ON LIQUID FUEL. 105 
Combustion of Hydrogen . 
f 
Quantity burnt, 1 lb. 
Equivalent evapo¬ 
ration of water. 
at 212° [ at GO 0 
Heat units. 
lbs. 
lbs. 
Total heat of combustion. 
62,032 
64-2 
_ 
Latent heat of water vapour. 
8,695 
— 
— 
Available heat. 
53,337 
— 
— 
Waste heat of furnace gas. 
11,520 
11-9 
— 
Effective heat. 
41,817 
43-3 
38 
Thus the maximum evaporative efficacy of carbon and of hydrogen is, for each pound 
burnt, respectively equal to the conversion of about 114 pounds and 434 pounds of water 
at 212° F., into steam of the same temperature, and under the ordinary atmospheric 
pressure. The extent to which this efficacy is realized in the ordinary application of fuel 
for producing steam will depend upon the relative facilities afforded by the rate of com¬ 
bustion and by the construction of the boiler, for the full absorption of the effective 
heat from the combustion products during their passage along the flues or tubes of the 
boiler before being discharged into the chimney. But whatever may be the influence of 
these conditions in regard to evaporative effect produced, they do not in any degree 
affect the foregoing considerations as to the maximum evaporative capabilities of the 
carbon and hydrogen of fuel when burnt in the manner stated, with a supply of air just 
twice as great as the quantity requisite for their conversion into carbonic acid gas and 
water vapour. 
From these considerations it will be evident that in the combustion of fuel, under 
ordinary conditions, there is always a great waste of heat actually generated and avail¬ 
able. The total waste is considerably greater in the combustion of hydrogen than it is 
in the combustion of carbon, amounting in the one case to 32'6 per cent., and in the 
other to 24 per cent, of the total heat of combustion, but still the evaporative efficacy 
of hydrogen is nearly four times as great as that of carbon. 
In the combustion of hydrocarbons under these conditions, whether they be solid, 
liquid, or gaseous, the total amount of heat generated will be determined by the rela¬ 
tive proportions of the carbon and hydrogen they contain. The amount of hydrogen 
in such substances generally ranges from one-seventh to one-fourth by weight, and for 
such limits the corresponding amounts of heat generated by their combustion, and their 
theoretical evaporative power would be as follows:— 
Hydro¬ 
carbon 
burnt. 
Carbon. 
Hydrogen. 
Total heat of com¬ 
bustion. 
Equivalent 
evaporation of 
water. 
at 212° 
at G0° [ 
lb. 
1 [ 
lbs. 
•86 
lbs. 
•14 
Heat units. 
x 14,500 = 12,470 
x 62,032 = 8,684 
lbs. 
lbs. 
21,154 
. 
21-9 
18-8 
1 { 
•75 
•25 
x 14,500 = 10,775 
x 62,032 = 15,508 
26,283 
27*1 
23-3 
It must be remembered that these results are above the truth, for this calculation 
does not take into account the quantity of heat expended in effecting the decomposi¬ 
tion of the hydrocarbon, i.e. the separation of the carbon from the hydrogen, nor does 
