_Oleum Bergamii_; _Essence or Essential Oil of Bergamot_; F. _Essence
de Bergamotte_; G. _Bergamottöl_.
=Botanical Origin=—_Citrus Bergamia_ var. _vulgaris_ Risso et
Poiteau,[472] a small tree closely resembling in flowers and foliage
the Bitter Orange. Its fruit is 2½ to 3 inches in diameter, nearly
spherical, or slightly pear-shaped, frequently crowned by the
persistent style; it is of a pale golden yellow like a lemon,[473] with
the peel smooth and thin, abounding in essential oil of a peculiar
fragrance; the pulp is pale yellowish green, of a bitterish taste, and
far less acid than that of the lemon.
The tree is cultivated at Reggio in Calabria, and is unknown in a wild
state.
=History=—The bergamot is one of the cultivated forms which abound in
the genus _Citrus_, and which constitute the innumerable varieties of
the orange, lemon and citron. Whether it is most nearly related to the
lemon or to the orange is a point discussed as early as the beginning
of the last century. Gallesio[474] remarks that it so evidently
combines the characters of the two that it should be regarded as a
hybrid between them. The bergamot first appeared in the latter part
of the 17th century. It is not mentioned in the grand work on orange
trees of Ferrari,[475] published at Rome in 1646, nor in the treatise
of Commelyn[476] (1676), nor in the writings of Lanzoni (1690),[477]
or La Quintinie (1692).[478] So far as we know, it is first noticed
in a little book called _Le Parfumeur François_, printed at Lyons in
1693. The author who calls himself _Le Sieur Barbe, parfumeur_, says
that the _Essence de Cedra ou Bergamotte_ is obtained from the fruits
of a lemon-tree which has been grafted on the stem of a bergamot pear;
he adds that it is got by squeezing small bits of the peel with the
fingers in a bottle or globe large enough to allow the hand to enter.
[472] _Histoire naturelle des Orangers_, Paris, 1818. p. 111. tab.
53, or the same work, new edition, by Dubreuil, 1873, p. 82. We
accept the name given by these authors for the sake of convenience
and definiteness, and not because we concur in their opinion that the
Bergamot deserves to be ranked as a distinct botanical species.
[473] Fig. in Bentley and Trimen, _Med. Plants_, part 31.
[474] _Traité du Citrus_, 1811. 118.
[475] _Hesperides, seu de malorum, aureorum cultura et usu_.
[476] _Nederlantze Hesperides_, Amsterd. 1676. fol. (an English
translation in 1683).
[477] _Citrologia_, Ferrariæ, 1690.
[478] _Instruction pour les Jardins fruitiers ... avec un traité des
Orangers_, ed. 2, 1692.
Volkamer of Nuremberg, who produced a fine work on the Citron tribe in
1708, has a chapter on the _Limon Bergamotta_, which he describes as
_gloria limonum et fructus inter omnes nobilissimus_. He states that
the Italians prepare from it the finest essences, which are sold at a
high price.[479]
But, as shown by one of us,[480] the essential oil of bergamot had
already, in 1688, a place among the stores of an apothecary of the
German town of Giessen.
The name Bergamotta was originally applied to a large kind of pear,
called in Turkish “beg-ârmûdî,” _i.e._ prince’s pear.[481]
=Production=—The bergamot is cultivated at Reggio, on low ground near
the sea, and in the adjacent villages. The trees are often intermixed
with lemon and orange trees, and the soil is well irrigated and cropped
with vegetables.
The essential oil (_Oleum Bergamottæ_) is obtained from the full-grown
but still unripe and more or less green fruits, gathered in the
months of November and December. They are richer in oil than any one
of the allied fruits. It was formerly made like that of lemon by the
sponge-process, but during the last 20 years this method has been
generally superseded by the introduction of a special machine for
the extraction of the essential oil. In this machine the fruits are
placed in a strong, saucer-like, metallic dish, about 10 inches in
diameter, having in the centre a raised opening which with the outer
edge forms a broad groove or channel; the dish is fitted with a cover
of similar form. The inner surface both of the dish and cover is
rendered rough by a series of narrow, radiating metal ridges of blades
which are about ¼ of an inch high and resemble the backs of knifes.
The dish is also furnished with some small openings to allow of the
outflow of essential oil; and both dish and cover are arranged in a
metallic cylinder, placed over a vessel to receive the oil. By a simple
arrangement of cog-wheels moved by a handle, the cover, which is very
heavy, is made to revolve rapidly over the dish, and the fruit lying
in the groove between the two is carried round, and at the same time
is subjected to the action of the sharp ridges, which, rupturing the
oil-vessels, cause the essence to escape, and set it free to flow out
by the small openings in the bottom of the dish. The fruits are placed
in the machine, 6, 8, or more at a time, according to their size, and
subjected to the rotatory action above described for about half a
minute, when the machine is stopped, they are removed, and fresh ones
substituted. About 7,000 fruits can thus be worked in one of these
machines in a day. The yield of oil is said to be similar to that of
lemon, namely 2½ to 3 ounces from 100 fruits.
