John Avery Lomax

Essential Oils—Source and Preparation—Properties—Artificial and Synthetic Perfumes.

The number of raw materials, both natural and artificial, at the disposal of the perfumer, has increased so enormously during recent years that the scenting of soaps has now become an art requiring very considerable skill, and a thorough knowledge of the products to be handled. Not only does the all-important question of odour come into consideration, but the action of the perfumes on the soap, and on each other, has also to be taken into account. Thus, many essential oils and synthetic perfumes cause the soap to darken rapidly on keeping, e.g., clove oil, cassia oil, heliotropin, vanillin. Further, some odoriferous substances, from their chemical nature, are incompatible with soap, and soon decompose any soap to which they are added, while in a few cases, the blending of two unsuitable perfumes results, by mutual reaction, in the effect of each being lost. In the case of oils like bergamot oil, the odour value of which depends chiefly on their ester content, it is very important that these should not be added to soaps containing much free alkali, as these esters are readily decomposed thereby. Some perfumes possess the property of helping the soap to retain other and more delicate odours considerably longer than would otherwise be possible. Such perfumes are known as "fixing agents" or "fixateurs," and among the most important of these may be mentioned musk, both natural and artificial, civet, the oils of Peru balsam, sandalwood, and patchouli, and benzyl benzoate.

The natural perfumes employed for addition to soaps are almost entirely of vegetable origin, and consist of essential oils, balsams, and resins, animal perfumes such as musk, civet, and ambergris being reserved principally for the preparation of "extraits".

As would be expected with products of such diverse character, the methods employed for the preparation of essential oils vary considerably. Broadly speaking, however, the processes may be divided into three classes—(1) expression, used for orange, lemon, and lime oils; (2) distillation, employed for otto of rose, geranium, sandalwood, and many other oils; and (3) extraction, including enfleurage, by which the volatile oil from the flowers is either first absorbed by a neutral fat such as lard, and then extracted therefrom by maceration in alcohol, or directly extracted from the flowers by means of a volatile solvent such as benzene, petroleum ether, or chloroform. The last process undoubtedly furnishes products most nearly resembling the natural floral odours, and is the only one which does not destroy the delicate fragrance of the violet and jasmine. The yield, however, is extremely small, and concrete perfumes prepared in this way are therefore somewhat costly.

The essential oils used are derived from upwards of twenty different botanical families, and are obtained from all parts of the world. Thus, from Africa we have geranium and clove oils; from America, bay, bois de rose, Canadian snake root, cedarwood, linaloe, peppermint, petitgrain, and sassafras; from Asia, camphor, cassia, cinnamon, patchouli, sandalwood, star anise, ylang-ylang, and the grass oils, viz., citronella, lemongrass, palmarosa, and vetivert; from Australia, eucalyptus; while in Europe there are the citrus oils, bergamot, lemon, and orange, produced by Sicily, aspic, lavender, neroli, petitgrain, and rosemary by France, caraway and clove by Holland, anise by Russia, and otto of rose by Bulgaria.

Attempts have been made to classify essential oils either on a botanical basis or according to their chemical composition, but neither method is very satisfactory, and, in describing the chief constituents and properties of the more important oils, we have preferred therefore to arrange them alphabetically, as being simpler for reference.

It is a matter of some difficulty to judge the purity of essential oils, not only because of their complex nature, but owing to the very great effect upon their properties produced by growing the plants in different soils and under varying climatic conditions, and still more to the highly scientific methods of adulteration adopted by unscrupulous vendors. The following figures will be found, however, to include all normal oils.

Anise Stell, or Star Anise, from the fruit of Illicium verum, obtained from China. Specific gravity at 15° C., 0.980-0.990; optical rotation, faintly dextro- or lÆvo-rotatory, +0° 30' to -2°; refractive index at 20° C., 1.553-1.555; solidifying point, 14°-17° C.; solubility in 90 per cent. alcohol, 1 in 3 or 4.

The chief constituents of the oil are anethol, methyl chavicol, d-pinene, l-phellandrene, and in older oils, the oxidation products of anethol, viz. anisic aldehyde and anisic acid. Since anethol is the most valuable constituent, and the solidifying point of the oil is roughly proportional to its anethol content, oils with a higher solidifying point are the best.

Aspic oil, from the flowers of Lavandula spica, obtained from France and Spain, and extensively employed in perfuming household and cheap toilet soaps; also frequently found as an adulterant in lavender oil. Specific gravity at 15° C., 0.904-0.913; optical rotation, French, dextro-rotatory up to +4°, rarely up to +7°, Spanish, frequently slightly lÆvo-rotatory to -2°, or dextro-rotatory up to +7°; esters, calculated as linalyl acetate, 2 to 6 per cent.; most oils are soluble in 65 per cent. alcohol 1 in 4, in no case should more than 2.5 volumes of 70 per cent. alcohol be required for solution.

The chief constituents of the oil are: linalol, cineol, borneol, terpineol, geraniol, pinene, camphene and camphor.

Bay oil, distilled from the leaves of Pimenta acris, and obtained from St. Thomas and other West Indian Islands. It is used to some extent as a perfume for shaving soaps, but chiefly in the Bay Rhum toilet preparation. Specific gravity at 15° C., 0.965-0.980; optical rotation, slightly lÆvo-rotatory up to -3°; phenols, estimated by absorption with 5 per cent. caustic potash solution, from 45 to 60 per cent.; the oil is generally insoluble in 90 per cent. alcohol, though when freshly distilled it dissolves in its own volume of alcohol of this strength.

