70 



Reuben T. Palton : 



The material was inch timber, and quite a number of the boards had 

 only two rings of growth. It may reasonably be expected that there 

 would be, in such timber, a great variation in the rate of diffusion. 

 No material could be obtained, however, to investigate this matter. 



In Table I. are given the results of the calculations for D. for 

 various timbers at 40 °C. and 50 per cent, humidity. 



Table I 



Timhei- 



Botanical Name 



Values of D 



Average 



Oak QuercKS 



robur .0012 .0026 .0032 .0048 .0056 0057 .0038 



Birch BituJa alba .0049 .0067 _ _ _ _ .0058 

 Beech Fagus 



sylvatica .0061 .0072 .0092 .0113 .0142 .0169 .0108 

 Elm U Imus 



campestris .0084 .0102 .0169 _ _ _ .0118 

 Scots Pi)ius 



Pine sylvestris .0051 .0115 .0195 .0240 .0266 — .0173 



The average values of Oak, Beech and Pine generally indicate the 

 positions of these timbers as regards drying in practice. Both Elm 

 and Beech are said to be difficult to dry, as they warp badly while 

 drying. Both Beech and Elm have a high moisture content, and 

 as we have found a high diffusion constant. These timbers lose 

 moisture rapidly, and unless the drying be uniform warping will 

 result. The cause of the warping of Elm is said to be due to its 

 twisted grain, but an examination of a large amount of elm lumber 

 does not bear this out. It is true that twisted grain will produce 

 warping, and this is freely borne out by such a timber as River Red 

 Gum {Eucalyptus rostrata) . It is doubtful if any other timber even 

 approaches this for irregularity of grain. A twisted grain, however, 

 does not appear to be a character of the elms. The warping of elm is 

 most likely to be due to uneven drying. 



In Victoria our timbers warp a great amount due to bad stacking. 

 The green sawn timber is frequently stacked in a mass, and no pro- 

 vision is made for circulation of air through the pile. The stack is 

 exposed to the fierce rays of the summer sun, and the top timber 

 warps badly in consequence. The pieces of timber in the interior of 

 the stack can only dry by their exposed ends, and these crack badly. 

 All kinds of timber are stacked out in the open in Eastern U.S.A., but 

 the stack is properly ventilated. There is a space between each board 

 laterally and vertically. The top of the stack is roofed with off cuts 

 from the logs. The timber comes out of these stacks in perfect con- 

 dition. 



Oak is difficult to dry because it has a high moisture content and 

 a low power of diffusion. Pine, on the other hand, has a low moisture 

 content, but a high power of diffusion, hence drying is rapid. 



If we knew the moisture content of a species of timber and its 

 diffusion constant, we might then be able to predict the time necessary 



