in oils of lavender, bergamot, petit grains, spike, and coriander. It is a colorless, fragrant liquid of sp. gr. 0.878, and boiling at 1970-198°. It forms a perfectly clear solution with 2 volumes or more of 70-per-cent. alcohol. Its most important esters are linaloyl acetate (known as bergamiol and constituting one of the chief constituents of bergamot oil) and linaloyl formate.

Geraniol, C10H17OH, is the chief constituent of the true geranium oils and of the Turkish geranium or Palmarosa oil. It has also been shown to be the chief constituent of the liquid portion of the oil of rose, and it occurs in addition in oils of citronella, oil of lavender flowers, and one of the eucalyptus oils. It is a colorless liquid with a fragrant rose-like odor, sp. gr. o.882 to 0.885, and boils at 230°. One part of geraniol requires from 12 to 15 volumes of 50-per-cent. alcohol to form a clear solution. Its most important esters are the geranyl acetate and geranyl formate. Both linalool and geraniol when oxidized with chromic acid mixture yield the same aldehyde citral.

16

Citral, C10H18O.-This compound is present to the amount of about 7.5 per cent. in oil of lemon, to which it gives its characteristic odor. It is a golden-yellow liquid of sp. gr. o.899, and boils at 116° under a pressure of 16 mm., or when perfectly pure at 228°-229° under ordinary pressure without decomposition.

Closely related to citral is another aldehyde-like body, Citronellal, C10H18O. This is found in oil of Eucalyptus maculata, in oil of citronella, and in small amount in oil of lemon. It is a colorless liquid with an agreeable odor, sp. gr. 0.880, and distilling between 205° and 210° with slight decomposition.

Menthol, C10H2O (Menthol, U. S. P.), is the most valuable constituent of the several varieties of peppermint oil. It "forms colorless, acicular crystals, having a strong and pure odor of peppermint, and a warm, aromatic taste, followed by a sensation of cold, when air is drawn into the mouth. It melts at 43° C. to a colorless liquid, boils at 212°, and volatilizes slowly at the ordinary temperature. Its alcoholic solution deviates polarized light to the left." Menthol is a secondary alcohol. When oxidized with chromic acid mixture it yields a ketone, menthone, C10H18O, which also occurs naturally in the peppermint oil. Menthol also forms esters, such as menthyl formate, menthyl acetate, and menthyl iso-valerianate. Of these the latter two are found naturally in the peppermint oil. By the action of dehydrating agents menthol is converted into the hydrocarbon menthene, C10H1g, which boils at 167°

III. THE ESSENTIAL OILS.

By the distillation of the blossoms, flowers, and fruit of many plants with steam are obtained a class of products known as the essential or volatile oils. They are distinguished both by physical and chemical differences from the fixed or fatty oils. These latter (see p. 621) are largely mixtures of the glycerin esters of the fatty acids, often containing, in addition, the fat acids in the free state. While the essential oils show some variations in their chemical composition, they are in the main mixtures of terpenes and camphors, although esters of these latter occur, and in a few instances we have aldehydes and ketones.

The fixed oils belong in the aliphatic or methane series of derivatives, while the essential oils all show cyclic or aromatic derivatives among their constituents. The essential oils also show a tendency to absorb oxygen on prolonged exposure to the air and to form resinous products.

Physically the essential oils are characterized by their entire volatility without residue, while the fatty oils are decomposed by heat before volatilization can be completed, and yield acrolein and similar products of decomposition.

The specific gravity of the essential oils is generally less than that of water, and hence they separate on its surface in the product of the steam distillation. They are only very slightly soluble in water, but easily soluble in strong alcohol, chloroform, ether, benzene, and fatty oils. They leave a transient spot only upon paper, while the fixed oils leave a permanent "grease-spot.' The extraction of the essential oils from the plants containing them may be effected:

1. By distillation, usually with steam, although in rare cases without. A Florentine receiver is frequently employed to collect the distillate, and by this means the separation of the light, oily layer from the accompanying water is effected.

2. By expression. This is followed in cases where the oil is abundant and readily separable, as with oil of lemon, orange peel, etc.

3. By extraction with solvents. This solvent may be a liquid fat, as in the case of maceration, a solid fat, as in the case of enfleurage, or a volatile solvent, as in the extraction of fine or costly perfumes.

