Oils (including Fats). The fats and fixed oils constitute an important and well-marked group of organic compounds, which exist abundantly both in the animal and vegetable kingdoms. They are not simple organic compounds, but each of them is a mixture of several such compounds to which the term glycerides is applied; and the glycerides which by their mixture in various proportions form the numerous fats and oils are mainly those of palmitic, stearic, and oleic acids, and to a less extent those of other fatty acids, such as butyric, caproic, caprylic, and capric acids, which are obtained from butter, myristic acid, which is obtained from cocoa-nut oil, &c. The members of this group may be solid and hard, like suet; semi-solid and soft, like butter, horse-grease, and lard; or fluid, like the oils. The solid and semi-solid are, however, usually placed together and termed fats, in contradistinction to the fluid oils. The most solid fats are readily fusible, and become reduced to a fluid or oily state at a temperature lower than that of the boiling-point of water. It is not until a temperature of between 500° and 600° F. is reached that they begin nearly simultaneously to boil and to undergo decomposition, giving off acrolein (an acrid product of the distillation of glycerine) and other compounds. In consequence of this property these oils are termed fixed oils, in contradistinction to a perfectly separate group of oily matters, on which the odoriferous properties of plants depend, and which, from their being able to bear distillation without change, are known as volatile oils. These, which are also known as essential oils, differ in toto in their chemical composition from the compounds we are now considering. All the fats and oils are lighter than water, and are perfectly insoluble in that fluid. Their specific gravity ranges from about 0.91 to 0.94. They dissolve in ether, oil of turpentine (one of the volatile oils), benzol, and to a certain extent in alcohol; while, on the other hand, they act as solvents for sulphur, phosphorus, &c. These bodies possess the property of penetrating paper and other fabrics, rendering them transparent, and producing what is well known as a greasy stain. They are not readily inflammable unless with the agency of a wick, when they burn with a bright flame. In a pure and fresh state they are devoid of taste and smell, but on exposure to the air they become oxidised and acid, assume a deeper colour, evolve a disagreeable odour, and are acrid to the taste; or, in popular language, they become rancid. The rapidity with which this change occurs is considerably increased by the presence of mucilaginous or albuminous bodies. The rancidity may be removed by shaking the oil in hot water in which a little hydrated magnesia is suspended.
The general diffusion of fats and oils in the animal kingdom has been already described (see FATS). In the vegetable kingdom they are equally widely distributed, there being scarcely any tissue of any plant in which traces of them may not be detected; but they are specially abundant in the seeds. The seeds of the Cruciferae are remarkably rich in oil; linseed yielding fully 20 per cent., and rape-seed about 40 per cent. of oil; and some fruits, as those of the olive and oil-palm, yield an abundance of oil.
The uses of oils and fats are numerous and highly important, many being extensively employed as articles of food, as medicines, as lubricating agents, in the preparation of soaps, ointments, varnishes, pigments, for candles, lamps, and other means of illumination, and for the purpose of dressing leather, &c. In Africa, Asia, and the Pacific animal and vegetable oils and fats are much used for anointing the person and smearing the hair, thus affording a protection against heat and the attacks of insects, and checking excessive perspiration. This practice conduces to health and preserves the skin smooth and soft. Oil thrown on the sea has a remarkable effect in subduing the force of the waves. A few gallons cast upon stormy seas moderates and prevents the waves breaking with force. This practice might be adopted by lifeboats when approaching wrecks, and rescuing the crews of stranded vessels. The composition of the fine oils required for watches and sewing-machines is often carefully kept secret. Those principally used are ben, almond, olive, and neat's-foot. The oils suitable for machine-shops and general cotton and woollen machinery require a good body, rather viscid. For woollen spindles a lighter oil, and for cotton spindles, which have a speed of 4000 revolutions per minute, an oil of still lighter body. For lubricating purposes mineral oils may with advantage be mixed with animal and vegetable oils to diminish their tendency to thicken; the more fluid an oil is the less friction takes place.
(1) Vegetable Fats.—The chief solid fats of vegetable origin are cocoa-nut oil, nutmeg-butter, cocoa-butter, and palm-oil. The fluid vegetable fats or oils are divisible into the non-drying and the drying oils; the latter being distinguished from the former by their becoming dry and solid when exposed in thin layers to the air, in consequence of oxygenation. Some of the drying oils, when mixed with cotton, wool, or tow, absorb oxygen so rapidly, and consequently become so heated, as to take fire, and many cases of the spontaneous combustion of heaps of oily materials that have been employed in cleaning machinery have been recorded. The chief non-drying oils are olive-oil, almond-oil, and colza-oil; while the most important drying oils are those of linseed, hemp, poppy, and walnut; castor-oil seems to form a link between these two classes of oils, since it gradually becomes hard by long exposure to the air.
