What are the different types of liquids used in liquid-in-glass thermometers?
There are many different liquids used in thermometers that range in environmental safety.
1. Enviro-Safe liquid - (exclusive to H-B Instrument) is a non-toxic mixture of biodegradable citrus liquid and a green, non-toxic dye. This liquid is used in Enviro-Safe, Easy-Read, Double-Safe and FRIO-Temp thermometers.
2. Mineral Spirits - Petroleum hydrocarbon, clear odorless liquid with a petroleum odor, usually mixed with blue, red or green colored dye.
3. Mercury - Metal, molecular formula: Hg, an odorless, silvery liquid with a metallic luster. Mercury based thermometers are banned from certain states because they are toxic.
4. Mercury/Gallium - Mercury and Gallium amalgam which increases the temperature range by increasing the mercury boiling point (used in thermometers up to 620 degree Celsius). Mercury based thermometers are banned from certain states because they are toxic.
5. Mercury/Thallium - Mercury and Thallium amalgam which lowers the temperature range of mercury to below -40 degree Celsius by lowering the solidification point of mercury. Mercury based thermometers are banned from certain states because they are toxic.
If the liquid in the column of a thermometer is separated, is the thermometer faulty?
Absolutely not! The liquid in any glass thermometer, regardless of type (e.g. mercury-filled, spirit-filled, etc.) can be separated within the in the liquid column. This may be a result of shipping and handling, or improper storage after the thermometer has left H-B Instrument’s possession.
Two simple methods have been developed to reunite separated fluid in a thermometer column. If employed correctly, the reunited liquid column will be as good as new.
Note: For each method we suggest you wear safety glasses and gloves when working with glass instruments.
Prepare a solution of shaved ice and salt or a solution of CO2 (Dry Ice) and alcohol. Place the thermometer bulb only in the solution. Keep the thermometer upright. Allow the liquid column to retreat into the bulb, swing the thermometer (bulb down) in an arc forcing the entrapped gas above the column. Allow the thermometer to return to room temperature slowly in an upright position.
Heat the thermometer bulb in an upright position away from your face in warm liquid, air, or over a soft flame enough to allow the liquid column to rise slowly until the separated portion of the column enters the expansion chamber at the top of the thermometer. Note that applying heat for too long will over-fill the expansion chamber which will break the thermometer. Tap the thermometer bulb gently on the tabletop in an upright position allowing the gas separating the column to rise above the column. Allow the thermometer to cool slowly in an upright position.