EVALUATION OF WOOD PRESERVATIVES 479 



theoretical residue increase related to the given loss data. The loss data 

 are those of Rhodes et al (loc. cit.) (see Table XXVII) with extrapola- 

 tion to a twelve- week period ; column 2. The same holds for the residue 

 data in column 5, from which the residual pounds per cubic foot below 

 355°C of Column 6 were calculated, by appl^dng the respective percent 

 residues to the pounds per cubic foot of total creosote remaining in the 

 blocks, column 4. The figures in column 8 were calculated in the same 

 way by using the theoretical percent residue figures in column 7. The 

 data in columns 7 and 8 are represented by the curves in Fig. 32, for 

 Creosotes I and 11. The curves approach each other closely enough for 

 the purposes of the present interpretation, particularly in the case of 

 the 19 per cent residue oil. 



Now, supposing that Rhodes et al had used two lower retentions, say 

 10 pounds and 8 pounds in their experiments in addition to the 16.7 

 pounds; and assuming that their losses would be of about the same 

 magnitudes for the 16.7 and 10-pound treatments and slightly higher 

 for the 8-pound treatment, one would come out with theoretical calcula- 

 tions like those shown in Table XXXI Y. The significance of the magni- 

 tudes of these amounts below 355°C will be suggested in the following 

 paragraphs. 



The Gross Characteristics of the Residual Creosotes in Soil-Block Tests 

 of Weathered Blocks 



Madison test data for average losses of creosotes by weight, from 

 treated blocks, during the periods of weathering and reconditioning are 

 rounded off and plotted in Fig. 33. The usual procedure was to bring 

 the weathered blocks into the laboratory and place them under constant 

 temperature and humidity of 80°F and 30 per cent until the blocks came 

 to approximate weight equilibrium. Examination of the figure indicates 

 very definitely (1) heavier losses in the lower retentions respectively for 

 all of the creosotes, and (2) lower losses for the higher residue oils than 

 for the lower residue oils. These conclusions follow naturally from a con- 

 sideration of the distillation ranges of the oils and the treatment con- 

 ditions, confirming the inferences from other loss data already discussed. 



These losses of creosote from 8- to 10-pound groups of weathered 

 treated wood blocks seem to be in the neighborhood of 40-50 per cent 

 by Aveight or by extraction. The aim of the weathering techniques now 

 being developed at Bell Telephone Laboratories is to reach some defi- 

 nable end point in the protective life of the preservative that will reflect 

 the end point or failure point of test plot specimens or poles in fine. 



