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PART V 
MINERAL FUELS 
CHAPTER XXII 
COAL AND ITS CLASSIFICATION 1 
FueLs are materials which give off sufficient heat when 
burnt to be of use in an ordinary fireplace, furnace, or burner. 
The burning of a fuel is the combination of one or more 
of its constituents with the oxygen of the air, Most bodies 
give off heat when combining with oxygen, but they are 
only regarded as fuel if they can be used extensively as a 
source of heat, 
The important mineral fuels are coal, mineral oil, and 
peat. Other minerals serve as fuel under special conditions ; 
pyrites is used in pyritic smelting, when both its constituents, 
iron and sulphur, give off heat; and oil is distilled from 
oil-shale. The chief fuels belong to the carbonaceous series, 
and depend on carbon or compounds of carbon with hydrogen. 
Coal is the fuel of supreme importance in the modern world. 
Wood and oil are its only serious rivals. Ordinary wood 
(e.g. ash, oak, and elm) has a calorific value of only 35420 
British Thermal Units (B.T.U.)% while coal varies from 
I For coal in general, cf. E. S. Moore, Coal, 1922. 
A B.T.U. is the heat required to raise the temperature of a pound 
of water 1° F. (usually taken from 60° to 61° F.). A calorie is the heat 
required to raise a gram of water 1° C., usually taken from 14°to 15°C. 
To convert B.T.U. to calories multiply by $.” Calorific value is deter. 
mined by combustion in a calorimeter ; but it can be estimated from the 
analysis by various formule such as that of Dulong. This formula, 
adapted to later determinations of the fue] values, is 8100 C + 24,500 
(H — 30) Sz2250 x 2, in which C,H, O and S are the weights of the 
carbon, hydrogen, oxygen, and S. “Hence of a good bituminous coal with 
e.g. sulphur 1 per cent., hydrogen 5 per cent, carbon 74 per cent., and 
oxygen 7 per cent., the calorific value would be 1 3,468 B.T.U. 
259