On account of their cheapness and faint odor, these three oils belong to the most favored and the most dangerous of adulterants. They may, however, be detected without difficulty in most cases by means of their physical properties, which differ from those of many of the volatile oils, namely their difficult solubility in 70 to 90 percent or even stronger alcohol, their high specific gravity (above 0,900), their high boiling temperature, above 250°, and finally their rotatory power.
All three oils turn the plane of polarized light more or less to the left. With copaiba balsam oil the [angle of rotation aD lies between - 7 and - 35°/) with cedar wood oil between - 25 and - 44°, and with gurjun balsam oil between - 35 and - 130°(!).
At present only cedar wood oil and copaiba balsam oil can be detected in a chemical way. For this purpose the oil is subjected to fractional distillation and the fraction that passes over at about 260° examined. The cedrene contained in cedar wood oil can be oxidized in acetone solution with potassium permanganate to a glycol C16H2602 which melts at 160°, whereas caryophyllene can be characterized by means of its hydrate (m. p. 94 to 96, see p. 333 and 334). For the detection of gurjun balsam oil the observation of Deussen and Philipp2) can possibly be utilized. If oxidized in acetone solution with potassium permanganate, the indifferent components yield a fraction 170 to 180° under 12 mm. pressure, which in turn yields a semicarbazone, C16H27N30, that melts at 234°.