COAL-TAR AND WATEE-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, 







































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Fig. 41. — Change in apparent free-carbon content of a tar with change 

 in time of digestion with different solvents. 



1. Insoluble in benzol. 



2. Insoluble in benzol and toluol. 



3. Insoluble in chloroform. 



4. Insoluble in carbon bisulphide. 



5. Insoluble in anihne. 



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 



