: Take of pitch, wax, resin, each, 10 ounces; olive oil, 1 pint. Melt them together, and express through linen, and when nearly cool, stir in four ounces of Scotch snuff.

King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.