268 



GENERAL SCIENCE 



FIG. 234. Preparation and 

 Collection of Carbon Dioxide. 



Test the carbon dioxide as you tested oxygen and hydro- 

 gen to determine whether or not it will burn and support 

 combustion. Pass some of the gas through limewater, 

 which is simply 'a clear solution of slaked lime in water. 



The white precipitate formed is 

 calcium carbonate. Test your 

 breath in the same way. What 

 does this prove about the air 

 which is expelled from the lungs 

 (Figure 235)? 



Properties and Uses of Carbon 

 Dioxide. Since we can collect 

 carbon dioxide by the downward 

 displacement of air, we would 

 infer that it is heavier than air and that it diffuses quite 

 slowly. It is one and one half times as heavy as air. 

 Since it does not support combustion, it is used in chemi- 

 cal fire extinguishers. Figure 236 shows such an extin- 

 guisher. The tank contains soda. 

 When the extinguisher is inverted, 

 the acid pours from the bottle 

 and the large quantity of carbon 

 dioxide made passes out through 

 the nozzle. The heavy gas ex- 

 cludes the oxygen from the fire 

 and thus extinguishes it. 



Carbon dioxide does not sup- 

 port respiration and if breathed 

 in any considerable quantity will produce death, not 

 because it is poisonous but because the necessary oxygen 

 is excluded. 



Because of its density carbon dioxide is often found at 

 the bottom of empty wells, and in abandoned mines and 



Suction 



FIG. 235. 



