28 BULLETIN 1136, U. S. DEPARTMENT OF AGRICULTURE. 
it}' of the surrounding atmosphere ; and the changes in the moisture 
content of the section will be portrayed by changes in the length 
and curvature of the individual prongs. Loss of moisture on one 
side of a thick section will usually be most plainly indicated by 
a change of shape, the prong bending toward the side that has been 
drying. If the prong be in the center and there is an equal loss of 
moisture from both sides, the only indication will be a shrinkage 
in the length. In thin sections this is apt to be the case anyway, 
because their very thinness precludes much difference in moisture 
between the two sides. Under ordinary circumstances, except after 
special treatments, the drying of stress sections will cause a con- 
traction or an inward turning, or both, to take place in all the 
prongs, the amount being proportional to the amount of moisture 
lost from each prong. The final shape of the section, then, is a 
criterion by which to judge the condition of the stock in the kiln 
after the drying has been completed. Caution must be used, how- 
ever, since the sections dry without further stress and the stock in 
the kiln probably does not. The more nearly dry the stock is when 
the stress section is cut, the more reliable an indicator will it be in 
this respect. 
Now that the meaning and function of stress sections have been 
explained, it is necessary to understand the significance of the story 
they tell and to learn how to correct matters if they are in need of 
correction. 
STRESS REMEDIES. 
RELIEF OF SURFACE TENSION, 
The first evidence of stress in green stock in the kiln is a tension 
in the outer shell. This is shown in the stress section by an outward 
turning of the prongs, and may be considered a normal condition of 
affairs, more or less unavoidable. If this tension becomes too severe, 
surface checks will result. As it is easier to watch for surface checks 
than to cut stress sections, the condition of the stock in the early part 
of the run is usually judged by the presence or absence of surface 
checks. Excessive tension in the surface and surface checks are 
caused by too steep a moisture gradient ; in other words, the moisture 
is being removed from the surface more rapidly than the rate of 
transfusion from the center to the surface. The remedy is to slow 
down the rate of evaporation by increasing the relative humidity of 
the air in the kiln. The effect of a definite increase in humidity will 
be apparent from a study of stress sections cut before and after the 
change in humidity. 
PRELIMINARY STEAMING OF AIR-DRIED STOCK. 
Air-dried or partially air-dried stock is frequently put into kilns 
for further drying. Its condition upon entering the kiln should be 
carefully determined so that suitable subsequent treatment may be 
accorded. If deep surface checks are present, the fact should be 
noted and recorded and the drying carried on with unusual care. 
Casehardening is frequently present in air-dried stock, and the sur- 
face is apt to be so dry that the transfusion of the moisture is badly 
hampered. For these reasons, and also to warm the stock through 