The oil contains eugenol, myrcene, chavicol, methyl eugenol, methyl chavicol, phellandrene, and citral.

Bergamot oil, obtained by expression from the fresh peel of the fruit of Citrus Bergamia, and used very largely for the perfuming of toilet soaps. Specific gravity at 15° C., 0.880-0.886; optical rotation, +10° to +20°; esters, calculated as linalyl acetate, 35-40 per cent., and occasionally as high as 42-43 per cent.; frequently soluble in 1.5 parts of 80 per cent. alcohol, or failing that, should dissolve in one volume of 82.5 or 85 per cent. alcohol. When evaporated on the water-bath the oil should not leave more than 5-6 per cent. residue.

Among the constituents of this oil are: linalyl acetate, limonene, dipentene, linalol, and bergaptene.

Bitter Almond Oil.—The volatile oil obtained from the fruit of Amygdalus communis. Specific gravity at 15° C., 1.045-1.06; optically inactive; refractive index at 20° C., 1.544-1.545; boiling point, 176-177° C.; soluble in 1 or 1.5 volumes of 70 per cent. alcohol.

The oil consists almost entirely of benzaldehyde which may be estimated by absorption with a hot saturated solution of sodium bisulphite. The chief impurity is prussic acid, which is not always completely removed. This may be readily detected by adding to a small quantity of the oil two or three drops of caustic soda solution, and a few drops of ferrous sulphate solution containing ferric salt. After thoroughly shaking, acidulate with dilute hydrochloric acid, when a blue coloration will be produced if prussic acid is present.

The natural oil may frequently be differentiated from artificial benzaldehyde by the presence of chlorine in the latter. As there is now on the market, however, artificial oil free from chlorine, it is no longer possible, by chemical means, to distinguish with certainty between the natural and the artificial product. To test for chlorine in a sample, a small coil of filter paper, loosely rolled, is saturated with the oil, and burnt in a small porcelain dish, covered with an inverted beaker, the inside of which is moistened with distilled water. When the paper is burnt, the beaker is rinsed with water, filtered, and the filtrate tested for chloride with silver nitrate solution.

Canada snake root oil, from the root of Asarum canadense. Specific gravity at 15° C., 0.940-0.962; optical rotation, slightly lÆvo-rotatory up to -4°; refractive index at 20° C., 1.485-1.490; saponification number, 100-115; soluble in 3 or 4 volumes of 70 per cent. alcohol.

The principal constituents of the oil are a terpene, asarol alcohol, another alcohol, and methyl eugenol. The oil is too expensive to be used in other than high-class toilet soaps.

Cananga or Kananga oil, the earlier distillate from the flowers of Cananga odorata, obtained chiefly from the Philippine Islands. Specific gravity at 15° C., 0.910-0.940; optical rotation, -17° to -30°; refractive index at 20° C., 1.4994-1.5024; esters, calculated as linalyl benzoate, 8-15 per cent.; soluble in 1.5 to 2 volumes of 95 per cent. alcohol, but becoming turbid on further addition.

The oil is qualitatively similar in composition to Ylang-Ylang oil, and contains linalyl benzoate and acetate, esters of geraniol, cadinene, and methyl ester of p-cresol.

Caraway oil, distilled from the seeds of Carum carui. Specific gravity at 15° C., 0.907-0.915; optical rotation, +77° to +79°; refractive index at 20° C., 1.485-1.486; soluble in 3 to 8 volumes of 80 per cent. alcohol. The oil should contain 50-60 per cent. of carvone, which is estimated by absorption with a saturated solution of neutral sodium sulphite. The remainder of the oil consists chiefly of limonene.

Cassia oil, distilled from the leaves of Cinnamomum cassia, and shipped to this country from China in lead receptacles. Specific gravity at 15° C., 1.060-1.068; optical rotation, slightly dextro-rotatory up to +3° 30'; refractive index at 20° C., 1.6014-1.6048; soluble in 3 volumes of 70 per cent. alcohol as a general rule, but occasionally requires 1 to 2 volumes of 80 per cent. alcohol.

The value of the oil depends upon its aldehyde content, the chief constituent being cinnamic aldehyde. This is determined by absorption with a hot saturated solution of sodium bisulphite. Three grades are usually offered, the best containing 80-85 per cent. aldehydes, the second quality, 75-80 per cent., and the lowest grade, 70-75 per cent.

Other constituents of the oil are cinnamyl acetate and cinnamic acid. This oil gives the characteristic odour to Brown Windsor soap, and is useful for sweetening coal-tar medicated soaps.

Cedarwood oil, distilled from the wood of Juniperus virginiana. Specific gravity at 15° C., 0.938-0.960; optical rotation, -35° to -45°; refractive index at 20° C., 1.5013-1.5030. The principal constituents are cedrene and cedrol.

Cinnamon oil, distilled from the bark of Cinnamomum zeylanicum. Specific gravity at 15° C., 1.00-1.035; optical rotation, lÆvo-rotatory up to -2°; usually soluble in 2 to 3 volumes of 70 per cent. alcohol, but sometimes requires 1 volume of 80 per cent. alcohol for solution; aldehydes, by absorption with sodium bisulphite solution, 55-75 per cent.; and phenols, as measured by absorption with 5 per cent. potash, not exceeding 12 per cent.

The value of this oil is not determined entirely by its aldehyde content as is the case with cassia oil, and any oil containing more than 75 per cent. aldehydes must be regarded with suspicion, being probably admixed with either cassia oil or artificial cinnamic aldehyde. The addition of cinnamon leaf oil which has a specific gravity at 15° C. of 1.044-1.065 is detected by causing a material rise in the proportion of phenols. Besides cinnamic aldehyde the oil contains eugenol and phellandrene.

Citronella Oil.—This oil is distilled from two distinct Andropogon grasses, the Lana Batu and the Maha pangiri, the former being the source of the bulk of Ceylon oil, and the latter being cultivated in the Straits Settlements and Java. The oils from these three localities show well-defined chemical differences.

Ceylon Citronella oil has the specific gravity at 15° C., 0.900-0.920; optical rotation, lÆvo-rotatory up to -12°; refractive index at 20° C., 1.480-1.484; soluble in 1 volume of 80 per cent. alcohol; total acetylisable constituents, calculated as geraniol, 54-70 per cent.

Singapore Citronella Oil.—Specific gravity at 15° C., 0.890-0.899; optical rotation, usually slightly lÆvo-rotatory up to -3°; refractive index at 20° C., 1.467-1.471; soluble in 1 to 1.5 volumes of 80 per cent. alcohol; total acetylisable constituents, calculated as geraniol, 80-90 per cent.

Java Citronella Oil.—Specific gravity at 15° C., 0.890-0.901; optical rotation, -1° to -6°; total acetylisable constituents, calculated as geraniol, 75-90 per cent.; soluble in 1-2 volumes of 80 per cent. alcohol.

The chief constituents of the oil are geraniol, citronellal, linalol, borneol, methyl eugenol, camphene, limonene, and dipentene. It is very largely used for perfuming cheap soaps, and also serves as a source for the production of geraniol.

Bois de Rose Femelle oil, or Cayenne linaloe oil, distilled from wood of trees of the BurseraceÆ species. Specific gravity at 15° C., 0.874-0.880; optical rotation, -11° 30' to -16°; refractive index at 20° C., 1.4608-1.4630; soluble in 1.5 to 2 volumes of 70 per cent. alcohol.

The oil consists almost entirely of linalol, with traces of saponifiable bodies, but appears to be free from methyl heptenone, found by Barbier and Bouveault in Mexican linaloe oil. This oil is distinctly finer in odour than the Mexican product.

Clove oil, distilled from the unripe blossoms of Eugenia caryophyllata, the chief source of which is East Africa (Zanzibar and Pemba). Specific gravity at 15° C., 1.045-1.061; optical rotation, slightly lÆvo-rotatory up to -1° 30'; phenols, estimated by absorption with 5 per cent. potash solution, 86-92 per cent.; refractive index at 20° C., 1.5300-1.5360; soluble in 1 to 2 volumes of 70 per cent. alcohol.

The principal constituent of the oil is eugenol, together with caryophyllene and acet-eugenol. While within certain limits the value of this oil is determined by its eugenol content, oils containing more than 93 per cent. phenols are usually less satisfactory in odour, the high proportion of phenols being obtained at the expense of the decomposition of some of the sesquiterpene. Oils with less than 88 per cent. phenols will be found somewhat weak in odour. This oil is extensively used in the cheaper toilet soaps and is an important constituent of carnation soaps. As already mentioned, however, it causes the soap to darken in colour somewhat rapidly, and must not therefore be used in any quantity, except in coloured soaps.

Concrete orris oil, a waxy substance obtained by steam distillation of Florentine orris root.

Melting point, 35-45° C., usually 40-45° C.; free acidity, calculated as myristic acid, 50-80 per cent.; ester, calculated as combined myristic acid, 4-10 per cent.

The greater part of the product consists of the inodorous myristic acid, the chief odour-bearing constituent being irone. The high price of the oil renders its use only possible in the very best quality soaps.

Eucalyptus Oil.—Though there are some hundred or more different oils belonging to this class, only two are of much importance to the soap-maker. These are:—

(i.) Eucalyptus citriodora. Specific gravity at 15° C., 0.870-0.905; optical rotation, slightly dextro-rotatory up to +2°; soluble in 4-5 volumes of 70 per cent. alcohol.

The oil consists almost entirely of citronellic aldehyde, and on absorption with saturated solution of sodium bisulphite should leave very little oil unabsorbed.

(ii.) Eucalyptus globulus, the oil used in pharmacy, and containing 50-65 per cent. cineol. Specific gravity at 15° C., 0.910-0.930; optical rotation, +1° to +10°; soluble in 2 to 3 parts of 70 per cent. alcohol; cineol (estimated by combination with phosphoric acid, pressing, decomposing with hot water, and measuring the liberated cineol), not less than 50 per cent. Besides cineol, the oil contains d-pinene, and valeric, butyric, and caproic aldehydes. It is chiefly used in medicated soaps.

Fennel (sweet) oil, obtained from the fruit of Foeniculum vulgare, grown in Germany, Roumania, and other parts of Europe. Specific gravity at 15° C., 0.965-0.985; optical rotation, +6° to +25°; refractive index at 20° C., 1.515-1.548; usually soluble in 2-6 parts 80 per cent. alcohol, but occasionally requires 1 part of 90 per cent. alcohol.

The chief constituents of the oil are anethol, fenchone, d-pinene, and dipentene.

Geranium oils, distilled from plants of the Pelargonium species. There are three principal kinds of this oil on the market—the African, obtained from Algeria and the neighbourhood, the Bourbon, distilled principally in the Island of RÉunion, and the Spanish. The oil is also distilled from plants grown in the South of France, but this oil is not much used by soap-makers. A specially fine article is sold by a few essential oil firms under the name of "Geranium-sur-Rose," which as its name implies, is supposed to be geranium oil distilled over roses. This is particularly suitable for use in high-class soaps. The following are the general properties of these oils. It will be seen that the limits for the figures overlap to a considerable extent.

The oil contains geraniol and citronellol, both free, and combined with tiglic, valeric, butyric, and acetic acids; also l-menthone. The African and Bourbon varieties are the two most commonly used for soap-perfurmery, the Spanish oil being too costly for extensive use.

Ginger-grass oil, formerly regarded as an inferior kind of palma-rosa but now stated to be from an entirely different source. Specific gravity at 15° C., 0.889-0.897; optical rotation, +15°.

The oil contains a large amount of geraniol, together with di-hydrocumin alcohol, d-phellandrene, d-limonene, dipentene, and l-carvone.

Guaiac wood oil, distilled from the wood of Bulnesia sarmienti. Specific gravity at 30° C., 0.967-0.975; optical rotation, -4° 30' to -7°; refractive index at 20° C., 1.506-1.507; soluble in 3 to 5 volumes of 70 per cent. alcohol.

The principal constituent of the oil is guaiac alcohol, or gusiol. This oil, which has what is generally termed a "tea-rose odour," is occasionally used as an adulterant for otto of rose.

Lavender oil, distilled from the flowers of Lavandula vera, grown in England, France, Italy and Spain. The English oil is considerably the most expensive, and is seldom, if ever, used in soap. The French and Italian oils are the most common, the Spanish oil being a comparatively new article, of doubtful botanical origin, and more closely resembling aspic oil.

English Oil.—Specific gravity at 15° C., 0.883-0.900; optical rotation, -4° to -10°; esters, calculated as linalyl acetate, 5-10 per cent.; soluble in 3 volumes of 70 per cent. alcohol.

French and Italian Oils.—Specific gravity at 15° C., 0.885-0.900; optical rotation, -2° to -9°; refractive index at 20° C., 1.459-1.464; esters, calculated as linalyl acetate, 20-40 per cent., occasionally higher; soluble in 1.5-3 volumes of 70 per cent. alcohol.

There was at one time a theory that the higher the proportion of ester the better the oil, but this theory has now to a very large extent become discredited, and there is no doubt that some of the finest oils contain less than 30 per cent. of esters.

Spanish Oil.—Specific gravity at 15° C., 0.900-0.915; optical rotation, -2° to +7°; esters, calculated as linalyl acetate, 2-6 per cent.; soluble in 1-2 volumes of 70 per cent. alcohol.

The chief constituents of lavender oil are linalyl acetate, linalol, geraniol, and linalyl butyrate, while the English oil also contains a distinct amount of cineol.

Lemon oil, prepared by expressing the peel of the nearly ripe fruit of Citrus limonum, and obtained almost entirely from Sicily and Southern Italy. Specific gravity at 15° C., 0.856-0.860; optical rotation, +58° to +63°; refractive index at 20° C., 1.4730-1.4750; aldehydes (citral), 2.5 to 4 per cent.

The principal constituents of the oil are limonene and citral, together with small quantities of pinene, phellandrene, octyl and nonyl aldehydes, citronellal, geraniol, geranyl acetate, and the stearopten, citraptene.

Lemon-grass (so-called verbena) oil, distilled from the grass Andropogon citratus, which is grown in India and, more recently, in the West Indies. The oils from these two sources differ somewhat in their properties, and also in value, the former being preferred on account of its greater solubility in alcohol.

East Indian.—Specific gravity at 15° C., 0.898-0.906; optical rotation, -0° 30' to -6°; aldehydes, by absorption with bisulphite of soda solution, 65 to 78 per cent.; refractive index at 20° C., 1.485-1.487; soluble in 2-3 volumes of 70 per cent. alcohol.

West Indian.—Specific gravity at 15° C., 0.886-0.893; optical rotation, faintly lÆvo-gyrate; refractive index at 20° C., 1.4855-1.4876; soluble in 0.5 volume of 90 per cent. alcohol.

Lime oil, obtained by expression or distillation of the peel of the fruit of Citrus medica, and produced principally in the West Indies.

Expressed Oil.—Specific gravity at 15° C., 0.870-0.885; optical rotation, +38° to +50°. Its most important constituent is citral.

Distilled Oil.—This is entirely different in character to the expressed oil. Its specific gravity at 15° C. is 0.854-0.870; optical rotation, +38° to +54°; soluble in 5-8 volumes of 90 per cent. alcohol.

Linaloe oil, distilled from the wood of trees of the BurseraceÆ family, and obtained from Mexico. Specific gravity at 15° C., 0.876-0.892; optical rotation, usually lÆvo-rotatory, -3° to -13°, but occasionally dextro-rotatory up to +5° 30'; esters, calculated as linalyl acetate, 1-8 per cent.; total alcohols as linalol, determined by acetylation, 54-66 per cent.; soluble in 1-2 volumes of 70 per cent. alcohol.

This oil consists mainly of linalol, together with small quantities of methyl heptenone, geraniol, and d-terpineol.

Marjoram oil, distilled from Origanum majoranoides, and obtained entirely from Cyprus. Specific gravity at 15° C., 0.966; phenols, chiefly carvacrol, estimated by absorption with 5 per cent. caustic potash solution, 80-82 per cent.; soluble in 2-3 volumes of 70 per cent. alcohol.

This oil is used in soap occasionally in place of red thyme oil.

Neroli Bigarade oil, distilled from the fresh blossoms of the bitter orange, Citrus bigaradia. Specific gravity at 15° C., 0.875-0.882; optical rotation, +0° 40' to +10°, and occasionally much higher; refractive index at 20° C., 1.468-1.470; esters, calculated as linalyl acetate, 10-18 per cent.; soluble in 0.75-1.75 volumes of 80 per cent. alcohol, becoming turbid on further addition of alcohol.

The chief constituents of the oil are limonene, linalol, linalyl acetate, geraniol, methyl anthranilate, indol, and neroli camphor.

Orange (sweet) oil, expressed from the peel of Citrus aurantium. Specific gravity at 15° C., 0.849-0.852; optical rotation, +95° to +99°; refractive index at 20° C., 1.4726-1.4732.

The oil contains some 90 per cent. limonene, together with nonyl alcohol, d-linalol, d-terpineol, citral, citronellal, decyl aldehyde, and methyl anthranilate.

Palmarosa, or East Indian geranium oil, distilled from Andropogon Schoenanthus, a grass widely grown in India. Specific gravity at 15° C., 0.888-0.895; optical rotation, +1° to -3°; refractive index at 20° C., 1.472-1.476; esters, calculated as linalyl acetate, 7-14 per cent.; total alcohols, as geraniol, 75-93 per cent.; solubility in 70 per cent. alcohol, 1 in 3.

The oil consists chiefly of geraniol, free, and combined with acetic and caproic acids, and dipentene. It is largely used in cheap toilet soaps, particularly in rose soaps. It is also a favourite adulterant for otto of rose, and is used as a source of geraniol.

Patchouli oil, distilled from the leaves of Pogostemon patchouli, a herb grown in India and the Straits Settlements. Specific gravity at 15° C., 0.965-0.990; optical rotation, -45° to -63°; refractive index at 20° C., 1.504-1.511; saponification number, up to 12; sometimes soluble in 0.5 to 1 volume of 90 per cent. alcohol, becoming turbid on further addition. The solubility of the oil in alcohol increases with age. The oil consists to the extent of 97 per cent. of patchouliol and cadinene, which have little influence on its odour, and the bodies responsible for its persistent and characteristic odour have not yet been isolated.

Peppermint oil, distilled from herbs of the Mentha family, the European and American from Mentha piperita, and the Japanese being generally supposed to be obtained from Mentha arvensis. The locality in which the herb is grown has a considerable influence on the resulting oil, as the following figures show:—

English.—Specific gravity at 15° C., 0.900-0.910; optical rotation, -22° to -33°; total menthol, 55-66 per cent.; free menthol, 50-60 per cent.; soluble in 3-5 volumes of 70 per cent. alcohol.

American.—Specific gravity at 15° C., 0.906-0.920; optical rotation, -20° to -33°; total menthol, 50-60 per cent.; free menthol, 40-50 per cent. The Michigan oil is soluble in 3-5 volumes of 70 per cent. alcohol, but the better Wayne County oil usually requires 1-2 volumes of 80 per cent. alcohol, and occasionally 0.5 volume of 90 per cent. alcohol.

French.—Specific gravity at 15° C., 0.917-0.925; optical rotation, -6° to -10°; total menthol, 45-55 per cent.; free menthol, 35-45 per cent.; soluble in 1 to 1.5 volumes of 80 per cent.

Japanese.—Specific gravity at 25° C., 0.895-0.900; optical rotation, lÆvo-rotatory up to -43°; solidifies at 17 to 27° C.; total menthol, 70-90 per cent., of which 65-85 per cent. is free; soluble in 3-5 volumes of 70 per cent. alcohol.

The dementholised oil is fluid at ordinary temperatures, has a specific gravity of 0.900-0.906 at 15° C., and contains 50-60 per cent. total menthol.

Some twenty different constituents have been found in American peppermint oil, including menthol, menthone, menthyl acetate, cineol, amyl alcohol, pinene, l-limonene, phellandrene, dimethyl sulphide, menthyl isovalerianate, isovalerianic aldehyde, acetaldehyde, acetic acid, and isovalerianic acid.

Peru balsam oil, the oily portion (so-called "cinnamein") obtained from Peru balsam. Specific gravity at 15° C., 1.100-1.107; optical rotation, slightly dextro-rotatory up to +2°; refractive index at 20° C., 1.569 to 1.576; ester, calculated as benzyl benzoate, 80-87 per cent.; soluble in 1 volume of 90 per cent. alcohol.

The oil consists chiefly of benzyl benzoate and cinnamate, together with styracin, or cinnamyl cinnamate, and a small quantity of free benzoic and cinnamic acids.

Petitgrain oil, obtained by distillation of the twigs and unripe fruit of Citrus bigaradia. There are two varieties of the oil, the French and the South American, the former being the more valuable. Specific gravity at 15° C., 0.886-0.900; optical rotation, -3° to +6°; refractive index at 20° C., 1.4604-1.4650; esters, calculated as linalyl acetate, 40-55 per cent., for the best qualities usually above 50 per cent.; soluble as a rule in 2-3 volumes of 70 per cent. alcohol, but occasionally requires 1-2 volumes of 80 per cent. alcohol.

Among its constituents are limonene, linalyl acetate, geraniol and geranyl acetate.

