Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/807

Rh OILS 747 the seeds of Garcinia indica, a tree native of western India. It contains, besides stearin and olein, the glyceride of myristic acid, and various free fatty acids of the volatile class. It is principally used in India to adulterate ghee, and for various medicinal uses ; but it is described as forming an excellent substitute for spermaceti nnd to be applicable for soap-making. The seeds of Garcinia pidoria and other allied species yield a similar fat. Oil of mace is the solid oil obtained from the NUTMEG (q.v. ). Shea butter, the fat of the seeds of the tropical African tree Bassia Parkii, is at ordinary tempera tures of a buttery consistency, with a dirty or greenish-white colour and a pleasant aromatic odour and taste. It consists principally of stearin and olein, and is an important article of food in the basin of the Niger and the adjoining regions. In European commerce it is employed for soap and candle making and in the preparation of pomades. Ghee or Indian butter, the solid fat obtained from the seeds of Bassia butyracea, an allied tree native of the sub- Himalayan ranges of northern India, is a most important food substance among the natives of the North-West Provinces, possess ing a delicate white colour, the consistency of lard, and a pleasant odour and taste. In the hot climate of India it will keep many months without acquiring bad odour or taste, on which account it is highly valued not only for food but also as an ointment, when perfumed, by the wealthier classes. It makes excellent soap &amp;lt;ind candles. Mahwa butter, obtained from the seeds of Bassia hitifolia, a tree cultivated generally throughout India, is used as a substitute for or as an adulterant of ghee. It possesses a greenish- yellow tinge, and becomes rancid more readily than genuine ghee. The fat is imported into England for soap and candle making, The seeds of Bassia longifolia and B. elliptica, natives of India, yield similar fats. Bayberry oil is the fat obtained from the seeds of the common bay or sweet laurel. It possesses a buttery granular consistence, a yellowish -green colour, a strong aromatic flavour, and a sharp bitter taste, due to the presence of an aromatic oil. It is pressed from the seeds principally in the south of Europe, Switzerland, and Holland, and finds its chief application in veterinary practice. Avocado oil is the produce of the fruit of the avocado pear tree, Persea gratissima, an edible fruit, native of the West Indies, but transported to other tropical regions. The fat consists of 30 per cent, of olein and 70 per cent, of lauro-stearin and palmitin, and is largely used in America for soap-making. In addition to the cocoa-nut palm and the oil palm, a large number of trees belonging to the same order, Palmaceae, yield useful fats, which, however, are little known in ordinary commerce. 3. Animal Oils. The only liquid animal oil of considerable importance other than the marine oils is Neafs-foot oil, a prepara tion from the feet of the common ox. For obtaining it the feet are split up and boiled in water over an open fire, or, preferably, treated with superheated steam in a closed cylinder. The oil is .skimmed from the surface of the decoction, and after some time it deposits a thick greasy fat, from which the liquid portion is sepa rated. Neat s-foot oil has a brownish colour and a mild animal taste and odour, and does not readily become rancid. It is very valuable for watchmakers purposes, and for oiling fine machinery generally, and is in great demand in connexion with the tools and machines of engineers. It is much adulterated, generally with fish oils. A large quantity of ox-foot oil is prepared in and exported from the River Plate region in South America. Shcep s-foot oil and Horse-foot oil are made to a limited extent, and sold as neat s- foot oil. Egg oil is obtained as a by-product of the preparation of egg albumen from the yolk or yellow of hens and ducks eggs. It is extracted either by pressure or by ether from the hard-boiled yolks, and has a fine brownish-yellow colour and a mild taste, except when extracted by ether, which brings with it a disagreeable fatty constituent. It is now being used to a considerable extent in place of olive oil in the manufacture of chamois or shamoy leather. The Seal oil of commerce is obtained from the bodies of nearly thirty species of SEAL (q.v.). The blubber or fat consists of a layer of variable thickness lying between the skin and the muscular tissue. Skin and blubber are first removed together from the carcases of the animals, and when the products are landed the fat is removed from the skin and reduced to oil, either by slow maceration and exudation in large vats or by rendering with steam. When heaped up in great wooden vats the mere pressure of the mass causes a flow at first of a fine clear oil, which is saved as a separate commer cial quality known as &quot;pale seal.