FIXED OILS - the fixed or fatty oils, although varying considerably in external appearance, form in reality a well-defined and homogeneous group of substances having great similarity of chemical composition. They appear to be essential constituents of the most highly-organized forms of animal and vegetable life, being found in plants chiefly in the seed, and in animals chiefly enclosed in the cellular tissue and in special body cavities, but some proportion of fatty matter is found in almost all tissues and organs. Although oils and fats are universally distributed and perform most important functions in animal and vegetable life, those used for technical purposes are not drawn from any very great number of sources ; and many bodies might be utilized for the production of oil which at present are not so employed.

As found in commerce, oils possess a faint characteristic taste, a slight odour, and some amount of colour, generally brownish yellow. These characteristics, however, are due to certain impurities ; in a really pure condition most oils have scarcely any characteristic taste, odour, colour, or physiological influence. In a few cases only they have special properties which appear to be inseparable characteristics, such as the purgative principle of castor oil, croton oil, and some others. At the ordinary temperatures most vegetable oils are fluid, but a few, produced especially by tropical plants, such as palm oil, cocoa butter, Chinese tallow, &c., are solid fats. Animal fats are for the most part solid, the oils of marine animals and neat's-foot oil being important exceptions. The .various solid fats differ greatly in consistency, and the hardness of individual samples is largely affected by the nature of the food and by the health of the animal yielding them, and by some other circumstances. The relative fluidity or solidity of the various oils and fats depends on the proportions of the three principal constituents of all oils - olein, stearin, and palmitin. The fluid oils contain olein in larger proportion, that body being itself liquid at ordinary temperatures, while solid stearin and palmitin predominate in the hard fats. The viscosity of the fluid oils also ranges between wide limits. The rate of flow of an oil, which is a matter of considerable importance in several industrial applications, is estimated by comparison with the standard rate at which water of the same temperature flows through an aperture of fixed dimensions. The most viscid of the fluid oils is castor oil, which at a temperature of 15° C. is more than two hundred times thicker or more slow-flowing than water. Olive oil at the same temperature is more than twenty times thicker, and linseed and hemp oils, though among the most limpid of fixed oils, still flow about ten times as slowly as water.

Oils communicate to paper and like substances a stain which remains an irremovable translucent grease spot. They are almost entirely insoluble in water, and, excepting croton and castor oils, in cold alcohol, but in boiling alcohol they dissolve more freely, and they are perfectly soluble in ether, bisulphide of carbon, chloroform, benzol, and light petroleum spirit. In their pure condition they are neutral bodies, but, on their becoming rancid, free fatty acids are developed which give them an acid reaction. Exposed to air they absorb oxygen freely, and the class containing linoleic acid, known as drying oils, of which linseed oil is the type, thereby harden into a solid translucent semi-elastic caoutchouc-like body, a property of the utmost value in the arts. When they are exposed in thin layers over a great surface the absorption of oxygen proceeds with such energy that heat is evolved sufficient to produce spontaneous combustion, a circumstance frequently exemplified in the heating and igniting of heaps of oily cotton waste. The non-drying oils also on exposure to air thicken and become greasy ; they acquire the peculiar disagreeable smell and acrid taste known as rancidity, owing to a kind of fermentation being set up in them through the agency of impurities, whereby the fixed fatty acids they contain are decomposed, and odorous volatile fatty acids formed by oxidation at their expense.

The specific gravity of all oils is lower than that of water, ranging from .900 in the case of cocoa butter to -970, the specific gravity of castor oil. Most fluid oils have a specific gravity between •915 and •930. The specific gravity of oils varies with the temperature far more than is the case with water. It is found that for each degree Centigrade rise of temperature whale oil increases in volume 1 per 1000, rape oil 0.89, and olive oil 0.83.

When a solid fat is heated slowly till it melts and is allowed gradually to cool, it remains fluid till it falls considerably under the temperature at which it melted, and at the moment of solidification there is a sensible increase in its temperature. Butter, for example, melts at 30° to 31°•5 C., but does not resolidify till it falls to 19° or 20° C. These phenomena have been investigated in the case of the pure fats stearin and palmitin by Duffy (Chem. Soc. Qu. v. 197), who finds that these bodies undergo with great readiness three isomeric modifications, each having a distinct melting point widely apart from each other (stearin from beef giving 51°, 63°, and 67°), the solidifying point being slightly- under the lowest of the three. The freezing point of the ordinary fluid oils ranges down to from – 27° to – 28° C. for hemp oil, nut oil, and linseed oil, while olive oil solidifies at + 2° to 4° C. Fluid oils heated to from 280° to 300° C., and solid fats to from 300° to 325° C., undergo destructive distillation, resolving into a mixture of rich inflammable gases and a peculiarly irritating acrid vapour, acrolein.

Oils and fats are compounds of carbon, hydrogen, and oxygen, in proportions ranging, as a rule, for carbon between 76 and 80 per cent., hydrogen from 11 to 13 per cent., and oxygen from 10 to 12 per cent. Their proximate constitution was first demonstrated by Chevreul, who indeed, in the great series of classical researches embodied in his Recherches sur les corps gran d'origine animate (1823), established the modern chemistry of oils.

