Oleum Cari (U. S. P.)—Oil of Caraway.
A volatile oil distilled from Carum Carvi, Linné.
"It should be kept in well-stoppered bottles, in a cool place, protected from light"—(U. S. P.).
SYNONYMS: Oleum carui, Oleum carvi.
Preparation and Description.—This oil is easily separated by distillation of the fresh fruit (caraway) with water, which yields from 3.2 to 3.6 per cent (Russian, wild), or 6 to 7 percent (Hessian, wild). The Dutch fruit, cultivated, yields from 4 to 6.5 per cent (Schimmel & Co.'s Report, April, 1897). The residue from the distillation of caraway seeds is used as feed for cattle. When fresh-prepared the oil is colorless, but by keeping it becomes yellow, and ultimately brown. It produces right-handed rotation on a ray of polarized light (+75° to +85°). The official oil is described as "a colorless, or pale yellow, thin liquid, having the characteristic, aromatic odor of caraway, and a mild, spicy taste. Specific gravity, 0.910 to 0.920 at 15° C. (59° F.). Soluble in an equal volume of alcohol, this solution being neutral to litmus paper"—(U. S. P.). Oil of caraway is little soluble in 70 per cent alcohol, but dissolves clear in 3 to 10 volumes of 80 per cent alcohol. Its boiling point is between 175° and 230° C. (347° and 446° F.).
Chemical Composition.—Oil of caraway is chiefly composed of two constituents, the hydrocarbon dextro-limonene (Schweizer's carvene, 1841), and the ketone dextro-carvone (C10H14O, Völckel, 1840; Wallach, 1893), formerly called carvol. The latter is the peculiar odoriferous principle of oil of caraway, and occurs therein to the extent of 50 to 60 per cent. Carvone is official in the German Pharmacopoeia under the name of Oleum Carvi or Carvol, specific gravity 0.96, boiling point 224° C. (435.2° F.); according to Schimmel & Co., 229° to 230° C. (444.2° to 446° F.) if mercurial column is surrounded by the vapors. Carvone is soluble in 20 parts of 50 per cent alcohol to a clear liquid; the presence of 2 per cent of carvene is indicated by turbidity (Schimmel & Co.). Carvone, if exposed to air, turns yellow, and then produces a red-violet coloration with a diluted solution of ferric chloride. Carvone is an unsaturated ketone, forms a crystallizable compound with hydrogen sulphide (C10H14O.H2S), by means of which it can be isolated and purified; with hydroxylamine (NH2OH) it forms a crystallizable, not very volatile oxime (C10H14:NOH), melting at 72° C. (161.6° F.). E. Kremers and O. Schreiner (Pharm. Review, 1896, p. 76) estimate the quantity of carvone in oil of caraway by converting it into the oxime and separating the latter from the volatile carvene by distillation with steam.
Carvone, when heated with sulphuric acid, phosphoric acid, chloride of zinc, or alkalies, etc., is converted into its isomer carvacrol (isopropyl-ortho cresol) which is also an isomer of thymol, the principal constituent of oil of thyme. Carvacrol occurs chiefly in Oleum Origani (which see), and occasionally in the oil of Monarda punctata (see Monarda).
Action, Medical Uses, and Dosage.—Oil of caraway is a warm diffusible stimulant and carminative. It is frequently used to allay the griping and sickening effects of medicines, also to increase their flavor. Like oil of anise it allays flatulent colic, and is a local anodyne. The dose is from 1 to 5 or 10 drops. Carvacrol, placed on cotton and introduced into the cavity of a carious tooth, is said to give prompt relief.