Chemical compound of carbon and oxygen with the formula CO. It is a colorless, odorless gas, about 3 percent lighter than air, and is poisonous to all warm-blooded animals and to many other forms of life. When inhaled it combines with hemoglobin in the blood, preventing absorption of oxygen and resulting in asphyxiation.
Carbon monoxide is formed whenever carbon or substances containing carbon are burned with an insufficient air supply. Even when the amount of air is theoretically sufficient, the reaction is not always complete, so that the combustion gases contain some free oxygen and some carbon monoxide.
An incomplete reaction is especially probable when it takes place quickly, as in an automobile engine; for this reason, automobile-exhaust gases contain harmful quantities of carbon monoxide, sometimes several percent, although antipollution devices are intended to keep the level below 1 percent. As little as 1/1000 of 1 percent of carbon monoxide in air may produce symptoms of poisoning, and as little as 4 of 1 percent may prove fatal in less than 30 min. Carbon monoxide is a major ingredient of the air pollution in urban areas.
Because it is odorless, carbon monoxide is an insidious poison. It produces only mild symptoms of headache, nausea, or fatigue, followed by unconsciousness. An automobile engine running in a closed garage can make the air noxious within a few minutes; a leaking furnace flue may fill a house with unsuspected poison. Fuel gas, which may contain as much as 50 percent carbon monoxide, often has small quantities of unpleasant-smelling sulfur compounds purposely added to make leaks noticeable.
Carbon monoxide is an important industrial fuel because it contains more than two-thirds of the heating value of the carbon from which it was formed. It is a constituent of water gas, producer gas, blast furnace gas, and coal gas. In smelting iron ore carbon monoxide formed from coke used in the process acts as a reducing agent, that is, it removes oxygen from the ore. Carbon monoxide combines actively with chlorine to form carbonyl chloride, or phosgene, and it combines with hydrogen, when heated in the presence of a catalyst, to form methyl alcohol. The direct combination of carbon monoxide with certain metals, forming gaseous compounds, is used in refining those metals, particularly nickel.
Carbon monoxide melts at -205° C (-337° F) and boils at -191.5° C (-312.7° F).