92 THE CHBMISTKY OF ESSENTIAL OILS
N. 0. LIL1ACE/E.
OIL OF GARLIC.This oil is distilled from the entire fresh plant Allium sativum. The
average yield of oil, according to Schimmel, is about 1 oz. from 1 cwt.
of the plants, although Wertheim obtained 3 to 4 oz. from this quantity.
The oil is a liquid possessing the characteristic unpleasant odour of gar-
lic, optically inactive, of specific gravity 1045 to 1060. It was examined
by Wertheim,
1
who stated that it contained allyl sulphide and allyl
oxide. The most modern and most trustworthy examination of the oil,
however, is due to Semmler.
2
He states that the garlic yielded 0
- 009
per cent, of oil of specific gravity 10525 at 145°. A small quantity of
crystals was deposited when the oil was cooled in a freezing mixture.
The oil contains no oxygen, and therefore no allyl oxide. When frac-
tionated under a pressure of 16 mm., four main fractions were obtained.
Fraction 1 (6 per cent.) consisted of allyl-propyl disulphide, C 6 H 12 S 2 , a
bright yellow oil of specific gravity 10231 at 15°, and boiling at 66° to
69° at 16 mm. Its odour is that of onions. Fraction 2 (60 per cent.)
consisted of diallyl disulphide, C 6 H 10 S 2 , a light yellow oil of garlic odour,
much resembling the last-named body, boiling at 78° to 80° at 16 mm.,
and decomposing at 150°. Its specific gravity is 10237 at 15°. Frac-
tion 3 (20 per cent.), boiling at 112° to 122° at the same pressure, con-
sisted of a body C 6 H 10 S 3 , the exact constitution of which was not
elucidated. Fraction 4 (10*5 per cent.) boiled above 122° at 16 mm.
pressure. It contained still more sulphur, and corresponded to the
empirical formula C 6 H 10 S 4. Semmler states that allyl sulphide (C 3 H 5 ) 2 S,
does not exist in the oil, as originally stated by Wertheim. Wertheim
also attributes to Beckett and Wright the statement that the oil contains
a sesquiterpene, which he (Semmler) also contradicts. In this, however,
Semmler is in error, as Beckett and Wright^3 examined the sesquiterpene
from oil of cloves, which was mistranslated into the Jahresbericht 4
as Knoblauchol: hence Semmler's mistake, which is reproduced in
Schimmel's report.^5
OIL OF ONION.
Oil of Onion is distilled from the bulb and fresh herb Allium cepa.
The average yield of the plant is 005 per cent, of an acrid oil of un-
pleasant odour and of dark brown colour. Its specific gravity is about
1038 and optical rotation — 3° to - 6°. The oil has been examined by
Semmler,6 who states that he obtained 005 per cent, of oil, which con-
tains no oxygen; its specific gravity was 1041 at 9°, and its optical
rotation - 5°. As it decomposes when boiled under ordinary pressure,
it was fractionated at 10 mm. The chief portion of the oil consisted of
a compound C 6 H 12 S 2 , an oil of specific gravity 1*0234 at 12°, boiling at
75° to 83° at 10 mm. From the higher boiling fractions a substance was
obtained, apparently identical with one of the constituents of oil of
asafcetida. No allyl sulphide was found. The employment of this oil,
which is somewhat disagreeable to manufacture, is quite similar to that
of oil of garlic.
^Annalen 3 51 (1844), 289. *Arch. Pliarm., 230 (1892), 434.
5 Jour. Chem. Soc., 1876, i. 6. * Jahresbericht, 1878, 398.Report, October, (^1893) -^6 Arch. Pharm., 230 (1892), 443.