140 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



The second — and more important — function of the soil-block eval- 

 uation is that incorporating a weathering or aging procedure. This puts 

 the test in the more practical category of testing the wood preservative 

 properties, viz., toxicity and permanence. In this respect it has something 

 in common with the German Standard DIN DVM 2176^^ for short time 

 mycological testing of wood preservatives by the block method and 

 covers a broad concept from the treating through partial aging of the 

 blocks. Separate German standards cover procedures for leaching^^ and 

 volatihty tests,^^ (p. 264 and Fig. 42 of Reference 78). 



The Laboratories' concept of the scope ol the soil-block test including 

 the weathering procedure is definite. It must be appreciated that this 

 method which employs manipulative procedures involving both toxicity 

 and permanency yields significant data in a period of only a few months. 

 The data derived must be correlated subsequently, of course, with the 

 data covering the results of tests of % inch stakes six to seven years 

 later, with the data on test posts some ten to fifteen years later, and 

 with data on poles in line some twenty-five years later. 



It is only being realistic to say that the Bell System cannot afford to 

 wait for physical life tests of new materials under natural conditions of 

 exposure before recommending them where techniques and extensive 

 experience permit acceptable estimates to be made from accelerated 

 evaluation in relatively short periods of time. 



Preparation of the Test Blocks — Manufacture 



Southern pine sapwood, free from stain or decay, is used as a base 

 material for the test blocks. The process of manufacture begins at the 

 saw mill, where freshly cut logs selected for the purpose are carefully 

 sawed into one inch boards. Straight grain material is most desirable. 

 The boards are kiln-dried immediately and shipped as soon as practicable 

 to the Laboratories. It has been the practice to store the boards in a 

 steam heated basement where the humidity is low enough to hold the 

 moisture content of the boards down to about 5 to 7 per cent. The sap- 

 wood only is used, which means that any small heart wood portions must 

 be marked out for rejection. The blocks are accurately cut %-inch cubes. 

 A J^-inch hole is drilled through the center of the tangential surfaces of 

 each block. It has been found that drilling the hole through the trans- 

 verse surface, which was the early practice with Waterman, Leutritz 

 and Hill^^* is a difficult procedure; and sometimes it amounts to an 

 impossibihty because the harder summerwood layers deflect and break 

 the drills. In any event, drilling through the tangential surface opens 

 up more paths for longitudinal absorption and penetration, as well as 



