PROPERTIES OF WOOD. 



shows that Scots pine, which is more resinous than spruce or 

 silver-fir, absorbs less water than either, and is therefore less 

 liable to saturation than they are. Such resinous wood, e.g., 

 of pines, larch, or deodar, will float longer and is less liable 

 to sink than the wood of spruce, or silver-fir. 



Boppe's "Technologie Forestiere" and Mathey's "Exploita- 

 tion Commerciale des Bois " give some practical results about 

 warping which are not given by Gayer, and form the subject 

 of the next section. 



8. Practical Result* of Warpimj. 



Duhamel de Monceau split some scantlings and poles by 

 two or three cuts in order to show longitudinal shrinkage, 

 and as seen in Fig. 31, each split piece curves outwards. 



This explains why planks 

 sawn through the centre 

 of a log (Fig. 3'2) gene- 

 rally crack, the crack being 

 the deeper, the thicker 

 the plank, the more sap- 

 wood it contains and the 

 wider the annual zones of 

 wood. 



The outer zones contract 

 fig. 31. (After Koppe.) more than the cenfcml oneg> 



and the central plank (Fig. 33) is curved convexly on both its 

 larger .surfaces. If planks are cut at distances more and more 

 removed from the centre of the wood, they tend, owing to 

 unequal warping, to become more and more concave on their 

 outer surfaces, as shown in Fig. 34. 



The shrinkage in width of such planks has been referred 

 to already (p. 68). If a floor be made with insufficiently 

 dried planks, they leave spaces between them on drying, while 

 if the planks are nailed on the joists of the floor with their 

 inner sides exposed to the air, they tend to shell-out. In 

 good flooring, planks are dovetailed into one another to render 

 the floor airtight. 



The centre of any log containing the pith, being frequently 

 knotty in coniferous wood and in broadleaved wood often 



