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 manufacturers 
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. 
