HAMII.TON SCIENTIFIC ASSOCIATION 26 



becoming warm, ascends, and the cold air enters the room 

 through openings to take its place. This causes a draft of 

 cold air into the room which should never occur, besides it 

 makes no provision for suppl}'ing the lack of moisture. It 

 cannot be used without a constant heat in the flue, and is in- 

 fluenced very much by the wind. If windows are opened the 

 reverse of the theory will often take place. In schools or 

 where there are several rooms connected to one shaft, the 

 foul air of one room will often pass through the ventilating 

 flue to another room. The one in charge of ventilation re- 

 quires to give constant and careful attention to the peculiar- 

 ities of the building. 



Many people think that- the air expelled from the 

 lungs is heavier than the surrounding air. Such is not the case, 

 carbon dioxide forms such a small proportion of the ex- 

 pired air that its extra weight does not make a perceptible 

 difference ; besides the air from the lungs contains a large 

 amount of moisture, is several degrees warmer than the 

 surrounding air, and therefore is much lighter and ascends. 

 This favors the openings for the escape of foul air being 

 placed high up, for if they are at the floor the breathed air 

 has to cross the breathing line. 



Each person requires 30 cubic feet of pure air per 

 minute, a school room for 50 pupils requires 1500 feet per 

 minute. The ordinary class room for that number of pupils 

 contains about 12,000 cubic feet, which, divided by 1500, gives 

 eight minutes as the time during which a complete change 

 should be made. You say this is a great waste of heat, true, 

 but we cannot have health without it. The amount of pure 

 air should be as definite as the amount of pure food, the air 

 should be changed completely every seven or eight minutes. 

 In many buildings it is not changed once in thirty minutes, 

 and in some no provision is made for change. 



It is much easier to warm pure, than impure air. The 

 amount of heat required to raise one pound of water one 

 degree will raise 48 cubic feet of air one degree, so that the 

 heat required to raise one gallon of water one degree will 



