In the Laboratory
Mercury Thermometer Replacements in Chemistry Laboratories Barbara L. Foster C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26506-6045;
[email protected] According to the Mallinckrodt Baker Material Safety Data Sheet for mercury, chronic exposure to mercury through any route can produce central nervous system damage (1). Common exposure routes include: inhalation, ingestion, and skin or eye contact. In academia, mercury mishaps in the laboratory include broken thermometers in the student drawers, broken thermometers on the bench tops and floors, and broken thermometers that are located inside of equipment, such as Mel-Temp instruments. In academic laboratories, the consequences of broken mercury-in-glass thermometers include: student and personnel exposure, laboratory and environmental contamination, mercury spill cleanup training, mercury spill equipment on hand, proper disposal of contaminated glass, and proper disposal of collected mercury. Mercury is heavy and expensive to ship and one will encounter mixed waste issues when disposing of mercury in Biohazard and Radiologically Controlled Areas. It has been estimated that the cleanup cost of one broken mercury thermometer is about $75.00–$110.00 and that the one-half gram of mercury contained in a mercury thermometer is enough to pollute five million gallons of water (2, 3). To eliminate this health and environmental hazard, many institutions are replacing their mercury-in-glass thermometers with suitable substitutes (4). The following universities are eliminating mercury thermometer use in teaching and research laboratories: Illinois, Michigan, Vermont, Northwestern, Stanford, Yale, and Harvard (5). Mercury-free thermometers can be used in many applications in the teaching laboratory, including water baths, incubators, and melting point instruments. For those applications that require the accuracy and precision of traditional mercury thermometers, breakage resistant Teflon-coated mercury thermometers have been recommended as replacements (3). A mercury thermometer replacement program should be designed to provide safe, suitable substitutes for student use in academic laboratories. Factors that should be considered during the mercury replacement process are: types of applications in the laboratories; temperature range, total length, immersion length, requisite scale divisions, cost, accuracy, and durability upon exposure to various caustic solutions and vapors. To avoid student and employee exposure to hazardous materials in the laboratory, effective mercury thermometer replacements have been identified, purchased, and implemented in the academic laboratories at the C. Eugene Bennett Department of Chemistry at West Virginia University (6). Mercury Thermometer Replacements in General Chemistry Laboratories
Long-Stem Digital Thermometers In 1998, chemistry faculty and staff performed side-byside comparisons with the standard mercury thermometer and tested various non-mercury thermometers for possible use in www.JCE.DivCHED.org
•
the general chemistry laboratories. They ultimately chose a long-stem digital thermometer for use in the general chemistry laboratories (7). This thermometer is constructed of almost unbreakable plastic and stainless steel, contains no glass and no mercury, has a long stem that makes it convenient to use in the glassware that is typically used in our laboratories, and is traceable to National Institute of Standards and Technology (NIST) standards. Although a concern regarding the durability of the metallic stem was mentioned in a previously published article on the subject of alternatives to mercury thermometers by Nezlin (8), the acids, bases, solvents, and various other solutions that are used in our general chemistry laboratories have not corroded the metallic stem of the thermometer. The bright display is 1/4-inch in height and is easier for the students to read than the standard mercury thermometer. The display range is ᎑50–150 ⬚C. The stem length is 8 inches and the overall length is 11 inches. The thermometer is shipped with a one-year battery and a protective sleeve. The advantages of this thermometer include: it has proven to be durable; it contains no glass or mercury; it is easy to read and use; it is cost-effective; it is easy to store and distribute when needed; and the battery life has proven to be approximately three years under normal conditions in our laboratories. The disadvantages of this thermometer include: some solvents can dissolve the plastic and ruin the thermometer, one should avoid applying direct heat to the thermometer since we typically lose 12 thermometers per year to meltdowns, and the battery contacts can corrode from exposure to acids and bases. However, scrubbing with steel wool can restore the contacts. Mercury Thermometer Replacements in Organic Chemistry Laboratories
Non-Mercury Glass Thermometers In 2001, our organic chemistry faculty and staff tested several types of mercury thermometer alternatives for use in the organic chemistry laboratories. After side-by-side testing with mercury thermometers, departmental personnel chose the Enviro-Safe Thermometer (9). Although the thermometer proved to be less accurate than the standard mercury thermometer at temperatures higher than 100 ⬚C, the organic chemistry faculty were confident that it would work well in the laboratory setting and prove to be a suitable replacement. The Enviro-Safe thermometer, manufactured by the H-B Instrument Company, is filled with a mixture of biodegradable technical white oil, natural citrus oils, and a dark green monoazo-anthroquinone dye (10). The display range is ᎑10– 260 ⬚C. The overall length of this thermometer is 355 mm and the partial immersion depth is 76 mm. The company offers both total and partial immersion thermometers. One must immerse the bulb and the entire liquid column to accurately measure the temperature with a total immersion thermometer. However, the column on a partial immersion