The phenomena of saponification, as exemplified on a great scale in the important industry of soap-making, furnished the key for discovering the intimate constitution of oils. Oils and fats treated with alkalis, alkaline earths, and basic metallic oxides in presence of water undergo decomposition and enter new combinations. A soap is formed by the union of the alkaline body with acid constituents of the oil, known as fatty acids, and the sweet body, glycerin, is liberated. The saponification of stearin with sodic hydrate, for example, may be thus represented : - By heating oil with steam under a pressure of from 10 to 12 atmospheres, or with water superheated to about 220° C., the oil is decomposed into free fatty acid and glycerin. Thus, again taking the simple fat stearin, we have : - (Cslip0)3 03+ 3H30 = 3C3811330H 1 C2H6"' n Calls " f 118 f Stearin. Water. Stearic acid. Glycerin.

In the above reactions it will be observed that three molecules of water are required for the formation of free stearic acid and glycerin from one molecule of stearin, and to that extent the resulting products are heavier than the original. Reading the equation in the inverse manner we find the formation of stearin takes place by the substitution of the three acid residues of stearic acid Ci811350 for the three hydroxyls 11.0 in the molecule of glycerin. No fat or oil is found in nature consisting of a single chemical fat such as stearin alone. All are mixtures of at least two and for the most part three or-more simple fats or glycerides of fatty acids closely allied in nature and constitution. These glycerides or combinations of glycerin and fatty acids are in their chemical relations ethers. Glycerin itself is a triatomic alcohol, and bears to the fatty acids and resulting ethers the same relation which a basic substance bears to an acid and to the salt which results from their combination. In all natural fats glycerin combines, as in stearin, by having substituted for its three replaceable hydrogen atoms three equivalents of fatty acids, whence the natural simple fats are all triacid com(C„H350)3 a tripalmitin 0,, pounds - tristcarin triolein (C18116 H3)- 03, &c., though commonly called stearin, palmitin, and olein, &c. (For further information as to the constitution of glycerides see GLYCERIN, vol. x. p. 697.) The three simple fats above named form by far the largest and most important constituents of all oils and fats, the only others which bulk largely being the glycerides of linoleic acid in drying oils, and of physeteleie acid characteristic of marine oils. The number of fatty acids found combined with glycerin in oils is, however, very considerable. They constitute members of homologous series, the first or stearic series of which possess the common formula C„112„02. Belonging to it are the following : - Another, the oleic series, contains two atoms less of hydrogen than the allied stearic series, having the general formula C„H2„ _202. To it belong the following : - To these there remain to be added, not members of either series, two important fatty acids, - liuoleie acid, C1B112202, characteristic of linseed oil and other drying oils, and ricinoleic acid C,8412403, the chief product of the saponification of castor oil. Among saponifiable bodies the true waxes are distinguished from other solid fats by containing no glycerin. They are principally ethers of the higher monatomic solid alcohols - cetylic and cerylic alcohol, Sze. Thus spermaceti, the solid wax obtained from the head matter of the sperm whale, is a cetyl palmitate cCii6H1131° 0. Certain of the vegetable waxes - e.g., Japanese wax - coutain some proportion of glycerides.

Extraction of Oil.

The ordinary method for separating vegetable oils and fats from the nuts, seeds, &c., of which they form constituent parts is by pressure, with or without the assistance of heat. They are also obtained by the agency of solvents, principally by the use of bisulphide of carbon and the light petroleum spirit benzin, these being methods of production of comparatively recent introduction. Animal oils and fats are principally isolated by simple melting or " rendering " by heat. The degrees of heat and pressure necessary for separating the several fats vary very much with the fluidity of the oils themselves, the proportion in which they are present in the substances, and the nature and consistence of the associated materials. Sperm oil is indeed obtained direct in its fluid condition from the head of the sperm whale. Virgin olive oil is obtained with the gentlest pressure, and palm oil and several other vegetable fats and waxes are liberated by the agency of boiling water.

T'egetable Oil Pressing. - Pliny describes in detail the apparatus and processes used for obtaining olive oil among his Roman contemporaries, by which it appears that they derived a knowledge of the screw press from the Greeks, and applied it to the pressure of oil from pulped olives. In the East, where vegetable oil forms a most important article for food and for other personal and domestic purposes, various ingenious applications of lever presses and of combined lever and wedge presses have been in use from the earliest times. The Chinese employ the same series of operations which are followed in the most advanced oil mills of modern times, viz., bruising and reducing the seeds to meal under an edge-stone, heating the meal in an open pan, and pressing out the oil in a wedge press in which the wedges are driven home by hand hammers. The apparatus used in Europe in modern times for the extraction of oil by pressure consists of forms of the screw press, the Dutch or stamper press, and the hydraulic press. With the screw press, even of the most improved form, the amount of pressure practically obtainable is limited from the failure of its parts under the severe inelastic strain which can be put on it. It is on this account only used in the pressure of olives and of animal fats, where the power necessary is not great. The Dutch or stamper press, which has played an important part in the oil industry, was invented, as its name indicates, in Holland in the 17th century. The invention of the hydraulic press in 1795 effected the greatest revolution in the oil industry, bringing a new, easily controlled, and almost unlimited source of power into play, and on the great scale that apparatus has practically superseded all other means of pressing.

