_Bitter Almonds_; F. _Amandes amères_; G. _Bittere Mandeln_.
=Botanical Origin=—_Prunus Amygdalus_ Baillon var. _a. amara_
(_Amygdalus communis_ L. var. _a. amara_ DC.). The Bitter Almond
tree is not distinguished from the sweet by any permanent botanical
character, and its area of growth appears to be the same (see p. 244).
[950] _Die Eiweisskörper der Getreidearten, Hülsenfrüchte und
Oelsamen_, Bonn, 1872. 199.
[951] Gmelin, _Chemistry_, xviii. (1871) 452.
[952] _Statement of the Trade and Navigation of Bombay for_ 1872-73,
pt. ii. 31.
=History=—(See also preceding article.) Bitter almonds and their
poisonous properties were well known in the antiquity, and used
medicinally during the middle ages. Valerius Cordus prescribed them as
an ingredient of trochisci.[953]
As early as the beginning of the present century, it was shown by the
experiments of Bohm, a pharmaceutical assistant of Berlin, that the
aqueous distillate of bitter almonds contains hydrocyanic acid and a
peculiar oil which cannot be obtained from sweet almonds. It was then
inferred that hydrocyanic acid itself might be poisonous, a fact which,
strange to say, had not been noticed by Scheele, when he discovered
that acid in 1782, as obtained by distilling potassium ferrocyanate
with sulphuric acid. The dangerous action of hydrocyanic was then
ascertained in 1802 and 1803 by Schaub and Schrader.[954]
=Description=—Bitter almonds agree in outward appearance, form, and
structure with sweet almonds; they exist under several varieties,
but there is none so far as we know that in size and form resembles
the long sweet almond of Malaga.[955] In general, bitter almonds are
of smaller size than sweet. Triturated with water, they afford the
same white emulsion as sweet almonds, but it has a strong odour of
hydrocyanic acid and a very bitter taste.
=Varieties=—These are distinguished in their order of goodness, as
French, Sicilian, and Barbary.
=Microscopic Structure=—In this respect, no difference between sweet
and bitter almonds can be pointed out. If thin slices of the latter are
deprived of fat oil by means of benzol, and then kept for some years in
glycerin, an abundance of crystals is slowly formed, of what we suppose
to be amygdalin.
=Chemical Composition=—Bitter almonds, when comminuted and mixed with
water, immediately evolve the odour of bitter almond oil. The more
generally diffused substances are the same in both kinds of almond, and
the fixed oil in particular of the bitter almond is identical with that
of the sweet. Bitter almonds however contain on an average a somewhat
lower proportion of oil than the sweet. In one instance that has come
to our knowledge in which 28 cwt. of bitter almonds were submitted
to pressure, the yield of oil was at the rate of 43·6 per cent. Mr.
Umney, director of the laboratory of Messrs. Herrings and Co., where
large quantities of bitter almonds are submitted to powerful hydraulic
pressure, gives 44·2 as the average percentage of oil obtained during
the years 1871-2.
[953] _Dispensator_., Paris, 1548. 336. 337. 343.
[954] J. B. Richter, _Neuere Gegenstände der Chymie_, Breslau, xi.
(1802) 65. J. B. Trommsdorffs _Journ. d. Pharm._ xi. (Leipzig, 1803)
262. Preyer, _Die Blausäure_, Bonn, 1870. 152.
[955] Hence to avoid bitter almonds being used instead of sweet, the
_British Pharmacopœia_ directs that _Jordan Almonds_ alone shall be
employed for Confection of Almonds.
Robiquet and Boutron-Charland in 1830 prepared from bitter almonds a
crystalline substance, _Amygdalin_, and found that bitter almond oil
and hydrocyanic acid can no longer be obtained from bitter almonds,
the amygdalin of which has been removed by alcohol. Liebig and Wöhler
in 1837 showed that it is solely the decomposition of this body (under
conditions to be explained presently), that occasions the formation of
the two compounds above named. Disregarding secondary products (ammonia
and formic acid), the reaction takes place as represented in the
following equation:
C₂₀H₂₇NO₁₁ + 3 OH₂ = OH₂ · 2 (C₆H₁₂O₆) · NCH · C₇H₆O.
