108 TECHNICAL QUALITIES OF THE TREES 



(i) Shrinkage. 



1. It is least along the fibre; it is up to 5 p. c. along the radius and is up to 10 p. c. along the tangent- 



Shrinl\age of over 5 p. c. of green volume occurs in walnut, linden, beech, elm, chestnut, birch. 

 Shrinloge of 3 to 5 per cent occurs in oak, maple, sycamore, ash, Cottonwood, yellow pine 

 Shrinkage of 2 to 3 per cent occurs in spruce, larch, fir, and white pine. 

 A large percentage of rosin, narrow annual rings and light specific gravity reduce shrinkage 

 within the same species. 



2. Tests at Biltmore as to the effect of shrinkage in volume and in grade on ^ , red oak lumber 

 have shown, in the course of four months, that:- 



(aa) 10,000 feet of green firsts and seconds shrink down to 8,514 feet of dry firsts and seconds, 



plus 1.096 feet of dry common =1; 

 (bb) 10,000 feet of green common =1 shrink down to 7.499 feet of dry common ^1, plus 



2,090 feet of dry common ~2; 

 (cc) 10,000 feet of green common =2 shrink down to 9,043 feet of dry common 2, plus 



547 feet of dry common = 3. 



(i) Checking. It depends on the rapidity of the drying process; on size of piles and of piling sticks; 

 on size and dimension of object; on presence or absence of bark from logs; on homogeneity of tissue. 



Checks (so-called season checks) are often of a temporary nature, disappearing when the inner layers 

 are as dry as the outer layers. 



Hardwoods check much worse than softwoods; rift sawed or quarter sawed lumber checks less than 

 bastard sawed lumber. 



1. Remedies against checking of logs are;- Winter cutting; strips of bark left near the end of 

 peeled logs; felling with the roots and leaving the crown on the undissected bole; deadening; 

 "S" shaped iron clamps driven into logs; boards nailed onto the ends of the logs; earth cover 

 at the end of the logs; end painting of logs. 



2. Remedies against checking of lumber are;— Quarter sawing; slow air drying under sheds; veneer 

 sawing; steaming or boiling; many and thin sticks placed close to the ends (or else far from the 

 ends) of tiers in lumber piles ; shading or end painting the piles on the side exposed to sun and wind. 



3. Checks are radial since the tangential shrinkage is greatest. The so-called wind (or ring) shakes 

 are not caused by the hygroscopicity of the timber; they are merely a form of disease of timber 

 due to frost, heat, fire, or insect plagues interfering with the radial cohesion of adjoining rings 

 in wind-e.xposed localities. 



(k) Swelling, warping, and working. These phenomena are due to re -absorption of water after 

 drying. The swelling is greatest tangentially. Heartwood warps less than sapwood, and conifers warp 

 less than hardwoods. Boards obtained from close to the slab warp worst of all. 



Remedies against working are steaming; varnishing; forming composite boards by gluing (crossbanding) 

 fine veneers squarely one upon another; allowing framework of doors to be sufficiently grooved for 

 receiving the panels; placing dimension stuff on edge to dry in the piles; quartersawing; impregnation 

 with oils or with colophony (e. g., beech flooring). 



VII. Duration of wood. 



(a) Duration of wood depends on:- 



1. The surrounding conditions (e.g., tropics or arid deserts); presence of insects and fungi; contact 

 with clay, limestone or sand soil; immersion in sweet or in salt water (teredo); exposure to 

 atmosphere; moisture and heat conditions; presence of preserving matter (salt water, humic 

 acid, copper mine water). 



2. The natural qualities of wood, especially the presence or absence of rosin, tannin, and other 

 preservatives; the specific gravity; the percentage of sapwood; the susceptibility to fungus and 

 insect diseases. Locust, Eastern red cedar, sequoia and bald cypress are less subject to fungus 

 diseases when dead than when alive. 



