_Lemon-gra.s.s_ (so-called _verbena_) oil, distilled from the gra.s.s 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 laevo-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 princ.i.p.ally in the West Indies.

Expressed Oil.--Specific gravity at 15 C., 0.870-0.885; optical rotation, +38 to +50. Its most important const.i.tuent 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 Burseraceae family, and obtained from Mexico. Specific gravity at 15 C., 0.876-0.892; optical rotation, usually laevo-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 quant.i.ties 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 const.i.tuents 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 gra.s.s 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 j.a.panese 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.

j.a.panese.--Specific gravity at 25 C., 0.895-0.900; optical rotation, laevo-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 const.i.tuents have been found in American peppermint oil, including menthol, menthone, menthyl acetate, cineol, amyl alcohol, pinene, l-limonene, ph.e.l.landrene, 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 quant.i.ty of free benzoic and cinnamic acids.

_Pet.i.tgrain 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 const.i.tuents 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 laevo-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, ph.e.l.landrene, and caryophyllene.

_Rose oil (otto of rose)_, distilled from the flowers of Rosa damascena, though occasionally the white roses (Rosa alba) are employed. The princ.i.p.al rose-growing district is in Bulgaria, but a small quant.i.ty 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 a.n.a.lysis, 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 const.i.tuents have been isolated from otto of rose, many of which are, however, only present in very small quant.i.ties. 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 laevo-rotatory const.i.tuent (laevo-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 laevo-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 laevo-rotatory.

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

_Sandalwood oil_, obtained by distillation of the wood of Santalum alb.u.m (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.

_Sa.s.safras oil_, distilled from the bark of Sa.s.safras 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 const.i.tuents are safrol, pinene, eugenol, camphor, and ph.e.l.landrene. 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 laevo-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.