Character And Origin. - Preparation. - Simple and Compound Oils. - Expressed Oils. - Quantity of Essential Oil Obtainable. - Composition. - Ordering Essential Oils. - A Pint is not a Pound. - Preparation of Essential Oils by the Carbonator. - Preservation. - Restoration. - Adulterations. - Fixed Oils and Tests. - Alcohol and Tests. - Chloroform and Tests. - Cheap Volatile Oils and Tests. - Detection of Oil of Turpentine. - Admixture of Water. - Detection of Adulterations by the Boiling Point. - Concentrated Essential Oils. - Patent or Artificial Essential Oils. - Cutting Essential Oils; what Cutting of Oil Means. - Magnesia Should Not be Used. - Va-rious Materials Recommended. - Purified Talcum, Artificial Pumice Stone and Asbestos Recommended. - The Best Method of Cutting Essential Oils. - Another Method of Cutting Oils. - Economizing Oil.

Character And Origin

Essential oils are volatile oils, but the latter are not always essential ones, as the term is understood. Petroleum and paraffine oils obtained by distillation are, for instance, no essential oils, although volatile. Essential oils are those proximate principles to which in the majority of cases the odor of plants is due. Their specific gravity usually ranges between 0.850 and 0.990; a few are still lighter, and some are heavier than water.

Essential oils, sometimes called essences, differ entirely from the fixed or fat oils in respect both to their physical and chemical properties. The greater number of these oils are generally liquid at the ordinary temperature; some are solid or partially crystallized; none of them are greasy or unctuous to the touch like the fixed oils, nor have they the appearance of being what is commonly called oily. All of them have a very persistent and penetrating odor, which generally recalls the substances from which they have been obtained, but they are never as fragrant. Their taste is acid, irritating and caustic. Light changes the color of volatile oils in a remarkable manner; it changes to yellow those that are colorless, darkens or decolorizes those that are colored. Exposed to the air they change color, lose their odor, thicken, and finally become a solid resin. They take fire suddenly on the approach of a flame, and burn with a very brilliant and dense flame. Highly soluble in alcohol, also in ether, chloroform, bisulphide of carbon, petroleum ether, but little so in water, they boil only at high temperatures, and are distilled without alteration. When heated along with water, they volatilize at a heat not exceeding 212 degrees, and frequently much below that. It is remarked that their volatility is usually in inverse proportion to their density, the most dense being the least volatile.

Cold produces notable effects on them; it congeals them, but at different degrees. Many become solid at some degrees above zero, others remain liquid many degrees below. By age, they undergo changes in color and consistency which are very unfavorable to them; others are so only in part. They become rancid, or lose their odor, and sometimes throw down a deposit which contains a resinous substance; have a consistence and odor similar to turpentine, while the supernatant volatile oil has lost none of its fluidity. This resin is dissolved in the oil when shaken; it does not separate from it again, and greatly hastens its destruction. When the oils of certain seeds, such as anise seed, have reached this condition of change, they are no longer susceptible of crystallizing by a slight degree of cold as before.

The light volatile oils, like those of lemon, orange, etc., experience the changes of which we have just spoken more promptly than the heavy volatile oils of cloves, sassafras, etc. It is easy to observe the beginning of the change in volatile oils, by the action of their acids on the corks, which they corrode and stain yellow, as is done by nitric acid.

Some essential oils being very changeable, the specific gravity of the same oil differs according to the state of alteration the oil has undergone.

Essential oils are contained in plants either in cells, glands, or, as in the fruits of the order umbellifera, in canals or ducts. Some are obtained from the rind of the fruit, as the lemon, orange and lime; others from the flower, as the rose, elder and chamomile; from the flower-buds, as the clove; from the wood, as turpentine and hemlock; from the leaves, as the tobacco plant; from the root, as ginger and orris; from the seeds, as the nutmeg; and from the entire over-ground plant, as the order of labiata, or mints, which yield many of the most important of the essential oils of commerce.