(2) Animal Fats.—The chief solid fats are beef and mutton suet or tallow, lard, butter, goose-grease, &c.; while among the fluids sperm-oil, ordinary whale-oil, cod-liver oil, and neat's-foot oil may be especially mentioned. In many of their characters spermaceti and beeswax resemble the solid fats. As a general rule, stearin and palmitin, both of which have comparatively high fusing-points (between 157° and 114° F.), preponderate in the solid fats; while olein, which is fluid at 32°, is the chief constituent of the oils.
When any of these bodies are heated with the hydrated alkalies they undergo a change which has long been known as Saponification, or conversion into Soap (q.v.), in which the fatty acid combines with the alkali to form a soap, while the sweet viscid liquid glycerine is simultaneously formed. When the fatty acids are required on a large scale, as for the manufacture of the so-called stearin candles, which in reality consist mainly of stearic and palmitic acids, sulphuric acid and the oil or fat are made to act upon each other at a high temperature (see CANDLE). The fatty acids may also be procured in a very pure form by the injection of superheated steam at a temperature of between 500° and 600° into heated fat. A complete list of even the chief fats and fixed oils would take up far more space than we can command. The more important are noticed in separate articles, such as Fixed Oil of Almonds, Castor-oil, Croton-oil, &c., and some account given of their properties and uses; or under the names of the substances from which they are procured—Linseed, Rape, Candle-nut, Cocoa-nut, Cotton (for Cotton-seed Oil), &c. Reference may also be made to the articles on Butter, Ghee, Lard, Cod-liver Oil, &c.
The Volatile or Essential Oils exist, in most instances, ready formed in plants, and are believed to constitute their odorous principles. They form an extremely numerous class, of which most of the members are fluid. Many used for flavouring are artificially compounded (see BUTYRIC ACID). Essential oils are much employed in perfumes, for flavouring liqueurs and confectionery, and for various purposes in the arts. They will be described at PERFUMERY. The mineral oils will be found discussed under the heads of Naphtha, Paraffin, Petroleum.
OILS IN THEIR COMMERCIAL RELATIONS.—Vegetable Oils.—The principal seeds imported for expressing oil are cotton, linseed, rape, and ground-nut; but many others are received in small quantities. Cotton-seed is now a very important product, which was formerly much neglected. The imports into Britain rose from about 20,000 tons in 1861 to over 314,000 tons in 1890, nearly all coming from Egypt: 100 lb. of seed yield about 2 gal. of oil. The seed fetches £5 to £6 a ton; the oil £18 to £21 a tun. Linseed.—British imports of this flax-seed now reach over 2,000,000 qr., of the value of £4,000,000. Nearly all the supply used to be obtained from Russia, which produces the best seed, but now the chief imports are from India; these arrive, however, very much mixed with rape and other seeds. India ships about 8½ million cwt. of linseed yearly, of which three-fourths is sent to England. One quarter of linseed will yield by pressure 120 lb. of oil and 2½ cwt. of oil-cake. The average annual production of linseed-oil in the United Kingdom may be taken to be about 120,000 tons. India is the chief source of supply for the small oil-seeds, the value of those exported annually ranging from £9,500,000 to £10,750,000, besides about £500,000 more for the oils of various kinds shipped. Africa alone supplies palm-oil and large quantities of ground-nuts; Ceylon, India, and the Pacific islands the cocoa-nut oil of commerce. Cocoa-nut Oil is expressed from the albumen or ripe kernel of the nut, known in commerce when dried as copra. The production of this oil does not make the same progress that palm-oil does, as the following decennial imports into the United Kingdom will show: 1870, 198,602 cwt.; 1880, 318,454 cwt.; 1890, 184,409 cwt. The price of the oil declined about £10 in 1883-90, the price being in the latter year £27 per ton. Palm-oil.—The average imports of this oil are 50,000 tons annually. Prices have advanced of late years, and in 1890 stood at £26 per ton. This oil forms a chief ingredient in the grease used for railway axles. Rape-seed.—The imports of rape range between 459,000 to 2,300,000 qr., of which about half come from Russia and half from India. The total exports of this seed from India now exceed 3 million cwt., valued at nearly £2,000,000 sterling; the great bulk of this is sent to France and Belgium. From the first pressure rape-seed will yield about 90 lb. of oil per quarter, and from a second pressure 60 to 70 lb. The Ground-nut (Arachis hypogaea) is now a large source of oil-supply, but the principal commerce and manufacture centre at Marseilles. It is principally cultivated on the west coast of Africa, but is now much grown in India. The price of the shelled kernels in the London market is from £11 to £13 per ton. Olive-oil used to be one of the most valuable vegetable oils used for food, but it is now much adulterated with or replaced by Gingelie and cotton-seed oils. The average imports are about 20,000 tons, the best Spanish fetching £37 per tun. For lubricating and woollen manufactures olive-oil has been largely replaced by other vegetable oils and lard-oil (see OLIVE). Gingelie or Til-oil is the produce of the seed of Sesamum indicum, which yields about 50 per cent. of oil; and the annual export of this seed from India is from to million cwt. It goes principally to France and Italy. The price is 40s. to 50s. the 384 lb. Poppy-seed.