TECHNICAL QUALITIES OF THE TREES 



105 



II. Hardness. By hardness is understood the resistance of the fibre to axe and saw worked vertically 

 to the fibre. 



Factors of hardness are:- 



(a) Density; wide rings in oak and narrow rings in pine increase the hardness; 



(b) Incrustation; heartwood is harder than sapwood; 



(c) Moisture contents; dry wood is, on the whole, harder than green wood. With some broad- 

 leafed species of loose tissue (willows and cottonwoods), however, moist wood is tougher and 

 therefore harder as well; 



(d) Frost, which increases hardness. 



SCHEDULE OF HARDNESS 



III. Cleavability or fissibility. Cleavability is the resistance of fibre to axe, saw and wedge, worked 

 lengthwise in the direction of the fibre. Radial cleavage is usually by 50 to 100 per cent easier than tangential 

 cleavage (except in black gum, dogwood, and bald cypress). 



Factors of cleavability are:- 



(a) A straight, long, elastic fibre; 



(b) Heavy and high medullary rays; 



(c) Straightness of growth; 



(d) Branchiness; 



(e) Moisture (very green and very dry wood splits best); 



(f) Frost (reduces the cleavability); 



(g) Hardness and softness (extremely hard and extremely soft wood splits badly; this rule holds 

 good only in hardwoods). 



SCHEDULE OF CLEAVABILITY 



Medium to split 



Oak, Ash Birch 



Larch Cottonwood 



Hickory Linden 



Maple Yellow poplar 



IV. Pliability. Under pliability is combined "flexibility" and "elasticity." 



(a) FLEXIBILITY:- Wood which is easily bent without breaking is flexile (flexible). Softwoods are 

 naturally less flexile than hardwoods. 

 Flexibility depends on : - 



1. Toughness and cohesive force of fibre. 



2. Moisture, which increases it very much. 



3. Heat, which increases it. 



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