WOOD SOIL CONTACT CULTURE TECHNIQUE 



133 



ation of the compounds. The advantage of the laborator>' method in the 

 matter of time is a decided one, but the field trial is valuable for testing the 

 permanence of the preservative. For example, mixture 4 was found in the 

 laborator}- test to be a very effective preservative, but the initial preserva- 

 tive properties were dissipated by exposure to the weather, since 50% of the 



FAILED 2H I!<"^ECTE;D Q3 SOUND Q^ ^OT EXPOSED [^ 



GREENSALT CU 



K. ARSENATE 



MIXTURES 



RETENT -* 



1.6 



m 



? 5 



0.17 0.7 0.7 0.8 



0.7 1.4 



2 3 12 3 



Fig. 10— Results of field exposures on the four mixtures of Table 3 and other compounds 

 creosote, Greensalt K, copper arsenate (retent in pounds per cuImc foot). 



specimens had to be removed because of failure within three >-ears. When 

 a compound is a poor preservative, as in the case of mixture 2. both labora- 

 tory and field trials ser\'e to eliminate it from further consideration. By the 

 soil-contact method every specimen treated with mixture 2 was badly 

 attacked by all the organisms used, whereas at a comparable retention only 

 35% of the specimens in the field trials had failed after three years' exposure. 



