Woods and Their Properties 49 



contains. When a piece of wood is left in water for a 

 long time, the water gradually finds its way into the 

 vessels and fibers, driving out the air. Then the wood 

 becomes " water-logged " and sinks. In green wood the 

 vessels of the sapwood are filled with water, and a piece 

 of green oak will sink in water. Some dense tropical 

 woods will sink even when well seasoned, but all the 

 timber produced in the United States north of Florida 

 will float after it has been dried. Have you in your 

 collection of woods any kinds that will sink in water? 



Shrinking, warping, and checking of woods. As 

 wood dries, it shrinks. A board 10 inches wide sawed 

 from a recently felled cottonwood tree will lose half 

 an inch of its width after drying in the open air. In soft 

 pine, spruce, cedar, and cypress, the shrinkage is hardly 

 one third of an inch in a lo-inch board ; in hickory and 

 young red oak it amounts to nearly i inch in 10. 

 When dried in a kiln, wood loses more water and shrinks 

 still more than air-dried wood. If furniture were made 

 of green boards fitted together, what effect would the 

 drying have? In general, the heavier a wood is the 

 more it shrinks when dried. 



Swelling is the reverse of shrinking. It is due to 

 thickening of the walls of the wood fibers and vessels 

 by absorption of water. This causes a board to become 

 wider and thicker. You have noticed the effect of this 

 on doors. If a door fits closely all around when it is 

 dry, it may stick at the top or bottom or at the sides in 

 damp weather. 



Checking is the forming of cracks in a piece of timber, 

 due largely to shrinking and swelling of the wood. 



