20 



TIMBF.K PINES OF THE SoUTllEKX UNITED STATES. 



WEIGHT AND MOISTXTRE. 



8(1 far tlie weight of only the kihidry wood has been considered. In fresli as well as all yard 

 anil air dried material there is contained a variable amount of water. The amount of water 

 contained in fresh wood of these pines forms more than half the weight of the fresh sapwood, and 

 about one-fifth to one-fourth of the heartwood. In yard-dry wood it falls to about 12 to 18 per 

 cent, while in wood kept in well-ventilated, and especially in heated rooms it is about 5 to 10 

 l)er cent, varying with size of piece, i)art of tree, species, temperature, and humidity of air. 

 Heated to 150° F. (G5^ (J.), the wood loses all but abi)ut 1|^ to 2 per cent of its moisture, and if the 

 temperature is raised to 175° F. there remains less than 1 per cent, the wood dried at 212° F. 

 being assumed to be (though it is not really) perfectly dry. Of course, large pieces are in prac- 

 tice never left long enough exposed to become truly kiln dry, though in factories this state is often 

 api)roached. 



As long as the water in the wood amounts to about 30 i)er cent or more of the dry weight of 

 the wood there is no shrinkage ' (the water coming from the cell lumen), and the density or specitic 

 gravity changes simply in direct i^roportion to the loss of water. When the moisture per cent 

 falls below abont 30, the water comes from the cell wall, and the loss of water and weight is accom- 

 panied by a loss of volume, so 

 that both factors of the frac- 

 tion 

 Specitic gravity — 



weight 



volume 

 arc affected, and the change 

 in the specific gravity no lon- 

 ger is simply proportional to 

 the loss of water or weight. 

 The loss of weight and vol- 

 ume, however, being unequal 

 and disproportionate, a marked 

 reduction of the specific grav- 

 ity takes place, amounting in 

 these ]>ines to about S to 10 i^er 

 cent of the specitic weight of 

 the dry wood. 



SHRINKAGE. 



The behavior of the wood of 

 the Southern i)ines in shrink- 

 age does not differ materially. 

 Generally the heavier wood 

 shrinks the most, and sapwood 

 °"""""'*' shrinks about one fourth more 



than heartwood of the same specific weight. Very resinous pieces ("light wood"') shrink much less 

 than other wood. In keeping with these general facts, the shrinkage of the wood of the upper 

 logs is usually 15 to 20 per cent less than that of the butt pieces and the shrinkage of the heavy 

 heartwood of old trees is greater than that of the lighter peripheral parts of the same, while the 

 shrinkage of the heavy wood of saplings is greatest of all. On the whole, the wood of these pines 

 shrinks about 10 per cent in its volume — 3 to 4 per cent along the radius and to 7 per cent along 

 the tangent or along the yearly rings. 



After leaving the kiln the wood at once begins to absorb moisture and to swell. In an 

 experiment with short pieces of loblolly and shortleaf, representing ordinary flooring or siding 



' lu oitlinary lumber anil all large size material the exterior parts commonly ilry so much sooner than the bulk 

 of the stick that checking often occurs though the moisture per cent of the whole stick is still far above 30. 



Fio. 4.— Diagram 



