ition, 1.2034 times the amount of steam would have been generated.
Expressed as a formula for use with any set of conditions, the factor
is,

H - h
F = ----- (2)
970.4

Where H = the total heat of steam above 32 degrees Fahrenheit from steam
tables,
h = sensible heat of feed water above 32 degrees Fahrenheit from
Table 22.

In the form above, the factor may be determined with either saturated or
superheated steam, provided that in the latter case values of H are
available for varying degrees of superheat and pressures.

Where such values are not available, the form becomes,

H - h + s(t_{sup} - t_{sat})
F = ---------------------------- (3)
970.4

Where s = mean specific heat of superheated steam at the
pressure existing in the trial from saturated
steam to the temperature existing in the trial,
t_{sup} = final temperature of steam,
t_{sat} = temperature of saturated steam, corresponding to
pressure existing,
(t_{sup} - t_{sat}) = degrees of superheat.

The specific heat of superheated steam will be taken up later.

Table 19 gives factors of evaporation for saturated steam boiler trials
to cover a large range of conditions. Except for the most refined work,
intermediate values may be determined by interpolation.

Steam gauges indicate the pressure above the atmosphere. As has been
pointed out, the atmospheric pressure changes according to the altitude
and the variation in the barometer. Hence, calculations involving the
properties of steam are based on _absolute_ pressures, which are equal
to the gauge pressure plus the atmospheric pressure in pounds to the
square inch. This latter is generally assumed to be 14.7 pounds per
square inch at sea level, but for other levels it must be determined
from the barometric reading at that place.

Vacuum gauges indicate the difference, expressed in inches of mercury,
between atmospheric pressure and the pressure within the vessel to which
the gauge is attached. For approximate purposes, 2.04 inches height of
mercury may be considered equal to a pressure of one pound per square
inch at the ordinary temperatures at which mercury gauges are used.
Hence for any reading of the vacuum gauge in inches, G, the absolute
pressure for any barometer reading in inches, B, will be (B - G) / 2.04.
If the barometer is 30