AMOUNT OF SHRINKAGE. 37 



To avoid "working" or warping and checking, ail high-grade stock 

 is carefully seasoned, preferably in a kiln, before manufacture. Thicker 

 pieces may be made of several parts glued together; larger surfaces are 

 made in panels or of smaller pieces covered with veneer. Boring is 

 sometimes resorted to to prevent the checkiug of wooden columns. 



Since repeated swelling increases the injuries due to seasoning, wood 

 should be protected against moisture when once it is dry. 



Since the shrinkage of our woods has never been carefully studied, 

 and since wood, even from the same tree, varies within considerable 

 limits, the figures given in the following table are to be regarded as 

 mere approximations. The shrinkage along the radius and that along 

 the tangent (parallel to the rings) are not stated separately in the 

 following table, and the figures represent an average of the shrinkage 

 in the two directions. Thus, if the shrinkage of soft pine is given at 

 3 inches per hundred, it means that the sum of radial and tangential 

 shrinkage is about 6 inches, of which about 4 inches fall to the tangent 

 and 2 inches to the radius, the ratio between these varying from 3 to 2, 

 a ratio which practically prevails in most of our woods. 



Since only an insignificant longitudinal shrinkage takes place (being 

 commonly less than 0.1 inch per hundred), the change in volume during 

 drying is about equal to the sum of the radial and tangential shrink- 

 age, or twice the amount of linear shrinkage indicated in the table. 



Thus, if the linear average shrinkage of soft pine is 3 inches per 

 hundred, the shrinkage in volume is about 6 cubic inches for each 100 

 cubic inches of fresh wood. 



Approximate shrinkage of a board, or set of boards, 100 inches wide, drying in the open air. 



Shrink- 



(1) All light conifers (soft pine, spruce, cedar, cypress) 



(2) Heavy conifers (hard pine, tamarack, yew), lioney locust, box elder, wood of old oaks 



(3) Ash, elm, walnut, poplar, maple, beech, sycamore, cherry, black locust 



(4) Ba'sswood, birch, chestnut, horse chestnut, blue beech, young locust 



(5) Hickory, young oak, especially red oak 



Inches. 

 3 

 4 

 5 

 6 

 Up to 10 



V.— MECHANICAL PROPERTIES OF WOOD. 



Every joist and studding, every rafter, sash, and door, the chair we 

 sit on, the floor we walk on, the wood of the wagon or boat w 3 ride in 

 are all continually tested as to their stiffness and strength, their hard- 

 ness and toughness. Every step from the simple splitting of s, shingle 

 or stave to the construction of the most elegant carriage or sideboard 

 involves a knowledge, not only of one, but of several, of the mechanical 

 properties of the material. 



In the shop the fitness of the wood for a given purpose never depends 

 on any one quality alone, but invariably upon a combination of several 

 qualities. A spoke must not only be strong, it must be stiff to hold its 



