206 SCIENCE OF COMMON THINGS. 



Use of oxygen in the air. Nitrogen, its properties and uss. 



~No ; when pure it is only known in the gaseous state ; 

 all efforts to reduce it to a liquid or solid condition by 

 cold or pressure have completely failed. 



1367 Of what use is oxygen in the atmosphere ? 



It sustains animal life and supports combustion. 



1368 If an animal were immersed in oxygen gas, would it continue to 

 live for a time? 



It would ; at the same time animal life could not be 

 sustained for any great length of time in an atmosphere 

 of pure oxygen. 



1369 What is meant when it is said that oxygen " sustains life f " 



It means this : if a person could not inhale oxygen, 

 he would die. 



1370 What good does this inspiration of oxygen do f 



1. It gives vitality to the blood ; and 



2. It is the cause of animal heat. 



1371 What is nitrogen f 



An invisible gas existing largely in atmospheric air, 

 and in most animal and vegetable substances. 



1372 What are its principal characteristics f 



1. It is not combustible / 



2. It does not support animal life ; and 



3. It is the principal ingredient in the composition 

 of atmospheric air. 



1373 What proportion of the air we breathe is composed of nitrogen f 



About four -fifths of the air is nitrogen / the other 

 one-fifth is oxygen. 



1374 Why is there so much nitrogen in the air f 



The uses of nitrogen are in a great measure unknown. 

 It has been supposed to act as a diluent to the oxygen, 

 but it most probably serves some useful purpose in the 

 economy of animals and vegetables, the exact nature of 

 which has not been discovered. 



1375 What would be the effect if the proportion of oxygen in the atmo- 

 sphere were increased f 



The inflammability of most substances would be in- 

 creased, fires would burn out very quickly, and the 



