In 1799, Davy became increasingly well known due to his experiments with the physiological action of some gases, including laughing gas (nitrous oxide). The gas was first synthesised in 1772 by the natural philosopher and chemist Joseph Priestley, who called it dephlogisticated nitrous air (see phlogiston). Priestley described his discovery in the book Experiments and Observations on Different Kinds of Air (1775), in which he described how to produce the preparation of "nitrous air diminished", by heating iron filings dampened with nitric acid. In another letter to Giddy, on 10 April, Davy informs him: "I made a discovery yesterday which proves how necessary it is to repeat experiments. The gaseous oxide of azote (the laughing gas) is perfectly respirable when pure. It is never deleterious but when it contains nitrous gas. I have found a mode of making it pure." He said that he breathed sixteen quarts of it for nearly seven minutes, and that it "absolutely intoxicated me."
In addition to Davy himself, his enthusiastic experimental subjects included his poet friends Robert Southey and Samuel Taylor Coleridge, as well as Gregory Watt and James Watt, other close friends. James Watt built a portable gas chamber to facilitate Davys experiments with the inhalation of nitrous oxide. At one point the gas  was combined with wine to judge its efficacy as a cure for hangover (his laboratory notebook indicated success). The gas was popular among Davys friends and acquaintances, and he noted that it might be useful for performing surgical operations. Anesthetics were not regularly used in medicine or dentistry until decades after Davy's death.