Related entries: Sapo (U. S. P.)—Soap - Acidum Stearicum (U. S. P.)—Stearic Acid - Acidum Oleicum (U. S. P.)—Oleic Acid
Other tomes: BPC - Cook (volatile oils) - Cook (fixed oils) - USDisp - Potter (volatile oils) - Potter (fixed oils) - AJP1871 - AJP1871 - AJP1885
The term Oil applies to a number of unctuous bodies not miscible with water, from both the vegetable and animal kingdoms, which are fluid at ordinary or slightly elevated temperature. When placed upon paper they render it translucent, or impart to it a greasy stain. Oils may be conveniently divided, with reference to their volatility, into two great classes: Fixed or fatty oils and fats, to which also belong the waxes (see Cera), and volatile or essential oils. Intermediate between the two, although chemically unlike either, stand the mineral oils and mineral waxes, or paraffins (see Petrolatum).
Olea Fixa.—FIXED or FATTY OILS (Olea pinguia). Fixed oils derive their name from not being volatilized by the vapors of boiling water. The difference between fatty oils and fats is merely one of consistency, the former being liquid, the latter solid or semisolid at ordinary temperatures. In the vegetable kingdom, fixed oils are mostly derived from the seeds of dicotyledonous plants, although monocotyledonous plants, such as the palm trees, furnish several of the technically important fixed oils. The oil often constitutes a large proportion of the seeds, e. g., not less than 25 per cent in linseed, 50 per cent in walnuts, about as much in almonds, as against about 2 per cent in cereals. It is obtained from the crushed oil-bearing material, either by cold or warm pressure, in hydraulic presses, or by extracting with such solvents as carbon disulphide, or by boiling the crushed material with water, whereby the oil floats on top and may be conveniently collected. The residual press-cakes, obtained in the first process (oil cakes), are valuable feed material for cattle, since they contain much nitrogenous and fatty matter (see table in Prof. S. P. Sadtler's Handbook of Indust. Org. Chem., 2d ed., 1895, p. 70).
The oils and fats derived from the animal kingdom, are obtained from various organs of the animal; thus, bone-oil from bones, by boiling with water, or extraction with solvents; neat's-foot oil from the feet of oxen by boiling with water; cod-liver oil and shark oil, from the respective livers, by spontaneous exudation and gentle expression; tallow and lard from the internal abdominal fat of sheep and hogs (see Sevum and Adeps), etc. The crude oils and fats as obtained in the manner alluded to, are mostly of a yellow, brown or even black color, and frequently require more or less purification. This is often effected by mechanical treatment, such as filtration with or without charcoal, etc., but more frequently, by chemical processes, especially treatment with 1 or 2 per cent of strong sulphuric acid (applicable, for example, to linseed oil), or with zinc chloride, or alkalies, tanning materials and oxidizers, such as potassium bichromate, hydrogen peroxide, etc.
The fatty oils of marine animals, and those from most vegetable sources, are fluid at ordinary temperature; palm oil, cacao-butter, nutmeg butter, cocoanut oil, and others, are semisolid like butter. When exposed to cold, fixed oils solidify at temperatures varying with the oil. Fatty oils are insoluble in water, rendering that fluid milky when agitated with it, but the oil finally rises upon the surface; if a mucilaginous substance, or alkaline carbonate be added, the oil is prevented from rising., and a permanent milky mixture called an emulsion is formed. With the exception of castor oil and croton oil, fatty oils are nearly insoluble in cold alcohol. They dissolve readily, however, in ether, carbon disulphide, chloroform, benzol, petroleum benzin, amyl alcohol, acetone, and oil of turpentine, and freely mix with one another, as well as with resins and volatile oils. They are all lighter than water, their specific gravities ranging from 0.879 to 0.968. Fatty oils are not volatile as such, but can be heated to boiling (at about 315° C., or 600° F.) whereby decomposition takes place, acrid fumes of acrolein (see Glycerin) being evolved, together with carbonic acid gas, some volatile organic acids and inflammable hydrocarbons. Upon condensing the vapors, an empyreumatic oil is obtained. When in the state of vapor, fixed oils take fire upon the approach of an ignited body; the products of combustion are water and carbonic acid gas.
