ASTM E1750-10(2016)
(Guide)Standard Guide for Use of Water Triple Point Cells
Standard Guide for Use of Water Triple Point Cells
SIGNIFICANCE AND USE
4.1 This guide describes a procedure for placing a water triple-point cell in service and for using it as a reference temperature in thermometer calibration.
4.2 The reference temperature attained is that of a fundamental state of pure water, the equilibrium between coexisting solid, liquid, and vapor phases.
4.3 The cell is subject to qualification but not to calibration. The cell may be qualified as capable of representing the fundamental state (see 4.2) by comparison with a bank of similar qualified cells of known history, and it may be so qualified and the qualification documented by its manufacturer.
4.4 The temperature to be attributed to a qualified water triple-point cell is exactly 273.16 K on the ITS-90, unless corrected for isotopic composition (refer to Appendix X3).
4.5 Continued accuracy of a qualified cell depends upon sustained physical integrity. This may be verified by techniques described in Section 6.
4.6 The commercially available triple point of water cells described in this standard are capable of achieving an expanded uncertainty (k=2) of between ±0.1 mK and ±0.05 mK, depending upon the method of preparation. Specified measurement procedures shall be followed to achieve these levels of uncertainty.
4.7 Commercially-available triple point of water cells of unknown isotopic composition should be capable of achieving an expanded uncertainty (k=2) of no greater than 0.25 mK, depending upon the actual isotopic composition (3). These types of cells are acceptable for use at this larger value of uncertainty.
SCOPE
1.1 This guide covers the nature of two commercial water triple-point cells (types A and B, see Fig. 1) and provides a method for preparing the cell to realize the water triple-point and calibrate thermometers. Tests for assuring the integrity of a qualified cell and of cells yet to be qualified are given. Precautions for handling the cell to avoid breakage are also described.
1.2 The effect of hydrostatic pressure on the temperature of a water triple-point cell is discussed.
1.3 Procedures for adjusting the observed SPRT resistance readings for the effects of self-heating and hydrostatic pressure are described in Appendix X1 and Appendix X2.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1750 −10 (Reapproved 2016)
Standard Guide for
Use of Water Triple Point Cells
This standard is issued under the fixed designation E1750; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The triple point of water is an important thermometric fixed point common to the definition of two
temperature scales of science and technology, the KelvinThermodynamicTemperature Scale (KTTS)
and the International Temperature Scale of 1990 (ITS-90). The ITS-90 was designed to be as close to
the KTTS as the experimental data available at the time of the adoption of the ITS-90 would permit.
The temperatures (T) on the KTTS are defined by assigning the value 273.16 K to the triple point of
water, thus defining the thermodynamic unit of temperature, kelvin (K), as 1/273.16 of the
thermodynamic temperature of the triple point of water (1, 2). The triple point of water, one of the
fixed points used to define the ITS-90, is the temperature to which the resistance ratios
W(T)=R(T)⁄R(273.16 K) of the standard platinum resistance thermometer (SPRT) calibrations are
referred.
The triple points of various materials (where three distinct phases, for example, their solid, liquid,
andvaporphases,coexistinastateofthermalequilibrium)havefixedpressuresandtemperaturesand
are highly reproducible. Of the ITS-90 fixed points, six are triple points. The water triple point is one
of the most accurately realizable of the defining fixed points of the ITS-90; under the best of
conditions, it can be realized with an expanded uncertainty (k=2) of less than 60.00005 K. In
comparison, it is difficult to prepare and use an ice bath with an expanded uncertainty (k=2) of less
than 60.002 K (3).
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This guide covers the nature of two commercial water
bility of regulatory limitations prior to use.
triple-point cells (types A and B, see Fig. 1) and provides a
1.5 This international standard was developed in accor-
method for preparing the cell to realize the water triple-point
dance with internationally recognized principles on standard-
and calibrate thermometers. Tests for assuring the integrity of
ization established in the Decision on Principles for the
a qualified cell and of cells yet to be qualified are given.
Development of International Standards, Guides and Recom-
Precautions for handling the cell to avoid breakage are also
mendations issued by the World Trade Organization Technical
described.
Barriers to Trade (TBT) Committee.
1.2 The effect of hydrostatic pressure on the temperature of
a water triple-point cell is discussed.
2. Referenced Documents
1.3 Procedures for adjusting the observed SPRT resistance
2.1 ASTM Standards:
readings for the effects of self-heating and hydrostatic pressure
E344Terminology Relating to Thermometry and Hydrom-
are described in Appendix X1 and Appendix X2.
etry
E1594Guide for Expression of Temperature
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
3.1 Definitions—ThedefinitionsgiveninTerminologyE344
This guide is under the jurisdiction ofASTM Committee E20 on Temperature
apply to terms used in this guide.
Measurement and is the direct responsibility of Subcommittee E20.07 on Funda-
mentals in Thermometry.
