TMt YROmCAL AGmCULTURIST. [OctbBER i, 
NOTE ON COMMERCIAL OIL OF CITRONELLA.* 
BY JOHN C. TTMNEY, 
Pharmaceutical Chemist, 
Tlie more common Indian grass oils, known in 
trade as verbena, ginger-grass, and citronella, tlie pro- 
ducts respectively of Andropoffon citratus. A, fichre- 
nanthis, and J. Nardvs differ considerably in ap- 
pearance. The first two are usually of a yellowish 
brown colour; the third varies, being sometimes 
yellow, at others emerald green, the yellow oil 
generally becoming green on exposure to light. 
In order to determine on what the difference in 
colour of this last and the change from yellow to 
green which takes place depend, eight samples of 
citronella oil were obtained from various sources, 
and a small quantity of each exposed to direct 
sunlight. Of this number five (a, e, c, f, g) were 
decidedly green before exposure, two (d and e) were 
yellow at first, but rapidly became green, whilst one 
"(h) was yellow originally and underwent no change. 
The fact that the presence Of copper has been shown 
(Guibourt and Histed) to be reason of the green 
colour of commercial cajeput oil, led me to suspect 
the same contamination in the case of this oil. 
(Since writing this note my attention has been 
called to the fact that Kremers t mentions inciden- 
tally the presence of copper in a sample of this oil 
which he examined.) 
2.50 c.c. of the sample a was shaken with a dilute 
solution of ferrocyanide of potassium, when a rapid 
separation of a red precipitate took place, which after 
washing with spirit to free it from traces of oil and 
then with water to remove any excess of potassium 
ferrocyanide, was proved to be ferrocyanide of copper. 
Examination was then made of all the samples, with 
the following results: — 
Sp. gr 
at 150 C 
A 
•896 
B 
■895 
C 
■890 
D 
•887 
B 
•896 
F 
■896 
G 
■897 
H 
■870 
Colour. 
Remarks. 
emerald green. copper present, 
greenish. ,, 
emerald green, 
greenish. 
absent. 
From the fact that only those samples which were 
green, or became so on exposure, contained copper, 
it appeared almost certain that the change in colour 
might be due directly to the presence of that hietal, 
which was readily proved by precipitating all the 
copper from the most markedly green sample, by 
treatment two or three times with solution of po- 
tassium ferrocyanide, when the oil became pale 
yellow in colour. One portion of this oil Was then 
exposed to sunlight for some days and a second to 
the heat of a water-bath in an open porcelain dish 
for twelve hours without any change whatever in 
colour taking place. A third portion of the oil was 
treated on a water-bath for a few minutes in pre- 
sence of a very small piece of copper foil, when the 
oil rapidly assumed its original green colour, thus 
showing conclusively that the green coloration of 
the oil is due to the presence of a trace of copper, 
and that its removal causes the oil to assume its 
natural color, namely, yellow. 
The green coloration of the oil •ivaa destroyed on 
heating to S0° C, and at a higher temperature an 
acid distillate was obtained which was proved after 
neutralization to consist principally of acetic acid. 
It seems possible, therefore, that the metal exists 
in combination with this acid, the change in colour 
on exposure to light either depending on oxidation 
of an aldehyde present to acetic acid, or on the 
partial decomposition of an ester of acetic acid 
• Read before the Pharmaceutical Society of Great 
Britain, at an Evening Meeting in London, April 8. 
t ' I'roceodings American Pharmaceutical Associ- 
ation,' 1887, p. 502. 
contained ni the oil. Varying statements exist as 
to the specific gravity of pure citronella oil, for whilst 
Messrs. Schimmel state that it should not fall below 
•895 at 15° C. {Pharni. Journ. [3], sx., 264), Dodge 
{Fharn:. Jmirn. fS], xx., 855) assigns to it a gravity of 
■877 at 16° C. It will be noticed that sample H, 
which contained no copper, was of lower specific 
g'ravity than the others, and fell considerably below 
the limit proposed by Messrs. Schimmel. This sample 
proved, on examination of its solubility in 80 per 
cent, spirit, to be adulterated with petroleum, as was 
readily proved by fractionation, and the absence of 
copper is probably due to its distillation in the ear- 
then or iron stills, now only used by the poorer 
native distillers. The quantity of copper present, 
without doubt derived from distillation in stills of 
that metal, is, of course, very minute, but it seems 
desirable to call attention to "it, as pointing out that 
pale yellow, and not green, is the natural colour of 
citronella oil. 
Discussion. 
Mr. 0. Umney said it was very desirable that 
pharmacists should be aware of the changes which 
took iDlace naturally in drugs and other matters with 
which they had to deal. Essential oils they all knew 
were prone to oxidation and change, as was seen 
in the case of essential oil of almonds, which one 
day might be quite limpid and the next almost a 
solid mass from crystallization due to oxidation, or 
in essential oil of camomile, which would be one 
morning quite white, and the next a beautiful blue 
colour. Oil of cajuput, again, was sometimes rejected 
because it was white and had not the green copper 
colour they were accustomed to, It was very im- 
portant to know when these changes were due to 
natural causes and when to sophistication or defects 
in manufacture. Citronella oil was a very large article 
of commerce, being imported enormously from Ceylon, 
where the grass from which the oil was distilled 
grew in such luxui-iance that they had nothing to 
do but gather it and put it into the still, and the 
oil came to this country almost for nothiiig, the 
price being only about one-tenth what it was some 
few years ago. It was quite clear that there was 
often a defect in manufacture which could be re- 
medied by having the head of the still well tinned, 
and by having the worm of tin or earthenware. That, 
however, would not prevent sophistication. Pe- 
troleum was very cheap in most places, and the 
citronella oil which came to London was often 
adulterated with it, sometimes only to so small an 
extent as to arouse suspicion, but sometimes to such 
a large extent that those who understood such matters 
simply marked "petroleum" against it in their 
catalogues and paid no further attention to it. 
This paper would put people on their guard, and would 
enlighten those who like himself had been under the 
impression that this charge of colour was due to a 
similar cause as that which took place in camomile oil 
and not to defects in manufacturing or sophistication, 
Mr. Holmes said the specimens of citronella oil in the 
Museum had never been green ; and it seemed there- 
fore that the method of distillation must have been 
altered of late years. The question of adulteration 
with petroleum was of great importance, as essen- 
tial oils were more frequently adulterated than most 
drugs, and the fraud was often difficult of detection. 
American essential oils were much worse than th ose 
in this country, which might account for the 
fact that the specific gravity mentioned in American 
text-books was not always correct. The same thing 
had been noticed in the case of sandal-wood oil. 
The Pkesident said it would appear that the so- 
called sophisticated oil was in fact pure, the green 
coloiu- being only due to distillation in copper. He 
did not know wheather anyone could throw any light 
on the reason for adding petroleum. Apart fi-om 
any question of gravity it would probably be useful 
in preserving the flavoiu- of the original oil. 
Mr. Charles Umney thought possibly the petro- 
leum was put into the still with the grass. Formerly 
this oil and also oil of verbena came to this cotmtry 
in bottles which had been sent out with wine or 
brandy, but these essential oils now came over either 
