5.B.8.1 Thermometers

Design a mercury thermometer replacement program to provide safe, suitable substitutes for use in laboratories. Factors that should be considered during the mercury replacement process are various applications in the laboratories, required temperature range, thermometer length, immersion depth, scale divisions, cost, accuracy in relation to application, and durability upon exposure to corrosive solutions. In some cases, these alternative thermometers have a more limited temperature range than a mercury thermometer. Perform tests for accuracy in the laboratory prior to a total replacement program to ensure that the mercury substitutes will be suitable for the methods that will be employed in that particular laboratory. To ensure accuracy, thermometers must be calibrated using approved methods such as ASTM E 77 (ASTM International, 2007a) and must be traceable to the National Institute of Standards and Technology (NIST).

There is a wide selection of mercury-free liquid-filled thermometers available, including spirit thermometers (filled with biodegradable petroleum-based mineral spirits and dyes) and alcohol-based thermometers. When broken, these thermometers present no hazardous material disposal problems. Some spirit thermometers had a history of the thread breaking more easily than a mercury thermometer, but many of the newer formulations have overcome this problem. In the event that the thread breaks, the simplest and safest method to reunite the liquid is to use a centrifuge. Carefully insert the thermometer, bulb down, in the centrifuge. Use cotton wadding at the bottom of the cup to prevent any damage to the bulb. Turn on the centrifuge and in just a few seconds all the liquid will be forced past the separation. Note that if the cup is not deep enough, and all the centrifuge force is not below the column, the column will split, forcing half the liquid in the bulb and half the liquid in the expansion chamber (Izzo, 2002).

For liquid-filled thermometers used to measure the temperature of liquids, accuracy will also depend on choosing the correct immersion depth. This is less of an issue for mercury thermometers because mercury generally has better thermoconductivity. A total immersion thermometer is designed to indicate temperatures correctly when the bulb and all but 12 mm of the liquid column are immersed in the bath medium. The top 12 mm of the liquid column should be above the bath medium so that the thermometer can be read and the material does not distill at high temperatures. Thermometers that have been graduated for total immersion usually have no markings on the back pertaining to immersion. A partial immersion thermometer is designed to indicate temperatures correctly when the bulb and a specified portion of the stem are exposed to the temperature being measured and the remainder of the stem is exposed to the ambient temperature. Partial immersion thermometers are clearly marked with a permanently placed line on the stem to indicate the proper immersion depth (ASTM International, 2007a).

In addition to thermometers that are filled with mercury-alternative liquids, long-stem digital thermometers are available with probes that are resistant to most laboratory chemicals, including acids, bases, and solvents. The bright displays, usually ¼ in. high, are easy to read and display the temperature in both degrees Fahrenheit and degrees Celsius, with ranges from -58 to 302 °F and –50 to 150 °C. Long-stem thermometers are constructed of plastic and stainless steel and do not contain glass or mercury, which make them ideal thermometers for use in academic laboratories. The stems are generally 8 inches long with an overall thermometer length of 11 in.

5.B.8.2 Digital Thermometers

Where a mercury thermometer is the only option, armor cases, which protect against breakage without affecting accuracy, or Teflon-coated mercury thermometers are recommended. These are particularly useful in high-temperature ovens, oil baths, and autoclaves, where cleaning up a mercury spill can be challenging and the spill creates a serious health hazard.

5.B.8.3 Differential Manometers

Depending on the measurement range, labs can substitute water or calibrated oils for mercury. Pressure transducers or electronic pressure gauges may also be an alternative to a conventional manometer.


5.C.1 Ordering Chemicals

Authority to place orders for chemicals may be centralized in one purchasing office or may be dispersed to varying degrees throughout the institution. The advent of highly computerized purchasing systems, and even online ordering, has made it feasible to allow ordering at the departmental or research group level. However, the ability to control ordering of certain types of materials through a central purchasing system (e.g., prohibiting flammables in containers over a certain size or ensuring appropriate licensing of radioactive material users) is almost completely lost when the purchasing function is decentralized. In these cases, other creative ways of exercising control need to be found.

Before purchasing a chemical, prudent laboratory personnel ask several questions:

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement