## 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 laboratoryoperations. In limnological studies, knowledge of water temperatures as a function of depth often are required. Elevated temperatures resulting from discharges of heated water mayhave 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 onwater 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 liquidcolumn 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 bemeasured 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 

#  ( T 1

 t )( T 1  V 0 ) K 

#  

#  1  ( T 1

 t )( T 1  V 0 ) K 

#  L



### where:  T correction to be added algebraically to uncorrected reading, T1 uncorrected reading at reversal,

t temperature at which thermometer is read, V

0 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 T 1 

### 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. S VERDRUP , H.V., M.W. J OHNSON & R.H. FLEMING . 1942. The Oceans. Prentice-Hall, Inc., Englewood Cliffs, N.J. AMERICAN S OCIETY FOR T ESTING AND M ATERIALS . 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 I NSTITUTE OF S TANDARDS 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.

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