A colorless, odorless gas, sparingly soluble in water and soluble in ethanol and benzene. Carbon monoxide is flammable (burning with a blue flame) and highly toxic. Its toxicity stems from its ability to bind to the iron in hemoglobin, forming the stable, bright red compound carboxyhemoglobin, thereby blocking the uptake of oxygen. (This happens if the inhaled air contains as little as 0.1 percent of carbon monoxide by volume.) Carbon monoxide is used as a reducing agent in metallurgy.
