Almonds, VOLATILE OIL or ESSENTIAL OIL OF.

Almonds, VOLATILE OIL or ESSENTIAL OIL OF. The cake which is left after the expression of the fixed oil from bitter almonds, contains, among other matters, a portion of two substances called, respectively, amygdalin, and emulsin or synaptase. When the cake is bruised and made into a paste with water, the synaptase acts as a ferment upon the amygdalin, splitting it up into the volatile oil of almonds, hydrocyanic (prussic) acid, grape-sugar, ammonia, formic acid, and water. The oil is not originally present in the bitter almonds; in fact, the latter do not contain a trace of the oil ready formed, so that the oil is purely the product of the fermentation of amygdalin, 100 parts of which yield 47 of crude oil. This action takes place very rapidly, and is complete within 24 hours. The paste having been placed in a retort, heat is very cautiously applied, to prevent the lumping and frothing to which the almond infusion is liable. In the distillation, the hydrocyanic acid and the volatile oil unite into an unstable compound, which passes over into the receiver, along with much water. The crude oil thus obtained decomposes gradually, the prussic acid being set free, and on this account it is very poisonous, many fatal cases having occurred from its wilful, accidental, or careless use. The crude oil is purified and freed from prussic acid by means of sulphate of iron and lime. On redistillation, it has a specific gravity of 1.049, as compared with 1.064 in the crude state, and must be carefully freed from water by being shaken with fused chloride of calcium. The yield of crude essential oil is very variable, ranging from 4 to 9½ lb. from 1000 lb. of bitter almonds, and this again is reduced by about 10 per cent. during its purification from prussic acid. The volatile oil (C₆H₆COH) is the aldehyde of benzoic acid (C₆H₅COOH), into which substance it rapidly changes when exposed to the air in a moist state. It has an agreeable odour, an acrid, bitter taste, and burns with a smoky white flame. It is soluble to the extent of 1 part in 30 parts of water, and is very soluble in alcohol and ether. Heated to 356° F. (180° C.), it boils, and distils over unaltered. In medicine, the crude oil used to be employed in place of prussic acid, but its variability in strength has led to its disuse for this purpose. The cook and confectioner employ the oil for flavouring custards, &c., and it forms the basis of several flavouring essences, as ratafia, peach, kernels, &c. For these purposes, none but the oil freed from prussic acid must be used.