. The Bell System technical journal . xic according to this method failed in outdoorexposure tests. In many cases such failures could not be ascribed toobvious conditions such as high volatility or solubility. Instanceswere also met wherein materials of little value according to the petridish method were able to prevent decay in the field. There is no dis-position to advise against all use of this method as it is a valuable toolin making initial judgments on a new material; but it should be verifiedby other means before the expense of a field trial can be justified, and a^ Numbers refer to bib
. The Bell System technical journal . xic according to this method failed in outdoorexposure tests. In many cases such failures could not be ascribed toobvious conditions such as high volatility or solubility. Instanceswere also met wherein materials of little value according to the petridish method were able to prevent decay in the field. There is no dis-position to advise against all use of this method as it is a valuable toolin making initial judgments on a new material; but it should be verifiedby other means before the expense of a field trial can be justified, and a^ Numbers refer to bibliography at end. 196 BELL SYSTEM TECHNICAL JOURNAL proper degree of skepticism should be exercised before condemning apreservative on the basis of this test alone. Parallel with the use of nutrient substrata of the malt-agar type inthis country, there grew up in Europe a technique which utilized thewood itself as a medium for dispersion of the toxic agent. This kolleflask method (Fig. 2) was standardized and accepted by a conference. Fig. 1—Assay by petri dish method. Test-fungus No. 517 on increasing amounts of coal-tar creosote. of European workers at Berlin in 1930.^ An outline of the methodfollows: Wood blocks of a convenient size are impregnated with thetoxic agent, usually in solution, and after evaporation of the solventthe blocks are placed in kolle flasks and supported on glass rods set inmalt-agar covered with the actively growing mycelia of the test conference advised the use of ConiophorQ cerehella as the test A LABORATORY EVALUATION OF WOOD PRESERVATIVES 197 fungus, but suggested that at least two species should be used in eachtest. After three or four months exposure to the wood-destroyingfungi, the blocks are removed from the flasks, freed from adheringmycelium, and the weights taken before and after the test period usedas a measure of the amount of decay. The kolle flask method has much to recommend it, overcoming asit does many of the difficulties
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