﻿44 BULLETIN 11, U. S. DEPARTMENT OP AGRICULTURE. 



CHARACTERISTICS OF THE WOOD. 1 



PHYSICAL PROPERTIES. 



Average weight of kiln-dried wood, 31 pounds per cubic foot. 



Average weight of kiln-dried wood lumber, 300 pounds per 1,000 board feet. 



Specific gravity varies from 0.40 to 0.80. 



Specific gravity most frequent range, 0.45 to 0.55; spring wood, about 0.40, 

 summer, wood, about 0.95; so that the weight of the wood increases with the 

 larger proportion of summer wood. 



Ash, 0.25 per cent of dry wood. 



Fuel value, 73 per cent of that of white oak. 



Breaking strength (modulus of rupture), 5,600 pounds per square inch, average. 

 (77 per cent of that of longleaf yellow pine according to Sargent.) 



Factor of stiffness (modulus of elasticity), 1,300,000 pounds per square inch, 

 average. (77 per cent of that of longleaf yellow pine according to Sargent.) 



Appearance of grain seen in cross section, variable, mostly very coarse; 3 to 12 

 rings, average 6 to the inch in structural lumber, generally wider than 

 short leaj, which averages 12. 



General character and qualities, medium heavy, strong, and tough; grain coarse, 

 even; summer wood broad, resin more abundant than in shortleaf, but less 

 than in longleaf; resin passages numerous, not prominent; medullary rays 

 numerous, obscure; heartwood orange yellow to light brown, the very thick 

 sapwood light yellow or often nearly white; not at all durable sapwood, 

 but takes preservative treatment readily; wood of "rosemary" pine close- 

 grained, less resinous, lighter, with much thinner sap. 



SHRINKAGE AND KILN DRYING. 



The wood of loblolly pine, in common with that of other of the southern pines, 

 shrinks about 10 per cent in cross section of volume (neglecting longitudinal shrinkage) 

 when dried from a green to an oven-dry state. From 3 to 4 per cent of this shrinkage 

 occurs along the radius, and from 6 to 7 per cent around the circumference. In green 

 loblolly lumber there is about 25 per cent of moisture. In the usual air-dry condition, 

 from 12 to 15 per cent of moisture still remains in the wood, so that the shrinkage from 

 the green to the air-dry condition is only a trifle over half of that from the green to the 

 absolutely dry state. Wood that has shrunk will return to its original size if soaked. 



The larger proportion of loblolly pine lumber is kiln dried before leaving the saw- 

 mill yard. This drying prevents "bluing," lessens the shipping weight, and reduces 

 the tendency to further shrinkage. 



For successful kiln drying, both the wood and the water it contains should be raised 

 to the temperature at which the drying is to take place. If the wood is slowly heated 

 and the surface moisture carried away, the surface will become entirely dry before 

 the interior is heated, and the lumber will shrink and check on the surface. Surface 

 drying should be delayed in the kiln by retaining the moisture first vaporized while 

 the heat penetrates to the interior. Steam may be used to wet the wood and raise it 

 to the drying temperature. When the inside as well as the surface of the wood is at 

 the proper temperature, drying may proceed, care being taken to replace the heat lost 

 from the wood by vaporization by the heat of the kiln. 



i Taken from Bulletin 99 and Circular 164 of the Forest Service. 



