10 



BULLETIN 607, U. S. DEPARTMENT OF AGRICULTURE. 



pressure were varied so as to obtain approximately 16 pounds absorp- 

 tion per cubic foot. 



Figure 5 indicates that when the amount of free carbon in the 

 mixtures was increased, the difficulty of securing a given absorption 



IMPREGNATION TESTS. 

 (Data in Tables 11, 12, and 13.) 











































2*- 18 





















































TAR M 









































1 1 





































y-TAR 



















*2w . 

 a a. |4 



< 











































VTAR 

































>a 12 

 < 



















































































10 

 1000 









































































































































































900 







































































































































































800 



































































































"^TAf 































































700 

























































































*" \ 















































































600 



















































































s 











^TAR 



























K 











































X 500, 



















































































ft 











































3 











































S2 400 



K ' 



a. 







<^*~. 



TAF 



\ N0.I 

























































































































































300 







































































































































































200 







































































































































































100 







































































































































































ooo 











































'"0 1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 

 PERCENT FREE CARBON IN MIXTURE 



Fig. 5. — Variation in time of treatment and pressure necessary to secure a given absorption in paving blocks 

 using mixtures of equal parts creosote No. 4 and tars having different amounts of free carbon. 



was increased. As in the penetrance tests, however, the effect of free 

 carbon was variable in the mixtures containing tar No. 3. The 

 retarding effect of free carbon apparently decreased when the amount 

 in the mixtures was increased beyond a certain point. This was 



