In the Penang market two kinds of oil, one _green_ and the other _gold-brown_, are distinguished. Though both are sold at the same price, there is a greater demand for the green oil. According to the statements of the distillers, the brown oil is derived from the leaves of old plants and the green oil from the leaves of young plants. It would seem, however, that the color is dependent on the soil upon which the plants are grown, as well as upon atmospheric influences. When ruku is distilled with patchouli leaves, the oil is yellow and thickly-fluid. In Germany, the oil is now distilled from imported leaves. It is thickly-fluid, of a brown color, and, in an undiluted state, possesses a disagreeable, almost musty odor. However, when sufficiently diluted and suitably mixed with other volatile oils, the odor is far more agreeable, and for this reason it has for some time played an important part in the manufacture of perfumery. It has the advantage of being very yielding and lasting, but, on the other hand, possesses the disadvantage of not combining with other perfumes, so that its odor is always perceptible. It should always be used in very small quantities or much diluted. In commerce Penang oil and French oil are distinguished, the first having a specific gravity of 0.959 and the latter of 1.012. When kept for any length of time the oil deposits patchouli-camphor (C_{15}H_{28}O) in prismatic crystals of 1.045 specific gravity and melting at 127 to 129° F. These crystals have a peculiar, very lasting odor. Patchouli oil is soluble in equal parts of 90 per cent. alcohol, the contrary indicating that it is not pure. It is chiefly adulterated with cedar oil. _Peppermint oil._--The _Mentha_ family furnishes commerce with three oils differing essentially from each other--_oil of curled mint_, _peppermint oil_, _and poley oil_. _Oil of curled mint_ (_oleum menthæ crispæ_) is separated by distillation with water from the leaves of _Mentha crispa, Linn._ It is limpid, yellowish, sometimes greenish; in time it becomes darker and more thickly-fluid. Its specific gravity varies between 0.890 and 0.965. It has a strong odor of curled mint and a pungent, somewhat cooling, slightly bitterish taste. It is soluble in all proportions in 90 per cent. alcohol. In commerce a distinction is made between German and American oil of curled mint, the latter generally containing oil of turpentine and oil of sassafras. Odor, taste, and the alcohol test suffice for the determination of the quality of the oil. Oil of curled mint contains a terpene, C_{10}H_{16}, and a body isomeric with carvol, the carvol of curled mint, C_{10}H_{14}O. Its specific gravity, boiling point and chemical properties are the same as those of the carvol of caraway oil, but it differs from it by its odor and turning the plane of polarization to the opposite direction. In conjunction with other volatile oils, oil of curley mint is sometimes used for perfuming soaps.