TECHNICAL QUALITIES OF THE TREES 



107 



Testing the strength of Douglas fir at the U. S. Forest Experiment Station, Seattle, Wash. 



3. The test pieces shall be dried in the air so as to contain 15 per cent of moisture. 



4. The test load shall be increased gradually at the rate of 20 kilograms per square centimeter 

 per minute. 



5. The observations shall be recorded after the lapse of one minute succeeding the appearance 

 of a change of form. 



VI. Hygroscopicity. 



(a) Timber changes form, coherence, and volume with greater or lesser ease under the influence 

 of moisture, applied in gaseous or liquid form. Hence shrinking, swelling, warping, checking, cracking, 

 casehardening, and working. 



(b) In fresh wood, water invariably saturates the cell walls; in addition, it may or may only 

 partially fill the lumina. 



(c) Sapwood invariably contains more water than heartwood. 



(d) Speed of drying depends on the species, looseness of tissue, dimensions of object to be dried, 

 presence or absence of bark-cover in logs, preceding treatment by floating, deadening, steaming, prevalence 

 of sapwood or heartwood, season of year, exposure to wind, climate, &c. 



(e) Boiling and steaming reduce hygroscopicity and produce, consequently, a more even shrinkage. 



(f) The evaporation from the cross section bears to that of the tangential and to that of the radial 

 section the ratio of 8 to 1 to 2. 



(g) In the dry kiln, temperatures of 160 to 180 degrees Fahrenheit are gradually produced. Drying 

 is accomplished by hot air, steam and moving air. 



Conifers stand the dry kiln process much better than hardwoods. The better qualities of hardwoods 

 undergo air-drying before being kiln dried, especially so in waggon, furniture, and barrel works. 



The dry kiln saves piling charges, insurance and interest on large stocks of lumber, and it allows the 

 lumberman to rapidly fill pressing orders for lumber. It prevents the staining of sapwood in summer. It 

 causes, on the other hand, existing defects to open up and knots to drop out of the boards. 



(h) Wood is least permeable for water in the direction of the tangent or vertically to the 

 medullary rays, a fact important for tight cooperage. 



