Units.
19 lb. of coal and air at the temperature
of the air contained 19 lb. × 520° × 0.238 2,350
Heat of combustion 14,727
-------
17,078
Deduct heat expended in displacing atmosphere 151 cubic feet - 422
------
Total potential energy 16,656

Hence work to be expected from the boiler:

/ 3,777° - 849° \
= 17,078 units X ( --------------- ) - 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

11.83
------- = 0.892.
13.27

I have already claimed for a boiler that it is a veritable heat
engine, and I have ventured to construct an indicator diagram to
illustrate its working. The rate of transfer of heat from the furnace
to the water in the boiler, at any given point, is some way