BUTACEJE 421
of aldehyde present. The determination is carried out by comparison
with solutions of citral of known strength.
The solution of magenta-sulphurous acid is prepared as follows :
0
- 5 grm. of magenta is dissolved in 100 c.c. of water and a solution con-
taining 16 grms. of sulphur dioxide is then added. The liquid is allowed
to stand until it is decolorised and its volume is made up to a litre with
water. Such a solution cannot be kept longer than two or three days.
Secondly, alcohol of 95 per cent, strength must be prepared absolutely
free from aldehyde. For this purpose the alcohol is kept for several
days in contact with a caustic alkali, it is then distilled and the distillate
is boiled under a reflux condenser for a few hours with meta-phenylene-
diamine hydrochloride (25 grms. of the hydrochloride per litre). The
alcohol is then separated by distillation and made up to the desired con-
centration.
Lastly, a O'l per cent, solution of citral in 50 per cent, alcohol is
prepared.
These solutions are made up at a temperature of 15° C., and all the
operations are carried out at this temperature. It is particularly recom-
mended that a higher temperature be avoided.
Two grms. of each of the essential oils to be examined are diluted to
100 c.c. with the alcohol free from aldehyde. Four c.c. of each of the
solutions are introduced into cylinders of identical dimensions, 20 c.c of
alcohol free from aldehyde are added, then 20 c.c. of magenta-sulphurous
acid, and the volume is made up to 50 c.c. with alcohol. After thoroughly
mixing, the solutions are placed in a water-bath at 15° C., and compared
in regard to their colours with the necessary standards. An error of 1
per cent., however, may be made in this determination.
K. S. Hiltner
l
has devised a process depending on the yellow colour
developed when citral reacts with meta-phenylene-diamine. The process
is best carried out as follows:—
A standard solution of citral is made containing O'OOl grm. per c.c.
A 1 per cent, solution of meta-phenylene-diamine hydrochloride in
dilute alcohol is prepared, well shaken with bone black and filtered.
About 1-5 grms. of oil of lemon are weighed into a 50 c.c. flask, and
made up to the mark with 95 per cent, alcohol. From 2 to 4 c.c. of this
solution are transferred to a Nessler tube, 10 c.c. of the reagent added,
and the liquid made up to 25 c.c. with alcohol. A similar amount of the
standard solution is treated in the same way, and the colours developed
accurately matched.
The amount of citral is easily calculated from the amount of the
standard solution used.
L. D. Little
2
has devised the following method:—
Reagent.—Dissolve '200 grm. of diaminophenol hydrochloride (com-
mercially known as Amidol) in 100 c.c. of 65 per cent, alcohol, preferably
distilled over KOH. The use of aldehyde-free alcohol does not seem to
make any difference in the results, as acetaldehyde has no apparent effect
upon the reagent. Eecently distilled absolute alcohol is sufficiently
exact, as the reagent remains clear and colourless for several hours.
Standard Citral Solution.—A solution of pure citral in 50 per cent,
alcohol, containing '001 grm. per c.c.
1
Jour. Ind. Enq. Chem., I (1909), 798.
2
Jour. Amer. Pharm. Assoc. (1914), 3, 553.