The sequence of operations in treating oil-seeds for the separation of their contained oils is ordinarily as follows : - (1) the crushing and Grinding. - As a preliminary operation oil-seeds are freed from dust, sand, and other impurities by sifting in an inclined revolving cylinder or screening machine, covered with woven wire having meshes varying according to the size and nature of the seed operated upon. In earlier times the seeds were pounded to meal by means of stamper mills. These consisted of a series of heavy wooden stampers or pestles made to rise and fall by the action of cams or wypers fixed on a revolving shaft, a pair of such stampers falling alternately with heavy force into an egg-shaped mortar about two-thirds filled with seed. As the process proceeded the material became heated, and from time to time had to be sprinkled with water. Stampers are now seen only in small old-fashioned establishments. In a modern oil-mill the screened seed is passed through crushing rollers to bruise or open the husk. The crushing rollers consist of a pair of cast-iron rollers horizontally mounted, commonly of unequal size, the larger being 4 feet in diameter, while the smaller is about 1 foot. The larger roller is revolved by power and the smaller moves by simple friction against the other. Between these rollers the seed is fed by a hopper, and in passing through it is bruised and broken and so prepared for the thorough grinding it receives under the revolving edge-stones to which it next passes. These are a pair of circular stones having a diameter of about 7 feet with a thickness at their running edge of 16 inches, each weighing from 24 to 3i tons. They are made of very compact limestone, granite, or fine-grained sandstone, and are mounted on a vertical driving shaft, to which they are attached by a horizontal axle passing through their centre. They revolve on a bed of similar hard compact stone, and the compound rubbing and bruising effect of their rotary motion quickly reduces the bruised seeds to a fine meal. The stones are provided with sweepers, which in their revolution bring the material pressed out towards the side again into their path, and there is a separate sweeper for clearing out the finished meal from the bed of the machine by way of a slide or door provided in the side. The edge-stones revolve about twenty times per minute, and a charge of seed which is slightly moistened during the process is sufficiently ground on an average in about twenty-five minutes.

Heating. - In dealing with certain oils which are easily separated, and especially with oils used in cookery and otherwise consumed, where it is desirable to preserve the pleasant, bland, and faint fruity or nutty taste, the ground oleaginous meal is taken direct to the press and pressed for cold-drawn or virgin oil. The cake from such cold pressing, as it still retains a large proportion of oil, is subsequently broken up, reduced to meal, and heated ; after which it is again subjected to pressure to obtain a further flow of oil. Ordinarily, however, the meal is artificially heated previous to any pressure, and it depends greatly on the nature of the seed and the individual manufacturer's method of working whether the material is fully pressed at first or twice submitted to the operation. The warming of the seed meal renders the contained oil more fluid and consequently more readily separable with moderate pressure. It also enables the oil-presser to obtain a larger proportion of the contained oil, coagulates and holds back the albuminous constituents of the seeds, and similarly dries and retains mucilaginous matter. On the other hand, oil from heated meal usually is more highly coloured and harsher to the taste than cold -drawn oil ; and the quality is seriously deteriorated if by chance the heat applied should exceed at most 80° C. The heat is applied either in open shallow iron kettles or pans heated over a direct fire or through a sand -bath ; but preferably, and now generally, the meal is heated by steam circulating freely between the casings of a jacketed or double-walled pan or pans. Mechanical stirrers are kept in continuous rotation within the pan, to ensure a uniform warming effect throughout the mass. A highly-approved and convenient form of heating apparatus consists of a double steam kettle, one pan being placed above the other, each steam jacketed and provided with mechanical stirrers. In this machine the heating action is continuous. The meal is first heated for ten or fifteen minutes in the upper pan, which is closed over with a sheet-iron cover, after which a slide in the bottom of the pan is opened and the charge is shot down into the lower pan, where it is raised to the full heat, while the upper pan is again recharged and worked up. When fully heated in the lower pan the charge is swept out at a door in the side of the pan by the action of the mechanical stirrers, and falling into a funnel is passed in measured quantities direct into bags, and without delay prepared for and placed in the press. The kettles are of a capacity sufficient to heat seed for charging three single presses at each operation. A form of heating kettle is also now in use in which the object is effected by direct injection of steam into the mass, whereby the meal is not only heated but a beneficial amount of moisture is distributed throughout the material. In mills of the most recent construction such steam kettles are used in connexion with an improved form of crushing rollers, - employment of edge-mills being dispensed with. These rollers consist of a series of four or five chilled iron or steel cylinders mounted in vertical order like the bowls of a calender. The seeds pass in succession between the first and second rollers in the series, then between the second and third, and so on till they are delivered by the lowest, sufficiently bruised, crushed, and ground.

