96 



FORKSTKY INVESTIGATIONS I", s. DEPARTMENT OF AGRICULTURE. 



Since the proportion of sap and heart wood varies with size, age, species, aiid individual, the 

 following figures must be regarded as mere approximations: 



Pounds of water lout in drying 100 pound* of green irooil in the kiln. 



The lighter kinds have the most water in the sapwood, thus sycamore' has more than hickory. 



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 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 couimoiily less than 0.1 

 inch per hundred), the change in volume during drying is about equal to the sum of the radial 

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



Thus, if the linear average shrinkage of soft pine is .'5 inches per hundred, the shrinkage in 

 volume is about C cubic inches for each 100 cubic inches of fresh wood. 



Approximate shrinkage of a board, or set of boards, 10H inches wide, drying in tlie open air. 



Shrink, 

 age. 



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



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



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



(4) liassvrood, birch, chestnut, horse-chestnut, blue beech, young locust 



(5) Hickory, young oak, especially red oak 



Inchrs. 

 3 

 4 

 5 



I 

 Up to 10 



Strength in compression of common American woods in well-seasoned seJeded pieces. 



[Approximate weight per square inch of cross section requisite to crush a piece of wood endwise.] 



Pounds. 



(1) Black locust, yellow and cherry bircli, hard maple, best hickory, longleuf nnd Cuban -pines, anil 



tamarack...' --- 9,000+ 



(2) Common hickory, oak, birch, soft maple, walnut, good elm, best ash, shortleaf and loblolly pines, western 



hemlock, and Douglas fir 7,000+ 



(3) Ash, sycamore, beech, inferior oak, Pacific white cedar, canoe cedar, Lawson's cypress, common red 



cedar, cypress, Norway and superior spruces, and fir 6, 000+ 



(4) Tulip, basswood, butternut, chestnut, good poplar, white and other common soft pines, hemlock, spruce, 



andiir 5,COO+ 



(5) Soft poplar, white cedar, and some Western soft pines, and firs 4,000+ 



Strength in cross-breaking of umll-neasoned, select pieces. 



