Juniper oil has a great tendency to thicken; it becomes resinous, acid and thickly fluid, formic acid being formed. It should be kept in well-closed bottles, and protected from light. It is frequently adulterated with oil of turpentine and juniper-wood oil. It may be tested by its behavior towards alcohol, as well as by the taste. A drop of the oil rubbed up with sugar, and shaken with 500 grammes of water, should not impart an acrid taste to the water. Juniper oil gives a clear solution with ½ part absolute alcohol; by a larger quantity it is rendered turbid. _Lavender oil_ (_oleum lavandulæ_.)--Large quantities of this oil are distilled in Southern France, in the neighborhood of Grasse and Nimes, from the flowers of _lavandula officinalis, Chaix_, which grows wild in that region. It is limpid, colorless, or yellowish, has a strong odor and a pungent, aromatic, somewhat bitter taste. With 90 per cent. alcohol it mixes clear in every proportion, boils at 320° F., and has a specific gravity of 0.876 to 0.905. It turns the plane of polarization to the left. 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.