Pressing. - With the least possible delay the meal is transferred from the heating kettles, so that the oil may be pressed out while the material still retains its heat. Measured quantities, say 10 to 12 lb of meal, are filled into woollen bags of strong, thick texture, sufficiently open and porous to allow free flow of the expressed oil, yet having consistency enough to resist rupture by the enormous pressure to which it is subjected. Each bag is further placed within "hairs," thick mats of horse -hair bound with leather. In some methods of working press-cloths - not bags - are used ; and the construction of recent presses is such as to dispense altogether with the use of bags or other coverings. The essentials of proper oil-pressing are a slowly accumulating pressure, so that the liberated oil may have time to flow out and escape, a pressure that increases in proportion as the resistance of the materials increases, and that maintains itself as the volume of material decreases through the escape of the oil. These essentials the Dutch or stamper press and the hydraulic press fulfil perfectly, and the prevalence of hydraulic pressure over the other and older method is only due to the greater convenience and ultimate economy of the power. Previous to the early years of the present century the Dutch press was almost exclusively employed in Europe for pressing oil-seeds. It consists of two principal parts, an oblong rectangular box with an arrangement of plates, blocks, and wedges, and over it a framework with heavy stampers, the fall of which produces the pressure. The press box is made either of cast-iron or, according to the older method, of strongly-bound oaken planks. At each extremity of the box there is placed a bag of oil-meal between two perforated iron plates, under which are a perforated bottom and channels for conducting away the expressed oil. Next are inserted filling-up pieces of wood, two of which - the speering-blocks - are oblique or bevelled on one face, forming ways for the two wedges which press against them. Between the speering-blocks, and separated also by a filling piece, are inserted the two wedges, one being the ordinary or driving wedge by which the pressure is applied to the seed-bags, and the other an inverted or spring wedge, which is only driven down to loosen and free the various parts when the pressing operation is complete. The stamper which drives home the ordinary wedge is a heavy log of wood about 16 feet long by 8 inches square, and it falls about fifteen times a minute through a maximum distance of 22 inches by the action of a pair of cams or wypers fixed on a revolving shaft. As soon as the pressure is complete the stamper suspended over the inverted wedge is brought into action, and by a single heavy blow knocking the wedge out of its key-like position it frees the various parts of the apparatus for the removal of the pressed cakes. In a double stamper press about 12 cwt. of finished cake is made per day. Since the introduction of the Bramah press, numerous modifications have been invented with the special object of improving its convenience as an oil-press. The various forms devised for oil-extracting may be comprehended under standing or vertical presses and horizontal or lying presses, with specially-modified seed-boxes and press plates in each instance. The most primitive form of upright press, and one which still recommends itself for simplicity where great pressures arc not essential, is a drum or box press, so called because on the platen are placed two circular metal tubs, one within the other, the inner perforated throughout for the escape of the oil. At the top of the press is secured a strong metal plate or table the same diameter as the inner box, and the seed is pressed by the working up of the ram carrying the box against the surface of this table. Within the perforated box the seed-bags are deposited with metal plates between them. Experience, however, has demonstrated that the best presses are those provided with separate trays or seed-boxes for each bag, and the ordinary oil-press of the present day is fitted with four seed-boxes, and presses four separate cakes at one working. A convenient form is the double oil-press of Blundell, which admits of continuous working, one division being under pressure, while the other division is being emptied and recharged. The final pressure applied in ordinary practice on the seed-trays in an hydraulic press is equal to a weight of about 300 tons. This weight is allowed to remain on for seven minutes, and the whole operation of charging, pressing, and emptying a press maybe finished in ten minutes. A Blundell double press is capable of working off about 5 cwt. of seed per hour. A form of press of the most recent and improved construction, called the "pack press," dispenses with bags, seed-boxes, and hair-mats. Consolidated cakes of seed enclosed in press-cloths to the number of sixteen for one charge are simply placed between corrugated plates. To enable the press to be charged with sufficient rapidity, and to allow the large number of bags to occupy as small a vertical space as practicable when placed in the press, a moulding or form machine, such as was invented by John Bennie of Glasgow and patented in October 1880, or a similar machine, worked on a modified principle, patented by Francis Virtue, is employed. In these machines, by mechanical contrivances, the measured quantity of heated meal is placed in a trapeziform tray enclosed in a cloth and submitted to a pressure which reduces the thickness of the mass from about 3 inches to a little more than 1 inch and forms it into a solid cake, in which state it packs in small space in the press. The whole time occupied in filling and forming a cake and placing it in the press is not more than a quarter of a minute, and a set of three pack presses in a day of ten hours will work off nearly 9 tons of seed, yielding in the case of linseed about 108 cwt. of cake, and 54 cwt. of oil. It is claimed for the pack press that it extracts a much larger proportion of oil than that worked with seed-boxes.

Horizontal presses are not much in favour in the United Kingdom, but in many Continental mills where two pressings are the rule a set of horizontal presses are kept for the first operation.

The oil, during the process of pressure, works its way from the centre to the edge of the cake, whence it exudes. For this reason an oblong form is the most favourable for the easy separation of the oil, and the trapeziform shape oil-cakes usually present has been selected on account of the wedge -like steadiness the mass has under pressure, and the readiness with which the entire cake frees itself once it is moved the smallest distance from the thin end of the box or tray in which it is pressed. The edges to which the oil is pressed almost invariably retain a considerable proportion of oil. They are pared off, and the parings are returned to the edge-stones to be ground up and again pressed with fresh meal. The oil from the presses flows into the receiver tanks placed under the level•of the floor, from which it is and into the storage tanks, where it is permitted to settle and clarify. After mechanical impurities and water, &c., have separated themselves, the oil is in some cases ready for the market, but for the most part it has to undergo a process of refining.

Extraction by Solvents. - The only method of obtaining vegetable oils which has come into practical competition with pressing is that in which the solvents bisulphide of carbon (CS,), the light spirit of petroleum, and common ether are used. In ordinary pressing about 10 per cent. of oil remains in the finished cake, while by means of solvents practically the whole of the oil may be separated. Solvents might therefore be used for extracting that remaining percentage of oil from any oil-cake were such desirable, or they can be employed for treating fresh unpressed seed. As a matter of fact, it is desirable to leave a proportion of oil in the cake which is used for feeding purposes, because its food value depends to no small extent on the oil it contains, and the perfect separation of oil in the solvent process is a drawback, on account of the poverty in fatty matter of the exhausted meal.

Extraction by the agency of bisulphide of carbon was first introduced in 1843 by Jesse Fisher of Birmingham. Twelve years later apatent was secured by E. Deiss of Brunswick, but for several years afterwards the process made little advance. The colour of the oil produced was high, and its taste sharp ; it retained traces of sulphur, which showed themselves disagreeably in the smell of soaps made from it, and in the blackening of paints in which it was used ; and the meal left by the process was so tainted with evil-smelling carbon bisulphide that cattle would not taste it. These drawbacks have now been perfectly surmounted, and the process appears likely to come into extended use on the Continent.

