EVALUATION OF WOOD PRESERVATIVES 



441 



§90 

 a. 



UJ 

 Q. 



70 



Q 

 §60 



UJ 



O 



a. 50 



40 



12 



1 23456 789 10 1 



TREATMENT RETENTION IN POUNDS PER CUBIC FOOT 



Fig. 26 — Theoretical lines for estimating threshold retention for creosote No. 

 5285A; %-inch southern pine sapwood stakes. 



will inevitably be some difference of opinion as to which level to use. In 

 the case of %-inch treated stakes it is quite evident that the preservative 

 is no longer functioning effectively if the stakes have reached a decay 

 rating of 7 or less. In such small specimens it is questionable whether 

 any purpose is served by allowing them to stay in the ground under the 

 conditions at the Gulfport test plot until they practically fall over by 

 being completely destroyed at the ground line. 



Anyone who has worked with small test plot specimens will appreciate 

 the many difficulties in the way of establishing standard procedure for 

 determining the "failed" point or the end point of specimen life. On 

 somewhat larger stakes Rennerfelt^^ has used a strength testing appara- 

 tus. To test the fitness of small poles in line some Associated Operating 

 Companies have used a spring scale dynamometer which is slipped onto 

 the base of a pike pole. In actual utility plant experience it is obvious 

 that it is impossible to wait for the complete decay of the wood unit. 

 Elaborate tables have been worked out as guides for pole line inspectors 

 to let them know how far decay can go under given load conditions before 

 a pole has to be removed from line. Generally speaking, such removal 

 must occur at some period well in advance of the time that the specimen 

 would have rotted clear through at the ground line. In the writer's 

 opinion it might be preferable to estimate the average life for ^-inch 

 stakes from the point where the depreciation curve passes downward 

 through the 60 per cent condition line, leaving all the units in any given 

 series in test until that time, except of course the stakes that may have 

 actually rotted off earlier. 



Study of Table XIII indicates clearly that both threshold and average 



