SHRINKAGE AND STKENGTH OF WOOD. 



79 



the other after being soaked for three mouths iu cold water. The results of these tests 011 White 

 Pine are embodied in the following table: 



Strength of contiguous blocks of the same scantling of White Pine, select material, in compression endwise. 



[Dimensions generally, 2.76 by 2.76 by 2.76 inches.] 



a Dried at 189 F. (to about 2 per cent moisture) before teating. 



It appears that in the tests ou dry material the greatest difference between any two contiguous 

 blocks of select quarter-sawed White Pine was 190 pounds per square inch, or 3.8 per cent of the 

 total strength; that generally it was.less than 2 per cent, and several times only about 0.2 per 

 cent, but that iu tests of this kind less then 200 pounds in the results can not be regarded as any 

 difference at all, this amount being due to indeterminable differences found even iu the best 

 material, and partly due also to imperfections in the means and methods of testing. It is also 

 clear that iu the same scantling, though select and of small dimension (only 6 feet long) a 

 difference of nearly 900 pounds per square inch, or 18 per cent of the strength, iu compression 

 endwise may be found, so that any inferences from scantling to scantling must be taken with 

 great caution, and any accurate relations, such as the influence of seasoning, etc., can be made 

 only in a manner similar to that employed in these uniformity tests. 



From the general series of tests, also from the tests on the select 2 by 2 inch pieces, and in 

 way of indication also from some of the tests in maximum uniformity, it appears that seasoning 

 affects the wood of White Pine to about the same degree as that of other pines. The strength of 

 greenwood, or wood soaked to a point where additional immersion no longer changes the volume, 

 is independent of differences in moisture. This is quite clear from the test in uniformity of the 

 scantling immersed for three months. Though the blocks differed (especially near the ends) 

 within wide limits as to the amount of moisture they contained, yet the strength was found to be 

 as uniform as in evenly dried timber. By drying green or fully saturated wood to about 2 per cent 

 moisture (kiln-drying at 80 C.), the strength is more than doubled; and even if pieces well air- 

 dried are kiln-dried the strength is still increased by over 40 per cent. For timber to be used 

 under cover and kept properly ventilated, it is safe to presume that the strength, once seasoned, 

 will be 50 per cent greater than when green, and if used in heated rooms, an increase of 100 per 

 cent on the strength of the green timber may reasonably be expected. The diagram (fig. 18) well 

 illustrates this feature. 



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