Pimento oil (allspice), distilled from the fruit of Pimenta officinalis, which is found in the West Indies and Central America. Specific gravity at 15° C., 1.040-1.060; optical rotation, slightly lÆvo-rotatory up to -4°; refractive index at 20° C., 1.529-1.536; phenols, estimated by absorption with 5 per cent. potash solution, 68-86 per cent.; soluble in 1-2 volumes of 70 per cent. alcohol.

The oil contains eugenol, methyl eugenol, cineol, phellandrene, and caryophyllene.

Rose oil (otto of rose), distilled from the flowers of Rosa damascena, though occasionally the white roses (Rosa alba) are employed. The principal rose-growing district is in Bulgaria, but a small quantity of rose oil is prepared from roses grown in Anatolia, Asia Minor. An opinion as to the purity of otto of rose can only be arrived at after a very full chemical analysis, supplemented by critical examination of its odour by an expert. The following figures, however, will be found to include most oils which can be regarded as genuine. Specific gravity at 30° C., 0.850-0.858; optical rotation at 30° C., -1° 30' to -3°; refractive index at 20° C., 1.4600-1.4645; saponification value, 7-11; solidifying point, 19-22° C.; iodine number, 187-194; stearopten content, 14-20 per cent.; melting point of stearopten, about 32° C.

A large number of constituents have been isolated from otto of rose, many of which are, however, only present in very small quantities. The most important are geraniol, citronellol, phenyl ethyl alcohol, together with nerol, linalol, citral, nonylic aldehyde, eugenol, a sesquiterpene alcohol, and the paraffin stearopten.

Rosemary oil, distilled from the herb Rosemarinus officinalis, and obtained from France, Dalmatia, and Spain. The herb is also grown in England, but the oil distilled therefrom is rarely met with in commerce. The properties of the oils vary with their source, and also with the parts of the plant distilled, distillation of the stalks as well as the leaves tending to reduce the specific gravity and borneol content, and increase the proportion of the lÆvo-rotatory constituent (lÆvo-pinene). The following figures may be taken as limits for pure oils:—

French and Dalmatian.—Specific gravity at 15° C., 0.900-0.916; optical rotation, usually dextro-rotatory, up to +15°, but may occasionally be lÆvo-rotatory, especially if stalks have been distilled with the leaves; ester, calculated as bornyl acetate, 1-6 per cent.; total borneol, 12-18 per cent.; usually soluble in 1-2 volumes of 82.5 per cent. alcohol.

Spanish.—The properties of the Spanish oil are similar to the others, except that it is more frequently lÆvo-rotatory.

Rosemary oil contains pinene, camphene, cineol, borneol, and camphor.

Sandalwood oil, obtained by distillation of the wood of Santalum album (East Indian), Santalum cygnorum (West Australian), and Amyris balsamifera (West Indian). The oils obtained from these three different sources differ very considerably in value, the East Indian being by far the best.

East Indian.—Specific gravity at 15° C., 0.975-0.980; optical rotation, -14° to -20°; refractive index at 20° C., 1.5045-1.5060; santalol, 92-97 per cent.; usually soluble in 4-6 volumes of 70 per cent. alcohol, though, an old oil occasionally is insoluble in 70 per cent. alcohol.

West Australian.—Specific gravity at 15° C., 0.950-0.968; optical rotation, +5° to +7°; alcohols, calculated as santalol, 73-75 per cent.; insoluble in 70 per cent. alcohol, but readily dissolves in 1-2 volumes of 80 per cent. alcohol.

West Indian.—Specific gravity at 15° C., 0.948-0.967; optical rotation, +13° 30' to +30°; insoluble in 70 per cent. alcohol.

In addition to free santalol, the oil contains esters of santalol and santalal.

Sassafras oil, distilled from the bark of Sassafras officinalis, and obtained chiefly from America. Specific gravity at 15° C., 1.06-1.08; optical rotation, +1° 50' to +4°; refractive index at 20° C., 1.524-1.532; soluble in, 6-10 volumes of 85 per cent. alcohol, frequently soluble in 10-15 volumes of 80 per cent. alcohol.

The chief constituents are safrol, pinene, eugenol, camphor, and phellandrene. The removal of safrol, either intentionally or by accident, owing to cooling of the oil and consequent deposition of the safrol, is readily detected by the reduction of the specific gravity below 1.06.

Thyme oil, red and white, distilled from the green or dried herb, Thymus vulgaris, both French and Spanish oils being met with. These oils are entirely different in character.

French.—Specific gravity at 15° C., 0.91-0.933; slightly lÆvo-rotatory up to -4°, but usually too dark to observe; phenols, by absorption with 10 per cent. aqueous caustic potash, 25-55 per cent.; refractive index at 20° C., 1.490-1.500; soluble in 1-1.5 volumes of 80 per cent. alcohol.

Spanish.—Specific gravity at 15° C., 0.955-0.966; optical rotation, slightly lÆvo-gyrate; phenols, 70-80 per cent.; refractive index at 20° C.; 1.5088-1.5122; soluble in 2-3 volumes of 70 per cent. alcohol.

In addition to the phenols, thymol or carvacrol, these oils contain cymene, thymene and pinene.

The white thyme oil is produced by rectifying the red oil, which is generally effected at the expense of a considerable reduction in phenol content, and hence in real odour value of the oil.

Verbena Oil.—The oil usually sold under this name is really lemon-grass oil (which see supra). The true verbena oil or French verveine is, however, occasionally met with. This is distilled in France from the verbena officinalis, and has the following properties: Specific gravity at 15° C., 0.891-0.898; optical rotation, slightly dextro- or lÆvo-rotatory; aldehydes, 70-75 per cent.; soluble in 2 volumes of 70 per cent. alcohol.

