PERIODICAL LITERATURE . 729 



It was determined that in saturated air at the temperature named 

 above the wood re-absorbed moisture until the fiber saturation point 

 was reached, and the author concludes that "timbers subjected to the 

 action of saturated air at 120° F. must be designed on a basis of con- 

 stants determined from tests on green timber." In the case of Douglas 

 fir, the specimens subjected to saturated air at this temperature had a 

 compressive strength of only 75 per cent, as compared with air-dry 

 timber. Submersion in water lowered the compressive strength ap- 

 proximately 40 per cent. Southern yellow pine showed a much more 

 rapid decrease in strength, the specimens subjected to saturated air 

 having a compressive strength of only 65 per cent, as compared with 

 air-dry timber, while immersion in water lowered the compressive 

 strength approximately 60 per cent. 



The author draws the following conclusions : 



1. "In the air-dry condition, with approximately equal moisture con- 

 tents, the compressive strength of hard pine is about 25 per cent greater 

 than Douglas fir." [Reviewer's note : Evidently doctors disagree. The 

 U. S. Forest Service, in Bulletin No. 556, states that in compression 

 parallel to the grain the maximum strength of Douglas fir (pounds per 

 square inch) is 10,680, while longleaf pine has a crushing strength of 

 10,880. In compression perpendicular to the grain, Douglas fir shows 

 a fiber stress at the elastic limit of 1,270 pounds, while longleaf pine 

 shows a fiber stress of 1,640 pounds.] 



2. "When exposed to air saturated with water vapor at 120° F. and 

 when immersed in fresh water at 70° F. the moisture re-absorption of 

 air-dried wood is greater and more rapid in the case of fir than of pine." 



3. "The temperature effect on strength decrease is of more impor- 

 tance on pine than on fir." 



4. "Pine shows a more rapid decrease in strength with the moisture 

 decrease than does fir. The more ra])id re-absorption by fir tends to 

 offset this effect when the time element is used as a basis, so that for a 

 given treatment the pine remains the stronger, although the strengths 

 tend to approach each other with more extended treatment." 



5. "For moisture contents above 1 1 per cent, when due to rc-absorp- 

 tion from air saturated at 120° F., the fir is stronger in compression 

 than pine. The same relation appears for moisture contents greater 

 than 20 per cent when due to soaking in fresh water at 70° F." 



r.. L. G. 



Effect of Moisture Rc-ahsorf>tioii an C'oiiif^ii'ssiz'c Strength of Air-Dried Tim- 

 ber. I. H. Cowdrcv. Jiiunial nf tlu- Aim-rican Society of .Mechanical ICngineers, 

 XL, May, 1918. 



