Page:EB1911 - Volume 20.djvu/74

 ointment the beneficent properties of which were known to Dioscorides in the beginning of the present era. Its chemical composition is exceedingly complex, and specially remarkable on account of the considerable proportions of cholesterol and isocholesterol it contains.

Commerce.—The sperm oils are generally sold in the same markets as the fish and blubber oils (see above). For beeswax London is one of the chief marts of the world. In Yorkshire, the centre of the woollen industry, the largest amounts of wool-fat are produced, all attempts to recover the hitherto wasted material in Argentine and Australia having so far not been attended with any marked success. Spermaceti is a comparatively unimportant article of commerce; and of Chinese wax small quantities only are imported, as the home consumption takes up the bulk of the wax for the manufacture of candles, polishes and sizes.

2. Essential or Ethereal Oils.

The essential, ethereal, or “volatile” oils constitute a very extensive class of bodies, which possess, in a concentrated form, the odour characteristic of the plants or vegetable substances from which they are obtained. The oils are usually contained in special cells, glands, cavities, or canals within the plants either as such or intermixed with resinous substances; in the latter case the mixtures form oleo-resins, balsams or resins according as the product is viscid, or solid and hard. A few do not exist ready formed in the plants, but result from chemical change of inodorous substances; as for instance, bitter almonds and essential oil of mustard.

Preparation from Plants.—Before essential oils could be prepared synthetically they were obtained from plants by one of the following methods: (1) distillation, (2) expression, (3) extraction, (4) enfleurage, (5) maceration.

Synthetic Preparation.—Since the chemistry of the essential oils has been investigated in a systematic fashion a large number of the chemical individuals mentioned above have been isolated from the oils and identified.

Applications.—Essential oils have an extensive range of uses, of which the principal are their various applications in (q.v.). Next to that they play an important part in connexion with food. The value of flavouring herbs, condiments and spices is due in a large measure to the essential oils contained in them. The commercial value of tea, coffee, wine and other beverages may be said to depend largely on the delicate aroma which they owe to the presence of minute quantities of ethereal oils. Hence, essential oils are extensively used for the flavouring of liqueurs, aerated beverages and other drinks. Nor is their employment less considerable in the manufacture of confectionery and in the preparation of many dietetic articles. Most fruit essences now employed in confectionery are artificially prepared oils, especially is this the case with cheap confectionery (jams, marmalades, &c.) in which the artificial fruit esters to a large extent replace the natural fruity flavour. Thus amyl acetate is used as an imitation of the jargonelle-pear flavour; amyl valerate replaces apple flavour, and a mixture of ethyl and propyl butyrates yields the so-called pine-apple flavour. Formic ether gives a peach-like odour, and is used for flavouring fictitious rum. Many of the essential oils find extensive use in medicine. In the arts, oil of turpentine is used on the largest scale in the manufacture of varnishes, and in smaller quantities for the production of terpineol and of artificial camphor. Oil of cloves is used in the silvering of mirror glasses. Oils of lavender and of spike are used as vehicles for painting, more especially for the painting of pottery and glass.

The examination of essential oils is by no means an easy task. Each oil requires almost a special method, but with the progress of chemistry the extensive adulteration that used to be practised with fatty oils has almost disappeared, as the presence of fatty oils is readily detected. Adulteration of expensive oil with cheaper oils is now more extensively practised, and such tests as the determination