Dictionary.net

A gas, CO2, said not to be poisonous, but to cause death by suffocation.

Syn. : carbonic anhydrid. A colorless gas, CO2, of a rather pungent acid odor and acid taste, often erroneously called carbonic acid or carbonic acid gas; found as a constant constituent of the atmosphere, of which it forms about 3 parts by volume (4½ by weight) in 10,000. It also occurs dissolved in considerable quantities in certain mineral waters, giving them their effervescence; and in some volcanic districts it is given off from clefts in the ground, from caves, and from volcanic craters. Its presence in the atmosphere or elsewhere is due to its production by the combustion of organic matter (coal, wood, etc.), by the respiration of animals, or by the decay of dead organic matter in the soil. Its accumulation in the atmosphere is prevented by the continual decomposition which it undergoes in the processes of vegetable assimilation. The chlorophyll of plants has the property of decomposing it, the oxygen being set free and the c. taken up by the plant cells. C. dioxid is very stable, parting with its oxygen only at a very high temperature, so that it is unfit to support respiration or combustion, although it does not seem to be directly poisonous when inhaled. Its sp. gr. is 1.53. It can readily be liquefied, and even obtained solid, by the combined use of cold and pressure. It dissolves in its own volume of water at ordinary temperatures and under a pressure of 1 atmosphere; by increased pressure several volumes may be dissolved in 1 volume of water, constituting the so-called soda water, or carbonic acid water. Such an aqueous solution contains true carbonic acid

See under carbon