94 THE PRODUCTION AND USE OF HEAT 



volatile matter to support a flame? What can you say about the 

 relative amounts of volatile matter in the two kinds of coal? 



Exercise 34. Distillation of Soft Coal 



Arrange to distil soft coal just as wood was distilled (Ex. 29) 

 except that the test tube is filled about one-third full of fine soft coal. 

 The liquid which collects in the test tube is called COAL TAR, the gas 

 which burned is the COAL GAS, while the solid portion left from the coal 

 is the COKE. 



107. Familiar Facts about the Burning of Wood and Coal. 



Wood and soft coal burn with long red flames because they 

 contain so much volatile matter, while hard coal, because it 

 contains so little volatile matter, does not produce such flames. 

 Wood and hard coal make but little smoke because they are 

 completely burned, including whatever volatile matter they 

 contain, while soft coal, because it contains so much volatile 

 matter, produces more or less black smoke. Hard. coal and 

 wood produce light fleecy ashes, while those from soft coal 

 often melt together in the fire, causing clinkers. For starting 

 a wood or a soft coal fire, a rather small amount of kindling is 

 needed, since these fuels catch on fire easily because of their 

 large amounts of volatile matter which easily ignites. Hard 

 coal, because it contains so little volatile matter, requires more 

 kindling and a hotter fire to start it. 



108. The Composition of Common Solid Fuels. In our 

 study of fuels it is important that we understand the behavior 

 of the fuel when heated. The following table gives: (1) The 

 percentage of carbon that does not pass away as volatile 

 matter, known as coke or fixed carbon; (2) the percentages 

 of volatile matter which is produced by the fuel when it is 

 heated; (3) the percentage of water; (4) the percentage of ash. 



In the construction of stoves and furnaces in which the 

 various fuels are to be burned, the manufacturer must keep 

 in mind these facts of composition. The customer who buys 

 a stove or furnace must know in general what kind of fuel is 

 to be burned. Even with all of these conditions in mind, 

 it is yet a difficult matter to burn soft coal, which produces 

 much volatile matter, in such a way as to avoid serious loss. 



