28 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



ignite easily, burn with a long yellow flame, and form much 

 soot, which makes it objectionable for railway and naval uses. 

 Besides volatile hydrocarbons, the volatile matter will contain 

 any moisture retained by clay present which is not expelled 

 at a temperature less than that necessary to decompose the 

 coal: it will also contain some sulphur, and if carbonate of lime 

 is present, carbonic dioxide. 



Fixed carbon is the chief combustible constituent in coal, 

 for although an equivalent weight of the volatile hydrocarbons 

 when properly burnt will evaporate more water than the fixed 

 carbon, yet so much of the former is lost by improper furnace 

 construction and careless firing, that the steaming value of a 

 coal is in .proportion to its percentage of fixed carbon. The 

 nature of a coal is not told by its percentage of fixed carbon, 

 but by its fuel ratio, as mentioned elsewhere. 



Moisture. Hygroscopic moisture in a fuel increases its 

 weight for transport; each per cent, of moisture means 22.41b. 

 less fuel for each long toil of coal. If the fuel is sold by 

 weight, and no deduction is made for the water absorbed by it 

 then such water is paid for as fuel. Moisture is further harm- 

 ful inasmuch as it abstracts a certain amount of heat in order 

 to evaporate it; but, on the other hand, it is doubtful whether 

 water should always be looked upon as a non-fuel, for in many 

 cases its elements become disassociated, leaving the hydrogen 

 available for fuel purposes, as in the manufacture of water gas 

 when steam is passed over red-hot coke. 



Though a coal may appear perfectly dry, it may still con- 

 tain a considerable quantity of water. That which is lost by 

 the coal when exposed to ordinary atmospheric conditions is 

 known as "pit water," but that which it still retains is known 

 as "hygroscopic moisture." When the hygroscopic moisture 

 is driven off, the coal becomes more tender and friable. The 

 contents of water in a coal is affected by the size of the coal. 

 When fine it contains less pit water, but more hygroscopic 

 moisture than when lumpy. 



Ash is a dilutant to a fuel, and by adding to its weight 

 increases cost of freight and is paid for as if a fuel. One per 

 cent, of ash is equivalent to nearly 22 Alb. in a long ton. If 

 excessive, it gives more work to stokers, and carries away a 

 certain amount of heat through the fire bars; it also hinders 

 complete combustion by entangling particles of fuel. If a 

 coking coal, the ash tends to weaken the coke, and may have 

 to be taken into consideration when calculating the slag of 

 a blast furnace. If the ash is readily fusible, it may form 

 clinkers on fire bars, and obstruct the free passage of air. A 

 rough idea of the percentage of iron in an ash may be obtained 

 by noting the colour of it; iron is objectionable, since it 

 makes the ash more fusible and increases its tendency to 



