SPECIFIC WEIGHT. 58 



from which that - most intrusive factor water has been 

 eliminated. 



If dry or green wood is placed in water, it at once absorbs 

 more water, till finally all the air-spaces in the wood are full. 

 Its weight then is that of saturated wood, which has always 

 a higher sp. weight than water (100), but lower than 

 that of the cell-walls (156). Saturated wood always sinks, 

 and wood that has been floated too long approaches in weight 

 that of saturated wood. As water is a possible factor in 

 nearly all wood industries, air-dry wood is always in demand, 

 though it is well known that much unseasoned wood is 

 used fraudulently. Even wood that has become seasoned 

 after being kept for years in a dry place is a material contain- 

 ing a variable amount of water, for wood is hygroscopic, and 

 its degree of wetness varies with the moisture of the atmo- 

 sphere. 



Air-dry wood when utilized varies in weight 



(1) With the relative atmospheric humidity ; 



(2) With the age of the tree. 



In 1861 Konig stated that the wood of all trees becomes 

 lighter as they become older, and his statement has been con- 

 firmed by more recent investigations. The younger a tree and 

 the shorter the felling rotation owing to a favourable soil and 

 a warm locality, the heavier is the wood, but Mayr has 

 often (<>p. cit.} remarked on the small importance attached in 

 forestry to the sp. weight of wood. 



(3) According to the parts of a tree. 



Roots have the lightest wood, and the wood of the upper 

 parts of roots is lighter than that which lies below, while the 

 thinner the roots the lighter they are. Then comes the bole, 

 the western side of it being lighter than its eastern part. 

 Woodmen term the eastern side of a tree its hard side, for 

 they know this fact by experience. Wood from the crown is 

 somewhat heavier than wood from the bole, but heavier and 

 harder wood is on the eastern side of the stump ; branch- 

 wood is still heavier and harder, especially on the under-side 

 of branches. 



