CHAPTER VI 



VENTILATION 



I. PRINCIPLES OF VENTILATION 



338. Need of Ventilation. While the beneficial effects of 

 outdoor life are being more and more recognized, still many 

 people must necessarily spend much of their lives indoors. 

 School children must spend many hours each day in the school- 

 room. Factories, shops, stores, and offices are filled with work- 

 ing men and women who find it impossible to spend much time 

 in the open air. Often their chief recreation is a visit to an 

 overcrowded theater or moving-picture show where adequate 

 ventilation is seldom provided. Even when at home few 

 people enjoy fresh air. Relatively few houses have been con- 

 structed with any recognition of the fact that fresh, pure air is 

 of even greater importance than is warmth. For these reasons, 

 what constitutes good ventilation and how it may be obtained 

 should receive careful study. 



339. Composition of Pure Country Air. Pure country air is 

 composed chiefly of nitrogen, oxygen, carbon dioxide, and water 

 vapor. The proportions of these constituents vary slightly 

 from day to day and at different places, by far the greatest 

 variation being in the amount of water vapor present. Pure 

 country air consists of about the following proportions: 



Nitrogen about 77 per cent, by volume 



Oxygen about 21 per cent, by volume 



Carbon dioxide about 0.03 per cent, by volume 



Water vapor variable, from 0.3 per cent, to 3 per cent, by volume. 



In addition to these constituents of air there are usually 

 present more or less dust, smoke, pollen from plants, and 

 microorganisms of different kinds. 



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