The oil is frequently adulterated with tincture of nutmeg prepared with absolute alcohol. Such an adulteration, as well as any content of alcohol, is recognized by shaking 0.5 cubic centimeter of the oil with a grain of rosaniline. In the presence of alcohol the oil acquires a red coloration, while pure oil remains uncolored. From the nutmegs, the seed of _Myristica fragrans_, freed from the seed-coat and aril, a volatile oil (_oleum nucistæ æthereum_) is also obtained by distillation. It is generally yellowish, seldom colorless, somewhat thickly-fluid and has the odor and taste of nutmegs. It is readily soluble in alcohol and ether and of specific gravity, 0.93 to 0.95. It consists of two oils, one specifically lighter and fluid, and the other heavy and crystalline. On standing it deposits a stearoptene, called myristicin. The nutmeg oils are but seldom used in perfumery. _Opopanax oil_ is obtained from opopanax.[7] It is of gold-yellow color and an agreeable balsamic odor reminding one somewhat of myrrh. Its specific gravity is 0.9016, and it boils between 392° and 572° F. [7] See later on under "Balsams and Resins." On account of its strength, the oil must be very carefully handled in perfuming, but if used in the correct proportion it is very advantageous. _Orange-peel oil_, also called _Portugal oil_ or _essence of Portugal_, is obtained in Italy from the fresh peels of the orange, the fruit of _Citrus vulgaris, Risso_. It is prepared in a manner similar to that of oil of lemons (which see). In commerce a distinction is made between the Messina oil, which is of inferior quality, and the Calabria oil, which is of a better quality. The Messina oil has a yellow color, frequently not much darker than that of oil of lemons, while the color of Calabria oil is dark yellow, nearly brown. The oil prepared from the peels of the bitter orange (_Citrus bigaradia, Duhamel_), is of the same color as the sweet Messina oil. It is more used in the preparation of liqueurs than for perfuming. Orange-peel oils are limpid and have a specific gravity of 0.819 to 0.9. One part of orange-peel oil should, according to its age, dissolve clear in 5 to 10 parts of 90 per cent. alcohol. Very similar to orange-peel oil, though differing somewhat in odor, is the _mandarin oil_ obtained from the fresh peels of the mandarin orange, the fruit of _Citrus sinensis_. It is brought into commerce from Reggio and is said to form a constituent of the genuine _ess-bouquet_. It has a specific gravity of 0.852 at 50° F. and is dextrorotatory. While from the peels the volatile oil is but seldom obtained by distillation, this process is exclusively used for gaining volatile oils from the flowers, leaves, and young branches. In this connection two kinds of volatile oil have chiefly to be considered, viz: _orange-flower oil_ and _petit-grain oil_.