Turpentine oil may be considered as the adulterant most often used. Very often it can be recognized by its characteristic odor, especially in those oils which contain no pinene, as this is the main constituent of turpentine oil. In general, its presence causes changes in the specific gravity, solubility, boiling temperature and optical rotation. It must here be remembered that there are dextro- as well as lasvogyrate turpentine oils.

The positive proof of the presence of turpentine oil in oils, which in their pure state contain no pinene, is furnished by the isolation of and characteristic derivates of pinene. The constituents boiling in the neighborhood of 160°, are fractionated out and, according to the method described on page 296, the pinene nitrosochloride, as well as pinene nitrolbenzylamine or pinene nitrolpiperidine are prepared. If the fraction is strongly optically active, it is better to identify the pinene by oxidation to pinonic acid (see p. 297), for the yield of pinene nitrosochloride decreases as the optical activity of pinene increases.

If pinene is a normal constituent of the oil, the addition of turpentine oil can be recognized by a comparison of the physical properties of the lowest boiling fractions of the adulterated oil with the corresponding portions of the pure oil. The detection of turpentine oil in rosemary oil furnishes an example (see this).