KILX DEYING HANDBOOK. 
27 
cut up several stress sections with varying numbers of slots. The 
direction in which the individual prongs turn and the relative lengths 
of the various prongs tell the story. If the outer prongs turn out, 
it is an indication of tension in the outer layers. If they turn in, 
there is compression in the outer layers. Cutting the section into 
prongs disturbs the balanced state and allows each prong or group 
of layers to make a new adjustment within itself. The compression 
side of each prong will immediately stretch and the tension side 
will contract, just as a spring under tension or compression will 
return to its original length when the deforming pressure is re- 
moved. In doing this the prong will be bent, the amount of the 
bend depending upon the thickness of the prong and upon the 
amount of stress originally present. The side which was originally 
in tension will become the concave side and the one originally in 
compression will become the convex one. The amount and distribu- 
tion of the drying stresses can be judged by the relative bending 
Fig. 5. — Typical stress sections. 1 represents a green board : 2 shows tension in the 
surface, typical of early stages in the drying ; 3 shows drying has progressed farther 
and the shrinkage of the interior has balanced that of the surface ; 4 shows typical 
casehardening ; 5 reveals slight reversal of stresses by treatment to relieve case- 
hardening ; 6 is the finished board free from stress. The changes in the length of 
the prongs bave been exaggerated slightly for emphasis. 
of the several prongs on each side, especially when the prongs all 
turn outward. When they turn inward the relative bending can 
not be judged so well, since they interfere with each other. In such 
cases it may be advantageous to cut the section into a larger number 
of prongs, thus reducing the amount of curve in each prong and 
permitting comparison of the relative lengths of the individual 
prongs. If they are thin enough there will be but little difference 
in stress between the two sides of each prong, and the state of stress 
will be indicated by the change in its length. All prongs in tension 
at the time of cutting will shorten, and those in compression will 
relieve themselves by lengthening. The top ends of all the prongs 
will form a curve, and the shape of this curve will indicate clearly 
the state of stress. If it is convex or high in the center, it indicates 
tension in the outer layers and compression in the core. If low in 
the center, the reverse is indicated. 
So far only general indications at the time of sawing the sections 
have been considered. If they be now set aside in a warm place 
they will soon dry down to an approximately uniform moisture con- 
tent, the actual amount depending upon the temperature and humid- 