The official essential oils and their proximate chemical composition are as follows:

Oleum Amygdalæ Amaræ, U. S. P. (Oil of Bitter Almond), is a clear yellowish, thin, and strongly refractive liquid, with a characteristic odor and a bitter, burning taste. Its sp. gr. is 1.06 to 1.07, and it boils at 180° It is essentially benzaldehyde, CH5.COH, with from 1.5 to 4 per cent. of hydrocyanic acid, and has resulted from the decomposition of the amygdalin of the bitter almond under the influence of the ferment emul sin. (For reaction see p. 714.) Benzaldehyde combines. on standing with hydrocyanic acid, to form the cyanhydrin or nitrile of mandelic acid, CH5.CH(OH). CN, a body having the sp gr. 1.124, and this is. therefore, often contained in oil of bitter almonds.

Oleum Anisi, U. S. P. (Oil of Anise), is "a colorless or pale yellow oil, with characteristic aromatic odor and taste." "At a temperature usually between 10° and 15° it solidifies to a white, crystalline mass." Over 90 per cent. of the oil consists of anethol (methoxy-propenyl-benzene) CH4 CH5 OCHS, the residue being apparently a terpene.

Oleum Aurantii Corticis, U. S. P. (Oil of Orange Peel), is obtained by expression from the fresh peel of either the Bitter Orange or the Sweet Orange. The chief constituent is the terpene limonene. Oil of sweet orange peel also contains a small amount of citral (geranial) and a lower boiling aldehyde.

Oleum Aurantii Florum, U. S. P. (Oil of Orange Flowers, or Neroli Oil), is distilled from the fresh flowers of the Bitter Orange. The oil contains, according to Semmler, about 20 per cent. of limonene, 30 per cent. of nerolol (a lævo-rotatory alcohol of the composition C10H18O, and closely related to linalool), 40 per cent of nerolyl acetate, and 3 per cent. of geraniol.

Oleum Bergamottæ, U. S. P. (Oil of Bergamot).-Obtained by expression from the rind of the fresh fruit of Citrus Bergamia. The oil contains limonene, dipentene, linalool, and linaloyl acetate, the last named amounting to from 36 to 39 per cent. Freshly-expressed bergamot oil deposits also bergapten, C12HO4. By fusion with caustic potash this compound yields phloroglucin, C ̧H ̧(OH) ̧.

Oleum Betulæ Volatile, U. S. P. (Oil of Sweet Birch), is a colorless or yellowish liquid with a characteristic strongly aromatic odor and taste, closely resembling that of gaultheria or wintergreen. It consists mainly of methyl salicylate (see p. 724), but contains in addition, as established by one of the authors, a small amount (less than 1 per cent.) of a sesquiterpene.

Oleum Cadinum, U. S. P. (Oil of Cade) is a product of the dry distillation of the wood of Juniperus Oxycedrus. It is a brownish liquid of a tarry odor and an empyreumatic, burning taste. The oil contains phenols and a sesquiterpene termed cadinene, boiling at 274°-275°.

Oleum Cajuputi, U. S. P. (Oil of Cajuput).—A thin, bluish-green liquid (after rectification colorless), with an agreeable camphoraceous odor and an aromatic, bitter taste. It contains cineol (cajuputol), terpineol, and one or more terpenes.

Oleum Cari, U. S. P. (Oil of Caraway), is distilled from the fruit of Carum Carvi. The oil contains dextro-rotatory limonene (formerly

known as carvene) and dextro-rotatory carvol. This body is chemically a ketone of the composition C10H1O, and is a liquid boiling at 224°. Oleum Caryophylli, U. S. P. (Oil of Cloves), is "a pale yellow, thin liquid, becoming darker and thicker by age and exposure to the air, with a strong aromatic odor of cloves, and a pungent and spicy taste." The oil contains eugenol (oxy-methoxy-allyl-benzene, CH, OCH,

OH

to the

amount of 80 to 90 per cent., and a sesquiterpene termed caryophyllene, which boils at 255°. Eugenol, the chief constituent, forms a colorless liquid with the odor and taste of cloves. It has a sp. gr. 1.072, and boils at 253°-254°. It is also found in other essential oils, such as pimenta, bay, Ceylon cinnamon, sassafras, and camphor.

Oleum Chenopodii, U. S. P. (Oil of Chenopodium, or American Wormseed), is a yellowish liquid, with a penetrating odor, and pungent, bitterish taste. It is stated to contain a terpene, C10H16, and a body of the formula C10H180.

Oleum Cinnamomi, U. S. P. (Oil of Cinnamon or Oil of Cassia).—“ A yellowish or brownish liquid, becoming darker and thicker by age and exposure to the air, with the characteristic odor of cinnamon, and a sweetish, spicy, and burning taste." It consists chiefly of cinnainic aldehyde, CH7.COH, with some cinnamyl acetate, СH.C2H ̧ ̧. The amount of cinnamic aldehyde should not be less than 75 per cent.

