RESULTS OF MECHANICAL TESTS. 



By J. B. Johnson. 



GENERAL SUMMARY. 



In Table I are given the principal re.sults of tests on the individual sticks of long-leaf pine, 

 made in 1S91 and 189:2. They comprise tests on twenty-six trees, all from Alabama. Ten of these 

 were normal, healthy, living trees, from two localities, averaging abont two hundred years old and 

 about 21 inches in diameter. Sixteen of them had been tapped for turpentine ("boxed"), eight of 

 them being taken from an orchard abandoned five years, ;ind eight from an orchard recently 

 boxed. These trees averaged 18 inches in diameter. The logs from the unboxed trees were cut 

 into both large and small beams. Those from the boxed trees we>-e cut wholly into four by four 

 inch sticks. There have been about 4.30 tests made on these sticks in each of five ways, or some 

 2,150 tests in all. These tests may be divided in general into two classes, "green" and "dry." 

 The green tests on the unboxed trees were made some six months after sawing, while those on the 

 boxed timber were made some two months after sawing. The dry tests on the unboxed timber 

 were made about eighteen mouths after sawing, and the dry tests on the boxed timber some 

 fourteen months after sawing. Some of the dry tests were made on sticks which had been 

 treated for a few days in a dry kiln which was operated by an exhaust fan drawing air over steam 

 coils, the temperature of the box being less than 100° F. 



The bold-faced type in this table indicates the experimental values reduced for 1.^ per cent 

 moisture. This is abont the ordinary percentage of nniisturc of sea.scnied Inndter, under shelter, 

 but out of doors. These are the values which have been used in all the subsequent .studies and 

 in Tables II, III and IV, 



VARIATION OF STRENGTH WITH MOISTURE. 



In Plates vii-x are shown the curves which exhibit the variation of strength due to differ- 

 ence in moisture of the test piece. No curves are given for speciiic gravity or for tensile strength, 

 as both of these properties seemed to be practically independcnit of moisture, as shown in Plates 

 XI and XII. The curves in Plates vii-x were obtained as follows: The average of observed 

 results of tests on specimens trom singletrees were lirst plotted on cross-section pai)er, with their 

 corresponding percentages of moisture, the several mean results (green and dry) on one tree being 

 joined by straight lines to indicate that they all belonged to one and tlie same tree. These results 

 scattered widely, since all other sources of strength entered into the result, aside from moisture. 

 A provisional curve was then drawn, showing the probable law of change of strength due to mois- 

 ture conditions alone, and this curve was then traced ott' upon aiiother sheet. The several i)airs 

 of mean observed results on single trees (green and dry) were now copied ui)on this sheet in their 

 true moisture relations, but without any reference to their ab.solute strength relation, any farther 

 than that they were made .symnietrical horizontally (strength cooi'dinate) with the assumed cur\e 

 already drawn. That is to say, each pair of results (green and dry) were moved horizontally until 

 they became symmetrical in a horizontal direction with this curve. Thus, while their relative 

 strength was left the same, their absolute strength was ignored. In this way all other sources of 

 influence upon strength were eliminated except that of moisture, and the law of variation of 

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