Fats, Fatty Oils; Huiles Graisses, Huilea fixes, Fr.; Fette, Fette Oele, G.; Olios, It.; Aceites, Sp.
These are sometimes termed fatty oils, because they constitute in part the vegetable and animal fats. The distinction between liquid and solid fats is for the most part a physical one only, as they contain the same chemical compounds, although in relatively different proportions. The fatty oils, though existing in greater or less proportion in various parts of plants, are furnished for use exclusively by the fruit, and, as a rule, are most abundant in the dicotyledonous seeds. They are obtained either by submitting the bruised seeds to pressure in hempen bags, or by boiling them in water, and skimming off the oil as it rises to the surface. When pressure is employed, it is customary to prepare the seeds for the press by exposing them to a moderate heat, so as to render the oil more liquid and thus enable it to flow out more readily. Another mode of extracting certain oils is by means of liquids having the power of dissolving them, and this method is now largely used in practice, carbon disulphide, carbon tetrachloride, and petroleum benzin being used. For the details of the process, see A. J. P., Nov., 1868, 549. Fixed oils may be clarified and decolorized by subsidence, filtration through animal charcoal, clays or earths, or porous solids, precipitation with tannin, lead acetate, plaster of Paris, albumin, gelatin, or other agents; cellulose and asbestos filters are often used, and on the large scale, for separating mechanical impurities, centrifugal machines like those employed for milk. Some oils are given a preliminary treatment with sulphuric acid which is later removed by treatment with alkali. Fixed oils containing stearin or palmitin are likely to deposit these fats in cold weather, leaving the olein in a liquid condition. The olein may be separated by filtration in the cold.
Hydrogenated Fats and Oils.—A. class of solid fats has appeared upon the market which are produced by a process known as hydrogenation, which is carried out in practice by bringing liquid fats into intimate contact with metallic catalyzers (finely divided nickel is usually employed), at elevated temperatures (160°-200° C. or 320°-392° F.). Under these conditions the unsaturated members of the fatty acid series which are usually liquid and are represented by oleic acid, become converted into the solid members of the series, which are saturated as stearic acid. The best known commercial product made in this way is the proprietary fat known as Crisco, largely used for culinary purposes.
The following scheme of classification of the fixed oils, both liquid and solid (Allen, Com. Org. Anal., 3d ed., vol. ii, Part I, pp. 88-102), gives a general view of their essential characters, points of difference, etc.
I. Olive Oil Group. Vegetable Non-drying Oils.—The oils of this group solidify on treatment with nitrous acid or mercuric nitrate, but do not lose their power of producing a greasy stain on paper, however long they may be exposed to the air. Their density varies from 0.914 to about 0.920, and hence is less than that of Groups III, IV, and V. Their viscosity is notably greater than that of the drying oils.
This group includes almond oil (from Amygdalus communis), peach oil (from kernels of Prunus Persica), apricot oil (from kernels of Prunus armeniaca), oil of ben (from Moringa oleifera), earth nut oil (from Arachis hypogaea), and olive oil (from Olea europaea).
II. Rape Oil Group.—The oils of this group are all derived from seeds of the family Cruciferae. They are non-drying but less distinctly so than the oils of Group I. They show higher saponification values, higher iodine absorption and less solid elaidins than Group I.
This group includes Colza oil and rape seed oil (from Brassica campestris, B. napus and other species); oil of black mustard (from seeds of Brassica nigra); oil of white mustard (from seeds of Sinapis alba).
III. Cotton Seed Oil Group.—The oils of this group occupy a position intermediate between the vegetable non-drying and the true drying oils (Groups I and IV). In density they somewhat exceed the oils of Group I, but are lighter than those of Groups IV and V. They form more or less elaidin on treatment with nitrous acid or mercuric nitrate, but do not become wholly solidified. On the other hand, they undergo more or less drying on exposure to the air, but not so markedly as the oils of Group IV.
This group includes beech nut oil (from Fagus sylvatica), cotton seed oil (from Gossypium species), hazel nut oil (from Corylus avellana, see Proc. A. Ph. A., 1893), sesame or teel oil (from Sesamum orientale), and sunflower oil (from Helianthus annuus; H. perennis), camelina oil (from Myagrum sativum), cress seed oil (from Lepidium sativum), and maize oil (Corn Oil).
