The different specimens which we have examined are readily miscible with bisulphide of carbon, but dissolve sparingly in spirit of wine (0·830). An equal weight of the oil and of spirit of wine forms a turbid mixture. No peculiar coloration is produced by mixture with perchloride of iron.
The oils are dextrogyre, but differ in their rotatory power, as may be illustrated by the following results, which we obtained by examining them in a column 50 millimetres long in the polaristrobometer of Wild. The oil of Signori Panuccio, due to the sponge-process ([p. 118, note 2]), deviated 20·9°, that of Monsieur Médecin (Essence de Citron au zeste) obtained by the éculle à piquer deviated 33·4° and his distilled oil 28·3°.
Chemical Composition—The prevailing portion of most essential oils of the Aurantiaceæ agrees with the formula C₁₀H₁₆; the differences which they exhibit chiefly concern their optical properties, odour, and colour. The boiling point mostly varies from about 170° to 180° C., the sp. gr. between 0·83 and 0·88. These oils are a mixture of isomeric hydrocarbons, and also contain a small amount of cymene, C₁₀H₁₄, and of oxygenated oils, not yet well known; of these we may infer the presence either from analytical results or simply from the fact that the crude oils are altered by metallic sodium. If they are purified by repeated rectification over that metal, they are finally no longer altered by it. Oils thus purified cease to possess their original fragrance, and often resemble oil of turpentine, with which they agree in composition and general chemical behaviour.
As to essential oil of lemons, its chief constituent is the terpene, C₁₀H₁₆, which, like oil of turpentine, easily yields crystals of terpin, C₁₀H₁₆ 3OH₂. There is further present, according to Tilden (1879) another hydrocarbon, C₁₀H₁₆, which already boils at 160° C., whereas the foregoing boils at 176° C. Lastly a small amount of cymene and of a compound acetic ether, C₂H₃O(C₁₀H₁₇O), would appear to occur also in oil of lemons. The crude oil of lemons already yields the crystalline compound C₁₀H₁₆ + 2HCl, when saturated with anhydrous hydrochloric gas, whereas by the same treatment oil of turpentine affords the solid compound C₁₀H₁₆ + HCl.
Essential oil of lemons (not the distilled) when long kept deposits a greasy mass, from which we have obtained small crystals apparently of Bergaptene ([p. 123]).
Commerce—Essence of lemons is shipped chiefly from Messina and Palermo, packed in copper bottles called in Italian ramiere and by English druggists “jars” holding 25 to 50 kilo. or more; sometimes in tin bottles of smaller size. The quantity of essences of lemon, orange and bergamot exported from Sicily in 1871 was 368,800 lb., valued at £144,520, of which about two-thirds were shipped to England.[471] In 1877 the export of these essential oils from Messina amounted to 306,948 kilogrammes, valued at 6,130,960 lire.
Uses—Essence of lemon is used in perfumery, and as a flavouring ingredient; and though much sold by druggists is scarcely employed in medicine.
Adulteration—Few drugs are more rarely to be found in a state of purity than essence of lemon. In fact it is stated that almost all that comes into the market is more or less diluted with oil of turpentine or with the cheaper distilled oil of lemons. Manufacturers of the essence complain that the demand for a cheap article forces them to this falsification of their product.
OLEUM BERGAMOTTÆ.
Oleum Bergamii; Essence or Essential Oil of Bergamot; F. Essence de Bergamotte; G. Bergamottöl.