72 THE CHEMISTEY OF ESSENTIAL OILS
leading up to a speculative view as to the actual type of grass used in
the distillation.
Stapf, in the admirable work on the Cymbopogon grasses described
under Citronella Oil (p. 60), has held that the soluble lemon-grass oils
are obtained from Cymbopogon ftexuosus as the parent plant, and that
the insoluble oils are derived from Cymbopogon citratus.
The chemists of the Imperial Institute,^1 however, hold the view that
the insolubility of much of the Cochin lemon-grass oils is due to the fact
that the oil is distilled by steam, which has carried over the less volatile
and insoluble fractions, whilst the soluble oils are distilled over a naked
fire in the old-fashioned manner.
The conclusions drawn by the Imperial Institute chemists do not
seem to have any great amount of evidence to support them. The
author observed, some years ago, that West Indian lemon-grass oil de-
creased considerably in c
i
tral value by keeping, and also became far less
soluble. The freshly distilled oil from Cymbopogon citratus distilled in
the West Indies was soluble in 3 volumes of 70 per cent, alcohol when
freshly distilled. Since then he has had the opportunity of examining
numerous samples of Cochin oil which had been tested before shipment,
and which on arrival in Europe had lost from 3 to 5 per cent, or even
more of their citral contents. In the author's opinion, there is room
for tha belief that the recently found insolubility of Cochin lemon-grass
oil may be due to differences in the exact type of grass used, and also in
the conditions of cultivation.
The oil-content of tfce individual parts of Cymbopogon citratus in
their various stages of development has been the subject of researches
by A. W. K. de Jong so as to ascertain which period is the most favour-
able one for the harvest and the distillation. According to him, the leaves
contain most of the oil, of which the quantity is always largest in the
leaf of the latest formation, whilst with the increasing age of the leaf,
the oil-content continuously diminishes. The citral-content of the oil
becomes slightly higher as the age of the leaf increases, viz., from 77 to
79 per cent, in the youngest, up to 83 per cent, in the oldest leaves.
The sheaths of the leaves also contain oil, but considerably less than the
leaves themselves. In the roots of" Cymbopogon citratus essential oil is,
according to de Jong, also present—not in the thin, fibrous roots, but
in the thick bulbs, and in the young bulbs more (about 0'5 per cent.)
than in the older ones (about 0
- 35 per cent.). For this reason de Jong
recommends that the roots should also be included in the distillation,
but unfortunately he gives no information as to the properties of the
root-oil. De Jong concludes from his experiments that it is inadvisable
to wait longer for the cutting of the grass than until four to five leaves
have been formed.
De Jong observed, that although the Java oil immediately after dis-
tillation is soluble in 2 volumes of 70 per cent, alcohol, the solubility
diminishes considerably after a few days, and after a prolonged time
the oil only forms a very cloudy solution from which, if left standing,
part of the oil again separates. The cause of this change is, in de Jong's
opinion, the polymerisation of a terpene; an oxidation process appears
to him out of the question, as the oil becomes insoluble if it is kept with
the air excluded. Various attempts made to prevent the change, re-
1
Bull. Imp. Instit., June, 1914.