Oleum Foeniculi (U. S. P.)—Oil of Fennel.
"A volatile oil distilled from Foeniculum capillaceum, Gilibert (Foeniculum vulgare, Gaertner) (Nat. Ord.—Umbellifeae). It should be kept in well-stoppered bottles, in a cool place, and, if it has partly or wholly solidified, it should be completely liquefied by warming before being dispensed"—(U. S. P.).
Description.—Oil of fennel is prepared from bruised fennel seeds, by distillation with water. The yield from different sources (Saxon, Galician, Moravian, Roumanian) varies from 4 to 6 per cent. As officially described, the oil is "a colorless or pale-yellowish liquid, having the characteristic, aromatic odor of fennel, and a sweetish, mild, and spicy taste. Specific gravity, not less than 0.960 at 15° C. (59° F.). Between 5° and 10° C. (41° and 50° F.) it usually solidifies to a crystalline mass, but occasionally it remains liquid at a considerably lower temperature. Soluble in an equal volume of alcohol, the solution being neutral to litmus paper; also soluble in an equal volume of glacial acetic acid"—(U. S. P.).
Chemical Composition and Tests.—Oil of fennel contains from 50 to 60 per cent of anethol (see Oleum Anisi) which crystallizes out upon cooling, and dextro-fenchone (C10H16O, Wallach and Hartmann, 1890), an oily, camphoraceous ketone of bitter taste, solidifying above the temperature of melting ice, boiling at 192° to 193° C. (377.6° to 379.4° F.) and forming with hydroxylamine a crystallizable oxime (C10H16:N.OH), characterized by its melting point, 164° to 165° C. (327.2° to 329° F.). Furthermore, dextro-pinene and dipentene are present. Tardy (1897) found in a specimen of French fennel oil, in addition, methyl-chavicol (see Oleum Anisi), and perhaps anise-ketone (C6H4.OCH3.CH2COCH3). The relative amounts of these constituents vary according to the geographical sources of the oil; thus, fenchone is entirely absent in sweet or Roman fennel from southern France and Macedonia, while Sicilian fennel (Foeniculum piperitum, De Candolle) contains but traces of anethol. Oil of bitter fennel, growing wild in France, Spain, and Algeria, contains principally dextro-phellandrene, and traces of fenchone and anethol. According to Gildemeister and Hoffmann (Die Aetherischen Oele, p. 740), oil of fennel from which part of its anethol is removed by refrigeration, does not solidify at or above 3° C. (37.4° F.). An addition of alcohol or oil of turpentine reduces the specific gravity of the oil. The specific gravities, according to Schimmel & Co. (Report, April, 1897), range from 0.920 (Spanish fruit) to 0.987 (Asia Minor or Aleppo fruit). The U. S. P. gives the following tests for the purity of oil of fennel: "The oil is not colored by the addition of a drop of ferric chloride T.S. (absence of some foreign oils containing phenols, and of carbolic acid). If the oil be dropped into water, without agitation, it should not produce a milky turbidity (absence of alcohol)"—(U. S. P.).
Action, Medical Uses, and Dosage.—Oil of fennel is principally used as a carminative, and for the purpose of correcting or concealing the unpleasantness of other medicines. It is emmenagogue, and increases the lacteal secretions. The dose is from 5 to 20 drops.