314 ELEMENTS OF FARM PRACTICE 



ed above must be known and also the fact that foul air is 

 heavier than pure air and is usually found near the floor of 

 the room. 



Ventilation Flue. — A stove with dampers open is very 

 good for taking foul air from a room, as it takes air from 

 near the floor. To provide ventilation when stoves are not 

 in use, a double flue chimney should be built, with one flue 

 opening near the floor to remove the foul air, and the other 

 flue to carry the smoke from the stove or furnace. The 

 heat in the smoke flue warms the ventilating flue and aids 

 in txic circulation of air. In this way foul air is removed 

 from near the floor, while warm air, which naturally rises 

 near the ceiling, is not removed until it becomes foul and 

 settles to the floor. 



Fresh Air Supply. — To supply fresh air is very simple 

 in rooms heated by the furnace, as the fresh air is brought 

 in from outside and heated in passing through the furnace 

 into the rooms. In buildings heated with stoves, steam or 

 hot water, air must be brought directly to the room from 

 outside, and the object is to do this without causing a 

 draught of cool air on the occupants of the room. There 

 are two good methods of letting fresh air into rooms. The 

 first and simpler is to let it in near the ceiling, as shown in 

 Figure 135, where it will spread out over the room and 

 gradually settle through the warm air, and as it becomes 

 foul be drawn out through the stove or ventilating flue 

 from near the floor. Another method, one frequently used 

 in schools, is to have a sheet iron jacket about the stove. 

 Air is let in under the stove, is warmed and rises between 

 the stove and jacket to near the ceiling, where it spreads 

 out over the room and is drawn from near the floor, as in 

 the other case. See Figure 136. 

 Questions: 



1. How can you prove that air expands when heated, and is 

 lighter than cool air? 



2. What causes air to move up a chimney? 



3. What is the object of ventilators? 



4. Describe two good methods of getting fresh air into a room. 

 Arithmetic: 



1. A man needs 20 cu. ft. of air per hour, hoAv much does he need 

 in 8 hours? How much air will two persons need while sleeping in a 

 room 8 hours? 



