In treating this subject it is necessary to limit it within comparatively narrow bounds, for bodies of the turpentine class are exceedingly numerous and not well understood.  In this definite class turpentine means the exudation from various trees of the natural order Coniferae, consisting of a hydrocarbon, C10 H16, and a resin.  The constitution of the hydrocarbons in turpentine from different sources, though identical chemically, varies physically, the boiling point ranging from 156 deg.  C. to 163 deg.  C., the density from 0.855 to 0.880, and the action on polarized light from -40.3 to +21.5.  They are very unstable bodies in their molecular constitution, heat, sulphuric acid, and other reagents modifying their properties.  The resins are also very variable bodies formed probably by oxidation of the hydrocarbons, and as this oxidation is more or less complete, mixtures are formed very difficult to separate and study.

Turpentine as met with in commerce is mainly derived from Pinus maritima, yielding French turpentine, and Pinus australis, furnishing most of the American turpentine.  The latter is obtained from North and South Carolina, Georgia and Alabama.  In Hanbury and Fluckiger’s Pharmacographia there is a full description of the manner in which the trees are wounded to obtain the turpentine.  Besides these there are Venice turpentine from the larch, Pinus Larix, Strassburg turpentine from Abies pectinata, and Canada balsam from Pinus balsamea.

The crude American turpentine is a viscid liquid of about the consistence of honey, but varying to a soft solid, known as gum, thus, according to the amount of exposure which it has undergone, it contains about 10 to 25 per cent. of “spirits,” to which the name of turpentine is commonly given, the rest being resin, or as it is usually called, rosin.

In Liverpool almost all the spirits of turpentine comes from America, so that it is almost impossible to get a sample of French.

The terpene from American turpentine is called austraterebenthene.  It possesses dextro-rotatory polarization of +21.5.  Its density is 0.864.  Boiling point 156 deg.  C.

In taking the boiling point of a commercial sample of spirits it is necessary to wait until the thermometer becomes steady.  Not more than 5 per cent. should pass over before this takes place, and then there is not more than two or three degrees of rise until almost all is distilled over.

The liquids of lower boiling point do not appear to have been much studied.  In French spirits they seem to be of the same composition as the main product, but with more action on polarized light.

French spirits of turpentine is mainly composed of terebenthene.  The boiling point and sp. gr. are the same as those of the austraterebenthene, but the polarization is left handed and amounts to -40.5.

Isomeric modifications.  Heated to 300 deg.  C. in a sealed tube for two hours, it becomes an isomeric compound, boiling at 175 deg.  C., while the density is lowered, being only 0.8586 at 0 deg.  C. The rotatory power is only -9 deg..  It oxidizes much more rapidly.  It is called isoterebenthene and has a smell of essential oil of lemons.