INFLUENCE OF MOISTURE ON STRENGTH. 



INFLUENCE OP MOISTURE. 



This influence is among the 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 influence of seasoning 

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

 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 cowskiu becomes thinner and 

 harder by drying. 



In the following tables and 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 moisture on strength. 



^ 4 S ff 78 9 



Flo. 3 Diagram showing variation of compression strength 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 moisture. 



