200 RADIATION. 



and polished; but the bottom and back 

 of the kettle are never cleaned. 



Q. Why should NOT the BOTTOM and BACK 

 of a kettle be CLEANED and polished ? 



A. Because they come in contact 

 with the fire, and (while they are covered 

 with black soot) absorb heat freely from 

 the burning coals. 



Q. Why should the FRONT and TOP of a 

 kettle be CLEAN and well polished ? 



A. Because polished metal will not 

 radiate heat ; and, therefore, (while the 

 front and top of the kettle are well 

 polished) the heat is kept in, and not 

 suffered to escape by radiation. 



Q. Why is the INSIDE of a KETTLE and 



SAUCEPAN WHITE ? 



A.. White will not radiate heat : if, 

 therefore, the inside of a boiler be white, 

 the liquor in it is kept hot much longer. 



Q. Wliy is the BOTTOM of a KETTLE nearly 

 COLD, when the WATER is BOILING HOT ? 



A. Black soot is a very bad conduc- 

 tor of heat; and, therefore, the heat of 

 the boiling water is some considerable 

 time, before it gets through the soot 