The oil contains citral.

Vetivert oil, distilled from the grass, Andropogon muricatus, or Cus Cus, and grown in the East Indies.

Specific gravity at 15° C., 1.01-1.03; optical rotation, +20° to +26°; saponification number, 15-30; refractive index at 20° C., 1.521-1.524; soluble in 2 volumes of 80 per cent. alcohol.

The price of this oil makes its use prohibitive except in the highest class soaps.

Wintergreen Oil.—There are two natural sources of this oil, the Gaultheria procumbens and the Betula lenta. Both oils consist almost entirely of methyl salicylate and are practically identical in properties, the chief difference being that the former has a slight lÆvo-rotation, while the latter is inactive.

Specific gravity at 15° C., 1.180-1.187; optical rotation, Gaultheria oil, up to -1°, Betula oil, inactive; ester as methyl salicylate, at least 98 per cent.; refractive index at 20° C., 1.5354-1.5364; soluble in 2-6 volumes of 70 per cent. alcohol.

Besides methyl salicylate, the oil contains triaconitane, an aldehyde or ketone, and an alcohol.

Ylang-ylang oil, distilled from the flowers of Cananga odorata, the chief sources being the Philippine Islands and Java. Specific gravity at 15° C., 0.924-0.950; optical rotation, -30° to -60°, and occasionally higher; refractive index at 20° C., 1.496-1.512; ester, calculated as linalyl benzoate, 27-45 per cent., occasionally up to 50 per cent.; usually soluble in 1/2 volume of 90 per cent. alcohol.

The composition of the oil is qualitatively the same as that of Cananga oil, but it is considerably more expensive and therefore can only be used in the highest grade soaps.

Artificial and Synthetic Perfumes.

During the past few years the constitution of essential oils has been studied by a considerable number of chemists, and the composition of many oils has been so fully determined that very good imitations can often be made at cheaper prices than those of the genuine oils, rendering it possible to produce cheap soaps having perfumes which were formerly only possible in the more expensive article.

There is a considerable distinction, however, often lost sight of, between an artificial and a synthetic oil. An artificial oil may be produced by separating various constituents from certain natural oils, and so blending these, with or without the addition of other substances, as to produce a desired odour, the perfume being, at any rate in part, obtained from natural oils. A synthetic perfume, on the other hand, is entirely the product of the chemical laboratory, no natural oil or substance derived therefrom entering into its composition.

The following are among the most important bodies of this class:—

Amyl salicylate, the ester prepared from amyl alcohol and salicylic acid, sometimes known as "OrchidÉe" or "TrÈfle". This is much used for the production of a clover-scented soap. It has the specific gravity at 15° C., 1.052-1.054; optical rotation, +1° 16' to +1° 40'; refractive index at 20° C., 1.5056; and should contain not less than 97 per cent. ester, calculated as amyl salicylate.

Anisic aldehyde, or aubÉpine, prepared by oxidation of anethol, and possessing a pleasant, hawthorn odour. This has the specific gravity at 15° C., 1.126; refractive index at 20° C., 1.5693; is optically inactive, and dissolves readily in one volume of 70 per cent. alcohol.

Benzyl Acetate, the ester obtained from benzyl alcohol and acetic acid. This has a very strong and somewhat coarse, penetrating odour, distinctly resembling jasmine. Its specific gravity at 15° C. is 1.062-1.065; refractive index at 20° C., 1.5020; and it should contain at least 97-98 per cent. ester, calculated as benzyl acetate.

Citral, the aldehyde occurring largely in lemon-grass and verbena oils, also to a less extent in lemon and orange oils, and possessing an intense lemon-like odour. It has a specific gravity at 15° C., 0.896-0.897, is optically inactive, and should be entirely absorbed by a hot saturated solution of sodium bisulphite.

Citronellal, an aldehyde possessing the characteristic odour of citronella oil, in which it occurs to the extent of about 20 per cent., and constituting considerably over 90 per cent. of eucalyptus citriodora oil. Its specific gravity at 15° C. is 0.862; refractive index at 20° C., 1.447; optical rotation, +8° to +12°; and it should be entirely absorbed by a hot saturated solution of sodium bisulphite.

Coumarin, a white crystalline product found in Tonka beans, and prepared synthetically from salicylic acid. It has an odour resembling new-mown hay, and melts at 67° C.

Geraniol, a cyclic alcohol, occurring largely in geranium, palma-rosa, and citronella oils. Its specific gravity at 15° C. is 0.883-0.885; refractive index at 20° C., 1.4762-1.4770; it is optically inactive, and boils at 218°-225° C.

Heliotropin, which possesses the characteristic odour of heliotrope, is prepared artificially from safrol. It crystallises in small prisms melting at 86° C.

Hyacinth.—Most of the articles sold under this name are secret blends of the different makers. Styrolene has an odour very much resembling hyacinth, and probably forms the basis of most of these preparations, together with terpineol, and other artificial bodies. The properties of the oil vary considerably for different makes.

Ionone, a ketone first prepared by Tiemann, and having when diluted a pronounced violet odour. It is prepared by treating a mixture of citral and acetone with barium hydrate, and distilling in vacuo. Two isomeric ketones, α-ionone and β-ionone, are produced, the article of commerce being usually a mixture of both. The two ketones have the following properties:—

Alpha-ionone.—Specific gravity at 15° C., 0.9338; refractive index at 16.5 C., 1.50048 (Chuit); optically it is inactive.

