Units.
1 lb. of carbon X 0.25 X 520 = 130
12.2 of air X 0.238 X 520 = 1,485
Heat of combustion = 14,544
------
16,159
Deduct heat equivalent to work of \
displacing atmosphere by products of }
combustion raised from 60° to 100°, } 32
or from 149.8 cubic feet to 161.3 }
cubic feet, /
------
Total units of heat available 16,127

Equal to 16.69 lb. of water evaporated from and at 212°. Hence the
greatest possible evaporation from and at 212° from a lb. of carbon--

16,159 u. X 0.891 - 32 u.
W = --------------------------- = 14.87 lb.
966 u.

I will now take a definite case, and compare the potential energy of a
certain kind of fuel with the results actually obtained. For this
purpose the boiler of the eight-horse portable engine, which gained
the first prize at the Cardiff show of the Royal Agricultural Society
in 1872, will serve very well, because the trials, all the details of
which are set forth very fully in vol. ix. of the _Journal_ of the
Society, were carried out with great care and skill by Sir Frederick
Bramwell and the late Mr. Menelaus; indeed, the only fact left