SAMPLING AND TESTING HIGHWAY MATERIALS. 
73 
the level of the oil in the still at the beginning of the test and 
gradually lowered when most of the water has distilled over. 
Continue the distillation until the vapor temperature, indicated 
by the thermometer with the bulb opposite the offtake of the con- 
necting tube, reaches 205° C. Collect distillate in separatory 
funnel. When the distillation is completed and a clear separation 
of water and oil in the funnel has taken place, read the water by 
volume and draw off ; and return any light oil distilled over with 
the water to the oil in the still. The dehydrated oil from the 
still shall be used for the distillation test. 
Filtering 
medium. 
Matter Insoluble in Benzol. 
5. (a) Extractor. — The extractor may be of any form in which Extractor. 
the oil is subjected to direct washing by the boiling vapors of the 
solvent. 
(&) F Uteri iifi medium. — The filtering medium may be either two 
thicknesses of S. & S. No. 575 hardened filter paper, 15 centimeters 
in diameter, arranged in cup shape by folding symmetrically, or 
alundum thimbles, flat bottom, 30X80 RA 98. If filter papers are 
used, prior to using they shall be soaked in benzol to remove any 
grease, dried in a steam oven and kept in a desiccator until ready 
to be used. The filter-paper cup may be suspended in the ex- 
tractor flask by a wire basket hung from two small hooks on the 
undersurface of the metal cover of the flask. If the alundum 
thimble is used, it may be supported by making two perforations 
in the top of the thimble and suspending from the cover by 
German silver or platinum wires. 
6. Weigh 10 grams of dry oil in a 100 cubic centimeter beaker. Method of test. 
Add about 50 cubic centimeters of pure benzol and transfer at 
once to the filter cup. The filter cup or thimble is previously 
weighed, and the paper cup shall always be kept in a weighing 
bottle until ready for use. Wash out the beaker with benzol, 
passing all washings through the filter cup, and place latter at 
once in the extraction apparatus. Extractor shall contain a suit- 
able quantity of pure benzol. Sufficient heat to boil the solvent 
shall be provided by means of an electric heater or a steam bath. 
Continue the extraction until the descendng solvent is practically 
colorless, and remove the filter cup and dry in steam oven until 
all solvent is driven off; cool in desiccator and weigh. The 
balance used for this purpose should be accurate to 0.5 milligram. 
SPECIFIC GRAVITY. 
7. (a) Hydrometer. — The hydrometer shall have the follow- Specific 
ing dimensions: gravity. 
Length of stem : 125 millimeters ; permissible variation. 
12.5 millimeters. 
Length of bulb: 105 millimeters: permissible variation, 
10.5 millimeters. 
Length of scale: 80 millimeters: permissible variation, 8.0 
millimeters. 
Diameter of stem: 6 millimeters; permissible variation, 0.5 
millimeters. 
Diameter of bulb: 22 millimeters: permissible variation, 
2.0 millimeters. 
A set of two hydrometers with ranges 1.00 to 1.08 and 1.07 to 
1.15 will suffice. 
(b) Cylinder. — The cylinder shall have the following dimen- 
sions : 
Length: 300 millimeters; permissible variation. 30 milli- 
meters. 
Diameter: 32 millimeters: permissible variation. 3 milli- 
meters. 
8. The oil shall be brought to a temperature of 38° C. (100° 
F. ), and the determination shall be made at that temperature 
unless the oil is not entirely liquid at 38° C. In case the oil 
