Tar, Wood Tar or Stockholm Tar, is obtained by the destructive distillation of the wood of the Scotch fir, Pinus sylvestris, Linn. (N.O. Coniferae), and other species of Pinus. It is also official in the U.S.P. It occurs as a dark brown or blackish, semi-liquid, bituminous substance, having a strong, peculiar, empyreumatic, terebinthinate, and aromatic odour, and a bitter, pungent, empyreumatic taste. Specific gravity, 1.020 to 1.150. In thin layers it is transparent if free from water. On keeping for some time, it separates into an under layer of granular character, due to minute crystallisation of pyrocatechin, resin acids, etc., and a surface layer of a syrupy consistence. On shaking with water and filtering, the filtrate is acid (distinction from coal tar, which is alkaline), and is coloured red by very dilute solution of ferric chloride (distinction from birch tar, which shows a greenish colouration); with lime water, it acquires a brownish-red colour. A petroleum ether extract shaken with a diluted solution of cupric acetate (1 in 1000) acquires a greenish colour (distinction from beech tar).
Almost insoluble in water, but the latter on agitation with it acquires a pale yellow or brownish colour, the sharp characteristic odour and taste of the tar, and an acid reaction due chiefly to the presence of acetic acid. Soluble in less than its own bulk of alcohol or chloroform, also in ether; in 4 per cent. solution of sodium or potassium hydroxide (1 in 3); slightly soluble in fixed or volatile oils; completely soluble in acetic acid of 95 per cent. strength (distinction from all other tars but that of beech).
Constituents.—Tar from wood is a very complex body, its composition varying with the kind of wood and method of preparation. The chief constituents are pyrocatechol, phenol, guaiacol, cresol, creosol, methyl-creosol, phlorol, toluene, xylene, naphthalene, and other hydrocarbons. The non-volatile portion is the pitch, a black, resinous, brittle mass, which may be softened by the heat of the hand, and has the odour of tar.
Action and Uses.—Tar is given internally as a disinfectant expectorant in chronic bronchitis and winter cough, and to allay cough in phthisis. It is also mixed with hot water, and the vapour inhaled for the same purposes. Externally, tar is a stimulating antiseptic, and is employed in chronic, scaly skin diseases, especially in psoriasis and eczema. Its action in allaying pruritus is not so marked as that of coal tar. Tar is administered enclosed in gelatin capsules containing 30 centigrams (5 grains) in each; or it may be made into a pill with a mixture of soap and powdered liquorice, but a large quantity of absorbent powder is required, so that the pills are somewhat bulky. It is used also as Aqua Picis, and as Syrupus Picis Liquidae; the latter is often given with syrup of codeine, and the mixture is extremely useful in allaying cough. For external use, Unguentum Picis is employed; this may be reduced in strength, or softened if required, by the addition of olive oil or lard. Tar may be used both externally and internally as Oleum Picis Liquidae.
Dose.—1 to 6 decigrams (2 to 10 grains).
- Aqua Picis, B.P.C.—TAR WATER.
- Used as a mild antiseptic and expectorant in bronchitis and chronic cough. Dose.—1/2 litre (18 fluid ounces), or more, daily.
- Carbasus Styptica, B.P.C.—STYPTIC GAUZE. Syn.—Tarred Gauze. 5 per cent. (approximately).
- Liquor Picis Ligni, B.P.C.—SOLUTION OF WOOD TAR. 1 in 20.
- Diluted with water (1 in 8 to 1 in 20) for use as a lotion in skin affections.
- Parogenum Picis, B.P.C.—TAR PAROGEN. Syn.—Tar Vasoliment. 1 in 4.
- This preparation is used as an antiseptic in psoriasis, eczema, and chronic skin diseases, in place of tar ointment.
- Stupa Styptica, B.P.C.—STYPTIC TOW. Syn.—Tarred Tow. 10 per cent. (approximately).
- Syrupus Picis Liquidae, B.P.C. and U.S.P.—SYRUP OF TAR.
- Tar, 0.5; alcohol, 5.25; magnesium carbonate, 1; sugar, 85; distilled water, to 100. Mildly antiseptic, and is used as a disinfectant expectorant in chronic cough, phthisis, and bronchitis. Dose.—4 to 8 mils (1 to 2 fluid drachms).
- Syrupus Picis Liquidae, C.F.—SYRUP OF TAR.
- Tar, by weight, 7.5; white sand, 10; glycerin, 10; sugar, 80; water to 100.
- Syrup Picis cum Codeina, B.P.C.—SYRUP OF TAR WITH CODEINE.
- Codeine, 0.1; alcohol (60 per cent.), 5; syrup of tar, to 100. Used for cough in chronic bronchitis and phthisis. Dose.—2 to 8 mils (1/2 to 2 fluid drachms).
- Unguentum Picis Liquidae, B.P.—TAR OINTMENT.
- Tar, 5; yellow beeswax, 2. Add the tar to the beeswax, previously melted at a low temperature, and stir until cold. Tar ointment is applied to relieve pruritus and as an antiseptic in eczema and psoriasis.
- Unguentum Picis Liquidae, U.S.P.—TAR OINTMENT, U.S.P.
- Tar, 50; yellow beeswax, 15; lard, 35.
- Unguentum Picis Molle, B.P.C.—SOFT TAR OINTMENT,
- Tar, 71.43; arachis oil, by weight, 14.28; beeswax, 14.28 This ointment is used similarly to Unguentum Picis Liquidae.
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.