The essential oils of thyme (chiefly Thymus vulgaris) and some related plants are very frequently used for scenting cheap soaps. The oils of these plants are light yellow, and so similar in odor that it is not possible to distinguish them except by direct comparison. OIL OF VANILLA, or, more correctly, vanilla camphor, the true odorous constituent of vanilla, also called vanillin, is a crystalline substance with a delightful odor, melting at 76° C. (169° F.). This is now extensively made artificially from the cambium sap of pines, the coniferin being converted by chemical processes into vanillin. One ounce of good vanillin is equivalent to about forty ounces of best Mexican vanilla beans. OIL OF VIOLET has thus far been produced in but very small quantities from the alcoholic extract of the true violet pomade; it has a greenish color and when pure a narcotic odor not to be recognized as that of the flower. The pleasant odor of violets manifests itself only in extreme dilution. OIL OF VERBENA is yellow, with a very pleasant odor of lemons. Its price being quite high, it is usually adulterated with oil of lemon-grass, or else the latter is sold under the name of oil of verbena (see p. 30). In fact the odors of the two oils are so similar that they are easily confounded. OIL OF VETIVER (OLEUM IVARANCHUSÆ), from Andropogon muricatus (see p. 30), is viscid, reddish-brown, with a very strong and lasting odor. OIL OF WINTERGREEN (OLEUM GAULTHERIÆ). This product is obtained by distillation from the leaves and twigs of Gaultheria procumbens or else by distilling the bark or leaves of Betula lenta with water, in which case the oil is generated by the action of the water, as it does not pre-exist in the birch, and, moreover, in this case the oil consists of nothing but methyl salicylate. It differs, like oil of meadowsweet, very markedly from the other aromatic substances and mainly consists of a so-called compound ether. It is a salicylate of methyl, boils at 220° C. (428° F.), is much heavier than water (specific gravity 1·173 to 1·184), and dissolves readily in alcohol and other solvents. It is used chiefly for scenting soap; the perfumes sold as wintergreen are usually mixtures of different substances which contain no oil of wintergreen. OIL OF YLANG-YLANG (OLEUM UNONÆ ODORATISSIMÆ) is imported from Manilla. It is colorless or yellowish, and has a most delightful characteristic odor, which is rather fugitive if not made resistant by other substances. It forms an important constituent of several of the most favorite and expensive essences. OIL OF HYSSOP (OLEUM HYSSOPI) is colorless, but rapidly becomes yellow in the air. It is used in some very cheap perfumes and in the manufacture of liqueurs. OILS OF CINNAMON (OLEUM CINNAMOMI).