KILN DRYING HANDBOOK. 55 
FLAT PILING. 
Cross piling (PL X) is most suitable for kilns with longitudinal 
circulation, and end piling for kilns with cross circulation. This 
is determined by the arrangement of the stickers. In cross piling 
they extend lengthwise of the kiln, thus aiding longitudinal circula- 
tion. In the same way, end piling (PL XI) favors cross circulation. 
A large number of kilns are, nevertheless, being operated contrary 
to these principles, particularly cross-circulation ventilated com- 
partment kilns with cross piling. These methods are not absolutely 
essential, but better results are obtained by following them. 
The spacing of the boards in the layer has an important bearing 
upon circulation, especially in ventilated kilns, and manufacturers of 
this type frequently recommend a wide spacing. This assists in 
permitting a freer circulation, especially in cross- circulation kilns 
with cross piling. The amount of space to leave in any particular 
case is a matter of judgment and depends upon the circulation. 
Ordinarily' 1-inch spaces do very well for almost all kinds of stock 
when there is ample circulation; when the circulation is poor, and 
uneven drying results, the spaces may be enlarged to 3 or 4 inches 
for wide boards. For narrow boards there is less need for widening 
the spaces. 
The thickness of the stickers may vary with local conditions ; how- 
ever, they should all be straight and of uniform thickness. Seven- 
eighths-inch stickers are commonly used for most classes of stock, 
except in edge-stacking, when the requirements of the stacking 
machine may determine the thickness. If stickers are made about 
one and one-half times as wide as they are thick, they will lie flat 
and not tend to roll when the boards are laid on them. 
The spacing between rows of stickers should be reasonably close. 
Four feet should be the maximum distance for most hardwoods and 
6 feet for easily dried softwoods. If the boards show a tendency 
to twist and warp, a closer spacing should be used, and great care 
must be exercised in the actual piling. To obtain best results, mate- 
rial dried at one time should be of thesame species and thickness 
and with moisture content as nearly uniform as circumstances per- 
mit. The supports for the lumber should be firm and even and 
arranged with one under each row of stickers. These rows should 
be kept perfectly vertical; otherwise there will be a tendency to 
warp the boards. The ideal is to have boards of only one length 
in each pile ; but where this is impossible the piles should be made 
long enough to cut down the number of projecting ends, and the 
short boards should be brought flush alternately at. both ends of 
the pile. In the case of cross-piled progressive kilns it is especially 
desirable that the piles should take up the full width of the kiln, 
so that there may be as little opportunity as possible for the short 
circuiting of the circulation around the lumber. For the same rea- 
son, the piles should extend the full length of the trucks. 
VERTICAL PILING. 
Under certain conditions vertical or edge piling is considered to 
be somewhat cheaper than flat piling, and is being used by a number 
of big mills in the softwood regions. (See PL XII.) Several dif- 