IV. Linseed Oil Group. Vegetable Drying Oils.—These oils are not solidified by treatment with nitrous acid or mercuric nitrate, but become gradually converted into solid masses or varnishes, by exposure to the air. In density the oils of this group vary from about 0.923 to 0.937, and hence are distinctly heavier than the non-drying oils and than most of the oils of Group III. On the other hand, they are lighter than the oils of Group V. The fluidity of the drying oils is also much higher than that of the non-drying oils.
This group includes niger seed oil (from Guizotia oleifera), hemp seed oil (from Cannabis sativa), linseed oil (from Linum usitatissimum; L. perenne), poppy seed oil (from Papaver somniferum), Scotch fir seed oil (from Pinus sylvestris), tobacco seed oil (from Nicotiana Tabacum), walnut oil (from Juglans regia), weld seed oil (from Reseda Luteola), and soya bean oil (from Soja hispidus).
V. Castor Oil Group.—The oils of this group are distinguished from those of Groups I, II, III, and IV, by their very high density and viscosity. They are also remarkable for their ready solubility in alcohol, and their marked purgative properties. In their drying characters and behavior with the elaidin test they resemble the oils of the cotton seed oil group. Both castor and croton oil are miscible in all proportions with glacial acetic acid.
This group includes castor oil (from Ricinus communis), croton oil (from Croton Tiglium), Japanese or Chinese wood oil (from seeds of Aleurites cordata or Elaeococca vernicia), boiled linseed oil, blown oils (made by oxidation of rape seed, cotton seed, linseed, lard, and other oils).
VI. Palm Oil Group. Solid Vegetable Fats — This group includes solid fats not containing notable quantities of glycerides of lower fatty acids. The densities for the melted fats at 98° and 99° C. (208.4°-210.2° F.) are compared with the density of water at 15.5° C. (60° F.) taken as 1.000, and vary from 0.920 to 0.995.
This group includes palm oil (from fruit of Elaeis guineensis), cacao butter (from nuts of Theobroma Cacao), nutmeg butter (from nuts of Myristica fragrans), and shea butter (from seeds of Bassia Parkii).
VII. Cocoanut Oil Group. Solid Vegetable Fats.—This group includes solid fats containing notable quantities of glycerides of lower fatty acids—that is, of acids distilling with more or less facility in a current of steam at 100° C. (212° F.). The group includes cocoa-nut oil (from the nuts of Corns nucifera), palm oil (from the kernels of the nuts from Elaeis guineensis), laurel oil (from fruit of Laurus nobilis), Japan wax (berries of Khus succedanea), myrtle wax (berries of Myrica cerifera). For a description with constants of some of the rarer fixed oils belonging to the vegetable group, see papers by J. A. Wijs, Ph. Ztg., 1903, 563; by Pancoast and Graham, A. J. P., 1904, 70; and by Lewkowitsch, P. J., 1904, 492.
VIII. Lard Oil Group. Animal Oleins.—This group includes those oils fluid at ordinary temperatures which are obtained from terrestrial animals. They resemble the whale or fish oils in their reaction with chlorine, but are not turned red or brown by boiling with caustic soda. On exposure to air and on treatment with nitrous acid or mercuric nitrate, they behave like the non-drying vegetable oils (Group I). This group includes bone oil, lard oil, tallow oil, and neat's-foot oil. For a paper by P. L. Simmonds on various animal oils, see Bull. Pharm., 1893, 297, 344.
IX. Tallow Oil Group. Solid Animal Fats. —This group .comprises oils that are solid or semisolid at ordinary temperatures. Their melting points vary somewhat, and; are capable of permanent alteration. The group includes bone fat, butter fat, hog's lard, horse fat, beef tallow and mutton tallow.
X. Whale Oil Group. Marine Animal Oils. —This group comprises the various fluid oils obtained from fish and cetaceous mammals. They are distinguished as a class by their offensive fishy odor, by the brown color they assume when subjected to the action of chlorine, and by the reddish color which is produced on boiling them with a solution of caustic alkali. With sulphuric acid they give colorations varying from light red to purple or brown. The fish oils do not dry on exposure to air, and mostly yield but little elaidin on treatment with nitrous acid. The term "train oil" includes whale, seal, shark, cod, and all similar oils. Cod oil (from Gadus morrhua and allied species), cod liver oil (from the same), menhaden oil (from Alosa menhaden), porpoise oil (from Delphinus phocaena and allied species), seal oil (from Phoca of various species), shark oil (from Squatus maximus and allied species), and whale oil (from Balaena mistecetus and allied species) are all members of this group.
