4i6 



THE TIMBERS OF THE WORLD 



further sample is taken from the same planks, and it is thus ascertained 

 if the requisite dryness has been attained. 



FLOOR PILIMG 



Door End 



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TRUCK PILING IN COMPARTMENT DRYER 



Supervision. — A timber dryer must work continuously, day and 

 night, as well as on Sundays. Apart from the bad effects of changes 

 in temperature, there is no economy in working only in the daytime, as 

 the heat cannot be resumed after a stoppage at the point arrived at 

 before it ceased, but must be regained gradually. The loss of time is 

 therefore much greater than the actual time of stoppage. The dryer 

 must be definitely in the charge of some responsible person who is 

 capable of attending to the instruments, of making moisture tests 

 and keeping records. This does not mean that his whole time will be 

 occupied on the dryer, but that visits must be made at regular intervals 

 during the day-tinle, and occasional superintendence provided for 

 during the night. Records of what is happening between the visits are 

 kept by the recording instruments. 



Besides splitting and warping, which are very obvious faults, there is 

 an error which can be made in drying timber which is not apparent to the 

 eye, but which is quite as harmful. If the restraining action of moisture is 

 omitted or improperly controlled, there is a tendency for the surface of 

 the timber to dry and harden to such an extent that it becomes quite 

 impervious to the passage of moisture, thereby preventing the interior 

 from drying, even if given a much longer time than usual. If the timber 

 is discharged in this " case-hardened " condition, and then sawn up, 

 the wet interior wood would lose its moisture and shrink, while the surface 

 wood remained dry. The result would be bad warping and twisting. 

 Case-hardened wood can sometimes be corrected by thoroughly 