Crystallized Anhydrous Hydro- Bitter
Amygdalin. Dextro- cyanic Almond
glucose. Acid. Oil.
This memorable investigation first brought under notice a body of the
glucoside class, now so numerous.
Amygdalin may be obtained crystallized when almonds deprived of their
oil are boiled with alcohol of 84 to 94 per cent. The product amounts
at most to 2½ or 3 per cent. Amygdalin _per se_ dissolves in 15 parts
of water at 8-12° C., forming a neutral, bitter, inodorous liquid,
quite destitute of poisonous properties.
It would appear from the investigations of Portes (1877) that in young
almonds, amygdalin is formed before the emulsin.
When bitter almonds have been freed from amygdalin and fixed oil, cold
water extracts from the residue chiefly emulsin and another albuminoid
matter separable by acetic acid. The emulsin upon addition of alcohol
falls down in thick flocks, which, after draining, form with cold
water a slightly opalescent solution. This liquid added to an aqueous
solution of amygdalin, renders it turbid, and developes in it bitter
almond oil. The reaction takes place in the same manner, if the emulsin
has not been previously purified by acetic acid and alcohol, or if
an emulsion of sweet almonds used. But after boiling, an emulsion of
almonds is no longer capable of decomposing amygdalin.
What alteration the emulsin itself undergoes in this reaction, or
whether it suffers any alteration at all, has not been clearly made
out. The reaction does not appear to take place necessarily in atomic
proportions; it does not cease until the emulsin has decomposed
about three times its own weight of amygdalin, provided always that
sufficient water is present to hold all the products in solution.
The leaves of _Prunus Lauro-cerasus_ L., the bark of _P. Padus_ L., and
the organs of many allied plants, also contain emulsin or a substance
analogous to it, not yet isolated. In the seeds of various plants
belonging to natural orders not botanically allied to the almond, as
for example in those of mustard, hemp, and poppy, and even in yolk
of egg, albuminous substances occur which are capable of acting upon
amygdalin in the same manner. Boiling dilute hydrochloric acid induces
the same decomposition, with the simultaneous production of formic acid.
The distillation of bitter almonds is known to offer some difficulties
on account of the large quantity present of albuminous substances,
which give rise to bumping and frothing. Michael Pettenkofer (1861) has
found that these inconveniences may be avoided by immersing 12 parts
of powdered almonds in boiling water, whereby the albuminous matters
are coagulated, whereas the amygdalin is dissolved. On then adding
an emulsion of only 1 part of almonds (sweet or bitter), the emulsin
contained in it will suffice to effect the required decomposition at a
temperature not exceeding 40° C. In this manner, Pettenkofer obtained
in some experiments performed with small quantities of almonds, as
much as 0·9 per cent. of essential oil. In the case alluded to on
the opposite page, in which 28 cwt. of almonds were treated, the
yield of essential oil amounted to 0·87 per cent. From data obligingly
furnished to us by Messrs. Herrings and Co. of London, who distill
large quantities of almond cake, it appears that the yield of essential
oil is very variable. The yearly averages as taken from the books of
this firm, show that it may be as low as 0·74, or as high as 1·67 per
cent., which, assuming 57 pounds of cake as equivalent to 100 pounds of
almonds, would represent a percentage from the latter of 0·42 and 0·95
per cent. respectively. Mr. Umney explains this enormous variation as
due in part to natural variableness in the different kinds of bitter
almond, and in part to their admixture with sweet almonds. He also
states that the action of the emulsin on the amygdalin when in contact
with water, is extremely rapid, and that 200 pounds of almond marc are
thoroughly exhausted by a distillation of only three hours.
In the distillation, the hydrocyanic acid and bitter almond oil unite
into an unstable compound. From this, the acid is gradually set
free, and partly converted into cyanide of ammonium and formic acid.
