EXAMINATION OF BITUMINOUS ROAD MATERIALS. 



37 



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 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 

 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 

 aggregate is thor- 

 oughly dry, it can be 

 brushed on a pan of 

 the rough balance 

 and weighed. The 

 difference between 

 this weight and tho 

 original weight taken 

 shows the amount of 

 bitumen extracted. 

 The aggregate may 

 then be tested as oc- 

 casion requires. 



When it is desired 

 to recover and exam- 

 ine the bitumen, the 

 apparatus shown hi 

 figure 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 tho distilling and 

 iving apparatus entirely separated. 



The solution of bitumen should bo allowed to stand overnight in 

 Order to permit the settling of any line mineral matter that is somo- 

 times carried through the felt ring in the extractor. Tho solution is 

 then decanted into the flask a, and the solvent is driven off by means 

 of heal from an incandescent lamp until the residue is of a thick 

 sirupy consistency. Meanwhile the solvent is condensed and recov- 

 ered in the flash I). The residue is poured into an 11-centimeter 



n^N^n 



Fig. 19.— Recovery apparatus. 