As to their chemical nature, most fatty oils are mixtures of salts of the trivalent alcohol glycerin (C3H5[OH]3), with the saturated palmitic (C16H32O2) and stearic acids (C18H36O2), both higher homologues of acetic acid, of the general formula CnH2nO2, and the unsaturated oleic acid (C18H34O2), which represents the series CnH2n-2O2. The salts are called glycerin esters, or glycerides, and are known respectively as palmitin, stearin, and olein. The former two are solid and preponderate in solid fats—e. g., lard-while olein is liquid and predominates in liquid fats—e.g., olive oil and almond oil. The solid and liquid constituents of a fatty oil are frequently separated by subjecting the oil to hydraulic pressure at about the temperature of melting ice. Olive oil, for example, is differentiated into a purified olive oil and solid olive oil stearin, lard into lard oil and lard stearin, sperm oil (from the head of Physeter macrocephalus) into purified sperm oil and solid spermaceti(see Cetaceum), etc. In some fats—e. g., butter—part of the fatty acid is replaced by lower fatty acids—e. g., butyric, or in porpoise oil, by valerianic acid—both occurring as glycerin esters, butyrin, valerin, respectively (see also Glycerinand Adeps). In drying oils (see below), oleic acid is in part replaced by the still more unsaturated linoleic acid (C16H28O2 of the type CnH2n-4O2), the chief constituent of linseed oil, which is the type of drying oils. The waxes have an analogous, yet different composition (see Cera and Cetaceum). The presence of certain albuminous matters in fatty oils, and other causes as well, often induce the liberation of free fatty acid, especially the ill-smelling lower volatile acids. Thus butyric acid is formed in old butter, causing what is known as rancidity. Olive oil, palm oil, etc., are also liable to become rancid with age. Oils which have a tendency to liberate free fatty acids are undesirable for lubricating purposes. Neat's-foot oil hardly possesses this tendency. Mineral oils (see Petrolatum) are now frequently employed as lubricants, owing to their indifferent chemical nature.
When fatty oils and fats are treated with caustic alkalies, they are decomposed (saponified) into glycerin and the alkali salts of the fatty acids that were combined with glycerin. These alkali salts are called soaps, and the process is that of saponification. Analogous decomposition may also be effected by means of caustic lime, or oxides of heavy metals (see Emplastrum Plumbi), or by superheated steam (see Glycerinumand Sapo). For analytical purposes, this reaction is likewise of great importance. Since each ester requires a definite amount of caustic potash solution for saponification, values expressing the number of grammes of the fat or oil which are saponifiable by one gramme-equivalent of the caustic alkali employed, have been obtained for all fatty oils and waxes (Koettstorfer's Saponification Equivalent). The values obtained present some striking differences in various classes of oils, and may serve as useful guides in the detection of adulterations by certain oils. Thus, paraffin oils, on account of being hydrocarbons, are unaffected by caustic alkali, and, if mixed with fatty oils, will raise the saponification equivalent of the latter upon saponification of the oil. Washing out the soap with water will allow of the recovery of the admixed paraffin oil (see table and comment, by A. H. Allen, Commercial Organic Analysis, Vol. II, Part I, 3d ed., Philadelphia, 1899, pp. 53-58, and p.111). An additional important analytical method is based upon the absorption of bromine (Mills) or iodine (Hübl) by the different oils when they are in contact with solutions of these elements. Oils in which the glycerides of saturated acids (carbon atoms united by single bonds) dominate, as, for example, cocoanut oil, absorb much smaller quantities of halogens than those oils containing a highly unsaturated fatty acid (with two pairs of carbon atoms united by double bonds)—e. g., the glyceride of linoleic acid, the chief constituent of linseed oil. (For details, see A. H. Allen, loc. cit., pp. 62-66; and S. P. Sadtler, loc. cit., 2d ed., 1895, pp. 78 and 79.)
Parallel with their capacity for absorbing halogens, runs the well-known quality of fatty oils to absorb oxygen by prolonged exposure to the air, and to become more or less dry and solid. Accordingly, fatty oils are differentiated into drying oils and non-drying oils. The type of drying oils is linseed oil, and of the non-drying, olive oil (see enumeration of both classes of oils in the table subjoined).
Drying oils are also characterized by not yielding solid elaïdin when treated with nitrous acid in form of gas or in solution, while non-drying oils by virtue of their olein contents, when treated with nitrous acid gradually become a hard mass of elaïdin, an isomer of olein (compare Acidum Oleicum). (For a special description of the more important oils, see the authorities quoted; the pharmacopoeial oils are described under their respective headings.)
