8 DEPARTMENT BULLETIN 1425, U. 8. DEPT. OF AGRICULTURE 
signed to aid this natural movement, permitting as far as possible 
an unobstructed and continuous downward flow of air. To obtain 
benefits from vertical circulation, it must be positive, and not only 
at a single point but throughout the pile from one side to the other. 
This makes it essential that vertical air channels be ample and well 
distributed. 
This natural downward movement of cool, moist air in a lumber 
pile results, however, in stagnation and slow drying in the lower 
section unless proper means are provided to insure the removal of 
such air. Therefore, horizontal circulation, particularly in the lower 
portion of the pile and beneath it, is a necessary adjunct to vertical 
circulation. If adequate means for circulation both in the yard and 
in and under the pile are provided, the air cooled and laden with 
&0 
woh FILE DESCRIPTION 
STOCKS NE NTE N02 CUVION HESTERN HHITE PINE 
BOX’ TVPE PILES 
16 FEET SQUARE -110 COURSES 
60 —_ I XF CROSSLRS 
Wy 2° SPACING BGLIMWELN BOARLS 
Moisture content, per cent 
8 S 3 
LN} 
Ss 
10 

oO 
43 20 27)\ 3 /0 (7 24) 3 i V22, 239 iS 12 19 26)\ 3 70 17 24 FW\\P 
DEC. 
AUG. SEPT. OCT. NOK JAN. 
Fic. 1.—Comparative rate of drying in different parts of typical lumber pile 
moisture by evaporation is replaced by warmer and drier air from 
the outside. This movement toward the outside of the pile is made 
possible by wind currents and to a lesser degree by the natural out- 
ward flow in the lower portion of the pile caused by the pressure of 
the downward movement. 
There is much misconception of the nature of air movement in a 
lumber pile. If the natural tendency of the moist air to drop toward 
the bottom of the pile is not adequately provided for, drying in the 
lower part of the pile will lag behind that above, and serious drying 
troubles are almost certain to develop. The average drying time will 
be lengthened, a portion of the stock may never reach a thoroughly 
air-dry condition, and in pine lumber the liability to stain develop- 
ment will be increased. ‘This lag in drying is well illustrated in 
Figure 1, which represents actual drying conditions in different parts 
of a typical lumber pile. 

