74 I'KOl'KKTIKS OK WOOD. 



out of the centre of a tree, it can be prevented from cracking 

 by driving in an S-shaped thin steel clamp, which holds the 

 wood together. 



The various methods of seasoning wood, injecting it with 



Fig. 35. (After Boppe.) Fig. 36. (After Boppe.) 



preservative materials and otherwise improving its quality, 

 are dealt with in a subsequent chapter (p. 502). 



Whilst in most of the industrial uses of wood rapid with- 

 drawal of water is required, there are some in which wood 

 should be rendered as watertight as possible. This is specially 



Fig. 37. (After Boppe.) l-'ig. 3S. (Aftor Boppe.) 



the case with staves for casks to contain liquids, that should 

 part with as little of their contents as possible. The direction 

 perpendicular to the medullary rays is that tli rough which 

 liquids pass least freely. Oak staves are split along the 

 radius of the stem, and the medullary rays arc parallel to 

 their longer surfaces, so that they are very impervious to 

 Liquids contained in thu casks. Beechwood is very permeable, 



