Skip to main content
HYDROCYANIC ACID 729
was detected in the liver, spleen and kidney. In his annual report for the
year 1942, the Chemical Examiner, Bengal, mentions that in a case of aconite
poisoning where there is a history of vomiting, aconite is rarely detected
in the viscera. However, he was able to detect it in the viscera of a woman
and a boy, who had vomiting before they died in about three hours after
taking the drug. A case is also recorded in which aconite was detected in
the viscera of the partially burnt body of a Hindu woman.53
HYDROCYANIC ACID (HYDROGEN CYANIDE OR PRUSSIC ACID) , *
This is obtained by distilling potassium cyanide or potassium ferro-
cyanide with dilute sulphuric acid. The pure, anhydrous acid is a colourless,
volatile liquid, possessing a characteristic odour similar to that of bitter
almonds or peach kernels. It is soluble in water, alcohol and ether, solidifies
at 14° C., boils at 26°C,, and is more or less rapidly decomposed by exposure
to light. It is a powerful protoplasmic poison, and prevents the tissues from
utilizing the oxygen of the blood.
Hydrocyanic acid is not found in commerce, but is only met with in
chemical laboratories. It is chiefly used to fumigate houses, ships, railway
carriages and warehouses for the destruction of rats and vermin.
According to the international agreement of 1930, an aqueous solution
of hydrocyanic acid, known as dilute hydrocyanic or prussic acid, should
contain 2 per cent by weight of the pure acid. It is a B.P.C. preparation under
the name of Acidum hydrocyanicum dilutum, having the dose of 2 to 5
minims. Scheele's acid contains approximately 4 per cent of the pure acid.
Hydrocyanic acid is widely distributed in nature. It occurs in combina-
tion in the leaves of the cherry-laurel, in bitter almonds, in the kernels of
the common cherry, plum, peach and other stone fruits, in ordinary bamboo
shoots, and in certain oilseeds and beans. These plants contain a crystalline
glycoside, known as amygdalin, which, in the presence of water and a natural
enzyme, called emulsin, is readily decomposed into hydrocyanic acid, glucose
Crude essential oil of bitter almonds contains from 2 to 10 per cent of
hydrocyanic acid. Cherry-laurel water contains 0.1 per cent of hydro-
cyanic acid, but it loses strength by keeping. These are used as flavouring
Hydrocyanic acid forms cyanides with metals. Of these potassium or
sodium cyanide, mercuric cyanide and silver cyanide are used in photo-
graphy, electroplating and dyeing. These are soluble in water, alkaline in
reaction and highly poisonous.
Symptoms. — This is the most rapid of all poisons. Hence with a large
dose the symptoms usually appear within a few seconds or even during the
act of swallowing. They are rarely delayed beyond one or two minutes.
During the interval the patient may be able to walk or speak or perform
some volitional act. The first symptoms are the odour of hydrocyanic acid
from the breath, loss of muscular power and giddiness. The patient staggers
about, the eyes are wide open, bright and shining, and the pupils are dilated
and do not react to light. Consciousness is lost. The respirations become
slow and stertorous, with sudden and short inspirations and prolonged
expirations. Tonic convulsions affect the jaw rendering it stiff. The pulse
is quick and feeble and later becomes imperceptible. These symptoms are
followed by cyanosis, cold, clammy skin and relaxation of the sphincters.
Death occurs from failure of respiration. Some say that it is due to the
53. Beng. Chem. cam. Annual Eep., 1940, p. 15.