216 FARM ARITHMETIC. 



product of one-fourth of a cord, what is the acre worth 

 before deducting the expense of marketing? 



781. If, in consequence of recurring ground fires and 

 lack of care, an adjoining wood lot has deteriorated so 

 that it bears only a partial stock of inferior trees which 

 when cut yield ten cords per acre of firewood, salable for 

 only $3 per cord, what is the loss due to the fire ? 



Strength of woods used in building. Timber is not 

 often used in tension. It is used in compression, as in 

 the uprights in buildings and in posts or columns support- 

 ing loads. It is also used in beams, as the joists in build- 

 ings. The two cases we will consider are: (1) Posts or 

 short columns compression and tension, and (2) beams 

 bending. 



782. What is the safe working load that may be sup- 

 ported by a 4-inch by 4-inch white pine post or column 

 that is too short to bend ? 



Process : Multiply the area of the cross section in square 

 inches by the safe working strength, per square inch, of the tim- 

 ber to be used. For white pine this may be taken as 500 pounds 

 per square inch. 



4 X 4 X 500 = 8,000 pounds, total safe load. 



Safe Working Tensile and Compressive Strengths of Some 

 Common Woods. 



Pounds per square inch. 



White ash, 750 



Yellow birch, 850 



Hickory, 800 



Soft maple, 750 



Yellow pine, 700 



White pine, 500 



Poplar, 550 



White oak, 850 



Red oak, 800 



Hemlock, 450 



783. What is the safe working load that may be sup- 



