Hydrogen cyanide odour

Following a published procedure for converting substituted anilines to isatins by reaction with chloral hydrate and hydroxylamine [1], it was noticed that at the end of the first stage (formation of an isonitrosoacetanilide), the odour of hydrogen cyanide was present, and this was confirmed by a Prussian blue test [2], In related work, concentrations of 100-200 ppm of hydrogren cyanide were found [3]. A mechanism for its formation from chloral hydrate and hydroxylamine was proposed [2], and the need for appropriate precautions was stressed [2,3],... 

Fulminic acid C = NOH is a gaseous, highly toxic substance with an odour resembling that of hydrogen cyanide. It is isomeric with other acids cf the same empirical formula HCNO. The chief of these is cyanic acid HCNO, which is obtainable only in the form of its salts free cyanic acid is unstable. The action of inorganic acids on cyanates leads to the evolution of cyanic acid which hydrolyses to form carbon dioxide and ammonia ... 

Mercury fulminate is relatively resistant to the action of dilute acids, in particular to that of nitric acid, but concentrated acids cause decomposition. Thus, under the influence of nitric acid decomposition occurs with evolution of NO, CO, acetic acid and mercuric nitrate. Under the influence of concentrated hydrochloric acid free fulminic acid is evolved (with an odour resembling that of hydrogen cyanide) as well as the decomposition products hydroxylamine hydrochloride, formic acid, mercuric chloride (Carstanjen and Ehrenberg [32] Scholl [33]). Mercury fulminate explodes on direct contact with concentrated sulphuric acid. 

Palladium is frequently estimated by precipitation of palladous cyanide. To this end the chloride solution is almost completely neutralised with sodium carbonate and a solution of mercuric cyanide added. On gently warming until the odour of hydrogen cyanide has ceased, a whitish precipitate of palladous cyanide separates out. This is well washed, ignited, and the palladium weighed as metal. 

Diphenylcyanoarsine melts at 28° to 30° C., 35° C., 81-5° C., B.pt. 191° C. at 11 mm., and crystallises in colourless, monoclinic plates, these having an odour of garlic and bitter almonds. Moist air liberates hydrogen cyanide from the compound, whilst aqueous or alcoholic alkali hydroxides convert it into the oxide. Concentrated nitric acid, 2 per cent, hydrogen peroxide or bromine water in the cold, transforms it into diphenylarsinic aeid. 

ON THE ODOUR OF HYDROGEN CYANIDE AND ITS RELEVANCE TO DETECTION OF AND BIOHAZARD FROM THE VAPOR... 

Hydrogen cyanide is a highly volatile liquid (b.p. 26 °C) with the odour of bitter almond. It is readily soluble in water but is still volatile in solution, especially at lower pH values. Its pulmonary and transdermal effect is also notable. 

Hydrogen cyanide is a colourless gas or bluish-white highly volatile liquid. It may smell to some of bitter almonds, although the ability to detect the odour is genetically determined. 

From the viewpoint of chemical and physical requirements the permissible indicators involve a number of criteria mercury, selenium, cadmium, vanadium, chromium, arsenic, silver, lead, barium, cyanides, hydrogen sulphide, fluorides, phenols, oil and oil substances, COD(Mn), colour, odour, taste and turbidity. The most stringent criterion concerns the content of mercury, followed by selenium, cadmium, vanadium, cyanides, oil and oil substances. Another important indicator is the content of organic matters characterized by COD(Mn). 

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