SEASONING. 29 



October) . It is very probable that winter-cut lumber could be sea- 

 soned with less loss of material. 



Some of the boards and planks sawed from the logs selected for 

 testing were piled under shelter and seasoned for about two years, 

 when they were in the same condition as regards warping and check- 

 ing as is usually found in eastern oaks similarly handled. Some of 

 the lumber showed a tendency to a "blue rot," apparently caused 

 by too close piling, since this defect was remedied by a wider piling 

 that gave more circulation of air. 



In the case of some 200 pieces for mechanical tests (2 by 2 by 30 

 inches), cut from material seasoned under shelter for two years and 

 then kiln dried, the pieces showed practically no checking. The 

 sides of the pieces were slightly depressed in a few instances, but on 

 the whole their condition was excellent. 



All things considered, the seasoning of tanbark oak seems to offer 

 little, if any, more difficulty than is experienced with eastern oaks. 



SHRINKAGE. ^) 



In order to determine the amount of shrinkage in tanbark oak, 

 62 pieces (2 by 2 by 10 inches) were dried out slowly from a green 

 to an oven-dry condition. The pieces were selected so that two 

 sides were tangential to the annual rings. They were weighed and 

 measured at intervals for a period of about one year. The drying 

 was carried on first in a warm room and finally in an oven. 



When a piece of green or wet wood is dried, no change in dimen- 

 sions takes place until a point called the fiber-saturation point 1 

 (generally in the neighborhood of 30 per cent moisture) is passed. 

 The wood then begins to shrink in cross-sectional area and continues 

 to do so uniformly with the removal of moisture until it is bone dry. 

 The longitudinal shrinkage is so small as to be negligible. Generally, 

 the heaviest wood shrinks the most and sapwood shrinks more than 

 heartwood of the same specific gravity. Shrinkage is greater in the 

 circumferential than in the radial direction. 



The results of the shrinkage tests on tanbark oak showed an 

 average shrinkage in volume of 18 per cent 2 when the pieces were 

 dried from a green to an oven-dry condition. Of this amount about 

 6 per cent is radial shrinkage and about 12 per cent tangential. Air- 

 dry wood generally contains about 15 per cent moisture, so that the 

 shrinkage from the green to the air-dry state is only about half that 

 from the green to the absolutely dry state. 



The average shrinkage in volume with red oak when dried from a 

 green to an oven-dry state is about the same as with tanbark oak. 

 Both woods vary considerably. 



1 For a full discussion of the fiber-saturation point, see Forest Service Circular 108, The Strength of Wood 

 as Influenced by Moisture, by H. D. Tiemann. 



2 This figure is based on dry volume. 



