EVALUATION OF WOOD PRESERVATIVES 451 



of low retention to decay showed up in the Gulf port plot/^ and it was 

 explained by Laboratories' extraction and analysis of the creosote in the 

 decaying or failed test stakes and test posts. One may say that such 

 results confirmed suspicions; and they did, because creosoted poles in 

 line — which were "related" to the decaying posts at Gulf port — were 

 found on inspection to be behaving badly. It is believed that corrective 

 measures in the way of supplemental ground line treatment were taken 

 in time to give the poorly treated poles a reasonably satisfactory Hfe. 



In another striking set of circumstances, however, a number of cases 

 of unprecedented premature failure of pine poles in line treated with a 

 mixture of creosote and copper naphthenate petroleum revealed that the 

 preservative solution had gone out of control and that in consequence the 

 poles had not received the specified protective amounts of copper. Bell 

 Telephone Laboratories' analyses of parts of the decaying poles showed 

 that the decaying areas contained less than, and the sound areas more 

 than, the Madison soil-block threshold of approximately 0.08 Ib/cu ft of 

 copper as metal. 



These poles were immediately traced back to the supplier by their 

 brand label. Present day pole treatment specifications in general require 

 branding of each pole unit with symbols or code letters for the supplier's 

 plant, the species of timber, the year of treatment, and the class and 

 length of the pole. Each such pole becomes automatically a unit in a sort 

 of universal service test in Bell System pole lines. 



Service tests and service records are a significant part of the over-all 

 process of evaluating wood preservatives, but insistence on service rec- 

 ords as the most important criterion simply perpetuates the reputation 

 of established preservatives and forever blocks or seriously impedes the 

 development of new and promising materials. In the very nature of the 

 case the results of service tests can be stated in the form of broad generali- 

 zations only. The truly technical approach must be made through better 

 methods of measuring the effectiveness of preservative materials by 

 accelerated field tests on a sufficiently large number of small stakes or by 

 controlled laboratory experiments such as the soil-block tests. 



DISCUSSION 



There are a number of things in connection with the soil-block test 

 procedure, its interpretation and the correlation of its results with the 

 results of other evaluation methods that require further discussion. For 

 example, questions have been raised vigorously on such matters as: 



(a) The effect of variation in growth rate and density of the wood; 



