SPECIFIC GRAVITY- STRATH RELATIONS FOR TCOOP- 
Studies at the Forest Products Laboratory have shown that tl 
specific gravity of wood substance is nearly the same for all species, 
and has a value of about 1.5. Since the "bulk specific gravity of woo 1 
is less than unity for most species, it is evident that a considerable 
oortion of the volume of a piece of wood is occupied by the various cell 
cavities and pores. For these reasons, the specific gravity of oven-dry 
" r ood is an excellent index of the amount of rood substance present, and 
hence of the strength properties. 
The relation of specific gravity to the mechanical properties of 
wood may be considered from the standpoint of (1) differences between 
species, and (?) differences between pieces of the same species. Gonri 1 - 
ering different species, the general relation of specific gravity to 
strength is illustrated by two widely different ^oods, mastic, a dense 
Florida species, and balsa, a very light Central American species. End- 
wise compression tests on green materi.nl gave the results of table 1, 
which show that mastic had nine tir.es the average specific gravity of 
balsa, and was also nine times as high in crushing strength along the 
grain. Weight for weight the endwise crushing strengths of tnese diverse 
species are substantially equal. 
Table 1. — A comprrison of the specific gravities and t rie strength values 
of two widely different ^oo^s in the green condition 
Species of wood 
Specific gravity 
based on weight 
and volume of 
wood when oven 
dry 
Crushing 
strength 
narallel 
to =rrain 
Specific 
strength 
Mastic. 
Balsa. . 
1 . 01 
.11 
Pounds r>er 
square in ch 
5,ggo 
(Col. 2 1 Col. 1) 
5,710 
5.8RO 
—This mimeograph is one of a series of progress reports issued by the 
Forest Products Laboratory to aid the ligation's d f :e effort. Results 
hero reported are preliminary and may be revised as additional Latj 
become av? a 1 ab 1 e . 
Kimeo No. 1303 
