Drying of Timber. IT 



of the drying period. A length of straight grained, freshly-felled birch, 

 was cut If" thick radially and 1" tangentially. This was then cut 

 into three 5 inch pieces. One length had the two transverse faces 

 exposed, and the sides sealed, in the second the tangential faces were 

 exposed, and in the third , the radial faces were exposed. The 

 blocks were dried at 25°C. Fig. 6 gives the result of the. 

 experiment. The percentage of moisture lost is calculated to the. 

 total amount of moisture present at the commencement of drying. The. 

 moisture percentages of the three blocks at the conclusion of the ex- 

 periment were as follow: — Radial, 10.7 per cent.; Tangential, 11.4: 

 per cent; Transverse, 11.1 per cent. These percentages are calculated, 

 to the dry weight of the wood. 



From a study of the curves of loss for oak, it was calculated that 

 if it were cut so that the dimensions in the tangential radial and 

 vertical directions were as 4: 5: 20, the curves of loss would meet, 

 towards the end of the drying period. Two sets of blocks were cut, 

 one to a size 1" x U'' x 4'', and the other 1" x 1\'' x 6''. The calcu- 

 lated length lay between the limits, 4'' and 6'". The blocks were dried 

 at 25 °C. The radial curve of loss was above the tangential until the. 

 50th day, when they met. The differences thereafter were very small. 

 The curve for the transverse face, in the case of the 4'' set, crossed 

 the other curves on the 92nd day. In the 6'' set the curve for the 

 transverse loss was still below the other curves on the 104th day, 

 when the experiment finished. In the 4'' set, at the close of the ex- 

 periment, the percentages of moisture, calculated to the dry weight of" 

 wood, of the radial, tangential and transverse specimens, were respec- 

 tively 11-8 per cent., 11-5 per cent, and 11*4 per cent. In the case- 

 of oak it appears that the ratio of the radial dimension to that of 

 length should have been only about 1:4. In the case of birch the ratio 

 could have been increased a little. The true ratio for inch material 

 probably is about 1-5. This ratio of dimensions for inch material 

 would not hold for larger material, since the decrease in the rate of 

 loss is faster for the radial than for the tangential, and faster for the 

 tangential than for the transverse. This is because in the expres- 

 sion for the curve of loss for the radial surface, the value of the 

 index of " ^" is lower than in the curve for the transverse. As thick- 

 nesses increase the ratios would also increase, but by what amount 

 remains to be determined. We cannot say that the transverse face 

 dries at a definite rate as compared with the radial, for the rate of 

 loss is constantly changing. If a rate of loss be specified, it must be 

 in relation either to time or moisture content. While we cannot say 

 how much faster one surface dries than another, we may say that as 

 far as inch material goes, quarter sawn boards, one inch in thickness, 

 will take as long to season as tangentially cut boards about 1^'' in 

 thickness. Normally, most timber seasons by lateral drying, but^ at 

 times end drying is important, as for instance, when large dimension 

 material is to be used in short lengths. As an example, a kiln was 

 being charged with long lengths of 9'' x 9'' lumber. This was to be 

 used subsequently in 3* ft. lengths. In this case if the timber had^ 

 been cut into short lengths first, time would have been saved, as the- 

 manufacturing length was less than five times the width. 



