one reason why the natural draft, or so-called moist-air kiln was
developed.

The advent of the moist-air kiln served as an education to kiln
designers and manufacturers, in that it has shown conclusively the
value of a proper degree of humidity in the receiving end of any
progressive dry kiln, and it has been of special benefit also in that
it gave the manufacturers of blower kilns an idea as to how to improve
the design of their type of kiln to overcome the difficulty referred
to in the old style blower kilns. This has now been remedied, and in a
decidedly simple manner, as is usually the case with all things that
possess merit.

It was found that by returning from one third to one half of the moist
air _after_ having passed through the kiln back to the fan room and by
mixing it with the fresh and more or less dry air going into the
drying room, that the humidity could be kept under convenient control.

The amount of air that can be returned from a kiln of this class
depends upon three things: (1) The condition of the material when
entering the drying room; (2) the rapidity with which the material is
to be dried; and (3) the condition of the outside atmosphere. In the
winter season it will be found that a larger proportion of air may be
returned to the drying room than in summer, as the air during the
winter season contains considerably less moisture and as a consequence
is much drier. This is rather a fortunate coincidence, as, when the
kiln is being operated in this manner, it will be much more economical
in its steam consumption.

In the summer season, when the outside atmosphere is saturated to a
much greater extent, it will be found that it is not possible to
return as great a quantity of air to the drying room, although there
have been instances of kilns of this class, which in operation have
had all the air returned and found to give satisfactory results. This
is an unusual condition, however, and can only be accounted for by
some special or peculiar condition surrounding the installation.

In some instances, the desired amount of humidity in a blower type of
kiln is obtained by the addition of a steam spray in the receiving end
of the kiln, much in the same manner as that used in the moist-air
kilns. This method is not as economical as returning the
moisture-laden air from the drying room as explained in the preceding
paragraph.

With the positive circulation that may be obtained in a blower kiln,
an