13 



SHRINKAGE, SWELLING AND WARPING OF CROSS- 

 GRAINED WOODS : No. 1, YANG {DIPTERO- 

 CARPUS sp.). 



By PERCY GROOM, 



Professor of the Technology of Woods and Fibres, 

 Imperial College, London. 



(With a Diagram.) 



No detailed investigations appear to have been conducted on the 

 changes of dimensions and shape occurring during the wetting and 

 drying of cross-grained woods. Yet such research bears upon problems 

 that are of scientific as well as industrial importance ; for many timbers 

 growing in hot countries are cross-grained, that is to say, their fibres 

 and other constituents in successive concentric layers round the 

 longitudinal axis are directed alternately in right-handed and left- 

 handed spirals. Moreover, a number of such timbers are of com- 

 mercial importance. 



The statistics available show that when straight-grained woods dry 

 from their fresh (green) condition to an air-dried (ordinary seasoned) 

 state the percentage shrinkages of their rods are as follows when cut: 

 longitudinally, usually -1 (-Ol-'S); radially, usually 3-5 (1-1-6); 

 tangentially, usually 6-10 (1-8-10-5). 



At first thought it might be anticipated that a cross-grained timber 

 would show increased longitudinal but decreased transverse shrinkage 

 or swelling, because of the existence of transverse and longitudinal 

 components respectively. The results obtained do not bear out such 

 an anticipation. 



In this investigation the Indo-Malayan cross-grained commercial 

 timber known as Yang, Dipterocarpus sp. (possibly D. tuherculatiis), 

 was used. When first imported into England it was tested as a 

 substitute for teak (in window-cills, doors, etc.), and was sometimes 



