328 VENTILATION 



4. How is Am TO BE KEPT FROM BECOMING VITIATED? 



It is not enough that the carbon dioxide in the air be kept 

 down to 0.06 or 0.07 per cent, and the oxygen be kept up to 20.5 

 per cent. These conditions may be worth while, but in addi- 

 tion, the wet-bulb temperature should be maintained near the 

 optimum point, which will vary probably from 50 or 55F. for 

 the gymnasium, work shop and factory to 65 or 70F. for the 

 home library; the humidity should be maintained at 50 to 

 55 per cent., if possible, and the air should be kept in constant 

 motion, this motion being sufficient to produce a pleasant, 

 stimulating sensation very much like that of the early summer 

 breeze. 



Some authorities insist that moderate fluctuation in tempera- 

 ture is preferable to constant temperature. They prefer to 

 have the room frequently " flushed out" to any system of ven- 

 tilation based upon the constant dilution of the vitiated air 

 (see the next section). Dr. W. A. Evans says, "A ventilating 

 system based on the dilution of breathed air is inefficient and, 

 at the same time, expensive. It is wasteful because it requires 

 2000 cu. ft. of fresh air per person per hour, while, if the tem- 

 perature is kept down, the humidity up and the room blown 

 out from time to time, a much less quantity gives better 

 results." 



5. WHAT THEN is THE REAL PURPOSE OF VENTILATION? 

 Adequate ventilation prevents the accumulation of vitiated 



air about the body, thereby securing those conditions which are 

 favorable to normal metabolism and the highest possible 

 vitality. Secondly, in crowded rooms it is highly desirable 

 to change the air either rapidly (constant dilution system) or 

 frequently (flushing out system) because it is likely to be more 

 or less laden with unpleasant odors and disease germs. 



II. SYSTEMS OF VENTILATION 



361. How Ventilation was Obtained in Colonial Days. 



With all its faults, the old fireplace of colonial days had its 

 advantages. Even the one room in which the fireplace was 



