PLANTS PRODUCING VOLATILE OILS Botanical source.
The Labiatece (the mint family), the Umbelbferie (the parsnip family), the Bosacree (the rose family), and the Composite (the sunflower family), are all rich in volatile oils and furnish a considerable part of the world's supply. This class of products is also widely developed throughout the flower-pro ducing section of the vegetable kingdom, and is found in the Verbcnaceee (the verbena family), in many of the evergreen trees, in the family which includes the orange and the lemon (Butaccel, and also in that which includes the wintergreen (Ericacew).
Place of production in the plant.
Not only are volatile oils produced by many widely separated members of the vegetable king dom, but they are contained in the most various parts of the plant. (1) In many cases they are de veloped in hair-like structures which grow on the leaves and stems of plants, chiefly herbaceous, and give to the herbage of these plants the odor charac teristic of them. Peppermint, spearmint, penny royal, sage, catnip, lavender and marjoram belong to this class. (2) In many cases the oils are formed in internal glands or secreting structures and there developed and retained. Such accumulation is seen in the fruits (sometimes called seeds) of the Umbel liferce, e. g., anise, caraway, coriander, fennel ; in the fruit, rind and the foliage of the orange and lemon trees ; in the leaves, bark and wood of the sassafras ; in the needles, bark and wood of many of the cone-bearing trees, as the fir balsam, long leaved pine, white cedar and juniper. (3) In still other cases, the volatile product does not exist in the plant, but is formed by chemical changes fol lowing preparatory treatment of the parts involved. In the case of those products in which the develop ment of prussic acid is a characteristic result, the leaves or fruits yielding it must be crushed and thoroughly moistened so as to bring together those substances which by their action on each other cause the development of this acid. Usually a sub stance belonging to the group of bodies known as enzymes acts on a substance belonging to the group of bodies known as glucosides. When water is present, this reaction results- in the formation of prussic acid and also of other less important substances.
This condition of things is encountered in obtain ing the so-called oil of bitter almonds, whose chief sources are the kernels of almonds and apricots. Peach kernels contain similar substances and yield this oil also. The same general condition exists also in the green leaves and the bark of the black cherry, which yields this poisonous principle only after such a chemical change takes place. Similar in its general features is the situation in mustard seeds and horseradish, which owe their pungency to a volatile oil that is produced by a chemical change taking place between substances present in the seeds and root respectively. The volatile oil of wintergreen illustrates a similar method of formation.
Thus it is clear that for the production of vola tile oils many different parts of plants are used, and also that these are treated in very different ways.
Method of obtaining volatile oils.
The process of obtaining volatile oils consists especially in exposing the. oil-containing herbage, seed, wood, or bark to the action of a current of live steam which is then condensed, yielding water and the oil. The most important parts of a dis tilling apparatus are the following : (1) The boiler which yields the live steam ; (2) the distilling chamber in which the substance to be distilled is packed and exposed to the live steam, which is usually admitted at the bottom ; (3) the condenser in which the pipes carrying the live steam laden with the vapors of the volatile oil are brought from an outlet near the top of the distilling cham ber into an artificially cooled series of tubes from which the condensed steam and oil flow out into some proper receptacle. The oil, usually somewhat impure, floats generally as a superficial layer on the water, from whence it is skimmed or otherwise drawn off for storage or purification. [Fig. 1391, Cyclopedia of American Horticulture, shows a mint still in section ; and there is a discussion of peppermints and spearmint, and a botanical account of the cultivated species of Mentha.] Volatile oil production in the United States.