Oleum Copaibæ, U. S. P. (Oil of Copaiba), is distilled from the socalled Balsam of Copaiba. "It forms a pale yellowish liquid, with the characteristic odor of copaiba, and an aromatic, bitterish, and pungent taste." The oil consists chiefly of caryophyllene, C15H24.

Oleum Coriandri, U. S. P. (Oil of Coriander), is distilled from the fruit of Coriandrum sativum. The oil contains linalool (formerly known as coriandrol) and pinene.

Oleum Cubeba, U. S. P. (Oil of Cubeb), is “a colorless, pale greenish or yellowish liquid, having the characteristic odor of cubeb, and a warm, camphoraceous, aromatic taste." The oil consists chiefly of cadinene, C15H24, with some dipentene, and when old, or distilled from old fruit, contains cubeb camphor, C15H24. H2O.

Oleum Erigerontis, U. S. P. (Oil of Erigeron or Fleabane), is “a pale yellow, limpid liquid, becoming darker and thicker by age and exposure to the air, having a peculiar, aromatic, persistent odor, and an aromatic, slightly pungent taste." It consists chiefly of dextro-rotatory limonene, together with a substance readily decomposing or polymerizing by heat.

Oleum Eucalypti, U. S. P. (Oil of Eucalyptus), is "a colorless or slightly yellowish liquid, having a characteristic, aromatic, somewhat camphoraceous odor, and a pungent, spicy, and cooling taste." The oil from the E. globulus contains cineol (eucalyptol), dextro-rotatory pinene, and small amounts of valeric, butyric, and caproic aldehydes. The oil from E. oleosa (which is also included as an official source of encalyptus oil) contains cineol and cuminol. Both of these eucalyptus oils have strongly antiseptic properties due to the cineol (eucalyptol) contained in them.

Oleum Fœniculi, U. S. P. (Oil of Fennel), is distilled from the fruit of Foeniculum capillaceum. It contains pinene, phellandrene, dipentene, fenchone, C10H16O, and anethol, C10H12O, the latter usually in amounts of about 60 per cent. The higher the temperature at which the crystals of anethol separate the better the quality of the oil. Oil of fennel from different sources may differ, and one or more of the above-named constituents may be absent.

Oleum Gaultheriæ, U. S. P. (Oil of Gaultheria or Wintergreen), is distilled from the leaves of Gaultheria procumbens. The oil is substantially identical with oil of sweet birch (see p. 787), and consists chiefly of methyl salicylate with a fraction of 1 per cent. of a hydrocarbon, C15H24.

Oleum Hedeomæ, U. S. P. (Oil of Hedeoma or American Pennyroyal), distilled from the leaves and tops of Hedeoma pulegioides. The oil contains pulegone, C10H18O, together with two ketones of the formula C10H18O (one being apparently menthone), and formic, acetic, and isoheptoic acids.

Oleum Juniperi, U. S. P. (Oil of Juniper).-It may vary in optical properties, and show either dextro-rotatory, lævo-rotatory, or inactive character. It consists chiefly of pinene, with some cadinene, C15H24, and an undetermined substance, probably an ester, to which the peculiar juniperlike odor and taste are due.

Oleum Lavandula Florum (Oil of Lavender Flowers).-The oil contains linalool, linaloyl acetate, geraniol, and a very small amount of cineol.

Oleum Limonis, U. S. P. (Oil of Lemon), is obtained by expression from fresh lemon peel, the rind of the recent fruit of Citrus Limonum. It contains a small amount of pinene with dextro-rotatory limonene, about 7 to 8 per cent. of citral (see p. 785), and a small amount of citronellal.

Oleum Mentha Piperitæ, U. S. P. (Oil of Peppermint).—" A colorless, yellowish or greenish-yellow liquid, becoming darker and thicker by age and exposure to the air, having the characteristic strong odor of peppermint, and a strongly aromatic, pungent taste, followed by a sensation of cold when air is drawn into the mouth."

The results of an investigation conducted in the laboratory of Fritsche Bros. at Garfield, N. J., show that the composition of American peppermint oil is quite complex, the following constituents having been noted:

Acetaldehyde.
Acetic acid.

Isovaleraldehyde.
Isovalerianic acid.

A liquid acid, CgH120g
Pinene.

Phellandrene.

A lactone, C10H1602.

Limonene.
Cineol.

Menthone.

Menthol.

Menthyl acetate.
Menthyl isovalerianate.
Cadinene.

Oleum Menthæ Viridis, U. S. P. (Oil of Spearmint), is distilled from the fresh herb of Mentha viridis. The oil contains lævo-rotatory carvol and lævo-rotatory limonene, with possibly some lævo-rotatory pinene.