THE TROWOAL AGRICULTURIST. [October i, 1891. 
NOTE ON COMMERCIAL OIL OP CITRONELLA.* 
BY JOHN C. 1'MNF.Y, 
Fhannaceuticnl Chemnt. 
The more common Indian prass oils, known in 
trade as verbena, pinper-grasB, and citronella, the pro- 
ducts respectively of Andi-ovogen cifratus, A. dcha- 
nanihut, and A. Nardna differ considerably in ap- 
E earance. The first two are nsnallv of a yellowish 
rown 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 m 
colour of this last and the change from yellow to 
green which takes place depend, eight samples of 
citronella oil were obtained from various sonroes, 
and a small quantity of each exposed to direct 
sunlight. Of this number five Ca. b, c, f, o) were 
decidedly green before exposure, two fn and r) 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 Kreraers t mentions inciden- 
tally the presence of copper in a sample of this oil 
which he examined.) 
S.'in c.c. of the sample it was shaken with a dilute 
solution of ferroeyanide of potassium, when arapid 
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 
ferroeyanide, was proved to he ferroeyanide of copper. 
Examination was tlien made of all the samples, with 
the following results: — 
Sp. gr. 
at 15° C 
A 
B 
•805 
Cj 
■K<.K) 
D 
•887 
E 
•80(i 
P 
•800 
G 
•807 
II 
•870 
Colour. 
emerald green, 
greenish. 
yol., becoming green. 
»> ♦» »J 
emerald green, 
greenish. 
brownish yellow. 
Remarks, 
copper present. 
If 
If 
II 
{ 
copper entirely 
absent. 
From the fact that only those samples which wore 
green, or became so on exposure, contained copper, 
it appeared almost certain that the change in colour 
might bo due directly to the presence of that metal, 
which was readily proved by precipitating all the 
copper from tlio most markedly green sample, by 
treatment two or three times with solution of po- 
tassium ferroeyanide, 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 cliango 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 asstimed 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 was destroyed on 
heating to 50° C., and at a higher tomporaturo 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 eater of acetic acid 
* Read before tlio Pharmaceutical Society of Groat 
Britain, at an Evening Meeting in London, Aprii 8. 
+ ‘Proceedings Ametioau Phumacontical Associ- 
ation,' 1887, p, 502. 
contained in the oii. 'Varying statements exist as 
to the specific gravity of pure citronella oil, for whilst 
Messrs. Scliiiumel state that it shouid not fall below 
■895 at 15° C. (Piiarm. Joiirn, [8], xx., 2C4), Dodge 
{Phann. •Tcmrn. [3], xx., 855) assigns to it a gravity of 
■877 at 1G° 0. It will be noticed that sample h, 
which contained no copper, was of lower specific 
gravity than the others, and fell considerably below 
the limit proposed by Messrs. Sohiramel. This sample 
proved, on examination of its solubility in 80 per 
cent, spirit, to bo adulterated with petroleum, as was 
readily proved by fractionation, and tbe 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 tho natural colour of 
citronella oil. 
Discussion. 
Mr. C. Umney said it was very desirable that 
pharmacists should be aware of the changes which 
took place 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 tho case of essential oil of almonds, which one 
day might be quite limpid and the next almost a 
solid mass from crystallization duo to oxidation, or 
in essential oil of camomile, which would be one 
morning quite white, and the next a licautiful litue 
colour. Oil of cajiiput, again, was sometimosrejected 
because it was white and liad not tlie green copper 
colour they were accustomed to, It was very im- 
portant to know when tlieso changes woie due to 
natural causes and when to so|)liiatioation or defects 
in manufacture. Oitronollauil was a very large article 
of commerce, being imported enormously from (’ey Ion, 
where tiie grass from wliicli the oil was distillf*d 
grew in such luxuriance that they liad nothing to 
do but gather it and put it into the still, and tlie 
oil came to this country almost for nothing, the 
price being only about one-tenth what it waR Boine 
few yearn ago. ^ It was qulio clear that there waa 
often a defect in manufacture which could bo re- 
medied by having the head of the Rtill well tinned, 
and by having tho worm of tiu 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, somotiniea only to ho small an 
extent as to arouse suspicion, but Bometinioa to such 
a large extent that those who understood such matters 
Bimply marked “petrolouin” against it in their 
catalogues and paid no further attontioii to it. 
This paper would put people on their guard, and would 
eulighteu thoso who fiko hiiuself 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 nianufactiuing or sophistication, 
Mr. UoiiMtiH said the specimens of citronella oil in the 
Mnaoum had never been green ; and it seemed there- 
fore that tho method of distillation must have been 
altered of late years. The Question of rtdultoration 
with petroleum was of great importance, as esbon- 
tial oils were more frequently adulterated than moat 
drugs, and tho fraud was often difficult of detection. 
American essential oils were much worse than thoso 
in this country,^ wffiich 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 PitKHiPKNT said it would appear that the so- 
called sophisticated oil was in fart pure, the gi*een 
colour being only duo to dirttillatiou in copper. He 
did not know’ wheather anyone could throw any light 
on tho reason for adding petroleum. Apart from 
any question of gravity it would probalily be useful 
in preserving tho Havour of the original oil. 
Mr. CiiARLKK Umnky thought possibly the petro- 
leum was put into the still with the grass. Formerly 
this oil and also oil of verbena came to this country 
in bottles which had boon sent out with wine or 
brandy, but these essential ells new came over either 
