26 Shritikage, Swelling, Warping of Cross-grained Woods 



Set C (Tables C i and C ii). 



The subjoined Table C i records the linear changes of dimensions 

 of the same board (yang 1) during the process of drying from an 

 approximately saturated condition to a state of aqueous equilibrium 

 with the air of the laboratory. Table C ii gives the averages of the 

 results obtained. 



In addition to details that will be discussed subsequently in 

 comparing swelling and shrinkage, two facts are worthy of note. 



1. During shrinkage there is reached a certain phase at which 

 the board elongates while still decreasing in width. This phase, when 

 judged by the amount of water contained, is not exactly synchronous 

 with the corresponding reverse one during swelling. As in the latter 

 case this reversal in the change of length is temporary and is succeeded 

 by longitudinal shrinkage that brings the board down to its earlier 

 shortened condition. 



2. Whereas the board when absorbing water at first widens more 

 rapidly at the ends than in the middle, when drying it contracts in 

 width more rapidly at the middle than at the ends. Two possible 

 explanations of this latter fact present themselves, (a) When drying 

 owing to the more rapid conduction along than across the grain there 

 is near the ends a rapid shortening which tends to cause the angle of 

 inclination of the crossing fibres to be increased with consequent tendency 

 towards widening; while in the middle of the board the loss of water 

 takes place more equally and more or less excludes this widening tendency. 

 (b) Or possibly at first during the drying the water near the ends is largely 

 in the luniina, as well as in the walls, so that the latter do not lose much, 

 while the evaporation draws water to the ends from the middle, which 

 probably contains less water in the lumina and becomes depleted of 

 this more rapidly than at the ends. Between these alternatives it is 

 impossible to decide until further researches are conducted on shrinkage 

 in general. 



Changes of dimensions of Yang 1 during Swelling 

 AND Shrinkage. 



During swelling the percentage average increases in linear dimensions 

 were: in length '079; in width at the ends and middle 6-98 and 7-4 

 respectively. Thus the percentage tangential elongation was 91 times 

 as great as the longitudinal. 



