Oil of Bit′ter Almonds. Syn. Essence of b. a.; Oleum amygdalæ amaræ, O. a. essentiale, L. From the ground cake of bitter almonds from which the fixed oil has been expressed. The common plan is to soak the cake (crumbled to fragments) for about 24 hours in
twice its weight of water, to which 1⁄3rd or 1⁄4th of its weight of common salt has been added, and then to submit the whole to distillation, allowing the first half of the water that passes over to deposit its oil, and to run back again into the still. Pale golden yellow; colourless when rectified; tastes and smells strongly nutty, like peach-kernels. It consists of 85% to 90% of hydride of benzoyl and 8% to 12% of hydrocyanic acid, with a variable quantity of benzoic acid and benzoin. The density varies a little with the age of the oil, and the temperature and rapidity with which it has been distilled. Sp. gr. (recent) 1·0525; (trade crude oil) 1·079 (G. Wippel); (old) 1·081 (1·0836—Pereira). “Essential oil of almonds, free from adulteration, should have a sp. gr. at most of 1·052.” (Ure.) According to Prof. Redwood, the density may vary from 1·0524 to 1·0822. The light oil contains the most hydride of benzoyl, and the heavy oil the most benzoin. Prod. From less than ·2 to ·5%.
Pur. This oil is generally adulterated with cheaper oils, and in nearly every case with alcohol. When it is pure—Mixed with oil of vitriol, it strikes a clear crimson-red colour, without visible decomposition,—Mixed with an alcoholic solution of potassa, crystals are eliminated.—Iodine dissolves only partially and slowly in it, without further visible results.—Chromate of potassa does not affect it.—Nitric acid (sp. gr. 1·42) causes no immediate reaction, and in the course of 3 or 4 days crystals of benzoic acid begin to appear; but if only 8% or 10% of alcohol or rectified spirit is present, a violent effervescence speedily commences, and nitrous fumes are evolved. By using nitric acid, sp. gr. 1·5, the smallest quantity of alcohol may be detected.
Obs. This oil does not pre-exist in the almond, but is formed by the action of water on a peculiar crystallisable substance, called amygdalin. It is essentially the hydride of benzoyl, but it always contains a portion of hydrocyanic or prussic acid, to which it owes its very poisonous properties. It is occasionally employed as a substitute for hydrocyanic acid in medicine; but its principal consumption is as a flavouring ingredient and a perfume by cooks, confectioners, liquoristes, and perfumers. For this purpose it is dissolved in rectified spirits. See Essence.—Dose, 1⁄4 to 1 drop.
An oil closely resembling that from bitter almonds is obtained by distillation from the leaves of the peach and cherry-laurel, the bark of the plum-tree, the bruised kernels of cherries, plums, and peaches, the pips of apples, and from several other vegetable substances that possess a nutty odour and flavour.
A NON-POISONOUS OIL OF ALMONDS has been introduced. This is simply the ordinary oil of commerce freed from hydrocyanic acid, and is intended to be substituted for the crude, poisonous oil for domestic purposes. Unfortunately, the purified essence does not keep well,
and is often converted after a few months into little else than a solution of benzoic acid, almost devoid of the usual odour and flavour of the bitter almond. “No wonder, then, under such circumstances, that the public preferred the preparations they had been accustomed to, which were not so liable to change.” (Redwood.) The following methods have been adopted for this purpose:—
1. (Liebig.) Agitate the crude distilled oil with red oxide of mercury, in slight excess, and after a few days’ contact, rectify the oil from a little fresh oxide of mercury. The product is quite pure, when the process is properly managed. The cyanide of mercury thus formed may be either employed as such, or reconverted into mercury and hydrocyanic acid.
2. (Mackay.) Commercial oil of almonds, 1 lb.; fresh-slaked lime, q. s. to form a milk-like liquid; afterwards add, of solution of potassa, 11⁄2 lb.; water, 3 pints; agitate occasionally for 48 hours, then distil over the oil, and rectify it from a fresh mixture of lime and potassa.
3. (Redwood.) The oil is mixed with an equal quantity of water, and the mixture is digested in a water bath with red oxide of mercury, and small quantities of fresh-slaked lime and protochloride of iron, with as little access of air as possible; as soon as decomposition of the acid has taken place, the whole is introduced into a copper retort, and submitted to distillation. The product is perfectly free from hydrocyanic acid. The first process is, however, the simplest, cheapest, and best.