WOOD 115 



dried before it is sawed, but from the commercial standpoint 

 this is impracticable ; the sawed lumber is therefore seasoned 

 by being carefully piled so as to permit a free circulation of 

 air around each piece. The pieces are laid flat and suf- 

 ficiently supported to prevent sagging. The weight of the 

 upper layers in the pile tends to prevent warping in the 

 lower ones. For many purposes the piling process is too 

 slow, and artificial drying is resorted to. Lumber is placed 

 in rooms and heat applied, the required degree of curing 

 being completed in a few days. Lumber thus cured is 

 known as kiln-dried in distinction to seasoned, for which 

 the curing is done in the air. The effect of exposure to the 

 atmosphere on kiln-dried lumber is much more severe than 

 on lumber seasoned in piles. Every effort should be made 

 to protect lumber from moisture in the atmosphere after 

 it is cured by having it placed in dry storage, treated with 

 wood preservatives, and, after construction, by the use of 

 fillers, oils, and paints. 



Sizes. As the lumber leaves the saw its actual dimen- 

 sions are the same as the nominal dimensions, any appre- 

 ciable amount of undersize placing the piece in a lower 

 grade. The nominal size as it comes from the mill is 

 retained, although the actual size is decreased by shrinkage, 

 surfacing, and additional machine work. The length is in 

 even feet, and changes by 2 feet, as 10 feet, 12 feet, and 14 

 feet. Lengths shorter than 10 feet or longer than 24 feet are 

 not regularly carried in stock, and the price usually increases 

 for lengths above 16 feet. The width begins at 4 inches and 

 increases by 2-inch gradations. Widths above 12 inches 

 are not always carried in stock and command a higher price. 

 The thickness may be }4 inch, 1 inch, 1^4 inches, ij4 inches, 

 and 2 inches, after which it increases by 2 -inch gradations 

 up to the thickest piece carried in stock. The table at 

 the top of page 116 gives the actual sizes of lumber after it 

 has been surfaced on one side and one edge, although it is 

 sold under the size which it had on coming from the saw. 



