EVALUATION OF WOOD PRESERVATIVES 493 



on red gum sapwood in large test tubes and testing matched specimens 

 for various strength properties as decay progressed. 



The Trendelenburg technique has possibilities, but it will be some time 

 before one can say whether it is practicable to take full advantage of it 

 in developing supplemental bioassay tests. The one outstanding difficulty 

 in the way of extensive use of strength tests on small specimens lies in 

 the procurement, in the very variable southern pine, for example, of a 

 requisite quantity of straight grained quarter saAved wood for the manu- 

 facture of the matched blocks. Small scale check tests are practicable, 

 according to the writer's experience. The cost of personal supervision and 

 manufacture of any large number of specimens would appear in advance 

 to be exorbitant. Still, strength loss as a result of attack in treated wood 

 is important, and Trendelenburg's ideas may win more proponents, if 

 only as a supplemental procedure, after the soil-block technique has 

 become more firmly established and appreciated. 



OTHER ACCELERATED BIOASSAY TESTS 



There are a number of items that must be mentioned before bringing 

 this long paper toward its conclusion. There are, for example, other types 

 of outdoor exposure tests on wood and of laboratory block tests than 

 those cited. Two types only will be used as illustrations of the efforts 

 that are being made to evaluate preservatives by other than the tradi- 

 tional service test, namely: Verrall's^^^' ^^^ above ground outdoor testing 

 procedure, and the experiments of Tippo et al with large block tests 

 devised to determine effective concentrations of preservatives for preven- 

 tion or control of decay in wooden ships. 



Since the soil-block test is essentially a laboratory simulation of con- 

 trolled ground line conditions, there is a need for some other type of test 

 that will approximate the above ground conditions to which treated wood 

 may be exposed. Verrall treats pieces of dressed nominal 2x4 inch 

 southern pine sapwood and exposes them to the varying wet and dry, 

 hot and cold weather conditions at Saucier, Miss. One of two pieces has 

 a 45° end cut. This end cut is toe-nailed to the side of the other piece, 

 which is then nailed upright on a supporting treated or untreated rail 

 support, with the A' up. This permits maximum hazard as far as catching 

 water is concerned. His results are furnishing valuable information about 

 pentachlorophenol, copper naphthenate and organic mercury com- 

 pounds, for example. His techniques are applicable to other preservative 

 problems, and other investigators are using his scheme in Canada for 

 general studies,^^"' ^^^ and at Ann Arbor, Mich., for testing the amount 



