ABSORPTION" AND PENETRATION OF COAL TAR AND CREOSOTE. 5 
EFFECT ON PENETRATION OF DIFFERENCES IN THE PRESERVATIVE, 
ESPECIALLY THE EFFECT OF FREE CARBON. 
Experiments with various mixtures of creosote and tars from which 
the free carbon had been removed were first made in the penetrance 
apparatus, the temperature, pressure, and time of treatment being 
kept constant. These tests were followed by cylinder treatments on 
paving blocks, with the same mixtures but with the time of treatment 
and the pressure varied to obtain an absorption of 16 pounds of pre- 
servative per cubic foot of wood. A similar series of penetrance and 
impregnation tests were made, using tar and creosote mixtures con- 
taining varying amounts of free carbon. Further tests were then 
made in the penetrance apparatus with five commercial coal-tar 
preservatives. 
In the series of tests to determine the effect of differences in the 
preservative on penetration, the operative features were always the 
same A pressure of 75 pounds per square inch and a treating period 
of two hours were used. The temperature of the preservative and of 
the penetrance oven, in which the specimens were treated, was 160° F. 
The treatments were made on two sets of specimens, each set con- 
taining from four to six matched specimens. Thus, each point on the 
curves of figure 4 represents the average of the results obtained on 
two specimens. The sets of specimens were not, however, matched 
with each other. For example (see Table 1, appendix), specimens 19a 
and 35 were not matched, but specimens 19a, 28, 32, 29, and 30, and 
specimen 35, 23a, 22a, 24a, and 20a were matched with each other. 
MIXTURES OF CARBON-FREE TAR AND CREOSOTE. 
Penetrance tests} — (Tables 1 to 4, inclusive, and figs. 1 and 2.) 
In these experiments, made with mixtures of tars Nos. 1, 2, and 3 
with creosote No. 4, it is evident that as the proportion of the carbon- 
free tar in the mixture was increased the specific gravity and vis- 
cosity of the mixture increased and the absorptions and penetrations 
decreased. Each point on the absorption and penetration curves of 
figure 1 represents the results obtained with one tar and creosote 
mixture. 
A comparison of these tars and their relative effect upon absorp- 
tion and penetration is given in Table 4 and figure 2. These treat- 
ments were made with mixtures of equal parts by volume of creosote 
and each of the three carbon-free tars. Each point on the curves of 
figure 2 represents the average of the results obtained on two speci- 
mens, as in figure 1 . 
Figure 2 also shows the results obtained with similar mixtures of 
the same tar, except that the free carbon was not removed, and hence 
1 The data are given in Tables 1 to 4 of the Appendix. 
