G 



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 



w 



1.180 



h! 

 o 



e 



2 1.140 



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a! 



w l.06o' 



a. 

 0.14 



I. 0.10 











































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Tar No. 1. 



100 20 40 €0 eo 100 

 PERCENT OF TAR 8Y VOLUME 



Tar No. 2. 

 b. 



Tar No. 3. 



Fig. 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 in 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. 



