HEATING AND VENTILATION OF LIVING ROOMS. 113 



how much impurity each pupil breathes into the room per 

 minute and multiply that by the number of pupils in the 

 room to find the total vitiation. Air ceases to be fit to 

 breathe before the impurities increase to ten cubic feet in ten 

 thousand. From these investigations the Fourth Class can 

 calculate how much fresh air should come into the room every 

 minute, and of course the same amount should pass out to 

 make space for the pure air to get in. 



Measure the incoming or outgoing current by the deflection 

 of a candle flame. If you carry a candle through the room at 

 the rate of 100 feet in 15 seconds will it blow out? Compare 

 the result with observed effect, setting the lighted candle in 

 the ventilator and thus estimate the rate of current. The 

 area of the ventilator and the rate of current enable you to 

 tell the quantity of air passing. The Ontario school law 

 prescribes that it shall be at least one-twentieth of the 

 capacity of the school-room per minute. 



Bring a ten-ounce bottle filled with water into the room. 

 Empty it there so as to fill it with the air you wish to test. 

 Put in a half ounce of limewater and shake thoroughly. If 

 there is enough carbon dioxide in the bottle of air to make 

 the limewater milky the air in the room is too foul for the 

 health of the pupils. Observe the effect on limewater of 

 passing the breath into it through a straw or tube. 



Close the ventilators, and charge the air in the room with 

 smoke. Open the ventilators ; if the room takes longer than 

 twenty minutes to become perfectly cleared of the smoke the 

 ventilation is below requirements. 



The best test is one that compares the quantity of air 

 circulated with the quantity of impurity put into it. This 

 admits suiting the amount of ventilation to the number of 

 pupils in the room. Children grow better, have better 

 appetite, and are better nourished in a well-ventilated school- 



