ASTM D3609-22

Standard Practice for Calibration Techniques Using Permeation Tubes

SIGNIFICANCE AND USE
5.1 Most analytical methods used in air pollutant measurements are comparative in nature and require calibration or standardization, or both, often with known blends of the gas of interest. Since many of the important air pollutants are reactive and unstable, it is difficult to store them as standard mixtures of known concentration for extended calibration purposes. An alternative is to prepare dynamically standard blends as required. This procedure is simplified if a constant source of the gas of interest can be provided. Permeation tubes provide this constant source, if properly calibrated and if maintained at constant temperature. Permeation tubes have been specified as reference calibration sources, for certain analytical procedures, by the Environmental Protection Agency (3).
SCOPE
1.1 This practice describes a means for using permeation tubes for dynamically calibrating instruments, analyzers, and analytical procedures used in measuring concentrations of gases or vapors in atmospheres (1, 2).2  
1.2 Typical materials that may be sealed in permeation tubes include: sulfur dioxide, nitrogen dioxide, hydrogen sulfide, chlorine, ammonia, propane, and butane (1).  
1.3 The values stated in SI units are to be regarded as standard.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 31-Oct-2022
• ICS: 17.020 - Metrology and measurement in general
• Technical Committee: D22 - Air Quality
• Drafting Committee: D22.01 - Quality Control

Relations

• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015
• Refers: ASTM D1356-14b - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Dec-2014
• Refers: ASTM D1356-14a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2014
• Refers: ASTM D1356-14 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Jan-2014
• Refers: ASTM E1-13 - Standard Specification for ASTM Liquid-in-Glass Thermometers
• Effective Date: 01-May-2013
• Refers: ASTM E2251-11 - Standard Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
• Effective Date: 01-May-2011
• Refers: ASTM E2251-10 - Standard Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
• Effective Date: 01-Nov-2010
• Refers: ASTM D1356-05(2010) - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Apr-2010
• Refers: ASTM E2251-07 - Standard Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
• Effective Date: 01-Nov-2007
• Refers: ASTM E1-07 - Standard Specification for ASTM Liquid-in-Glass Thermometers
• Effective Date: 01-Nov-2007
• Refers: ASTM E1-05 - Standard Specification for ASTM Liquid-in-Glass Thermometers
• Effective Date: 01-Nov-2005
• Refers: ASTM D1356-05 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2005

Overview

ASTM D3609-22 is the internationally recognized standard practice for calibration techniques using permeation tubes. Developed by ASTM International, this standard offers detailed guidance for dynamically calibrating analytical instruments, analyzers, and procedures through the use of permeation tubes to measure gas or vapor concentrations in various atmospheres. This practice addresses the need for a constant and reliable gas source-especially for reactive and unstable air pollutants that cannot be stored in standard blends over time-by offering calibration options that ensure accuracy in environmental and industrial monitoring.

Key Topics

• Calibration Methods: Describes gravimetric calibration, where weight loss from the permeation tube equals the mass of emitted gas, ensuring accurate and reproducible generation of standard gas mixtures.
• Temperature Control: Emphasizes the necessity of maintaining a constant temperature for permeation tubes, as permeation rates are highly temperature-dependent. Variations can significantly impact calibration reliability.
• Materials for Permeation Tubes: Lists suitable gases, such as sulfur dioxide, nitrogen dioxide, hydrogen sulfide, chlorine, ammonia, propane, and butane, for use in permeation tubes.
• System Design: Outlines the required apparatus, including flowmeters, temperature-controlled water baths, mixing bulbs, and dry carrier gases.
• Interferences and Precautions: Discusses the importance of tube integrity, material compatibility, proper storage, purity of contents, and handling to minimize contamination or tube failure.
• Recalibration Procedures: Provides recommendations for calibration frequency based on gas type and tube performance to assure sustained accuracy over time.

Applications

ASTM D3609-22 plays a critical role in several areas requiring precise calibration of gas detection and measurement systems:

• Ambient Air Monitoring: Essential for calibrating instruments used in environmental air quality monitoring, where accurate trace gas analysis is vital for public health and regulatory compliance.
• Industrial Hygiene: Supports workplace safety by enabling the calibration of analyzers that detect hazardous gases, ensuring reliable detection and quantification.
• Research Laboratories: Facilitates the preparation of accurate calibration mixtures for experimental setups measuring gas-phase concentrations, supporting scientific rigor and repeatability.
• Regulatory Compliance: Assists operators in meeting requirements set forth by bodies such as the Environmental Protection Agency (EPA), which recognize permeation tubes as valid calibration sources.

Related Standards

ASTM D3609-22 refers to several other standards that support the calibration process:

• ASTM D1356 - Terminology Relating to Sampling and Analysis of Atmospheres
• ASTM D3195 - Practice for Rotameter Calibration, supporting accurate gas flow measurements
• ASTM E1 - Specification for ASTM Liquid-in-Glass Thermometers, ensuring precise temperature measurement
• ASTM E2251 - Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids

Practical Value

Implementing ASTM D3609-22 ensures:

• Calibration Accuracy: Delivers consistent and traceable gas standards for analytical device calibration.
• Process Reliability: Reduces measurement uncertainty for critical applications in environmental monitoring and industrial safety.
• Global Recognition: Aligns calibration practices with internationally approved methods, facilitating cross-border compliance and reporting.
• Operational Flexibility: Allows for on-demand preparation of standard gas blends, eliminating storage issues associated with unstable pollutants.

