hydrocyanic acid

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Related to hydrocyanic acid: prussic acid

hydrocyanic acid

(hī'drōsīăn`ĭk): see hydrogen cyanidehydrogen cyanide,
HCN, colorless, volatile, and extremely poisonous chemical compound whose vapors have a bitter almond odor. It melts at −14°C; and boils at 26°C;. It is miscible in all proportions with water or ethanol and is soluble in ether.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Hydrocyanic Acid


(also hydrogen cyanide, prussic acid, formonitrile), HCN, a colorless, mobile liquid with an odor of bitter almonds. Hydrocyanic acid was discovered in 1782 by K. W. Scheele. In 1811, J. Gay-Lussac obtained anhydrous hydrocyanic acid and determined its quantitative composition.

Hydrocyanic acid has a density of 0.688 g/cm3 at 20°C, a boiling point of 25.7°C, and a freezing point of – 14°C. It burns in air to yield H2O, CO2, and N2; a mixture of hydrocyanic acid vapors and air explodes when ignited. Hydrocyanic acid, a very weak acid, decomposes upon storage, especially in the presence of impurities. Its salts are called cyanides, and its organic derivatives, nitriles. Hydrocyanic acid is formed upon hydrolysis of amygdalin, present in bitter almonds and apricots. An aqueous hydrocyanic acid solution can be obtained by the distillation of potassium ferrocyanide, K4[Fe(CN)6], with dilute sulfuric acid, H2SO4. The commercial method of hydrocyanic acid preparation is based on the interaction of a mixture of ammonia, methane, and air in the presence of a catalyst (Pt or an alloy of Pt and Rh):

2NH3 + 2CH4 + 3O2 = 2HCN + 6H2O

Hydrocyanic acid is highly toxic. It is used in railroad cars, granaries, and ships for disinsectization and deratization. Hydrocyanic acid serves as source material in the synthesis of certain high-molecular compounds.


Poisoning with hydrocyanic acid and its compounds can occur during the processing of ore (cyanidation) and the galvanization of metals, as well as during disinsectization and deratization. Entering the body through the respiratory passages or, more rarely, through the skin, hydrocyanic acid blocks the respiratory enzyme cytochrome oxidase and induces oxygen starvation in tissue. Symptoms of acute poisoning include irritation of the mucous membranes, asthenia, vertigo, nausea, and vomiting. These symptoms are followed by such respiratory disorders as infrequent, deep breathing, painful dyspnea, and, finally, slow breathing and respiratory arrest. Chronic poisoning is accompanied by headache, fatigue, and low arterial pressure. Changes are observed in electrocardiograms, and the blood is seen to-have a reduced sugar level and an increased content of, among other things, hemoglobin and lactic acid. The effect of potassium and sodium cyanides on the skin can be seen in cracking and eczema.

First aid treatment for acute poisoning involves, after conveying the victim into fresh air, the administration of amyl nitrite, carbogene, and oxygen vapors, the use of lobeline, cytiton, and cardiovascular agents, and the parenteral injection of solutions of sodium nitrite and sodium thiosulfate.

Preventive measures include the observation of safety rules, the use of protective garments for the skin, and periodic medical examinations.


Navrotskii, V. K. Gigiena truda, 2nd ed. Moscow, 1974.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

hydrocyanic acid

[¦hī·drō·sī′an·ik ′as·əd]
(inorganic chemistry)
HCN_A highly toxic liquid that has the odor of bitter almonds and boils at 25.6°C; used to manufacture cyanide salts, acrylonitrile, and dyes, and as a fumigant in agriculture. Also known as formonitrile; hydrogen cyanide; prussic acid.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
C = C 3200-3000 Ethylene [C.sub.2][H.sub.4] 3200-3000 Acetylene [C.sub.2][H.sub.2] 3300-3250 Carbon dioxide C[O.sub.2] 2500-2200 Carbon monoxide CO 2250-2050 Carbon disulpfhide C[S.sub.2] 1550-1450 sulphur Dioxide S[O.sub.2] 1400-1300 Carbonyl Sulphide COS 2100-1970 Benzene [C.sub.6][H.sub.6] 1500-1400 Toluene [C.sub.6][H.sub.5]-C[H.sub.3] 1665-1430 MAH [C.sub.6][H.sub.5]-X 1665-1430 Methanol C[H.sub.3]-OH 3700-2400 Acetone C[H.sub.3]-CO-C[H.sub.3] 2000-1500 Ammonia N[H.sub.3] 1800-1400 Hydrocyanic acid HCN 3400-3200 Nitrous oxide [N.sub.2]O 2300-2000 Nitrogen oxide NO 2000-1800 Nitrogen dioxide N[O.sub.2] 1700-1550 Sample Assignment Methane [[nu].sub.C-H] Hydrocarbons [[nu].sub.C-H] Hydrocarbons uns.
Hydrocyanic acid content is heritable and subjected to modification through selection and breeding, as well as by climate, stage of maturity, stunting of plant, type of soil and fertilizer (Khatri et al., 1997).
The police also believe that hydrocyanic acid gas, which is released when petroleum products are burned, filled the top floors of the four-story building.
Hydrocyanic acid content of certain sorghums under irrigation as affected by nitrogen fertilizer and soil moisture stress.
Jorgensen [8] reported that plants that are grown in soil with low potassium content or high nitrogen have high hydrocyanic acid concentration in their tubers; and also as the plants get older, the hydrocyanic acid content of the tubers increases, attains a peak and then begins to decline.
Chokecherries contain hydrocyanic acid a very potent poison that can cause death in concentrated doses.
* Other limits for hydrocyanic acid; 4-Allyl-1,2-dimethoxybenzene; Pulegone; Quassin; and 1-Allyl-3,4-methylene dioxy benzene, safrole.
Under certain conditions, some grasses, particularly forage sorghums, may accumulate hydrocyanic acid (prussic acid) in their tissues.
The compound thought of as the parent of all these salts is variously called hydrogen cyanide, hydrocyanic acid, or prussic acid.
Florakirk bermudagrass has a high hydrocyanic acid potential ([HCN.sub.p]), especially under high levels of N fertilization However, no demmental effects on grazing cattle at Ona have been attributed to [HCN.sub.p] in this grass.
For hydrocyanic acid (HCN), the Baker and Schippers (1987) was followed in Kings B medium (King et al., 1954), supplemented with 4.4g/ L of glycine.