CHAPTER XXIV 



THE AIR AND VENTILATION 



376. Composition of air. Every 100 parts of air are 

 composed of about 20 parts of oxygen and 80 parts of 

 nitrogen : T ^ per cent of the air is carbonic acid gas. 

 Air contains water in varying amount. Some dust par- 

 ticles are always floating about, and also a few living 

 germs of plants like those producing mold and yeast. 

 These substances are found in all air, and none are 

 harmful. 



377. Ozone in the air. There is a form of oxygen called 

 ozone which is much more active than common oxygen. It 

 can be made by passing a strong current of electricity 

 through a tube of oxygen. During thunderstorms some is 

 formed, which imparts a peculiar odor and exhilarating 

 property to the air. Some is formed in pine forests, and 

 to it the beneficial effects of the forests upon consumptives 

 may be due. It is never found in any great amount in 

 the air. 



378. Argon. It was discovered in 1894 that the part 

 of the air supposed to be pure nitrogen contains a gas 

 hitherto unknown, to which the name argon has been given. 

 One per cent of the air is argon. Like nitrogen, it cannot 

 be made to unite with any substance directly from the air, 

 and so both act simply to dilute the oxygen. But, unlike 

 nitrogen, it does not form a chemical combination with 

 anything at all, but is always found simply mixed with the 



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