Current edition approved May 1, 2016. Published May 2016. Originally
approved in 1995. Last previous edition approved in 2010 as E1750–10. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/E1750-10R16. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1750 − 10 (2016)
4. Significance and Use
4.1 This guide describes a procedure for placing a water
triple-point cell in service and for using it as a reference
temperature in thermometer calibration.
4.2 The reference temperature attained is that of a funda-
mental state of pure water, the equilibrium between coexisting
solid, liquid, and vapor phases.
4.3 The cell is subject to qualification but not to calibration.
The cell may be qualified as capable of representing the
fundamental state (see 4.2) by comparison with a bank of
similar qualified cells of known history, and it may be so
qualifiedandthequalificationdocumentedbyitsmanufacturer.
4.4 The temperature to be attributed to a qualified water
triple-point cell is exactly 273.16 K on the ITS-90, unless
corrected for isotopic composition (refer to Appendix X3).
4.5 Continued accuracy of a qualified cell depends upon
sustainedphysicalintegrity.Thismaybeverifiedbytechniques
described in Section 6.
4.6 The commercially available triple point of water cells
describedinthisstandardarecapableofachievinganexpanded
uncertainty (k=2) of between 60.1 mK and 60.05 mK,
depending upon the method of preparation. Specified measure-
ment procedures shall be followed to achieve these levels of
uncertainty.
4.7 Commercially-available triple point of water cells of
unknown isotopic composition should be capable of achieving
an expanded uncertainty (k=2) of no greater than 0.25 mK,
depending upon the actual isotopic composition (3). These
types of cells are acceptable for use at this larger value of
uncertainty.
5. Apparatus
5.1 The essential features of type A and type B water
triple-point cells are shown in Fig. 1.Atransparent glass flask
free of soluble material is filled with pure, air-free water and
thenispermanentlysealed,air-free,atthevaporpressureofthe
water. A reentrant well on the axis of the flask receives
thermometers that are to be exposed to the reference tempera-
FIG. 1 Configurations of two commonly used triple point of wa-
ter cells, Type A and Type B, with ice mantle prepared for mea-
ture.
surement at the ice/water equilibrium temperature. The cells are
5.2 Forthelowestlevelofuncertainty,thewaterusedasthe
used immersed in an ice bath or water bath controlled close to
0.01°C (see 5.4) reference medium shall be very pure and of known isotopic
composition. Often it is distilled directly into the cell. The
isotopic composition of cells filled with “rain water” is
expected not to vary enough to cause more than 0.05 mK
difference in their triple points. Extreme variations in isotopic
3.2 Definitions of Terms Specific to This Standard:
composition, such as between ocean water and water from old
3.2.1 inner melt, n—a thin continuous layer of water be-
polar ice, can affect the realized temperature by as much as
tween the thermometer well and the ice mantle of a water
0.25 mK (4). In cases where the isotopic composition is
triple-point cell.
unknown, or if the cell has not been qualified by comparison
3.2.2 reference temperature, n—the temperature of a phase
with a cell of known isotopic composition, the larger value of
equilibriumstateofapuresubstanceataspecifiedpressure,for
uncertainty (60.25 mK) should be assumed.
example, the assigned temperature of a fixed point.
3.2.2.1 Discussion—At an equilibrium state of three phases 5.3 For use, a portion of the water is frozen within the cell
of a substance, that is, at the triple point, both the temperature to form a mantle of ice that surrounds the well and controls its
and pressure are fixed. temperature.
E1750 − 10 (2016)
5.4 The temperature of the triple point of water realized in Therefore, the impurity concentration of the unfrozen water
a cell is independent of the environment outside the cell; increases as the ice mantle thickens. The ice is purer than the
however, to reduce heat transfer and keep the ice mantle from unfrozen water. Consequently, the inner melt (see section
melting quickly, it is necessary to minimize heat flow between 7.1.3) that is formed from the ice mantle is purer than the
the cell and its immediate environment. This may be done by unfrozen water outside of the mantle.
immersing the cell in an ice bath that maintains the full length 6.3.2.2 Prepare a relatively thick ice mantle, according to
of the outer cell wall at or near the melting point of ice.
Section 7, by maintaining the dry ice level full for about 20
Alternatively, commercial automatic maintenance baths, built minutes. Make certain that the ice does not bridge to the cell
specifically for this purpose, are available. In such baths, the
wall (see 7.1.9).
triple point of water equilibrium of the cell, once established,
6.3.2.3 Prepare an inner melt according to 7.1.13. Using an
can be maintained for many months of continual use.To avoid
SPRT, make measurements on the cell and determine the
radiation heat transfer to the cell and to the thermometer, the
zero-power resistance according to Section 8 and Appendix
outer surface of the maintenance bath is made opaque to
X1.
radiation.
