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 in the 
penetration and absorption curves upon the addition of larger per- 
IMPEEGNATION TESTS. 
(Data in Tables 5, 6, and 7.) 
7^° 
°^IP 
•r^ 18 
FAR Nl 
S K 14 
rTAR N0.1 
— ^: 
-TAR NO 
.3 
^ 
^. 
Urn 
10 
1000 
900 
800 
700 
tar h 
3 
600 
u 
^ 
z 
H 
TAR N 
,2 
X 500 
tal 
a, 
Ktar 
no. 
D 
ft 400 
a 
a. 
300 
200 
100 
000 
25 
50 
PERCENT OF TAR BY VOLUME 
75 
ICO 
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 
