COMPOUNDS 



205 



Experiment 130. Carefully balance a thin glass beaker on a 

 delicate set of scales. The beaker of course contains air. Now 

 pour the CO 2 from one jar into the beaker, as in Fig. 136. If the 

 balance is not changed, repeat the experiment carefully. Compare 

 the weights of CO 2 and air. 



Experiment 131. Into the other jar of CO 2 thrust a lighted 

 stick or taper, and note what happens. What does this show with 

 regard to CO 2 ? Try to explain why 

 the gas should behave in this way. 



Carbon dioxide is not a 

 direct poison to animals, but 

 because it does not supply 

 the free O that they must 

 breathe, animals cannot live 

 in it. For the same reason it 

 is injurious to man. Oil and 

 gas heaters give out large 

 quantities of CO 2 , using up 

 the O from the air; they 

 should not be used in rooms 

 unless a constant supply of fresh air is possible. CO 2 

 neither burns nor supports combustion. 



When C is burned with a poor supply of air, another 

 gas is formed, called carbon monoxide (CO). This gas 

 is very poisonous to man, even in small amounts. It 

 is often formed in coal fires, from which it may be 

 given off ; hence the danger of sleeping in rooms with 

 a coal fire. 



238. Ammonia. Ammonia is a compound of N and 

 H, its symbol being NH 3 . It is formed when certain 

 animal matter decomposes in air, though it is generally 



FIG. 136 



