EVALUATION OF WOOD PRESERVATIVES 497 



plans could have been more closely harmonized before the most recent 

 Ottawa work was started, at least to the point of some tests with the 

 same procedures and same test fungi. However, nothing in Sedziak's 

 results negates the general conclusions reached at Madison and at Bell 

 Laboratories about the value of the present soil-block technique for the 

 testing of creosote and other oil type preservatives. 



CONCLUSIONS 



1 . In the course of this paper evidence and interpretations have been 

 presented to show that the soil-block technique incorporating a weather- 

 ing procedure is a practical, rapid method of bioassay and that the 

 results obtained from this method are in general agreement with acceler- 

 ated stake and long time pole-diameter post tests on the same or similar 

 preservatives. For example, it is shown that a creosote retention at 

 treatment of 9-10 pounds per cubic foot is necessary to insure a satis- 

 factory degree of preservative permanence in test blocks, in J^-inch 

 stakes and in the outer 1 inch of test posts. There is no reason to believe 

 that this minimum limit does not apply to the outer 1 inch of poles in 

 Une. 



2. The good reputation of well creosoted material is reaffirmed by 

 these findings. Moreover, thej^ show why failures have occurred and 

 indicate what should be done to forestall such failures. 



3. Since the results of the block tests are essentially the same as the 

 results of the much longer stake and post tests, the block test data can 

 be used at once as a basis for the establishment of the necessary amounts 

 of the respective preservatives distribution in the wood where they will 

 do the most good. The possibilities of bleeding increase as the retention 

 is increased, so the bioassay technique becomes an essential tool for 

 closer appraisal of effective wood preserving power. 



4. It is important now to recognize that the soil-block results with 

 creosote, for example, reveal the fact that the results of the European 

 agar-block tests are — in all cases — too low to represent indices of 

 actual requirements in treated wood . Therefore, the results for creosote 

 tabulated by Schulze, Theden and Starfinger^^ ^^^ have to be corrected 

 upward by some multiplying factor; perhaps of the order of three or four, 

 before they can be correlated with the results on blocks, stakes and posts 

 presented in this paper. For the true scientific solution of the problems 

 of these different techniques, perhaps an international task force may be 

 required. 



5. The interpretations presented in this paper indicate that the use of 



