TREES AND LUMBER 19 



up with broad surfaces horizontal and separated one from an- 

 other by thin strips of wood known as sticks. The boards in 

 a particular layer are placed so that edges will not touch; 

 hence, air is permitted to circulate throughout the pile and 

 come in contact with all surfaces. The piles are set up a foot 

 or more from the ground, one end being a few inches higher 

 than the opposite one. They are covered with boards to pro- 

 tect the drying lumber from rain and sun. 



In order to produce lumber quickly for construction use, it 

 is artificially seasoned or kiln-dried. This reduces the mois- 

 ure of the wood to perhaps five per cent, whereas, in the 

 natural process, ten per cent is the approximate minimum. 

 However, kiln-dried lumber will more quickly re-absorb mois- 

 ture. As most lumber nowadays is seasoned by some artifi- 

 cial means, it is advisable to pile it in shops as for air-season- 

 ing. In case there is a tendency to warp, it is sometimes ad- 

 visable to clamp a board to a flat surface, concave surface 

 down, or clamp two boards together with the concave surfaces 

 facing each other. 



Whenever a board is dressed, it is well to plane both broad 

 surfaces, especially in the case of air-dried lumber, in order to 

 open the pores, as it were, on both sides and thus make the ex- 

 posure conditions uniform throughout. If the ordinary 

 means of overcoming warping are not sufficient, it is some- 

 times possible to straighten a board by heating the convex 

 side and, possibly, at the same time moistening the concave 

 side. The heating can be done by laying the board on top of 

 a furnace. 



