STRENGTH TESTS OF STRUCTURAL TIMBERS. 7 
average strength at elastic limit and stiffness. In the air-seasoned 
beams the untreated butt cuts were higher in strength and stiffness 
than the treated top cuts, but, on the other hand, the untreated top 
cuts fell below the treated butts in strength and stiffness in nearly 
every case. In the partially seasoned stringers the treated and 
untreated material falls together somewhat more closely. 
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3 - Butts T = Tops 
Fig. 3.— Effect of preservative treatment on the strength and stiffness of loblolly-pine stringers treated 
partially air dry. 
DOUGLAS FIR. 
Figures 5 and 6 show the strength and stiffness of treated and 
untreated stringers of green and seasoned Douglas fir, respectively, 
treated by the so-called "boiling " process as used in this case. There 
appears to be a marked weakening of the breaking strength with the 
particular treatment, used. The average breaking strength of the 
stringers tested green and after seasoning is 33 per cent and 39 per 
cent, respectively, less than the average strength of the natural 
stringers. The fiber stress at elastic limit also appears to be reduced, 
although to a somewhat less extent. In the green material no 
weakening is apparent in the stiffness. The seasoned stringers, 
however, show a falling off in stiffness in the treated material. 
Figure 7 shows the strength and stiffness of green 1 Douglas fir 
treated by the so-called "steaming" process. The breaking strength 
1 The air-seasoned material is not yet tested, July, 1915. 
