Oil of citron is usually merely a synonym for “oil of lemon.” But in perfumery it has been customary to designate the oil of lemon which was extracted by the écuelle process, as “oil of citron-zeste” or “oil of citron,” while “oil of lemon” meant the distilled oil. Since there is no difficulty at the present time in obtaining all the hand-pressed oil that may be required, and of the finest quality, there is no longer any necessity for making the before-mentioned distinction. OIL OF LEMON (OLEUM LIMONIS, OLEUM CITRI) is one of the most important essential oils for the perfumer as well as the manufacturer of liqueurs, confectioner, etc. The oil is pale yellow, and of a very strong refreshing odor which it loses rapidly in contact with the air, when it acquires a disagreeable odor of turpentine and gradually resinifies. This change is particularly marked under the influence of light. Its spec. grav. is 0·850 at 20° C. (68° F.). It is soluble in an equal volume of strong alcohol or glacial acetic acid. The hand-pressed oil has a much finer aroma than that obtained by distillation. OIL OF CITRONELLA. This oil is hardly ever made in Europe, since it is imported in excellent quality and at low prices from India and especially the island of Ceylon. (See above, p. 29.) OIL OF LEMON-GRASS. This oil, which is imported in considerable quantities from India (chiefly Ceylon), is colorless and possesses a very pleasant odor of lemon which at the same time recalls that of roses and still more that of geranium, which is not rarely adulterated with it. (See above, p. 33.) OIL OF CORIANDER (OLEUM CORIANDRI) has a pale yellow color and a burning, sharp, aromatic taste. Like oil of cubebs (oleum cubebæ), oil of dill (oleum anethi), and oil of fennel (oleum fœniculi) which latter also has a rather low congealing point (-8° C. or +17° F.), this oil is used less in perfumery than for scenting soap and in the manufacture of liqueurs. But it should be noted that these oils, as well as those of bergamot, caraway, star-anise, and some others, could well be employed for cheap perfumes and for scenting soap. Oil of dill also finds application alone in the preparation of some face washes, and the dried fennel herb in cheap sachets. OIL OF LILAC can be made at slight cost from the flowers, as the raw material is obtainable without much trouble; it forms a yellow, strong-scented oil. In perfumery, however, use is generally made only of the pomade made from the fresh flowers or the alcoholic extract prepared from it. Or else the odor is imitated by means of terpineol, which is now on the market under the name of lilacin. OIL OF GERANIUM. It is necessary to distinguish clearly between oil of true geranium distilled in Southern France and Algiers from species of Pelargonium; and Turkish oil of geranium, also known as Palmarosa oil, oil of geranium grass, oil of Rusa grass, etc., which is distilled in India from ginger grass. (See above, p. 33.)