XI. Sperm Oil Group. Liquid Waxes.—The members of this group differ from all the fatty oils of previous classes in not being glycerides, consisting essentially of esters of monatomic alcohols of the ethylic series, in which respect they resemble the true waxes, but are fluid at ordinary temperatures. They are less dense than glycerides, they do not dry or thicken notably on exposure to air, but they yield solid elaidins on treatment with nitrous acid. The group includes sperm oil (from cranial cavities of Physeter macrocephalus), doegling or bottle-nose oil, and dolphin oil.
XII. Spermaceti Group. Waxes Proper.— Spermaceti and the various waxes differ from the true fixed oils and fats in not forming glycerin when saponified, yielding instead certain of the higher monatomic alcohols, the identity of which varies with the nature of the wax. These alcohols are insoluble in water, and dissolve to but a limited extent in alcohol, but they are soluble in ether, chloroform, carbon disulphide, benzene, and petroleum benzin, and are apt to be mistaken for added paraffin wax when the substance is saponified and the soap extracted with a solvent.
This group includes beeswax (from honeycomb of various species of bees), Carnauba or Brazil wax (from the leaf-coverings of Copernicus cerifera), Chinese wax or Pela wax (produced by a species of Coccus which punctures the branches of certain trees), myrtle wax (from berries of Myrica cerifera), Ocuba wax (from Myrica Ocuba), palm wax (from bark of Ceroxylon andicola, of the Cordilleras), and spermaceti (deposit from the oil found in the cranial cavities of the sperm whale, Physeter macrocephalus). "Wool fat, which consists largely of cholesterol (an alcohol), belongs to this group.
When oils are decomposed by heat they emit vapors of acrolein allyl aldehyde, CH2CHCHO, a highly volatile liquid resulting from the decomposition of glycerin, upon which the fumes of oils mainly depend for their irritating effects on the eyes and nostrils. Exposed to a red heat, in closed vessels, they yield, among other products of the destructive distillation, a large quantity of combustible and illuminating gases, among which ethylene and acetylene are readily recognized. Heated in the open air, they take fire, burning with a bright flame, and producing water and carbon dioxide. When kept in air-tight vessels, they remain unchanged for a great length of time, but exposed to the atmosphere they attract oxygen and undergo change.
Effervescent Oils.—K. Dieterich recommends oils and fats which have been supersaturated with carbon dioxide and introduced by him under the name of "effervescent oils." (See Proc. A. Ph. A., 1900, 494.) Under the influence of carbon dioxide, compounds which are easily split with the fatty acids are produced, which, particularly in the case of cod liver oil, permit the more complete absorption of the oil than is the case with oil not treated with carbon dioxide. The latter, moreover, acts as a preservative of the oils and renders them more palatable, destroying the unpleasant taste of cod liver oil, and to a certain extent also that of added medicaments, very materially. The absorbability of carbon dioxide is, however, not the same in all oils. Cod liver oil is capable of absorbing the largest quantity, castor oil the smallest, while olive oil stands intermediate. (Ph. Centralh., 1901, 485.)
Some fixed oils, in drying, lose their unctuous character, and are converted into a transparent, yellowish, flexible solid. These are called drying oils. Others, especially such as contain mucilaginous impurities, become rancid, acquiring a sharp taste and an unpleasant odor. This change is owing to the development or liberation of free fatty acids, from which the oil may be freed by boiling it for a short time with magnesium hydroxide and water.
Cloes has made investigations in relation to the influence of light in promoting oxidation, and obtained some curious results. The general influence of light is very great, as oils undergo comparatively little change in the dark for a long time; though in relation to some of them the change is at length as great as under the light. Thus, while the oil of poppies had in 30 days increased about 5 per cent. in weight under white light, and had gained only a 5000th in the dark, yet at the end of 150 days the weight in the former condition was rather lessened than augmented, and in the latter, or in the dark, had increased 6.4 per cent. The effect of the different colored rays is also very different. The change is at first most rapid under the white light, less so under the blue, and much less under the red, yellow, and green, being least of all with the green; but with the advance of time the blue overtakes and even passes the white and at the end of three or four months all are about equal in effect. Heat also accelerates the concretion of the oils, by favoring their oxidation; and the same effect is produced by introducing into the unchanged oil a little which has already been altered by exposure to the air. The oxidation of an oil may be very greatly hastened in this way without the aid of heat.
