ASTM E104-02(2007)
(Practice)Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions
Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions
SCOPE
1.1 This practice describes one method for generating constant relative humidity (rh) environments in relatively small containers.
1.2 This practice is applicable for obtaining constant relative humidities ranging from dryness to near saturation at temperatures spanning from 0 to 50C.
1.3 This practice is applicable for closed systems such as environmental conditioning containers and for the calibration of hygrometers.
1.4 This practice is not recommended for the generation of continuous (flowing) streams of constant humidity unless precautionary criteria are followed to ensure source stability. (See Section 9 .)
1.5 Caution-Saturated salt solutions are extremely corrosive, and care should be taken in their preparation and handling. There is also the possibility of corrosive vapors in the atmospheres over the saturated salt solutions.
1.6 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. For more specific safety precautionary information see 1.5 and 10.1 .
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Designation:E104–02 (Reapproved 2007)
Standard Practice for
Maintaining Constant Relative Humidity by Means of
Aqueous Solutions
This standard is issued under the fixed designation E104; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D1356 Terminology Relating to Sampling and Analysis of
Atmospheres
1.1 This practice describes one method for generating con-
2.2 Other Document:
stant relative humidity (rh) environments in relatively small
DIN50008 “Konstantklimate uber waesserigen Loseungen”
containers.
(Constant Climates Over Aqueous Solutions).
1.2 This practice is applicable for obtaining constant rela-
Part 1: Saturated Salt and Glycerol Solutions.
tive humidities ranging from dryness to near saturation at
temperatures spanning from 0 to 50°C.
3. Terminology
1.3 This practice is applicable for closed systems such as
3.1 non-hygroscopic material—material which neither ab-
environmental conditioning containers and for the calibration
sorbs nor retains water vapor.
of hygrometers.
3.2 For definitions of other terms used in this practice refer
1.4 This practice is not recommended for the generation of
to Terminology D1356.
continuous (flowing) streams of constant humidity unless
precautionary criteria are followed to ensure source stability.
4. Summary of Practice
(See Section 9.)
4.1 Standard value relative humidity environments are gen-
1.5 Caution—Saturated salt solutions are extremely corro-
erated using selected aqueous saturated salt solutions.
sive, and care should be taken in their preparation and
handling.Thereisalsothepossibilityofcorrosivevaporsinthe
5. Significance and Use
atmospheres over the saturated salt solutions.
5.1 Standard value relative humidity environments are im-
1.6 This standard does not purport to address all of the
portant for conditioning materials in shelf-life studies or in the
safety concerns, if any, associated with its use. It is the
testing of mechanical properties such as dimensional stability
responsibility of the user of this standard to establish appro-
and strength. Relative humidity is also an important operating
priate safety and health practices and determine the applica-
variable for the calibration of many species of measuring
bility of regulatory limitations prior to use. For more specific
instruments.
safety precautionary information see 1.5 and 10.1.
6. Interferences
2. Referenced Documents
6.1 Temperature regulation of any solution-head space en-
2.1 ASTM Standards:
vironment to 60.1°C is essential for realizing generated
D1193 Specification for Reagent Water
relative humidity values within 60.5 % (expected).
6.2 Some aqueous saturated salt solutions change composi-
This practice is under the jurisdiction ofASTM Committee D22 onAir Quality
tion following preparation by hydrolysis or by reaction with
and is the direct responsibility of Subcommittee D22.11 on Meteorology.
environmental components (for example, carbon dioxide ab-
Current edition approved Oct. 1, 2007. Published December 2007. Originally
sorption by alkaline materials). These solutions should be
approved in 1951. Last previous edition approved in 2002 as E104 - 02. DOI:
10.1520/E0104-02R07.
freshly prepared on each occasion of use.
Opila, R., Jr., Weschler, C. J., and Schubert, R., “Acidic Vapors Above
Saturated Salt Solutions Commonly Used for Control of Humidity,” IEEE Trans.
Components, Hybrids and Manufacturing Technology, Vol 12, No. 1, March 1989,
pp. 114–120.