6.3.2.4 After 6.3.2.3, remove the SPRT. Gently invert the
water triple-point cell and then return it to the upright position
6. Assurance of Integrity
several times to exchange the unfrozen water on the outside of
6.1 The temperature attained within a water triple-point cell the ice mantle with the inner melt water. (Warning—When
is an intrinsic property of the solid and liquid phases of water inverting the cell, do not allow the floating ice mantle to
under its own vapor pressure. If the water triple-point condi- severely strike the bottom of the water triple-point cell.)
tions are satisfied, the temperature attained within the cell is
6.3.2.5 Reinsert the pre-chilled SPRT used in 6.3.2.3 into
more reproducible than any measurements that can be made of the well. Make measurements on the cell and determine the
it.
zero-power resistance, according to Section 8 and Appendix
X1.
6.2 The accuracy of realization of the water triple-point
6.3.2.6 Typically, for high quality water triple-point cells,
temperature with a qualified cell depends on the physical
the results of 6.3.2.3 and 6.3.2.5 will not differ by more than
integrity of the seal and of the walls of the glass cell and on
60.03 mK.
their ability to exclude environmental air and contaminants.
6.4 Any cell that had previously been qualified by compari-
6.3 Initial and continued physical integrity is confirmed by
son with cells of known integrity (as in 4.3), that has not
the following procedures:
thereafter been modified, and which currently passes the tests
6.3.1 Test for the Presence of Air:
of 6.3.1 and 6.3.2, is qualified as a water triple-point cell.
6.3.1.1 Remove all objects from the thermometer well.
6.3.1.2 The solubility and the pressure of air at 101325 Pa
6.5 Any cell that fails to pass the tests of 6.3.1 and 6.3.2,
lower the ice/water equilibrium temperature 0.01°C below the
even though previously qualified, is no longer qualified for use
triple-point temperature. Since air is more soluble in water at
as a water triple-point cell.
lower temperatures, the test for air shall be done at room
temperature. The test is less definitive when performed on a
7. Realization of the Water Triple-Point Temperature
chilledcell.Atroomtemperature,withthecellinitiallyupright
7.1 The ice mantle that is required to realize the triple-point
andthewellopeningupward,slowlyinvertthecell.Astheaxis
temperature of water can be prepared in a number of ways.
ofthecellpassesthroughhorizontalandasthewaterwithinthe
Theyproduceessentiallythesameresult.Acommonprocedure
cell strikes the end of the cell, a sharp “glassy clink” sound
is as follows:
should be heard.The distinctive sound results from the sudden
7.1.1 Empty the well of any solids or liquids.Wipe the well
collapse of water vapor and the “water hammer” striking the
clean and dry, and seal the well opening with a rubber stopper.
glass cell. The smaller the amount of air, the sharper the clink
7.1.2 If the triple point of water cell has not already been
sound;alargeamountofaircushionsthewater-hammeraction
tested for the presence of air, perform the tests indicated in
and the sound is duller.
6.3.1 for presence of air.
6.3.1.3 With a type A cell, continue to tilt the cell to make
7.1.3 To obtain an ice mantle of fairly uniform thickness
a McLeod-gauge type test until the vapor (water saturated air)
that extends to the top, immerse the cell completely in an ice
bubble is entirely captured in the space provided in the handle.
bath, and chill the cell to near 0°C.
The vapor bubble should be compressed to a volume no larger
7.1.4 Removethecellfromthebathandmountituprighton
than about 0.03 cm (4 mm diameter). It may even vanish as it
a plastic foam cushion. Wipe the cell dry around the rubber
is compressed by the weight of the water column.As in the tilt
stopper before removing the rubber stopper.
test, the bubble test is more definitive when the cell is at room
temperature (see 6.3.1.2). Since type B cells do not have a 7.1.5 Remove the rubber stopper and place about 1 cm of
dryalcoholinthewelltoserveasaheat-transfermediumwhile
space to capture the vapor, the amount of air in the cell is
estimated by comparing the sharpness of the clink sound with forming an ice mantle around the well within the sealed cell.
that of a type A cell. 7.1.6 Place a small amount of crushed dry ice at the bottom
6.3.2 Test for the Presence of Water Soluble Impurities: of the well, maintaining the height of the dry ice at about 1 cm
6.3.2.1 When ice is slowly formed around the thermometer for a period of 2 to 3 min. In repeated use of the cell, the ice
well,impuritiesarerejectedintotheremainingunfrozenwater. mantle melts mostly at the bottom; hence, it is desirable that
E1750 − 10 (2016)
theicemantlebethickeratthebottom.Crusheddryicemaybe not be harmed by the growth of ice. Before using the cell, melt
preparedfromablockorbyexpansionfromasiphon-tubetank any ice that bridges the mantle and the cell wall by momen-
of liquid CO . tarily immersing the cell in a large container of water, by
running water from the faucet over the cell, or by warming
7.1.7 At the interface of the well, the water is initially
with your hands. (Warning—Do not warm the water tri
...
