492 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



attention to the fact that the German Standard^^ for testing wood pre- 

 servatives contains a stipulation that a weight loss of less than 5 per 

 cent shall not be considered significant unless there is visual evidence of 

 actual wood destruction by the test fungus. He presents data to show 

 that a loss of 50 per cent of the relative original impact strength in 

 spruce and fir occurred after about fifteen days in test, and that the 

 weight loss for the test pieces was about 3 per cent only. Impact strength 

 seems to be affected much more than the bending or compression 

 strength. He was confident that his method would not only shorten the 

 time of the bioassay test but also give more reliable and more significant 

 results than those based on weight loss alone. 



After Trendelenburg's death his ideas have been further tested and 

 developed by von Pechmann and Schaile.^^^ In addition to trying out the 

 suitability of the strength test procedure, they have explored the changes 

 in the wood structure with the microscope, and, as decay progressed, 

 they have determined the gross relation between weight loss and solu- 

 bility in sodium hydroxide. 



They present as an example comparable data for the German Standard 

 agar-block test and a test run by Trendelenburg's method, using pine 

 wood (presumably Pinus sylvestris) and the test fungus Coniophora cere- 

 hella, against a proprietary preservative. The absorption of the preserva- 

 tive was essentially the same in each test; but not enough preservative 

 was used to permit determination of the threshold. The main results 

 were that in the impact strength test procedure in fifty days the strength 

 reduction was 66.4 per cent and the weight loss 12.7 per cent; whereas 

 in the standard agar-block procedure in four months the weight loss was 

 only 2.0 per cent. Von Pechmann and Schaile feel that it is possible to 

 save 23^ to 3 months time by using the strength test technique, and that 

 with proper attention to detail the results will be more definite and just 

 as reliable as those obtained in the longer period required for the standard 

 agar-block tests. 



The precise Trendelenburg technique has not been tried out in this 

 country in any comparative tests on wood preservatives but toughness 

 test data on small specimens of wood and veneer, sound, fungus stained 

 and decayed, treated and untreated, have been accumulating at the 

 Forest Products Laboratory at Madison, Wis. The fact that strength 

 loss begins earlier and may increase more rapidly than weight loss or 

 than change in specific gravity in natural infections in the heartwood was 

 shown by the writer^^ and his colleagues shortly after the end of World 

 War I. Confirming data were secured in later tests.^^' ** Scheffer^^ showed 

 the same results, on a more definite basis, by growing Polystictus versicolor 



