A LABORATORY EVALUATION OF WOOD PRESERVATIVES 211 



leaching. The losses in weight on the unleached specimens are also 

 present in the controls and are presumably due to an extremely soluble 

 non-toxic salt known to be present. Analysis of the leach waters 

 indicates that the toxic substances were also slowly but definitely 

 soluble. Field results on this same preservative were favorable for a 

 year, but considerable decay was found the second year in all but the 

 two highest concentrations. Table III presents the results obtained 

 with a well-known proprietary preservative of the organic type. 

 The concentrations given are for the preservative as purchased, which 

 consists of a 25 per cent solution of solids in a volatile solvent. This 

 solvent was allowed to evaporate completely before exposure of the 

 test blocks to the fungus. For comparative purposes Table IV 

 illustrates a test of a typical coal-tar creosote. Included as a matter 

 of special interest, Table V outlines the wood-block assay on a material 

 which the petri dish method indicated to be worthless. 



This adaptation of the kolle flask method has been in constant use 

 more or less in its present form for the past three years. Hundreds of 

 complete assays have been made with results to date in good agree- 

 ment with the slower and more expensive outdoor tests. By the use 

 of a range of concentrations the relative efficacy of various preserva- 

 tives can be judged, but definite expressions of the absolute value of 

 any preservative have been avoided. With conditions controlled for 

 maximum decay, this test is admittedly severe. This very severity, 

 however, is probably an asset in the elimination at the outset of the 

 poor and mediocre materials unworthy of further study. 



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