nitrous oxide or nitrogen (I) oxide, chemical compound, N2O, a colorless gas with a sweetish taste and odor. Its density is 1.977 grams per liter at STP. It is soluble in water, alcohol, ether, and other solvents. Although it does not burn, it supports combustion since it decomposes into oxygen and nitrogen when heated. The gas is prepared commercially by the thermal decomposition of ammonium nitrate, NH4NO3, at about 240°C to produce nitrous oxide and water; the reaction must be carefully controlled to prevent explosive decomposition of the nitrous oxide. The gas is purified, liquified by compressing and cooling it, and stored in metal cylinders. A major use of nitrous oxide is in anesthesia, e.g., in dentistry. It is commonly called laughing gas since it produces euphoria and mirth when inhaled in small amounts. It is also used in making certain canned pressurized foods, e.g., instant whipped cream. Nitrous oxide was discovered (1772) by Joseph Priestley, who called it "diminished nitrous air"; he prepared it from "nitrous air" (nitric oxide, NO) by treatment with iron powder or a mixture of iron and sulfur powders. Its properties were further studied (1799) by Sir Humphry Davy.