EVALUATION OF WOOD PRESERVATIVES 457 



might cause a measurable loss of volatile creosote fractions from freshly 

 treated blocks; but such losses appear to be negligible in the case of 

 weathered blocks. At Bell Telephone Laboratories control data on these 

 possible losses are being determined by extraction of control blocks after 

 the steriUzation phase. Such blocks are run through all the steps in the 

 bioassay procedure up to planting in the soil-cultures. It mil be recog- 

 nized by anyone familiar with pressure treating methods that the 100°C 

 temperature, usually held for 15 minutes only, represents a much gentler 

 set of conditions than the after-treatment steaming for several hours at 

 240-259 °F which is permitted in many specifications for creosoted poles. 



The Weathering of Creosote and Creosoted Wood 



Creosote is a remarkably good wood preservative, and nothing in the 

 following paragraphs is intended to detract from its reputation in that 

 respect. Sometimes the creosote oozes or bleeds from the surfaces of 

 treated units such as poles and crossarms, especially on hot, sunny days; 

 and when such bleeding occurs the treated material is unsatisfactory for 

 use in mam^ parts of the telephone plant. In order to prevent bleeding 

 difficulties and the consequent unhappy employee and public relations 

 that result, the retention requirements have been held down to the com- 

 mercial standard level of 8 pounds per cubic foot for southern pine poles, 

 and the residue above 355°C limitations on the creosote have been kept 

 in actual practice at 25 per cent or below except when war or post-war 

 emergencies have interfered. 



The creosotes Ymy in the proportion of readily volatile materials they 

 contain, and these materials are lost from creosoted wood — largely by 

 evaporation — under many different use and exposure conditions. The 

 general facts about such losses have been reported over and over again 

 since the turn of the century. The significance of such losses is still not 

 broadly understood or appreciated. Their possible bearing on the weath- 

 ering procedure to be used in the soil-block tests is of fundamental im- 

 portance. Paraphrasing the quotation from Schmitz^^ cited in an earlier 

 paragraph: It is really necessary to know how much creosote to inject 

 into wood to allow for loss by volatility and to insure a residual of the 

 preservative, remaining in sufficient amount, to protect the wood for an 

 economical service period. Bell Laboratories has been deeply concerned 

 Avith the question whether it is practicable under commercial conditions 

 to specify enough retention at treatment to provide the necessary pro- 

 tective residual and at the same time require clean, satisfactory, treated 

 poles and crossarms for Operating Company use. 



