60 FOREST UTILIZATION 



checks flexibility. (Heartwood less flexi- 

 ble than sap wood.) 

 6. Root wood more flexible than stem wood. 



Remarks: Heat and moisture as a means to in- 

 crease flexibility are applied in these industries : 



Cooperage; for bending staves and hoop poles. 



Carriage works ; for bending poles, shafts, felloes, 

 top frames, seats etc. 



Furniture ; bent wood furniture. 



Ship building. 



Veneer peeling. 



Basket work. 



Manufacture of musical instruments, 

 (b) Elasticity and flexibility are not always found in 

 the same piece of wood. On the contrary, quali- 

 ties which increase flexibility frequently reduce 

 elasticity, and vice versa. Elasticity is the force 

 with which an object resumes its old shape when 

 pressed out of shape and released. 



The factors of elasticity are : 



1. Long and straight fibre. 



2. Narrow rings in conifers. 



3. Dryness (moisture reduces elasticity). 



4. Frost (which destroys elasticity). 



5. Excessive contents of rosin (which in- 



creases the elasticity). 



SCHEDULE OF ELASTICITY. 



Very elastic are: Less elastic are-: 



Yew Cottonwood 



Larch Birch 



Fir Maple 



Locust Elm 



Chestnut. Alder 



Hickory Walnut 



Osage orange Yellow pine 



Red cedar . Yellow poplar 



Lancewood Beech 

 Spruce 

 White pine 

 Ash 

 Oak 



V. Strength. 



Strength is resistance to : 



(a) Tension; to which timber is usually not exposed. 



(Yoke of oxen pulling the cart by the pole.) 



(b) Compression (arches, pillars, scantling). 



(c) Torsion (shafts, screws, axles). 



(d) Shearing. 



(e) Transverse straining (beams, girders, joists). 



Factors of strength are : 



1. Specific gravity. 



2. Soundness of tissue. 



3. Freedom from branches. 



Timber, like any other material, should never be 



