66 Introduction to the Study of Science 



the draft through the range, thus saving fuel. Means for the 

 control of the draft are often provided at the top as well as the 

 bottom of the fire box of the range. It may be noted that one 

 of the chief defects of heating appliances is the waste of fuel 

 and loss of heat, although this is controlled in some measure 

 by dampers. 



Exercise. Make a sketch of the course of air through a range, 

 and show how and to what parts of the range it may be deflected by 

 dampers. 



Stoves sometimes smoke disagreeably when the fire is first kindled. 

 Making use of the facts just observed, explain the smoking stove and 

 how it may be remedied. What must be the conditions before the draft 

 is fully established and the smoke passes out through the chimney? 



Forced draft. Intense heat is frequently necessary in gen- 

 erating steam for locomotives and stationary engines. One 

 way of securing this is by increasing the draft. Locomotives 

 make use of the exhaust steam to increase the draft. As this 

 means a great loss of energy and an increased cost of work 

 performed (cf. page 295), other devices have been coming into 

 use, such as fans and compressed air. Fans may be used either 

 in the flues to accelerate the movement of the waste gases, 

 or to force air under and through the grates. For the same 

 purpose chimneys of great height are built. The height of 

 the chimney adds to the volume of warmed and therefore lighter 

 air which is being forced out by the colder air rushing into and 

 through the furnace. The result is a greatly increased draft. 

 Have you known of smoky chimneys remedied by being built 

 higher? What other ways do you know for forcing draft? 

 Explain the operation of the blacksmith's forge. 



32. The sun's heat. The natural and direct source of heat 

 energy is the sun. Upon this energy we depend for light and 

 heat and life. How great is our dependence is not always 

 recognized. The sources and materials of artificial heat 

 coal, oil, natural gas, and the like are stored-up energy 

 derived from the sun, millions of years ago. It is diffi- 



