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 33 J 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.) 
25|CRE0, 
275$ TAR 
TAR AND CREOSOTE MIXTURES 
TREATING TEMP. 220° F. 
PRES. 200LBS.PERSQ.IH. 
PRES. 75 LBS. 
TEMP. W0°T. 
CREOSOTE 
PRES. & TEMP. VARIED 
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 creosote 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 
