Chapter II. 



PROPEETIES OF WOOD. 



There are many properties of wood, — some predominant in one 

 species, some in another, — that make it suitable for a great variety 

 of nses. Sometimes it is a combination of properties that gives value 

 to a -wood. Among these properties are hygroscopicity, shrinkage, 

 weight, strength, cleavability, elasticity, hardness, and toughness. 



THE HYGKOSCOPICITY' OF WOOD. 



It is evident that \\-alei' plays a large part in tlie economy of the 

 tree. It occurs in wood in three different ways : In the sap which 

 fills or i)artly fills the cavities of the wood cells, in the cell walls which 

 it saturates, and in the live protoplasm, of which it constitutes 90 

 per cent. The younger the wood, the more water it contains, hence 

 the sap-wood contains much more than the heart-wood, at times even 

 twice as much. 



In fresh sap-wood, 60 per cent, of the water is in the cell cavities, 

 35 per cent, in the cell walls, and only 5 per cent, in the protoplasm. 

 There is so much water in green wood that a sappy pole will soon 

 sink when set afloat. The reason why there is much less water in 

 heart-wood is because its cells are dead and inactive, and hence with- 

 out sap and witliout protoplasm. There is only what saturates the 

 cell walls. Even so, there is considerable water in heart-wood." 



'Hygroscopicit.y, "the property possessed by vegetal)] e tissues of absorb- 

 ing or discharging moisture and expanding or shrinking accordingly." — 

 Gentiirii Dictionary. 



= This is shown by the following table, from Forestry Bulletin Ko. 10, 

 p. .31, Tiniher, by Filibert Roth: 

 POU.NDS OF WATER LOST IN DRYI?IO 100 POUNDS OF OKEEN WOOD IN THE KILN. 



Sap-wood or Heart-wood 



outer part, or interior. 



1. Pines, cedars, spruces, and firs 45-65 lG-25 



2. Cypress, extremely variable 50-65 18-60 



3. Poplar. Cottonwood, basswood 60-65 40-60 



4. Oak. beech, ash, elm, maple, birch, hickory, chestnut , 



walnut, and sycamore 40-50 30-40 



41 



