Anthracite 14,500 Br. Heat Units.
Bituminous 14,200 " " "
Petroleum 20,300 " " "
Coal gas 20,200 " " "
Generator gas 3,100 " " "
Water gas 8,500 " " "

Reducing the above to terms of pounds of water evaporated from 212° F.,
we have:

POUNDS OF WATER EVAPORATED FROM 212° F.

Anthracite 15.023
Bituminous 14.69
Petroleum 21.00
Coal gas 20.87
Generator gas 3.21
Water gas 8.7

The results of experiments show the efficiency of fluid-burning furnaces
to be about ninety per cent., while with coal sixty per cent. may be
taken as a good figure. The great difference in the efficiencies is due
to the fact that fluid fuels require for combustion very little air
above the theoretical quantity, while with the solid fuels fully twice
the theoretical quantity must be admitted to dilute the products of
combustion.

Correcting our previous results for these efficiencies, we have:

POUNDS OF WATER ACTUALLY EVAPORATED FROM 212° F., PER POUND OF FUEL.