_Almond oil_ (_bitter_) (_oleum amygdalæ amaræ_) is obtained by submitting bitter almond cake (left after the expression of the fixed oil from bitter almonds) to distillation with water. The volatile oil does not exist ready formed in the bitter almond, nor in the almond cake, but results from the decomposition of a glucoside called "amygdalin," contained in the cake, under the influence of emulsin and water, the emulsin acting as a ferment, into benzylic aldehyde, glucose and prussic acid. The almond tree grows wild, but is also cultivated in Southern Europe, Africa, Barbary, Palestine and Syria. The bitter almonds brought from Barbary are considered the best. Besides, in almonds, amygdalin occurs in various other plants; for instance, in the leaves of the cherry laurel, the leaves and kernels of the peach, the kernels of the black cherry and other varieties of _prunus_ and _amygdalus_, they all yielding, after maceration with water, a distillate containing prussic acid and oil of bitter almonds. Instead of the comparatively expensive bitter almonds, peach kernels freed from their hard shells are extensively used in the fabrication of oil of bitter almonds. The oil is prepared as follows: The press cakes of bitter almonds or peach kernels are ground and soaked about twenty-four hours in twice their weight of water to which one-third their weight of salt has been added. The whole is then submitted to distillation. The temperature of the water should not exceed 113° to 122° F. The emulsin contained in the almonds possesses only within certain limits of temperature the power of decomposing amygdalin, and, if heated to 176° F., becomes inoperative. Hence, if the almond paste is quickly heated to boiling, the emulsin becomes inoperative before all the amygdalin is decomposed, and a portion of it being consequently lost, the yield is insufficient. The distillation of the almond paste is effected in a current of steam. A portion of the prussic acid formed by the decomposition of the amygdalin adheres tenaciously to the oil. This content of prussic acid makes the oil of bitter almonds exceedingly poisonous, while in itself it is non-poisonous. It can be freed from the prussic acid by shaking with ferrous sulphate (blue vitriol) solution. By then distilling over burnt lime the originally yellow or yellowish oil is obtained colorless. It is then thinly fluid, of a peculiar agreeable odor and strongly nutty taste. Its specific gravity is 1.043 at 59° F., but varies a little with age. It boils at 356° F., and dissolves in 13 parts of water, but more readily in alcohol and ether. In the air it is rapidly converted into benzoic acid by the absorption of oxygen. It has to be carefully protected from air and light and kept in well-closed bottles in a dark place. The crude oil, containing from 2 to 5 per cent. prussic acid, has generally a yellowish color.