one of several oxides of nitrogen, a colourless gas with pleasant, sweetish odour and taste, which when inhaled produces insensibility to pain preceded by mild hysteria, sometimes laughter. Nitrous oxide was discovered by the English chemist Joseph Priestley in 1772; another English chemist, Humphry Davy, later named it nitrous oxide and showed its physiological effect. The principal use of nitrous oxide is as an anesthetic in surgical operations of short duration; prolonged inhalation causes death. The gas is also used as a propellant in food aerosols. It is prepared by the action of zinc on dilute nitric acid, by the action of hydroxylamine hydrochloride (NH₂OH·HCl) on sodium nitrite (NaNO₂), and, most commonly, by the decomposition of ammonium nitrate (NH₄NO₃).