26 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE. 
2 wash bottles; 1 for solvent, 1 for water. 
i Bunsen burner. 
1 nichrome triangle. 
1 iron tripod. 
- 1 drying oven. 
1 desiccator with calcium chloride. 
i thermometer reading from —10° ©. to 110° CG. Fi 
1 yacuum pump and connections. 
1 analytical balance, capacity 100 grams, sensitive to 0.1 milligram. 
METHOD. 
This test consists in dissolving the bitumen in carbon disulphide 
and recovering any insoluble matter by filtering the solution through 
an asbestos felt. The form of Gooch crucible best adapted for the 
determination is 4.4 centimeters wide at the top, tapering to 3.6 
centimeters at the bottom, and is 2.5 
centimeters deep. 
For preparing the felt the necessary 
apparatus is arranged as shown in figure 
14, in which a is the filtering flask, 6 a 
rubber stepper, c the filter tube, and d 
a section of rubber tubing which tightly | 
clasps the Gooch crucible e. The asbes- 
tos is out with scissors into pieces not 
exceeding 1 centimeter in length, after 
which it is shaken up with just suffi- 
cient water to pour easily. The cruci- 
ble is filled with the suspended asbestos, | 
which is allowed to settle for a few mo- 
ments. A light suction is then applied 
Fic. i4.—Apparatus for determining solu- {6 draw of all the water and leave a 
goeioe firm mat of asbestos in the crucible. 
More of the suspended material is added, and the operation is repeated 
until the felt is so dense that it scarcely transmits light when held so 
that the bottom of the crucible is between the eye and the source of 
light. The felt should then be washed several times with water, and 
drawn firmly against the bottom of the crucible by an increased suc- 
tion. The crucible is removed to a drying oven for a few minutes, 
after which it is ignited at red heat over a Bunsen burner, cooled in 
a desiccator and weighed. 
From 1 to 2 grams of bitumen or about 10 grams of an asphalt 
topping or rock asphalt is now placed in the Erlenmeyer flask, 
which has been previously weighed, and the accurate weight of the 
sample is obtaimed. One hundred cubic centimeters of chemically 
pure carbon disulphide is poured into the flask in small portions, with 
continual agitation, until all lumps disappear and nothing adheres 
to the bottom. The flask is then corked and set aside for 15 minutes. 
