COMBUSTION. 43 



Q. Why does COAL make such EXCELLENT 

 FUEL? 



A. Because it is so very hard and 

 compact, that it burns away very slowly. 



Q. Why will CINDERS become RED HOT, 

 quicker than COALS ? 



A. Because they are more porous 

 and less solid ; and are, therefore, sooner 

 reduced to a state of combustion. 



Q. Why will not IRON CINDERS burn ? 



A. Iron cinders are cinders saturated 

 with oxygen; they are unfit for fuel, 

 because they can imbibe no more oxygen, 

 being saturated already. 



Q. Why are CINDERS lighter than COALS? 



A. Because their vapour, gases, and 

 volatile parts, have been driven off by 

 previous combustion. 



Q. Why will not STONES do for fuel, as well 

 as COALS ? 



A. Because they contain no hydro- 

 gen (or inflammable gas) like coals. 



Q. Why will not WET KINDLING light ajire P 



A. 1st Because the moisture of the 

 wet kindling prevents the oxygen of the 

 air from getting to the fuel to form it 

 into carbonic acid gas : and 



