Nitrous oxide

Nitrous oxide, also called dinitrogen oxide or dinitrogen monoxide and commonly known as laughing gas or simply nitrous, is a nitrogen oxide with the chemical formula N₂O. At room temperature, it is a colorless, non-flammable gas with a slightly sweet smell and taste. When heated, it becomes a strong oxidizer, similar to molecular oxygen. Medically, it is used as an anesthetic and pain reliever, particularly in surgery and dentistry, and is included on the World Health Organization's List of Essential Medicines. Its nickname "laughing gas" was coined by Humphry Davy, referring to the euphoric, brief high it produces when inhaled, which also makes it a recreational drug with dissociative effects. Chronic abuse can cause neurological damage by inactivating vitamin B12. Beyond medicine, nitrous oxide serves as an oxidizer in rocket propellants and motor racing fuels, and as a propellant for whipped cream. Environmentally, it is a pollutant: in 2020, atmospheric levels reached 333 parts per billion, increasing by about 1 ppb each year. It is a major destroyer of stratospheric ozone, comparable to CFCs, and is the third most important greenhouse gas, contributing significantly to global warming. About 40% of human-caused emissions come from agriculture, where soil microbes break down nitrogen fertilizers into nitrous oxide. Reducing these emissions is a key goal in climate change policy.

The gas was first synthesized in 1772 by English natural philosopher and chemist Joseph Priestley, who called it dephlogisticated nitrous air or inflammable nitrous air. He described its production—by heating iron filings dampened with nitric acid—in his 1775 book *Experiments and Observations on Different Kinds of Air*. The first major medical application came through Thomas Beddoes and James Watt, who co-authored *Considerations on the Medical Use and on the Production of Factitious Airs* (1794). This work was significant for two reasons: Watt had invented a machine to produce "factitious airs" (including nitrous oxide) and a breathing apparatus to inhale them, and Beddoes proposed that tuberculosis and other lung diseases could be treated by inhaling these gases. The machine had three parts: a furnace for burning material, a water vessel with a spiral pipe to wash impurities from the gas, and a gasometer-equipped cylinder from which the gas could be transferred into portable, airtight silk bags. The breathing apparatus connected one of these bags via a tube to a mouthpiece. By 1794, this equipment was ready, paving the way for clinical trials. These began in 1798 when Beddoes founded the Pneumatic Institution in Hotwells, Bristol. In its basement, a large-scale machine produced gases under the supervision of young Humphry Davy, who was encouraged to experiment with new gases for patients. Davy’s first major work was studying nitrous oxide, published in *Researches, Chemical and Philosophical* (1800). In that book, he noted the gas’s analgesic effect (page 465) and its potential for surgical use (page 556). He also coined the name "laughing gas." Despite Davy’s discovery that inhaling nitrous oxide could relieve pain in conscious people, another 44 years passed before doctors tried it as an anesthetic. Meanwhile, recreational use at "laughing gas parties" for the British upper class became popular starting in 1799. The gas typically makes users feel stuporous, dreamy, and sedated, though some experience euphoria and uncontrollable laughter. One of the first commercial producers in the U.S. was George Poe, a cousin of poet Edgar Allan Poe, who also first liquefied the gas. The first use of nitrous oxide as an anesthetic on a patient occurred on December 11, 1844, when dentist Horace Wells, with help from Gardner Quincy Colton and John Mankey Riggs, demonstrated pain insensitivity during a tooth extraction. Over the following weeks, Wells treated 12 to 15 patients in Hartford, Connecticut, failing in only two cases. Despite reporting these results to the Boston medical society in December 1844, the method was not immediately adopted—likely because Wells’s first public demonstration in January 1845 was partly unsuccessful, leaving colleagues doubtful. It did not come into general use until 1863, when Colton began using it in his "Colton Dental Association" clinics in New Haven and New York City. Over the next three years, Colton and his associates administered it successfully to more than 25,000 patients. Today, nitrous oxide is used in dentistry as an anxiolytic and an adjunct to local anesthetic. It was not found strong enough for major surgery in hospitals, where diethyl ether became the preferred agent.