452 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



(b) The size and shape of the test block ; 



(c) The use of toluene or any other diluent with creosote to get low 

 retention; 



(d) The distribution of the preservative in the block; 



(e) The practice of heat sterilization of the creosoted blocks; 



(f) The whole philosophy of the weathering procedure; and 



(g) The methods of control assay, such as weight, creosote extraction, 

 analysis of extracted creosote, and lime fusion chloride determinations 

 as applied to pentachlorophenol. 



None of these questions can be simply brushed aside, in spite of the 

 fact that some of the points raised have a little of the nature of quasi- 

 technical road blocks that may temporarily slow the approach to any 

 standard laboratory test for creosote. Experimental work now under way 

 at Madison^^ and our own laboratories at Murray Hill will help answer 

 some of the questions. The following discussion will at least explain the 

 nature of the problems involved. 



Density and Growth Rate 



Data on the relation of block density and absorption at treatment 

 have already been presented (Tables I, IV, V and VI). It is not yet 

 evident that either density or growth rate has any material effect on the 

 treatment retention thresholds for creosote when the tests are run on 

 outdoor (or equally depleted) weathered blocks, and when the steps in 

 the gradient retentions are properly spaced. When some present experi- 

 ments are finished the matter may be resolved more conclusively. 



Size and Shape of the Test Blocks 



Some critics of the soil-block test have objected rather strenuously to 

 the ^^-inch cube because the two transverse faces are so close to each 

 other. The inference is that either (a) the preservative, and in this case 

 creosote is usually meant, is lost too rapidly through the end grain of the 

 wood or (b) that in the evaporation process, or in the course of the 

 weathering procedures, the preservative may be concentrated on the 

 transverse faces. The validity of these contentions is under investigation. 

 However, the importance of block size and shape can be greatly exag- 

 gerated. 



One need not assume, in order to plan for comparative tests of oil 

 preservatives, that a block must or can be cut so that creosote will be 

 lost from it at exactly the same rate or manner as creosote may be lost 

 radially from the concentric annual rings of a post or pole. Block shape 



