Chemistry of Essential Oils

518 THE CHEMISTEY OF ESSENTIAL OILS

First Quality Oils. Second Quality Oils.

30°

Specific gravity ^-... 0-911 to 0-958 0-896 to 0-942

Refractive index at 30°.. 1-4747 „ 1-4940 1-4788 „ 1-5082

Optical rotation... - 27° to - 49-7° - 27-4° to - 87°

Ester number .... 90 „ 138 42 to 94

(in one case 169)

According to Bacon, in first-class oils the ester number is mostly 100

or more, the refractive index rarely above 1*4900, optical rotation rarely

above - 45°, but mostly between — 32° and — 45°. In the case of the

second grade or cananga oils, however, the ester number is rarely higher

than 80, the refractive index approaches 1*5000 owing to the larger

content of sesquiterpenes and resins, and the optical rotation amounts to

• 60° and more. Low values for optical rotation and ester number
  usually point to second-class oils, which have mostly also a low specific
  gravity. Oil with a low refractive index, low rotation, and a high ester
  number can with a fair amount of certainty be considered as good, whilst
  a high refractive index, high rotation, and low ester number point to oils
  of lower quality. The figures for the specific gravity did not indicate
  any special regularities, but in an oil with a high specific gravity and a
  high ester-content (ester number above 100), the refractive index also
  will usually be found high, and the oil can therefore be considered as
  good.
  Attempts made to arrive at oils of better quality by distilling inferior
  oils in vacuo gave no favourable results, as the odour suffered distinctly,
  and could only be improved by passing air through the oil—a process
  which is also employed to remove the burnt odour caused when the
  blossoms are allowed to be slightly burnt in the distillation. It appears
  that the highest boiling portions of the oil fix the fragrant volatile con-
  stituents, for the resinous distillation-residues always showed an odour
  which lasted for a remarkably long time. It was further found that
  first-class oils contained over 50 per cent, of portions boiling below 100°
  at 10 mm. pressure.

KEUNION YLANG-YLANG OIL

Specific gravity 0*930 to 0-967

Optical rotation....•....- 34° „ - 65°

Ester value 96 „ 160

Refractive index 1-500 „ 1-5100

JAVA CANANGA OIL.

Specific gravity

Optical rotation

Refractive index

Ester value

(after acetylation)

0-906 to 0-956

• 15° „ - 52°
  about 1-4900 to 1-5050
  10 to 60 (rarely above 35)
  45 to 100

Four samples of ylang-ylang oil distilled in Amani (East Africa)
were examined by Schimmel & Co.
1
with the following results:—

(^1) Report, October, 1911, 102.