COAL-TAR AND WATER-GAS TAR CREOSOTES. 
89 
such substances as carbon bisulphide, chloroform, benzol, or toluol. 
Different results are obtained by the use of different solvents because 
the hydrocarbons of creosote or tar are not uniformly soluble in these 
solvents. This is particularly true of the bitumens in the pitches. 
J. M. Weiss has conducted a number of tests on tar with different 
solvents. His method of procedure was to allow tar to digest with 
cold solvent for a number of hours and then to filter off the undis- 
solved portion and extract it with the boiling solvent. When benzol, 
S2« 
^t_-— 
_2__ 
a 
4 
-J-*" 
-& 
^ 
^ 
/■ 
-6 — 
i 40 60 80 100 120 140 160 
TIME-HOURS 
Fig. 41. — Change in apparent free-carbon content of a tar with change 
in time of digestion with different solvents. 
ieo 
200 
1. Insoluble in benzol. 
2. Insoluble in benzol and toluol. 
3. Insoluble in chloroform. 
4. Insoluble in carbon bisulphide 
5. Insoluble in aniline. 
6. Insoluble in pyridine. 
7. Insoluble in glacial acetic acid. 
benzol and toluol, chloroform, or carbon bisulphide was used as the 
cold extractive the same material served as the hot extractive; but 
when he used aniline, pyridine, or glacial acetic acid as a cold extrac- 
tive he followed them with benzol as a hot extractive. The data 
obtained have been plotted in figure 41. From these curves it is 
apparent that the insoluble matter in this tar after one-half hour's 
digestion varied from 5 to 6.6 per cent, but that after 144 hours' 
digestion it varied from 4.6 to 9.3 per cent. With the exception of 
