METHODS OF HEATING BUILDINGS 17 



,. f 

 above 75 . I if> above this temperature, it looks cloudy,, 



you may be sure that it too is adulterated with fat. 



8. Methods of Heating Buildings. Open Fireplaces and 

 Stoves. Before the time of stoves and furnaces, man heated 

 his modest dwelling by open fires alone. The burning logs 

 gave warmth to the cabin and served as a primitive cooking 

 agent ; and the smoke which usually accompanies burning 

 bodies was carried away by means of the chimney. But in 

 an open fireplace much heat escapes with the smoke 

 and is lost, and only a 

 small portion streams into 

 the room and gives warmth. 



When fuel is placed in 

 an open fireplace (Fig. 12) 

 and lighted, the air im- 

 mediately surrounding the 

 fire becomes warmer and, 

 because of expansion, be- 

 comes lighter than the cold 

 air above. The cold air, be- 

 ing heavier, falls and forces 

 the warmer air upward, 

 and along with the warm 

 air goes the disagreeable 

 smoke. The fall of the 

 colder 



FlG. 12. The open fireplace as an early 

 method of heating. 



and heavier air, 

 and the rise of the warmer and hence lighter air, is similar to 

 the exchange which takes place when water is poured on oil; 

 the water, being heavier than oil, sinks to the bottom and 

 forces the oil to the surface. The warmer air which escapes 

 up the chimney carries with it the disagreeable smoke, and 

 when all the smoke is got rid of in this way, the chimney is 

 said to draw well. 



CL. GEN. SCI. 2 



