228 FIRST BOOK OF FORESTRY 



If wood is sawed or split, so that it is exposed to air, this 

 water evaporates. At ordinary temperature, as in a wood 

 shed, it will dry so far that a hundred pounds of wood will 

 contain only about ten pounds of water. If we put this lumber 

 in a hot room or "dry kiln," it dries out still more. When it 

 comes out of the " dry kiln " it absorbs water again, and after 

 a few days may have as much as six pounds per hundred. 



Shrinkage. While drying, the wood shrinks, i.e., it 

 grows smaller. It shrinks about ten times as much side- 

 wise as endwise, and shrinks less radially, i.e., in the 

 direction from the pith to bark, than tangentially, so that 

 a "rift" or "quartered" board shrinks only about one 

 half to two thirds as much as a tangent board. 



When a board lies on the wet ground in the sun it dries 

 and shrinks on one side and less or not at all on the other, 

 and therefore curls or warps. 



If a peeled log or a thick board dries rapidly the outer 

 part shrinks before the inner, and thus the "jacket" is 

 too small ; it bursts, and the wood is said to " check " or 

 crack. After the inner part dries these checks close up; 

 but in larger pieces some stay open and grow larger for a 

 long time. This kind of checks is permanent and is due 

 to the greater shrinkage in the tangential direction. 



Coniferous wood shrinks less, warps and checks less than 

 hard wood, and generally heavy woods shrink more than 

 light ones. To avoid the mischief of shrinking we use 

 flooring in narrow strips, so that the change is distributed 