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E1750 − 10 (Reapproved 2016)
Standard Guide for
Use of Water Triple Point Cells
This standard is issued under the fixed designation E1750; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The triple point of water is an important thermometric fixed point common to the definition of two
temperature scales of science and technology, the Kelvin Thermodynamic Temperature Scale (KTTS)
and the International Temperature Scale of 1990 (ITS-90). The ITS-90 was designed to be as close to
the KTTS as the experimental data available at the time of the adoption of the ITS-90 would permit.
The temperatures (T) on the KTTS are defined by assigning the value 273.16 K to the triple point of
water, thus defining the thermodynamic unit of temperature, kelvin (K), as 1/273.16 of the
thermodynamic temperature of the triple point of water (1, 2). The triple point of water, one of the
fixed points used to define the ITS-90, is the temperature to which the resistance ratios
W(T) = R(T) ⁄R(273.16 K) of the standard platinum resistance thermometer (SPRT) calibrations are
referred.
The triple points of various materials (where three distinct phases, for example, their solid, liquid,
and vapor phases, coexist in a state of thermal equilibrium) have fixed pressures and temperatures and
are highly reproducible. Of the ITS-90 fixed points, six are triple points. The water triple point is one
of the most accurately realizable of the defining fixed points of the ITS-90; under the best of
conditions, it can be realized with an expanded uncertainty (k=2) of less than 60.00005 K. In
comparison, it is difficult to prepare and use an ice bath with an expanded uncertainty (k=2) of less
than 60.002 K (3).
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This guide covers the nature of two commercial water
bility of regulatory limitations prior to use.
triple-point cells (types A and B, see Fig. 1) and provides a
1.5 This international standard was developed in accor-
method for preparing the cell to realize the water triple-point
dance with internationally recognized principles on standard-
and calibrate thermometers. Tests for assuring the integrity of
ization established in the Decision on Principles for the
a qualified cell and of cells yet to be qualified are given.
Development of International Standards, Guides and Recom-
Precautions for handling the cell to avoid breakage are also
mendations issued by the World Trade Organization Technical
described.
Barriers to Trade (TBT) Committee.
1.2 The effect of hydrostatic pressure on the temperature of
a water triple-point cell is discussed.
2. Referenced Documents
1.3 Procedures for adjusting the observed SPRT resistance
2.1 ASTM Standards:
readings for the effects of self-heating and hydrostatic pressure
E344 Terminology Relating to Thermometry and Hydrom-
are described in Appendix X1 and Appendix X2.
etry
E1594 Guide for Expression of Temperature
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
3.1 Definitions—The definitions given in Terminology E344
This guide is under the jurisdiction of ASTM Committee E20 on Temperature
apply to terms used in this guide.
Measurement and is the direct responsibility of Subcommittee E20.07 on Funda-
mentals in Thermometry.
Current edition approved May 1, 2016. Published May 2016. Originally
approved in 1995. Last previous edition approved in 2010 as E1750 – 10. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/E1750-10R16. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1750 − 10 (2016)
4. Significance and Use
4.1 This guide describes a procedure for placing a water
triple-point cell in service and for using it as a reference
temperature in thermometer calibration.
4.2 The reference temperature attained is that of a funda-
mental state of pure water, the equilibrium between coexisting
solid, liquid, and vapor phases.
4.3 The cell is subject to qualification but not to calibration.
The cell may be qualified as capable of representing the
fundamental state (see 4.2) by comparison with a bank of
similar qualified cells of known history, and it may be so
qualified and the qualification documented by its manufacturer.
4.4 The temperature to be attributed to a qualified water
triple-point cell is exactly 273.16 K on the ITS-90, unless
corrected for isotopic composition (refer to Appendix X3).
4.5 Continued accuracy of a qualified cell depends upon
sustained physical integrity. This may be verified by techniques
described in Section 6.
4.6 The commercially available triple point of water cells
described in this standard are capable of achieving an expanded
uncertainty (k=2) of between 60.1 mK and 60.05 mK,
depending upon the method of preparation. Specified measure-
ment procedures shall be followed to achieve these levels of
uncertainty.
4.7 Commercially-available triple point of water cells of
unknown isotopic composition should be capable of achieving
an expanded uncertainty (k=2) of no greater than 0.25 mK,
depending upon the actual isotopic composition (3). These
types of cells are acceptable for use at this larger value of
uncertainty.
