Turpentine is a semi-solid resinous substance secreted by various coniferous trees. The name turpentine is commonly understood to mean the product of the Scotch pine, the swamp pine of America, and the Pinus maritima of France. Venice turpentine is obtained from the larch, and Chian turpentine from the 'Turpentine-tree' (see PISTACIA); but from a commercial point of view they are practically unused. The chief supplies of turpentine are obtained from America, and to a less extent from France. Cavities are cut through the bark and into the wood about one foot from the ground, and the bark hacked a little above. The exuded turpentine runs into these cavities, commencing to flow in May, and if the bark is hacked a little higher up every ten days a constant supply is obtained throughout the summer. In consequence of the necessity of injuring the bark at a higher and higher point, in the course of years the hacking takes place at a height of 12 to 15 feet, the tree remaining productive for about fifty years. The first year's yield is the purest, having the shortest distance to run down the trunk into the cavity; but afterwards a portion concretes as it passes down, and constitutes the common frankincense or gum thus of commerce. The turpentines are mixtures of resin and essential oil. The latter, amounting to from 15 to 30 per cent., consists chiefly of hydrocarbons having the chemical formula . When distilled along with water the oil of turpentine passes over, and the Resin (q.v.) or rosin remains behind.
Oil of Turpentine does not always possess the same properties. Its boiling-point ranges from 305° to 341° (152° to 172° C.), and the specific gravity from .856 to .870. Some samples rotate the plane of polarisation to the right, and others to the left. These variations are due to the presence of different isomeric compounds. Oil of turpentine, or turpentine as it is often called, is a powerful solvent of resins and oils, and is much employed in the manufacture of varnishes and oil paints. It is very inflammable, and unites with chlorine so energetically as to burst into flame when brought in contact. When air is passed through it it becomes powerfully antiseptic. Applied to the skin it acts as a local irritant, and is much employed in the treatment of rheumatism, &c. When agitated with sulphuric acid and allowed to separate it yields on distillation a fragrant liquid, terebene, which is much employed as an antiseptic and internally in the treatment of coughs.