The seed for treatment with bisulphide of carbon is prepared as for pressing, except that it is not reduced to a fine meal, which would prevent the percolation of the solvent freely through the mass. It is only bruised and placed in a series of four or five upright cylinders, which are hermetically closed andprovided with a complicated arrangement of pipes leading to and from each other in various ways, - all being controlled by stop-cocks. Into the first cylinder A bisulphide of carbon is admitted from an overhead reservoir, till the whole mass is saturated with the fluid. After allowing the bisulphide to act on the contents of the cylinder for about fifteen minutes, communication between cylinders A and B is opened, the fluid from A passss into B, and a fresh supply of bisulphide comes from the reservoir into A. Again, after the lapse of fifteen minutes, the pipe leading into cylinder C is opened, and the fluid contents of B enter C. B is filled from A, which again is replenished from the reservoir. The extraction thus goes on, pure bisulphide of carbon always entering the weakest, most nearly exhausted cylinder, and passing on with gradually increasing percentage of oil to cylinders having more and more oil in their contents, till at the end, in the most recently charged cylinder the bisulphide is fully saturated with oil and passes off to the distil. ling apparatus, where the oil and the bisulphide are separated. When the contents of a cylinder have been fully extracted that vessel is isolated from the others, the remaining bisulphide of carbon is forced out by the admission of compressed air, and thereafter steam is run through the exhausted meal till not a trace of the solvent remains. The bisulphide, boiling at 46° C., is easily separated from the oil by simple distillation, and the last traces of the sulphur compound are removed by blowing steam through the oil in the distilling apparatus. Careful provision is made for the prevention of escape and for the recovery and proper storing of the bisulphide of carbon in use.

In addition to the use of bisulphide of carbon claimed under iris patent of 1855 (English patent 1856), E. Deiss enumerates as solvents chloroform, ether, and benzin or benzol. In 1863 an English patent was secured by Messrs Richardson, Lundy, and Irvine for obtaining oil from crushed seeds, or from refuse pressed cake, by the solvent action of " volatile hydrocarbons from petroleum, earth oils, asphaltum oil, coal oil, or shale oil, such hydrocarbons being required to be volatile under 212° Fahr." Since that time the development of the American petroleum industry and improvements in the apparatus employed have raised this system of extraction to the rank of a competing practical method of oil production. The most approved apparatus for this method. of extraction at present in use is that of Vohl. In the separation of oil from oil-seeds by means of light petroleum spirit heat is required. Void uses a light petroleum spirit boiling at not more than 60° C., which lie calls canadol, and by a very ingenious arrangement of extractors, boiling and collecting kettle, and condenser, all brought into connexion by a system of pipes, he percolates the crushed seed in the extractor cylinders with heated. canadol, which passes down into the kettle laden with extracted oil. Here the volatile canadol is distilled off by steam heat, and passes into the condenser, whence it again goes into the extractors, still further exhausting the seed and carrying an additional portion of fixed oil into the kettle. In this way the original charge of canadol keeps circulating till it completely exhausts the charge of seed. in the extractors. The canadol is then distilled off from the fixed oil collected in the kettle, the condensed spirit going this time into a separate receiver, and finally the oil is perfectly freed from canadol by having steam blown through it. As pure petroleum spirit extracts neither resinous nor gummy matters from the oil-seed, and moreover takes up little or no colouring matter, the oil obtained by this solvent is remarkably pure, and the process is quite adapted for extracting even the oils used for food and for pharmaceutical purposes. The extraction of oils by means of ether, although presenting many advantages, has never been successfully undertaken on a commercial scale, chiefly through the apparently insurmountable waste of the costly menstruum.

Rcfining. - The refining of vegetable oils is generally carried on as a separate industry. A kind of clarification of an expressed oil takes place by simple settling in oil-tanks, but the action is too tedious and the result too imperfect for practical purposes. The all but universal method of oil-refining now practised was invented and patented by Charles Gower in 1792. It consists of treating the oil with a small percentage of sulphuric acid, which, owing to the avidity with which it takes up water, acts on the suspended impurities by depriving them of the water they contain, and then carbonizes the substances themselves, which precipitate in dark-coloured flocky masses. To a certain extent also the acid influences the oil itself, liberating fatty acids and combining with the freed glycerin ; and these new products remain dissolved in the oil. It is thus of great importance to use no more than that proportion of sulphuric acid which is capable of separating the impurities. The ordinary operations of refining are briefly as follows. The oil is placed in a large tank, within which is a coil of pipe for heating by steam. When the oil is sufficiently hot, sulphuric acid is slowly added to the extent of from 1 to 11 per cent. of commercial acid, according to the nature and impurities of the oil. After the contents of the tank have been in vigorous agitation for about an hour, it is left at rest for about five hours to allow the charred impurities to collect and precipitate. The oil is then conveyed into a washing vat, where it is mixed with about 20 per cent. of boiling water, with the addition of a little soda, and kept briskly stirred for an hour. From this the mixture passes to clearing tanks, in which the oil is allowed to rest about a week in order to thoroughly separate the remaining water. The addition of about 5 per cent. of common salt, by increasing the specific gravity of the water, considerably hastens this separation. Finally the oil is passed. through a filter composed of alternate layers of tow, dried moss, canvas, and similar porous substances. Numerous modifications of the above sequence and other processes of refining have been introduced, and more or less adopted. One of the best distinct processes is that of Bareswil, which consists in heating the oil and adding to it 2 to 3 per cent. of caustic soda. Thereby a corresponding proportion of soap is formed, which, rising to the surface as a strong, frothing scum, brings with it the impurities `which are rendered insoluble. The scum is subsequently allowed to precipitate, in doing which it perfectly clarifies the oil. The coagulum so formed is used as a lubricant. Rudolph von Wagner proposed the use of concentrated chloride of zinc, instead of sulphuric acid, in refining ; and various other mineral acids as well as salts and tannin have also been suggested and tried. The most recent process of refining, and certainly the simplest and most expeditious if experience demonstrates its sufficiency, is that introduced by Mayer of the Hernalser Actien Oelfabrik. It consists simply in submitting oil direct from the press to the action of a centrifugal machine. Thereby the albuininoid, mucilaginous, and other impurities are driven against the sides of the drum, on which I they deposit as a solid coating, leaving the oil pure and clear. The effect is, of course, due to the difference in density between the oil and its suspended. impurities.

