EVALUATION OF WOOD PRESERVATIVES 



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100 



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70 



60 



50 



Q 



z 

 o 



O 40 

 UJ 



o 

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S 30 



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TREATMENT RETENTION IN POUNDS PER CUBIC FOOT 



12 



Fig. 23— Theoretical lines for estimating threshold retention for creosote No. 

 5283, in ^-inch southern pine sapwood stakes, empty-cell and full-cell (toluene 

 dilution) treatments, and for greensalt K; Gulf port test plot. See text, Tables XI 

 and XIII, and companion Figs. 24, 25 and 26. 



The tendency for the 7-year Unes to fall off to the right shows the effect 

 of increasing decay in the 8-pound group. In the higher residue creosotes 

 the earlier decay of the toluene dilute 8-pound treated specimens — that 

 is, specimens that were treated below the threshold retention — tends 

 to pull the lines so far down as to spoil their usefulness as tools for 

 estimating thresholds. Obviously the slopes of the Unes will be influenced 

 by the depreciation rating of the 4-pound as well as the 8-pound groups. 

 Furthermore it would appear that the utility of the specimens treated 

 with toluene-creosote solutions for estimating thresholds does not extend 

 much beyond the 6th year of exposure under conditions such as those 

 prevaihng at the Gulf port plot. 



The estunated thresholds at the 3-, 6- and 7-year inspection periods, 

 and the estimated average life values for the different groups are sum- 

 marized in Table XIII. The average hfe is estimated from the intersec- 

 tion of the depreciation curves and the 50 per cent condition Hues. There 



