^Some Applications of Heat 



105 



stayed in the house. It was discovered that the smoke caused 

 less unpleasantness and escaped more readily if not allowed to 

 spread. This led to the invention of the chimney, which is merely 

 a long tube, leading from the fire through the roof, up which 

 smoke and gases pass owing 

 to the formation of convec- 

 tion air currents. These 

 make a movement of air 

 called a draft. If the air in 

 the chimney is warmer than 

 the outside surrounding air 

 the draft carries the smoke 

 and all gases upward and out 

 the top opening of the chim- 

 ney. Whenever a fire is 

 started in a stove the heated 

 air immediately causes a draft 

 upward. In order to work to 

 the best advantage, a chimney 

 should be straight and should 

 have a smooth inside surface. 

 The efficiency of a chimney 

 increases with its height. 



The Fireplace. Our 

 forefathers used the open fire 

 extensively. The old-fash- 

 ioned fireplace, built of brick 

 or stone, was usually about 

 five to eight feet wide and 

 two to three feet deep. Large logs of wood were used for 

 fuel. Most of the heat went up the huge chimney. The small 

 part that was left spread through the room by radiation and 

 convection. 



In the old days the fireplace was used not merely for heating ; 

 it was the only means of cooking food. Potatoes were roasted 

 in the coals, and meats and vegetables were cooked in pots and 

 kettles hung on an iron crane so attached to the wall of the fire- 



Eastman Kodak Company. 



A TALL CHIMNEY 



The taller the chimney, the better the draft. 