Animal Fat Jiendering. - The animal fats, butter only excepted, are liberated from the cells in which the fatty matter is enclosed by the agency of heat alone. The heat applied melts the fat, and by thereby causing its expansion as well as by acting on the moisture in the tissue it bursts the cell membrane and allows the liquid fat to flow together. The process is a noxious and disagreeable one owing to the intolerable stench given off by the putrefying animal matter while under the influence of heat ; and it is practically impossible to have the fatty matter heated on a large scale in its pure and sweet condition. It becomes an object of importance, therefore, to prevent the escape of such disagreeable fumes into the air, and the apparatus used is principally modified with that view. The simplest method of tallow-rendering consists in cutting the fatty matter by hand or machine into small fragments, which are placed in a copper vessel, with a small quantity of water, over an open fire. While the fire is applied the mass is kept stirring, and gradually the oil exudes and collects as the membraneous matter - greaves or cracklings - becomes shrunken and shrivelled. The fat is then ladled out of the boiler and strained through a sieve or filter, and the greaves, placed in a hair or woollen bag, are submitted to pressure, by which a further portion of tallow is separated. The pressed greaves are useful for dog's food or for feeding swine, &c., or they may be still a source of tallow, which can be obtained by treating them with bisulphide of carbon or with petroleum spirit. An improved method of rendering tallow consists in crushing the suet under a pair of edge-stones, whereby the cells are ruptured, and heating the product over an open fire with about one-fifth part of water acidified with from two to seven parts of strong sulphuric acid. added in the boiler. The means, however, of most effectually separating animal fat and at the same time avoiding the pollution of the air consists in the use of air-tight cylinders or kettles heated by steam. According to certain methods of working, superheated steam is forced. into the kettle and acts direct on the shred suet, &c. ; in other cases the steam circulates in a coiled pipe within the vessel ; and a third. way consists in the use of steam -jacketed rendering vessels. Strained tallow, however prepared, is further purified or refined. before using by melting and thorough washing with hot water, after which it is allowed to cool slowly, so as to throw down impurities with the separating water. The same effect is also produced by blowing steam through molten tallow (comp. LARD, VOL xiv. p. 312).

I. Fluid Oils.

Non-drying or greasy oils, containing chiefly olein.

Drying oils, containing linolein.

Fish or train oils, containing physetolein.

II. Fats and Waxes.

Solid glycerides, principally paliuitin and stearin.

Non-glycerides or waxes.

In a pure condition the non-drying oils undergo little change through the influence of the atmosphere, but by degrees a process of slow fermentation is set up by the agency of the natural impurities they contain, developing an offensive rancid smell, and rendering the oils thick and greasy. Even in very thin layers, however, they never dry. Under the influence of nitrous acid and mercuric nitrate the olein of non-drying oils undergoes a molecular change into elaidin, and the oil becomes solid. Castor oil, the characteristic glyceride of which is ricinolein, occupies an intermediate position between drying and non-drying oils. The influence of nitrous acid on ricinolein changes the molecular constitution of the body forming ricinclaidin, with simultaneous solidification, as in the case of olein. The drying oils are those which contain as principal constituents linolein or analogous glycerides. They absorb oxygen from the atmosphere with much rapidity, giving off at the same time carbonic acid and water, whereby the composition of the oil is modified, the proportion of oxygen much increased, and the physical properties of the oils changed. They do not solidify under the influence of nitrous acid. The fish oils do not dry on exposure to the air, but they thicken and present physical features intermediate between drying and non-drying oils.

The following list embraces the whole of the oils, fats, and waxes ordinarily met with in commerce. Such of them as are of considerable importance are indicated by an asterisk, and notices of these will follow or be found under their own headings, or under the name of the producing material. The oils, &c., of local,Aimited, or otherwise minor importance are marked with an obelisk.

tion of chloride of zinc and of hydrochloric acid with the addition of about 2 per cent. of sugar.