The following general classification of the fatty oils and waxes is adapted from A. H. Allen (Commercial Organic Analysis, 3d ed., Philadelphia, 1899, Vol. II, Part I, p. 88; and S. P. Sadtler, Handbook of Indust. Org. Chem., 2d ed., 1895, p. 51):
Classification of Fatty Oils and Waxes.—I. OLIVE-OIL GROUP. Vegetable oleins, Vegetable non-drying oils. Lighter than Groups III, IV, and V. Specific gravity, 0.914 to 0.920. Yields solid elaïdins with nitrous acid. Moderate saponification equivalents and iodine absorptions. Includes olive, almond, peach, and earthnut oils.
II. RAPE-OIL GROUP.—All oils from Cruciferae. Less perfectly non-drying oils. Yield pasty elaïdins; have higher iodine absorptions and high saponification equivalents. Includes oils of rape-seed (colza), cabbage seed, black and white mustard.
III. COTTON-SEED OIL GROUP.—Specific gravity, 0.920 to 0.926. Intermediate between drying and non-drying oils. Undergo more or less drying on exposure. Yield little or no elaïdin. Includes oils of cotton-seed, grape-seed, maize, sesame, sunflower, hazelnut, and beechnut.
IV. LINSEED-OIL GROUP.—Drying oils. Specific gravity, 0.924 to 0.937. Yield no elaïdin. Less viscous than the preceding groups. Includes oils of linseed, hemp-seed, poppy seed, tobacco seed, niger seed, Scotch fir-seed, and walnut.
V. CASTOR-OIL GROUP.—Medicinal oils. Very viscous and of high specific gravity (0.937 to 0.985). Includes castor and croton oils, both distinguished by their solubility in alcohol and glacial acetic acid.
VI. PALM-OIL GROUP.—Solid vegetable fats. Do not contain notable quantities of esters of lower fatty acids. Includes palm-oil, cacao butter, nutmeg butter, bayberry tallow, and shea or galam butter.
VII. COCOANUT-OIL GROUP.—Solid vegetable fats, of high specific gravity and low saponification equivalents. Members of sub-group A (cocoanut, palm-kernel, laurel, and macassar oils) contain notable proportions of esters of lower fatty acids, distilling over in a current of steam. Sub-group B are wax-like and of peculiar composition. (Japan wax, Myrtle wax.)
VIII. LARD-OIL GROUP.—Animal oleins. Do not dry notably on exposure, and give solid elaïdins with nitrous acid. Not turned brown by boiling with caustic alkalies (difference from marine animal oils). Includes neat's-foot oil, bone oil, lard oil, and tallow oil.
IX. TALLOW GROUP.—Solid animal fats. Predominantly glycerides of palmitic and stearic acids, although butter contains glycerides of lower acids, notably butyric acid. Includes tallow (suet), lard, bone fat, wool fat (saint), butter fat, oleomargarine, and manufactured stearin.
X. WHALE-OIL GROUP.—Marine animal oils. Offensive fishy odor, especially on warming; Reddish-brown color upon warming with caustic alkali. Dries more or less upon exposure, and yields but little elaïdin. Includes whale, porpoise, seal, menhaden, cod-liver, and shark-liver oils.
XI. SPERM-OIL GROUP.—Liquid waxes. Are not glycerides, but are esters of higher monatomic alcohols of the methane series. Yield solid elaïdins. Includes sperm oil, bottle-nose oil (doegling oil), and dolphin oil.
XII. SPERMACETI GROUP.—Waxes proper. Are esters (organic salts) of higher monatomic alcohols with higher fatty acids in free state. Includes spermaceti, beeswax, Chinese wax, and carnauba wax.
In the early days of Eclecticism a few plant preparations in which the natural oil of the drug was intimately associated with other proximate constituents, were introduced under the name oil, and as such are still employed. Among these may be named oil of stillingia, oil of capsicum, and oil of lobelia. These preparations are made by exhausting the thoroughly dried drug (stillingia root, capsicum, and lobelia seed) with official alcohol, and then distilling the alcohol until the residue is syrupy. This product in each case is a mixture that carries the therapeutical qualities of the drug in a marked degree of concentration, but consists largely of foreign substances. The "oil of stillingia" is prone to gelatinize, but the others keep fairly well. (Compare Oleoresinae.)
