Chemistry of Essential Oils

76 THE CHEMISTEY OF ESSENTIAL OILS

On distillation, the first fractions passing over are much more volatile
and lighter than those which come over with difficulty towards the end
•of the distillation. These " light " and " heavy " oils can be separated
by using a steam-jacketed still with steam at a pressure of about 10 lb.,
until no more oil comes over. The heavy oil is then obtained by passing
steam at a higher pressure direct into the retort. The oil distilled in
Europe, however, is usually, if not always, a single distillate, and the
fractionated oils are scarcely commercial articles. Be"union distilled oil
is, however, of much lighter specific gravity than European distillates,
and is usually found to vary from 0

• 980 to 0'995. The yield of oil is a
  matter of much disagreement. According to Piesse, 100 lb. of oil yield
  about 9 to 10 oz. of oil, whilst Watts states that only 2 oz. are obtained.
  Other observers give from 4 to 9 per cent. Probably about 1 per cent,
  is the usual average.
  In order to determine the yield of cus-cus oil from the roots grown
  in various localities, Puran Singh examined the following seven samples
  from different localities in India with the following results :—

Locality.

1. Godhra Range, Panch Mahal
   District, Bombay


2. Ajmer, Rajputana


3. Pilibhic, United Provinces.


4. Ditto, and inferior sample,
   .thin White Roots


5. Belgaun Forest Division,
   Bombay


6. Yeotmal Forest Division,
   Central Provinces


7. Delhi, from the Bazar. The
   best long Fibres used by
   Native Perfumers.

Month of

Collection.

April, 1913

March, 1913

April, 1913

July, 1913

May, 1913

Aug., 1913

Jan. to Feb.,

1914

Ji

Moisture,

per

C

8-51

10-14

10-46

9-51

10-88

9-45

9-81

E3 <" ~ '

xs^5 -?

Ash

(per CentWashed

R<

Calculated.Dry

Mater

i

2-66

3-10

4-30

4-71

3-84

3-10

2-97

Oil

(per Cent.)

Steam

Distillat

0 - 72

1-13

0-69

0-37

0-99

0-45

1-14

A sample distilled in India by Puran Singh,^1 and rectified by steam
distillation, had the following characters :—

Specific gravity

Optical rotation

Refractive index

Acid value

Ester „

,, ,, (after acetylation)

1-011

- 30-65°

1-5165

10*5

69-6

132-8

The resinous matter left in the still had the following characters:—

Specific gravity at 30°

Optical rotation.

Acid value

Ester „

1-132

+ 488°

46-9

64-3

Vetivert oil of commerce, however, is always dextro-rotatory, obvi-

(^1) Chemist atid Druggist, 85 (1914), 225.