2550 TEMPERATURE*

2550 A. Introduction

Temperature readings are used in the calculation of various

forms of alkalinity, in studies of saturation and stability with

respect to calcium carbonate, in the calculation of salinity, in

a number of colorimetric tests, and in general laboratory

operations. In limnological studies, knowledge of water temperatures as a function of depth often are required. Elevated

temperatures resulting from discharges of heated water may

have significant ecological impact. The source of water supply, such as deep wells, often can be identified by temperature

measurements alone. Industrial plants often require data on

water temperature for process use or heat-transmission calculations.

2550 B. Laboratory and Field Methods

1. Laboratory and Other Non-Depth Temperature

Measurements

Normally, temperature can be measured using any standard liquid-in-glass or electronic thermometer with an analog or digital

readout. The device should be able to distinguish temperature

changes of 0.1°C or less, and equilibrate rapidly (have a minimal

thermal capacity). Abstain from using mercury-filled thermometers

whenever possible to avoid the possibility of releasing mercury into

the environment if the thermometer breaks. To prevent breakage in

field operations, use a thermometer with a metal case.

Periodically check the device’s bias (within the temperature

range of use) against a reference thermometer certified by the

National Institute of Standards and Technology (NIST, formerly

National Bureau of Standards) and using tolerances suggested in

NIST Handbook 105-6.† The certified thermometer must be used

with its certificate and correction chart.

A total immersion thermometer is designed to indicate temperatures correctly when the bulb and the entire liquid column

are exposed to the temperature being measured (except for a

minimal emergent length for handling). A partial-immersion

thermometer has a line around it at the immersion distance from

the bottom. It indicates correctly when the bulb and the liquid

column to that line are exposed to the temperature being measured and the emergent stem is at ambient temperature.

The quality control (QC) practices considered to be an integral

part of each method are summarized in Table 2020:II.

2. Depth Temperature Measurements

Depth temperatures required for limnological studies may be

measured with a reversing thermometer, thermophone, or thermistor. The thermistor is most convenient and accurate; however,

higher cost may preclude its use. Before field use, verify a temperature measurement device’s calibration according to NIST specifications. Make readings with the thermometer or device immersed in

water long enough to permit complete equilibration. Report results

to the nearest 0.1 or 1.0°C, depending on need.

A reversing type thermometer is commonly used for depth

measurements. It often is mounted on the sample-collection

apparatus so a water sample can be obtained simultaneously.

Correct reversing-thermometer readings for changes due to differences between temperature at reversal and temperature at time

of reading. Calculate as follows (all units in degrees):

T 

(T1t)(T1V0)

K  1(T1

t)(T1V0)

K  L

where:

T correction to be added algebraically to uncorrected reading,

T1 uncorrected reading at reversal,

t temperature at which thermometer is read,

V0 degree volume of thermometer, the volume of small bulb

end of capillary up to 0°C graduation,

K constant depending on relative thermal expansion of

mercury and glass (usual value of K 6100), and

L calibration correction of thermometer depending on T1

.

If series observations are made, it is convenient to prepare graphs

for a thermometer to obtain T from any values of T1 and t.

3. Bibliography

WARREN, H.F. & G.C. WHIPPLE. 1895. The thermophone—A new instrument for determining temperatures. Mass. Inst. Technol. Quart.

8:125.

SVERDRUP, H.V., M.W. JOHNSON & R.H. FLEMING. 1942. The Oceans.

Prentice-Hall, Inc., Englewood Cliffs, N.J.

AMERICAN SOCIETY FOR TESTING AND MATERIALS. 1949. Standard Specifications for ASTM Thermometers, No. E1-58. American Society

for Testing and Materials, Philadelphia, Pa.

REE, W.R. 1953. Thermistors for depth thermometry. J. Amer. Water

Works Assoc. 45:259.

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY. 1997. NIST Handbook 105-6. Specifications and Tolerances for Reference Standards

and Field Standard Weights and Measures. National Institute of

Standards and Technology, Gaithersburg, Md.

* Approved by Standard Methods Committee, 2010.

† Some commercial thermometers may be as much as 3°C in error.

1