—The trade in this seed from India is a fluctuating one, ranging from 450,000 to 730,000 cwt.; the exports are chiefly to France and Belgium. The seeds yield 45 per cent. of oil, which is used for culinary purposes. The seed sells at about 43s. the bag of 368 lb. Castor-oil seed.—From 600,000 to 700,000 cwt. of this seed are exported annually from India, and 2,000,000 to 2,600,000 gal. of the castor-oil. The expression of the oil is chiefly carried on in Italy and America, besides India. The various species of Bassia of India and Africa yield good oils, some of which are semi-solid and esteemed for soap-making. Under the name of Malirwa about 100,000 cwt. are shipped from India (see BUTTER-TREE).—One or two species of Aleurites produce what are known as candle-nuts in commerce; these yield 50 per cent. of oil. Some species of Garcinia yield kokum-butter, which is used as a substitute for ghee or clarified butter by the poorer classes of India. Many species of nuts, such as the Brazil, hazel, walnut, and others, yield oil which is used locally, but does not enter largely into commerce. In China oil is obtained from the Soy bean (Soja hispida), and it yields about 18 per cent. of a drying oil. The bean-cake is employed for feeding men and animals, and is also largely used for manure. Another oil made there is from the seed or fruit of the Camellia oleifera. It is of remarkable purity, of an amber colour, and possesses a pleasant taste. In the United States corn or maize oil and pea-nut oil are manufactured, as well as cotton-seed oil, linseed-oil, and castor-oil. The cocoa seeds or beans of commerce contain from 18 to 20 per cent. of a concrete fat, which being separated in the preparation of cocoa and chocolate, throws a large amount of cocoa-butter on the market. Several thousand tons of it in flattened cakes are now sold annually in London and Holland. It is used for pharmaceutical purposes and confectionery. Nutmeg-butter, Galam butter (Bassia), Carapa, Carnauba, and certain vegetable tallows and waxes partake of this solid character.
Animal Oils.—The principal solid animal oils found in commerce are butter and lard, tallow, mares' grease, neat's-foot oil, and unrefined yolk of egg oil. The first two are fully described under their names. Tallow is the fat of oxen and sheep, but more especially the fat which envelops the kidneys and other parts of the viscera, rendered down or melted. The qualities of this solid oil make it particularly well adapted for making candles, and until the end of the first quarter of the 19th century candles for ordinary use were almost wholly made of it. Britain obtains probably about 60,000 tons of tallow yearly at home, and receives as much from abroad, chiefly imported from North and South America and Australia. Russia used to furnish the chief supply, but the pastoral progress in the new countries has quite changed the sources of supply of animal fats. The imports of tallow and stearin do not vary greatly from year to year; they were, in 1870, 1,523,298 cwt.; 1880, 1,316,379 cwt.; 1890, 1,385,517 cwt. The value of the last-named year's imports was £1,729,349. The oleins, obtained by pressure from animal fats, are known in commerce as tallow-olein, lard-olein, and neat's-foot oil; they come next in value to sperm-oil. The two former are included under animal oils. Many thousand tons of these oleins are sent from the United States to Europe for artificial butter-making. Besides the home production of butter, which is large (about 130,000 tons), the United Kingdom imported in 1890 over 100,000 tons, valued at £10,500,000, and 54,000 tons of an artificial compound prepared from tallow, chiefly in Holland, and which has to be labelled as 'margarine' when sold; for this more than £3,000,000 is paid (see BUTTERINE). Of lard-oil Britain imports 91,000 cwt., besides about 27,000 cwt. of other animal oils, such as mares' grease, tallow-oil, &c. Lard-oil from which the stearin has not been pressed is known as 'neutral oil.' An olein is extracted from beef-suet in the United States, of which there are three qualities. Several thousand tons of this animal oil are sent from Chicago to Holland for the manufacture of oleomargarine. The export of this olein from the United States averages now 30,000,000 lb. yearly, valued at £600,000. Horse-grease is received from the River Plate states, where there are over five million horses. The mares, which are never used for the saddle, are annually slaughtered in large numbers in the republics of Uruguay and Argentine. A little horse-grease is also obtained in Britain from the slaughtered horses, 400 to 500 dying weekly in London alone. They furnish about 28 lb. of grease each, which is valuable as a lubricant. Neat's-foot oil is obtained in boiling down the feet of cattle. It does not turn rancid, and remains fluid at 32°. When part of its stearin has been abstracted it is used for oiling church and steeple clocks (as it does not solidify), for softening leather, and other purposes. In North America, where swine are bred so largely, the melted fat of the pig is a very important secondary product. The United States, with its 50 million pigs, sends away lard to the value of £5,500,000 yearly. It is a very important food-product, and in the West Indies it is much used instead of butter. The imports of lard from America into Britain now average 60,000 tons yearly, of the value of £2,000,000. The imports increased fivefold in 1870-90. Another animal fat is the suint obtained in the process of washing wool. This potassic sudorate forms no less than a third of the weight of raw wool in the grease.
