This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Adulteration by common volatile oils is more difficult of detection. It consists in mixing with certain volatile oils the more common and cheaper oils, such as the rectified oil of turpentine, lavender, rosemary, etc. This adulteration, before which all the tests of chemistry have failed, can be detected only by comparison with an oil of unquestionable purity. It is to be observed, however, that, by saturating a piece of cloth or paper with this sort of mixed oils, the more volatile oil is first dissipated, and that whose odor is most enduring is evaporated last, and may thus be distinguished, that of turpentine easiest of all.
The adulterations of oil of rose with oil of rose-geranium, oil of peppermint with oil of erigeron, and oil of origanum with oil of turpentine, etc., are more difficult to detect, and each individual case requires special treatment. In the case of the oil of rose, the sophistication may be detected by the higher congealing point of the otto. The presence of oil of erigeron in oil of peppermint is shown by its changing to an orange red color, when treated with a strong solution of potassa, while the presence of turpentine in almost any essential oil may be discovered -when the nasal faculties are well cultivated - by taking a long, steady smell of the suspected oil, or rubbing a sample between the hands, or lighting some and blowing out the flame after a while. In both cases turpentine, if present in the oil, would be perceptible.
In smelling essential oils and extracts, one should avoid trying the odors of various materials in succession, for if this is done only one odor will finally be distinguished, into which all the others will blend. It is best to make the tests in the open air, and not in rooms filled with other odors. Under the respective headings of the various oils we will append the proper directions for their special treatment in detecting adultera-tions, and give the tests that are known in chemistry.