460 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



wood preserving procedures. His discussion of the importance of ''weath- 

 ering" tests and of his own results with such tests make up one of the 

 best, if not the best consideration of this important phase of evaluation 

 tests that had appeared up to that time. 



Numerous references to weathering techniques will be found in van 

 Groenou, Rischen and van den Berge;"^ and van Groenou's own paper"^ 

 in 1940 is an excellent short review of previous work, giving his views of 

 the pros and cons of different procedures with emphasis on the essential 

 nature of some test to determine what changes are likely to take place 

 in a preservative as a result of leaching or evaporation. 



The f oUoAving examples will be interesting as illustrations of the differ- 

 ent techniques that have been employed in testing the toxicity, or the 

 potential preservative value of creosotes. F. H. Rhodes and Gardner^^ 

 in 1930 determined evaporation losses of creosote fractions from thin 

 pads of dried ground Sitka spruce pulp. The whole creosote and the 

 fractions were introduced in an ether solution. The impregnated pads 

 were placed on top of agar cultures in Petri dishes. The test fungus was 

 the usual Fomes annosus, more recently called simply Madison 517. They 

 state that: 



"It was found that under these conditions (the Petri dish covers 

 loosely fitting — not water sealed) the more volatile preservatives vapor- 

 ized from the test specimen, so that at the end of the month only a 

 relatively small portion of the fungicide remained in the pulp." 



They were using a domestic creosote with a specific gravity of 1.065 

 at 38/15. 5°C and a residue above 355°C of 21 per cent. They tested 

 fractions of the dead oil from which the tar acids and tar bases were 

 removed, and fractions of the tar bases and the tar acids themselves. 

 They determined percentage losses by evaporation for all lots by letting 

 the treated pulp disks remain in covered Petri dishes for one month at 

 25°C. All of these reported losses for the dead oil occurred in fractions 

 boiling below 316°C, for the tar acids in fractions with the same upper 

 limit, and for the tar bases in the fractions boiling below 308°C. The 

 losses varied inversely as the boiling range, the greater being in the 

 low-boiling fractions, as was to be expected. The toxic limits for Fomes 

 annosus that they determined showed a gradual increase as the boiling 

 point increased, i.e., in agreement with other workers with agar tests 

 they found the lower boiling fractions the most toxic. Their bibliog- 

 raphy, with one or two exceptions, covers American articles only. 



Rhodes and Erickson,^^ continuing the same general technique, but 

 substituting mechanical pine pulp for spruce pulp, showed that much 



