402 APPLIED SCIENCE 



the ends of the boards toward the alley endwise piling; 

 and (2) with the sides toward the alley sidewise piling. 

 The stacks are arranged to slope from front to rear and to 

 lean forward so that water dripping from the top falls to the 

 ground without trickling down over the courses below. The 

 stacks should be so located in the yard that the prevailing 

 winds blow through them rather than against their ends. 

 Lumber loses from 15 to 20% of its moisture by this method 

 of drying. It is generally sold in this condition and is ready 

 to be used for such purposes as rough construction, sheath- 

 ing, siding, studding, subfloors, and other structures in 

 which subsequent shrinkage, if any should take place, would 

 not be a serious factor. Lumber destined for use in the in- 

 terior of heated buildings, however, especially in places where 

 considerable shrinkage would be evident, as in flooring or 

 furniture, must be dried still more so that no shrinkage will 

 occur after the wood is in place. Wood for such purposes 

 should contain only between 5 and 8% of moisture. 



448. Kiln-Drying. Lumber is kiln-dried (Fig. 192) when 

 it needs to be seasoned quickly, or when the yard-owner 

 does not wish to carry large stocks in his yard. A kiln 

 is used also to dry partially air-seasoned, or even fully air- 

 seasoned material, for special uses. The main problem in 

 kiln-drying lumber is to prevent moisture from evaporating 

 from the surface of the pieces faster than it is brought to 

 the surface from the interior. When this happens the surface 

 becomes considerably drier than the interior and begins to 

 shrink and split. The evaporation from the surface of wood 

 in a kiln can be controlled to a large degree by regulating 

 the humidity and the amount of air passing over the wood. 

 A correctly designed kiln, especially one for drying the more 



