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 deg. to 100 deg., } 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 deg.. Hence the greatest possible evaporation from and at 212 deg. 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 undetermined was the temperature of the furnace, an omission due to the want of a trustworthy pyrometer, a want which has not been satisfied to this day.[2] [Footnote 2: In the fifty-second volume of the _Proceedings_ (1887-78), page 154, will be found a remarkable experiment on the evaporative power of a vertical boiler with internal circulating pipes. The experiment was conducted by Sir Frederick Bramwell and Dr. Russell, and is remarkable in this respect, that the quantity of air admitted to the fuel, the loss by convection and radiation, and the composition of the smoke were determined. The facts observed were as follows: Steam pressure 53 lb................................... = 300.6 deg. F. lb. Fuel--Water in coke and wood........................... 26.08 Ash.............................................. 10.53 Hydrogen, oxygen, nitrogen, and sulphur.......... 7.18 ------ Total non-combustible..................... 43.79 Carbon, being useful combustible................. 194.46 ------ Total fuel................................ 238.25