THE EEASON WHY 45 



1 And the strong shall be as tow, and the maker of it as a spark, and they shall 

 both burn together, and none shall quench them." ISAIAH I. 



105. Why is there so little smoke ivhen the fire is red? 

 Because the hydrogen and the volatile parts of the coal have 



already been driven off and consumed, and the combustion that con- 

 tinues is principally caused by the carbon of the coals, and the 

 ox v gen of the air. 



106. Will carbon, burnt in oxygen, produce flame and 

 smoke ? 



It burns brightly, but it produces neither flame nor smoke. 



107. Why do not charcoal and colce fires give flame ? 

 Because the hydrogen has been driven off by the processes by 



which charcoal and coke are made. 



108. What is a conductor of heat ? 



A conductor of heat is any substance through which heat is 

 readily transmitted. 



109. What is a non-conductor of heat? 



A non-conductor is any substance through which heat will not 

 pass readily. 



110. Name a few good conductors. 



Gold, silver, copper, platinum, iron, zinc, tin, stone, and all dense 



solid bodies. 



111. Name a few non-conductors. 



Fur, wool, down, wood, cotton, paper, and all substances of a 

 spongy or porous texture. 



112. How is heat transmitted from one lody to another ? 

 By Conduction, Radiation, Reflection, Absorption and Convection. 



113. What is the Conduction of heat? 



It is the communication of heat from one body to another by con- 

 tact. If I lay a penny piece upon the hob, it becomes hot by 



conduction. 



114. What is the Radiation of heat? 



The transmission of heat by a series of rays. If I hold my hand 



