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a weak poisonous acid (HCN) used in fumigating and in synthesis of organic compounds

Hydrogen cyanide (HCN); A toxic liquid or colorless gas. It is found in the smoke of various tobacco products and released by combustion of nitrogen-containing organic materials.

Poisonous acid consisting of hydrogen and cyanogen.

This acid exists in a great variety of native combinations in the vegetable kingdom, and imparts to them certain properties, which have been long known and esteemed; as in the bitter almond, cherry laurel, leaves of the peach tree, kernels of fruit, pips of apples. When concentrated, it is liquid, colourless, of a strong smell and taste, at first cool, afterwards burning. Its s.g. at 7 Centigrade, is 0.7058. It is very volatile, and enters into ebullition at 80 Fahr. It speedily undergoes decomposition, sometimes in less than an hour, and consists of a peculiar gazeous and highly inflammable compound of carbon and azote, to which the name Cyan'ogen has been assigned; and of hydrogen, which acts as the acidifying principle; hence its name Hydrocyanic acid. In the Pharmacopoeia of the United States, (1851,) two formulae for the preparation of the Acidnm hydrocyan'icum dilu'tum- Acidum hydrocyan'icum, Ph. U.S. of 1842- are given; the one from the Ferro-cyanuret of Potassium; the other from the Cyanuret of Silver. According to Magendie, the acid, prepared after Scheele's method- the one in common use- is of irregular medicinal power: he, therefore, recommends Gay Lussac's acid, diluted with 6 times its volume, or 8.5 times its weight of distilled water, for medicinal purposes, and this he calls Medicinal Prussic Acid. Dr. Ure has proposed, that the specific gravity should indicate that which is proper for medicinal exhibition; and, after comparative experiments of the gravity of the acids, obtained by different processes, he states, that the acid, usually prescribed, is of s.g. 0.996 or 0.997. Great caution is, however, necessary. One drop of pure prussic acid may instantly destroy, and the animal show hardly any traces of irritability, a few moments after death. It has been advised in laryngeal phthisis, in pulmonary phthisis, pulmonary inflammation and irritation, dyspepsia, uterine affections, hectic cough, cancer, chronic rheumatism, and mania, and as a local remedy in impetiginous affections; but, although possessed of powerful sedative properties, it is so unmanageable and the preparation so uncertain, that it is not much used. The Dose of Scheele's Acid, or of the Medicinal Prussic Acid, is from a quarter of a drop to two drops.

a volatile poisonous liquid, HCN, from bitter almonds, peach leaves, cherry leaves, etc. ; used diluted as a sedative.

HCN, liquid, volatile, poisonous; from bitter almonds, cherry leaves, etc.; diluted, used as a sedative.