It is a curious fact that the essential oils of bitter almonds and mustard are not existent in the bitter almond or mustard-seed from which they are distilled, but are brought into being by the rupture of the cells containing separate chemical principles, the union of which, in combination with water, gives birth to the volatile oil. This happens in the mouth when bitter almonds are masticated. The emulsine and amygda-line, hitherto locked up in distinct cells, are brought into contact with each other and with the saliva, and the bitter almond flavor is evolved. Both almonds and mustard-seed yield by pressure a bland, greasy oil, without the least flavor of the oils obtained by distillation from the same seeds. In the lemon, orange, lime and other fruits of the genus Citrus, the rind is so saturated with the oil, that it is mostly obtained by simple pressure; all others are obtained by distillation. Among the oils obtained in this country from native plants are wintergreen, sassafras, peppermint, pennyroyal, tansy, tobacco and turpentine. Among the imported oils are those of cloves, pimento, cubebs, and bay leaves. China supplies us with two oils, the consumption of which is very great - cassia and star anise; India and Ceylon with cinnamon, mace and nutmeg, and Roumelia with attar of proses and oil of geranium. Lemon, orange and bergamot come from Sicily; thyme, lavender and petit grain (orange leaves) from the south of France. Some fine oils are manufactured in Tunis and Algiers. The great bulk of the essential oils are distilled in Germany, from both native and foreign materials. The oils distilled in England have a high reputation, those of peppermint and lavender bringing great prices, both being made from highly cultivated plants, the growth of which has been an important industry in Surrey and Kent for over a century. The English lavender-oil sells higher than the best French. The manufacture of soaps absorbs the largest quantity of the cheaper oils, such as cassia, citronella, lavender and lemon-grass. Rose-oil and bitter almond go in large quantities to the makers of perfumed snuffs. Confections take the bulk of the peppermint, wintergreen and sassafras, and much of the lemon, orange, clove and cassia. The finer oils are used by the perfumers, the chief being rose, geranium, ylang-ylang, patchouly, orris and cinnamon - all of very high price. Some of the aromatic oils, as that yielded by the caraway-seed, are used, in the manufacture of cordials.

With a few exceptions the essential oils are destitute of any decided medicinal properties, and all those of agreeable flavor or aroma are devoid ' of any injurious qualities whatever. Many are of a secondary value in medicine, the citronic and aromatic oils being used to mask the disagreeable taste of active drugs, and the mint and seed oils being highly prized for their stomachic virtues. An exception to the statement that all agreeable oils are wholesome is found in the oil of bitter almonds, one of the constituents of which is an active poison; but conscientious manufacturers never use it until the dangerous principle has been eliminated.

Preparation

The essential oils are obtained from their sources in four principal ways, viz.: by distillation, by expression, by enfleurage or absorption, and by maceration. The process of distillation is most important, and is applicable to a large number of substances, owing to the ease with which essential oils distil unchanged. Their general insolubility in water is turned to account in the process, the odoriferous materials being placed in a simple still with a small quantity of water, the steam from which carries over with it the vapor of the essential oil. In distilling from certain bodies, it is necessary to cohobate or return into the still the first distillate, and that operation may require to be repeated more than once before the raw material is exhausted. Again, in dealing with some substances, solutions of common salt or chloride of calcium must be used in place of pure water; and these, by raising the boiling point, send over the vapor more richly laden with essential oil. After condensation and resting a sufficient time, the distillate separates into two portions, the oil floating or sinking, according to its specific gravity. The process of expression is applicable to the obtaining of the essential oils which reside in the rind of the orange, lemon and other citrine fruits.

Enfleurage is a method by which the odors of several substances are dealt with. The aroma, in such cases, is present to a small extent, and is too tender and liable to loss and deterioration to permit of being separated by distillation. The process consists of exposing the flowers in contact with purified lard, or with fine olive oil, in suitable frames, whereby the fatty substances take up and become impregnated with the essential oil. The process is principally employed in preparing pomades and perfumed oils, as is also the analagous method of maceration, which consists in extracting the aromatic principles by macerating the raw materials in heated oil or molten fat. See pages 493 to 499 and Figs. 395 to 407. The practical application of the theory and principle above described requires much experimenting and long experience.

Before the seeds, roots, spices, leaves, woods, etc., can be subjected to distillation, they must undergo a preliminary treatment in rooms specially arranged for the purpose. These contain various kinds of mills, operated by hand or steam-power. The appended figure represents such an apparatus, operated by hand or steam, where the latter is available. A and B are two smooth metal cylinders. D is the filling box, and E the sliding board for the crushed material. After the raw materials are properly prepared they are brought into the still-house. Here we find in the receivers, so-called Florence flasks (Fig. 395), not only the essential oil of domestic products, such as fennel seed, coriander seed, angelica seed, camomile, spearmint, marjoram, calmus, etc., but also the products from the wood of the cedar of Lebanon, laurel from Italy, orris from Russia, sandal wood from India, caraway seed from Holland, cinnamon, mace and cardamom from India, etc. It would lead us too far to mention all the raw materials which are treated for essential oils. But not only that these oils are directly obtained; they must also be subjected to the most careful rectification, in order to obtain the state of purity and excellence in which they are brought into commerce.

Fig. 417.   Drug Mill

Fig. 417. - Drug Mill.