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]).
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.
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 Amygdalin. | Anhydrous Dextroglucose. | Hydro- cyanic acid. | Bitter Almond Oil. |
This memorable investigation first brought under notice a body of the glucoside class, now so numerous.