62 FOREST UTILIZATION 



occurs in walnut, linden, beech, elm, 

 chestnut, birch. 



Shrinkage of 3 % to 5 % occurs in oak, 

 maple, sycamore, ash, cottonwood, yellow 

 pine. 



Shrinkage of 2 % to 3 % occurs in spruce, 

 larch, fir and white pine. 



A large percentage of rosin, narrow annual 

 rings and light specific gravity reduce 

 shrinkage within the same species. 



Checking. 



It depends on the rapidity of the drying 

 process; on size and dimension of ob- 

 ject; on peeling of logs; on homogeneity 

 of tissue. 



Checks are often of a temporary 'nature, 

 disappearing when the inner layers are 

 as dry as the outer layers. 



Hardwoods check much worse than soft- 

 woods; and rift sawed or quarter sawed 

 lumber checks less than, bastard sawed 

 lumber. 



Remedies against checking of logs are : 

 Winter cutting; strips of bark left near 

 the end of peeled logs; felling with the 

 roots and leaving the crown on the un- 



dissected bole; deadening; "S" shaped 

 iron clamps driven into logs ; boards 

 nailed onto the ends of the logs ; earth 

 cover at the ends of the logs ; red lead 

 painting for export logs. 



Remedies against checking of lumber are: 

 Quarter sawing; slow air drying under 

 sheds; veneer sawing; steaming or boil- 

 ing; sticks placed close to the ends of 

 tiers in lumber piles. 



Checks are radial since the tangential 

 shrinkage is greatest. The so-called wind 

 (or ring) shakes are not caused by the 

 hygroscopicity of the timber; they are 

 merely a form of disease of timber, due 

 to frost, heat, fire or insect plagues inter- 

 fering with the radial cohesion of ad- 

 joining rings. 



Swelling, warping and working. 



These phenomena are due to reabsorption 

 of water after drying. The swelling is 

 greatest tangentially. Heartwood warps 



