ABSORPTION AND PENETRATION OF COAL TAR AND CREOSOTE. 
9 
larger than those in tars 1 and 2, and formed a less impervious mat. 
It seems probable that the mat formed with this tar containing its 
normal amount of free carbon contained openings as large and as 
easily penetrated as those formed when part of the carbon was 
removed. 
PENETRANCE TESTS. 
(Data in Tables 8, 9, and 10.) 
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Tar No. 1. 
a. 
234 56780 I 234 5 6 7 8 9 10 If 12 13 14 15 
PERCENT OF FREE CARBON BY WEIGHT 
Tar No. 2. Tar No. 3. 
b. c. 
Fig. 4.— The relative absorptions and penetrations into longleaf pine using mixtures of equal parts of 
creosote No. 4 and tars containing different amounts of free carbon. Time of treatment, 2 hours; pressure, 
75 pounds per square inch; temperature of preservative, 160° F. 
Impregnation tests. — (Tables 11 to 13 and Hg. 5). 
Impregnation tests were made on paving blocks, using the same 
mixtures, with varying amounts of free carbon, that were used in 
the penetrance tests. 
As in the impregnation treatments with carbon-free tar and creosote, 
two blocks were used for each test, and the time of treatment and 
