"Bitter Almond is the ripe seed of Prunus Amygdalus, Stokes, var. amara, Baill." Br.
Semen Amygdali Amarum; Amandes ameres, Fr. Cod.; Amygdalae Amarae, P. G.; Bittere Mandeln, G; Mandorle amare, It.; Almendra amarga, It.
Bitter almond was not made official in the U. S. P. IX.
The almond tree resembles that of the cherry. The leaves are elliptical, petiolate, minutely serrated, and are of a bright green color. The flowers are large, of a pale red color varying to white, with very short peduncles, and petals longer than the calyx, and usually stand in pairs upon the branches. The fruit is a drupe with the outer covering thin, tough, dry, and marked with a longitudinal furrow, where it opens when fully ripe. Within this covering is a rough shell, containing the kernel or almond.
There are several varieties of this species of Amygdalus, differing chiefly in the size and shape of the fruit, the thickness of the shell, and the taste of the kernel. The two most important are the var. dulcis and the var. amara, the former bearing sweet, the latter bitter almonds. Both of these varieties have been known since ancient times. The var. dulcis yields the hard and paper-shelled variety. The latter, owing to the thin endocarp, is particularly suitable for table use. Another variety grows wild in Turkestan and has a nearly smooth endocarp or "stone." The almond tree is a native of sub-tropical China, Middle Asia and probably also Turkestan. It is now cultivated not only in the Orient, but in the Mediterranean countries of Southern Europe and Northern Africa, and also in Southern England, Scandinavia and California. Bitter almonds are chiefly imported from Morocco and Sicily.
Bitter Almonds.—These are smaller than the sweet almonds, and are " ovate or oblong-lanceolate, 20 to 30 Mm. long; seed-coat thin, brown, finely downy; embryo straight, white, and with two plano-convex cotyledons; taste bitter and oily; when triturated with water Bitter Almond yields a milk-white emulsion which emits an odor of hydrocyanic acid." U. S. VIII.
"Resembles the Sweet Almond in general appearance, but is distinguished by being shorter and proportionally broader, by its bitter taste, and by the characteristic odor resembling that of prussic acid given off by its aqueous emulsion." Br.
They have the bitter taste of the peach kernel, and, though when dry, inodorous or nearly so, have, when triturated with water, the fragrance of the peach blossom. They contain nearly the same ingredients as sweet almonds, and like them form a milky emulsion with water. It was formerly supposed that they also contained hydrocyanic acid and volatile oil, to which their peculiar taste and odor and their peculiar operation upon the system were ascribed. It was, however, ascertained by Robiquet and Boutron that these principles do not pre-exist in the almond, but result from the reaction of water; and Wohler and Liebig proved, what was suspected by Robiquet, that they are formed out of a peculiar substance denominated amygdalin, which is the characteristic constituent of bitter almonds. This substance, which was discovered by Robiquet and Boutron in 1830, is white, crystallizable, inodorous, of a sweetish bitter taste, unalterable in the air, freely soluble in water and hot alcohol, very slightly soluble in cold alcohol, and insoluble in ether. It is decomposed by the action of diluted acids or in the presence of water by the nitrogenous ferments, like emulsin, which accompany it in the bitter almond. The reaction is as follows:
It is recognized as belonging to the glucoside class, compounds which, when decomposed by diluted acids, alkalies, or ferments, yield glucose and some other characteristic decomposition product. They may be considered as esters of glucose analogous to the esters of glycerin which exist in the fats under the name of glycerides. Liebig and Wohler give the following process for obtaining amygdalin, in which the object of the fermentation is to destroy the sugar with which it is associated. Bitter almonds, previously deprived of their fixed oil by pressure, are to be boiled in successive portions of alcohol till exhausted. From the liquors thus obtained all the alcohol is to be drawn off by distillation, care being taken, near the end of the process, not to expose the syrupy residue to too great a heat. This residue is then to be diluted with water, mixed with good yeast, and placed in a warm situation. After the fermentation which ensues has ceased, the liquor is to be filtered, evaporated to the consistence of syrup, and mixed with alcohol. The amygdalin is thus precipitated in connection with a portion of gum, from which it may be separated by solution in boiling alcohol, which will deposit it upon cooling. If pure, it will form a perfectly transparent solution with water. Any oil which it may contain may be separated by washing with ether. One pound of almonds yields at least 120 grains of amygdalin. (Ann. Pharm., xxii, 329.) Amygdalin appears to be extensively diffused in plants, having been noticed not only in the different genera of the Rosaceae, as Amygdalus, Cerasus, and Prunus, but also by Wieke in various Pomaceae, as Pyrus Malus, Sorbus Aucuparia, Sorbus hybrida, Sorbus torminalis, Amelanchier vulgaris, Cotoneaster vulgaris, and Crataegus Oxyacantha. (Ann. Ch. Ph., lxxix, 79.) It may be advantageously procured from peach kernels, which have been found to yield 80 grains for each avoirdupois pound, or more than 1 per cent. (A. J. P., xxvii, 227.) According to the researches of Johannen, the emulsin is contained in the radicle and plumule, and in the vascular bundles of the cotyledons, while the parenchyma of the cotyledons contains the amygdalin. (P. J., March, 1888.)
Amygdalin, mixed with emulsion of sweet almonds, gives rise, among other products, to the volatile oil of bitter almond and hydrocyanic acid,—the emulsin in the sweet almonds acting the part of a ferment, by causing a reaction between the amygdalin and water; and the same result is obtained when pure emulsin is added to a solution of amygdalin. It appears, then, that the volatile oil and hydrocyanic acid developed in bitter almonds when moistened result from the mutual reaction of amygdalin, water, and emulsin. Certain substances have the effect of preventing this reaction, as, for example, alcohol and acetic acid. It is asserted that emulsin procured from other seeds, as those of the poppy, hemp, and mustard, is capable of producing the same reaction between water and amygdalin, though in a less degree. (Ann. Pharm., xxviii, 290.) Amygdalin appears not to be poisonous when taken pure in the stomach, unless there be emulsin in the food in the stomach.
Bitter almonds yield their fixed oil by pressure, and at the present time this oil is an article of commerce, and is frequently sold as expressed oil of almond, this being now officially permitted. It is usually produced from North African bitter almonds; the volatile oil, impregnated with hydrocyanic acid, may be obtained from the residue by distillation with water. (See Oleum Amygdalae Amarae.)
Uses.—Bitter almonds are used solely for their flavoring powers. For medicinal purposes the oil is preferable. (See Oleum Amygdalae Amarae.) It has been ascertained that bitter almond paste, and other substances which yield the same volatile oil, such as bruised cherry-laurel leaves, peach leaves, etc., have the property of destroying the odor of musk, camphor, most of the volatile oils, creosote, cod liver oil, the balsams, etc.; and Mahier, a French pharmacist, has employed them successfully to free mortars and bottles from the odor of asafetida and other substances of disagreeable odor. All that is necessary is first to remove any oily substance by means of an alkali, and then to apply the paste or bruised leaves.
Bitter almonds, on account of the hydrocyanic acid developed in them, have sometimes proved poisonous.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.