6 
BULLETIN 607, U. S. DEPARTMENT OF AGRICULTURE. 
gives a direct comparison for studying the effect of the free carbon 
on absorption and penetration. 
The results of the tests indicate that smaller penetrations and 
absorptions were obtained with the mixtures of those tars which had 
contained the larger amounts of free carbon, whether the free carbon 
was present or had been removed. Variations in absorption and 
penetration of the different tar mixtures, therefore, appeared to be 
PENETRANCE TESTS. 
(Data in Tables 1, 2, and 3.) 
p 1.220 
o 
10 
""" 1.180 
k.' 
o 
e 
2 1.140 
< 
£ t-ioo 
oT 
W 1.060' 
>< 
Q ' 
»- o 
OS 
. 
, . ._- ., , . 
v^ 
■9^ r* ^ 
aS X 4 ' |X 
s v y 
s** / y^ 
~f ir ,^ 
^ ^ ^ y 
.».— — "-"'"' :wmm «•- { r mW0t ( _ ..♦-— — -—i 
^i • 
"^"^5*. t^ 
f^^*x '^ y ' ,, ^ ^V 
• "^^ ^S^ ^ 
^>vJ S» 
s, ^^.^ 
^> * 
^"5s» ^ 
r s "^ v ^. 
" ^^ "^^ '^ 
s<l "*^— — ^.— l— 
Tar No. 1. 
80 100 20 40 60 80 100 
PERCENT OF TAR BY VOLUME 
Tar No. 2. 
b. 
20 40 60 80 
Tar No. 3. 
c. 
FlG - 1— The relative absorptions and penetrations into longleaf pine of mixtures of creosote No. 4 and car- 
bon-free tars Nos. 1, 2, and 3. Time of treatment, 2 hours; pressure, 75 pounds per square inch; tempera- 
ture of preservative, 160° F. 
caused by a difference in the composition of the bitumens hi the 
three tars, as well as by the amount and character of the free carbon 
present. 
Impregnation tests.— (Tables 5 to 7 and fig. 3.) 
The paving block specimens were treated in a small cast-iron 
cylinder, inclosed in the penetrance oven, and with air pressure and 
vacuum connections. Two blocks were employed for each test, and 
the results averaged for each piont on the curves shown in figure 3. 
