406 THE CHEMISTEY OF ESSENTIAL OILS
apricot kernels. No distinction will be made between these three oils,,
as they differ in no sensible degree, except for the fact of their actual
origin.
Bitter almond oil does not exist as such in the almond kernel, but
results from the hydrolysis of a glucoside, amygdalin, under the influence
of the naturally existing ferment emulsin. The fatty oil is obtained
from the kernels by expression, and the press-cake crushed and digested
with water, when the following reaction ensues :—^u + 2H 2 0 = C 7 H 6 0 + 2C 6 H 12 O 6 + HCN.
Amygdalin. Benzaldehyde. Dextrose.
Amygdalin, taking up two molecules of water, yields benzaldehyde
dextrose, and hydrocyanic acid. Amygdalin is a crystalline body, with-
out any smell of the bitter almond, and does not yield the oil except
under the influence of a hydrolytic agent, such as the natural ferment
emulsin, or by boiling with dilute acids. The action of the ferment is-
destroyed by heat or by warm alcohol. Hence if dried and powdered
b.tter almonds are shaken with boiling water and distilled, no oil is
obtained. After the fixed oil has been expressed the press cakes are
ground up and soaked for about twenty-four hours in twice their weight
of water, to which a quantity of salt is usually added. The whole is then
subjected to distillation. Some trouble, however, is experienced during,
the process, as the large quantity of albuminoids present causes excessive
frothing. To remedy this, the press-cakes are coarsely powdered and at
once immersed in boiling water to coagulate the albuminoids and dissolve
the amygdalin. The emulsin is, of course, rendered inactive, so that on
cooling, a quantity of emulsin of the fresh cake in cold water is added
to the previously treated mass. This is allowed to stand, until the
emulsin will have converted the whole of the amygdalin into essential
oil. The mixture is now distilled. As hydrocyanic acid is a very deadly
substance, it is necessary to use great care that none of the vapour is
allowed to escape into the air. The distillation is effected by direct steam
in most cases. The oil of almonds so obtained contains a considerable
amount of hydrocyanic acid, the remainder being principally benzalde-
hyde, C 6 H 5. COH. The absolutely natural oil is a regular commercial
article, but much is deprived of its hydrocyanic acid before being sold,
and is then listed at a correspondingly high price as " Oil of Almonds
(S.A.P.)" (i.e. Sine Acid. Prussic.). The following methods are used
to deprive the oil of this poisonous constituent:—
The oil is mixed with its own volume of water, and the mixture left
on a water-bath with red oxide of mercury, slaked lime, and ferrous
chloride, out of contact with the air. After all the prussic acid has been
decomposed, the oil is rectified and contains no trace of prussic acid.
This process was suggested by Redwood. Liebig used oxide of mercury
only. Mackay prefers agitating at intervals for forty-eight hours with a
mixture of lime and liquor potassae. To detect any traces of prussic acid
left in the oil, a little of it is dissolved in alcohol, and a few drops of
solutions of ferrous sulphate and ferric chloride are added. Slight excess
of caustic soda solution is then added, and the precipitate is dissolved by
the addition of dilute hydrochloric acid, when a blue colour or precipitate
(due to the formation of Prussian blue) appears if any hydrocyanic acid
is present. Benzaldehyde is very readily oxidised by the oxygen of the
atmosphere to benzoic acid, so that the oil almost invariably contains