TIMBER PHYSICS UNIFORMITY OF STRENGTH. 



369 



In addition, the difficulty of seasoning oak without defects or even securing perfect material may have influenced 

 the results of tests so as to cloud the relationship with the genus. 



If further close study, supplemented by additional series of tests carefully devised to investigate this relation- 

 ship, should uphold the truth of it, this result may be set down as the most important practical one that could be 

 reached by these tests, for it would at once give into the hands of the wood consumer a means of determining the 

 relative value of his material as to strength and all allied properties by a simple process of weighing the dry material; 

 of course with due regard to the other disturbing factors like crossgrain, defects, coarseness of grain, etc. 



Be8iiUs of tests in compression across grain («) and shearing with grain. 



[Pounds per .square inch.] 



No. 



D 







rt 



8 

 9 



10 

 11 

 12 

 13 

 14 

 15 



Species. 



Reduced to lf> per cent moisture. 



Longleaf pine . 

 Cuban pme ... 

 Shortleaf pine. 

 Loblolly pme.. 



Reduced to 12 per cent moisture. 



White pine 



1-ied pme 



Spruce pine 



Bald cypress 



"White* cedar 



Douglas spruce 6. 



White oak 



Overcup oak 



Post oak 



Cow oak 



Ked oak 







Shearing 





.Num- 

 ber of 



tests. 



Compres- 

 sion 

 across 



with 

 grain not 

 reduced 



No. 





gram. 



lor 



moisture. 





1,210 



1,000 



700 





400 



1,000 



700 



16 



330 



900 



700 



17 



690 



1, Q00 



700 



18 

 19 

 20 

 21 



130 



700 



400 



22 



100 



1,000 



500 



23 



175 



1,200 



800 



24 



650 



800 



500 



25 



87 



700 



400 



26 



41 



800 



500 



27 



218 



2, 200 



1,000 



28 



216 



1,900 



1,000 



29 



49 



3, 000 



1,100 



30 



256 



1,900 



900 



31 



57 



2, 300 



3,100 



32 



Species. 



Reduced to 12 per cent moisture- 

 Conlinued. 



Southern red oak. . 



Black oak 



"Water oak 



Willow oak 



Spanish oak 



Shagbaek hickory. 

 White hickory . . . 



Water hickory 



Bittern ut hickory. 

 Nutmeg hickory .. 



Pecan hickory 



Pignut hickory 



White elm 



Cedar elm 



Whiteash 



Green ash 



Sweet gum 



Hum- 



Compres- 



Der of 



sion 



tests. 



across 





gram. 



117 



2,000 



40 



1,800 



30 



2, 000 



153 



3,600 



255 



1,800 



135 



2,700 



75 



3,100 



14 



2,400 



25 



2,200 



72 



2,700 



37 



2,800 



30 



3,200 



18 



1,200 



44 



2,100 



S7 



1,900 



10 



1,700 



118 



1,400 



Shearing 



with 

 grain not 

 reduced 



for 

 moisture. 



900 

 1,100 

 1,100 



900 



900 

 1,100 

 1,100 

 1,000 

 1,000 

 1,100 

 1,200 

 1,200 



800 

 1,300 

 1,100 

 1,000 



800 



aTo an indentation of 3 per cent of the height of the specimen. & Actual tests on "dry " material not reduced for moisture. 



Having fully established the great influence of moisture on the strength of wood, the practi- 

 tioner still needed information as to the rate and manner of drying and as to the way in which 

 moisture is distributed during seasoning. Several thousand moisture determinations were made 

 and it was established beyond doubt that moisture is generally least abundant at the ends, is 

 quite evenly distributed throughout the length, but is not always uniform in different parts of the 

 same cross section, often varying in this respect within astonishing ranges, so that the use of 

 timber in a half-seasoned condition, and where uniform seasoning can not be obtained by the 

 material, requires that these facts be duly considered in designing. 



Tests of Maximum Uniformity. 



Both in this country and abroad small differences in strength values were often interpreted 

 as deciding for or against any given material. This same problem arose also in every case where 

 many results were to be compiled, and it seemed especially desirable once for all to find just how 

 much uniformity could be expected of wood materials. From a large series of well-selected 

 quarter-sawed pieces representing several kinds of pine, cypress, and hardwoods it was found 

 that even contiguous blocks, 2 J inches long, may differ by as much as 2 to 4 per cent in conifers 

 and as much as 13 per cent in oak, and that in a scantling only 6 feet long the butt might differ from 

 the top by 10 to 20 per cent in conifers and over 35 per cent in oak. This extremely valuable set 

 of results throws much light upon discussions of the past, and is well suited to show that many 

 boastful claims rested on very flimsy and entirely unreliable differences, such as might well be 

 accounted for by a little more extended examination of materials. It will also assist in judging 

 test results in the future and help to avoid useless controversy and prejudice. The following 

 more fully illustrates the results of this series: 



Scantlings of air-dry material, 6 to 10 feet long, of white pine, longleaf pine, tuliptree (poplar), and white oak, 

 and of perfectly green material of loblolly pine and cypress, fresh from the saw, were cut partly into blocks 2 by 2 

 by 21 inches, but mostly into cubes of 2£ inches. All material was quarter sawed, carefully prepared, and in all 

 cases treated alike, either perfectly green or dried together at the same temperature. Altogether 529 tests in 

 endwise compression were made, namely, 100 on white pine, 72 on longleaf pine, 99 on loblolly pine, 40 on white 

 oak, 115 on tuliptree (poplar), 103 on cypress. 

 H. Doc. 181 24 



