10 BULLETIN 676, U. S. DEPARTMENT OF AGRICULTURE. 
with a comparatively small increase in specific gravity. For instance, 
a wood with twice the specific gravity of another would be expected 
to have four times as much strength in tension. Yellow buckeye is 
a very light wood and woods of more than double its specific gravity 
may easily be found. Such woods, even though they may run some- 
what less in tension strength than the average wood of their weight, 
may have a tension strength considerably in excess of that of yellow 
buckeye. Thus, the red oaks, having a specific gravity of about 
wice that of yellow buckeye, are several times as strong in tension 
perpendicular to the grain, although they are very little above the 
average wood of their weight in this respect. 
tt may be seen from these examples that in comparing different 
timbers or species, in estimating their various properties, and in find- 
ing species with exceptional strength in some properties which may 
render them valuable for special uses, a knowledge of the specific- 
gravity strength relations is a valuable aid. It must be borne in 
mind, however, that such equations can never take the place of 
tests of species whose properties are unknown. If any particular 
mechanical property is known, the specific gravity may be approxi- 
mated and the other properties estimated; even the properties of 
woods upon which no test data are available can be estimated with 
a fair degree of accuracy from the results of specific gravity determi- 
nations. Nevertheless, it is apparent from a study of the table and 
diagrams that no one kind of test can replace a complete series of 
tests. 
