Cannon Instrument CMRV-5000 - Manual (Page 121)

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CANNON ® Mini-Rotary Viscometer CMRV-5000 Instruction & Operation Manual
Version 1.0b—August, 2011; CANNON ® Instrument Company
2139 High Tech Road • State College, PA • 16803 • USA
NBS Monograph150: Joining separated mercury columns
The following text outlines procedures for joining separated mercury
columns in thermometers. The text is adapted from:
NBS MONOGRAPH 150 Liquid-In-Glass Thermometry
Wise, Jacquelyn A.
NOTE Many inquiries are received concerning separated mercury column
which occur especially during shipment. Since no means of avoiding
such occurrences has yet been found, some directions for joining mer-
cury may be helpful and are described below.
(A) The bulb of the thermometer may be cooled in a solution of common
salt, ice, and water (or other cooling agent) to bring the mercury down
slowly into the bulb. If the salt solution does not provide sufficient
cooling, carbon dioxide snow (dry ice) may be used. Since the tempera-
ture of dry ice is approximately -78°C (-108°F), and mercury freezes at
approximately -40°C (-40°F), the mercury will solidify. Cool only the
bulb and never the stem or mercury column. Moderate tapping of the
bulb on a rubber stopper or similar soft spongy object, or the application
of centrifugal force, by swinging the thermometer in a short arc (i.e. use
of centrifugal force), usually serves to unite the mercury in the bulb.
Care must be taken to warm the top of the bulb first, so pressures in the
bulb due to expanding mercury may be relieved.
(B)
If there is a contraction chamber above the bulb or an expansion chamber
at the top of the thermometer, the mercury can sometimes be united by
warming the bulb until the column reaches the separated portions in
either enlargement. Great care is necessary to avoid filling the expansion
chamber completely with mercury, which might produce pressures large
enough to burst the bulb. (The expansion chamber should never be more
than 2/3 full). Joining the mercury is more readily accomplished if the
quantity in either cavity has been shattered into droplets by tapping the
thermometer laterally against the hand.
This procedure should not be used it if requires the thermometer to be
heated above 260°C (500°F) and the bulb should never be heated in an
open flame.
(C)
As a last resort, especially for thermometers having no expansion
chambers, small separated portions of the column can sometimes be
dispersed if mercury is warmed into droplets tiny enough to leave space
for the gas to by-pass. The thermometer is heated, and the droplets are
collected by the rising mercury column.
Organic liquid procedures The procedure for thermometers containing organic liquids is similar.
Separated liquid in the stem can be vaporized and permitted to drain
down the capillary. Another method consists of gently tapping the stem
above the separation against the palm of the hand, forcing the organic