10 BULLETIlSr 676, U. S. DEPAETMENT OF AGEICULTURE. 



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, havnig a specific gravity of about 

 twice 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. 



It 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 

 mechanicar property is known, the specific gravity may be approxi- 

 mated and the other properties estimated; even the properties 6i 

 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. 



