2 BULLETIN 556, U. S. DEPARTMENT OF AGRICULTURE. 



properties making a particular wood valuable for a certain purpose 

 are known, the comparison is made the easier. 



As an example of the foregoing, suppose it is desired to find a wood 

 for flooring for use in the place of maple. For flooring, hardness 

 is the ruling factor, providing, of course, the wood possesses other 

 strength properties to a reasonable degree. Using hardness as a 

 basis for comparison, white oak should be as good or better than 

 maple for flooring, which is true. Using modulus of rupture, which 

 is a very important strength value in structural material but of very 

 little importance in flooring, as a basis for comparison, longleaf pine 

 or Douglas fir would unjustly be given preference to oak. 



In addition to their value in expediting the search for substitute 

 woods, the data presented in this bulletin are of use to manuf acturers 

 and others in furnishing definite information concerning the proper- 

 ties of all commercial woods. This information is used in many 

 different ways, several of which are briefly discussed in the following 

 paragraph. 



In the preparation of specifications and grading rules for structural 

 timber it is essential to know the relation between physical and 

 mechanical properties, and the results of the tests here reported have 

 been used by a number of associations and societies in preparing 

 such rules. They are also used by architects and engineers in deter- 

 mining safe working stresses for wood in structures, in connection 

 with tests upon full-sized members. In the case of new uses for wood, 

 which frequently arise in special constructions, such as airplanes, for 

 instance, these data are of much help in selecting the species which 

 have the specific properties best fitting them for these uses. 



In order to cover the ground successfully, this bulletin must fur- 

 nish information on all mechanical properties of wood; and with that 

 end in view no effort has been spared in making a complete compila- 

 tion of the information at hand. There are few uses of timber where 

 at least some of the properties given in the table are not of importance. 



The Forest Service tests are standardized and the data contained 

 herein on any one species are directly comparable with similar data 

 on any other species listed. These tests obviously eliminate a great 

 amount of duplication which would result from individual investi- 

 gations. Industries anxious to find new species to supplant waning 

 supplies of present material would doubtless make tests adapted 

 to their own particular purpose which would probably throw no 

 light on other properties valuable for uses not in their fine. In many 

 cases the tendency would be to keep secret such findings in order to 

 meet more effectively competition from other firms; and even 

 though the data from all such individual tests were available, an intel- 

 ligent comparison of species could not be made because of the lack 

 of standardization of methods of test. 



