Drying of Timber. 85 



dried at each temperature, and at the humidities given in the table. 

 After the completion of the experiment the blocks were left on the 

 shelf in the laboratory for twelve months, before the final measure- 

 ments were made for the amount of shrinkage. The moisture con- 

 tents of the blocks at the final measuring were very similar. 



Table VIII. 



Temperature. 



Humidity. 



Shrinkage. 



2..''c. 



80% 



.13 cms. 



30" 



44 



.15 



40° 



25 



.17 



50° 



15 



.20 



Amount of shrinkage increases with better drying conditions. 



That the greatest amount of shrinkage occurred at the highest 

 temperature is evidence that there was no case hardening, so-called. It 

 has been shown (4) that a rapid loss of moisture from the surface 

 prevents shrinkage to a certain extent. It has also been shown (4) 

 that steaming timber prior to seasoning induces shrinkage. Both 

 high temperatures and steaming are recommended in ordinary com- 

 mercial operations in kiln drying. In Fig. 9 are given the drying 

 curves of two series of blocks, one drying at 20°C. and other at 50^C. 

 The drying conditions of the series at 50°C. are representative of the 

 best drying conditions found in nature in this State during the sum- 

 mer. The highest temperature recorded in this State is 123- 5 °F. The 

 equivalent temperature of this in degrees centrigrade is 51°. 



Humidities lower than 15 per cent, are frequently recorded. The 

 blocks were radially cut, and were -81 inches thick. This thickness 

 would take about the same time to dry as tangentially cut specimens 

 one inch thick. The lower curve is representative of drying under 

 more or less average weather conditions. The upper tends to prove 

 What has already been pointed out (4) that inch boards can season 

 in this State in a few weeks. 



BIBLIOGRAPHY. 



1. Regional Spread of Moisture in the Wood of Trees. W. G. Craip. 



(Notes Roy. Bot. Garden, Edinburgh, Nov., 1918.) 



2. Kiln Drying of Lumber. H. D. Tiemann. 



3. Seasoning of Wood. J. B. Wagner. 



4. On the Seasoning of Hardwoods. Proc. Roy. Soc. Vict., 1919, by 



R. T. Patton. 



