EVALUATION OF WOOD PRESERVATIVES 151 



Fig. 7 — Three unpainted stacked handling trays. The trays have plastic screen 

 bottoms on which the blocks can be arranged with free air space all around, to 

 promote even drjdng conditions. 



has been followed up to this time at Madison. The principal difference 

 is the omission of any tests of unweathered blocks. Instead, the emphasis 

 is placed on the development of a weathering or aging cycle that will 

 bring about total overall preservative losses Hke those that occur in 

 %-inch stake specimens or in pole-diameter posts in the Gulf port test 

 plot. The character and extent of such losses will be discussed later. 



Two systems of weathering have been employed up to the time of this 

 writing. The first consists in soaking the blocks over the week in water 

 that is changed morning and night and drying them at room temperature 

 over the weekend, in accordance with German standard for leaching; 

 and the second is the same method that is employed in the Madison 

 tests^^' ^^ in which the blocks are strung on nylon thread, separated by 

 glass beads, and exposed to outdoor weathering under natural conditions 

 for sixty days. The duration of this outdoor test has been limited to 

 sixty days, regardless of the season or month of the year. The effective- 

 ness of the climatic conditions at the Chester Field Station during the 

 period from October, 1951, to April 1, 1952, compared with the roof 

 weathering as conducted at Madison with the same creosote sample re- 

 mains to be seen. 



As for the German standard leaching procedure,^^ experience up to 

 April 1, 1952, indicates that the method does not result in the removal of 

 creosote, for example, in the same degree or manner as preservative 

 materials of this type are removed by outdoor weathering conditions. It 

 definitely is not comparable with the latter in its effect. The German 

 leaching procedure simply uses too much water and not enough air and 

 heat; and Bavendam^ quotes Falck as saying that creosote is insoluble 

 in water and that it cannot be washed out of wood. The failure of the 



