EXAMINATION ‘OF BITUMINOUS ‘ROAD MATERIALS: 87 
disulphide 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 nig oD 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 
dissolved 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 operation is repeated from four to six 
times with 150 cubic centimeters of disulphide. With a little expe- 
rience 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 care- 
fully laid aside on the » ) 
paper and, when the 
aceregate is thor- 
oughly 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 extracted. 
The ageregate may 
then be tested as oc- 
casion requires. 
When it is desired 
to recover and exam- 
ine the bitumen, the 
apparatus shown in 
ficure 19 will be found 
convenient and fairly safe for the distillation and recovery of such 
inflammable solvents as carbon disulphide. In the laboratory of the 
Office of Public Roads and Rural Engineering 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 some- 
times 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 recov- 
ered in the flask 6. The residue is poured into an 11-centimeter 
Fie. 19. —Recovery apparatus. 
