ABSORPTION AND PENETBATION OP 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.1 



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). 



1.0483 



1.0475 

 1.0576 

 1.0710 



1.1050 

 1.0470 



1 



2 

 3 

 4 



5 



By-product coke-oven tar 



B v-product coke-oven tar 



Per cent. 

 6.0 



16.0 



3 





30.0 



4. 

 5 



Coal-tar creosote containing coal tar (esti- 

 mated at less than 5 per cent). 



By-product coke oven-refined 



tar. 

 By-product coke-oven tar 



7.0 

 14.0 



fi 



Coal-tar creosote 











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. 



