t
the dew-point.

EXAMPLE 9. To correct readings of the hygrometer for changes
in barometric pressure:

A change of pressure affects the reading of the wet bulb.
The chart applies at a barometric pressure of 30 inches,
and, except for great accuracy, no correction is generally
necessary.

Find the relative humidity as usual. Then look for the
nearest barometer line (indicated by dashes). At the end of
each barometer line will be found a fraction which
represents the proportion of the relative humidity already
found, which must be added or subtracted for a change in
barometric pressure. If the barometer reading is less than
30 inches, add; if greater than 30 inches, subtract. The
figures given are for a change of 1 inch; for other changes
use proportional amounts. Thus, for a change of 2 inches use
twice the indicated ratio; for half an inch use half, and so
on.

Example: Dry bulb 67 deg., wet bulb 51 deg., barometer 28 inches.
The relative humidity is found, by the method given in
example 1, to equal 30 per cent. The barometric line--gives
a value of 3/100H for each inch of change. Since the
barometer is 2 inches below 30, multiply 3/100H by 2, giving
6/100H. The correction will, therefore, be 6/100 of 30,
which equals 1.8. Since the barometer is below 30, this is
to be added, giving a corrected relative humidity of 31.8
per cent.

This has nothing to do with the vapor pressure (concave)
curves, which are independent of barometric pressure, and
consequently does not affect the solution of the previous
problems.

EXAMPLE 10. At what temperature must the condenser be
maintained to produce a given humidity?

Example: Suppose the temperature in the drying room is to be
kept at 150 deg. Fahr., and a humidity of 80 per cent is
desired. If the humidity is in excess of 80 per cent the air
must be cooled to the dew-point corresponding to this
condition (see example 4), which in this case is 141.5 deg..

Hence, if the condenser cools the air to this dew point the
required condition is obtained when the air is again heated
to the initial temperature.

EXAMPLE 11. Determination of relative humidity by the
dew-point:

The quantity of moisture present and relative humidity for
any given temperat