ASTM E104-85(1996)
(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 two methods 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 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 problems 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.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: E 104 – 85 (Reapproved 1996)
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 E 126 Test Method for Inspection and Verification of Hy-
drometers
1.1 This practice describes two methods for generating
2.2 Other Document:
constant 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
Part 2: Sulfuric Acid Solutions. (1981)
temperatures spanning from 0 to 50°C.
1.3 This practice is applicable for closed systems such as
3. Terminology
environmental conditioning containers and for the calibration
3.1 non-hygroscopic material—material which neither ab-
of hygrometers.
sorbs nor retains water vapor.
1.4 This practice is not recommended for the generation of
3.2 For definitions of other terms used in this practice refer
continuous (flowing) streams of constant humidity unless
to Terminology D 4023.
precautionary criteria are followed to ensure source stability.
(See Section 9.)
4. Summary of Practice
1.5 Caution—Both saturated salt solutions and sulfuric
4.1 Standard value relative humidity environments are gen-
acid-water solutions are extremely corrosive, and care should
erated using selected aqueous saturated salt solutions or
be taken in their preparation and handling. There is also the
various strength sulfuric acid-water systems.
possibility of corrosive vapors in the atmospheres over the
2 3
saturated salt solutions and over the sulfuric acid solution.
5. Significance and Use
1.6 This standard does not purport to address all of the
5.1 Standard value relative humidity environments are im-
safety concerns, if any, associated with its use. It is the
portant for conditioning materials in shelf-life studies or in the
responsibility of the user of this standard to establish appro-
testing of mechanical properties such as dimensional stability
priate safety and health practices and determine the applica-
and strength. Relative humidity is also an important operating
bility of regulatory limitations prior to use. For more specific
variable for the calibration of many species of measuring
safety precautionary information see 1.5 and 10.1.
instruments.
2. Referenced Documents
6. Interferences
2.1 ASTM Standards:
6.1 Temperature regulation of any solution-head space en-
D 1193 Specification for Reagent Water
vironment to 60.1°C is essential for realizing generated
D 4023 Terminology Relating to Humidity Measurements
relative humidity values within 60.5 % (expected).
6.2 Sulfuric Acid—Water systems are strongly hygroscopic
and can substantially change value by absorption and desorp-
This practice is under the jurisdiction of ASTM Committee D-22 on Sampling
and Analysis of Atmospheres and is the direct responsibility of Subcommittee
tion if stored in an open container. Only freshly prepared
D22.11on Meteorology.
solutions, or solutions which values have been independently
Current edition approved Feb. 22, 1985. Published June 1985.
2 tested for strength, should be used.
Opila, R., Jr., Weschler, C. J., and Schubert, R., “Acidic Vapors Above
Saturated Salt Solutions Commonly Used for Control of Humidity,” IEEE Trans. 6.3 Some aqueous saturated salt solutions change composi-
Components, Hybrids and Manufacturing Technology, Vol 12, No. 1, March 1989,
tion following preparation by hydrolysis or by reaction with
pp. 114–120.
Kawasaki, K., and Kanou, K., “Control of Atmospheric Humidity for Aqueous
Sulfuric Acid Solutions,” Vol. III (A. Wexler, ed.), Reinhold Publishing Corporation, Annual Book of ASTM Standards, Vol 14.03.
NY, 1964, pp. 531–534. Published by Deutsches Institut für Normung, 4-10 Burggrzfenstrasse Postfach
Annual Book of ASTM Standards, Vol 11.01. 1107, D-1000 Berlin, Federal Republic of Germany. Also available from ANSI
Annual Book of ASTM Standards, Vol 11.03. Publication Office, New York, NY.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 104
environmental components (for example, carbon dioxide ab- 9.4 The compatibility of any constant relative humidity
sorption by alkaline materials). These solutions should be system used for instrument calibration testing should be
freshly prepared on each occasion of use. confirmed by reference to the instrument manufacturer’s in-
structions.
7. Apparatus
9.5 Important considerations leading to stability should
include (but are not necessarily limited to) the following:
7.1 Container—The container, including a cover or lid
which can be secured airtight, should be made of corrosion 9.5.1 Elimination of leakage paths.
resistant, non-hygroscopic material such as glass. A metal or 9.5.2 Elimination of heat sources or heat sinks, or both, for
plastic container is acceptable if the solution is retained in a temperature stability.
dish or tray made of appropriate material. Refer also to 9.2 for 9.5.3 Limiting flow rate to preclude source carry-over.
size restrictions.
10. Preparations of Aqueous Solutions
7.2 Hydrometers—One or more hydrometers may be used
10.1 Caution—Saturated salt-water systems and sulfuric
to test sulfuric acid solution specific gravities for the range of
acid solutions should be regarded as hazardous materials. Refer
humidities concerned. The hydrometer(s) should have a mini-
to 1.5 and 1.6 for guidelines.
mum scale division of 0.001. (Refer to Test Method E 126.)
10.2 Saturated Salt-Water Systems:
10.2.1 Select a salt of characteristic value from Annex A1.
8. Reagents and Materials
The reference document by Greenspan contains information
8.1 Purity of Reagents—Reagent grade chemicals shall be
on many other saturated salt solutions which may be used.
used for preparation of all standard solutions. Unless otherwise
These additional systems, however, are less accurately or less
indicated, it is intended that all reagents conform to the
completely defined in value. Also, some may only be used
specifications of the Committee on Analytical Reagents of the
when freshly prepared (to limit the influence of chemical
American Chemical Society where such specifications are
instability such as hydrolysis or acid gas absorption). The salts
available. Other grades may be used, provided it is first
listed in Annex A1 can be used for a year or more.
ascertained that the reagent is of sufficiently high purity to
10.2.2 Place a quantity of the selected salt in the bottom of
permit its use without lessening the accuracy of the determi-
a container or an insert tray to a depth of about 4 cm for low
nation.
rh salts, or to a depth of about 1.5 cm for high rh salts.
8.1.1 Saturated salt solutions may be prepared using either
10.2.3 Add water in about 2-mL increments, stirring well
amorphous or hydrated reagents (that is, reagents containing
after each addition, until the salt can absorb no more water as
water of crystallization). Hydrated reagents are often preferred
evidenced by free liquid. Although a saturated solution
...
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