Oleo-Pine Application

The simple application of either of the above methods produces a dark-coloured resin, owing to the great difficulty in removing suspended foreign matter from the molten resin, which is very viscid. Consequently it is usual to subject the oleo-resin to a preliminary process of purification before it is distilled; it is first warmed to render it fluid, then allowed to form a sediment, and finally filtered under pressure. Centrifugal machines have also been devised for the purpose.

The volatile oil produced is oil of turpentine, and the resin is known variously as colophony, colophony resin, resin, or rosin. The oil contains traces of resin mechanically carried over during distillation, which although unobjectionable in ordinary use must be removed from oil intended for medicinal use. This is effected by re-distillation with water and potassium carbonate, and the fluid product constitutes the official Oil of Turpentine.

Constituents:
Pinene, the dextro- and laevo- forms-'in American oil, and chiefly the few-form in French oil. Camphene, and traces of resin acids and other oxidation products such as camphoric aldehyde (giving the characteristic odour of old oil of turpentine) are also present.

Adulteration:
Oil of Turpentine is commonly adulterated with a fraction of petroleum spirit which boils over the same range. Oil of Turpentine absorbs a large proportion of iodine whereas petroleum spirit absorbs very little. The determination of the iodine value forms therefore an important means of detecting adulteration with petroleum spirit. Special conditions are prescribed for the determination to prevent loss of oil of turpentine by volatilization. Other reported adulterants are :

1. a product of destructive distillation of colophony; it causes the oil to leave a permanent stain on paper.
2. wood turpentine, obtained by distillation from the roots and stumps of various species of Pinus; it has a higher weight per ml. and a lower iodine value than oil of turpentine.

    

Terebene :
This is prepared from oil of turpentine by shaking the oil (usually mixed with a small proportion of alcohol) with small successive portions of sulphuric acid, separating and rejecting the non-oily liquid and distilling the oily liquid in a current of steam. The optical rotation of terebene is + 2 to - 2. Terebene consists chiefly of dipentene, an optically-inactive form of limonene, produced by the action of the sulphuric acid on the pinene present in oil of turpentine.

OILS CONTAINING OXYGENATED CONSTITUENTS.
In this class the medicinal properties and odour are due to substances containing oxygen in combination with carbon and hydrogen. Most volatile oils belong to this class, and for description they will be classified according to the chemical nature of the principal oxygenated compound present.