_Storage of volatile oils._--In storing volatile oils, they should be carefully protected from light and air. Some oils become darker on exposure to light, while others, for instance, lemon oil, become colorless. Most volatile oils, as previously mentioned, absorb oxygen from the air with avidity and combine chemically with it. Thinly-fluid oils become perceptibly more thickly-fluid and finally even rigid, the product of oxidation being a resinous body. Some volatile oils containing aldehydes are converted, by the absorption of oxygen, into acids, cinnamic acid being, for instance, formed in cinnamon oil, and benzoic acid in oil of bitter almonds. To prevent evaporation, as well as the above-mentioned effects of light and air, the volatile oils should be preserved in not too large glass bottles kept as full as possible, and closed with a good cork, over which it is best to tie a piece of bladder. The bottles should be stored in a cool, shady place. The preservation of the oils is assisted by the addition of 0.5 to 1 per cent. of anhydrous alcohol. CHAPTER III. TESTING VOLATILE OILS. Volatile oils are much adulterated, the adulterations consisting chiefly in mixing an expensive oil with a cheaper one and with alcohol; more rarely with chloroform and fat oils. To these adulterations, which have been common for many years, has recently been added the previously mentioned hydrocarbon called terpene or camphene, which is separated in the preparation of concentrated oils. For the recognition of the quality of a volatile oil, serve first of all its physical properties, especially its color, odor and taste. The specific gravity varies too much and is not always a sufficient criterion. Reagents can only be employed with a few oils. The chemical detection of adulterations is rendered especially difficult by the fact, that most of the volatile oils form a mixture of terpenes with other combinations, in which the separate constituent parts do not appear in fixed, but in changeable proportions, and in which the constituents themselves suffer alteration by storing, air and light. _Odor and taste_ are so characteristic for every volatile oil as to suffice in most cases. For testing as to odor, bring a drop of the oil to be examined upon the dry palm of one hand and for some time rub with the other, whereby the odor is more perceptibly brought out. To determine the taste, vigorously shake one drop of the oil with 15 to 20 grammes of distilled water and then test with the tongue.