74 Reuben T. Fatton : 



If the contained water passed from cell to cell as is necessitated 

 by the fibre saturation theory, then there would have to be osmotic 

 substances present in the cavities of the cells, and these do not exist. 

 There is only one path for the moisture to reach the exterior, and that 

 path is along the cell walls. This loss continues until the vapour 

 pressure on the outside of the face is equal to the vapour tension of 

 the face. 



In other words, when the moisture in the wood and the moisture 

 of the air are in equilibrium, the wood is seasoned. When exposed to 

 the air, the weight of a piece of seasoned timber is not a constant, 

 however, as it varies with the humidity of the atmosphere. 



Evaporating Surface. — The third factor influencing the drying of 

 timber is the face or surface exposed. There are three faces in. 

 timber — the transverse, the tangential, and the radial; and it is well 

 known that these have different rates of drying. Wagner (3) says: 

 " A very moist piece of pine or oak will, during one hour, lose more 

 than four times as much water per square inch from the cross section, 

 but only one half as much from the tangential as fro-m the radial 

 section." Tiemann(2) says: "The transfusion endwise of the grain is 

 very much greater, probably ten or twenty times as rapid as it is 

 across the grain." Again, Tiemann says: " Quarter sawed lumber 

 will generally require 25 to 50 per cent longer to dry than plain 

 sawed." These two authors differ widely in their opinions. 



In order to ascertain what were the actual rates of loss from each 

 face, cubes were used, and for these freshly felled timber was 

 obtained. The timber was cut square, usually 2" x 2'', two faces being 

 parallel to the annual rings, and two parallel to the medullary rays. 

 This can be done if timber from large trees be used. The length was 

 cut transversely into cubes. Thus each cube had the same annual 

 rings. Each cube had four faces sealed, and two corresponding faces 

 exposed. For sealing, paraffin is undoubtedly the best material to 

 use. The paraffin was heated to a temperature just above the boiling 

 point of water, and the face of the cube brought into contact with it 

 for a moment. The surface layer of moisture was evaporated, and 

 the paraffin then came into intimate contact with the wood. All four 

 faces of the cube were sealed in this way. After the paraffin set, the 

 cubes were given a second coating. By this means a perfect seal was 

 secured. For higher temperatures, the seal recommended by Tie- 

 mann (2) was used. This mixture is unsatisfactory for the first few 

 days, when high humidities are used, as it sticks to the supports. It 

 has this advantage, however, in that it readily indicates the shrinkage 

 of wood, for as the wood shrinks the seal forms very fine wrinkles. 

 When the cubes were coated they were placed in a saturated atmos- 

 phere for 24 hours at the temperature at which they were to dry sub- 

 sequently. When the cubes were dried it was found in all cases that 

 the transverse face lost the most moisture in a given unit of time. A 

 large number of timbers, both European and Australian, have been 

 tried, and they all give the same type of drying curves as shown in 

 Fig. 5. A study of these curves of loss shows that the curve of 

 loss for the transverse face always rises very sharply, and turns over 



