Carbon Dioxide
or Carbonic Acid Gas, a well known compound containing one atom of carbon and two of oxygen. It is colorless. It exists in small quantities in atmospheric air, from three to four parts in every ten thousand being carbon dioxide. It escapes from many mineral springs, and is found at the bottom of mines and in caves. It is formed also by the imperfect burning of fuel, by the breathing of animals, by fermentation, and by the decay of animal and vegetable matter. Like other animals, people emit carbon dioxide in breathing. Carbon dioxide is incombustible. It will put out the flame of a lighted candle, gas jet, or even a piece of burning phosphorus, when these are placed in a jar filled with the gas. It is not poisonous, but it does not support animal life. Carbon dioxide in the air prevents the lungs from obtaining needed oxygen. A person dies in air containing an excess of carbon dioxide just as he dies in water, not by reason of poisonous qualities belonging to the carbon dioxide or to the water, but because air is shut out of the lungs. For this reason dwelling houses, especially sleeping rooms, should be ventilated thoroughly. Being heavier than air the carbonic gas settles to the floor. In Paris the city poundmaster incloses stray dogs, thirty at a time, in an iron lethal chamber and drives in carbonic acid gas. In forty seconds death ensues from suffocation--want of air.
In volcanic regions where the crust of the earth is thin in places, carbon dioxide sometimes issues so abundantly as to form white, cloud-like masses above the fissures. In the region of Vesuvius, there are several such thin-crusted places. One is the crater of the extinct volcano, Solfatara; another is the so-called Grotta del Cane, or Cave of Dogs, near Naples. This cave receives its name from the fact that if dogs were thrown into it, or witlessly entered it, death followed in a few seconds. The Romans of Caesar's time used to throw in slaves whom they wished to kill or other helpless creatures whom they desired to free themselves. This cave, the Grotta del Cane, can be seen today in the same condition in which it existed during the time of the Roman Empire. The Upas Valley in Java, about three-fourths of a mile long, is another region in which carbon dioxide is fatal to animal life. No animal can live here. It is said that the valley is strewn with the bones of animals which have been suffocated by the fumes and with the remains of birds that have perished while flying over it.
While it is true that air is unfit to breathe if it contains an excess of carbon dioxide the reader should get away from the idea that it is a poison. In fact, the gas, like water, is one of the beneficent provisions of nature. It is present in small quantities in the atmosphere. Taken in through the breathing pores, the stomata of plants, it forms a large part of the tissues of the vegetable world. The starch of rice, wheat, corn, potatoes, and bananas, in short, of all starchy food plants, is built up out of carbon dioxide and water. The gas is inhaled with air by the leaves; the water is imbibed by the roots. Sugar-cane, the sugar beet, and all the fruits, build up their sweets from the same two materials obtained likewise by leaf and roof. Fats are built up of starches or sugars, and are likewise composed of carbon dioxide and water. The farmer who sells fat hogs, fat steers, butter, cheese, sugar beets, sugar-cane, fine flour, and potatoes is marketing little but water and a gas, millions and billions of pounds of which are dissolved in the atmosphere.
Carbon dioxide is in the way in the lungs and it is cast out by the blood, yet it is, as we have seen, an important constituent of foods. While carbon dioxide is out of place when inhaled, it can be taken into the stomach and is then refreshing. For that reason, it is used to charge the so-called "carbonated waters" and give them sparkle.
Shells, corals, and chalk are composed of a compound of carbon dioxide with calcium and oxygen.
See Ventilation; Lungs; Carlsbad; Mineral Springs; Starch; Chokedamp