16 



BULLETIN 607, U. S. DEPARTMENT OF AGRICULTURE. 



longitudinal penetration of about 17 per cent resulted from the 

 increase in the proportion of tar. 



When the mixture containing 33 J per cent of tar was used, it was 

 noted that after the specimens had been treated for a certain length 

 of time (see Table 15, footnote) no increase in the absorption was 

 obtained. Hence it was not possible in this test (where the tem- 

 perature of the preservative was 160° F. and the pressure 80 pounds 

 per square inch) to obtain an absorption with the mixture equal to 

 that obtained with the creosote, even when the time of treatment 

 was increased to eight hours*. The average longitudinal penetration 

 was about 33 per cent less than obtained with the creosote. 



PENETRANCE TESTS. 

 (Data in Tables 16 and 17.) 



• 66.7% CREO. 



33.3% TAR 



* IT W«S NOT POSSIBLE TO OBTAIN THI PEOUIP5D 

 ABSORPTION WITH THIS MIXTURE AS A FURTHER 

 INCREASE IN THE TIME OF TREATMENT DID HOT 

 INCREASE THE ABSORPTION 



TIME OF TREATMENT VARIED 



33.3% TAR 



PRESSURE VARIED 



Tig. 8. — The relative effect of varying (1) time of treatment and (2) pressure in order to secure approxi- 

 mately the same absorption in longleaf pine using mixtures of tar No. 4 and creosote No. 6. With time 

 varied the treating temperature was 160° F. and the pressure 80 pounds per square inch. With pressure 

 varied the time of treatment was 2 hours and the temperature 160° F. 



i 



Time of treatment and temperature of preservative constant and pres- 

 sure varied. — (Tables 16 and 17 and fig. 8.) 



The specimens used in these tests were matched with those just pre- 

 ceding, and hence the results are directly comparable. The pressure 

 required to obtain a given absorption in the test in which the tempera- 

 ture of the preservative and the time were constant was approximately 

 proportional to the amount of the tar in the mixture. With almost the 

 same absorption of preservative the penetrations of the two tar and 

 creosote mixtures were from 27 to 29 per cent less than those obtained 



