METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 89 
by means of rhe regulator to cause the dissolved bitumen to flow from the 
spout in a thin stream. When the flrst 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 
experience 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 cover plate uppermost on a sheet of 
manilla paper. The cover 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 extracted. The aggre- 
gate may then be tested as occasion requires. 
2. When it is desired to examine the bitumen, or recover the solvent, a suit- 
able distillation apparatus may be used, taking necessary precautions when 
handling inflammable solvents. 
3. 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, 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. The residue is poured into an 11-centimeter porce- 
lain 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 continual stirring, until foam- 
ing 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 evaporation 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. The dish 
of bitumen should then be set in a hot-air oven maintained at 105° C. for about 
an hour, after which it should be allowed to cool. Its general character is noted 
and any tests for bitumen that are necessary are then made upon it. 
4. The difference between the final aggregate and the original amount taken 
give- the amount of bitumen extracted, which is subject to correction, dependent 
on the amount of ash determined from the washings. 
5. Ash correction shall be made in the following manner : The total solution 
of bitumen, well stirred, is rapidly measured and an aliquot portion taken, 
usually 100 cubic centimeters, and poured into a previously weighed suitable 
flat-bottom dish, preferably quartz. The solvent is evaporated over a very low 
flame and the residual coke is then ignited with a burner capable of furnishing 
high temperature, such as a Meker. (Caution: When an inflammable solvent 
is used evaporation should be conducted on a steam bath and care should be 
taken that no flames are in the immediate vicinity.) The dish and contents are 
then cooled in a desiccator and the percentage of ash calculated. 
HOT EXTRACTION METHOD 
6. The New York testing laboratory extractor consists of a large brass cylin- 
der, through the bottom of which projects a 16-candlepower incandescent carbon- 
filament bulb to supply heat to the extraction apparatus proper, which is held 
in the upper portion of the cylinder. This apparatus is composed of a cylin- 
drical brass vessel for holding the solvent, a cylindrical wire basket made of 
80-mesh wire cloth, suspended in the cylinder, and an inverted conical condenser 
which serves as a top. 
7. The aggregate is prepared for analysis by heating it in a tin dish on the 
hot plate until it is sufficiently soft to be disintegrated by means of a large 
spoon. The disintegrated aggregate is then allowed to cool. Not less than 500 
grams of aggregates containing particles larger than three-quarters inch in 
diameter or 200 grams of aggregates with all particles smaller than three- 
quarters inch are then closely packed in the wire basket or suitably sized 
extraction thimbles and covered with a disk or wad of absorbent cotton or felt. 
From 175 to 200 cubic centimeters of carbon disulphide (carbon tetrachloride, 
benzol, or chloroform may be used) are next placed in the inside vessel, in 
which the wire basket should be suspended. The top is then placed in position 
and cooling water circulated through it. Heat is applied by means of the 
electric-light bulb. The solvent is boiled in the lower part of the extractor and 
