a. Accuracy Requirements. The routine laboratory thermometers,
ASTM 9F, 12F and 58F, have scales including 32 degrees F (O degrees
C) and must be verified for accuracy by determining the ice point.
ASTM 18F shall be verified at 100 degrees F (37.8 degrees C) ASTM 7F,
low-distillation thermometers, must be verified for accuracy at 200
degrees F (93.3 degrees C). ASTM 10F, Pensky-Marten, high range
thermometer, must be verified for accuracy at 212 degrees F (100
degrees C). ASTM 7F, 10F and 18F must be verified for accuracy by
direct comparison with a certified precision thermometer. The two
certified precision thermometers (ASTM 64F and 68F) must be certified
by the A-level calibration facility. The precision thermometer must
be certified at 360-day intervals. The error of the certified
thermometers cannot be more than the maximum scale error of the
specification (ASTM E-l).
b. Procedures for Determining Ice Point.
The ice point may be
determined by either of the following methods:
(1) Method one.
(a) Ice used to determine the ice point must be made
for chemical-pure (distilled or deionized) water.
(b) Crush or shave ice, avoiding contact with chemi-
cally unclean objects. Fill a chemically clean Dewar jar with the
crushed or shaved ice and add precooled chemical-pure water to form a
slush, but not enough to float the ice.
(c) Immerse the thermometer to be tested in the ice
bath to a depth that covers the 32 degrees F (O degrees C) graduation.
Gently pack the ice around thermometer stem. As the ice melts, drain
off excess water and add crushed or shave ice to maintain the slush
(d) The thermometer shall remain immersed in the ice
bath long enough to assure that the thermometer being tested and the
ice bath have reached equilibrium (at least 3 minutes). Raise the
thermometer a few millimeters to expose the meniscus and gently tap
the stem and observe the reading. Successive readings taken at
intervals of at least 1 minute should agree within 0.1 of a scale
(2) Method two. An alternate method of observing the ice
point is to heap the ice around the stem above the 32 degrees F (O
degrees C) division and form a channel in the ice to permit observa-
tion of the meniscus. Temperature readings may then be made without
raising the thermometer. The initial reading is taken after the
thermometer and bath have reached equilibrium; successive readings
are taken at intervals of at least 1 minute.