Mercury Use in Measuring Devices

The only metal that is liquid at room temperature, mercury expands and contracts evenly with temperature and pressure changes. These characteristics have made mercury useful in devices measuring temperature and pressure, such as thermometers and barometers. The function of the mercury in each measuring device included in this fact sheet is described below.

Barometers measure atmospheric pressure. Mercury barometers contain elemental mercury exposed to air in a thin glass column. The mercury rises and falls with changes in atmospheric pressure.

Hydrometers measure the specific gravity of liquids. Mercury is used in hydrometers as a weight. It is encased in a thin glass tube with a bulb at one end. The tube is sealed and floats upright in the sample liquid like a fishing bobber. Hydrometers sometimes contain a thermometer for measuring the temperature of liquids. These are called thermohydrometers and may contain additional mercury in the thermometer.

Manometers measure the difference in gas pressure. Mercury manometers are generally U-shaped glass or plastic tubes containing elemental mercury that have one end closed. The difference in the levels of mercury in each side of the tube indicates the pressure of the gas being measured. Manometers are frequently used to measure air pressure within air ducts or compressed air lines.

Psychrometers and hygrometers are instruments used for measuring humidity. They contain two thermometers, a "dry bulb," or ordinary thermometer, and a "wet bulb" thermometer, which has a bulb that is kept constantly wet. Humidity is computed from the difference in the temperatures shown by the two thermometers. Mercury is contained in the two thermometers.

Sphygmomanometers are a type of mercury manometer that is used for measuring blood pressure. Sphygmomanometers measure both maximum arterial pressure, when the heart beats and sends blood through the arteries, and minimum pressure, when the heart relaxes and fills with blood again. Mercury is contained inside a plastic or glass tube.

Strain gauges measure forearm blood flow, or arterial inflow, using a technique called strain gauge plethysmography. Mercury is contained in a fine rubber tube which is placed around the forearm. The gauge measures the increase in forearm circumference as pressure is applied.

Thermometers measure temperature. Mercury thermometers contain mercury encased in a thin glass tube that rises and falls with temperature.

Amount of Mercury Used in Measuring Devices

Table 1 presents the average amount of mercury in each type of measuring device. Manufacturers, importers and distributors of mercury-added products may report the amount of mercury used as an exact number, an average with upper and lower bounds, or as a range. The number of manufacturers refers to the number of manufacturers reporting use of a particular amount of mercury.

A number of important caveats must be considered when reviewing the data summarized in this fact sheet:

• The information does not represent the entire universe of measuring devices using elemental mercury and therefore underestimates the total amount of mercury reported for this category of products. The states participating in IMERC continuously receive Product Notification Forms from mercury-added product manufacturers, and the data presented in this fact sheet may underestimate the total amount of mercury sold in these products.
• The data presented summarize mercury in measuring devices sold nationwide in the U.S. in calendar year 2001. It does not include products that were sold prior to January 1, 2001.
• Reported data only includes mercury that is used in the product, and does not include mercury emitted during mining and/or manufacturing.
• Reported data only includes mercury that is used in the product, and does not include mercury emitted during the mining and/or manufacturing.

Table 1: Amount of Mercury in Measuring Devices
Mercury-added Component	Amount of Mercury in Individual Product (grams)	Number of Manufacturers
Barometer	395-622	1
Thermohydrometer	>11	1
Manometers, U-Tubes, and Replacement Tubes	28-74	5
Psychrometers	5.2-6	2
Sphygmomanometers	54.3-137	2
Strain Gauge	>1	1
Thermometers2	>0-.005 >.005-.01 >1	2 1 11
1 This thermohydrometer contained mercury only in the thermometer. 2 The thermometer category includes medical, laboratory, industrial, and cooking thermometers. Due to the way the data are reported it is not possible to separate the data by type of thermometer when providing information on the amount of mercury used. Generally, however, 0.5 grams of mercury are added to fever thermometers and 3 grams are added to laboratory thermometers. Industrial thermometers can contain significantly more than 1 gram. The maximum amount of mercury added to an industrial thermometer was reported to IMERC at 117 grams.

Total Amount of Mercury in Measuring Devices

Table 2 presents the total amount of mercury in measuring devices sold in the U.S. during calendar year 2001. Approximately 9,945.5 pounds, or 5 tons, was sold in 2001 in all the measuring devices covered in this fact sheet. Note that replacement mercury sold by one the manufacturers is also included in the total amount.

TABLE 2: Total Mercury in Measuring Devices Sold in the US Calendar Year 2001
Product	Total Mercury in Products Sold, Calendar Year 2001 (pounds)		Manufacturers Reporting
	Grams	Pounds
Barometer	160,000	353	Princo Instruments
Hydrometer/Thermometer	3,632	8	Francis L. Freas Glassworks
Manometer1	878,072	1,9362	Hach Scientific Glass & Instruments Meriam Instrument Motion Pro Inc. Princo Instruments
Psychrometers	1,260	33	Princo Instruments Taylor Precision Products
Spyhgmomanometers	1,952,580	4,305	W.A. Baum American Diagnostic Corporation
Strain Gauge	6664	1.5	D.E. Hokanson
Thermometers	1,460,652	3,2215	Brooklyn Thermometer Co. Inc. Hach Taylor Precision Products PSG Controls, Inc Anderson Instrument Company Barnstead International Palmer Instruments, Inc. Miller & Weber Watson McDaniel (H. O. Trerice) Francis L. Freas Glassworks Yuil Measure Lux Products Corporation Miljoco6
Replacement mercury	53,964	118	Meriam Instruments
Total for all measuring devices:       9,945.5 pounds
1 gram = 0.002205 pounds 1 Dwyer Instrument also makes mercury manometers but reportedly does not sell these manometers in the IMERC states. For information on Dwyer's products see http://www.dwyer-inst.com/ 2 This value under-represents the total amount of mercury sold in manometers in 2001 as reported to IMERC because one manufacturer did not report the total amount of mercury sold in its products. 3 This value under-represents the total amount of mercury sold in psychrometers in 2001 as reported to IMERC because the amount of mercury that was sold by one of the manufacturers, Taylor Precision Products, was included with the thermometer category. 4 This value under-represents the total amount of mercury sold in thermometers in 2001 as reported to IMERC because one manufacturer did not report the total amount of mercury sold in its products. 5 This figure is for Calendar Year 2002; 2001 data was not available. 6 Miljoco did not sell mercury thermometers in the IMERC states during 2001.

Mercury Product Phase-Outs

Published in December 2004