56 
BULLETIN &49, U. S. DEPARTMENT OF AGRICULTURE. 
amount of grease or resin that may be present, although a proper grade of felt should be 
practically free from such products. The bowl is now placed on the motor shaft and 
the slot and pin are carefully locked. An empty bottle is placed under the spout and 
150 c.c. of carbon disuphide (carbon tetrachloride, benzole, or chloroform may also 
be used as solvents) is poured into the bowl through the small holes. The cover is put 
on the copper box and, after allowing the material to digest for a few minutes, the motor 
is started slowly at first in order to permit the aggregate to distribute uniformly. The 
speed should then be increased sufficiently by means of the regulator to cause the dis- 
solved bitumen to flow from the spout in a thin stream. When the first charge has 
drained, the motor is stopped and a fresh portion of disulphide is added. This opera- 
tion is repeated from four to six times with 150 c.c. of disulphide. With a little experi- 
ence the operator can soon gauge exactly what treatment is necessary for any given 
material. When the last addition of solvent has drained off, the bowl is removed and 
placed with the brass plate uppermost on a sheet of manila paper. The brass plate 
and felt ring are carefully 
laid aside on the paper 
and, when the aggregate is 
thoroughly dry, it can be 
brushed on a pan of the 
rough balance and weighed. 
The difference between 
this weight and the original 
weight taken shows the 
amount of bitumen ex- 
tracted. The aggregate 
may then be tested as oc- 
casion requires. 
When it is desired to re- 
cover and examine the 
bitumen, the apparatus 
shown in figure 31 will be 
found convenient and fairly 
safe for the distillation and 
recovery of such inflam- 
mable solvents as carbon 
disulphide. In the labora- 
tory of the Bureau of Pub- 
lic Roads this apparatus is 
arranged so that the glass tubing passes through a stone partition between two 
sections of a small hood, thus keeping the distilling and receiving apparatus entirely 
separated. 
The solution of bitumen should be allowed to stand overnight in order to permit 
the settling of any fine mineral matter that is sometimes carried through the felt ring 
in the extractor. The solution is then decanted into the flask a, and the solvent is 
driven off by means of heat from an incandescent lamp until the residue is of a thick 
sirupy consistency. Meanwhile the solvent is condensed and recovered in the flask b. 
The residue is poured into an 11-cm. porcelain evaporating dish and evaporated on 
a steam bath. The most scrupulous care must be taken at all times that no flames 
are in its immediate vicinity. Evaporation is carried on at a gentle heat, with con- 
tinual stirring, until foaming practically ceases. It is advisable to have a large 
watch glass at hand to smother the flames quickly should the material ignite. As the 
foaming subsides, the heat of the steam bath may be gradually raised, and evapora- 
tion is continued until the bubbles beaten or stirred to the surface of the bitumen 
fail to give a blue flame or odor of sulphur dioxide when ignited by a small gas jet. 
n^ ir^ 
Fig. 31.— Recovery apparatus. 
