The horizontal line then reads 6 per
cent relative humidity. The same operation applies to
reductions in temperature. In the above example what is the
humidity at 60 deg.? Following parallel to the same curve in the
opposite direction until it intersects the 60 deg. ordinate
gives 90 per cent; at 57 deg. it becomes 100 per cent, reaching
the dew-point.

EXAMPLE 6. To find the amount of condensation produced by
lowering the temperature:

Example: At 150 deg. the wet bulb reads 132 deg.. How much water
would be condensed if the temperature were lowered to 70 deg.?
The intersection of the hygrometer curve for 18 deg. (150 deg.-132 deg.)
with temperature line for 150 deg. shows a relative humidity of
60 per cent. The vapor-pressure curve (concave) followed up
to the 100 per cent relative humidity line shows 45 grains
per cubic foot at the dew-point, which corresponds to a
temperature of 130 deg.. At 70 deg. it is seen that the air can
contain but 8 grains per cubic foot (saturation).
Consequently, there will be condensed 45 minus 8, or 37
grains per cubic foot of space measured at the dew-point.

EXAMPLE 7. To find the amount of water required to produce
saturation by a given rise in temperature:

Example: Take the values given in example 5. The air at the
dew-point contains slightly over 5 grains per cubic foot. At
150 deg. it is capable of containing 73 grains per cubic foot.
Consequently, 73-5=68 grains of water which can be
evaporated per cubic foot of space at the dew-point when the
temperature is raised to 150 deg.. But the latent heat necessary
to produce evaporation must be supplied in addition to the
heat required to raise the air to 150 deg..

EXAMPLE 8. To find the amount of water evaporated during a
given change of temperature and humidity:

Example: At 70 deg. suppose the humidity is found to be 64 per
cent and at 150 deg. it is found to be 60 per cent. How much
water has been evaporated per cubic foot of space? At 70 deg.
temperature and 64 per cent humidity there are 5 grains of
water present per cubic foot at the dew-point (example 2).
At 150 deg. and 60 per cent humidity there are 45 grains
present. Therefore, 45-5=40 grains of water which have been
evaporated per cubic foot of space, figuring all volumes a