SEASONING. 301 



This arrests the upward progress of sap from the roots ; and 

 when all the sap that was in the tree at time of girdling 

 becomes evaporated through the foliage, the leaves die, and 

 gradually (within about two years at most) the twigs, and the 

 small branches, and the bark are shed ; while the tree gradually 

 becomes seasoned and less likely to warp or shrink after con- 

 version, and also lighter in weight and rendered more floatable 

 and less heavy to transport. Conifers cannot, however, be 

 safely girdled, as they at once become infested with bark- 

 beetles, and the best way of seasoning them is to bark them as 

 soon as felled, leaving only narrow rings at both ends to 

 prevent them splitting arid getting long deep cracks. Wood in 

 the round usually takes from two to four years to season if 

 barked, and longer if unbarked ; while for hardwood planks 

 about a year is allowed for each inch of thickness before 

 seasoning is complete. But seasoning is much more rapid if the 

 wood has been previously floated or soaked in running water for 

 some time to remove some of the sap by dissolving it. Of 

 course, light porous wood seasons sooner than heavy dense wood, 

 and sawn or split wood seasons sooner than wood in the log. 

 Unless well raised off the ground, wood will not season 

 thoroughly. If boards fresh from the saw-bench be set on end, 

 this helps the seasoning of some kinds of wood (e.g., Beech). 



2. Seasoning artificially may take place either by evaporating 

 the sap in properly ventilated hot-air chambers, or by steaming 

 it in closed cylinders. 



In seasoning by hot air the converted wood is ranged so that 

 the air can circulate freely between the pieces ; and the dry super- 

 heated air, warmed either by steam-pipes or hot-air tubes, is 

 kept in circulation by large revolving fans, while ventilation is 

 provided by circulating vanes and cowls. Whatever the size of 

 the drying-chamber, about one-third is filled with wood and 

 two-thirds with the hot air. Drying should only take place at 

 a temperature not above 110 to 140 Fahr., though 95 to 



