AMERICAN WOODS. 



J)7 



From the following table of strength in tension and compression it will be seen that these 

 two are not always proportional, the stiller conifers excelling in the latter, the tougher hardwoods 

 in the former : 



Ratio of strength in tension and compression, showing the difference between rigid (onifers and tough hard woods. 



Ratio : 



Tensile 



strength. 



R=r 



comprehensive 

 strength. 



A stick 1 square inch 



in cross section. 

 Weight required to — 



Pull apart. 



Hickory 



Elm 



Larch. 



Longleaf pine , 



3.7 

 3.8 



2.2 



Pounds. 

 32, 000 

 29, 000 

 19, 400 



17, 300 



Crush 

 endwise. 



Pounds. 

 8,500 

 7,500 

 8,600 

 7,4U0 



Table of stiffness {modulus of elasticity) of dry wood. — General averages. 



Species. 



(1) Live oak, good tamarack, longleaf, Cuban, and shortleaf pine, good Douglas spruce, -western 



hemlock, yellow and cherry birch, hard maple, beech, locust, and the best of oak and hickory 



(2) Birch, common oak, hickory, white and black spruce, loblolly and red pine, cypress, best of ash, 



elm, and poplar and black walnut 



(3) Maples, cherry, ash, elm, sycamore, sweet gum, butternut, poplar, basswood, white, sugar, and 



bull pine, cedars, scrub pine, hemlock, and fir 



(4) Box elder, horse chestnut, a number of western soft pines, inferior grades of hard woods 



Modulus of 

 elasticity 



per square 

 inch. 



Pounds. 

 1, 680, 000 



1, 400, 000 



1, 100, 000 

 1, 100, 000 



Approximate weight which 

 deflects by 1 inch a piece— 



1 by 1 inch 



and 12 inches 



long. 



Pounds. 

 3, 900 



3,200 



2, 500 

 1 2, 500 



2 by 2 inches 



and 10 feet 



long. 



Pounds. 



62 



51 



40 

 40 



1 Less than. 



In general wet or green wood shears about one-third more easily than dry wood,- a surface 

 parallel to the rings (tangent) shears more easily than one parallel to the medullary rays. The 

 lighter conifers and hard woods offer less resistance than the heavier kinds, but the best of pine 

 shears one-third to one-half more readily than oak or hickory, indicating that great shearing 



strength is characteristic of " tough" woods. 



Resistance to shearing along the fiber. 



Per 

 square 

 inch. 



(1) Locust, oak, hickory, elm, maple, ash, birch 



(2) Sycamore, longleaf, Cuban, and shortleaf pine, and tamarack 



(3) Tulip, basswood, better class of poplar, Norway, loblolly, and white pine, spruce, red cedar. 



(4) Soft poplar, hemlock, white cedar, fir 



Pounds. 



1 1, 000 



600 



400 



2 400 



1 Over. 2 Less than. 



Note.— Resistance to shearing, although a most important quality in wood, lias not been satisfactorily studied. The values in the 

 above table, taken from various authors, lack a reliable experimental basis and can be considered as only a little better than guesswork. 



The following indicales the hardness of our common woods: 



1. Very hard woods requiring over 3,200 pounds per square inch to produce an indentation 

 of one- twentieth inch : Hickory, hard maple, osage orange, black locust, persimmon, and the best 

 of oak, elm, and hackberry. 



2. Hard woods requiring over 2,400 pounds per square inch to produce an indentation of one- 

 twentieth inch : Oak, elm, ash, cherry, birch, black walnut, beech, blue beech, mulberry, soft maple, 

 holly, sour gum, honey locust, coffee tree, and sycamore. 



3. Middling hard woods, requiring over 1,600 pounds per square inch to produce an indentation 

 of one-twentieth inch: The better qualities of Southern and Western hard pine, tamarack, and 

 Douglas spruce, sweet gum, and the lighter qualities of birch. 



4. Soft woods requiring less than 1,600 pounds per square inch to produce an indentation of 

 one- twentieth inch : The greater mass of coniferous wood; pine, spruce, fir, hemlock, cedar, cypress, 

 and redwood; poplar, tulip, basswood, butternut, chestnut, buckeye, and catalpa. 



H. Doc. Eo. 181 7 



