Carbon monoxide is a compound of carbon and oxygen with the chemical formula CO. It is a colorless, odorless, tasteless, toxic gas. It has a density of 1.250 g/L at 32°F (0°C) and 760 mm Hg pressure. Carbon can be converted into a liquid at its boiling point of -312.7°F (-191.5°C) and then to a solid at its freezing point of -337°F (-205°C).

The discovery of carbon monoxide is often credited to the work of the English chemist and theologian Joseph Priestley. From 1772-1799, Priestley gradually recognized the nature of this compound and showed how it was different from carbon dioxide, with which it often appeared. Nonetheless, carbon monoxide had been well known and extensively studied in the centuries prior to Priestley's work. As early as the late 1200s, the Spanish alchemist Arnold of Villanova described a...