90 
BULLETIN 1036, TJ. S. DEPARTMENT OF AGRICULTURE. 
the method in which glacial acetic acid was employed, that in which 
benzol was used as a solvent gave the highest results. All the 
solvents except aniline gave higher results with longer digestions. 
With the use of aniline the insoluble matter decreased from 5 per 
cent after one-half hour to 4.6 per cent after 144 hours, and this was 
the lowest result obtained. 
Weiss further showed that the insoluble residue, after digestion with 
chloroform, contained noticeable amounts of chlorine. Sulphur was 
also found in the residue resulting from the digestion with carbon 
bisulphide. 
Monroe and Broderson {££) investigated the action of benzol and 
chloroform on the free-carbon content of three classes of tar. The 
results of their work are plotted in figure 42. Here again they found 
that benzol yields a greater insoluble 
residue than does chloroform, not- 
withstanding the fact that consid- 
erable quantities of chlorine were 
found in the residue. This amount 
increased with the time of digestion. 
From the above it is apparent 
that, if this test is designed to deter- 
mine the free carbon in tars, a di- 
gestion with aniline would give the 
more nearly correct result. But if 
a purely empirical determination is 
all that is desired, then any one of 
the solvents is satisfactory provided 
that the test is made standard and 
the conditions of the test are defined 
and rigidly adhered to. 
The method adopted as standard 
by the American Society for Testing Materials, the American Rail- 
way Engineering Association, and the American Wood Preservers' 
Association is as follows : 
Apparatus. — (A) Extractor may be of the form shown in figure 43 or similar form 
in which the oil is subjected to direct washing by the boiling vapors of the solvent. 
(B) Filtering medium may be either two thicknesses of S. and S. No. 575 or What- 
man No. 5 hardened filter paper, 15 cm. in diameter, arranged in cup shape by folding 
symmetrically; or alundum thimbles, flat bottom, 30X80 RA 98. If filter papers 
are used they shall be soaked in benzol prior to using to remove grease, dried in a 
steam oven, and kept in a desiccator until ready to be used. The filter-paper cup 
may be suspended in the extractor flask by a wire basket hung from two small hooks 
on the under surface of the metal cover of the flask. 
If the alundum thimble is used it may be supported by making two perforations in 
the top of the thimble and suspending from the cover by German silver or platinum 
wires. 
It 
9 
e 
x 
7 
Is 
r 
« *5 
s w 
U J 
« 3 
w - 
2, 
2 
X 
-t\ 
t-e — 
40 60 60 
TIME-HOURS 
70 80 90 100 
Fig. 42.— Change in apparent free carbon content 
of tars with change in time of digestion. 
Numbers represent tars No. 1, 2, and 3. 
X. Extractions made with benzol. 
O. Extractions made with chloroform. 
