EVALUATION OF WOOD PRESERVATIVES 485 



5.90 and 7.97 pounds per cubic foot at the end of the nine-week weath- 

 ering cycle (Table XXXIII); and by extraction these residuals con- 

 tained 3.03 and 3.12 pounds per cubic foot of the fractions distilling 

 below 355°C. On the basis of residue change alone these amounts are 

 calculated at 2.73 and 2.36 pounds respectively. Rhodes states^^ ^' ^^ 

 "In no case was a weathered specimen attacked by the fungus". Para- 

 phrasing his next sentence, this proved that both Creosote I and Creo- 

 sote II at a treatment retention of 16.7 pounds per cubic foot "were affording 

 adequate protection at the end of nine weeks, equivalent to many years 

 of actual service". Was there any reason to expect such specimens to 

 decay? 



It is easier to attempt an answer to that question now than it was in 

 1934. Duncan^^ shows a treatment threshold retention for "conditioned", 

 i.e., unweathered, blocks of 1.6 pounds per cubic foot by agar-block 

 tests, which is in close agreement with an average of 1.56 calculated 

 from recent European tests reported by Schulze, Theden and Star- 

 finger. ^^^^ Of more importance for the question at hand is Duncan's 

 weathered agar-block creosote threshold, given as 5.0 pounds per cubic 

 foot. The loss in creosote at this 5 pound level was 57 per cent, which 

 left 2.2 pounds per cubic foot of residual creosote in the blocks. The 

 residue is calculated to have risen, as a result of weathering losses of 

 the lower fractions, from an original 20.9 per cent (Table II) to 48.5 

 per cent; and on the basis of this figure the 2.2 pounds of residual oil 

 consisted of 1 .07 pounds per cubic foot of the fraction above 355°C and 

 1.13 pounds of the fraction below 355°C. 



The Rhodes' nine-week weathered blocks still contained roughly two 

 to three times this amount below 355°C. One may conclude that the 

 nine weeks weathered blocks should not have shown decay under the 

 culture conditions; and certainly none of the more briefly weathered 

 blocks should have shown evidence of attack. If original retentions of 

 10 and 8 pounds of creosote had been used in the experiments the test 

 fungus might have attacked nine and twelve weeks weathered 8-pound 

 blocks treated with either Creosote I or Creosote II (Table XXXIV). 



Using the results of the Madison tests shown in Table XXXV and 

 Fig. 34 as indices of what might have happened if Rhodes, Roche and 

 Gillander had used 16.7, 10.0 and 8.0 pounds at treatment and if — 

 instead of employing an approximate agar-block technique — they had 

 run their evaluation tests by the soil-block method, one would have 

 expected decay to show up as indicated by the horizontal lines in the 

 data columns in Table XXXIV. In other words, in the 16.7 pound treat- 

 ments Lentinus lepideus would probably have attacked the blocks if they 



