KELATIOXS OF WOOD TO WATER. 



tially as radially, and that experience shows radial shrinkage to 



be 4 per cent, and tangential, 8 per cent. Thns in the case with 



planks, the central plank a b (fig. 5), falls almost in the radial 



direction, whilst the side-planks 



c d, are more tangential and 



therefore shrink much more than 



a h* A floor made of planks 



like c d, which are not tlioroughly 



seasoned, will soon show wide 



gaps between the planks. 



(b) Cracks in Dried Wood. — If 

 wood were a homogeneous sub- 

 stance, and its shrinkage uniform 

 in all directions, only a reduction 

 of volume would follow. As, 

 however, wood shrinks unequally 

 in different directions, and varies in structure in its different 

 parts, the amount of shrinkage is quite irregular and the 

 wood becomes distorted when it warps, and thus cracks and 

 crevices appear in round wood. As shrinkage is greatest 

 tangentially these cracks are chiefly radial, which is also the 

 easiest direction in which wood splits, and this fact increases its 

 tendency to crack radially. 



The more rapidly a wood shrinks the greater is its tendency 

 to crack. AYood felled during summer therefore cracks more 

 than winter-felled wood, and completely peeled wood cracks more 

 freely than wood on which strips of bark still remain, as is the 

 case with wood barked during winter. The greater the amount 

 of shrinkage of which a wood is susceptible, the more exposed 

 it is to crack ; thus, large pieces crack more than smaller ones, 

 especially large transverse sections of wood and barked round 

 logs, in which wide cracks are formed. 



Split and quartered beams crack much les« ; still less, broad 

 beams, planks and scantling, in which cracks occur only at the 

 ends ; least of all, veneer, which cabinet-makers therefore prefer 

 to be as fine as possible. 



* [Planks for flooring should be laid with the inner layers of wood against the 

 beams which support them, as when laid otherwise, the central part of the plank 

 is liable to shell-out and impair the evenness of the surface. (Laslett's Timber 

 and Timber Trees.)— Tu. 



