Analyses of 1 lb. of Coal.Oxygen required for Combustion.
Pounds.		Products of Combustion at 32° F.
Cubic feet.Volume per cent.
Carbon0.84972.26625.311.1
Hydrogen0.04260.3097.63.4
Oxygen0.0350———
Sulphur0.0042———
Nitrogen0.1045—0.18}85.5
Ash0.0540——
Total1.00002.572—
9-1/3.lb nitrogen——118.9
6 lb. excess of air.——71.4
Total cubic feet of products per 1 lb. of coal——226.4100.0

The temperature of the furnace not having been determined, we must calculate it on the supposition, which will be justified later on, that 50 per cent more air was admitted than was theoretically necessary to supply the oxygen required for perfect combustion. This would make 18 lb. of air per 1 lb. of coal; consequently 19 lb. of gases would be heated by 14,727 units of heat. Hence:

T =14,727 u.= 3,257°
19 lb. × 0.238

above the temperatures of the air, or 3,777° absolute. The temperature of the smoke, t, was 849° absolute; hence the maximum duty would be

3,777° - 849°= 0.7752.
3,777°

The specific heat of coal is very nearly that of gases at constant pressure, and may, without sensible error, be taken as such. The potential energy of 1 lb. of coal, therefore, with reference to the oxygen with which it will combine, and calculated from absolute zero, is:

Units.
19 lb. of coal and air at the temperature of the air contained 19 lb. × 520° × 0.2382,350
Heat of combustion14,727
17,078
Deduct heat expended in displacing atmosphere 151 cubic feet- 422
Total potential energy16,656

Hence work to be expected from the boiler:

17,078 units × (3,777° - 849°) - 422 units
3,777°
=—————————————————= 13.27 lb.
966 units

of water evaporated from and at 212°, corresponding to 12,819 units. The actual result obtained was 11.83 lb.; hence the efficiency of this boiler was