Supposing bitter almonds to contain 3·3 per cent. of Amygdalin, they
must yield 0·2 per cent. of hydrocyanic acid. Pettenkofer obtained by
experiment as much as 0·25 per cent., Feldhaus (1863) 0·17 per cent.
Some manufacturers apply bitter almond oil deprived of hydrocyanic
acid, but such purified oil is very prone to oxidation, unless
carefully deprived of water by being shaken with fused chloride of
calcium. The sp. gr. of the original oil is 1·061-1·065; that of the
purified oil (according to Umney) 1·049. The purification by the action
of ferrous sulphate and lime, and re-distillation, as recommended by
Maclagan (1853), occasions, we are informed, a loss of about 10 per
cent.
Bitter almond oil, C₆H₅(COH), being the aldehyde of benzoic acid,
C₆H₅(COOH), is easily converted in that acid by spontaneous or
artificial oxidation. The oil boils at 180°C. and is a little soluble
in water; 300 parts of water dissolve one part of the oil.
There are a great number of plants which if crushed, moistened with
water, and submitted to distillation, yield both bitter almond oil and
hydrocyanic acid. In many instances the amount of hydrocyanic acid is
so extremely small, that its presence can only be revealed by the most
delicate test,—that of Schönbein.[956]
Among plants capable of emitting hydrocyanic acid, probably always
accompanied with bitter almond oil, the tribes _Pruneæ_ and _Pomeæ_ of
the rosaceous order may be particularly mentioned.
The farinaceous rootstocks of the Bitter Cassava, _Manihot utilissima_,
Pohl, of the order _Euphorbiaceæ_, the source of tapioca in Brazil,
have long been known to yield hydrocyanic acid.
A composite, _Chardinia xeranthemoides_ Desf., growing in the Caspian
regions, has been shown by W. Eichler also to emit hydrocyanic
acid.[957] The same has been observed by the French in Gaboon[958] with
regard to the fruits of _Ximenia americana_ L. of the order _Olacineæ_,
and the fact has been confirmed by Ernst of Caracas,[959] near which
place the plant abounds. Mr. Prestoe of the Botanical Garden, Trinidad,
informs us (1874) that in that island a convolvulaceous plant, _Ipomœa
dissecta_ Willd., contains a juice with a strong prussic acid odour.
According to Lösecke, a common mushroom, _Agaricus oreades_ Bolt.,
emits hydrocyanic acid.[960]
[956] Applied in the following manner:—Let bibulous paper be imbued
with a fresh tincture of the wood or resin of guaiacum, and after
drying, let it be moistened with a solution composed of one part of
sulphate of copper in 2000 of water. Such paper moistened with water
will assume an intense blue coloration in the presence of hydrocyanic
acid.
[957] _Bull. de la Soc. imp. des nat. de Moscou_, xxxv. (1862) ii. 444.
[958] Exposition Univers. de 1867.—_Produits des Colonies Françaises_,
92.
[959] _Archiv der Pharmacie_, 181 (1867) 222.
[960] _Jahresbericht_ of Wiggers and Husemann for 1871. 11.
This acid is consequently widely diffused throughout the vegetable
kingdom. Yet amygdalin has thus far only been isolated from a few
plants belonging to the genus _Prunus_ or its near allies.[961] In
all other plants in which hydrocyanic acid has been met with, we know
nothing as to its origin. Ritthausen and Kreusler (1871) have proved
the _absence_ of amygdalin in the seeds of a _Vicia_, which yield
bitter almond oil and hydrocyanic acid. These chemists followed the
process which in the case of bitter almonds easily affords amygdalin.
=Commerce=—See preceding article.
=Uses=—Bitter almonds are used almost exclusively for the manufacture
of _Almond Oil_, while from the residual cake is distilled _Bitter
Almond Oil_. An emulsion of bitter almonds is sometimes prescribed as a
lotion.
=Adulteration=—The adulteration of bitter almonds with sweet is a
frequent source of loss and annoyance to the pressers of almond oil,
whose profit largely depends on the amount of volatile oil they are
able to extract from the residual cake.