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KILN DRYING HANDBOOK 69 
Storerooms need only a little heat to make them dry enough for 
most dry-wood storage. All that is required is sufficient rise in tem- 
perature to bring the humidity down to 25 to 40 per cent, and ordi- 
narily a temperature of about 30° IF’. above the outside atmosphere 
is enough. Assume, for instance, that it is desired to store flooring 
stock at 6 per cent moisture content and that the outside temperature 
and humidity are, respectively, 35° F. and 90 per cent. At 65° to 
70° F., a humidity of 28 per cent corresponds to a moisture content 
of 6 per cent, and if the 35°-90-per-cent atmosphere is warmed to 67° 
F. its humidity will be the desired 28 per cent. (See also “ Reliev- 
ing casehardening during storage ” on p. 42. 
MOISTURE CHANGE IN TRANSIT 
Studies on carload shipments of western yellow pine from the 
Inland Empire? and of Douglas fir from Oregon, all to the Chicago 
territory more than halfway across the continent, have shown that the 
moisture change in transit is neghgible when the stock is shipped in 
tight box cars. With kiln-dried boards averaging 8 per cent moisture 
content, the average change in moisture was only 0.2 per cent. Ina 
car of molding the change was 0.8 per cent. Similar data are not 
available for hardwoods, but no greater change should be expected. 
TYPES OF KILNS 
Dry kilns for wood are of many forms and of varied types, and 
accordingly they can be classified in several ways. For the purpose 
of describing both their construction and their operation they have 
been divided in this publication into two groups, namely, progres- 
sive and compartment. Progressive kilns are sometimes called 
“ continuous,” and compartment kilns are known also as “ box” and 
as “charge.” ‘The essential differences between the two types are 
the result of the methods of handling the stock through them. In 
the progressive kiln (fig. 9), a number of truck loads of lumber, 
extending through the kiln in an unbroken line and all in different 
stages of drying, make up the total charge. Comparatively small 
amounts of stock are periodically fed in at the receiving end, each 
load in effect pushing along the trucks ahead of it and at its entry 
forcing out a load occupying equal track space at the discharge end. 
The stock thus moves progressively through the kiln until it emerges, 
supposedly dry, after a specified time of continuous drying under 
the various conditions of the long kiln. In the compartment class, 
on the other hand, the kiln is loaded fully at one time, the entire 
charge remaining in place throughout the drying period. Again, in 
the progressive kiln the temperature and the humidity at any point 
are intended to remain constant, but the kiln is hotter and drier at 
the dry end than at the green end; in contrast, the temperature and 
the humidity are as nearly uniform as possible throughout the com- 
partment kiln at any given time, and, although in it these conditions 
usually are changed from time to time as the stock dries, for certain 
classes of drying they are kept constant throughout the drying 
2The wooded basin lying in northwestern Montana, Idaho north of the Salmon River, 
Washington east of the Cascade Mountains, and the northeastern tip of Oregon. 
