Volatile oils are numerous in the vegetable kind dom. They are so called on account of the ready manner in which they may be volatilized under the influence of heat. The facility with which they are diffused in the atmosphere renders them easy of detection, and it is to this class of sub stances that plants owe their peculiar odours. Many of them are employed in perfumery, others are used as stimulants in medicine, and some are poisonous. Many natural orders of plants are characterized by yielding volatile oils. Thus the Lamiacem, Myrtacem, and others, embrace species all of which contain volatile oil in their leaves. Many of the limbelliferat yield a volatile oil in their fruits. The petals are often the seat of these secretions, ai especially those most prized, as the rose, the jasmine, the heliotrope, and many others. Many of the essential or volatile oils employed in medical practice are almost all powerful stimu lants and carminatives. They are chiefly obtained from species of amomum, amygdalus, anethum, andropogon, anthemis, carum, caryophyllus, dryo balanops, eugenia, foeniculum, illicium, juniperus, laurus, lavandula, melaleuca, mentha, moringa, myristica, ocimum, origanum, pimpinella, piper, rosmarinus, ruts, and sassafras.
The essential oils are obtained from various parts of the odoriferous plants, chiefly by dis tillation, but also by the chemical perfuming process of enflowering, as also by infusion. The best .known in commerce are the oils of almonds, aniseed, bergamot, cajaputi, camomile, camphor, caraway, cassia, cinnamon, cloves, juniper, laven der, lemons, mint, nutmeg, orange, peppermint, pimento, rhodium, rosemary, roses (otto), ravine, sassafras.
Scented oils, erroneously termed volatile,' obtained by the repeated distillation of fragrant herbs, etc., over into a receiver containing a portion of any fixed oil, to which the aroma is imparted, are prepared to some extent in the E. Indies, but chiefly for native use. Sandal-wood oil and the large varieties of atr, attar, or otto, etc., which form the principal part of native perfumery, arc included in this class. The atrs of India contain the essential oils of the plants and substances sufficient to produce a perfume which is perfectly overpowering, even producing headache. The natives of British India have the phrase in their language, dimagh mu'attar hona,' to be stupefied with fragrance. These atrs are principally made in Hindustan. Sandal-wood, jasmine, nutmegs, indeed, every odoriferous plant is by the perfumers (attars) made to yield an essential oil.
In the process of enflowering, layers of flowers, four inches thick and two inches square, are laid on the ground and covered over with 'equal layers of sesamum or any other oil-yielding seed, over which a second layer of flowers like the first is placed. The seed is wetted with water, and the
whole mass covered with a sheet held down at the ends and sides by weights, and allowed to remain for eighteen hours in this form. It is now fit for the mill, unless the perfume is desired to be very strong, when the faded flowers are removed, and fresh ones put in their place. The seeds thus impregnated are ground in the usual way in the Kolhoo or mill, and the oil expressed has the scent of the flower. At Ghazipur, the jasmines are chiefly employed ; the oil is kept in leathern bottles or dubbers, and sold for about Rs. 2 a seer. The newest oils afford the finest perfumes. In Europe, a fixed oil, usually that of the ben or moringa nut, is employed for enflower ing. Cotton is soaked in this and laid over layers of flowers, the oil being squeezed out so soon as impregnated with perfume.
Mineral oils are obtained in Turkish Arabia, Batku, N. Persia, Northern India, China, Burma. From the oil pits of Burma the Burmese Govern ment used to obtain 93,000 tons annually, the oil on the spot fetching about a shilling per cwt. Chemically treated, it supplies half-a-dozen of products of the greatest beauty, several being oils, one a hard wax of snowy whiteness, and one a rich perfume. In several places in the Jhelum district along the Salt Range, at Kafir Kot, at Jabba in the Shahpur district, and in very small quantities at Shah-ka-Nurpur, in the Rawal Pindi district, a petroleum exudes out of the rocky soil, but efforts to utilize it in a commercial point of view failed, chiefly owing to the enormous cost of carriage, and to the difficulty of retaining the substance itself with any other vessels than those made of tin or glass. Price and Co., of London, reported favourably upon it, and asked for some tons of it for further experiments. Their appli cation could not be complied with to the extent of the requisition, not more than eight maunds a day being obtainable, and the yield of oil being greater in the hot than in the cold weather. Wood smeared with mineral oil is effectually preserved from the ravages of white ants. The oil burns with a bright flame, but the smoke is insufferable. The natives call it Gandak-ka-tel, and use it only for burning in their lamps. The Jabba spring is the most extensive.
Animal oils are in frequent use amongst the people of India as medicinal substances, for ex ternal application, such as that from the pea-fowls' fat, from the neats' foot, the crocodile, and the iguana; also the oils from the sharks, the rays, and the cod-fish, and spermaceti and its oil.