Wood Tar

Wood tar, Pix liquida, is obtained from the dry distillation of wood, and depending on the raw material, several varieties of wood tar are distinguished. In medical practice, the following are used: 1. Pix liquida (Ph. VII)—pine tar, obtained from various conifers, mainly Pinus silvestris and Larix sibirica—dark brown, translucent in a thin layer, a viscous liquid, heavier than water, with a characteristic burnt smell, soluble in absolute alcohol, ether, chloroform, gasoline, fatty and essential oils. The main components of pine tar are various benzene derivatives: toluene, xylene, styrene, pyrogallol, pyrocatechol, phenol, and in addition naphthalene, acetic and other organic acids, with the larger part of oxybenzenes being present in the form of methyl and other complex esters. 2. Pix liquida Betulae (Ph. VII) s. Oleum Rusci s. Oleum Betulae empyreumaticum—birch tar—obtained from the distillation of bark and roots of various birches, similar in appearance and smell to pine tar, soluble in the same solvents; sp. gr. at 20°—0.920-0.945. The main components—guaiacol, cresol, xylenol, only traces of phenol and resin. 3. Oleum cadinum s. Oleum Juniperi empyreumaticum—juniper tar from Juniperus Oxycedrus—dark, yellow in a thin layer, a viscous liquid with a burnt smell and pungent aromatic taste; sp. gr.—0.990-1.050; soluble in ether, but soon precipitates in flakes, partially soluble in alcohol and chloroform, insoluble in water. The main components: resins, guaiacol, creosol, ethylguaiacol, propylguaiacol, homologs of acetic acid and hydrocarbons with boiling point 210-400°.—Identification. Pix liquida: 1) after vigorous shaking of the tar with water (1 + 10), a yellowish colored aqueous solution of acidic reaction is obtained; 2) this aqueous extract, diluted with an equal amount of water, turns dark green on the addition of a small amount of ferric chloride; 3) such an extract with an equal amount of lime water turns dark brown. Pix liquida Betulae: 1) after vigorous shaking for 5 min., 2 g of tar with 25 cm³ of water gives a filtrate that turns litmus paper red and rapidly reduces on cold the ammoniacal solution of silver nitrate; 2) 10 cm³ of the same filtrate with 3 drops of diluted ferric chloride (1+9) gives a solution from dark red to dark violet color; 3) 10 cm³ of the same filtrate with 10 drops of potassium dichromate solution gives a solution from dark yellow to dark red color, which soon becomes turbid and opaque. Oleum cadinum: 1) on distillation of 100 cm³ of tar at 300°, not less than 50 cm³ should distill over; 2) after vigorous shaking of 2 g of tar with 25 cm³ of water for 5 minutes, a filtrate from yellowish to dark yellow color is obtained, which turns litmus paper red and rapidly reduces on cold the ammoniacal solution of silver nitrate; 3) and 4)—the same reactions as 2 and 3 with Pix liquida Betulae. All the varieties of wood tar listed have similar pharmacological properties in their main parts, which are most strongly expressed in pine tar and weakest in the other two. These properties consist of disinfecting and local irritating, general toxic, as well as some keratolytic action. Both the irritating and general toxic action of wood tar is considerably weaker than that of similar pharmacologically active substances—carbolic acid and its homologs—due to the fact that the larger part of various oxybenzenes is present in wood tar in a bound state—in the form of complex esters. With careless use of wood tar, even externally, e.g., when applied for too long and on extensive areas of skin, it can cause poisoning of varying degrees, since it is absorbed not only by mucous membranes but also by the skin, similar to phenol. The consequences of poisoning may be: nausea, vomiting, diarrhea, headache, dizziness, unconsciousness, convulsions, and various kidney lesions—from transient irritation to severe nephritis. In this case, the urine is colored dark green.—Wood tar is used externally against pediculosis and in chronic skin diseases (psoriatic eczema, prurigo, psoriasis) in the form of ointment 1-5:10 with fat or vaseline, as well as per se by applying a thin layer to the skin with a brush; treatment of skin diseases with wood tar is applied repeatedly—every 3 days, until the skin returns to normal appearance. Wood tar is an ingredient in Wilkinson's ointment (scabies). The internal administration of wood tar, previously used for intestinal disinfection and as an expectorant, has almost been abandoned; even for external use nowadays, preparations of wood tar are more often used than wood tar itself. In large quantities, wood tar is used as a cheap disinfectant for pouring infectious excreta, cesspools, etc. A saturated aqueous solution of wood tar, or tar water—Aqua Picis, is used as an antiseptic for washings and for spraying and inhalation in bronchitis with abundant sputum, gangrene of the lungs; internally (rarely) by the tablespoon in chronic catarrhs of the respiratory tract and bronchitis. At present, tar is one of the means for producing experimental cancer.—Tar soap—Sapo Picis s. piceus—a former official preparation, a mixture of wood tar and potassium soap, has a dark brown color, uniform consistency and smell of tar. Preparations of wood tar: Emulgorium—a product of condensation of wood tar with formaldehyde—a dark gray powder, soluble in acetone and chloroform, a good substitute for wood tar, as it does not irritate the skin and is little toxic; in 5-10-20% ointments and pastes, 5-15% liniments or 1-5% solution in acetone.—Pittylen—a compound of wood tar with formaldehyde, an amorphous powder of dark yellow color, soluble (up to 10%) in alcohol, ether, chloroform, acetone, does not have an irritating property; externally as a powder, as well as in the form of a plaster, soap, mixture, mainly in chronic eczema.—Cadogel is obtained from Oleum cadinum, does not irritate the skin and is little toxic; in 10-30% ointments.—Kresophen—a preparation of pine tar with a pleasant smell, almost colorless, does not irritate the skin.—Pinosol—a preparation of pine tar, a syrup-like liquid of dark yellow color, easily soluble in most organic solvents, mixes with fats and oils, gives with weakly alkaline water a stable emulsion.—Valpasid—a preparation of pine tar, a dark brown liquid of acidic reaction, used for preparing slightly acidic tar baths (100-200 cm³ for general and 20-50 cm³ for local bath), as well as for preparing soaps, plasters, etc.—Fagacid—a similar preparation to the previous one, soluble in caustic alkalis, used for preparing alkaline tar baths.—Pixavon—a preparation of potassium soap and Pittylen, a liquid odorless soap for disinfection and cleansing of hairy parts of the head.—Inosol—a preparation of pine tar against mange in horses. Coal tar, see Coal.