THERMOMETERS

TM 5-6640-213-14

THERMOMETERS.

3-23.

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.

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

condition.

(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

division.

(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.