CARBONIC-ACID GAS 



1179 



CARBONIFEROUS PERIOD 



sulphide is manufactured by heating its ele- 

 ments, carbon and sulphur, together. The 

 form of carbon commonly used is coke, and 

 the temperature required is a bright red heat. 

 Electric furnaces are now used almost exclu- 

 sively for the purpose. J.F.S. 



CARBONIC -ACID GAS, or CARBON DI- 

 OXIDE, dyox'ide, or dyox'id, a gas formed 

 when charcoal, wood, coal, oil or almost any 

 material containing the element carbon burns 

 in a free supply of air. The name carbon 

 dioxide signifies that the molecules of the gas 

 consist of one atom of carbon combined with 

 two atoms of oxygen. The name carbonic-acid 

 gas has reference to the faintly-acid character 

 of the liquid obtained by dissolving the gas in 

 water. Under the misleading name of soda- 

 water, this solution is familiar as an effervescent 

 drink. Carbonic-acid gas is colorless and has 

 only a very faint odor. It is about one and a 

 half times as heavy as air, and a common lec- 

 ture experiment is to pour it from vessel to ves- 

 sel like water. When so poured upon a lighted 

 candle it extinguishes the flame, for carbon 

 dioxide does not support combustion. Indeed 

 the gas is often used to extinguish fires (see 

 FIKE DEPARTMENT, subhead Fire Extinguisher). 



Carbon dioxide exists in the atmosphere in 

 the small proportion of three parts in 10,000. 

 Air containing ten times this proportion of 

 carbon dioxide can be breathed without 

 danger, but in pure 'carbon dioxide or in 

 air containing a large proportion of it men 

 and animals are quickly suffocated. Since 

 they suffer much the same as in drowning, it 

 is thought that the gas is not an active poison 

 and that the evil effects are really due to lack 

 of free oxygen, for animals cannot separate 

 the oxygen of the compound from the carbon. 



Interchange Between Plants and Animals. 

 All animals, including man, give off carbonic- 

 acid gas in breathing; it is also produced by 

 fires, and from these sources it is constantly 

 poured into the atmosphere. But what the 

 animals give off the plants absorb, for to them 

 it is a life-sustaining element, as is oxygen to 

 animals, so that the relative proportion of the 

 gas in the atmosphere does not change. Under 

 the action of sunlight the leaves of plants 

 absorb carbonic-acid gas through their pores 

 and liberate part of the oxygen, returning it to 

 the air. Thus plants and animals supply the 

 atmosphere in a measure with what each group 

 needs to enable it to live and grow. 



Choke Damp. Carbonic-acid gas is produced 

 in fermentation and decay. Being heavier than 



the air, it is liable to remain for a long time 

 in wells and silos, as well as in caves and mines, 

 in sufficient quantities to suffocate one entering 

 these places. A lighted lantern lowered into 

 the suspected place shows at once whether or 

 not the gas is present. If the light is extin- 

 guished the place is unsafe. This gas is formed 

 in mine explosions and often accumulates in 

 poorly-ventilated chambers, where many miners 

 lose their lives by suffocation. See MINING. 



Liquid Carbon Dioxide. Carbon dioxide, 

 when subjected to a pressure of about 450 

 pounds to the square inch and a temperature 

 of 5 F. below zero, is easily changed to liquid. 

 This acid is manufactured on a large scale by 

 forcing the gas into steel cylinders by means 

 of a powerful pump, until the pressure becomes 

 sufficient to change the gas into liquid. The 

 large quantities of carbon dioxide produced in 

 the process of brewing are now saved and used 

 in this way. Liquid carbon dioxide is also 

 made directly in factories established for the 

 purpose. It is used in the making of soda 

 water, beer, champagne, mineral waters and 

 other effervescent drinks, to which it imparts a 

 sparkling appearance and biting taste. J.F.S. 



CARBONIFEROUS, karbonij' erous, PE- 

 RIOD, that period of geologic time during 

 which many of the world's coal beds were 

 formed. A more recent name given by Amer- 

 ican geologists is Pennsylvania Period. The 

 rocks formed during this period are also known 

 as the Carboniferous System. They lie between 

 the Devonian System below and the Permian 

 System above (see GEOLOGY), and include the 

 coal measures that is, the layers of rock 

 between which the coal is found. The rocks 

 include coarse masses or clusters known as mill- 

 stone grit, limestone, sandstone and shales. 

 Some of these, particularly the limestones and 

 sandstones, are valuable building stone. In 

 some localities the rocks of the system contain 

 valuable deposits of iron ore. 



Extent. During the Carboniferous Period it 

 is probable that all of North America east of 

 the Rocky Mountains was above the sea, and 

 the Carboniferous System is found at various 

 places from the eastern slope of the Appa- 

 lachian Mountains westward as far as Kansas. 

 The great coal fields of the Appalachian field 

 extend from the northern part of Pennsylvania 

 to Alabama, and reappear in Nova Scotia. 

 There are large coal fields in Ohio, Indiana and 

 Illinois, and also in Iowa, Missouri, Kansas and 

 Texas and in the provinces of Nova Scotia and 

 New Brunswick, Canada. These locations are 



