326

FLUIDITY AND PLASTICITY

60 (±0.15) cc. The lower end of the outlet tube is enclosed
by a larger tube3 which when stoppered by a cork N, acts as a
closed air chamber and prevents the flow of oil through the outlet
tube until the cork is removed and the test started. A looped
string is attached to the lower end of the cork as an aid to its
rapid removal. The bath is provided with two stirring paddles
K and operated by two turn-table handles F. The temperatures
in the standard oil tube and in the bath are shown by ther-
mometers, A and B. The bath may be heated by a gas ring
burner P, steam U-tube H, or electric heater C. The standard
oil tube is cleaned by means of a tube cleaning plunger I7, and
all oil entering the standard oil tube shall be strained through a
30-mcsh brass wire strainer Q. A stop watch is used for taking
the time of flow of the oil and a pipette, fitted with a rubber
suction bulb, is used for draining the overflow eup of the stand-
ard oil tube.

"(&) The standard oil tube / should be standardized by the
U. S. Bureau of Standards, Washington, D. C., and shall conform
to the following dimensions:

Dimensions
Minimum, centimeters
Normal, centimeters
Maximum, centimeters

Inside diameter of outlet tube. . . Length of outlet tube ..........
0.1750 1.215
0.1765 1.225
0.1780 1 235

Height of overflow rirn above bottom of outlet tube .....
12.40
12 50
12 60

Diameter of container of standard oil tube
2 955
2 975
2 995

Outer diameter of outlet tube at lower end ...............
0.28
0 30
0 32

"3. Method.—Viscosity shall be determined at 100°F (37.8°C),
130°F (54.4°C), or 210°F (98.9°C). The bath shall be held
constant within 0.25°F (0.14°C) at such a temperature as will
maintain the desired temperature in the standard oil tube. For
viscosity determinations at 100 and 130°F, oil or water may be
used as the bath liquid. For viscosity determinations at 210°F,
oil shall be used as the .bath liquid. The oil for the bath liquid
should be a pale engine oil of at least 350°F flash-pomt (open