96 THE CHEMISTRY OF ESSENTIAL OILS
IRIDE^E.
OIL OF ORRIS ROOT.
Three species of the Iris are used for the preparation of this oiL
These are (a) Iris germanica, common in the districts near Florence,
and also found in Central Europe, Northern India, and Morocco; (b)>
Iris pallida, found in Istria, Florence, and Lucca; (c) Iris florentina,
occurring on the Macedonian coast, and near the coasts of the Black
Sea, and also in the neighbourhood of Florence and Lucca. The finest
roots are produced in the Tuscany district, and are known as Florentine
orris root, but it must be remembered that Florentine root is not synony-
mous with the root of Iris florentina, but embraces the three varieties,
which grow to the highest degree of perfection in this district. After
the Tuscany root, the Veronese is most valued. The roots, or more
correctly the rhizomes, exported from Morocco and East India are of
very secondary value, and do not arrive in the market in very good
condition. The plant used to be left entirely to itself to grow wild, but
extensive plantations are now cultivated. The plants are grown on hills,
generally on sunny open spaces, or between rows of vines. A dry cal-
careous soil is most suitable. The plants are left undisturbed for two
or three years, when the harvesting commences. Locally the plants
are known as giaggiolo. The fresh rhizome has very little odour, and
must be carefully dried before being sent away. Certain changes ap-
pear then to set in and the odour develops.
The odour of the dried rhizomes resembles the delicate violet per-
fume, and the powdered substance is a usual constituent of violet powder..
The earlier application of this delicate perfume was in the form of an
alcoholic extract, often known as essence of violets. But non-odorous,
substances are also extracted from the root by alcohol, and the odour is
not so delicate as that of the carefully distilled oil. Pure concrete orris
oil melts at about 40° to 50° and has an acid value between 204 and 236.
Its ester value should not exceed 10. The yield of oil is from
- 1 to
2
per cent.; but when the rhizome is treated with dilute sulphuric acid,
the starch granules are broken up and liberate more essential oil, but
the odour is much impaired. The essential oil obtained from the plant
is of a buttery consistence, and contains certain non-volatile fatty bodies
which are carried over mechanically by the steam. Fliickiger, who in-
vestigated this substance, showed that it consisted chiefly of myristic
acid with traces of the true volatile oil. Our present knowledge of the
oil, however, is chiefly due to Tiemann and Kriiger.
1
These chemists
obtained the oil by extracting the roots with ether, and steam distilling
the residue left on evaporation. The non-volatile portion contains a
little myristic acid, whilst the volatile oil contains a large amount of
myristic acid and its methyl ester, oleic acid, an oleic ester, oleic alde-
hyde, and a body which is responsible for the characteristic odour which
they termed irone. This body was separated in a pure state by con-
verting it into its phenylhydrazone and decomposing this with dilute
sulphuric acid. Irone C 13 H 20 O is an oil almost insoluble in water,
readily soluble in alcohol, etc., boiling at 144° at 16 mm., of specific
gravity
- 939 at 20
°
. It is dextro-rotatory. In the pure form the odour
is sharp and unlike violets, but when diluted it somewhat resembles.
1
Bericht, 26 (1893), 2675.