152 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



Fig. 8— Creosoted test blocks, arranged on pins on a metal rack in a large glass 

 tube to facilitate handling during sterilization and the subsequent operation of 

 planting in the soil cultures. 



leached creosoted blocks to decay in the reported soil-block tests on the 

 cooperative creosotes^^ confirms European experience. Schulze, Theden 

 and Starfinger^^ ^^^ (p. 15, Tab. 13 of Reference 54) indicate that there is 

 little if any reduction in the preservative value of creosote as a result of 

 their standard leaching tests. Therefore, in order to accelerate the weath- 

 ering process new techniques are being worked out at the Laboratories 

 in which the wet cycle is shortened (Cf . Rhodes et al,^°' ^^) and in which, 

 without the use of a wheel, controlled artificial heat is used to speed up 

 evaporation during the rest of the cycle. 



Conditioning 



Convenient unpainted wood trays (Fig. 7) with plastic screen bottoms 

 are used for handUng the blocks in groups at any time during their 

 processing schedule. At the end of the weathering cycle, indoor or out- 

 door, the blocks are arranged on such trays and conditioned to an 

 approximate constant weight and about 12 per cent moisture content on 

 shelves in the 80°F and 70 per cent relative humidity of the incubation 

 room. Weights before test, to the nearest 0.01 gram, are taken at the 

 end of the conditioning period. The relative amounts of wood, water and 

 creosote in the blocks are determined by weight from test blocks, and 

 by weight and extraction from control blocks after steriHzation. 



Sterilizing 



The test blocks are arranged for sterilization on metal racks in large 

 glass tubes (Fig. 8). The autoclave temperature is held at 100°C for 15 

 minutes. 



Flow Chart for the Bioassay Test 



The various steps in the whole evaluation procedure are indicated in 

 the flow chart shown in Fig. 9. Rhodes^' used a similar idea to illustrate 

 his procedure. 