Marine oils are obtained from various mammals and fishes in different localities. Much of the oil obtained passes under the general name of 'train-oil.' The whale-fishing has been much abandoned of late years by the nations which formerly pursued it; but the seal-fishing, which is less precarious and hazardous, is extensively prosecuted. The value of the oil shipped from Newfoundland annually exceeds £100,000. The average value of the fish-oil imported into Britain is only about £420,000; about 1880 it used to be double that amount. In America and the north of Europe fish oils are principally obtained from the liver of the cod and shark, from the dogfish, porpoise, Menhaden (q.v.), pilchard, herring, sardine, and other Clupea. In the Mediterranean the tunny yields a large quantity of oil, extracted by boiling, often in sea-water. It is of a pale amber colour and an agreeable flavour.
Fish oils are often confounded with the oils obtained from the blubber of the whale, seal, and other marine mammals, and their oil is much mixed with these. The great trade in animal oils and fatty substances indicates the care with which oily matters rich in carbon and hydrogen are sought for, supplying as they do a great number of wants in countries the most civilised as well as among people still in their primitive state. Some of these oleaginous substances are employed as food by man, some in manufactures, and others in medicine. The fish oils are usually thick, with a strong odour, and of different colours, according to quality and preparation, ranging from white to blonde and brown. In northern countries they still serve for illumination, but of late years have been largely superseded in this use by gas, petroleum, and electric lighting. Fish oils are valuable for soap-making and also much employed by curriers for dressing leather; and the oil is again recovered and sold for further use under the name of degras and sod-oil. Sharks are largely caught off the Norway coast and in the Indian seas, chiefly for their oil. In Greenland 300 or 400 are taken every season, their livers yielding 2500 barrels of oil, which is much valued for lubricating. Spermaceti, or 'head matter,' as it is commercially termed, from the oil being principally found in the enormous head of Physter macrocephalus, has, like whale-oil, been declining largely of late years. Britain only receives some 1430 tons, valued at £56,325, against three times that quantity imported about the year 1880. It used to be much employed in candle-making, mixed with about 5 per cent. of beeswax to prevent crystallisation (see WHALE). Seal-oil is hence included with train or fish oil. The exports from Newfoundland range from 3500 tons to 6000 tons yearly, according to the catch of seals. In 1889 Great Britain imported from that island 7000 tons of oil, valued at nearly £67,000. There was a large decline—fully 50 per cent.—in the prices of fish oils in the years 1889–90. The current prices in 1890 per tun of 252 gallons were, for sperm, £45 to £46; whale-oil, £21 to £23; pale seal-oil, £24 to £26; and cod-oil, £22. The medicinal cod-liver oil realises higher prices. Fuller information on the preparation of these will be found under the various heads. In 1878 the British imports of fish oils of all kinds were 20,656 tons, valued at £810,891; in 1890, 20,302 tons received were only valued at £419,296. In various quarters a considerable quantity of oil is obtained from different birds, such as the fulmar, the penguin, puffins, and species of Procellaria, the Guacharo (q.v.), the goose, ostrich, emu, and rhea, the passenger pigeon, and others; but, with the exception of penguin-oil from the Falklands, none of these appear to any extent in commerce, and are only used locally.
The large and growing importance of the oil trade is manifest from a consideration of the statistics of imports and exports alone in a year, independent of the various industries and labour interested therein. Taking the English Board of Trade figures for 1889, we find that the value of the imports of animal oils and fats, including butter, lard, tallow, &c., amounted to £18,395,518, the vegetable oils to £3,718,074, the mineral oils to £2,963,834, and the nuts and seeds imported for expressing oil to £8,269,678, making a total of £33,347,104. The imports are nearly all used in Britain, the re-exports being merely to the value of £3,531,242. If to this we add the £1,701,106 for oil-seed cake imported, and the export of oil, soap, and candles of British manufacture, amounting to £2,507,095, we have a total capital involved in the trade of over £37,500,000, and this quite irrespective of the home production of tallow, butter, fish oils, and the like.