56 



BULLETIN 949, 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. 



csS^Sa 



Fig. 31. — Recovery apparatus. 



