Oleum Bergamottae. Oil of Bergamot.

Related entries: Sweet orange peel - Bitter orange peel - Lemon peel - Oil of orange - Oil of lemon - Oil of Neroli

Synonym.—Essence of Bergamot.

Oil of bergamot is obtained by mechanical means from the fresh peel of the fruit of Citrus Bergamia, Risso. (N.O. Rutaceae), a plant of which the botanical origin is obscure, cultivated mostly in Southern Calabria. It occurs as a greenish or brownish-yellow liquid, having a pleasant odour, and a bitter and very unpleasant taste. The green colour of the oil is due to chlorophyll, not to copper as frequently stated. Specific gravity, 0.882 to 0.886; rotation +8° to +20°, occasionally higher. Adulteration of oil of bergamot is very easily detected by changes in the physical constants. Oil of turpentine diminishes the specific gravity; fatty oils, cedar wood oil, and gurjun oil increase it; lemon and orange oils increase the rotation, and decrease the specific gravity, ester content, and solubility. Fatty oils also decrease the solubility, and increase the amount of residue on evaporation. This residue is normally 5 to 6 per cent., and would be lessened by adulteration with oil of turpentine, oil of orange, or rectified bergamot oil.

Soluble in about one-fourth to one-half its volume of alcohol, the solution not becoming turbid on the further addition of alcohol. Soluble also in twice its volume of alcohol (80 per cent.), though not always to a perfectly clear solution.

Constituents.—The principal constituent is the ester, linalyl acetate, C12H20O₂, which is the chief source of the fragrance of the oil. The amount of this body is a guide to the value of the oil; it should be present to the extent of 35 to 40 and may reach 45 per cent. Besides this ester there is usually about 6 per cent. of free l-linalool (C₁₀H₁₈O); and d-limonene, dipentene, pinene, camphene, octylene, and acetic acid. The ester content is determined by saponification in the usual way. The oil is sometimes rectified, but it suffers in consequence, the ester being partially decomposed. The oil, on keeping, deposits a crystalline magma (5 or 6 per cent.) of bergaptene (C12H₈O₄), a non-volatile substance, which is inodorous at ordinary temperatures, but gives off aromatic vapours on heating, and melts at 188°.

Uses.—Oil of bergamot is largely employed in perfumery, especially in oils and pomades for the hair; in pharmacy, it is used to disguise disagreeable odours and to perfume ointments.

Preparations: Violet Powder

The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.