The best French lavender oil, distilled from pure flowers only, is brought into commerce under the name, "Essence de Lavande Montblanc." It is distinguished from all other kinds, in the preparation of which more or less stems and leaves are used, by its extremely agreeable odor.
Lavender is also extensively cultivated in Mitchan and Hitchin, England, and used for the preparation of an especially fine oil, the odor of which surpasses even that of the best French product. It is, however, comparatively expensive.
From the leaves and flowers of lavandula spica the spike oil is obtained by distillation. It is colorless, or yellow, and in odor approaches rosemary oil more than lavender oil. Its boiling point, like that of lavender oil, is at 366.8° F., and its specific gravity 0.96. Spike oil turns the plane of polarization only slightly to the left, the deviation scarcely ever exceeding 0.8°.
Lavender oils are very sensitive to light and air, they becoming ozonized under their influence, and acquire an odor like turpentine. Hence they must be kept in well-closed vessels in a dark place.
Oil of lavender is frequently adulterated, chiefly with alcohol, fat oils, oil of turpentine, and spike oil. To test the oil, mix a drop of it with 10 cubic centimeters of warm water, and test the odor, which should be pure and agreeably lavender-like. The taste of the vigorously agitated water should be transiently bitter aromatic. One volume of the oil should give a turbid mixture with one volume of dilute alcohol (specific gravity 0.895), but a perfectly clear one with three volumes. On shaking 0.5 cubic centimeter of the oil with a few grains of rosaniline it remains uncolored, but, in the presence of even a trace of alcohol, it acquires a red coloration. By mixing in a graduated cylinder equal volumes of the oil and distilled water, and shaking vigorously, the oil, after the water has settled, shows a decrease in volume if alcohol be present. The presence of fat oil can be readily recognized by bringing a drop of the oil to be tested upon filtering paper; a grease stain is formed, which disappears neither at the ordinary temperature nor by heating. Adulteration with oil of turpentine is recognized by the boiling point, that of oil of turpentine being 312.8° F., and that of oil of lavender, as previously stated, 366.8° F.
Spike oil should mix clear with equal parts of 90 per cent. alcohol; the contrary would indicate adulteration with oil of turpentine.
For perfumery, lavender oil is of great importance, it being much employed by itself, as well as mixed with other oils.
Lemon oil (oleum limonis) is obtained by various processes from the rinds of lemons. The best and most delicately-scented oil is obtained by the so-called sponge process in use in Southern Italy and Sicily. The rinds are soaked from fifteen to twenty-five minutes in water, to which sometimes a little soda is added. They are taken up singly in the right hand and the outer surface of each is firmly pressed against a large and rather hard-grained sponge held in the left hand and secured by a strap. Two or three sharp turns of the wrist impart what may be called a screw-pressure to the rind, thus effectually fracturing the oil cells, the sponge absorbing the contents. The sponge is constantly held over an earthen jar and occasionally squeezed into it. The fluid in the jar quickly separates into three different products—the dregs or deposit of mucilaginous and cellular matter, some fruit juice, and the pure oil, which floats on the top. The latter, when bright and clear, is passed, by means of a small glass siphon, into the cans of thin copper, in which, after sealing, it is stored away for export.
The above described primitive mode of fabrication furnishes the most highly prized oils of commerce; they are called hand-pressed oils or essences preparées a l'éponge. In the same manner are obtained the oils from the sweet and bitter pomegranate, the bergamotte, and mandarin orange.