]Vith a Dr\ Kiln in the Northwest 



123 



slight warping in the two outside tiers is frequently the result. If 

 some method could be devised whereby the slack could be taken 

 up in the rings which hold the I-beams together, this difficulty 

 could be largely overcome. Occasionally there is checking and 

 cracking, perhaps a board or two to the car. An occasional 

 red cedar board will be case-hardened. The principal loss en- 

 tailed both before and after drying is that of rough handling. 

 Of every 100,000 feet kiln-dried perhaps from 3,000 to 5,000 

 feet of boards are broken up. From this broken lot, however, 

 many of the best boards are sorted out and sent to the box 

 factory, so the loss in reality is not as great as it first appears. 

 The mechanical unloader at the "discharge" end of the kiln 

 breaks about a tenth of the stickers from each car unloaded. 

 Repeated passage through the kiln causes the stickers to become 

 brittle and only a slight pressure at one end is necessary to break 

 them. Brittleness is the very point made by those who are op- 

 posed to kiln-drying. It does become a factor if the lumber is 

 left in the kiln too long at a high temperature, but the operator 

 must guard against that. There is a reason for every thing, even 

 bread left in the oven too long will be burnt. 



A great many of the defects, like brittleness, are chargeable 

 to the operator. Case-hardening in cedar and checking and 

 cracking in that and in other species are due largely to the fact 

 that the air in the kiln was not sufficiently moist, when drying 

 began, to promote the action of capillarity. When the action of 

 capillarity is checked, the moisture in the board cannot be removed 

 except by such means as checks and cracks. Excessive warping is 

 frequently caused by the lumber remaining in the kiln longer 

 than the scheduled time. It is apparently more dangerous to over 

 dry than to under dry, for in the former case much of the lumber 

 might be damaged but in the latter case there is only an incon- 

 venience since it can be restacked and run through again. 



The following table gives the time that the different species 

 remain in the kiln and the purposes for which they are to be used : 



