CHAPTER XXX 



Ordinary Air 



Expired Air 



Oxygen 20.<# 



Carbon dioxid 0.03# 



Oxygen 16.4* 

 Carbon dioxid 4.1 



Nitrogen 78.09^ Nitrogen 78.09g 



FIG. 51. Effect of breathing on 

 the air 



The ratio of oxygen to carbon dioxid 

 is changed from 700.1 to 4.1 



VENTILATION 



185. Air requirements. The blood in the lungs absorbs 

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

 each breath. 1 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 1 600 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 



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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