1. The pure hydrocarbons are for the most part fluid, and have a lower specific gravity, a lower boiling point, and a higher refractive power than the oxygenous oils. They absorb oxygen, and are converted into oxygenons oils and resins. They may be sepa rated from oxygenous oils, with which they are usually associated, by fractional distilla tion. They include oil of turpentine and the oils of bergamot, birch, chamo mile, caraway, cloves. elemi, hop, juniper, lemons, orange, parsley, savine, and valerian, most or all of which contain the same hydrocarbon as nil of turpentine (q.v.), and in addition to it an oxidized compound; oil of copaiva (020II14), attar of roses etc.
2. The oxygenous essential oils may be either fluid or solid, the latter being also termed camphors. A. stearopten separates from most of the fluid oils on cooling. They are more soluble in water and spirit of wine than the pure hydrocarbons. They may be divided into (1) those which are fluid at ordinary temperature, such as those of anise-seed, chamomile,* cajeput, caraway,* cinnamon, cloves,* fennel, lavender, peppermint, rue, spines, thyme,* winter-green, etc. Those marked with a (*) are associated with the pure hydrocarbons already described. (2) The camphors, such as ordinary camphor (Cs.Flisb,), Borneo camphor etc.
3. The salpharons essential oils am chiefly obtained from the crucifcro3. They proba bly all contain the radical allyl The oils of garlic and of mustard (both of which have been described in special articles), and those of horse-radish, scurvy-grass, and asa foetida, are the best illustrative of this division 4. Among the essential oils obtained by fermentation. dry distillation, etc., may be mentioned the oils of bitter almonds and of black mustard, the oils of milfoil, plantain, centaury. etc. (whose leaves have no smell until they have been moistened for some time with water, when a kind of fermentation is set up, and oil is yielded in abundance), fur furamide (q.v.), etc. • The British pharmacopoeia contains the essential oils of anise, cajeput, caraway, chamomile, cinnamon, cloveS, copaiva, coriander, cubebs, dill, juniper, lavender, lemon, nutmeg, peppermint, pimento, rosemary, rue, savine, spearmint, and turpentine. Of these the oils of anise, cajeput, caraway, chamomile, coriander, dill, peppermint, pimento, and spearmint are used as stimulants and antispasmodics in cases of tiatiikame, griping, etc.; and to disguise the nauseous taste of various medicines. The oils of cajeput, cinnamon, and rue act similarly but more powerfully. The oils of eopa iva and cubebs act in the same manner as the substances from which they are derived; oil of juniper is a powerful diuretic, and oil of savine (and to a less extent oil of rue) an einmenagogue. The oils of lavender and lemon are used to conceal the smell of sulphur ointment, and to give an agreeable odor to lotions, etc. The oil of rosemary is chiefly employed as a stimulating liniment, especially in cases of baldness; and the oil of nut meg is seldom given medicinally except in the form of aromatic spirit of ammonia, into the composition of which it enters.
A very admirable paper on the essential oils was read Dr. Gladstone before the chem ical society, in the mouth of Dec., 1863; and thereader who is anxious to pursue the sub ject further will find it advantageous to refer to this excellent production.
Bland oils—such, for example, as olive-oil—were much used by the ancients as exter nal applications in various forms of disease. Celsus repeatedly speaks of the use of oil
applied externally with friction in fevers, and in various other diseases. Pliny says that olive-oil warms the body and at the same time cools the head, and that it was used with these objects previously to taking cold baths. Aretteus recommends a sitz-bath of oil in cases of renal calculi, and Josephus relates that a similar mode of treatment was employed in the case of Herod. Galen prescribed "oil and wine" for wounds in the head; and the parable of the good Samaritan affords additional evidence that this was a common mode of treating wounds. The use of oil preparatory to athletic exercises is referred to by numerous Greek and Latin writers.
As a cosmetic—that is to say, as a means of giving to the skin and hair a smooth and graceful appearance—its use has been prevalent in hot climates from the earliest times. There is abundant historical evidence of this usage of oil amongst the Egyptians, the Jews, the Greeks, and the Romans; and Pliny's statement that butter is used by the negroes, and the lower class of Arabs, for the purpose of anointing, is confirmed by the i observation of all recent African travelers. In hot climates there is doubtless a practi cal as well as an aesthetic object in anointing. The oil, being a bad conductor of heat, affords a certain amount of protection against the direct action of the solar heat; it is likewise serviceable as a protection against the. attacks of insects, and as a means of check ing excessive perspiration. The fact of oily and fatty matters being had conductors of heat, serves also to explain why the Esquimaux and other dwellers in Arctic regions have recourse to the inunction of the blubber, etc. In their case the oily investment serves to prevent the escape of the bodily heat.
The Greeks and Romans not only employed oil for the purposes already mentioned, but in their funereal rites: the bodies of their dead being anointed with oil, with the view probably of postponing incipient decomposition. A similar practice existed amongst the Jews, and in the Gospels we find various passages in which our Lord referred to his own body being anointed by anticipation. It appears from the evidence of St. Chrysostom, and other writers, that this ancient usage of anointing the bodies of the dead was long retained in the Christian church. See UNCTION: EXTREME UNCTION.
In conclusion we may remark that the ancient anointing as a means of medical treatment, has to a certain extent been revived in modern dines. Many physi cians of the present day combine the inunction of cod-liver oil with its internal adminis tration, a combination first recommended by professor Simpson cf Edinburgh; and sir Henry Holltind advocates the practice of anointing the harsh, dry skin of dyspeptic patients with warm oils. There can, we think. be little doubt that there are many forms of disease in which the local application of medicinal oils would prove advantageous; but the great drawback to their use is that the time required for properly rubbing them into the skin is more than most patients are willing to concede. For much curious information on the subject of this article, the reader is referred to a very interesting paper•by Mr. Hunter, " On the External Application of Oils," in the second volume of'771e Edinburgh Medical and Surgical Journal.