Carbon Dioxide, a colorless, odorless gas composed of carbon and oxygen. Carbon dioxide does not burn nor does it support the combustion of most other substances. The gas is soluble in water, with which it forms carbonic acid. Carbon dioxide is about 1 1/2 times as heavy as air and makes up about 0.03 per cent of the atmosphere by volume. Carbon dioxide is needed by photosynthetic organisms (most plants and algae, and some bacteria) to manufacture food. .) In unusually high concentrations, such as sometimes occur in mines, carbon dioxide can cause death by asphyxiation.

Carbon dioxide is formed by the respiration of plants and animals; by the fermentation and decay of organic matter; and by the combustion of fuels containing carbon, such as fossil fuels and wood. Carbon dioxide is also formed when certain carbonates are treated with an acid or heated. Since the middle of the 19th century, the burning of fossil fuels in ever greater amounts has gradually increased the amount of carbon dioxide in the atmosphere. The increase, though small, may eventually raise the average atmospheric temperature of the earth, because the carbon dioxide traps infrared (heat) radiation that would otherwise escape from the earth into space.

For commercial use, carbon dioxide is obtained primarily from gas wells and as a by-product of fermentation, the manufacture of ammonia, or the combustion of fossil fuels. For some uses, carbon dioxide is liquefied or solidified.

Carbon dioxide is used to carbonate beverages. In baking, it leavens dough. A major use of carbon dioxide is in enhanced oil recovery; the gas is pumped into largely exhausted petroleum deposits to force petroleum to the surface. Carbon dioxide is also used in extinguishing fires and in the manufacture of a number of chemical products.

Liquid carbon dioxide is used in processes that involve chilling; it is used, for example, to achieve cooling of certain plastics in molds and rapid freezing of foods.

Solid carbon dioxide (dry ice) is used for refrigeration, especially when transporting perishable items.

Chemical formula: CO2.