180 PRACTICAL LESSONS IN SCIENCE. 



the product is carbon dioxide, formula C0 2 , one atom of car- 

 bon uniting with two of oxygen. It is ordinarily prepared by 

 treating calcium carbonate, limestone, with hydrochloric or some 

 other strong acid. It may be collected over water, or as it is 

 much heavier than air it can be collected in an open jar. The 

 chemical equation is CaC0 3 -f2HCl CaCl 2 -f H 2 0-fC0 2 . Calcium, 

 a bivalent element, replaces two atoms of hydrogen forming 

 calcium chloride, the two atoms of hydrogen taking one atom 

 of oxygen form water setting free (C0 2 ) carbon dioxide, which at 

 ordinary temperatures is a colorless, tasteless, odorless gas. If 

 a lighted stick or candle be put into a jar of this gas, it is extin- 

 guished as promptly as if thrust into water; if a bird or mouse 

 be confined in it, life is quickly destroyed. 



Carbon dioxide will not support combustion, will not sup- 

 port animal life, and for the same reason that water does not, 

 they each contain plenty of oxygen, but it is so firmly bound 

 to the other members of the compound that it cannot be 

 utilized for the processes of life or combustion. Water and 

 the dioxide of carbon are cinders, the affinities of the oxygen, 

 hydrogen and carbon have been satisfied, their energy has been 

 expended, they are like rocks at the foot of a hill, work must 

 be done on them before they are in a condition to do any more 

 work ; and that work must be equal to the work they did as they 

 clashed together into molecules of water and carbon dioxide. 



This gas sometimes accumulates in wells, abandoned mines and 

 caves. As a test of its presence a lighted candle is lowered into 

 places where its presence is suspected ; if the light is not extin- 

 guished or dimmed, the air does not contain a dangerous amount 

 of the dioxide. Carbon dioxide is a product of respiration. Im- 

 merse a jar in water and invert it so as to keep the mouth under 

 water; then through a tube fill the jar with air from the lungs, 

 displacing the water; cover the mouth of the jar with the hand 

 or piece of board and place it upright on the table and test the 

 contents with a lighted candle for carbon dioxide. If the air is 

 held in the lungs for a little time before being breathed into the 

 jar the effect will be more marked. This experiment will show 



