Page 36 - Pipeline Rules of Thumb Handbook

General Information 23

Reuniting separated mercury in thermometers

The largest single cause for failure of precision thermome- immersion thermometers) provided only the bulb is immersed
ters is due to separated mercury columns. This can occur in in the CO 2 .
transit or in use. The mercury may be reunited by cooling the
thermometer in a solution of solid CO 2 (Dry-Ice) and alcohol
so that the mercury column retreats slowly into the bulb. Do
not cool the stem or mercury column. Keep the bulb in the Caution: Do not touch the bulb until it has warmed suffi-
solution until the main column, as well as the separated ciently for the mercury to emerge from the bulb into the
portion retreats into the bulb. Remove and swing the ther- capillary.
mometer in a short arc, forcing all of the mercury into the bulb. Never subject the stem or mercury column to the CO 2 solu-
Most mercury thermometers can be reunited using this tion as it will freeze the mercury column in the capillary and
method regardless of range (with the exception of deep may cause the bulb to fracture.

Typical wire resistance

(Stranded Copper Conductors at 59°F)

Wire Size AWG Resistance (ohms/ft)

0000 0.00005
000 0.00006
00 0.00008
0 0.00010
1 0.00012
2 0.00016
4 0.00025
6 0.00039
8 0.00063
10 0.00098
12 0.00160