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THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



the average and total spread in grams of preservative absorbed. The 

 effect of selection for density is shown clearly — within the particular 

 treatment groups — by the figures for charges 75 and 76. In the latter 

 the use of selected even density blocks reduced the spread to below half 

 of that in charge 75, and reduced the coefficient of variability by two- 

 thirds. 



Regression lines for pickup in grams per cc of block volume on oven 

 dry density are shown for the two groups of charges in Fig. 6. The flatter 

 slope of the lines for charges 19, 20 and 21 seems to reflect the difference 

 in specific gravity and viscosity of the treating solutions. Higher den- 

 sities have greater effect on absorption of higher gravity solutions. The 

 fact remains that there is considerable uncertainty as to the significance 

 of strict selection of the blocks for density if one uses a series of closely 

 spaced gradient retentions. 



Data for 8-pound charges for comparative soil-block tests of two of 

 the cooperative creosotes, Nos. 7 and 9, a low residue domestic oil, low 

 in tar acids and naphthalene, and a British vertical retort tar creosote, 

 respectively, are condensed in Table VII. The differences in the treat- 

 ment results are not considered to be significant. 



Weathering 



The blocks remain on the racks on the laboratory tables for about one 

 week, which is long enough to permit the evaporation of most if not all 

 of the toluene. Experiments have shown that when blocks are treated 

 with toluene alone the toluene is all lost, on a weight basis, within 24 

 hours. When treating solutions of creosote in toluene are used the evap- 

 oration rate, also determined by weight loss, is slower; but it is believed 

 that all of the toluene is gone before the blocks are ready for test. In any 

 event, after the above-mentioned prefiminary drying period the blocks 

 are handled in a manner that differs somewhat from the procedure that 



Table VII — Retention for Full-Cell 8-Pound 

 Treatment Data 

 For parallel comparative soil-block tests of cooperative creosotes No. 7 and 

 9 against Lentinus lepideus, Mad. 534: toluene-creosote treating solution. 



