14 BULLETIN 143*7, U. S. DEPARTMENT OF AGRICULTURE 
Table 4. — Schedules suggested for drying red alder 1 
Schedule I 
Schedule II 
Moisture content (per cent) 
Dry- 
bulb 
tempera- 
ture 
Wet- 
bulb 
tempera- 
ture 
Relative 
humid- 
ity 
Dry- 
bulb 
tempera- 
ture 
Wet- 
bulb 
tempera- 
ture 
Relative 
humid- 
ity 
Initial ' 
°F. 
140 
145 
150 
155 
160 
165 
170 
°F. 
132 
135 
137 
136 
135 
127 
116 
Per cent 
79 
75 
70 
59 
50 
34 
20 
°F. 
135 
140 
145 
150 
155 
160 
165 
°F. 
128 
130 
133 
132 
131 
124 
112 
Per cent 
81 
40. 
75 
30 
71 
25__ . 
60 
20 - 
51 
15. 
35 
10 to final. „ 
20 
1 Schedule I is for basswood and yellow poplar; Schedule II is for cottonwood. 
Table 4 gives drying schedules recommended by the Forest Prod- 
ucts Laboratory: Schedule I for basswood and yellow poplar, and 
Schedule II for cottonwood. One or the other of these schedules 
should give satisfactory results with red alder. It should be borne 
in mind, however, that the tendency of different woods to check is 
an individual characteristic, at least to a large extent, and that 
checking does not follow the relative density or shrinkage of the 
wood. For example, maple checks more easily than birch, although 
both are of about the same density. Therefore, while the drying 
schedules for yellow poplar and basswood should prove satisfac- 
tory for red alder, it is recommended that higher humidities be 
used if excessive checking is encountered. 
These schedules are intended to be applied by means of kiln sam- 
ples, the changes in temperature and humidity being made as the 
moisture content of the samples passes the percentages indicated. It 
should be possible to obtain good results with faster drying, but the 
use of schedules more severe than these will require most careful 
judgment on the part of the kiln operator. 
Preliminary steaming is recommended for the relief of air-drying 
stresses in partly dry stock. The temperatures may be from 10° to 
15° above the starting point of the schedule. One-inch stock with 
a moisture content of less than 18 per cent should be subjected to a 
humidity of 70 or 85 per cent for a period of 24 to 30 hours, de- 
pending on the severity of the stresses present in the stock. Pre- 
liminary steaming is also recommended for green stock, not to re- 
lieve stresses, but as a convenient means of bringing the stock up to 
drying temperature. It is not necessary to steam green stock so long 
as partly seasoned stock, one hour per inch of thickness being suf- 
ficient. 
The schedules are equally applicable to green and to partially dried 
stock. The operator should start at the point of the schedule cor- 
responding to moisture content, disregarding everything above that 
point, just as if the previous drying had been done in the kiln in 
accordance with the upper part of the schedule. 5 
5 Those interested in a discussion of the fundamental facts about the drying of wood 
are referred to the following bulletin : Thelen, R., Kiln Drying Handbook. U. S. Dept. 
Agr. Bui. 1136, 64 pp., illus, 1923. The major portion of the bulletin deals with the 
kiln drying of lumber, but there are also included specific suggestions concerning the 
drying of other forms of wood. The general information is applicable to all kinds of 
drying. 
