PRINCIPLES OF VENTILATION 327 



down. In practice it is found that the humidity of the air 

 delivered to the room above a furnace equipped with such a 

 humidifier is fairly constant. 



359. Humidifying the Air of Schoolrooms. The humidify- 

 ing device which is adequate for ordinary schoolroom use north 

 of the 40th parallel of latitude must be capable of evaporating 

 about 2 gal. of water per hour for each room. We have 

 already seen that 2% gal. are required for the proper humidify- 

 ing of a typical 30-pupil room, well ventilated. To evaporate 

 this amount of water is difficult. Nevertheless, many school- 

 room heaters are so constructed that a humidifier similar to 

 that shown in the last article may be installed with good 

 results. 



360. Summary. 1. WHEN is AIR VITIATED? 



When its temperature is too high, when its humidity is too 

 great, when foul odors are noticeable, or when its stagnation 

 is such that one's body is continually wrapped in an envelope 

 of unchanged air. The air may also be too low in tempera- 

 ture, or have too low humidity for good health and comfort. 

 Any ordinary increase in percentage of carbon dioxide, or any 

 ordinary decrease in percentage in oxygen is now considered 

 relatively unimportant. 



2. WHY DOES VITIATED Am PRODUCE IMMEDIATE 

 DISCOMFORT? 



Because abnormal conditions of temperature, humidity, or 

 air motion cause a disturbance of, and overtax the heat-regu- 

 lating mechanism of the body, and fail to stimulate properly 

 the respiration, circulation, and metabolism of the body. Vital 

 energy is being consumed and when carried to extreme, great 

 discomfort and physical exhaustion results. 



3. W T HY is CONTINUED LIVING IN VITIATED AIR TO BE 

 AVOIDED? 



Because abnormal metabolism means decreased vitality. 

 Decreased vitality means decreased power of resistance to 

 disease. Moreover, conditions which produce vitiated air 

 are generally favorable for the spread of infectious diseases. 



