COMPARISON OF DIFFERENT KINDS OF FUEL. 45 



These figures apply to dry coal. The fine grades of anthra- 

 cite coal and the bituminous coals are frequently moist from 

 exposure to the weather. In the moist or even wet condition 

 which exists when the purchaser buys coal, this comparison 

 does not indicate the true relative performance. The quantity 

 of moisture which such coal contains is uncertain and variable. 

 Three per cent, may be allowed for an average, but in indi- 

 vidual cases it may run up to 6 per cent, or more. While 

 this allowance serves to reduce the evaporation with the coals 

 named, the coarse grades of anthracite coal in practice require 

 an allowance which, though of different nature, operates in the 

 same manner. The figures of the tests are based on the weight 

 of coal obtained by deducting unconsumed fuel left at the end 

 of the test, and no deduction of much consequence requires to 

 be made except when the large grades of anthracite coal are 

 used. In the practical work of operating boilers much of this 

 unconsumed coal is thrown away with the ashes. It readily 

 amounts to 3 per cent. , and this corresponds to the allowance 

 which with other fuels may be made for moisture. The quan- 

 tities given may therefore be used, as they stand, for purposes 

 of comparison, although taken individually they do not show 

 precisely the work of the various fuels in the conditions in 

 which they are bought and used. 



In the comparison of relative quantity of water evaporated 

 by the different fuels, it is seen that Cumberland coal easily 

 takes the lead. As Table No. 7 shows, the evaporation of this 

 coal is 12.8 per cent. more, than that of anthracite coal. In 