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 Published by Deutsches Institut für Normung, 4-10 Burggrzfenstrasse Postfach
Standards volume information, refer to the standard’s Document Summary page on 1107, D-1000 Berlin, Federal Republic of Germany. Also available from ANSI
the ASTM website. Publication Office, New York, NY.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E104–02 (2007)
TABLE 1 Humidity Fixed Point (HFP) Salt Solutions
HFP Designation Salt Name Chemical Symbol Temperature Range (°C)
HFP 4 Caesium fluoride CsF 15 to 80
HFP 7 Lithium bromide LiBr 5 to 80
HFP 12 Lithium chloride LiCl 5 to 80
HFP 23 Potassium acetate CH COOK 10 to 30
HFP 33 Magnesium chloride MgCl 5to80
HFP 43 Potassium carbonate K CO 5to30
2 3
HFP 59 Sodium bromide NaBr 5 to 80
HFP 70 Potassium iodide KI 5 to 80
HFP 75 Sodium chloride NaCl 5 to 80
HFP 85 Potassium chloride KCl 5 to 80
HFP 98 Potassium sulfate K SO 5to50
2 4
7. Apparatus typesofcontainers).Theventshouldbeassmallaspracticalto
minimize loss of desired equilibrium conditions when in use.
7.1 Container—The container, including a cover or lid
9.2 The container should be small to minimize the influence
which can be secured airtight, should be made of corrosion
of any temperature variations acting upon the container and
resistant, non-hygroscopic material such as glass. A metal or
3 2
contents. A maximum proportion of 25 cm volume/cm of
plastic container is acceptable if the solution is retained in a
solution surface area is suggested, and overall container
dish or tray made of appropriate material. Refer also to 9.2 for
headspace volume should be no larger than necessary to
size restrictions.
confine a stored item.
8. Reagents and Materials 9.3 Measurement accuracy is strongly dependent on the
ability to achieve and maintain temperature stability during
8.1 Purity of Reagents—Reagent grade chemicals shall be
actual use of any solution system. Temperature instability of
used for preparation of all standard solutions. Unless otherwise
60.1°C can cause corresponding instabilities in generated
indicated, it is intended that all reagents conform to the
values of relative humidity of 60.5 %.
specifications of the Committee on Analytical Reagents of the
9.4 The compatibility of any constant relative humidity
American Chemical Society where such specifications are
system used for instrument calibration testing should be
available. Other grades may be used, provided it is first
confirmed by reference to the instrument manufacturer’s in-
ascertained that the reagent is of sufficiently high purity to
structions.
permit its use without lessening the accuracy of the determi-
9.5 Important considerations leading to stability should
nation.
include (but are not necessarily limited to) the following:
8.1.1 Saturated salt solutions may be prepared using either
9.5.1 Elimination of leakage paths.
amorphous or hydrated reagents (that is, reagents containing
9.5.2 Elimination of heat sources or heat sinks, or both, for
water of crystallization). Hydrated reagents are often preferred
temperature stability.
to amorphous forms for their solvating characteristics.
9.5.3 Limiting flow rate to preclude sour
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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:E104–85 (Reapproved 1996) Designation:E104–02 (Reapproved 2007)
Standard Practice for
Maintaining Constant Relative Humidity by Means of
Aqueous Solutions
This standard is issued under the fixed designation E 104; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope
1.1 This practice describes two methodsone method for generating constant relative humidity (rh) environments in relatively
small containers.
1.2 This practice is applicable for obtaining constant relative humidities ranging from dryness to near saturation at temperatures
spanning from 0 to 50°C.
1.3 This practice is applicable for closed systems such as environmental conditioning containers and for the calibration of
hygrometers.
1.4 This practice is not recommended for the generation of continuous (flowing) streams of constant humidity unless
precautionary criteria are followed to ensure source stability. (See Section 9.)
1.5 Caution—Both saturated —Saturated salt solutions and sulfuric acid-water solutions are extremely corrosive, and care
should be taken in their preparation and handling. There is also the possibility of corrosive vapors in the atmospheres over the
saturated salt solutions. and over the sulfuric acid solution.
1.6 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. For more specific safety precautionary information see 1.5 and 10.1.
2. Referenced Documents
2.1 ASTM Standards:
D 1193 Specification for Reagent Water
D4023Terminology Relating to Humidity Measurements
E126Test Method for Inspection and Verification of Hydrometers
2.2 1356 Terminology Relating to Sampling and Analysis of Atmospheres
2.2 Other Document:
DIN50008 “Konstantklimate uber waesserigen Loseungen” (Constant Climates Over Aqueous Solutions).
Part 1: Saturated Salt and Glycerol Solutions. Part 2: Sulfuric Acid Solutions. (1981)
3. Terminology
3.1 non-hygroscopic material—material which neither absorbs nor retains water vapor.
3.2 For definitions of other terms used in this practice refer to Terminology D4023D 1356.
This practice is under the jurisdiction of ASTM Committee D-22 on Sampling and Analysis of Atmospheres and is the direct responsibility of Subcommittee D22.11
on Meteorology.
Current edition approved Feb. 22, 1985. Published June 1985.
This practice is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.11 on Meteorology.
Current edition approved Oct. 1, 2007. Published December 2007. Originally approved in 1951. Last previous edition approved in 2002 as E104 - 02.