The fixed oils are insoluble in water, but are miscible with that fluid by means of mucilage, forming mixtures which are called emulsions. They are in general very sparingly soluble in alcohol, but readily dissolved by ether, which serves to separate them from other vegetable proximate principles. By the aid of heat they are enabled to dissolve sulphur and phosphorus. The stronger acids decompose them, giving rise, among other products, to oleic, palmitic, and stearic acids. Boiled with diluted nitric acid, some of them give rise to malic and oxalic acids, besides other substances usually resulting from the action of this acid upon vegetable matter. Several acids are dissolved by them without producing any sensible change. They are saponified by various alkalies. The compounds which these acids form with potassium and sodium hydroxide are the common detergent soaps, although strictly speaking, a soap is the combination of a fatty acid with any metal or base. By the addition of one part of potassium or sodium carbonate, 160 parts of oil may be brought with distilled water into the form of an emulsion. The potassium and sodium soaps and the alkaline sulphides have a similar effect, but not the bicarbonates. The fixed oils also serve as good vehicles for various metallic bases and subsalts, which form soaps to a certain extent soluble in the oil, and thus become less irritant to the tissues. Oils thus impregnated may, like the pure oils, be brought to the state of emulsion with water, for convenient administration, by the addition of a small proportion of potassium carbonate. The fixed oils dissolve many of the alkaloids, the volatile oils, resin, and other proximate principles of plants. The alkaloids are more readily dissolved in them by being first combined with oleic acid, the oleates being more .soluble than the alkaloids themselves. According to Buignet, they are, with very few exceptions, indifferent to polarized light; of all those used in medicine, the only exceptions are the liver oils of the ray and dog fish, which have a very feeble laevo-rotatory power, and castor oil, which is decidedly dextrogyrate.
It is very likely that, with the exception of castor oil, whose rotatory power is due to the asymmetric carbon atom of the ricinoleic acid, the rotatory power is not due to the glycerides themselves but to small proportions of optically active substances such as cholesterol. (Lewkowitsch, Chem. Analysis of Oils Fats and Waxes, p. 121.)
The fixed oils, whether animal or vegetable, in their natural state consist in most cases of at least two or three distinct constituents, one liquid at ordinary temperatures, and the other two solid or semisolid. The liquid is a distinct proximate principle, called olein; the more solid principles consist of stearin and palmitin, the former being found most largely in animal and the latter in vegetable oils or fats, and the two in most cases existing together in the same oil. The substance formerly known as Margarin is now generally recognized to be a mixture of palmatin and stearin. As the most frequent of these proximate constituents of the fixed oils, and existing in many different oleaginous substances, olein, palmitin, and stearin merit a special notice. Preliminarily to their individual consideration, it will be proper to refer to their nature and composition generally.
These three substances, olein, palmitin, and stearin, together with butyrin, caprin, and other minor fat principles, are glycerides; that is, esters or salts of the triatomic alcohol glycerol, C3H5(OH)3, and of the several fatty acids, oleic, palmitic, stearic, etc., all of which are monobasic acids. The three mentioned glycerides have the following composition:
There are also mixed glycerides exemplified by the following formula:
When these substances, or oils composed principally of them, are treated with alkali with the aid of heat, decomposition takes place, which may be illustrated as follows:
|C3H5||OC18H33O + 3NaOH =||C3H5||OH + 3Na.OC28H33O|
that is, olein is decomposed by sodium hydroxide into glyceryl hydroxide, or glycerin, and sodium oleate, or a sodium soap.
The waxes differ from the fats proper in being esters of the higher monatomic alcohols like cetyl alcohol, C15C33.OH, and myricyl alcohol, C30H61.OH, instead of being glycerides. The fatty acids present are partly palmitic and stearic, but more largely still higher ones, like cerotic acid, C27H54O2.
Other fatty acids represented in fixed oils are: butyric acid, C4H8O2; valeric acid, C5H10O2; caproic acid, C6H12O2; caprylic acid, C8H16O2; capric acid, C10H20O2; lauric acid, C12H24O2; myristic acid, C14H28O2; arachidic acid, C20H40O2; erucic acid, C22H42O2; hypogaeic acid, C16H30O2. The first few members of the above list are known as the volatile fatty acids, which serve as the basis for the determination of what is known as the Reichert-MeissI number.
