88 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
is suspended in the oil, the bulb not touching the bottom of the box. The tem- 
perature of the oil is kept at from 249° to 260° C. (480° to 500° F.) and the 
oil is stirred from time to time with the thermometer to prevent overheating 
in any part. Depending upon the nature of the oil, as usually indicated by its 
flash, consistency at 25° C. (77° F.), and specific gravity, the operator can 
with experience tell about what percentage it will be necessary to evaporate 
before cooling and taking a penetration of the residue. It is sometimes neces- 
sary to make several trials before the desired result is obtained. When the re- 
quired penetration is reached, the residue left from evaporation is weighed and 
its per cent of the original sample taken is computed. 
2. Ordinarily a residue shall be considered as satisfactorily obtained on the 
basis of 100 penetration being specified when its penetration is within 25 points 
of that desired. When it is necessary to determine more precisely the per cent of 
reesidue for a specified penetration, such percentage shall be computed by 
interpolation between percentages of two residues, one having a penetration 
greater, and one having a penetration lower than that specified. 
57. CALCIUM-CHLORIDE METHOD FOR DETERMINATION 
OF PERCENTAGE OF WATER IN BITUMINOUS EMUL- 
SIONS 
(Not applicable to clay emulsions) 
Approximately 10 grams of the emulsion is accurately weighed in an Erlen- 
meyer flask and exactly 25 cubic centimeters of a 10 per cent solution of cal- 
cium chloride added and thoroughly agitated by shaking. The liquid content 
of the flask is then poured into a graduated cylinder. Carbon disulphide is 
then added to the Erlenmeyer flask and the separated asphalt dissolved and 
washed with carbon disulphide into the graduated cylinder above referred to 
containing the decanted liquid. The total contents of the cylinder are then 
thoroughly shaken and after standing the quantity of separated supernatant 
water read. 
Calculations: Per cent water="-^— X100 
A= volume of supernatant water, 
Z?=volume of 10 per cent calcium chloride, solution originally used, 
C=weight of emulsion taken for water determination. 
58. METHOD FOR EXAMINATION OF BITUMINOUS 
MIXTURES 
CENTRIFUGAL METHOD 
1. 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. Not less than 
500 grams of aggregate containing particles larger than three-quarter inch in 
diameter or 200 grams of aggregate with all particles smaller than three-quarter 
inch are placed in the bowl of the centrifuge extractor, and a ring three- 
quarters of an inch wide, cut from felt paper, is fitted on the rim, after which 
the cover plate is placed in position and drawn down tightly by means of 
the milled nut. If the bitumen is to be recovered and extracted, the felt ring 
should be treated previously in the empty extractor with a couple of charges 
of carbon disulphide in order to remove any small 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 then placed on the motor shaft of the 
extractor and the slot and pin are carefully locked. An empty bottle is placed 
under the spout and 150 cubic centimeters of carbon disulphide (carbon tetra- 
chloride, benzol, or chloroform may also be used as solvents) is poured into 
the bowl through the small holes. After allowing the material to digest for a 
few minutes, the motor is started, slowly at first, in order to permit the aggre- 
gate to distribute uniformly. The speed should then be increased sufficiently 
