70 PROPERTIES OF WOOD. 



than rootwoocl, uncoloure<J lieartwood more than the outer 

 layers. 



This reaction of sapwood and lieartwood in spruce, silver- 

 fir, birch, beech and hornbeam, which have no normal colour- 

 ing matter in their heartwood, is not contrary to 1, where 

 sapwood is said to shrink more than heartwood. It is truly 

 a case of the amount of shrinkage, after sapwood and heart- 

 wood have attained a similar degree of moisture, namely their 

 air- dry volume. 



5. When lieartwood is coloured, as in oak, larch, pines, etc., 

 it shrinks more than the sapwood ; in robinia (Hartig) by 

 8 per cent., in larch by 10 per cent. 



6. The contents of a wood in resin affects its shrinkage, for 

 in coniferous woods resin can penetrate the cell-walls only 

 after they have parted with their water. Hence only after a 

 tree has been felled can the reduction of warping, owing to a 

 deposit of rosin, be noted. The more slowly coniferous wood 

 is dried (Mayr) the greater the accumulation of hard rosin and 

 the less the wood will warp. Species of wood that are naturally 

 very resinous, therefore, shrink less than less resinous woods. 

 Hence the wood of Weymouth pine (in opposition to the law 

 of greater shrinkage in heavier woods) shrinks less than Scots 

 pinewood, the latter less than spruce, and that less than silver- 

 fir. Pitch-pine shrinks less than Weymouth pine or Scots pine, 

 and hence the preference given to pitch-pinewood. 



7. The washing-out of soluble salts by placing wood in 

 water, according to Nordlinger, has no influence, and 

 (D. Bersch) only a slight influence on the shrinkage (in 

 floating and rafting). 



8. The unequal changes in wood due to drying and wetting 

 result not only in an alteration in its volume, but also in 

 warping (withdrawal of a piece of wood from its original planes). 



