CARBON DIOXIDE AND MONOXIDE. Every animal that lives is constantly breathing forth carbon dioxide (often called "carbonic acid gas"), and every fire where carbon Compounds are burned gives off this colorless, tasteless gas. Plants with green foliage, on the contrary, take up carbon dioxide from the air during the daytime, consume the carbon in it, and give back the oxygen to the air (see Leaves).
Carbon dioxide contains one atom of carbon to two atoms of oxygen, hence its chemical symbol is It forms about of the earth's atmosphere. Car bon dioxide is heavier than air, and can be carried in a vessel and poured like water. Unlike oxygen, it does not support combustion, but will put out a fire.
Some chemical fire extinguishers, therefore, are con structed so as to give off carbon dioxide. If the pure gas is breathed, or air containing considerable quan tities of it, it will cause death through suffocation, because the lungs do not get the necessary oxygen.
Under the name of " choke damp" it is one of the perils most dreaded by the miner.
Under pressure of 600 pounds to the square inch carbon dioxide is liquefied. When this liquid escapes through a small jet it evaporates rapidly and the cold produced by the evaporation causes part of the liquid to freeze and look like snow. Carbon dioxide dis solves in water, forming carbonic acid. When pres sure has been used to make a greater amount dissolve than is ordinarily taken up, " charged" or carbonated water—soda water, seltzer water, etc.—is produced.
Hence carbon dioxide is frequently transported in cylinders in a liquid form for use in soda fountains.
Carbon monoxide is an even more dangerous gas.
It differes from carbon dioxide in containing only one atom of oxygen to one of carbon; its chemical symbol therefore is CO. It is this highly poisonous gas which causes death when a person remains too long in a tightly closed bathroom with a gas heater in operation, or in a closed garage with the auto mobile engine running. It is because of its presence in ordinary illuminating gas that it is • dangerous to in hale even small quantities of the latter. Carbon monoxide escaping from coal stoves or furnaces sometimes asphyxiates whole families.