12 
BULLETIN 509, U. S. DEPARTMENT OF AGRICULTURE. 
conduct it back to the pump, the water being recirculated through 
the sprays. G is a pipe condenser for use toward the end of the 
drying operation. K is a baffle plate for diverting the heated air and 
at the same time shielding the under layer of boards from direct 
radiation of the steam pipes. 
The operation of the kiln is simple. The heated air rises above the 
pipes H H at the sides of the piles of lumber. As it comes in con- 
tact with the piles portions of it are cooled and pass downward and 
inward through the layers of boards into the space between the con- 
Fig. 2. — Diagrammatic section of improved dry kiln with spray chambers on sides. Double- 
truck form. 
densers G G. Here the column of cooled air descends into the spray 
flue B, where its velocity is increased by the force of the water spray. 
It then passes out from the baffle plates to the heaters and repeats the 
cycle. 
Various modifications of this arrangement may be made. For 
instance, a single-track kiln may be used. This form would be repre- 
sented by simply dividing the diagram vertically into two parts by 
extending the wall G (on the left side) upward to represent the outer 
wall, and erasing the part to the left of this line. Or, again, the 
spray chambers may be kept on the sides as shown in figure 2. The 
lumber would then slope in the opposite direction with respect to 
