_Oleum Limonum_; _Essential Oil or Essence of Lemon_; F. _Essence de
Citron_; G. _Citronenöl_.
=Botanical Origin=—_Citrus Limonum_ Risso (see p. 114).
=History=—The chemists of the 16th century were well acquainted with
the method of extracting essential oils by distillation. Besson in
his work _L’art et moyen parfaict de tirer huyles et eaux de tous
medicaments simples et oleogineux_, published at Paris in 1571,
mentions _lemon_-(citron) and orange-peel among the substances
subjected to this process. Giovanni Battista Porta,[468] a learned
Neapolitan writer, describes the method of preparing _Oleum ex
corticibus Citri_ to consist in removing the peel of the fruit with
a rasp and distilling it so comminuted with water; and adds that the
oils of lemon and orange may be obtained in the same manner. Essence
of lemon of two kinds, namely _expressed_ and _distilled_, was sold in
Paris in the time of Pomet, 1692.
=Production=—Essential oil of lemon is manufactured in Sicily, at
Reggio in Calabria, and at Mentone and Nice in France.
The lemons are used while still rather green and unripe, as being
richer in oil than when quite mature. Only the small and irregular
fruit, such as is not worth exporting, is employed for affording the
essence.
The process followed in Sicily and Calabria may be thus described;[469]
it is performed in the months of November and December.
[468] _Magiæ Naturalis libri xx._ Neapoli. 1589. 188.
[469] Through the kindness of Signor Mallandrino of Giampilieri near
Messina, I had the pleasure of seeing how the essence is made. Though
the time of my visit (13 May 1872) was not that of the manufacture,
Signor M. sent for one of his workmen, and having procured a few
lemons, set him to work on them in order that I might have ocular
demonstration of the process.—D. H.
The workman first cuts off the peel in _three_ thick longitudinal
slices, leaving the central pulp of a three-cornered shape with a
little peel at either end. This central pulp he cuts transversely in
the middle, throwing it on one side and the pieces of peel on the
other. The latter are allowed to remain till the next day and are then
treated thus: the workman seated holds in the palm of his left hand a
flattish piece of sponge, wrapping it round his forefinger. With the
other he places on the sponge one of the slices of peel, the outer
surface downwards, and then presses the zest-side (which is uppermost)
so as to give it for the moment a convex instead of a concave form.
The vesicles are thus ruptured, and the oil which issues from them is
received in the sponge with which they are in contact. Four or five
squeezes are all the workman gives to each slice of peel, which done
he throws it aside. Though each bit of peel has attached to it a small
portion of pulp, the workman contrives to avoid pressing the latter.
As the sponge gets saturated the workman wrings it forcibly, receiving
its contents in a coarse earthen bowl provided with a spout; in this
rude vessel, which is capable of holding at least three pints, the
oil separates from the watery liquid which accompanies it and is then
decanted.
The yield is stated to be very variable, 400 fruits affording 9 to 14
ounces of essence. The prisms of pulp and the exhausted pieces of peel
are submitted to pressure in order to extract from them lemon juice,
and are said to be also subjected to distillation. The foregoing is
termed the _sponge-process_; it is also applied to the orange. It
appears rude and wasteful, but when honestly performed it yields an
excellent product.
Essence of lemon is prepared at Mentone and Nice by a different method.
The object being to set free and to collect the oil contained in the
vesicles of the peel, an apparatus is employed, which may be thus
described:—a stout saucer or shallow basin of pewter, about 8½ inches
in diameter with a lip on one side for convenience of pouring. Fixed
in the bottom of this saucer are a number of stout, sharp, brass pins,
standing up about half an inch; the centre of the bottom is deepened
into a tube about an inch in diameter and five inches in length, closed
at its lower end. This vessel, which is called an _écuelle à piquer_,
has therefore some resemblance to a shallow, dish-shaped funnel, the
tube of which is closed below.
The workman takes a lemon in the hand, and rubs it over the sharp pins,
turning it round so that the oil-vessels of the entire surface may be
punctured. The essential oil which is thus liberated is received in the
saucer whence it flows down into the tube; and as this latter becomes
filled, it is poured into another vessel that it may separate from
the turbid aqueous liquid that accompanies it. It is finally filtered
and is then known as _Essence de Citron au zeste_. A small additional
produce is sometimes obtained by immersing the scarified lemons in warm
water and separating the oil which floats off.
