8 



BULLETIN 607. U. S. DEPARTMENT OF AGRICULTURE. 



of free carbon in the mixture there was a decrease in the absorption 

 and penetration. However, in the case of mixtures with tar No. 3 

 (fig. 4, c) after a certain point was reached there was a rise hi the 

 penetration and absorption curves upon the addition of larger per- 



IMPREGNATION TESTS. 

 (Data in Tables 5, 6, and 7.) 



z^ u 











































Ota. 











































































s-'-M 



g«'6« 



I/JM 



ffl0., 4 



j3« 

























£TAR 



























































-TARN 

































































































































10 

 1000 









































































































































































900 







































































































































































800 







































































































































































700 





























*^Tta 





































































































































600 



















































































s 











































H 























TAR 



HO 



2 

















X 500 



kl 



OC 













































































































KtAR 









3 











































S3 400 



ee 



ft, 





































































































































































300 







































































































































































200 







































































































































































100 







































































































































































nflfl 











































25 



50 

 PERCENT OF TAR BY VOLUME 



73 



100 



Fig. 3. 



-The variation in time of treatment and pressure necessary to secure a given absorption in paving 

 blocks using mixtures of creosote No. 4 and carbon-free tars Nos. 1, 2, and 3. 



centages of free carbon to the mixture. It is probable that this was 

 caused by the character of the free carbon mats formed on the sur- 

 face of the wood as the mixture was forced into the interior of the 

 specimens. The free carbon particles in tar No. 3 were very much 



