106 TECHNICAL QUALITIES OF THE TREES 



4. Age of tree, inasmuch as young shoots are tougher than old wood. 



5. Impregnation, natural as well as artificial, checks flexibility. Heartwood is less flexible than sapwood. 



6. Root wood is more flexible than stem wood. 



REMARK: -Heat and moisture as a means to increase flexibility are applied in the following industries: — 

 Cooperage, for bending staves and hoop poles; carriage works, for bending poles, shafts, felloes, top 

 frames, seats, &c. ; furniture works, for bent wood furniture; ship building; veneer peeling; basket work; 

 manufacture of musical instruments. 



(b) Elasticity is the force with which an object resumes its old shape when released after being 

 pressed out of shape. Qualities which increase flexibility frequently reduce elasticity, and vice-versa. 

 The factors of elasticity are:- 



1. Length and straightness of fibre. 



2. Width of rings in conifers. 



3. Moisture (which reduces elasticity). 



4. Frost (which destroys elasticity). 



5. Excessive contents of rosin (which increase elasticity). 



SCHEDULE OF ELASTICITY 

 Very elastic are Less elastic are 



Yew, Larch Red cedar Cottonwood Walnut 



Fir, Locust Lancewood Birch Yellow pine 



Chestnut Spruce Maple Yellow poplar 



Hickory White pine Elm Beech 



Osage orange Ash, Oak Alder 

 V. Strength. 



(a) Strength IS resistance TO: -Tension, to which timber is usually not exposed; compression 

 (arches, pillars, scantling); torsion (shafts, screws, axles); shearing (railroad ties); transverse straining 

 (beams, girders, joists). 



(b) Factors of strength are:- 



1. Specific gravity. 



2. Soundness of tissue. 



3. Freedom from branches. 



4. The locality where the timber was grown. 



5. The quality of the soil producing it: whether good, bad, or indifferent. 



6. The sylvicultural form under which the timber was produced. 



7. The rate of growth. 



8. The age of the tree. 



9. The season of the year at which the tree was cut. 



10. The method of storing and of drying the timber since it was cut. 



11. The position of the test piece within the log producing it. 



Timber, like any other material, should never be loaded to over one fourth of its indicated strength. 



Transverse strength is always proportioned to length of girder; to width of girder; and to the square 

 of the depth of girder. It is the quality of timber which is most valuable in material used for building 

 and construction. 



The "International Association for Testing Raw Materials" has passed a resolution, at a meeting in 

 Copenhagen in 1896, with reference to the unification of the methods and sizes used in timber tests. The 

 resolution in question covers the following points notably :- 



1. The strength of the timber shall be tried by pressing, by bending, by shearing, by tearing, 

 and by cleavage. 



2. The size of the test pieces and their position in the log from which they are obtained is 

 stipulated for each test series. 



