SAMPLING AND TESTING HIGHWAY MATERIALS. 
55 
IV. ACCURACY. 
(9) The 13 mit of accuracy of the test is 0.5° C. (0.9° F.). 
V. PRECAUTIONS. 
(10) The use of freshly boiled distilled water is essential, as otherwise air bubbles 
may form on the specimen and affect the accuracy of the results. Rigid adherence 
to the prescribed rate of heating is absolutely essential in order to secure accuracy 
of results. 
A sheet of paper placed on the bottom of the glass vessel and conveniently weighted 
will prevent the bituminous material from sticking to the glass vessel, thereby saving 
considerable time and trouble in cleaning. 
33. METHOD FOR EXAMINATION OF BITUMINOUS MIXTURES. 
A. CENTRIFUGAL METHOD. 
The extractor shown in figure 30 was designed upon lines suggested by an examina- 
tion of machines in use by A. E. Schutte and C. N. Forrest. 10 It consists of a one-fifth 
horsepower, 1,100 revolutions per minute ver- 
tical-shaft electric motor, a, with the shaft 
projecting into the cylindrical copper box b, 
the bottom of which is so inclined as to drain 
the spout c. A three-sixteenths-inch circular 
brass plate 9^ inches in diameter is shown in - «/- 
d, and upon this rests the sheet-iron bowl e, k- 
which is 8^ inches in diameter by 2| inches 
high, and has a 2-inch circular hole in the 
top. Fastened to the inner side of the bowl 
is the brass cup /, having a circle of one- 
eighth-inch holes for the admission of the 
solvent, and terminating in the hollow axle, 
which fits snugly through a hole at the cen- 
ter of the brass plate. The bowl may be 
drawn firmly against a felt-paper ring g, three- 
fourths inch wide, by means of the 2§-inch 
milled nut h, for which the hollow axle is 
threaded for a distance of three-fourths inch 
directly below the upper surface of the plate. 
The axle fits snugly over the shaft of the 
motor, to which it is locked by a slot and 
cross pin, i. 
The aggregate is prepared for analysis by 
heating it in an enamel-ware pan on the hot 
plate until it is sufficiently soft to be thoroughly disintegrated by means of a large 
spoon. Care must be taken, however, that the individual particles are not crushed. 
If a section of pavement is under examination, a piece weighing somewhat over 1 
kilogram may be cut off with hammer and chisel. The disintegrated aggregate is then 
allowed to cool, after which a sufficient amount is taken to yield on extraction from 50 
to 60 grams of bitumen . It is placed in the iron bowl and a ring three-fourths of an inch 
wide^cut from the felt paper, is fitted on the rim, after which the brass plate is placed 
in position and drawn down tightly by means of the milled nut. If the bitumen is to 
be recovered and examined, the felt ring should be previously treated in the empty 
extractor with a couple of charges of carbon disulphide in order to remove any small 
Fig. 30. — Centrifuge extractor, 
type.) 
(Reeve 
i° Any extractor of similar design may be used. 
