THK FAKM HOLDING. L83 



The Practical Use of Timbers.* 



Although the following notes refer more particularly to western timbers, 

 the principles enunciated apply nevertheless equally to timbers from other 

 districts. 



All trees that provide us with timber are outward growing trees — that is 

 to say, they increase in girth by developing successive layers round the 

 trunk next to the bark. Each year generally adds one of the layers or rings, 

 and consequently they are called " annual rings." In addition to the 

 annual rings, trees have medullary rays, which are thin and generally broken 

 lines, radiating from the centre, or pith, to the bark, and vice versa. These 

 rays are not very apparent in some trees, but in dry cypress pine they are 

 easily seen. Cabinetmakers call these rays the " silver grain." 



The trunks and branches of trees consist of two kinds of wood — the hard, 

 dead heartwood, or duramen, and the soft sapwood, or alburnum. The latter 

 is much lighter in colour than the former. The bark consists of an outer 

 and inner layer. 



Heartwood is much stronger and more durable than sapwood, and the 

 outer portion of the heartwood is stronger than that near the centre, or pith, 

 more particularly if the wood is " pipy," because then it has been subjected 

 to decay and is very brittle. 



Old wood is stronger, though lighter, than young wood. The strength of 

 timber is influenced by the quality of soil on which it grows. Evennesa of 

 grain in the annual rings denotes strong wood. 



By strength of wood we mean the resistance it offers to force acting at 

 right angles to its grain. This is called " transverse strength." 



It must be patent to all that where the strongest parts of timber are 

 preserved the structure built would have a much longer life than where the 

 weaker tissues are made to stand the strain. 



Cypress pine is v^ry fissile, but 

 will stand very little transverse 

 strain ; and therefore, when using 

 it, knowing of its weakness, workers 

 should aim at conserving the 

 strength in every possible way. 

 Anyone familiar with pine used in 

 stockyards knows that the rails 

 most frequently break at or near 

 the middle and at the tenon, which 

 fits the mortise of the post. When 

 pine saplings are used as rails the 

 posts should be close together to Fig. 25. 



lessen the strain when stock bump 



against the rails. Tattle or nothing but the bark should be removed from 

 young pine in making a tenon, because the young wood is much weaker than 

 that from mature tre^s, and by removing the harder heartwood of an already 

 weak timber the strength and durability are very materially lessened. 



* C. J. Woollett, Stock Inspector, Tamworth. 



