4 BULLETIN 77, U. S. DEPARTMENT OF AGRICULTURE. 
graphically in figures 1 and 2. The increase in strength of the props 
due to seasoning is very evident in each species, and the average 
strength of the seasoned props of all species is 2.3 times that of the 
green ones at both maximum load and elastic limit. In the case of 
the caps the average strength of the dry timbers at the maximum 
load is 1.6 and at elastic limit 2.2 times the strength of the green 
timbers. While at the elastic limit the influence of the moisture 
2000 3000 4000 5000 6000 7000 8000 
MODULUS OF RUPTURE - POUNDS PER SQUARE INCH 
Fig. 2.— Comparison of different species; 6-inch round mine caps— air-dried and green. 
was practically the same for both the crushing and bending tests, at 
the maximum load it is much more pronounced in the crushing tests. 
Stiffness in bending was increased by seasoning to 1.4 times the 
green value. There appears to be no marked variation in this 
strength ratio among the various species tested. It is slightly below 
the average in Douglas fir, due to the consistently high values for 
the green material in comparison with the other species. 
