NITRIC OXIDE

(NO), colourless, toxic gas, formed from nitrogen and oxygen by the action of electric sparks or high temperatures or, more conveniently, by the action of dilute nitric acid upon copper or mercury. It was first prepared about 1620 by the Belgian scientist Jan Baptist van Helmont, and it was first studied in 1772 by the English chemist Joseph Priestley, who called it nitrous air. Nitric oxide liquefies at -151.8 C (-241.2 F) and solidifies at -163.6 C (-262.5 F); both the liquid and the solid are blue in colour. The gas is almost insoluble in water, but it dissolves rapidly in a slightly alkaline solution of sodium sulfite, forming the compound sodium dinitrososulfite, Na2(NO)2SO3. It reacts rapidly with oxygen to form nitrogen dioxide, NO2. Nitric oxide is one of the few stable compounds containing an odd number of electrons; it can gain or lose one electron to form the ions NO- or NO+, which are present in the nitrosyls, compounds somewhat similar to the carbonyls formed from carbon monoxide and transition metals. An industrial procedure for the manufacture of hydroxylamine is based on the reaction of nitric oxide with hydrogen in the presence of a catalyst. The formation of nitric oxide from nitric acid and mercury is applied in a volumetric method of analysis for nitric acid or its salts.