Chemistry of Essential Oils

34 THE CHEMISTEY OF ESSENTIAL OILS

Juniperus nana Willd., with rather longer berries and a prostrate habit.
Especially where bands jof limestone occur, as on some of the Scottish
mountains and on the limestone hills in the Lake district, it is a common
plant.
The berries take two years to come to maturity, so that there are
always mature and immature berries on the same plant, and the collec-
tion by hand, unless the branches are beaten over a tray, is, owing to
the sharp points of the leaves, rather a prickly matter. The blackish
berries that are imported are apparently all mature, indicating that the
green immature berries are separated. The immature berries, however,
darken on keeping.
Whether imported oil of juniper is always distilled from Juniperus
communis is open to question, since the oil of some red juniper berries
imported from Smyrna, and attributed to Juniperus phoznicea, has been
found to correspond in all its properties with those of Juniperus com-
munis. But on examination of an oil distilled in Cyprus from the berries
of Juniperus phanicea at the Imperial Institute, it was shown to differ
from that of Juniperus communis in optical rotation, which was + 5°,
whilst that of Juniperus communis distilled from the berries is usually

• 3° to - 15^0.^1
  The yield of oil from imported berries varies from O5 to 1
  
  
  • 5 per cent,
    the Italian averaging 1 to 15 per cent., the Bavarian 1 to 12 per cent.,
    the Hungarian O8 to 1 per cent. The berries imported from East Prussia,
    Poland, and Thuringia average 06 to 0'9 per cent., and Swedish berries
    only 0'5 per cent, of oil, the berries of the more southern plants yielding
    the most oil. This indicates that sunny slopes are likely to be the best
    places to cultivate the plant for the berries. The yield of oil, however,
    varies considerably in different years.
    The known constituents of juniper oil are the terpenes, a-pinene, and
    camphene, the sesquiterpene cadinene, and a small amount of oxygenated
    constituents. The principal of these bodies is terpinenol. A second
    alcohol (or possibly a mixture of alcohols) has also been separated,
    having the following characters: boiling-point, 218° to 226° ; specific
    gravity, O9476 ; optical rotation, - 4° 30'; and refractive index, 14825.
    In old oils a crystalline substance is sometimes to be found, which has
    been described as juniper-camphor. Its constitution is unknown, but
    it is possibly a sasquiterpene alcohol. Traces of esters are also present.
    The physical characters of juniper oil vary so enormously according
    to the age of the oil, that it is very difficult to suggest limit values. For
    reasonably fresh oil that has been kept under proper conditions the fol-
    lowing figures will usually apply :—
  
  
  
  

Specific gravity... 0-865 to 0-890

Optical rotation... - 3° ,, - 20° (rarely slightly dextro-rotatory)

Refractive index... 1-4750 to 1-4880

Acid value... 1 to 4

Ester ,,...2 „ 8

„ ,, (after acetylation) 15 „ 25

The oil is usually soluble, when freshly distilled, in four volumes of

95 per cent, alcohol. But too much reliance must not be placed on this

test, as insolubility rapidly results from age. The approximate propor-

tions of pinene and cadinene should be determined by a fractional dis-

tillation. The results vary according to the fractionating apparatus

(^1) P. and E.O.R., 1913, 291.