January 25. 1917 



The Strength of Wood 



Hu Maxwell. 



Editor's Note 



s^o far as this articli' discusses tlie sln-iiyth ol' wucnl, it aiiproadies tlic iiractical ratlior thau 

 the technical side, and holds that in the luoderu factory strength often dotermines the use to 

 which a wood shall be put. and the wei;,'ht in pro portion to strength very properly receives consid 

 'ration from those wlio aim at the highest economy ;ind efficiency in the use of wood. 



Tlie wildest savage that ever let fly an arrow, or cracketl tlie 

 slciill of an enemy with a war club, knew something about tlie 

 strength of wood and selected his material with that idea in view. 

 Wliat he knew liad been learned by experience, and he knew it 

 well. He made his boat and picked out his tent poles with a judg- 

 ment as unerring as that which actuates the petroleum operator in 

 selecting the hickory sucker rods for an oil well. It has been a 

 long time since the stonehatchet man shaped a hornbeam handle 

 to use in mauling the life out of 



the leather-tailed rhamphorliyn , 



chus haunting the jdeistocene 

 swamps; but during all of that 

 long term of years, the wood 

 users among men have gone on, 

 trying out different woods, and 

 determining whicli is liest for 

 this purpose and for tliat. 

 If every man were loft to his 



own experience and experiments 



to determine the strength of the 



woods which directly interest 



him, there would be a few well- 

 posted wood users and many 



with meager information. Tlic 



deacon made his famous "one- 



horse sha.y" on information of 



that sort, and it happened to be 



a success; but, ordinarily the 



clumsiest results would grow 



out of attempts to follow the 



deacon 's example. 



There are scientific methods of determining the strengtii of wood. 



They are more sjieedy and less costly than the slow process of ex 



perience where every mistake causes a loss, and every failure is th- 



measure of ground which must be slowly gone over again. 



An Early Lesson 

 One of -the first things siiown by an application of scientific 



WOODEN C.\R PROVES ITS STRENGTH 

 ek of Chicago-New York Eightecn-Hnur Train Near Fort Wayne 

 ana, .\ngust .SI. li)11. Steel Car I'ensader Lying On Its Side 

 Crushed: Woodi-n Diner T'liright and Cnhroken 



methods in determining the strength of wood is the fact that dif- 

 ferent woods vary greatly, and that differences little less remarka- 

 ble may be found between samples of woods of the same species. 

 Sucli differences may run as high as one hundred per cent even 

 when pieces from the same tree are compared. That is true when 

 the ordinary conditions, such as dryness and freedom from defects, 

 are apparently the same. 



Tlic fact that sucli differences in strength exist, and are common 



tliroughcuit nearly the whole list 



of woods, has stimulated search 



for the real factors on which the 

 strength of woods is based. The 

 amount of moisture is found to 

 liavc much to do with the mat- 

 ter. A very green and water- 

 soaked stick may be only one 

 half, or possibly little more than 

 one-fourth, as strong as the same 

 stick thoroughly seasoned. The 

 condition of wood in respect of 

 moisture has so great an influ- 

 ence on tlie strength of the piece 

 tlmt figures |iur])ortiug to show 

 what load a beam will carry, 

 mean very little unless the de- 

 gree of diviu'ss of (he wood is 

 known. The dryer the wood, 

 below a certain point, the greater 

 its strength. This rule holds, at 

 least, until the moisture within 

 is reduced to a very small per- 

 centage. The exjiulsion of all moisture from wood is so difficult 

 that its accomplishment is theoretical rather than ]>ractical. To 

 take it all out would require so much heat that the wood's fiber 

 might be damaged, thereby lessening rather than increasing the 

 strength of the stick or beam. 



.Strength may be lessened by the presence of defects, be they 

 knots, wiudsliakes, frost cracks, checks, crossgrain, or decay. If 



ILLUSTRATING "MODULUS OP RUPTURE" OF WHITE OAK 



Breaking a Stick Two and Five-eighths Inches Square and One Foot 



Between Supports, and Measuring the Weight Required to Do 



It — That is the Modulus ot Rupture 



—18— 





END CO.MI'RESSION ItREAKS .MINE I'RUPS 



Force Applied in a Similar Way Puts to Severe Test Car Sills and Ship 



Timbers Which Receive Strains, Thrusts. ,ind 



Bumps of the Heaviest Sort 



