STKKNGTH. 95 



Contents of resin has a slightly reducing influence on 



strength, for very resinous wood is hrittle and weak. 



The employment of wood in high air-temperatures is 

 conducive to strength, because the wood becomes dry. 

 Temperatures below /ero weaken the strength of wood con- 

 siderably ; when wet wood is frozen it becomes brittle and 

 approaches ice in its strength. 



That humidity weakens wood lias been already slated, and 

 the experiments of Schwappach and Rudeloff confirm this. 



To the season of felling an influence on the strength of wood 

 has been assigned ; wood felled in Dei-ember is said to be the 

 strongest. Anyone, however, who has undertaken to test this 

 and who knows the numerous sources of error that arise in 

 such investigations, can only warn practical men to beware of 

 such a statement. 



K very disease in wood reduces its strength considerably. 



No list of woods ranged in the order of their elasticity can 

 be drawn up without a suspicion of prejudice, especially with 

 regard to the method adopted for testing them, and also 

 because individual trees of the same species vary greatly in 

 strength, even when taken from the same crop. Soil, climate, 

 the method of rearing trees, etc., also cause great differences 

 in strength. Sometimes oakwood, sometimes ashwood, is 

 chosen as the strongest and most clastic material. Actual 

 3 have placed conifers above broadleaved trees in strength. 

 Scots pinewood that is so hrittle when exposed to snow has 

 been placed first among elastic woods. Tests have shown 

 that beechwood possesses considerable strength, while in 

 practice, beech, birch and alder are reckoned as woods with 

 the least transverse strength, but with considerable resistance 

 to crushing. There is no doubt that certain foreign woods are 

 more elastic than our indigenous woods, <'.</., hickory (Himi-ia 

 allta), teak, sundri (Ileriticra), lancewood (l)u.ynctia) and 

 bamboos. 



4. Toniihncxs <>r Pliability. 



A wood is said to be tough or pliable when it can be bent 

 beyond the limits of perfect elasticity and is then susceptible 

 of permanent deformation without breaking. The greater the 

 interval between its limits of elasticity and rupture the 



