50 TECHNICAL PROPERTIES OF WOOD. 



are important to the forester. The subject will be cousidered 

 below as rejjards the drying or seasoning of wood, its power of 

 absorbing water, und the changes of shape in wood owing to 

 these two processes. 



1. Srasoniit;! of Wood. 



Wood must generally become air-dry before it can bo utilized. 

 The quantity of water which wood contains has been already 

 shown to vary according to the season of the year, the part of the 

 tree from which the wood has been taken, and the species of 

 tree. Wood loses its water chiefly by evaporation, the fsictors 

 influencing the degree of dryness which it can attain being 

 its anatomical structure, its contained resin, the amount of 

 surface of the wood exposed to the air and the degree of dryness 

 of the air. 



(a) Anatomical Structure. — All wood parts with its water most 

 readily along the grain, and most slowly parallel to the medullary 

 rays ; hence transverse sections of wood become dry soonest. 

 Porous wood dries sooner than close-grained wood. 



The rate of drying for the diflerent species of trees is not yet 

 satisfactorily established, but it appears that rapidity of drying 

 is not directly att'ected by the anatomical structure of wood, and 

 that for practical purposes the following statements hold good : — 



Sapwood dries easier than heartwood or semi-hcartwood, at 

 least as long as the log is in the round. 



Logs of silv6i--fir, under similar conditions, dry more slowly 

 than spruce logs of like dimensions, and beechwood dries more 

 quickly and thoi'oughly than elmwood. 



Hartig gives the following percentages, by volume, of water in 

 green wood of the following species : — 



