Essential Oils; Volatile Oils. The essential or volatile oils are an extensive and important class of bodies derived from the vegetable kingdom, and found in almost every part of the larger number of the plants which produce them, except the cotyledons of the seeds, which, in general, form the exclusive repository of the fixed oils. It is the volatile oils which confer upon flowers, leaves, fruit, seeds, roots, barks, and woods, their peculiar and characteristic odors; but among these they are not equally distributed in the same individual, and are often altogether absent from some of them. To them we are indebted for our most delightful perfumes, and our choicest aromatics and spices. All of them, when perfectly pure, are colorless; though, before rectification, nearly the whole of them have a pale yellow tint, and some of them are brown, blue, or green. They mix in all proportions with the fixed oils, dissolve freely in both alcohol and ether, and are sparingly soluble in water, forming perfumed or medicated waters. (See Nos. 1080 (To Prepare Aromatic Waters from Essential Oils), etc..) Their boiling point usually ranges between 310° and 325° Fahr., and is always considerably higher than water. They resist saponification and (excepting oil of cloves) do not combine with the salifiable bases. Their density fluctuates a little on either side of water. The lightest oil is that of citrons (specific gravity 0.847), and the heaviest, that of sassafras (specific gravity 1.096). When cooled sufficiently they all soldify. The common temperature of the atmosphere is sufficient for this with some of them, as the oils of roses and aniseed; whilst others require to be cooled below the freezing point of water before they assume the solid form. By exposure to the air they rapidly absorb oxygen, and become partially converted into resin. This is the cause of the deposit that usually forms in them (especially in the expressed oil of orange) when kept in an imperfectly stopped bottle. (Cooley.)

1465. To Obtain Essential Oils

1465. To Obtain Essential Oils. All essential oils which are more or less volatile can be obtained from substances by distilling the articles along with an equal weight (some use a larger proportion) of water; but some substances that give out their oil with difficulty, are first soaked for 24 hours in twice their weight of water, to each gallon of which 1 pound of common salt has been added, by which its boiling point is raised, and consequently the oil comes over more easily. In such cases a quick fire is used, and when one half the water has come over, it is returned into the still, and this is repeated until the distilled water ceases to come over mixed with oil. The heat of steam or a salt water bath should be preferably employed; but if a naked fire be used, the still should be deep and narrow, by which means the bottom will be more perfectly covered when the quantity of water becomes small, and burning prevented. When the distilled water is to be repeatedly poured back on the ingredients, a very convenient plan is to so arrange the apparatus that, after the water has separated from the oil, it shall flow back again into the still, by which much time and trouble will be saved. The separation of the oil and water is effected by allowing the mixed liquids to drop into a Florentine receiver (see Fig. 1), when the oil is lighter than water, by which means the latter accumulates at a, and the water flows over by the spout, 6. The essential oil is obtained in this manner from the following: Anise, caraway, wormseed, cubebs, fennel, pennyroyal, juniper, lavender, lemon, cinnamon, peppermint, spearmint, horsemint, origanum, pimento, rosemary, savine, sassafras, valerian, etc.. The empyreumatic oil of tobacco is obtained by introducing the dry leaves in coarse powder into a green glass retort, heating it in a sand-bath to a dull red heat. Separate the oily liquid from the watery portion as it comes over, and keep for use. (See No. 46 (To Extract Essential Oil from Wood, Barks, Roots, Herbs etc).) The same receiver may be employed for oils heavier than water, by reversing the arrangement; but a glass separator (see Fig. 2) will be found more convenient. In this case the oil accumulates at the bottom of the vessel, and may be drawn off by the cock. The oil of cloves and other heavy essential oils are obtained by macerating 5 pounds coarsely powdered material for 48 hours in 10 pounds water containing 1 pound salt; and distilling until the product is no longer milky. After the oil has deposited, the remaining water is again distilled, and this repeated until all the oil has been extracted from the water. After 10 days, the oil is cleaned and clarified by filtering. The essential oil of cloves, cinnamon, rhodium-wood, sandal, calamus, aloes, etc., are thus obtained. That of bitter almonds and of mustard are obtained by making a thin paste of the material with water; and, after 24 hours' maceration, distilling by steam-bath. The essential oils of lemons, oranges, and some other fruits, are chiefly obtained by submitting the yellow rind to powerful pressure; but in this way they are not so white, nor do they keep so well as when distilled. Volatile oils should be kept in well-closed and nearly full bottles, in the dark, and opened as seldom as possible, as by age and frequent exposure they become resinous. The process of distillation should be done as rapidly as possible, and the light oils collected soon after its separation from the water.

Fig. 1.

Fig. 2.