5. Apparatus
5.1 The essential features of type A and type B water
triple-point cells are shown in Fig. 1. A transparent glass flask
free of soluble material is filled with pure, air-free water and
then is permanently sealed, air-free, at the vapor pressure of the
water. A reentrant well on the axis of the flask receives
thermometers that are to be exposed to the reference tempera-
FIG. 1 Configurations of two commonly used triple point of wa-
ter cells, Type A and Type B, with ice mantle prepared for mea- ture.
surement at the ice/water equilibrium temperature. The cells are
5.2 For the lowest level of uncertainty, the water used as the
used immersed in an ice bath or water bath controlled close to
0.01°C (see 5.4)
reference medium shall be very pure and of known isotopic
composition. Often it is distilled directly into the cell. The
isotopic composition of cells filled with “rain water” is
expected not to vary enough to cause more than 0.05 mK
difference in their triple points. Extreme variations in isotopic
3.2 Definitions of Terms Specific to This Standard:
composition, such as between ocean water and water from old
3.2.1 inner melt, n—a thin continuous layer of water be-
polar ice, can affect the realized temperature by as much as
tween the thermometer well and the ice mantle of a water
0.25 mK (4). In cases where the isotopic composition is
triple-point cell.
unknown, or if the cell has not been qualified by comparison
3.2.2 reference temperature, n—the temperature of a phase
with a cell of known isotopic composition, the larger value of
equilibrium state of a pure substance at a specified pressure, for
uncertainty (60.25 mK) should be assumed.
example, the assigned temperature of a fixed point.
3.2.2.1 Discussion—At an equilibrium state of three phases 5.3 For use, a portion of the water is frozen within the cell
of a substance, that is, at the triple point, both the temperature to form a mantle of ice that surrounds the well and controls its
and pressure are fixed. temperature.
E1750 − 10 (2016)
5.4 The temperature of the triple point of water realized in Therefore, the impurity concentration of the unfrozen water
a cell is independent of the environment outside the cell; increases as the ice mantle thickens. The ice is purer than the
however, to reduce heat transfer and keep the ice mantle from unfrozen water. Consequently, the inner melt (see section
melting quickly, it is necessary to minimize heat flow between 7.1.3) that is formed from the ice mantle is purer than the
the cell and its immediate environment. This may be done by unfrozen water outside of the mantle.
immersing the cell in an ice bath that maintains the full length
6.3.2.2 Prepare a relatively thick ice mantle, according to
of the outer cell wall at or near the melting point of ice. Section 7, by maintaining the dry ice level full for about 20
Alternatively, commercial automatic maintenance baths, built
minutes. Make certain that the ice does not bridge to the cell
specifically for this purpose, are available. In such baths, the wall (see 7.1.9).
triple point of water equilibrium of the cell, once established,
6.3.2.3 Prepare an inner melt according to 7.1.13. Using an
can be maintained for many months of continual use. To avoid
SPRT, make measurements on the cell and determine the
radiation heat transfer to the cell and to the thermometer, the
zero-power resistance according to Section 8 and Appendix
outer surface of the maintenance bath is made opaque to
X1.
radiation.
6.3.2.4 After 6.3.2.3, remove the SPRT. Gently invert the
water triple-point cell and then return it to the upright position
6. Assurance of Integrity
several times to exchange the unfrozen water on the outside of
6.1 The temperature attained within a water triple-point cell the ice mantle with the inner melt water. (Warning—When
is an intrinsic property of the solid and liquid phases of water inverting the cell, do not allow the floating ice mantle to
under its own vapor pressure. If the water triple-point condi- severely strike the bottom of the water triple-point cell.)
tions are satisfied, the temperature attained within the cell is 6.3.2.5 Reinsert the pre-chilled SPRT used in 6.3.2.3 into
more reproducible than any measurements that can be made of
the well. Make measurements on the cell and determine the
it.
zero-power resistance, according to Section 8 and Appendix
X1.
6.2 The accuracy of realization of the water triple-point
6.3.2.6 Typically, for high quality water triple-point cells,
temperature with a qualified cell depends on the physical
the results of 6.3.2.3 and 6.3.2.5 will not differ by more than
integrity of the seal and of the walls of the glass cell and on
60.03 mK.
their ability to exclude environmental air and contaminants.
6.4 Any cell that had previously been qualified by compari-
6.3 Initial and continued physical integrity is confirmed by
son with cells of known integrity (as in 4.3), that has not
the following procedures:
thereafter been modified, and which currently passes the tests
6.3.1 Test for the Presence of Air:
of 6.3.1 and 6.3.2, is qualified as a water triple-point cell.
