CHAPTER XXX 



VENTILATION 



Ordinary Air 



Expired Air 



Oxygen 20.0^ 



Carbon dioxid 0.0 



Oxygen 16.4^ 

 Carbon dioxid 4.1^ 



185. Air requirements. The blood in the lungs absorbs 

 from the air about 5 per cent of the oxygen taken in with 

 each breath.^ In the course of an hour an ordinary man will 

 give off about 1000 cubic inches of carbon dioxid when at 

 rest; with moderate work, about 1600 cubic inches; and with 



hard work, about 3000 cubic inches. 

 This means that in order to 

 keep up the working power a 

 person must be supplied with 

 enough fresh air to keep up the 

 oxygen requirement and to carry 

 off the carbon dioxid excreted. 

 Of course the air in a given room 

 does not all have to be changed 

 for every breath. It is safe to use air in which the amount 

 of carbon dioxid has been increased from 4 parts in 10,000 

 (what it is in ordinary pure air) to 6 parts in 10,000, or even 

 much more. 



A great many studies have been made, to find out the amount 

 of fresh air that should be supplied for each person in a room, 

 for the purpose of establishing standards for ventilation of 

 schools, factories, theaters, and so on. Some of the results 

 of the experiments showed that a person needs at least 

 3600 cubic feet of air per hour. Others called for three times 

 that much. It has been supposed that the change of air was 



Nitrogen 18.09% Nitrogen 78.09^ 



Fig. 51. Effect of breathing on 

 the air 



The ratio of oxygen to carbon dioxid 

 is changed from 700:1 to 4:1 



1 A comparison of expired air with ordinary air shows that the amounts of 

 oxygen and carbon dioxid are changed, whereas the nitrogen and other parts 

 remain constant (Fig. 51). 



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