Vol. 82 No. 2 February 2005
•
Journal of Chemical Education
269
In the Laboratory
thermometer is marked with a line at the correct immersion distance from the bottom. The thermometer is immersed to the depth that is noted on the liquid column to accurately measure the temperature with a partial immersion thermometer (11). Although the author of a recent article on mercury thermometer replacements found the accuracy of the EnviroSafe thermometer to be too dependent on the degree of immersion, his study was based upon the use of a total immersion Enviro-Safe thermometer (12). The 76-mm depth partial immersion model has proven to be ideal for our needs in the academic organic chemistry laboratories. The advantages of the Enviro-Safe thermometer include: the thermometer contains a nonhazardous, biodegradable liquid filling; a broken thermometer presents no hazardous materials disposal problems; the thermometers are available in several lengths; and the thermometers exhibited excellent accuracy up to 100 ⬚C. The disadvantages include: during side-by-side testing with mercury thermometers conducted by chemistry faculty, these thermometers proved to be less accurate at temperatures greater than 100 ⬚C. The EnviroSafe thermometer is advertised to be accurate within 1 ⬚C up to 105 ⬚C, within 1.5 ⬚C above 105 ⬚C, and within 2 ⬚C above 200 ⬚C. We discovered that the inaccuracies that were encountered at the higher temperatures were negligible in our laboratory applications and thus did not constitute a significant disadvantage. Additionally, we have experienced separated green columns in these thermometers that we cannot repair. A simple method to avoid the separated columns is to store the thermometers in an upright position when not in use (2). Melting Point Apparatus with Digital Thermometer In 2002, chemistry faculty replaced the existing, outdated melting point equipment that contained mercury thermometers with Barnstead International Manual Mel-Temps with precision digital thermometers (13). The organic laboratories are now completely mercury-free. The Barnstead MelTemps literature lists the heat up time from 25 ⬚C to 400 ⬚C in five minutes and from 400 ⬚C to 500°C in four minutes. The accuracy is listed in the literature as ±(0.05% + 0.3 ⬚C) for temperatures above 100 ⬚C and ±(0.2% + 0.3 ⬚C) for temperatures below 100 ⬚C . We have completed a full academic year with the new equipment. All feedback from students, teaching assistants, and faculty has been positive in nature. The advantages of these instruments include: extreme accuracy; they are student-friendly and eliminate guesswork; efficient heat up and cool down times; and they facilitate the identification of student unknowns and derivatives. A disadvantage is that the digital readout is supplied as an attachment.
270
Journal of Chemical Education
•
Acknowledgments The author would like to acknowledge the support of Albert G. Taylor, Jr., Björn C. G. Söderberg, Kung K. Wang, Harry O. Finklea, and the C. Eugene Bennett Department of Chemistry in the implementation of the mercury thermometer replacement program at West Virginia University. Disclaimer The author has no personal or financial interest or affiliation with VWR Scientific, Enviro-Safe, H-B Instrument Company, or Barnstead International. Literature Cited 1. Material Safety Data Sheet #M1599, Mercury (CAS Number 7439-97-6), Mallinckrodt Baker, Inc: Phillipsburg, New Jersey, November 2001. 2. Treviño, L., New Program Aims to Eliminate Mercury Thermometers. Stanford Online Report, July 12, 2000, http://newsservice.stanford.edu/news/july12/mercury-712.html (accessed Nov 2004). 3. Harvard University, University Operations Services, Environmental Health and Safety, Broken Mercury Thermometers, Fact Sheet, Online Resources, http://www.uos.harvard.edu/ehs/ onl_fac_env_mer.shtml (accessed Nov 2004). 4. Martinez, T. P.; Grundemann, R. F.; Cournoyer, M. E. J. Am. Soc. Mech. Eng. Proceeding from ICEM 2001, the 8th International Conference on Radioactive Waste Management and Environmental Remediation, September 30–October 4, 2001. 5. McDonald, B. Mercury Thermometer Replacement Program. REM NEWS, Purdue University Radiological and Environmental Management, April 2002. 6. Occupational Safety and Health Administration. Occupational Exposure to Hazardous Chemicals in Laboratories; 29 CFR; Part 1910.1450, 1990. 7. VWR Scientific Products; catalog number 61220-416; list price $22.50. 8. Nezlin, A. J. Chem. Educ. 2001, 78, 342. 9. VWR Scientific Products; catalog number 61019-010; list price $22.05. 10. Material Safety Data Sheet #20525, Enviro-Safe Liquid Inside Thermometer, H-B Instrument Company: Trappe, Pennsylvania, January 2001. 11. The University of Vermont. The UVM Mercury Thermometer Swap, The University Initiative, http://esf.uvm.edu/ chemsource/thermoswap/ (accessed Nov 2004). 12. Everett, T. S. J. Chem. Educ. 1997, 74, 1204. 13. VWR Scientific Products; catalog number 51009-004; Barnstead International model number 1101D; list price $1178.00.
Vol. 82 No. 2 February 2005
•
www.JCE.DivCHED.org
