SELLINGLUMBER 337 



mer wood is considerably in excess of the minimum require- 

 ments. 



The density requirements for first grade select structural 

 material then becomes six rings per inch with one-third summer 

 wood in the 3, 4 and 5 inches from the pith center. Wide ring 

 material not coming within this rule may be accepted, provided 

 the amount of dark or summer wood be one-half or more. 



Modifications for this requirement are provided for in the 



grading rules, where the pith center is not contained in the stick Modifications 



measured, or where the material is comparatively a small cross o f the 



section. Requirements 



Parenthetically, it may be said that some dealers, through 

 selfish motives, have sought to evade the explicit requirements of 



the "Density Rule" by counting the individual ring of spring and 



,. . An iLiifort to 



summer wood as indicating total annual growth that is, one ring Misconstrue 



of either representing a year's increase; whereas, as a matter of theRule 

 fact, one ring of summer wood and one ring of spring wood taken 

 together should be counted as one year's growth. 



It will be noted that this measurement of strength makes no 

 distinction between the botanical species of Southern Yellow Piue. 

 The tests have shown, as a matter of fact, that there is no differ- Botanical 

 ence whatever in strength qualities when the material shows the Considered* 

 required density of growth. Therefore, it is entirely possible for 

 timbers of short leaf or loblolly pine to possess the measure of 

 strength requisite for ordinary structural purposes. 



The dependability of this measure of strength was thoroughly 

 established by the forestry department before it was given pub- 

 licity. The American Society for Testing Materials had already 

 devoted much time and study to the problem of accurately grad- 

 ing structural timbers for strength qualities, and that organization p orma y 

 was quick to realize the practicability of the Forest Service rule, Adopted as 

 and after a thorough analysis of the rule gave it its formal adop- Stan(Jard 

 tion as standard. The engineers of the Southern Pine Association 

 also quickly recognized its practical value and placed their en- 

 dorsement on it. The simplicity of the rule has since won the 

 unqualified approval of many of the foremost structural experts 

 of the country. 



The Density Rule has been accepted and endorsed by the 

 American Railway Engineering Association, the Illinois Society of 



