■42 TECHNICAL PEOPERTIKS OF \VOOD. 



fissibility, but it should be noted that this is less dependent on 

 the species than on the individual growth of trees : — 



Very easy to split : Spruce, silver-fir, Weymouth-pine, Scotch 

 pine, larch, alder. 



Easy to spHt : Oaks, sweet-chestnut, beech, ash, Cembran pine. 



DiflBcult to split : Common maple, hornbeam, elms, sallow, 

 birch, sycamore, poplar, mountain-pine, lime, black pine. 



Section YII. — Pliability. 

 1. General Account. 



Pliability is that property of material owing to which it maj' 

 undergo changes of shape without fracture. 



\^ ood possesses this property in a high degree, and it gives 

 rise to many wood-industries. In order that wood may be 

 pliable, a certain power of extension must be possessed by its 

 fibres, which is chiefly the case iji long and straight-fibred wood, 

 but not in wood Avith short or crooked fibres. The presence of 

 knots, wounds which have been occluded, burrs or wavy wood, 

 defects due to decay, &c., may nullify the pliability of a wood. 

 Woods which are not pliable are termed brittle. 



AVood which is pliable may be either elastic, or merely 

 flexible. AVhcn a pliable piece of wood has been subjected 

 to a force — for instance, has been bent — and resumes its 

 former shape, as soon as that force ceases to act, it is said 

 to be elastic. The action of the force, however, must not be 

 great enough to exceed the limit of elasticity, for then the 

 form of the piece of wood will be permanently changed, and 

 the other kind of pliability arises termed flexibility. If the 

 limit of flexibilit}' be exceeded for any piece of wood, a fracture 

 will ensue. Every wood possesses both elasticity and flexibility, 

 but the latter property generally exceeds the former ; a wood 

 ma}', therefore, be termed flexible when its elasticity is almost 

 insignificant, and elastic, when the limits of its elasticity nearly 

 approach those of its flexibility. 



The pliability of a piece of wood is not constant under 

 different circumstances, but may be favoured under certain 

 conditions in difl'erent degrees. The most important of these 

 is the degree of moisture in the wood. Dryness makes a 



