COMBUSTION 213 



close the draft, the check-damper should not be opened at 

 the same time; not until a little later. For too rapid cooling 

 off of the fire may also cause fusion. Another cause of 

 clinkers is poor coal; sometimes you get coal which is so 

 poor that even the most intelligent firing will not prevent 

 clinkering. In such cases the coal-dealer should be com- 

 pelled to give a rebate, or even to take the coal away. 



It is evident that a good deal may be learned from taking 

 care of a furnace. Just as a boy who takes care of a lawn 

 intelligently will learn a good deal about botany, so, in 

 taking care of a furnace, he has an excellent opportunity 

 to learn something about physics and chemistry. 



Some of the Products of Combustion. Let us consider 

 now what are some of the products of combustion. This 

 depends entirely, of course, upon what it is that is being 

 oxidized. You can get no products except those that 

 result from the combination with oxygen of the materials 

 which are already present. In the rusting of iron, you get 

 only iron oxide. In the burning of wood or coal, you get 

 a number of products; while in the combustion of sub- 

 stances within living bodies, you get an even greater variety. 



Take the burning of a candle. By holding a saucer in 

 the flame you can collect soot. Soot is carbon. It burns 

 in the flame and becomes carbon dioxide. If you collect 

 the gas given off from a burning candle, or from any other 

 kind of burning, you will find that it is largely made up 

 of carbon dioxide. Smoke is unconsumed carbon. The 

 more smoke that a fire gives off, the less efficient it 

 is in consuming its fuel; smoke indicates that some 

 carbon, before it is oxidized, gets away from the range 

 of sufficient heat to oxidize it. So smoke should be, 



