CARBON DIOXIDE, a colourless gas at ordinary temper atures. It is found to be the most common oxide (q.v.) of car bon and is one of the usual products of combustion (q.v.) of all carbon compounds; it is the chief constituent of the breath exhaled by animals (see RESPIRATION). Commercially it is used extensively in the manufacture of aerated waters (q.v.). Solid carbon dioxide (the so-called carbonic acid snow) is used as a freezing agent, alone or in conjunction with ether (q.v.). (See also CARBON and LIQUEFACTION OF GASES.)