Oil of bitter almonds is often adulterated with oil of mirbane; this can be demonstrated by shaking 1 volume of the oil with 17 volumes of alcohol of 45%, and setting the mixture aside to settle. The nitrobenzol (oil of mirbane) will then collect at the bottom. Oil of Rose may be tested as follows: Mix the oil with an equal quantity of concentrated sulphuric acid. Neither the color nor the odor of the oil should be changed, but if oil of geranium was present a disagreeable odor and a darker color is produced. It has been proposed, too, to test the oils by heating with iodine or nitric acid and determining the purity by the reaction; but the results with the different oils are so similar that the test is almost worthless. We have had the same experience with the test by nitro-prusside of copper which on being heated with essential oils gives colored precipitates differing with various oils, but still so similar that they cannot be relied upon. We have found in all cases that a comparison of an oil with a sample of known purity is the best, or else the tests given in the preceding pages. CHAPTER X. THE ESSENCES OR EXTRACTS EMPLOYED IN PERFUMERY. The term _essence_ or _extract_ in perfumery means a solution of an aromatic substance in strong alcohol. These solutions are generally made as concentrated as possible and in this form find application in the manufacture of handkerchief perfumes and of certain odors bearing a special name. The so-called extrait d’œillet, extract of pink, or the favorite perfumes known as new-mown hay have nothing in common with either pink or hay except the name; like many other odors, both are merely mixtures of different essences or extracts. Besides the manufacture of true perfumes, essences or extracts are also used for scenting fine soaps, sachets, mouth washes, etc. For the latter, too, use is often made of the so-called aromatic waters (eaux aromatisées) which are obtained as a by-product in the distillation of fragrant plants, and have a very fine odor owing to the small amount of the aromatic substance they hold in solution. To this class belong orange-flower water (Aqua Naphæ triplex, eau de fleurs d’oranges), peppermint water (Aqua Menthæ, eau de menthe), and many others. Essences or extracts can be made in two ways: in the case of aromatic substances which are obtainable in the pure state—that is, essential oils—by dissolving them in strong alcohol in definite proportions; in the case of aromatics combined with a fatty substance by one of the processes described above, by treating the pomade (lard, or other perfectly bland, sweet, and in itself odorless fat combined with the aromatic) or huile antique (fixed oil holding the aromatic substance in solution) with the strongest alcohol.