The discovery of carbon monoxide is often credited to the work of the English chemist and theologian Joseph Priestley. In the period between 1772 and 1799, Priestley gradually recognized the nature of this compound and showed how it was different from carbon dioxide, with which it often appeared. None the less 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 poisonous gas produced by the incomplete combustion of wood that was almost certainly carbon monoxide.
In the five centuries between the work of Arnold and that of Priestley, carbon monoxide was studied and described by a number of prominent alchemists and chemists. Many made special mention of the toxicity of the gas. Johann (or Jan) Baptista van Helmont in 1644 wrote that he nearly died from inhaling gas carbonum, apparently a mixture of carbon monoxide and carbon dioxide.
An important milestone in the history of carbon monoxide came in 1877 when the French physicist Louis Paul Cailletet found a method for liquefying the gas. Two decades later, a particularly interesting group of compounds made from carbon monoxide, the carbonyls, were discovered by the French chemist Paul Sabatier.