Olein. Elain. Liquid Principle of Oils.—It is extremely difficult to obtain olein pure. Being in most oils associated with the solids stearin and palmitin, it must be separated by pressure and other mechanical means, which separation is not always perfectly effected. As ordinarily procured, therefore, olein contains more or less of palmitin or stearin, or both. In this somewhat impure state it is obtained either by the agency of alcohol or by expression. When one of the oils, olive oil, for example, is dissolved in boiling alcohol, 'the solution, on cooling, deposits the concrete principles, still retaining the olein, which it yields upon evaporation. The other method consists in compressing one of the solid fats, or one of the liquid oils rendered concrete by cold, between folds of bibulous paper, which absorb the olein, and give it up afterwards by compression under water. Olein is a liquid of oily consistence, congealing at -6° C. (21.2° F.), colorless when pure, with little odor and a sweetish taste, insoluble in water, soluble in boiling alcohol and ether. Its formula, as already stated, is C3H5(OC18H33O)3, being an oleate of the triad radical glyceryl, C3H5. By reaction with nitric acid, or, more exactly stated, under the influence of nitrous acid fumes, olein is converted into a deep yellow butyraceous mass. If this be treated with hot alcohol, a deep orange-red oil is dissolved, and a peculiar fatty matter remains, called elaidin. This is white, crystalline, fusible at 34° C. (93.2° F.), insoluble in water, readily soluble in ether, and appears to be isomeric with olein. It is resolved by saponification with the alkalies into elaidic acid and glycerin.
Palmitin.—Palmitic acid occurs in the more liquid fats, such as palm oil and cocoa-nut oil, as well as in butter and human fat, as glyceride, while in spermaceti and some forms of wax it is combined with monatomic alcohol radicals. Palmitin is the palmitic acid glyceride, or glyceryl tripalmitate. It is best obtained from palm oil.
Stearin.—This exists abundantly in tallow and other animal fats. It may be obtained by treating the concrete matter of lard, free from olein, by cold ether so long as anything is dissolved. The palmitin is thus taken up, and stearin remains. A better method is to dissolve suet in heated oil of turpentine, allow the solution to cool, submit the solid matter to expression in unsized paper, repeat the treatment several times, and finally dissolve in hot ether, which deposits the stearin on cooling. This is concrete, white, opaque in mass, but of a pearly appearance as crystallized from ether, pulverizable, fusible at 66.5° C. (151.7° F.), soluble in boiling alcohol and ether, but nearly insoluble in those liquids cold, and quite insoluble in water. It consists of glyceryl and stearic acid in combination as a glyceride, C3H5(OC18H36O)3, and has been formed synthetically by heating a mixture of these two materials to 280° to 300° C. (536°-572° F.).
Commercially the fixed oils are frequently sold under the names summer pressed and winter pressed. These were once really seasonal designations, as an oil pressed during the warmer months would contain more dissolved stearin and would consequently congeal or cause a deposit when chilled, while an oil pressed during cold weather would remain transparent at low temperatures, and thus winter pressed oils were safer for lubricating purposes and commanded a higher price. Artificial refrigeration now makes it possible to make either grade of oil at any season of the year, although the former seasonal names are still used.
The fixed oils are liable to certain spontaneous changes, which have been investigated by Pelouze and Boudet. It appears from their researches that the oils are accompanied, in the seeds which contain them, with principles which act as a ferment and cause the oils to resolve themselves spontaneously into the several fatty acids which they afford on saponification, and into glycerin. This change takes place in the seeds as soon as the cells containing the oils are broken, so as to permit the contact of the fermenting principle existing in the grain. The decomposition of fats by the action of enzymes has been made a working method capable of technical application, by Connstein, Hoyer and Wartenburg. The enzyme contained in the castor oil bean has been found best adapted for this. An emulsion of fats, water, 10 per cent. of ground castor oil beans and a small amount of free acid are used, when the decomposition proceeds rapidly. As rancidity in fats renders them altogether useless in pharmacy, and as it is not always readily discoverable by the senses in its earlier stages, it becomes desirable to possess a test by which it may be detected. Such a test is to be found, according to Thos. B. Groves, in potassium iodide, which is rapidly decomposed by the new principles developed, and the orange-brown discoloration produced by the liberation of the iodine indicates the existence 'of rancidity, and the degree of that discoloration, approximately, the extent of the change. The alteration of color is said by Groves to be plainly perceptible when only one-twentieth of rancid fat is present. The presence of water in a fatty oil favors the production of rancidity.