Olea Volatilia.—VOLATILE OILS (Essential oils). Volatile oils (essential oils) are aromatic liquids of vegetable origin, practically insoluble, or but slightly soluble in water, and capable of being distilled with more or less facility in the vapors of boiling water, even though their own boiling points lie considerably higher. Like fatty oils, they render paper translucent, but the oily stain produced gradually disappears upon exposure. With one exception (Oil of Aspidium) essential oils have been obtained from phanerogamous plants only, in which, as a rule, they occur ready-formed. Some oils, e. g., of bitter almond, black mustard, or sweet birch, originate in definite compounds contained in the plants (amygdalin, sinigrin, gaultherin respectively), and are evolved therefrom in the presence of water by the action of certain ferments or enzymes (emulsin, myrosin, betulase) that are likewise present.
All parts of a plant, leaves, flowers, fruits, stems, and roots may yield essential oils, although the oil is in most cases derived only from one or two of these organs. In a few cases, such as Chinese cinnamon (Cassia cinnamon), oil of uniform quality may be obtained in fair quantities from various parts of the plant, while reversedly, in Ceylon cinnamon (Cinnamomum zeylanicum) the oils yielded by the bark, the leaves, and the root differ materially in their chemical composition.
Some essential oils, e. g., of bitter orange, oil of lemon, etc. (which see), are prepared by expressing the rind of the fruit containing the oil. Certain oils used in perfumery which are sensitive to heat, e. g., the odoriferous principles of hyacinth, jasmine, etc., are obtained by maceration, especially by abstracting the aroma by means of liquid fats or semisolid paraffins (enfleurage). Again, synthetic oils, such as artificial methyl salicylate, are obtained by laboratory processes which are briefly described under their respective headings. All other oils are obtained by distillation with the vapors of boiling water. Directions for the pharmaceutical preparation of essential oils were given by the older pharmacopoeias, for example, the Edinburgh and the Dublin Pharmacopoeias (see this Dispensatory, preceding editions).
The technical preparation of essential oils in the different countries producing them is carried out by distilling the oil from the oil-bearing material, mixed with water, by means of steam, which either runs into the material direct, or is applied to the vessel externally by in means of a steam-jacket. In some cases (e.g., eucalyptus oils) the oil-bearing material is deprived of its oil by direct steam without previous maceration. Rectification of the crude oils thus obtained is effected by fractional distillation either at atmospheric pressure, or, if decomposition is to be feared, at reduced pressure, whereby the boiling point is lowered.
The advances made within comparatively recent years in the theoretical study of essential oils has been the cause of a simultaneous development of this branch of chemical industry. By operating upon the basis of exact physical and chemical investigation, the manufacture of essential oils has been carried to a degree of refinement well illustrated by the classical work now before us, Die Aetherischen Oele, by E. Gildemeister and Frederick Hoffmann, published within recent months by Messrs. Schimmel & Co., of Leipzig. We are greatly indebted to this invaluable work, which we freely consulted in the preparation of this paper, but which, in its complete form, should be in the hands of every pharmacist.
Most essential oils are colorless or yellowish, although some are greenish or bluish-green, while others, like oil of thyme, soon acquire a dark red-brown color. Some oils deposit a crystalline body upon standing, often called a stearopten or camphor; the fluid portion being termed an elaeopten. Such deposits are formed, for example, in the oils of neroli, chamomile, matico leaves (Flückiger's matico camphor), elecampane (alant camphor), etc. Other oils produce crystalline deposits at low temperatures, e.g., anise oil deposits anethol, American peppermint oil menthol; Japanese peppermint oil is a semisolid mixture of menthol and liquid oil.
The specific gravities of essential oils vary more than those of fatty oils. While all of the latter class are lighter than water, a number of essential oils, such as those of bitter almond, cassia, cinnamon, cloves, sassafras, mustard, and wintergreen, are heavier than water. The specific gravities vary from 0.800 for oil of heracleum and 0.833 for oil of rue, to 1.187 for oil of wintergreen. All essential oils are soluble in absolute alcohol, ether, chloroform, benzene, benzol, carbon disulphide, etc.; most of them also form clear solutions with weaker alcohol, of even as low strength as 70 per cent by volume. This property assists us in recognizing many adulterations, e. g., mineral oils and most fatty oils. An important agency in the identification of an essential oil consists in its behavior toward a ray polarized light, which is determined by means of polarimeters (polariscopes). (See article on "The Polarimeter and Its Use in Pharmacy," by Dr. Charles Symes, in Amer. Jour. Pharm., 1880, p. 44, where there is also appended a list of specific gravities and optical rotations for a number of essential oils.)
