212 ELEMENTARY SCIENCE 



this new evidence, the phlogiston theory was exploded, and 

 the rest was comparatively easy. 



Taking Care of a Furnace Fire. Now to go back to 

 the matter of taking care of a furnace fire. Two important 

 things to accomplish are to get as much heat as possible 

 out of the fuel used, and to prevent the formation of 

 clinkers. These two things go together; you cannot 

 succeed in the first if you fail to succeed in the second. A 

 clinker is a mass which results from the fusion of coal 

 which has been only partly burned; by its fusion it is 

 so changed that it will not burn any more. This 

 fusion of coal indicates that, due to overheating, coal may 

 actually melt and run together before it burns up; the fused 

 masses (clinkers) which result from this are useless for fuel, 

 hinder the shaking down of ashes, and interfere with the 

 draft. 



So we see that to get the most heat out of coal we must 

 not try to get it too fast; we must nurse the fire along; 

 there is such a thing as giving it too much draft. The 

 aim should be to provide a good circulation of air through 

 the whole burning mass, so that it may become thor- 

 oughly oxidized in all its parts, and not fuse. Hence you 

 may spoil your fire by giving it too much air from below; 

 it is rather dangerous to leave the ash-door open. At the 

 same time, this risk of too much air from below gives no 

 excuse for letting the ashes accumulate. This will pre- 

 vent access of air evenly to all parts of the fire; also, if 

 the heap of ashes rises till it touches the grate-bars, it will 

 (by adding to their heat through conduction) cause them 

 to "burn out" (melt). Another thing which may cause 

 clinkers is too rapid checking of the fire. When you 



