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) , * HCN 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 and benzaldehyde. 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 agents. 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.