98 TlMEHRI. 
fuel, depends upon the wood, and the sugar, diminished 
by the water contained. 
The following data, taken from Box's " Treatise on 
Heat," enable us to calculate the relative values roughly. 
A unit of heat means such an amount of heat as is 
required to raise the temperature of i lb. water, at 32° 
Fahrenheit, i° Fahrenheit. The amount of heat required 
to raise the temperature of 1 lb. water i° Fahrenheit 
increases slightly as the temperature increases, so that 
i8o'9 units of heat are required to raise 1 lb. of water 
from 32 Fahrenheit to 21 2°. The amount of increase 
is so small that it has been neglected in the following 
calculations : — 
The specific heat of vapour of water with pressure constant is "475. 
The latent heat of vapourization is g66°. 
The heat evolved by the combustion of lib carbon is 12906 units. 
I ft) wood perfectly dry contains "51 lb carbon. 
The value of sugar as fuel arises solely from the car- 
bon it contains ; the hydrogen being combined with a 
sufficient quantity of oxygen to form water, giving no 
useful heat. 
The chemical composition of cane sugar being 
I2 C 22 H 1 1 , it contains 42'i per cent, of carbon. 
The weight of air required for combustion, taking 
twice the theoretical weight, is — 
For wood (dry) I2'25 lbs. per lb. wood. 
,, coal 224. ,, coal. 
,, carbon 24 ,, carbon. 
The temperature of the water contained in the fuel and 
the air required for combustion is assumed at 86° Fahr. 
The temperature of the gases passing up the chimney 
is assumed at 6oo° Fahrenheit. The specific heat of 
air is '238 with pressure constant. 
