Let's Make Mercury Spills Extinct by Courtney Drayer
Mercury is a neurotoxin that bioaccumulates in the environment, and mercury spills are difficult, timely and expensive to clean up. In an effort to reduce the quantity of elemental mercury at the Columbia campuses and prevent accidental release of mercury into the environment, EH&S has provided a free mercury thermometer substitution program for the past ten years. EH&S will provide your laboratory with a certified (±1°C accuracy), National Institute of Standards (NIST) traceable, 12‟‟ partial immersion organic liquid in glass (LiG) thermometer for measurements from -20°C to +110°C (VWR Catalog #33600-036) in exchange for an intact mercury thermometer. Similar partial immersion, LiG thermometers with the same length and same ±1°C accuracy are offered at the at more than triple the price (e.g.: VWR Catalog #61017-823).
NIST is a government organization that, among other responsibilities, offers thermometry calibration services. NIST is currently working with the American Society for Testing and Materials (ASTM) to rewrite temperature and measurement consensus standards in order to discontinue the use of mercury thermometers, where possible. NIST is also working with the Environmental Protection Agency (EPA) to develop non-mercury solutions for elevated temperature applications (e.g; autoclave operations) where traditional organic liquids will fail. Additionally, organic LiG thermometers can both be NIST traceable and ASTM certified for accuracy. One remaining concern is that organic LiG thermometers are not as sensitive as mercury thermometers. However, thoughtful engineering and selection of the appropriate alcohol for the temperature range needed can give results comparable, if not better than, mercury. To illustrate, the sensitivity of a thermometer can be measured by the following equation;
Where T is temperature, H is height, V is volume, β' is the cubical coefficient of thermal expansion corrected for the rate of expansion of glass, and d is the diameter of the capillary bore. In the case of a small mercury thermometer, with a volume of 300 mm3 and capillary diameter of 0.2 mm, the sensitivity of the thermometer will be 0.97 mm/°C – there will be almost a millimeter between each one degree marking.. In order to achieve this same sensitivity (0.97 mm/°C) using ethanol as the filling liquid in a thermometer of the same volume, the capillary bore should be 0.65 mm. As an added bonus, a thermometer that has a larger diameter should also be easier to read. For those who are concerned about the low boiling point of ethanol, other filling liquids cover various ranges of temperature (for example, i-amyl benzoate is reliable through +220°C and pentanol is reliable down to -115°C). Non-metal thermometers are appropriate for use in temperature ranges for many standard laboratory scale experimentation.
For additional information in selecting a mercury alternative, NIST provides a guidance document that addresses the technical issues regarding substitute devices in an article by Ripple and Straus, 2005.
In an effort to reduce the quantity of elemental mercury at the
Columbia campuses and prevent accidental release of mercury into the environment, EH&S has
provided a free mercury thermometer substitution program for the past ten years.