[479] _Hesperides Norimbergenses_, 1713. lib. 3. cap. 26. and p. 156 b.
(We quote from the Latin edition.)
[480] Flückiger, _Documente zur Geschichte der Pharmacie_, Halle, 1876.
72.
[481] Information, for which I am indebted to Dr. Rice.—The name has no
reference to the town of Bergamo, where bergamots cannot succeed.—F. A.
F.
Essence of bergamot made by the machine is of a greener tint than that
obtained by the old sponge-process. During some weeks after extraction
it gradually deposits a quantity of white greasy matter (bergaptene),
which, after having been exhausted as much as possible by pressure, is
finally subjected to distillation with water in order to separate the
essential oil it still contains.
The fruits from which the essence has been extracted are submitted to
pressure, and the juice, which is much inferior in acidity to lemon
juice, is concentrated and sold for the manufacture of citric acid.
Finally, the residue from which both essence and juice have been
removed, is consumed as food by oxen.
=Description=[482]—Essential oil of bergamot is a thin and mobile fluid
of peculiar and very fragrant odour, bitterish taste, and slightly
acid reaction. It has a pale greenish yellow tint, due to traces of
chlorophyll, as may be shown by the spectroscope. Its sp. gr. is 0·86
to 0·88; its boiling point varies from 183° to 195° C.
The oil is miscible with spirit of wine (0·83 sp. gr.), absolute
alcohol, as well as with crystallizable acetic acid. Four parts
dissolve clearly one part of bisulphide of carbon, but the solution
becomes turbid if a larger proportion of the latter is added.
Bisulphide of carbon itself is incapable of dissolving clearly any
appreciable quantity of the oil. A mixture of 10 drops of the oil, 50
drops of bisulphide of carbon and one of strong sulphuric acid has
an intense yellow hue. Perchloride of iron imparts to bergamot oil
dissolved in alcohol a dingy brown colour.
Panuccio’s oil of bergamot examined in the same way as that of lemon
(p. 120) deviates 7° to the right, and has therefore a dextrogyre
power very inferior to that of other oils of the same class.[483] But
it probably varies in this respect, for commercial specimens which we
judged to be of good quality deviated from 6·8° to 10·4° to the right.
=Chemical Composition=—If essential oil of bergamot is submitted to
rectification, the portions that successively distill over do not
accord in rotatory power or in boiling point, a fact which proves it to
be a mixture of several oils, as is further confirmed by analysis. It
appears to consist of hydrocarbons, C₁₀H₁₆, and their hydrates, neither
of which have as yet been satisfactorily isolated. Oil of bergamot,
like that of turpentine, yields crystals of the composition C₁₀H₁₆ +
3H₂O, if 8 parts are allowed to stand some weeks with 1 part of spirit
of wine, 2 of nitric acid (sp. gr. 1·2) and 10 of water, the mixture
being frequently shaken. No solid compound is produced by saturating
the oil with anhydrous hydrochloric gas.
The greasy matter that is deposited from oil of bergamot soon after
its extraction, and in small quantity is often noticeable in that
of commerce, is called _Bergaptene_ or _Bergamot Camphor_. We have
obtained it in fine, white, acicular crystals, neutral and inodorous,
by repeated solution in spirit of wine. Its composition according
to the analysis of Mulder (1837) and of Ohme (1839) answers to the
formula C₉H₆O₃, which in our opinion requires further investigation.
Crystallized bergaptene is abundantly soluble in chloroform, ether, or
bisulphide of carbon; the alcoholic solution is not altered by ferric
salts.
[482] The characters are taken from some Essence of Bergamot presented
to one of us (15 May 1872) as a type-sample by Messrs. G. Panuccio e
figli, manufacturers of essences at Reggio and also large cultivators
of the bergamot orange.
[483] See however _Oleum Neroli_, p. 127.
=Commerce=—Essence of bergamot, as it is always termed in trade, is
chiefly shipped from Messina and Palermo in the same kind of bottles as
are used for essence of lemon.
=Uses=—Much employed in perfumery, but in medicine only occasionally
for the sake of imparting an agreeable odour to ointments.
=Adulteration=—Essence of bergamot, like that of lemon, is extensively
and systematically adulterated, and very little is sent into the market
entirely pure. It is often mixed with oil of turpentine, but a finer
adulteration is to dilute it with essential oil of the leaves or with
that obtained by distillation of the peel or of the residual fruits.
Some has of late been adulterated with petroleum.
The optical properties, as already mentioned, may afford some
assistance in detecting fraudulent admixtures, though as regards oil of
turpentine it must be borne in mind that there are _levogyre_ as well
as _dextrogyre_ varieties. This latter oil and likewise that of lemon
is less soluble in spirit of wine than that of bergamot.