A second kind of essence termed _Essence de Citron distillée_ is
obtained by rubbing the surface of fresh lemons, or of those which have
been submitted to the process just described, on a coarse grater of
tinned iron, by which the portion of peel richest in essential oil is
removed. This grated peel is subjected to distillation with water, and
yields a colourless essence of very inferior fragrance, which is sold
at a low price.
=Description=[470]—The oil obtained by the sponge-process and that of
the _écuelle à piquer_ are mobile liquids of a faint yellow colour, of
exquisite fragrance and bitterish aromatic taste.
[470] For specimens of the _Essence au zeste_ and of the _Essence
distillée_ of guaranteed purity we have to thank M. Médecin, distiller
of essences, Mentone; and Messrs. G. Pannucio e figli, for an authentic
sample of the essence made by the sponge process in their establishment
at Reggio. We have also had a small quantity prepared by the _écuelle_
by one of ourselves near Mentone, 15th June 1872.—D. H.
The different specimens which we have examined are readily miscible
with bisulphide of carbon, but dissolve sparingly in spirit of wine
(0·830). An equal weight of the oil and of spirit of wine forms a
turbid mixture. No peculiar coloration is produced by mixture with
perchloride of iron.
The oils are dextrogyre, but differ in their rotatory power, as may be
illustrated by the following results, which we obtained by examining
them in a column 50 millimetres long in the polaristrobometer of
Wild. The oil of Signori Panuccio, due to the sponge-process (p. 118,
note 2), deviated 20·9°, that of Monsieur Médecin (_Essence de Citron
au zeste_) obtained by the _éculle à piquer_ deviated 33·4° and his
distilled oil 28·3°.
=Chemical Composition=—The prevailing portion of most essential oils
of the _Aurantiaceæ_ agrees with the formula C₁₀H₁₆; the differences
which they exhibit chiefly concern their optical properties, odour, and
colour. The boiling point mostly varies from about 170° to 180° C., the
sp. gr. between 0·83 and 0·88. These oils are a mixture of isomeric
hydrocarbons, and also contain a small amount of cymene, C₁₀H₁₄, and of
oxygenated oils, not yet well known; of these we may infer the presence
either from analytical results or simply from the fact that the crude
oils are altered by metallic sodium. If they are purified by repeated
rectification over that metal, they are finally no longer altered by
it. Oils thus purified cease to possess their original fragrance, and
often resemble oil of turpentine, with which they agree in composition
and general chemical behaviour.
As to essential oil of lemons, its chief constituent is the terpene,
C₁₀H₁₆, which, like oil of turpentine, easily yields crystals of
terpin, C₁₀H₁₆ 3OH₂. There is further present, according to Tilden
(1879) another hydrocarbon, C₁₀H₁₆, which already boils at 160° C.,
whereas the foregoing boils at 176° C. Lastly a small amount of cymene
and of a compound acetic ether, C₂H₃O(C₁₀H₁₇O), would appear to occur
also in oil of lemons. The crude oil of lemons already yields the
crystalline compound C₁₀H₁₆ + 2HCl, when saturated with anhydrous
hydrochloric gas, whereas by the same treatment oil of turpentine
affords the solid compound C₁₀H₁₆ + HCl.
Essential oil of lemons (not the distilled) when long kept deposits a
greasy mass, from which we have obtained small crystals apparently of
_Bergaptene_ (p. 123).
=Commerce=—Essence of lemons is shipped chiefly from Messina and
Palermo, packed in copper bottles called in Italian _ramiere_ and by
English druggists “_jars_” holding 25 to 50 kilo. or more; sometimes in
tin bottles of smaller size. The quantity of essences of lemon, orange
and bergamot exported from Sicily in 1871 was 368,800 lb., valued at
£144,520, of which about two-thirds were shipped to England.[471]
In 1877 the export of these essential oils from Messina amounted to
306,948 kilogrammes, valued at 6,130,960 lire.
[471] Consul Dennis, _On the Commerce, &c. of Sicily in 1869, 1870,
1871_. _Reports from H.M. Consuls_. No. 4. 1873.
=Uses=—Essence of lemon is used in perfumery, and as a flavouring
ingredient; and though much sold by druggists is scarcely employed in
medicine.
=Adulteration=—Few drugs are more rarely to be found in a state of
purity than essence of lemon. In fact it is stated that almost all that
comes into the market is more or less diluted with oil of turpentine
or with the cheaper _distilled_ oil of lemons. Manufacturers of the
essence complain that the demand for a cheap article forces them to
this falsification of their product.