Chemistry of Essential Oils

LABIATE 341

the portion of the oil coming over below 215° C. is set aside. The next
fraction coming over between 215° and 240° C. is then secured, leaving
a thick tar-like mass in the retort, which, so far as is known at present,
has no value. The first fraction may contain about 25 to 30 per cent,
of thymol, the cymene acting as a solvent of it, and preventing crystal-
lisation. This fraction is, therefore, redistilled, and the fraction redis-
tilling between 215° and 240° C. saved.
This fraction, added to the first which was distilled at the same
temperature, is cooled in a shallow dish, and a crystal of thymol added
to start crystallisation. After standing overnight the crystals are separated
from the mother liquor by means of a centrifuge, and the crystals washed
with water whilst the centrifuge is running at full speed. If there is a
large quantity of mother liquor left, it probably contains a considerable
portion of the lower boiling fraction and should be redistilled, removing
any that comes over between 215° and 240° C.
The oil thus treated gives a commercial yield of 663 per cent, of
thymol of a perfectly white crystalline character. Carvacrol is also
probably resent in the oil, as well as cymene, and traces o
f
^-limonene.
Monarda citriodora.—This plant is known in North America under
the name of Lemon Mint. It yields about 1 per cent, of essential oil
on distil ation, which has the following characters :—
Specific gravity 0-9437 to 0-9603 at 20°
Phenols........ 65 „ 80 per cent.
Aldehydes.1-2 „ 4 „
Ths oil contains a considerable amount of carvacrol, with a little
thymol. T hymo-hydroquinone is also present, and probably citral and
cymene.
Monarda myristica.—The oil d
;
stilled from the seeds of this plant,
known as " Owere' seeds on the Gold Coast, has been examined at the
Impei ial Ins itute.
1
The oil has the following characters:—

1. 
   
   
   
   2. Specific gravity 0-849 0-8592
      Optical rotation - 44° 40' - 57° Q
      r
      Acid value ........ 1-2 14
      Eatec „ 1-9 64
      „ „ (after acetylation) .... 52-9 35'5
      Monarda didyma.— L'his plant is indigenous to North America.
      The dtied herb yie ds about 003 per cent, of e sential oil, the twigs and
      leaves ibout 0'(M per cent, and the half-open flowers 0
   
   
   
   

• 26 to 0*32 per
  cent.
  The oils have th^ follow ng characters:—

No.

1

2

3

4

5

From

Dry Herb.

Half-drv Herb.

Dry Twigs and Leaves

Half open Fiowers

Specific Gravity

at 15°.

0-902 at 20°

0-8786

0-8855

0- 665

0-8740

Rotation.

- 10°

- 24° 36'

- 32 38'

- 7° 30'

- 15° 45

Re'ractive

Index.

1-4676

1-4689

1-4689

1-4674

Acid

Value.

5-5

2-i

4 6

Ester

Value.

20-4

, 4-4

5-6

VOL. I.

l

Bull. Imv. Just., 13 1915), 346.

16