of beheuic acid 0„11410, and myristic acid Oi4H, Ben oil is used by perfumers for O A. obtaining essential oils by enfleurage, as a hair oil and ointment, as a salad oil in the West Indies, and as a lubricant for watches and small machinery. It is, however, principally consumed in the regions of its production. Candle-nut oil is obtained from the nuts of Aleurites triloba, a tree native of the South Sea Islands, but grown also generally throughout tropical countries. The nuts are about the size of a horse-chestnut, with kernels which yield as ranch as from 60 to 66 per cent. of oil. The name given to these fruits is due to the fact that they are used in the Sandwich Islands, spitted on a stick, as lamps or candles, in which condition they burn with a clear steady light. The oil, cold-pressed, is a clear, almost colourless, rather viscid fluid, with a pleasant taste and smell, and medicinal properties akin to those of castor oil. Hot-pressed, it has a brown colour and a rather disagreeable odour and taste. It contains glycerides of linoleic acid and myristic acid in addition to those of palmitic acid and oleic acid, and possesses strong drying properties which make it useful for varnishes, and otherwise as a substitute for linseed oil ; it is also an excellent illuminant and a valuable soap-making material. On account of the cheapness of linseed oil, and the superior value of linseed cake, candle-nut oil does not find a very extensive market in Europe, but it is the basis of an industry of some importance in the South Sea Islands, whence a large quantity of the oil is annually exported to the west coast of America. The nuts of Aleurites cordata yield JVood oil, a power-frilly drying oil, of much importance in China and Japan for use as a natural varnish and in medicine. It does not enter into Western commerce. Cotton-seed oil, obtained from the decorticated seed of the varieties of cultivated cotton, is now, on account of the enormous extent of its production, one of the most important of the fluid vegetable oils. Its preparation is quite a recent industry, dating only from 1852, when the first importation of the material was made from Egypt. Since that period the trade has developed with extraordinary rapidity. Egyptian seed, containing about 25 per cent. of oil, is chiefly pressed in European countries (England, France, Germany) ; the American seed pressed in the United States shows not more than 20 per cent. of oil. The oil as expressed has a dark-brown turbid appearance, owine.' to the presence of a resin with albuminous impurities, and in the early days of the industry much difficulty was experienced in refining the product sufficiently for commercial purposes. It is now purified by as far as possible coagulating and separating the impurities by treatment with boiling water and steam. After the coagulum so formed has precipitated and been separated, the oil is treated with weak alkaline ley, briskly agitated, and allowed to settle, when the coloured resinous matter goes to the bottom ; over that comes a proportion of saponified oil, and the clear refined oil forms the upper portion. The refined oil has a clear straw-yellow colour, a faint earthy odour, and a pleasant nut-like flavour. It consists entirely of a mixture of palmitin and olein, the former beginning to solidify and separate out between 12° C. and 6° C. There is no doubt that cotton-seed oil is very extensively and generally used to adulterate other and more costly oils, especially olive oil. It also is largely used in soap-making, and it constitutes a principal ingredient in compound lubricating oils. The quantity of cotton seed available for pressing annually is estimated to be not less than 800,000 tons, from which about 120,000 tons of oil and 250,000 tons of oil-cake may be produced. German Sesame or Canieline oil is procured from the small yellow or ruddy seeds of the cruciferons plant called Gold of Pleasure, Cantelina saliva (Myagrum sativum, Linn.). The oil has a golden-yellow colour, a distinctive smell, and a somewhat sharp taste. In addition to other glycerides it contains that of erucasic acid, and of some analogue of linoleic acid. The oil dries only slowly on exposure to the air, and its chief applications are found in soap-making and for burning in lamps. It is principally produced and consumed in Germany and Russia. Grape-seed oil is used in the south of Germany and north of Italy for food and for burning in lamps. The seeds yield from 10 to 20 per cent. of a pleasant brownish-yellow very fluid oil, which dries very slowly on exposure to the air. Ground-nut oil (see GROUND NUT) is an excellent edible oil, largely used as a substitute for olive oil, and to no small extent passing into consumption either separately or mixed with olive oil under the name of the latter. The inferior hot-pressed qualities are employed in soap-making, being a principal staple of the soap industry of Marseilles, into which city not less than from 700,000 to 800,000 tons of the nuts are annually imported from West Africa. Nadia oil is obtained from the fruit of Maclia saliva, a plant native of Chili, but introduced into Europe within this century on account of its oil-yielding properties. The seeds contain from 35 to 40 per cent. of a dark-yellow oil, of peculiar smell and mild taste, which has a tendency to become rancid. It has only faint drying properties, and occupies a place intermediate between drying and non-drying oils. When cold-pressed, madia oil may be used for food purposes, but it is principally consumed in lamps, or employed as a lubricant and in soap-making. Maize oil is a product of the seed-germs, which, in the preparation of maize meal and starch and fermented and distilled liquors from maize, have to be removed as carrying in them a disagreeable acrid substance. The germ contains about 15 per cent. of a clear golden-yellow oil, useful for burning, or oiling wool, and for lubricating machinery. Niger oil is the produce of the seeds (properly achenes) of Guizotia oleifera, a plant native of the east coast of Africa, but cultivated throughout India and to some extent in Germany. The fruits, which are small, tooth-like in form, and shining black in colour, contain from 40 to 45 per cent. of oil, which first came into the English market about 1851. The oil is limpid, clear, pale-yellow in colour, with a pleasant nutty mild flavour. It possesses little drying property, and is not fitted for use either in paints or varnishes. It is much used in India - in the Deccan especially - as a substitute for ghee with the poorer sections of the population, and in other parts of the country both as a culinary oil and for burning. In Western countries tiger oil is principally employed in soap-making and as a lubricant. Nut oil is the produce in Europe of the nuts of the walnut tree, Juglans regia, and in America a similar oil is obtained from hickory nuts, Carya alba. The European walnut kernels yield from 40 to 50 per cent. of a fine limpid oil, which when cold-pressed is almost colourless, with a sweet nutty taste and pleasant odour, but the hot-pressed oil has a greenish-yellow colour and a rather sharp taste. Nut oil consists in large proportion of linolein, with olein and the glycerides of myristic and lauric acid. It is one of the most fluid of all