of Wooi I. 



139 



of vegetation, the older wood being generally heavier than the 

 young, and the weight greater iii the active, rather than the dor- 

 mant season. 



51)2. This water is not chemically united, and a part of it is -riven 

 out when exposed to the air. But at a certain point it ceases to be- 

 come lighter, and after that it gains or looses in weight, as the 

 temperature and moisture of the atmosphere vary. The following 

 table shows the changes, in percentage of weight, that occur with 

 some kinds of woods by seasoning : 



Percentage in uriyht of Water in Woods, at different periods after 



( 'tiffiny. 



563. It appears from this table, that there is generally nothing 

 gained, but something lost in keeping woods any longer than eighteen 

 months, as some of them, such as the beech, lir and pine, become 

 damp rather than dry by longer keeping, and the others gain in 

 dryness but feebly after that time. Mr. Marcus Bull, in his experi- 

 ments upon the properties of woods, many years since, ascertained 

 that wood, after being perfectly dried, when exposed in a room 

 without fire for a year, absorbed on an average, of 46 kinds, 

 10 per cent of their weight, in common states of the weather, and 

 8 per cent in the dry. A coincidence was noticed in the weight 

 of charcoal from these woods similarly exposed. The amount of 

 moisture absorbed was not found to diminish with their increase of 

 density, while green woods in drying lost uniformly less in weight, 

 according as their density was greater. Hickory, from green to ab- 

 solutely dry, lost ?>~\ per cent; white oak, 41; and maple, 48. 

 Assuming the general average at 42 per cent, we have a striking 

 illustration of the economy in freight, between the carrying of wood 

 green or dry, and in burning wood before or after seasoning. 



