ASTM E104-02(2012)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E104 − 02 (Reapproved 2012)
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 U.S. Department of Defense.
1. Scope 2. Referenced Documents
1.1 This practice describes one method for generating con- 2.1 ASTM Standards:
stant relative humidity (rh) environments in relatively small D1193 Specification for Reagent Water
containers. D1356 Terminology Relating to Sampling and Analysis of
Atmospheres
1.2 This practice is applicable for obtaining constant rela-
2.2 Other Document:
tive humidities ranging from dryness to near saturation at
DIN50008 “Konstantklimate uber waesserigen Loseungen”
temperatures spanning from 0 to 50°C.
(Constant Climates Over Aqueous Solutions).
1.3 This practice is applicable for closed systems such as
Part 1: Saturated Salt and Glycerol Solutions.
environmental conditioning containers and for the calibration
of hygrometers.
3. Terminology
1.4 This practice is not recommended for the generation of
3.1 non-hygroscopic material—material which neither ab-
continuous (flowing) streams of constant humidity unless
sorbs nor retains water vapor.
precautionary criteria are followed to ensure source stability.
3.2 For definitions of other terms used in this practice refer
(See Section 9.)
to Terminology D1356.
1.5 Caution—Saturated salt solutions are extremely
corrosive, and care should be taken in their preparation and
4. Summary of Practice
handling.Thereisalsothepossibilityofcorrosivevaporsinthe
2 4.1 Standard value relative humidity environments are gen-
atmospheres over the saturated salt solutions.
erated using selected aqueous 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
5. Significance and Use
responsibility of the user of this standard to establish appro-
5.1 Standard value relative humidity environments are im-
priate safety, health, and environmental practices and deter-
portant for conditioning materials in shelf-life studies or in the
mine the applicability of regulatory limitations prior to use.
testing of mechanical properties such as dimensional stability
For more specific safety precautionary information see 1.5 and
and strength. Relative humidity is also an important operating
10.1.
variable for the calibration of many species of measuring
1.7 This international standard was developed in accor-
instruments.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
6. Interferences
Development of International Standards, Guides and Recom-
6.1 Temperature regulation of any solution-head space en-
mendations issued by the World Trade Organization Technical
vironment to 60.1°C is essential for realizing generated
Barriers to Trade (TBT) Committee.
relative humidity values within 60.5 % (expected).
This practice is under the jurisdiction ofASTM Committee D22 on Air Quality
and is the direct responsibility of Subcommittee D22.11 on Meteorology.
Current edition approved April 1, 2012. Published July 2012. Originally For referenced ASTM standards, visit the ASTM website, www.astm.org, or
approved in 1951. Last previous edition approved in 2007 as E104 – 02 (2007). contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
DOI: 10.1520/E0104-02R12. Standards volume information, refer to the standard’s Document Summary page on
Opila, R., Jr., Weschler, C. J., and Schubert, R., “Acidic Vapors Above the ASTM website.
Saturated Salt Solutions Commonly Used for Control of Humidity,” IEEE Trans. Published by Deutsches Institut für Normung, 4-10 Burggrzfenstrasse Postfach
Components, Hybrids and Manufacturing Technology, Vol 12, No. 1, March 1989, 1107, D-1000 Berlin, Federal Republic of Germany. Also available from ANSI
pp. 114–120. Publication Office, New York, NY.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E104 − 02 (2012)
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
6.2 Some aqueous saturated salt solutions change composi- 9. Technical Precautions
tion following preparation by hydrolysis or by reaction with
9.1 Although a container capable of airtight closure is
environmental components (for example, carbon dioxide ab-
described in Section 7, it may be desirable to have a vent under
sorption by alkaline materials). These solutions should be
certain conditions of test or with some kinds of containers
freshly prepared on each occasion of use.
(changes in pressure may produce undesirable cracks in some
typesofcontainers).Theventshouldbeassmallaspracticalto
7. Apparatus
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
American Chemical Society where such specifications are
9.4 The compatibility of any constant relative humidity
available. Other grades may be used, provided it is first
system used for instrument calibration testing should be
ascertained that the reagent is of sufficiently high purity to
confirmed by reference to the instrument manufacturer’s in-
permit its use without lessening the accuracy of the determi-
structions.
nation.
9.5 Important considerations leading to stability should
8.1.1 Saturated salt solutions may be
...