Opila, R., Jr., Weschler, C. J., and Schubert, R., “Acidic Vapors Above Saturated Salt Solutions Commonly Used for Control of Humidity,” IEEE Trans. Components,
Hybrids and Manufacturing Technology, Vol 12, No. 1, March 1989, pp. 114–120.
Kawasaki, K., and Kanou, K., “Control ofAtmospheric Humidity forAqueous SulfuricAcid Solutions,” Vol. III (A. Wexler, ed.), Reinhold Publishing Corporation, NY,
1964, pp. 531–534.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. ForAnnualBookofASTMStandards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 11.01.
PublishedbyDeutschesInstitutfürNormung,4-10BurggrzfenstrassePostfach1107,D-1000Berlin,FederalRepublicofGermany.AlsoavailablefromANSIPublication
Office, New York, NY.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E104–02 (2007)
4. Summary of Practice
4.1Standard value relative humidity environments are generated using selected aqueous saturated salt solutions or various
strength sulfuric acid-water systems.
4.1 Standard value relative humidity environments are generated using selected aqueous saturated salt solutions.
5. Significance and Use
5.1 Standard value relative humidity environments are important for conditioning materials in shelf-life studies or in the testing
of mechanical properties such as dimensional stability and strength. Relative humidity is also an important operating variable for
the calibration of many species of measuring instruments.
6. Interferences
6.1Temperature regulation of any solution-head space environment to 60.1°C is essential for realizing generated relative
humidity values within 60.5 % (expected).
6.2Sulfuric Acid—Water systems are strongly hygroscopic and can substantially change value by absorption and desorption if
storedinanopencontainer.Onlyfreshlypreparedsolutions,orsolutionswhichvalueshavebeenindependentlytestedforstrength,
should be used.
6.3Some aqueous saturated salt solutions change composition following preparation by hydrolysis or by reaction with
environmental components (for example, carbon dioxide absorption by alkaline materials). These solutions should be freshly
prepared on each occasion of use. Interferences
6.1 Temperature regulation of any solution-head space environment to 60.1°C is essential for realizing generated relative
humidity values within 60.5 % (expected).
6.2 Some aqueous saturated salt solutions change composition following preparation by hydrolysis or by reaction with
environmental components (for example, carbon dioxide absorption by alkaline materials). These solutions should be freshly
prepared on each occasion of use.
7. Apparatus
7.1 Container—The container, including a cover or lid which can be secured airtight, should be made of corrosion resistant,
non-hygroscopic material such as glass.Ametal or plastic container is acceptable if the solution is retained in a dish or tray made
of appropriate material. Refer also to 9.2 for size restrictions.
7.2Hydrometers—One or more hydrometers may be used to test sulfuric acid solution specific gravities for the range of
humidities concerned. The hydrometer(s) should have a minimum scale division of 0.001. (Refer to Test Method E126.)
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used for preparation of all standard solutions. Unless otherwise
indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American
Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the
reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
8.1.1 Saturated salt solutions may be prepared using either amorphous or hydrated reagents (that is, reagents containing water
of crystallization). Hydrated reagents are often preferred to amorphous forms for their solvating characteristics.
8.2 Purity of Water—Reagent water produced by distillation, or by ion exchange, or reverse osmosis followed by distillation
shall be used. See Specification D 1193.
8.3 Nomenclature for Salts—The proper nomenclature for the Humidity Fixed Point (HFP) salt chemicals and the
corresponding acceptable temperature ranges are provided in Table 1. The scale encompasses relative humidity ranges from 2 %
to 98.5 % and a temperature range from 5°C to 80°C. When the salt solutions are used at temperatures above 40°C, the risk of
salt crystals settling on the surface rather than being immersed in the solution must be taken into account.
9. Technical Precautions
9.1 Although a container capable of airtight closure is described in Section 7, it may be desirable to have a vent under certain
conditions of test or with some kinds of containers (changes in pressure may produce undesirable cracks in some types of
containers). The vent should be as small as practical to minimize loss of desired equilibrium conditions when in use.
9.2 The container should be small to minimize the influence of any temperature variations acting upon the container and
3 2
contents. A maximum proportion of 25 cm volume/cm of solution surface area is suggested, and overall container headspace
volume should be no larger than necessary to confine a stored item.
9.3 Measurement accuracy is strongly dependent on the ability to achieve and maintain temperature stability during actual use
of any solution system. Temperature instability of 60.1°C can cause corresponding instabilities in generated values of relative
humidity of 60.5 %.
Annual Book of ASTM Standards, Vol 11.03.Reagent Chemicals, American Chemical Society Specifications , American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.
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