Essential Oils

ESSENTIAL OILS (Olea aetherea) (Ph. VII), mixtures of various chemical substances occurring in plants, characterized by volatility, strong odor, spicy-burning taste, and difficulty of solubility in water; on paper, E. O. leave a transparent greasy spot that disappears upon heating; they burn with a smoky flame. Most often they are easily mobile liquids, rarely viscous, of various colors, taste, and odor. Upon cooling of many E. O., sometimes even at ordinary temperature, a crystalline mass separates from them, called stearoptene, while the remaining liquid is called eleoptene. According to chemical composition, in E. O. are found compounds that are saturated and unsaturated, with both open chains and cyclic, which in turn are divided into hydroaromatic-terpenes and their derivatives, and derivatives of the aromatic series. E. O. may be contained in any part of the plant (fruits, flowers, leaves, stems, roots), but if they are in different parts, their quantity is by no means the same, and often the quality is different (e.g. orange oil from peel and flowers). From some plants, E. O. are obtained by splitting a complex compound, for example from the glycoside amygdalin in the seeds of bitter almond, from the glycoside sinigrin from the seeds of mustard, obtaining respectively essential almond oil and essential mustard oil. The role and significance of E. O. in plants and the path of their formation are at present almost unknown; E. O. in the plant may serve to protect the plant from pests (insects, fungi, etc.); vapors of E. O. surrounding the plant may protect it from daily and more sharp temperature fluctuations or the odor attracts insects and thus promotes pollination. E. O. are found in plants in special cells, passages, glands, or in the form of tiny droplets in the cell contents. The quantity of E. O. in various plants ranges from 0.001% to 20% and more. E. O. are obtained, depending on the state in which they are in the plant, in different ways; most often by steam distillation, whereby E. O. are distilled under these conditions at a temperature below the boiling point of water; in other cases they are obtained by mechanical expression, if there is much E. O. and fats are absent, as for example orange oil, lemon oil, etc., and by this method oil of higher quality is obtained; finally, when in the flowers of some plants, especially delicate ones (jasmine, lilac, mignonette, lily of the valley, etc.), there is little E. O. and its odor is strongly spoiled by heating, extraction is used, for example with fat (proces d'enfleurage), for which petals are laid on a thin layer of fat on a glass plate (lard, vaseline, etc.), and a number of such plates are placed in an enclosed space; the fat becomes enriched with the corresponding odor, after which, if the E. O. is extracted with alcohol and the alcohol is distilled off, the so-called essence (Oleum essentiale) is obtained.-E. O. in most cases are colorless liquids, although there are colored ones, for example in green color from chlorophyll (O. Bergamottae, O. Cajeputi, etc.), in blue color from azulene (O. Chamomillae, O. Millefolii, etc.), in brown (O. Cinnamomi, O. Caryophyllorum). The odor of E. O. is one of the main characteristics by which they sharply differ from each other; its determination however is subjective and cannot be described. By specific gravity E. O. are usually lighter than water (0.80-0.99); but many oils, in particular those whose composition includes derivatives of benzene, are heavier than water (1.025-1.182). Most E. O. are optically active, especially those containing terpenes and their derivatives in their composition; the angle of rotation for E. O. ranges from a few degrees to several hundred degrees. The index of light refraction in E. O. is high (1.34-1.57), which is why they are readily used in microscopy with immersion systems (O. Cedri, O. Caryophyllorum, etc.). E. O. are little soluble in water, but water shaken with them takes on their odor, forming corresponding aromatic waters, often used in medicine (Aq. Rosarum, Aq. Menthae, Aq. Cinnamomi, etc.); they are easily soluble in alcohol, ether, chloroform, and in each other. When stored in the presence of oxygen and moisture of the air, especially in the light and at elevated, even slightly, temperature, E. O. thicken and resinify (those containing terpenes) or oxidize to form free acids (O. Amygdalarum aeth., O. Cinnamomi) or finally hydrolyze, releasing acids that affect the odor (O. Valerianae and some others). In the specialized literature more than 1,300 E. O. are described, of which not all are widely used. E. O. are used mainly in perfumery and in the varnish industry, and then also in medicine. Of those most frequently used in medicine, the following can be named: turpentine oil, lemon oil, orange oil, lavender oil, eucalyptus oil, cajuput oil, mint oil, caraway oil, dill oil, anise oil, clove oil, cinnamon oil, sandalwood oil, and others. In general, E. O. act on the organism similarly to representatives of phenols, i.e. disinfecting. Individual representatives also have cooling, sedative (menthol and mint oil), carminative (caraway oil, dill oil, mint oil, etc.) and other actions. Locally on the skin and mucous membranes they produce an irritating effect, causing burning, hyperemia and inflammation. When taken internally, E. O. are excreted by the kidneys and, as terpenes in general, irritate parenchymatous elements and cause increased secretion of urine; at large doses E. O. can even cause kidney damage. Being excreted in part by the lungs, these substances increase bronchial secretion and thus promote expectoration, acting at the same time antiseptically. E. O. as volatile substances also penetrate into the blood through the skin and lungs; general poisoning often occurs only from staying in an atmosphere rich in vapors of E. O., for example in sleeping in rooms with fragrant flowers (magnolias, hemlock, etc.), on fresh hay, etc. E. O. are used for medical purposes in different forms. Spraying in rooms and wards aims to refresh and disinfect the air; in ointments and rubs-for refreshing, mild irritation and disinfection of the skin; internally-as carminatives, disinfecting the intestine and especially the urinary tract, as expectorants and disinfectants of the respiratory tract, as well as as spices. Essential oils in histological technique- see Oil.

A. Akizborg.