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FOREST PRODUCTS LABORATORY. 





TIMBER PHYSICS. 



KILN DRYING. 



A knowledge of the physical properties of wood is of importance to 

 almost every industry using wood and is essential in kiln drying, impreg- 

 nation with preservatives, distillation, and other treatments. These 

 physical properties include density, shrinkage, transfusion of moisture, 

 hygroscopicity, specific heat, heat conductivity, heat of absorption of 

 water in wood, and permeability of wood by liquids and gases. 



It is often necessary for financial reasons to reduce the time required 

 properly to season wood by open-air drying. Moreover, for many pur- 

 poses it is desirable to dry the wood more thoroughly than is possible in 

 the open air and to employ conditions which will reduce its hygroscopicity, 

 or tendency to shrink or swell. For these reasons dry kilns are almost 

 universally employed for high-grade lumber, and frequently even for the 

 poorer grades. In the drying of hardwoods it is estimated that about 

 10 per cent of the material dried is either ruined or lowered in grade. 

 Much of this loss could be avoided by proper methods and kilns, and the 

 present results might be greatly improved in other respects. 



ESTABLISHING SCIENTIFIC PRINCIPLES. 



The Forest Products Laboratory bases all its kiln-drying practice on 

 fundamental studies to determine the principles underlying the trans- 

 fusion of moisture through wood, the effect of changes in atmospheric 

 conditions upon the rate of transfusion, the effect of various methods of 

 drying and of various drying treatments upon the properties of the wood 

 being dried, and similar studies. 



DRYING SCHEDULES. 



A comprehensive series of experiments is being conducted to determine 

 the proper "drying schedules" for all important commercial woods. 

 These drying schedules will show the proper conditions of temperature 