6.3.1.1 Remove all objects from the thermometer well.
6.3.1.2 The solubility and the pressure of air at 101 325 Pa
6.5 Any cell that fails to pass the tests of 6.3.1 and 6.3.2,
lower the ice/water equilibrium temperature 0.01°C below the
even though previously qualified, is no longer qualified for use
triple-point temperature. Since air is more soluble in water at
as a water triple-point cell.
lower temperatures, the test for air shall be done at room
temperature. The test is less definitive when performed on a
7. Realization of the Water Triple-Point Temperature
chilled cell. At room temperature, with the cell initially upright
7.1 The ice mantle that is required to realize the triple-point
and the well opening upward, slowly invert the cell. As the axis
temperature of water can be prepared in a number of ways.
of the cell passes through horizontal and as the water within the
They produce essentially the same result. A common procedure
cell strikes the end of the cell, a sharp “glassy clink” sound
is as follows:
should be heard. The distinctive sound results from the sudden
7.1.1 Empty the well of any solids or liquids. Wipe the well
collapse of water vapor and the “water hammer” striking the
clean and dry, and seal the well opening with a rubber stopper.
glass cell. The smaller the amount of air, the sharper the clink
7.1.2 If the triple point of water cell has not already been
sound; a large amount of air cushions the water-hammer action
tested for the presence of air, perform the tests indicated in
and the sound is duller.
6.3.1 for presence of air.
6.3.1.3 With a type A cell, continue to tilt the cell to make
7.1.3 To obtain an ice mantle of fairly uniform thickness
a McLeod-gauge type test until the vapor (water saturated air)
that extends to the top, immerse the cell completely in an ice
bubble is entirely captured in the space provided in the handle.
bath, and chill the cell to near 0°C.
The vapor bubble should be compressed to a volume no larger
7.1.4 Remove the cell from the bath and mount it upright on
than about 0.03 cm (4 mm diameter). It may even vanish as it
a plastic foam cushion. Wipe the cell dry around the rubber
is compressed by the weight of the water column. As in the tilt
stopper before removing the rubber stopper.
test, the bubble test is more definitive when the cell is at room
7.1.5 Remove the rubber stopper and place about 1 cm of
temperature (see 6.3.1.2). Since type B cells do not have a
space to capture the vapor, the amount of air in the cell is dry alcohol in the well to serve as a heat-transfer medium while
forming an ice mantle around the well within the sealed cell.
estimated by comparing the sharpness of the clink sound with
that of a type A cell. 7.1.6 Place a small amount of crushed dry ice at the bottom
6.3.2 Test for the Presence of Water Soluble Impurities: of the well, maintaining the height of the dry ice at about 1 cm
6.3.2.1 When ice is slowly formed around the thermometer for a period of 2 to 3 min. In repeated use of the cell, the ice
well, impurities are rejected into the remaining unfrozen water. mantle melts mostly at the bottom; hence, it is desirable that
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the ice mantle be thicker at the bottom. Crushed dry ice may be not be harmed by the growth of ice. Before using the cell, melt
prepared from a block or by expansion from a siphon-tube tank any ice that bridges the mantle and the cell wall by momen-
of liquid CO . tarily immersing the cell in a large container of water, by
running water from the faucet over the cell, or by warming
7.1.7 At the interface
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1750 − 10 E1750 − 10 (Reapproved 2016
Standard Guide for
Use of Water Triple Point Cells
This standard is issued under the fixed designation E1750; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The triple point of water is an important thermometric fixed point common to the definition of two
temperature scales of science and technology, the Kelvin Thermodynamic Temperature Scale (KTTS)
and the International Temperature Scale of 1990 (ITS-90). The ITS-90 was designed to be as close to
the KTTS as the experimental data available at the time of the adoption of the ITS-90 would permit.
The temperatures (T) on the KTTS are defined by assigning the value 273.16 K to the triple point of
water, thus defining the thermodynamic unit of temperature, kelvin (K), as 1/273.16 of the
thermodynamic temperature of the triple point of water (1, 2). The triple point of water, one of the
fixed points used to define the ITS-90, is the temperature to which the resistance ratios
W(T) = R(T) ⁄R(273.16 K) of the standard platinum resistance thermometer (SPRT) calibrations are
referred.
The triple points of various materials (where three distinct phases, for example, their solid, liquid,
and vapor phases, coexist in a state of thermal equilibrium) have fixed pressures and temperatures and
are highly reproducible. Of the ITS-90 fixed points, six are triple points. The water triple point is one
of the most accurately realizable of the defining fixed points of the ITS-90; under the best of
conditions, it can be realized with an expanded uncertainty (k=2) of less than 60.00005 K. In
comparison, it is difficult to prepare and use an ice bath with an expanded uncertainty (k=2) of less
than 60.002 K (3).
1. Scope
1.1 This guide covers the nature of two commercial water triple-point cells (types A and B, see Fig. 1) and provides a method
for preparing the cell to realize the water triple-point and calibrate thermometers. Tests for assuring the integrity of a qualified cell
and of cells yet to be qualified are given. Precautions for handling the cell to avoid breakage are also described.