&quot; Fermentation and putrefaction meantime progress in the mass, which begins to give off an almost unbearable stench, and the exuding oil gradually assumes a dark- brown colour, with a disagreeable animal odour and taste. By degrees the exudation of oil ceases, and finally the remaining oil is obtained by boiling up the mass with fatty muscular scraps, the product of which also forms a separate class of seal oil. The oil rendered by the action of steam heat on the fat has the advantage of being promptly obtained, free from the disagreeable odour of the greater portion of the seal oil obtained in open vats. According to its quality seal oil varies in specific gravity from 915 to 930 ; at a temperature of 5 C. a proportion of stearin solidifies out, and at - 2 to - 3 C. it entirely solidifies. In chemical composition it consists principally of a glyceride of physetoleic acid with propor tions of the glycerides of stearic acid, palmitic acid, a little oleic acid, and traces of some of the volatile acids. The oil is only very slightly soluble in alcohol, a circumstance which affords a means of detecting adulterations. It is used for the various purposes to_ which the allied whale oils are applied ; regarding these see WHALE. Shark oil, obtained from the liver of various species of shark, is analogous in properties and applications to COD- LIVER OIL (q.v.). Shark oil is distinguished from all others by its low specific gravity, which ranges from 870 to 880, It contains, but in different proportions, the same constituents as cod-liver oil ; particularly it is rich in iodine ; and it possesses a peculiar, highly- disagreeable odour and a very acrid taste. Under the name of Fish oil may be embraced the oil obtainable by boiling from the refuse of various fish as well as from the entire fish which may for any reason be unfit or not applicable for human food. Such oils have a fishy odour and taste, a brownish colour, and a specific gra vity ranging from 925 to 930. The most important of these products is Menhaden oil, obtained from the MENHADEN (q.v.) on the west coast of North America. 4. Animal Fats. The few solid animal fats which enter into commerce are articles of such importance that they have special articles devoted to them (see LARD, vol. xiv. p. 312, and TALLOW), or of so little consequence that they do not demand special notice. Bear s grease, beef marrow, and goose fat are highly valued for use in pomades for the hair, but comparatively little of what passes under these names is obtained from the sources to which they are attributed. 5. Waxes. The waxes of both animal and vegetable kingdoms will be dealt with under the heading WAX. ESSENTIAL OILS. The essential 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 whence they are obtained. The oils are usually contained in special cells, glands, cavities, or canals within the plants, either in a separate condition or intermixed with resinous substances, and 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 whence they are obtained, but result from chemical change of inodorous principles, examples of this class being oil of bitter almonds and essential oil of mustard. Esser/^1 oils are for the most part insoluble, or only with difficulty and sparingly soluble, in water ; but in alcohol, ether, the fatty oils, and mineral oils they dissolve freely. They ignite with great ease, and burn with a fierce smoky flame, depositing a large amount of carbon. In many important respects they differ from the fatty oils : they are not oleaginous to the touch, and make no permanent grease spot ; they distil at various tempera tures unchanged; they have an aromatic smell and hot burning taste ; and in chemical constitution they present no relationship to the fats and oils. Crude essential oils are at ordinary temperatures nearly all limpid liquids, but some are viscid ; and the essential oil or otto of roses is solid. Many on exposure to low temperatures separate into two portions, one solid, called &quot; stearoptene,&quot; the other liquid, called &quot; elaeoptene.&quot; The essential oils possess high refractive power. Their influ ence on the plane of polarized light is various: some rotate to the right, others give left -handed rotation, while with several no effect is visible. In their fresh condition many are colourless, but some are yellow or brown, others be come brown by exposure, and in exceptional instances oils are green or blue in colour. They are all powerfully acted on by oxygen, which affects their colour, consistency, odour, and constitution. In specific gravity they range from about 850 to 1 142, most of them being specifically lighter than water, and averaging 90. In chemical con stitution the essential oils are diverse, but they are invari ably rich in carbon. They consist, first and principally, of hydrocarbons, associated with which generally are, secondly, oxygenated compounds, sometimes the product of oxidation of the hydrocarbons, although in many