attract moisture, which evaporates when the
thermometer is ventilated. Evaporation will yield false
low readings. A daily cleaning of the thermometers
may be necessary in this situation.
Changing the wick on wet-bulb thermometers
should be done weekly aboard ship and monthly ashore.
The procedure is detailed in NAVAIR 50-30FR-518.
Alcohol thermometers may be used to measure
temperatures from -115°C (freezing point of alcohol) to
785°C (boiling point of alcohol). The standard
thermometer for environmental measurements need
only cover the range -20°F to 120°F, or about -30°C to
Because alcohol is a volatile fluid, the column in the
thermometer frequently becomes separated by
mechanical shock. The column may be reunited by
dropping the thermometer on a wood surface that is
covered with several sheets of paper.
thermometer in a vertical position, bulb end down, 4 to 6
inches over the wood surface covered with paper, and
then drop. After the thermometer bulb strikes the paper,
catch the thermometer with your other hand to prevent
breakage. Small amounts of alcohol may cling to the
portion of the capillary tube above the alcohol column.
Heating the high-temperature end of the thermometer
under an incandescent light may force the alcohol back
to the column. Allowing the thermometer to stand in a
vertical position overnight will also allow the alcohol to
drain down to the column. Do not use a thermometer
with a separated fluid column; it will give you
Recently, several Naval Headquarters have
recommended that alcohol thermometers be used in
place of mercury thermometers when possible.
NAVSEAINST 5100.3, Mercury, Mercury
Compounds, and Components Containing Mercury or
Mercury Compounds; Control of, identifies mercury as
a toxic substance that requires special handling and
control. Overboard discharge of any amount is
prohibited. This instruction also defines mercury-spill
decontamination requirements and mercury-handling
Liquid or vaporous mercury is a hazardous
material. It is toxic to humans and most forms
of marine life, and is highly corrosive to
The use of mercury thermometers in sling
psychrometers is strongly discouraged, since users of
sling psychrometers sometimes strike objects during
the spinning operation, breaking the glass and releasing
mercury. The release of even a small amount of
mercury from a broken thermometer is a "mercury
spill," which must be handled in accordance with
NAVSEAINST 5100.3. Unbroken mercury
thermometers, either in use or in storage, are classified
"functional mercury" and are subject to shipboard
mercury inventory reporting as directed by
Separated mercury columns in thermometers
should be rejoined by slowly heating the thermometer
bulb under an incandescent lamp. Withdraw the
thermometer from the heat source as the mercury
approaches the top of the thermometer. Then, carefully
control the heating so that the mercury rises slowly in
the column and just reaches the end of the thermometer.
Overheating at this point will cause the mercury to
expand until it ruptures the thermometer, resulting in a
spill. Allow the thermometer to cool; the columns of
mercury should rejoin as the mercury recedes.
MAXlMUM AND MINIMUM
Maximum and minimum thermometers are
alcohol-filled thermometers mounted on a Townsend
support inside an instrument shelter. These
thermometers are strictly backup equipment for the
maximum and minimum temperature function of
automatic and semiautomatic observation systems.
Proper use and care are detailed in NA 50-3OFR-518.
Figure 2-15 shows the instruments mounted on the
Townsend support, and figure 2-16 shows the detail of
the Townsend support.
Figure 2-16.ML-54 Townsend support details.