INFLUENCE OF MOISTURE ON STRENGTH. 



19 



INFLUENCE OF MOISTUUE. 



TIlis iiiflueuce is among tlio most important, hence all tests have been made with due regard 

 to moisture contents. Seasoned wood is stronger than green and moist wood ; the difference between 

 green and seasoned wood may amount to 50 and even 100 per cent. The inlhience of seasoning 

 consists in (1) bringing by means of shrinkage about 10 per cent more libers into the same scjiiare 

 inch of cross section than are contained in the wet wood; (2) shrinking the cell wall itself by about 

 50 per cent of its cross section and thus hardening it, just as a eowskiu becomes thinner and 

 harder by drying. 



In the following taldes aud diagram this is fully illustrated; the values presented in these 

 tables and diagrams are based on large numbers of tests and are fairly safe for ordinary use. They 

 still require further revision, since the relations to density, etc., have had to be neglected in this 

 study. 



Influence of ntoiature on strength. 



Bending strength: 



Green 



Half dry 



Yard dry 



Room dry 



Crushing endwise: 



Green 



Half dry 



Yard dry 



Room dry 



Mean of both bending and crushing strength 



Green 



Half dry 



Yard dry 



Room dry 



Per 

 cent of 

 mois- 

 ture. 



i3+ 

 20 

 15 

 10 



33+ 

 20 

 15 

 10 



33-1- 

 20 

 15 

 10 



Average uf aU valid tests. 



Cuban. 



8,450 



10. 050 



11, 950 

 15, 300 



5,000 

 6,600 

 7,850 

 9,200 



Long- 

 leaf 



7,060 

 8,900 

 10, 900 

 H, 000 



4,450 

 5,450 

 6,850 

 9,200 



Lob- 

 lolly. 



7,370 

 8, 650 

 10, 100 

 12, 400 



4,170 

 5,350 

 6,500 

 8,650 



Short- 

 leaf 



6,900 

 8,170 

 9,230 



11,000 



4,160 

 5,100 

 5,900 

 7,000 



Relative values. 



Cuban. 



100 

 118 

 142 

 181 



100 



132 

 157 

 184 



100 

 125 

 149 

 182 



Aver- 

 age. 



100 

 117 

 139 

 173 



100 

 126 

 152 

 191 



100 

 122 

 146 

 182 



4 S S 7 8 9 



rio. 3.— Diagram showing variation of compression atrongth with moisture. 



It will be observed that the strength increases by about 50 per cent in ordinary good yard 

 seasoning, and that it can be increased about 30 per cent more by complete seasoning in kiln or 

 house. 



Large timbers require several years before even the yard-seasoned condition is attained, but 

 2-inch and lighter material is generally not used with more than 15 per cent of moistui'e. 



