18 Shvhikafje, Swelling, Warjiing of Cross-grained Woods 



One marked character of at least some cross-grained woods is their 

 Uabihty to twist during wetting and drying, and the tangential boards 

 of yang displayed this character. The two tangential boards of 

 yang showed on their faces the grain running obliquely apparently 

 in the same sense in each board, but in opposite senses in the two 

 boards. Thus on each face of yang 1 the grain tended to run from the 

 right hand to the left hand down the board, whereas in yang 2 it 

 tended to run from left to right downwards. Considering either of 

 these boards on one face the one diagonal running rather with than 

 across the grain changes relatively slightly in length as the board becomes 

 wetter or drier, whereas the other diagonal on the same face changes 

 more in length becoming concave when drying or convex when wetting : 

 the diagonals superposed on these on the reverse face behave in an 

 opposite manner. The result is that each face of the board becomes 

 convex along one diagonal, and concave along the other; that is to say 

 a twisting movement results from the establishment of a couple. That 

 this explanation is correct is confirmed by the fact that the twist is in 

 the opposite sense during the swelling and drying of the same board; 

 and is in the opposite sense in the two boards yang 1 and yang 2 when 

 these are undergoing the same kind of change of water contents, whether 

 this change be drying or wetting. 



Moreover if such be the true explanation of the twisting a radially 

 cut board should not exhibit this behaviour. The radially cut yang 

 board showed no trace of twisting either when wetted or dried. These 

 facts suggest, on the one hand, that possibly the twisting of so-called 

 straight-grained boards in general is due to a less marked and differential 

 obliquity on the two faces, and on the other hand that cross-grained 

 woods now excluded from commercial use by reason of their twisting 

 propensities could be utilized if they were cut into radial ("quartered," 

 "rift-sawn") boards. The facts also emphasize the advisability of 

 seasoning cross-grained woods not only thoroughly, but also slowly, 

 the latter because the extent of the twist is largely influenced by the rate 

 of drying of the surface. 



In a transverse direction the tangential boards at their ends 

 remained nearly straight, the very slight amount of curvature possibly 

 conforming with the moderate degree of tangential shrinkage or swelling. 



Observations on Yang 1. 



This board was tangentially cut, its length and width slightly 

 exceeding fil cm. and 12-85 cm. respectively. 



