SOAP PERFUMES.
_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.
_________________________________________________________________________
| | | | | |
| | African. | Bourbon. | Spanish. | French. |
|_________________________|___________|___________|___________|___________|
| | | | | |
| Specific gravity | | | | |
| at 15° C. | .890-.900 | .888-.895 | .895-.898 | .897-.900 |
| Optical rotation. |-6° to -10°|-9° to -18°|-8° to -11°|-8° to -11°|
| Esters, calculated as | 20-27 | 27-32 | 20-27 | 18-23 |
| geranyl tiglate | per cent. | per cent. | per cent. | per cent. |
| Total alcohols, as | 68-75 | 70-80 | 65-75 | 66-75 |
| geraniol. | per cent. | per cent. | per cent. | per cent. |
| Solubility in 70 per | | | | |
| cent. alcohol. | 1 in 1.5-2| 1 in 1.5-2| 1 in 2-3 | 1 in 1.5-2|
|_________________________|___________|___________|___________|___________|
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, [alpha]-ionone and [beta]-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.