1.2 The effect of hydrostatic pressure on the temperature of a water triple-point cell is discussed.
1.3 Procedures for adjusting the observed SPRT resistance readings for the effects of self-heating and hydrostatic pressure are
described in Appendix X1 and Appendix X2.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
E344 Terminology Relating to Thermometry and Hydrometry
E1594 Guide for Expression of Temperature
This guide is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.07 on Fundamentals
in Thermometry.
Current edition approved May 1, 2010May 1, 2016. Published June 2010May 2016. Originally approved in 1995. Last previous edition approved in 20092010 as
E1750 - 09.E1750 – 10. DOI: 10.1520/E1750-10.10.1520/E1750-10R16.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1750 − 10 (2016
FIG. 1 Configurations of two commonly used triple point of water cells, Type A and Type B, with ice mantle prepared for measurement
at the ice/water equilibrium temperature. The cells are used immersed in an ice bath or water bath controlled close to 0.01°C (see 5.4)
3. Terminology
3.1 Definitions—The definitions given in Terminology E344 apply to terms used in this guide.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 inner melt, n—a thin continuous layer of water between the thermometer well and the ice mantle of a water triple-point
cell.
3.2.2 reference temperature, n—the temperature of a phase equilibrium state of a pure substance at a specified pressure, for
example, the assigned temperature of a fixed point.
3.2.2.1 Discussion—
At an equilibrium state of three phases of a substance, that is, at the triple point, both the temperature and pressure are fixed.
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4. Significance and Use
4.1 This guide describes a procedure for placing a water triple-point cell in service and for using it as a reference temperature
in thermometer calibration.
4.2 The reference temperature attained is that of a fundamental state of pure water, the equilibrium between coexisting solid,
liquid, and vapor phases.
4.3 The cell is subject to qualification but not to calibration. The cell may be qualified as capable of representing the
fundamental state (see 4.2) by comparison with a bank of similar qualified cells of known history, and it may be so qualified and
the qualification documented by its manufacturer.
4.4 The temperature to be attributed to a qualified water triple-point cell is exactly 273.16 K on the ITS-90, unless corrected
for isotopic composition (refer to Appendix X3).
4.5 Continued accuracy of a qualified cell depends upon sustained physical integrity. This may be verified by techniques
described in Section 6.
4.6 The commercially available triple point of water cells described in this standard are capable of achieving an expanded
uncertainty (k=2) of between 60.1 mK and 60.05 mK, depending upon the method of preparation. Specified measurement
procedures shall be followed to achieve these levels of uncertainty.
4.7 Commercially-available triple point of water cells of unknown isotopic composition should be capable of achieving an
expanded uncertainty (k=2) of no greater than 0.25 mK, depending upon the actual isotopic composition (3). These types of cells
are acceptable for use at this larger value of uncertainty.
5. Apparatus
5.1 The essential features of type A and type B water triple-point cells are shown in Fig. 1. A transparent glass flask free of
soluble material is filled with pure, air-free water and then is permanently sealed, air-free, at the vapor pressure of the water. A
reentrant well on the axis of the flask receives thermometers that are to be exposed to the reference temperature.
5.2 For the lowest level of uncertainty, the water used as the reference medium shall be very pure and of known isotopic
composition. Often it is distilled directly into the cell. The isotopic composition of cells filled with “rain water” is expected not
to vary enough to cause more than 0.05 mK difference in their triple points. Extreme variations in isotopic composition, such as
between ocean water and water from old polar ice, can affect the realized temperature by as much as 0.25 mK (4). In cases where
the isotopic composition is unknown, or if the cell has not been qualified by comparison with a cell of known isotopic composition,
the larger value of uncertainty (60.25 mK) should be assumed.
5.3 For use, a portion of the water is frozen within the cell to form a mantle of ice that surrounds the well and controls its
temperature.
5.4 The temperature of the triple point of water realized in a cell is independent of the environment outside the cell; however,
to reduce heat transfer and keep the ice mantle from melting quickly, it is necessary to minimize heat flow between the cell and
its immediate environment. This may be done by immersing the cell in an ice bath that maintains the full length of the outer cell
wall at or near the melting point of ice. Alternatively, commercial automatic maintenance baths, built specifically for this purpose,
are available. In such baths, the triple point of water equilibrium of the cell, once established, can be maintained for many months
of continual use. To avoid radiation heat transfer to the cell and to the thermometer, the outer surface of the maintenance bath is
made opaque to radiation.
6. Assurance of Integrity
6.1 The temperature attained within a water triple-point cell is an intrinsic property of the solid and liquid phases of water under
its own vapor pressure. If the water triple-point conditions are satisfied, the temperature attained within the cell is more
reproducible than any measurements that can be made of it.
6.2 The accuracy of realization of the water triple-point temperature with a qualified cell depends on the physical integrity of
the seal and of the walls of the glass cell and on their ability to exclude environmental air and contaminants.
