76 



Reuben T. Fatton 



would lose moisture at the same rate as, or even less than, the radial. 

 The micellae of the walls of the medullary rays are arranged in a 

 radial direction, and it is in this direction that the water moves in 

 them when the tree is alive. The movement of water in the plant is 

 in some way closely associated with the structure of the cell wall, and 

 we find in the drying of timber that the greatest losses in unit time are 

 in the direction of greatest water movement in the living plant. 

 Since the organisation of the cell walls of the woods of all timbers 

 is the same, it is not surprising that the ratios of losses from the 

 three faces are approximately the same for all timbers. While these 

 ratios of loss may be the same, the rates of loss are not the same. All 

 three faces have different rates of drying, and the equations to the 

 curves are different. 



As will be shown later, the curve of loss for any one face is a 

 composite curve, and is made up of two types of curves. It is only 

 the first type of curve that we are here considering. This curve 

 varies, according to the drying conditions, from a straight line to a 

 parabola. The slower the drying the nearer the curve approaches a 

 straight line, and the faster the drying, up to a certain point, the 

 nearer the curve approaches a parabola. 



Not o-nly does each face lose moisture at a different rate, but each 

 rate of loss decreases differently. The face with the greatest initial 

 loss, the transverse, has also the slowest rate of decrease. Hence we 

 cannot cut a piece of timber so that all three faces will have the 

 same rate of loss. Of course they could be cut so that all faces would 

 have the same initial loss, but the losses on the subsequent days would 

 be different. However, it is possible so to cut a piece of timber that 

 all the curves of loss shall meet, or just cross each other, towards 

 the end of the drying period. The curves of lofs for White Birch 

 were studied, and it was considered that if a piece of this wood was 

 cut so that the dimensions in the tangential radial and vertical direc- 

 tions were as 5 : 6 : 30, the curves of loss woulo meev towards the end 



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Time in days. 

 Corves of Loss fok Blocks of Birch lf"xl"x5" 