Most essential oils readily undergo a change in color, consistency, and composition if exposed to air and light, and gradually change in odor; hence the necessity of keeping them in well-stoppered bottles, preferably of amber color, protected from air and light. The constituents of essential oils are of a far greater variety than those of fatty oils, and may be conveniently classed as follows (adapted from the work above quoted):
1. HYDROCARBONS.—Paraffins (CnH2n+2), and olefines (unsaturated paraffins CnH2n-4) are sometimes found in essential oils, such as arnica flowers, matricaria (matricaria-camphor), oil of bay (myrcen, C10H16), etc. Other hydrocarbons of occasional occurrence are para cymol (C10H14) in oil of thyme, etc., and styrol (C6H5.CH:CH2) in oil of storax. By far the most important essential oil hydrocarbons are those known as the TERPENES. They are isomers of the formula C10H16, unsaturated, boiling between 150° and 180° C. (302° and 356° F.) They are optically dextro- or laevo-rotatory, or inactive, and comprise the following: (1) Pinene; (2) camphene, solid, melting at 50° C. (122° F.); (3) fenchene; (4) limonene; (5) dipentene; (6) sylvestrene; (7) terpinene; (8) phellandrene.
SESQUITERPENES are hydrocarbons of the formula C15H24; they boil between 250° and 280° C. (482° and 536° F.); their specific gravity is above 0.90; they comprise: (1) cadinene; (2) caryophyllene; (1) humulene; (4) cedrene, etc.
POLYTERPENES.—Diterpenes and triterpenes, boiling above 300° C. (572° F.). They have been little investigated.
The following classes comprise substances which constitute the characteristic odoriferous principles of the oils in which they occur:
II. ALCOHOLS.—(1) hexyl- (C6H13OH) and octyl-alcohol (C8H17OH) in heracleum oils; (2) linalool (coriandrol) (C10H18O) in oils of bergamot, coriander, etc.; (3) geraniol (rhodinol) (C10H18O) in oils of rose and lemon grass; (4) citronellol (C10H20O), in oils of geranium and rose; (5) terpineol (C10H18O), in oils of cajeput and camphor; (6) borneol (C10H18O) in Borneo camphor; (7) menthol (C10H20O).
III. ALDEHYDES.—(1) Citral (Geranial) (C10H16O), the aldehyde of geraniol; in lemongrass oil; (2) Citronellal (C10H18O), in citronella oil; (3) furfurol (C4H4O), in oil of cloves; (4) benzaldehyde (C6H5.CHO), in oils of bitter almond and cherry laurel; (5) salicylic aldehyde (C6H4OH.CHO), in spiraea oil; (6) anis-aldehyde (C6H4.OCH3.CHO), in old anise oil; (7) cumin aldehyde (C6H4.C3H7.CHO), in oil of Roman chamomile; (8) vanillin (C6H3.OH.OCH3.CHO); (9) heliotropin, in spiraea oil; (10) cinnamic aldehyde (C6H5CH:CH.CHO), in cassia and cinnamon oils; (11) ortho-cumar-aldehyde methyl-ether (C6H4.OCH3.CH:CH.CHO), in oil of cassia.
IV. KETONES.—(1) Methyl-amyl-ketone (CH3.CO.C5H11), in oil of cloves; (2) methyl-heptenone (C8H14O), allied to linalool; (3) carvone (C10H14O), in oil of caraway; (4) anis-ketone (C6H4.OCH3.CH2.CO.CH3); (5) Japan camphor (C10H16O) (see Camphora); (6) fenchone (C10H16O), liquid, in oil of fennel; (7) thujone (tanacetone) (C10H16O), in oil of thuja; (8) pulegone (C10H16O), in oil of pennyroyal; (9) menthone (C10H18O), in oil of peppermint; (10) irone (C13H20O), in oil of orris root.
