KILN DRYING HANDBOOK. 
43 
record is the drykig of 1 by 4 inch Douglas fir flooring strips in 24 
hours ; the slowest, the drying of some southern oak wagon bolsters, 
which were in the kiln almost a year, and then were not drier than 15 
per cent. 
The average periods required to dry several common hardwoods 
are presented in Table 14. While these drying rates can readily be 
secured in kilns with high velocity of circulation, it does not neces- 
sarily follow that they can be duplicated under all conditions. 
Table 14. — Average drying time for 1-inch stock, green from the saw to 5 per 
cent moisture. 
Species. 
Yellow birch. 
Red gum 
Sugar maple. 
Mahogany... 
Black walnut 
Original 
moisture 
content. 
Per cent. 
80 
100 
80 
80 
Drying 
time. 
Days. I 
21 
26 
23 
22 
30 
Original 
moisture 
content. 
Oak, red and white: 1 
Northern highland stock. . . 
Northern lowland stock. .. . 
Southern highland stock. . . 
Southern lowland stock 
Per cent. 
SO 
\ 80 
80 
Drying 
time. 
Days. 
1 Plain sawed only; quartered takes about one-third longer with the same schedule. 
Maple last blocks can be dried in about 60 days, and walnut gun- 
stock blanks in about the same length of time. Heavy oak wagon 
stock takes from one and one-half to two months per inch of thick- 
ness to dry down to 15 per cent moisture. The common diying times 
for 1-inch softwoods, such as Douglas fir, the southern yellow pines, 
and the white pines, run from two to four days, there being excep- 
tions in both directions. Quartered stock may usually take a higher 
schedule, and thus make up for some of its natural slowness in dry- 
ing. It has already been mentioned that certain woods, like red- 
wood, western red cedar, and cypress, are subject to collapse at high 
moisture and temperatures. The hardwoods, as a rule, are more 
plastic when hot and moist than the conifers, and in consequence are 
more easily bent. This fact is taken advantage of in the drying of 
red gum, for instance, which has a natural tendency to warp, but 
seems plastic enough at high temperatures to overcome this tendency, 
drying with but little trouble if properly " stickered." 
FINAL MOISTURE CONTENT. 
As has been stated, the final moisture content should be slightly 
lower than that which the finished product would naturally have 
after it had been in service for some time. The first thing to con- 
sider, therefore, is the ultimate use to which the finished product is 
to be put and the climatic conditions at the point of use. Whether 
the product is for use indoors or outdoors also is a determining 
factor. Sometimes it is desired to have the stock swell after it is 
put in service, and in these cases it is dried lower than it otherwise 
would be. 
A study of the weather reports for various parts of the country 
shows that the average atmospheric temperature and humidity con- 
ditions vary greatly in the different regions and that they also have 
important seasonal variations in each place. The relative humidities 
for a number of cities are o^iven in Table 15 to show these variations. 
