310 THE CHEMISTEY OF ESSENTIAL OILS
The principal constituent of the oil is anethol, and the oil also con-
tains fenchone, a-phellandrene, dipentene, camphene, d-pinene, and
methyl-chavicol. As anethol is the principal constituent of fennel oil,
the congealing-point may be regarded as a fair criterion of the value.
A good oil will contain as much as 60 per cent, of anethol. If
necessary the crystalline stearoptene may be separated and examined,
but as a rule added solid bodies will alter the other characters of the
oil. The oil is soluble in an equal volume of 90 per cent, alcohol.
The above tests will guard against the abstraction of anethol, or the
addition of the residue of oil from which this body has been abstracted.
One observer gives as the specific gravity and optical rotation of
the oil distilled from French bitter fennel, -910 to -955 and + 22° to
+ 48° respectively. Tardy,^1 however, has examined a sample of this oil,
and states that its specific gravity is 1*007 at 0°, and its optical rotation
+ 18° 20'. In the oil he found pinene, dipentene, cymene, phellan-
drene (?), d-fenchone, methyl-chavicol, and anethol, together with
anise aldehyde and anisic acid, and a ketone of the constitution
OCH 3\CH 2. CO. CH 3
Schimmel & Co. have examined a sample of Japanese oil, and give the
specific gravity as *9754, and the optical rotation as + 10° 3'. Umney
gives
- 9754 and + 15° 5' for a sample of the same oil. He found 10'2
per cent, of fenchone in the oil.
Foeniculum piperitum yields an oil (Sicilian fennel oil) of specific
gravity about '950. Spanish fennel oils, when pure, do not differ materi-
ally from other genuine sweet and bitter fennel oils. But much of the
commercial Spanish oil is a mixture distilled from the so-called wild, and
other fennel species.
The sweet Eoman fennel, as it is termed, usually contains much
anethol and little or no fenchone. It has the following characters :—
Specific gravity 0-976 to 0'980
Optical rotation..+ 5° to + 16° 30'
Congealing-point 10° to 14-5°
Macedonian fennel yields a very similar oil. Wild bitter fennel,
growing in France, Spain, and Algeria, yields an oil of specific gravity
0-905 to 0'925 and an optical rotation up to + 50°. It is practically
free from anethol. Indian fennel oil has a specific gravity '970 and an
optical rotation + 21°.
Tardy has examined an Algerian oil of specific gravity 0991 and
optical rotation + 62°. He found present: pinene, phellandrene,
fenchone, methyl-chavicol, anethol, a sesquiterpene, and a little thymo-
hydroquinone. Schimmel & Co. find camphene in fennel oil, but are
not able to confirm the presence of cymene. Traces of basic com-
pounds were also detected.
Wild bitter fennel oil differs considerably from the above-described
oils. Its specific gravity varies from 0
%
£05 to 0925, and optical rota-
tion + 40° to + 65°. Anethol is present only in traces, but a fair
amount of phellandrene is present. Tardy isolated from this oil a
crystalline compound melting at 213°, which is possibly di-para-
1
Bull. Soc. Chim., xvii., 660.