Beta-ionone.—Specific gravity at 15° C., 0.9488; refractive index at 16.8° C., 1.52070 (Chuit); optically it is inactive also.

The product is usually sold in 10 or 20 per cent. alcoholic solution ready for use.

Jasmine.—This is one of the few cases in which the artificial oil is probably superior to that obtained from the natural flowers, possibly due to the extreme delicacy of the odour, and its consequent slight decomposition during preparation from the flowers. The chemical composition of the floral perfume has been very exhaustively studied, and the artificial article now on the market may be described as a triumph of synthetical chemistry. Among its constituents are benzyl acetate, linalyl acetate, benzyl alcohol, indol, methyl anthranilate, and a ketone jasmone.

Linalol, the alcohol forming the greater part of linaloe and bois de rose oils, and found also in lavender, neroli, petitgrain, bergamot, and many other oils. The article has the specific gravity at 15° C., 0.870-0.876; optical rotation, -12° to -14°; refractive index at 20° C., 1.463-1.464; and when estimated by acetylation, yields about 70 per cent. of alcohols.

Linalyl acetate, or artificial bergamot oil, is the ester formed when linalol is treated with acetic anhydride. It possesses a bergamot-like odour, but it is doubtful whether its value is commensurate with its greatly increased price over that of ordinary bergamot oil. It has the specific gravity at 15° C., 0.912.

Musk (Artificial).—Several forms of this are to be obtained, practically all of which are nitro-derivatives of aromatic hydrocarbons. The original patent of Baur, obtained in 1889, covered the tri-nitro-derivative of tertiary butyl xylene. The melting point of the pure article usually lies between 108° and 112° C., and the solubility in 95 per cent. alcohol ranges from 1 in 120 to 1 in 200, though more soluble forms are also made.

An important adulterant, which should always be tested for, is acetanilide (antifebrin), which may be detected by the characteristic isocyanide odour produced when musk containing this substance is boiled with alcoholic potash, and a few drops of chloroform added. Acetanilide also increases the solubility in 95 per cent. alcohol.

Neroli Oil (Artificial).—Like jasmine oil, the chemistry of neroli oil is now very fully known, and it is therefore possible to prepare an artificial product which is a very good approximation to the natural oil, and many such are now on the market, which, on account of their comparative cheapness, commend themselves to the soap-perfumer. These consist chiefly of linalol, geraniol, linalyl acetate, methyl anthranilate, and citral.

Mirbane Oil or Nitrobenzene.—This is a cheap substitute for oil of bitter almonds, or benzaldehyde, and is a very coarse, irritating perfume, only suitable for use in the very cheapest soaps. It is prepared by the action of a mixture of nitric and sulphuric acids on benzene at a temperature not exceeding 40° C. Its specific gravity is 1.205-1.206; refractive index at 20° C., 1.550; and boiling point, 206° C.

Niobe oil, or ethyl benzoate, the ester obtained from ethyl alcohol and benzoic acid, and having the specific gravity at 15° C., 1.094-1.095; refractive index at 20° C., 1.5167; boiling point, 196.5°-198° C.; soluble in 1.5 volumes of 70 per cent. alcohol.

Oeillet is a combination possessed of a sweet carnation-like odour and having as a basis, eugenol or isoeugenol. Its properties vary with the source of supply.

Rose Oil (Artificial).—Several good and fairly cheap artificial rose oils are now obtainable, consisting chiefly of citronellol, geraniol, linalol, phenyl ethyl alcohol, and citral. In some cases stearopten or other wax is added, to render the oil more similar in appearance to the natural article, but as these are inodorous, no advantage is gained in this way, and there is, further, the inconvenience in cold weather of having to first melt the oil before use.

Safrol, an ether which is the chief constituent of sassafras oil, and also found in considerable quantity in camphor oil. It is sold as an artificial sassafras oil, and is very much used in perfuming cheap toilet or household soaps. Its specific gravity at 15° C. is 1.103-1.106; refractive index at 20° C., 1.5373; and it dissolves in fifteen volumes of 80 per cent. alcohol.

Santalol, the alcohol or mixture of alcohols obtained from sandalwood oil. Its specific gravity at 15° C. is 0.9795; optical rotation, -18°; and refractive index at 20° C., 1.507.

Terebene, a mixture of dipentene and other hydrocarbons prepared from turpentine oil by treatment with concentrated sulphuric acid, is used chiefly in medicated soaps. Its specific gravity at 15° C. is 0.862-0.868; the oil is frequently slightly dextro- or lÆvo-rotatory; the refractive index at 20° C., 1.470-1.478.

Terpineol, an alcohol also prepared from turpentine oil by the action of sulphuric acid, terpene hydrate being formed as an intermediate substance. It has a distinctly characteristic lilac odour, and on account of its cheapness is much used in soap perfumery, especially for a lilac or lily soap. Its specific gravity at 15° C. is 0.936-0.940; refractive index at 20° C., 1.4812-1.4835; and boiling point about 210°-212° C. It is optically inactive, and readily soluble in 1.5 volumes of 70 per cent. alcohol.

Vanillin, a white crystalline solid, melting at 80°-82° C. and prepared by the oxidation of isoeugenol. It has a strong characteristic odour, and occurs, associated with traces of benzoic acid and heliotropin, in the vanilla bean. It can only be used in small quantity in light-coloured soaps, as it quickly tends to darken the colour of the soap.