V. ACIDS.—Acetic, propionic, butyric, valerianic, tiglinic acids, seldom free, mostly as esters, combined with higher alcohols. Furthermore, benzoic, salicylic, and cinnamic acids. LACTONES.—coumarin and hydrocoumarin, alanto-lactone (helenin) in oil of elecampane; OXIDES.—Cineol (eucalyptol) C10H18), occurring in many oils, especially from Artemisia cina, cajeput and eucalyptus.
VI. PHENOLS and PHENOL-ETHERS.—(1) Vanillin; (2) anethol; (3) para-cresol methyl-ether (C6H4.CH3.OCH3), in ylang-ylang oil; (4) carvacrol (iso-propyl ortho-cresol), in oil of Monarda fistulosa, etc.; (5) thymol (iso-propyl meta-cresol), in oil of thyme, etc.; (6) chavicol (para-allyl-phenol), in Java betel-leaf oil, and oil of bay; (7) methyl-chavicol, in anise oil; (8) eugenol (allyl-guaiacol) (C6H3.C3H5.OCH3OH), in oil of cloves; (9) safrol (C10H10O2), in sassafras and camphor oils; (10) asaron (C12H16O3), in oil of Asarum europaeum; (11) apiol (C12H14O4), from oil of parsley.
VII. MUSTARD OILS.—Contain sulphur compounds.
The more important of these constituents will be briefly described under the oils wherein they chiefly occur. Since the chemical nature of essential oils is in many cases well-defined, it often permits of a more or less exact quantitative determination of their characteristic constituents. Thus, esters, e. g., linaloyl acetate in oil of bergamot, may be determined by their saponification value (compare Fatty Oils; also see Cera); certain aldehydes, e. g., cinnamic aldehyde in oil of cassia, by means of the crystalline compounds they form with sodium bisulphite; phenols, e. g., eugenol in Ceylon cinnamon oil, by the loss of volume which the oil incurs by being shaken with solution of caustic potash. An interesting analytical method, applicable to oils containing an alkyl-oxy-group (e. g., methoxy, OCH3) as anethol in anise oil (which see), consists in determining the methyl-number, i. e., the number of milligrammes of methyl that is split off when 1 gramme of oil is boiled with hydriodic acid (measured by the amount of silver iodide that is precipitated when the vapors of the methyl iodide formed are conducted into an alcoholic solution of silver nitrate). Since alcohol also gives a methyl-number when subjected to this reaction, the latter may serve as a good test for alcohol in such oils as do not contain a methoxy-group, and consequently do not yield a methyl number, as bitter almond, bergamot, caraway, lemon, cubeb, eucalyptus, lavender, peppermint oils, etc.
Owing to their high price, essential oils are frequently subject to adulteration. If a few drops of the oil in question be placed on filtering paper, the odor will sometimes indicate impurities. An addition of alcohol reduces the specific gravity of the oil. Larger quantities may be recognized by shaking out with water, distilling the aqueous liquid and testing the distillate for alcohol by the iodoform test, viz., by warming with sodium carbonate and iodine, whereby iodoform is precipitated. Or, shaking the oil with dry chloride of calcium (Borsarelli), or acetate of potassium (J. J. Bernoulli), will separate the alcohol from the essential oil. Oil of turpentine is the adulterant most frequently used. It may often be recognized by its odor. Its presence affects the specific gravity and the solubility of the oil in 70 per cent alcohol. Its chief constituent being pinene, the presence of this body in oils not naturally containing it, proves the presence of turpentine. Addition of fatty oils to essential oils may be recognized by a permanent greasy stain they leave on paper, upon prolonged exposure. Their presence may also be detected by distilling the essential oil with the vapors of boiling water, and heating a portion of the residue on platinum foil, or in a dry test-tube with acid potassium sulphate, whereby the irritant vapors of acrolein are evolved. Treatment with 70 per cent alcohol, in which all fatty oils, including castor oil, are insoluble, will also reveal their presence in many Oils. Mineral Oils (petroleum) are easily separated and recognized by reason of their insolubility in alcohol, their low specific gravity, and their inability to saponify with alkalies. Some essential oils as stated above, contain small quantities of paraffins as regular constituents. Oils of cedar, copaiba, and gurjun balsam, are also used as adulterants of essential oils, and are detected with difficulty. They dissolve with difficulty in alcohol of 70 to 90 per cent, are strongly laevo-rotatory, and boil at temperatures above 250° C. (482° F.).