ABSORPTION AND PENETRATION OF COAL TAR AND CREOSOTE. 17 



with the creosote. Comparing these results with those in which the 

 time of treatment was varied, it is noted that when the 20 per cent 

 tar mixture was used better penetrations were obtained by length- 

 ening the time of treatment than by increasing the pressure, the ab- 

 sorption being the same in both cases. This comparison can not 

 properly be made with the mixture containing 33J per cent tar, 

 because the desired absorption was not obtained in this case when 

 only the time of treatment was increased. (See note on fig. 8.) 



IMPREGNATION TESTS. 

 (Data in Table 18.) 



TAR AND CREOSOTE MIXTURES 



TREATING TEMP. 220° F. 

 PWES. 200 LBS.PER SQ. IN. 



Fig. 9.— The time of treatment required to secure a given absorption in paving blocks using mixtures of 

 creosote No. 4 and tar No. 5; also the increase in time of treatment required to secure a given absorption 

 of creesote when the treating pressure and temperature were decreased. 



IMPREGNATION TESTS WITH COAL-TAR CREOSOTE NO. 4 AND COAL-TAR NO. 5. 



Temperature of preservative and pressure constant and time of treatment 



varied. — (Tables 19 and 20 and figs. 9 and 10.) 



Tests to determine the effect of varying the time were made on 

 matched paving-block specimens with mixtures containing 25 per 

 cent tar and 75 per cent creosote, 50 per cent tar and 50 per cent 

 creosote, and 75 per cent tar and 25 per cent creosote. Similar tests 

 were made on penetrance specimens. (Fig. 10.) The creosote un- 

 mixed with tar was used for comparison. In these tests the time of 

 treatment required to obtain a given absorption increased rapidly as 

 the amount of tar in the mixture was increased, especially when 50 

 per cent and 75 per cent of tar were used. The desired absorption 

 was obtained in the shortest time with creosote. In order to secure 



