78 



Reuben 2\ Patton : 



End drying is important in this state owing to the loss which is 

 caused, both in stacks of sawn timber, and in logs, through the large 

 cracks occurring in the ends. Much of our tall, straight-grained timber 

 is very fissile, and, therefore, splits much more easily than most 

 timbers. The cause of the cracks at the ends of both logs and stacked 

 timber is mainly the prevention of lateral drying. In the log, lateral 

 drying is prevented either by the bark or by the thickness of the log, 

 or by both. In stacked timber lateral drying is prevented, if no ven- 

 .tilation is provided for. Only the outside pieces can dry laterally, 

 and then only from one side. As we have already seen, shrinkage 

 commences as soon as a gradient is formed. Shrinkage, however, 

 is prevented from taking place where only end drying is occuring, 

 owing to the rigidity of the adjacent portions of the timber. End 

 drying affects only a few inches, and the timber in this short length is 

 held in position by the remainder of the length. As the wood is dry- 

 ing, it tends to occupy a smaller volume, but if it cannot do so as a 

 whole it must do in parts, and it therefore splits. That some of our 

 timber will split even when correctly stacked is true, and this can 

 only be overcome by sealing the ends with paint, or with Tiemann's 

 mixture. In usual commercial sizes this does not affect time taken in 

 drying, as the length is generally very many times greater than 

 the thickness. In commercial sizes lateral drying is almost always 

 the means by which timber is dried. 



Thickness. — The fourth factor concerned in seasoning is that of 

 thickness. For the study of the effect of thickness on time taken in 

 drying, lengths of straight grained, freshly felled timber were used. 

 Thicknesses up to five inches have been used. The timber was cut as 

 in the diagram: — 



The sides were coated as in the previous experiments. Where 

 possible, three of each thickness were used, and the average loss of 

 the three taken as the loss for that thickness. Each thickness had 

 the same evaporating surface, and the various blocks differed only in 

 thickness. 



