442 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



life estimates for any given set of small specimens will vary, depending 

 on the time at which the estimates are made. Taking the 6-year inspection 

 data as perhaps representing the best figures from which to make thresh- 

 old and average life estimates of this kind, it appears that in the case of 

 all of the four creosotes something more than 8 pounds of creosote per 

 cubic foot was necessary to protect the %-inch stake specimens against 

 decay. There seems to be no material difference in the performance of 

 creosotes 5283 and 5286B as far as the estimated thresholds are con- 

 cerned. For both the empty-cell and full-cell treatments it appears to be 

 somewhere in the neighborhood of 9.5 pounds or above. In the case of 

 the higher residue oils 5286A and 5285A there appears to be a significant 

 difference between ratings obtained from the empty-cell specimens and 

 from the toluene dilute full-cell specimens. Estimates of average life from 

 the 8-pound empty cell specimens appear to be significantly higher than 

 estimates from the 8-pound full cell toluene-creosote specimens, except 

 in the case of oil No. 5286B (Table XIII). The estimated thresholds for 

 the full-cell toluene-creosote specimens lie within the same general mag- 

 nitude as the retention at treatment thresholds found in the soil-block 

 tests. (Cf. Tables XIII and XXXV). 



How far one is justified in comparing straight 8-pound empty-cell 

 treatments and 8-pound full-cell toluene-creosote treatments in ^-inch 

 stakes is still not clear. It certainly cannot be done without taking into 

 account the much greater variability in the retentions in empty cell 

 stakes and the different but difficult to describe variations in distribution 

 of the creosote from outside to inside, particularly in the case of empty 

 cell treatments with high residue oil. Unless the empty-cell stakes are 

 carefully selected within limited variations from the average retention, 

 it has been found that the empty-cell coefficient of variability for reten- 

 tion in an 8-pound treatment, for example, may run as high as 35-40 

 per cent, against a coefficient of 8-10 per cent only for companion full-cell 

 treatments with toluene-creosote solutions. The comparisons among the 

 latter treatments appear to be more rational and fairer; and they may 

 give a truer picture of effective threshold requirements. 



The analysis of the stake test data here presented is intended merely 

 to illustrate one set of procedures that may be used in the interpretation 

 of small stake tests. The four sets of data are part of a much larger group 

 of results that are being worked up for publication. Among the latter 

 there are numerous lots indicating that truly protective thresholds of 

 creosote for %-inch stakes lie somewhere between 10 and 12 pounds per 

 cubic foot, which is not far out of line with the estimates given above. 

 Final analysis and publication will either confirm or modify such esti- 

 mates. 



