FOREST SERVICE WATER SPRAY DRY KILN. 7 
long in the kiln as 1-inch stock. Quarter-sawed stock requires from 
25 to 35 per cent longer to dry than plain-sawed. Stock which 
needs to be dried only to 10 to 14 per cent, such as vehicle material, 
etc., will require one-fourth to one- third less time than that given 
in the table. More rapid drying is possible, but not without injury 
of some kind to the wood. The drying time as here given is not 
limited by the type of dry kiln but by the physical behavior of the 
wood itself. 
Table 1. — Approximate drying period for 1-inch green and partially air-dry stock to 6 
per cent moisture content, under mild conditions in any hind of kiln tuhere circulation is 
adequate and temperature and humidity are suitably controlled. 
Dryin 
j time. 
Partially 
air-drv— 
25 per 
Species. 
Green 
cent 
moisture 
from the 
(based 
saw. 
on the 
dry 
weight 
of the 
wood). 
HAKDWOODS. 
Bays. 
Days. 
Swamp oak 
45 to 50 
20 to 25 
30 to 40 
22 to 30 
17 to 20 
Walnut, cherry 
13 to 15 
Mahogany, beech 
16 to 22 
9 to 12 
Gum, tupelo 
20 to 26 
10 to 14 
Birch, ash, sycamore 
15 to 21 
9 to 12 
8 to 10 
4 to 6 
17 to 23 
9 to 13 
CONIFERS. 
Western larch 
9 to 12 
10 to 18 
4 to 6 
4 to 6 
Cypress, redwood 
6 to 8 
3 to 4 
PILING. 
Even circulation is of prime importance, and the manner of piling 
has a direct influence on the character of the circulation. The 
lumber must be so piled that the air can pass through the load with 
the least resistance. 
In the water-spray kiln the stock should be piled lengthwise of the 
kiln on stickers which run across the pile in the direction of the air 
currents. The stickers should not be less than 1 inch thick for stock 
up to If inches thick and li inches thick for stock 2 inches and over. 
There is a natural tendency for the air passing through the lumber 
to descend on account of the cooling effect of the lumber. The pile 
can be constructed to take advantage of this natural circulation, as 
by flat open piling or slant piling. In flat open piling the boards 
are separated horizontally about the width of the stickers, which 
permits a slight downward or diagonal circulation across the pile. 
The slant piling allows a more direct path for the moving air than 