oils, and, as it possesses with colourlessness strong drying properties, it is much valued by artists for oil-painting ; it also yields a fine transparent varnish. In the hilly districts of northern India and Persia - the native regions of the walnut - the oil is used for culinary purposes and for lighting. Several closely-allied nuts, both in Europe and in America, yield oil, similar in quality to that of the walnut. Para-nut or Brazil-nut oil, yielded by the kernels of Bertholletia excelsa, is employed in South America as a food-oil and for soap-making. To a limited extent it is also pressed in England and Germany from nuts which become unfit for table use. The oil becomes rapidly rancid. Sa-pucaia oil, yielded by Lecythis ollaria, also a South-American tree, allied to the Bertholletia, is analogous in properties and uses. Pine oils are got from the seeds of various species of pine and fir trees containing some proportion of resinous matter ; they have a turpentine odour and possess powerful drying properties. They are useful for mixing painters' colours, for making varnishes, and for burning in lamps. Poppy oil is yielded by the seeds of the opium poppy (see OPIUM). In the valley of the Ganges, the great region of opium culture, the poppy seed is consumed as an article of food by the native population, and, is their principal source of oil. The exceedingly minute seeds contain as much as 60 per cent. of a fine transparent, nearly colourless limpid oil, of pleasant taste and faint characteristic odour. The qualities obtained by cold and hot pressing respectively are distinguished from each other, the former being an esteemed salad oil, while the latter, of yellow colour, sharp taste, and linseed-oil-like odour, is used for soap-making, &c. Poppy oil consists principally of the glyceride of linoleic acid, linolein, and has therefore powerful drying properties, on which account it is much used by artists. To some extent the finer qualities are used for adulterating olive oil. Purging-nut oil is obtained from the seeds of Jatropha Curcas, a small tree native of India, but cultivated in tropical countries. It is a violent purgative, and contains, like castor oil, ricinoleic acid. It is comparatively limpid and odourless, and forms an excellent lamp oil. It is also used in the soap trade and as a lubricant. Safflower oil is yielded by the seeds (achenes) of the composite plant Carthamus tinetorius, which contain from 30 to 35 per cent. of a light-yellow clear limpid oil. It is extensively used in Egypt, the East Indies, and China (where the plant is cultivated as a source of the dye-stuff safflower), its principal applications being, for culinary purposes and burning, and also as an ointment in paralytic affections and ulcers. A thick sticky charred oil is obtained from the seed in India by a process partly of burning and partly of distillation. The dark fluid so obtained is used by the native agriculturist for greasing leather-work exposed to the action of water. Sesame or Gingelly oil, one of the most highly esteemed of vegetable oils, is the produce of Sesamumorientale. The plant is grown especially in India as an annual ; it ripens in about three months, and two crops are reaped yearly. The seeds are very small, weighing not more than one-tenth of a grain, and they vary in colour from a dirty white through brown to nearly black. They are highly oleaginous, containing as much as from 50 to 56 per cent. of a clear limpid oil of a pale-yellow colour, inodorous, bland and sweet of taste, and not liable to rancidity. It consists of about three parts of olein to one part of stearin and palmitin, with a small proportion of the glyceride of myristic acid ; and it does not solidify till it reaches 5° C. Both seed and oil are of much importance in the East Indies and China as food substances. The seed itself is used directly as food ; the oil comes next to cocoa-nut fat in the variety and extent of its applications for food, personal use, and soap-making ; and the pressed cake is even an article of food among the poorer classes. As a salad oil the cold-pressed qualities are in every respect equal to the finest olive oil, its mild piquancy of taste causing it to be preferred by many. Indeed sesame oil may be used with advantage for every purpose to which olive oil is applied, excepting, probably, the Turkey-red dyeing, and it is in extensive consumption in food, lighting, soap-making, and as a lubricant. The oil is the subject of much adulteration, especially with the cheaper ground-nut oil. It can by itself, or as an adulterant of olive oil, be readily recognized by a peculiar green coloration it takes when shaken up with mixed sulphuric and nitric acids, a reaction peculiar to sesame oil. Sesame seed is principally crushed at Marseilles and Trieste, to which ports it comes partly from the Levant, but more largely from the East Indies and Java. The quantity of seed imported into France alone yearly is not less than from 70,000 to 80,01'0 tons. Sunflower oil is a clear pale-yellow limpid oil, with scarcely any smell and a mild pleasant characteristic taste, obtained from the so-called seeds (achenes) of the sunflower plant, Helianthus annurts, which yield when freed from their husk about 30 per cent, of the oil. It contains glycerides of acids allied to linoleic acid, and possessing certain drying properties. It is of much importance in the east of Russia as an article of food, the sunflower being extensively cultivated in the government of Saratoff solely for its oil seed. Tea-seed oil is a commercial product in China, where it is used for food, lighting, and soap-making. It is said to yield a fine hard soap. The oil contains 75 per cent. of olein and 25 parts of stearin, has a yellow colour, and is destitute of taste and smell.

the seeds of Careinia 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 and to be applicable for soap-making. The seeds of Garcinia pictoria 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. Parka, is at ordinary temperatures 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, possessing 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, ou 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 and candles. Mahwa butter, obtained from the seeds of Bassia latifolia, 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 Thee. The fat is imported into England for soap and candle ma_thig. The seeds of Bassia longifolia and B. elliptiea, 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 pahnitin, 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, Palmacete, yield useful fats, which, however, are little known in ordinary commerce.

consists principally of a glyceride of pbysetoleic acid with proportions of the glycerides of stearic acid, pahnitic 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 - LtvEn OIL (q.v.). Shark oil is distinguished from all others by its low specific gravity, which ranges from 0.870 to 0.880. 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 gravity ranging from 0.925 to 0.930. The most important of these products is Menhaden oil, obtained from the 14IENnADEN (q.v.) on the west coast of North America.

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.

Waxes. - The waxes of both animal and vegetable kingdoms will be dealt with under the heading WAX.