PURE AIR 115 



of oxygen, and the wire, as well as the splinter, will 

 burn brightly. These experiments show~ oxygen to 

 be a wonderful supporter of combustion, and prove 

 how fortunate it is that this gas is diluted with a large 

 amount of nitrogen in the air we breathe. 



To produce carbonic acid gas, place powdered mar- 

 ble and hydrochloric acid in a test-tube. Without 

 heating, carbonic acid gas will be set free from the 

 marble and will quickly fill a bottle. Put a lighted 

 candle in a bottle of this gas, and the candle will at 

 once go out. If a mouse be placed in a jar of gas made 

 in this way, it will quickly die unless air is let in. Thus 

 we see that carbonic acid gas will not support com- 

 bustion, and is destructive to animal life. 



Pour a half-pint of lime-water into a bottle of pure 

 air or oxygen, shaking briskly, and no change in the 

 appearance of the lime-water will result. Try the 

 same experiment, using lime-water and carbonic acid 

 gas, and the former at once changes to a milky color. 

 This is a sure test for carbonic acid gas, for any unusual 

 amount always turns lime-water a milky color. Let us 

 use this test in a few simple experiments to see what 

 it will tell us of combustion and its products. 



If we burn a lighted splinter in a bottle of air or 

 oxygen and then pour in lime-water, the latter becomes 

 milky. This shows that the burning of the splinter 

 must have produced carbonic acid gas. If we breathe 

 through a tube into a bottle of lime-water, the latter 

 becomes milky, and, on this account, we know car- 



