ABSORPTION AND PENETRATION OF COAL TAR AND CREOSOTE. 3 
mens, and comparisons can not be made by combining data used in 
separate figures. 
The number of specimens used in each test is shown in the tables 
in the appendix. Specimens for the cylinder treatments discussed 
on pages 6 and 9 were paving blocks 4 inches long cut from two sticks 
of air-dry commercial paving block stock approximately 4 inches by 
8 inches in cross section. In each of the tests a treatment was made 
on one block from each stick, thus giving two blocks treated with the 
same preservative. Blocks used in the tests on the effect of varying 
time, pressure, and temperature were all cut from the same stick, 
the material being similar to that used in the impregnation tests. 
Four blocks were treated with each preservative. In all of the im- 
pregnation tests, the results for each treatment were averaged. 
Comparisons of individual tests from different sets of specimens 
should not be made, because such comparisons would not represent 
matched specimens. Specimens in the different sets may have been 
obtained from different trees. 
PRESERVATIVES.! 
Six commercial coal-tar creosotes from different sources and of 
varying specific gravities and five coal tars from by-product ovens 
and gas-house plants were used in the experiments. The general 
characteristics of these preservatives were as follows: 
Characteristics of preservatives used. 
Coal-tar creosotes. 
Coal tars. 
No. 
Kind. 
Specific 
gravity 
at 60°C. 
No. 
Kind. 
Free 
carbon. 
1 
? 
Coal-tar creosote containing coal tar (esti- 
mated at about 10 per cent). 
Coal-tar creosote 
1.0483 
1.0475 
1.0576 
1.0710 
1. 1050 
1.0470 
1 
2 
3 
4 
5 
By-product coke-oven tar 
By-product coke-oven tar 
Per cent. 
6.0 
16.0 
T 
30.0 
4 
5 
Coal-tar creosote containing coal tar (esti- 
mated at less than 5 per cent). 
High boiling coal-tar creosote 
By-product coke oven-refined 
tar. 
By-product coke-oven tar 
7.0 
14.0 
fi 
PREPARATION OF MIXTURES FOR THE TESTS ON THE EFFECT OF DIFFERENCES IN THE 
PRESERVATIVE. 
The free carbon was extracted 2 from tars Nos. 1, 2, and 3. Each 
of these tars was then mixed with creosote No. 4 in the following 
proportions (by volume at 160° F.) : 
i Analyses of the creosotes are given in the Appendix. Distillation analyses of the tars were not made. 
2 See appendix for method of extraction. 