It is also extremely important to be able to protect fats against this change. The complete exclusion of air, light, and moisture—and, when in relation to air this may not be entirely practicable, the destruction by heat of the ferment-germs contained in the air, by which the decomposition is 'often originated— will go far to effect this object; but it would often be very inconvenient, if not impossible, to carry these measures into complete effect, and hence the discovery of substances which may have the effect of retarding, if not wholly preventing, these fermenting processes, whether by the destruction of the ferment-germs or otherwise, is extremely desirable; this preservative effect has been known and practically used many years, and since the principle upon which they are supposed to act has been discovered the number has been extended. Thus, benzoin rubbed up with fats is well known to preserve them long against rancidity, and benzoinated lard, made by extracting ten per cent. of benzoin with melted lard, is one of the official preparations, and the buds of the poplar (Populus nigra) are perhaps still more effectual, as, according to Deschamps, lard impregnated with their virtues will keep good indefinitely. In the French Codex the poplar buds are employed in the Pommade de Bourgeon de Peuplier, in which 8 parts of the dried buds are used to 40 parts of the ointment, consisting of lard impregnated with the virtues of several narcotic substances, the fresh narcotic plants being boiled with lard until all their water is evaporated, and the buds afterwards digested in the strained liquid for twenty-four hours. Groves made experiments with many volatile oils and other analogous substances to test their preservative power. (See A. J. P., 1865, 54, 61.) Hirzel says that animal fats may be kept in a good condition for a year by the following plan. Mix 14 pounds of the recently melted fat with 5 drachms of common salt and 15 grains of alum, in fine powder, heat till a scum is formed on the surface, separate the scum, and, when the clear liquid has cooled, wash it many times with water with malaxation, so as to remove all the salt, then evaporate the water at a heat insufficient to injure the fat. (A. J. P., 1868, 334.)
The adulteration of the fixed oils may be effected in several ways—by admixture with the fatty oil of substances distinctly foreign to the fats, and by adding a cheaper or inferior oil to one of greater value. In the former case we may have the addition of paraffin wax, ceresine, mineral oils, neutral tar 'oils, resin oils, resin, and waxes. Of these, the first three are entirely unsaponifiable, resin oils contain but small quantities of saponifiable substances, waxes are partly saponifiable, and resin almost completely saponifiable. The determination of unsaponifiable matter is therefore of great importance. The common method for this is to saponify the suspected sample with alcoholic potassium hydroxide and then to shake out the unsaponifiable matter with ether or petroleum ether. From this solution, on evaporation, will be obtained the mineral, resin, or tar oils that may have been present. For these there are appropriate tests elsewhere noted. In case a cheaper oil or fat has been added for the purpose of adulterating a more valuable one, we must be guided by the determination of certain constants, such as those mentioned below by Cowley, or by the indication of certain qualitative color tests. The constants referred to are much more to be depended upon in such a case.
R. C. Cowley (P. J., 1897, 331) regards the following as the most important determinations in examining fats and fixed oils. 1. Specific gravity. 2. Melting and solidifying points. 3. Melting and solidifying points of fatty acids. 4. Behavior with solvents. 5. The Hehner value. 6. The Reichert-Meissl value. 7. The saponification value. 8. The iodine value. To these have been added during recent years: 9. The refractive index. 10. The acetyl number. 11. The temperature rise with sulphuric acid (Maumene number).
It is sometimes desirable to deprive the fixed oils of color. The following process for this purpose is recommended by Brunner. The oil is first brought to the state of emulsion by strongly agitating it with water rendered mucilaginous by gum or starch; the emulsion is treated for each part of oil with two parts of wood charcoal, previously well heated and coarsely powdered, the finer particles being sifted out; the pasty mass is then completely dried at a heat not exceeding 100° C. (212° F.), and exhausted by cold ether in a percolator; finally, the ethereal solution, having been allowed to stand, in order that any charcoal present in it may subside, is submitted to distillation, so as to separate the ether, and the oil remains colorless in the retort. (J. P. C., Sept., 1858.) Berlandt recommends the following method: Shake strongly for some minutes 900 parts of the fixed oil with 120 parts of water holding in solution 3 parts of potassium permanganate, allow the mixture to stand for some hours in a warm place, and then filter. The oil becomes colorless. (J. P. C., Oct., 1867.)
The modern method of decolorizing vegetable oils is to filter them through kaolin or Fuller's earth. Preliminary treatment with acids and alkalies is sometimes advisable.