6.3 Initial and continued physical integrity is confirmed by the following procedures:
6.3.1 Test for the Presence of Air:
6.3.1.1 Remove all objects from the thermometer well.
6.3.1.2 The solubility and the pressure of air at 101 325 Pa lower the ice/water equilibrium temperature 0.01°C below the
triple-point temperature. Since air is more soluble in water at lower temperatures, the test for air shall be done at room temperature.
The test is less definitive when performed on a chilled cell. At room temperature, with the cell initially upright and the well opening
upward, slowly invert the cell. As the axis of the cell passes through horizontal and as the water within the cell strikes the end of
the cell, a sharp “glassy clink” sound should be heard. The distinctive sound results from the sudden collapse of water vapor and
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the “water hammer” striking the glass cell. The smaller the amount of air, the sharper the clink sound; a large amount of air
cushions the water-hammer action and the sound is duller.
6.3.1.3 With a type A cell, continue to tilt the cell to make a McLeod-gauge type test until the vapor (water saturated air) bubble
is entirely captured in the space provided in the handle. The vapor bubble should be compressed to a volume no larger than about
0.03 cm (4 mm diameter). It may even vanish as it is compressed by the weight of the water column. As in the tilt test, the bubble
test is more definitive when the cell is at room temperature (see 6.3.1.2). Since type B cells do not have a space to capture the vapor,
the amount of air in the cell is estimated by comparing the sharpness of the clink sound with that of a type A cell.
6.3.2 Test for the Presence of Water Soluble Impurities:
6.3.2.1 When ice is slowly formed around the thermometer well, impurities are rejected into the remaining unfrozen water.
Therefore, the impurity concentration of the unfrozen water increases as the ice mantle thickens. The ice is purer than the unfrozen
water. Consequently, the inner melt (see section 7.1.3) that is formed from the ice mantle is purer than the unfrozen water outside
of the mantle.
6.3.2.2 Prepare a relatively thick ice mantle, according to Section 7, by maintaining the dry ice level full for about 20 minutes.
Make certain that the ice does not bridge to the cell wall (see 7.1.9).
6.3.2.3 Prepare an inner melt according to 7.1.13. Using an SPRT, make measurements on the cell and determine the zero-power
resistance according to Section 8 and Appendix X1.
6.3.2.4 After 6.3.2.3, remove the SPRT. Gently invert the water triple-point cell and then return it to the upright position several
times to exchange the unfrozen water on the outside of the ice mantle with the inner melt water. (Warning—When inverting the
cell, do not allow the floating ice mantle to severely strike the bottom of the water triple-point cell.)
6.3.2.5 Reinsert the pre-chilled SPRT used in 6.3.2.3 into the well. Make measurements on the cell and determine the
zero-power resistance, according to Section 8 and Appendix X1.
6.3.2.6 Typically, for high quality water triple-point cells, the results of 6.3.2.3 and 6.3.2.5 will not differ by more than 60.03
mK.
6.4 Any cell that had previously been qualified by comparison with cells of known integrity (as in 4.3), that has not thereafter
been modified, and which currently passes the tests of 6.3.1 and 6.3.2, is qualified as a water triple-point cell.
6.5 Any cell that fails to pass the tests of 6.3.1 and 6.3.2, even though previously qualified, is no longer qualified for use as a
water triple-point cell.
7. Realization of the Water Triple-Point Temperature
7.1 The ice mantle that is required to realize the triple-point temperature of water can be prepared in a number of ways. They
produce essentially the same result. A common procedure is as follows:
7.1.1 Empty the well of any solids or liquids. Wipe the well clean and dry, and seal the well opening with a rubber stopper.
7.1.2 If the triple point of water cell has not already been tested for the presence of air, perform the tests indicated in 6.3.1 for
presence of air.
7.1.3 To obtain an ice mantle of fairly uniform thickness that extends to the top, immerse the cell completely in an ice bath,
and chill the cell to near 0°C.
7.1.4 Remove the cell from the bath and mount it upright on a plastic foam cushion. Wipe the cell dry around the rubber stopper
before removing the rubber stopper.
7.1.5 Remove the rubber stopper and place about 1 cm of dry alcohol in the well to serve as a heat-transfer medium while
forming an ice mantle around the well within the sealed cell.
7.1.6 Place a small amount of crushed dry ice at the bottom of the well, maintaining the height of the dry ice at about 1 cm for
a period of 2 to 3 min. In repeated use of the cell, the ice mantle melts mostly at the bottom; hence, it is desirable that the ice mantle
be thicker at the bottom. Crushed dry ice may be prepared from a block or by expansion from a siphon-tube tank of liquid CO .
7.1.7 At the interface of the well, the water is initially supercooled, and the well becomes abruptly coated with fine needles of
ice frozen from the supercooled water.
7.1.8 After a layer of ice forms around the bottom of the well, fill the well with crushed dry ice up to the vapor/liquid interface.
7.1.9 Replenish the dry ice as
...
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