QUANTITY AND TRANSMISSION OF HEAT 151 



the air in a school building is three hundred feet a 

 minute, the area of the opening required for each person 

 is about fifteen square inches. 



Need of Moisture in the Air. It is . quite important 

 that the air in our homes, schoolrooms, and other such 

 buildings have the proper amount of moisture in it; 

 When the humidity of the air is less than 40, it takes 

 up the perspiration from our bodies too rapidly, and the 

 skin becomes dry. When the humidity is more than 60, 

 the perspiration does not evaporate rapidly enough, and 

 the air seems oppressive or " muggy. " 



As cold air enters a heating system and is heated, its 

 capacity for holding moisture is greatly increased, while 

 the amount of moisture in it has not been changed. As 

 a result the amount of moisture present in the air of our 

 homes is usually too small. 



In hot-air furnaces care should be taken to keep the 

 water pan in the air box full of water. If other systems 

 of heating are used, water should be kept in the rooms in 

 open dishes, or small buckets of water may be hung on 

 small wires in the registers. 



QUESTIONS 



1. How is your building heated? 



2. What is the objection to forcing air into a room faster than 

 350 feet a minute? 



3. Explain why the old-fashioned fireplace furnished good 

 ventilation. 



4. Why do we need more air during sleep? 



5. How are most ordinary dwelling houses ventilated? 



