408 THE CHBMISTKY OF ESSENTIAL OILS
Another adulterant, of a much grosser character, is oil of mirbane.
This is the cheap almond oil substitute so largely used for perfuming
common toilet soaps. Chemically it is nitrobenzene C 6 H 5 NO 2 , more or
less mixed with impurities, of which the most common is nitrotoluene,
-which sometimes itself forms the greater part of cheap nitrobenzene.
Indeed, nitrotoluene in any great quantity may be regarded as an adulter-
ant of nitrobenzene. The latter, when pure, is a yellowish liquid of
specific gravity at 0° of 1 200, boiling at about 206°, and solidifying at
-t- 2° to +• 3°. It has a coarse almond-like odour, and is poisonous when
taken internally, and irritating to the skin when used externally. The
cheapness of artificial benzaldehyde should discourage its use in even the
very cheap toilet soaps. Nitrotoluene C 6 H 4 (CH 3 )NO 2 exists in three
isomeric modifications, and nitroxylene (BgHgXCH^NOg in more still.
These bodies are found to a considerable extent in the cheaper qualities
of nitrobenzene. Consequently it is important that commercial samples
should have physical characters in approximate agreement with those
Above quoted.
To detect the presence of this objectionable substitute in oil of almonds
a little of the oil is warmed with iron filings and acetic acid. The nitro-
benzene is reduced to aniline C 6 H 5 NH 2 , which is distilled off and col-
lected. To the distillate a few drops of solution of ordinary chloride of
lime is added. If aniline be present the liquid yields the characteristic
^violet colour. Pure benzaldehyde combines with sodium bisulphite to
iorm a crystalline compound without the characteristic almond odour.
Samples adulterated with nitrobenzene, when shaken with excess of
bisulphite of sodium solution, so that the benzaldehyde is entirely com-
bined, then have the characteristic coarse nitrobenzene odour.
The determinations of importance in the examination of this oil are
(1) the determination of chlorine, or at all events its detection qualitatively,
if present; (2) the determination of benzaldehyde, and (3) the determina-
tion of hydrocyanic acid.
The Determination of Chlorine.—Many methods have been suggested
for the detection and determination of chlorine, but most of them are
merely qualitative. Of these the following are useful:—
(a) By simple combustion. This method depends on the fact that on
combustion a portion of the chlorine present in the organic compounds
existing as impurities, forms hydrochloric acid, which can be detected by
means of silver nitrate.
A piece of filtering paper about 2 inches by 1 inch and rolled in the
shape of a spill, is saturated with the oil, the excess of oil is thrown off
and the paper is placed in a small porcelain dish which in its turn re-
poses in a larger dish, measuring about 8 inches in diameter. The paper
is ignited, and a beaker of a capacity of about 2 litres, moistened inside
with distilled water, is quickly placed over the paper. The sizes of the
dishes used must be such that the rim of the larger dish must stand out
well all round from the beaker. After the flame is extinguished the
beaker should be left in position for about one minute, after which the
products of combustion which have been deposited against the moist
sides of the beaker are rinsed out with a little distilled water, and
filtered. The filterate, acidulated with a drop of nitric acid, must remain
dear when silver nitrate solution is added.
Care must be taken that the filter paper is free from chlorine. This
should be determined by a blank experiment. This process has been