CXLVI. DISCUSSION, 
at present to fully use this heat. Fig. 1 shews the total amount 
Love SF 0 ay 
nm 
800 1000 1200 1400 
THERMAL UNITS. 
400 600 
200 
0 
45 65 85 105 125 145 165 185 205 225235 260 
BOILER PRESSURE POUNDS PER SQUARE INCH. 
A—Heat required to raise 11b. of water from 32° Fah. to boiling point- 
B—Heat absorbed per pound of steam in overcoming the internal resistance 
0 vaporisation. : 
C—Heat disappearing per pound of steam in overcoming the external resis- 
tance to expansion. 
of heat measuring from 32° Fah. contained in a pound of steam 
at varying pressures, this is made up of three portions, first the 
heat required to raise the water from 32° to the temperature of 
the steam A, second the heat required to overcome the internal 
resistance to vaporation B, that is the heat required to convert 
the water into a gas, and third the heat expended in overcoming 
the external resistance to expansion C, A and C increase with 
the pressure at a greater rate than the total heat increases, 80 
that it will be seen at a glance that the higher the pressure the 
greater the amount of total heat that is available for useful work, 
as all the heat due to the resistance to internal evaporation, 
corresponding to the pressure at which the steam is exhausted 
from the cylinder, goes to waste. 
Fig. 2 shews graphically the maximum possible efficiency in per 
ceutages that is obtainable when using steam at any pressure UP 
to 285ibs., the top curve shews the corresponding temperature in 
Fah. degrees, and the second one shews the percentage of heat 
