AMERICAN WOODS. 



97 



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

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

 in the former: 



Ratio of strength- in tension and r-ompri-xiion, showing tin; difference belim-n rii/iil i-nulfcrs and tough hard wood*. 



Table of xiijl'iirxit (inoili/lnx <if tlaxticitij) of dry iroott. (ieniral averages. 



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 otter 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. 



ill Liii-ust. oak, hickory, elm, maple, ash, birch '. 



C-i Sycamore, louglent'. Cuban, and shortleaf pirn-, and tamarack , 



t:i) Tulip. bass\voinl, better class of poplar, Norway, lohlolly, and white pine, spruce, re<i cedar. 



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



Pounds. 



'1,000 



600 



400 



'400 



'Over. 'Less than. 



XOTE. Resistance to shearing, although a most important quality in wood, has 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 indicates 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. No. 181 7 



