ns existing in the trial, is, therefore,
called the equivalent evaporation "from and at 212 degrees."

The factor for reducing the weight of water actually converted into
steam from the temperature of the feed, at the steam pressure existing
in the trial, to the equivalent evaporation under standard conditions is
called the _factor of evaporation._ This factor is the ratio of the
total heat added to one pound of steam under the standard conditions to
the heat added to each pound of steam in heating the water from the
temperature of the feed in the trial to the temperature corresponding to
the pressure existing in the trial. This heat added is obviously the
difference between the total heat of evaporation of the steam at the
pressure existing in the trial and the heat of the liquid in the water
at the temperature at which it was fed in the trial. To illustrate by an
example:

In a boiler trial the temperature of the feed water is 60 degrees
Fahrenheit and the pressure under which steam is delivered is 160.3
pounds gauge pressure or 175 pounds absolute pressure. The total heat of
one pound of steam at 175 pounds pressure is 1195.9 B. t. u. measured
above the standard temperature of 32 degrees Fahrenheit. But the water
fed to the boiler contained 28.08 B. t. u. as the heat of the liquid
measured above 32 degrees Fahrenheit. Therefore, to each pound of steam
there has been added 1167.82 B. t. u. To evaporate one pound of water
under standard conditions would, on the other hand, have required but
970.4 B. t. u., which, as described, is the latent heat of evaporation
at 212 degrees Fahrenheit. Expressed differently, the total heat of one
pound of steam at the pressure corresponding to a temperature of 212
degrees is 1150.4 B. t. u. One pound of water at 212 degrees contains
180 B. t. u. of sensible heat above 32 degrees Fahrenheit. Hence, under
standard conditions, 1150.4 - 180 = 970.4 B. t. u. is added in the
changing of one pound of water into steam at atmospheric pressure and a
temperature of 212 degrees. This is in effect the definition of the
latent heat of evaporation.

Hence, if conditions of the trial had been standard, only 970.4 B. t. u.
would be required and the ratio of 1167.82 to 970.4 B. t. u. is the
ratio determining the factor of evaporation. The factor in the assumed
case is 1167.82 / 970.4 = 1.2034 and if the same amount of heat had been
absorbed under standard conditions as was absorbed in the trial
cond