Keywords: ASTM D3609-22, permeation tubes, gas calibration, air pollutant measurement, analytical instrument calibration, sulfur dioxide calibration, nitrogen dioxide calibration, environmental monitoring, industrial hygiene, calibration standards.

Standards Content (Sample)

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: D3609 − 22
Standard Practice for
Calibration Techniques Using Permeation Tubes
This standard is issued under the fixed designation D3609; 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.
1. Scope 4. Summary of Practice
1.1 This practice describes a means for using permeation 4.1 Aliquefiable gas, when enclosed in an inert plastic tube,
tubes for dynamically calibrating instruments, analyzers, and escapes by permeating the tubing wall at a constant,
analytical procedures used in measuring concentrations of reproducible, temperature-dependent rate.
gases or vapors in atmospheres (1, 2).
4.2 Permeationtubesarecalibratedgravimetrically,withthe
1.2 Typicalmaterialsthatmaybesealedinpermeationtubes weight loss of the tube equated to the weight of the escaping
include: sulfur dioxide, nitrogen dioxide, hydrogen sulfide, material.
chlorine, ammonia, propane, and butane (1).
4.3 Permeation tubes are held at constant temperature in a
1.3 The values stated in SI units are to be regarded as carrier-gas stream of dry air or nitrogen to produce a gas
standard. concentration dependent on the permeation rate and the flow of
the carrier gas.
1.4 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 Most analytical methods used in air pollutant measure-
priate safety, health, and environmental practices and deter-
ments are comparative in nature and require calibration or
mine the applicability of regulatory limitations prior to use.
standardization, or both, often with known blends of the gas of
1.5 This international standard was developed in accor-
interest. Since many of the important air pollutants are reactive
dance with internationally recognized principles on standard-
andunstable,itisdifficulttostorethemasstandardmixturesof
ization established in the Decision on Principles for the
known concentration for extended calibration purposes. An
Development of International Standards, Guides and Recom-
alternative is to prepare dynamically standard blends as re-
mendations issued by the World Trade Organization Technical
quired. This procedure is simplified if a constant source of the
Barriers to Trade (TBT) Committee.
gas of interest can be provided. Permeation tubes provide this
2. Referenced Documents
constant source, if properly calibrated and if maintained at
constant temperature. Permeation tubes have been specified as
2.1 ASTM Standards:
reference calibration sources, for certain analytical procedures,
D1356 Terminology Relating to Sampling and Analysis of
by the Environmental Protection Agency (3).
Atmospheres
D3195 Practice for Rotameter Calibration
6. Interferences and Precautions
E1 Specification for ASTM Liquid-in-Glass Thermometers
E2251 Specification for Liquid-in-Glass ASTM Thermom- 6.1 Permeation tubes are essentially devices to provide a
eters with Low-Hazard Precision Liquids constant rate of emission of a specific gaseous substance over
period of time.They consist of a two-phase (gas-liquid) system
3. Terminology
to maintain a constant vapor pressure (at constant temperature)
3.1 Definitions—Refer to Terminology D1356. which is the driving force for emission of the gas through a
semipermeable membrane (tube walls). They can be expected
1 to maintain a constant emission rate that is temperature
This practice is under the jurisdiction ofASTM Committee D22 on Air Quality
and is the direct responsibility of Subcommittee D22.01 on Quality Control.
dependent as long as a significant amount of liquid is present
Current edition approved Nov. 1, 2022. Published December 2022. Originally
inthedevice.Theliquidshallbepure,elseitscompositionmay
approved in 1977. Last previous edition approved in 2014 as D3609 – 00 (2014).
change during the life time of the tube, due to differential
DOI: 10.1520/D3609-22.
evaporation, with consequent vapor pressure changes. Care
The boldface numbers in parentheses refer to a list of references at the end of
this standard.
must also be exercised that the diffusion membrane (tube
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
walls) is not damaged or altered during use. The contents of
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
permeation tubes are under relatively high pressure.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Accordingly, there is the possibility of violent rupture of tube
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3609 − 22
NOTE 1—This system has the advantage of smaller uncertainty of the temperature of the permeation tube.
FIG. 1 Optional System for Laboratory Use of a Permeation Tube
walls under high temperature exposure. Permeation rates have 7. Apparatus
temperature coefficients up to 10 % per degree Celsius. When
7.1 Permeation Tube sized in accordance with and cali-
temperature coefficients are large, above 3 % per degree
brated to concentrations needed or expected for the analysis
Celsius, stringent temperature control is required. Furthermore
method. The user should check calibration as described in
permeation tubes exhibit temperature hysteresis so that they
Section 9.1.
must be temperature equilibrated from 2 to 24 h before use,
depending upon the temperature differential between storage
7.2 Flow and Temperature Control System—Prepare or
and use (4). It is important that permeation tubes are filled with
purchase a system that will dry the carrier gas, and control and
anhydrous constituents of high purity. They shall be handled
measure its flow as it passes over the permeation tube that is
with care to minimize contact with moisture, oil, and foreign
being held at constant temperature. If lower concentrations are
substances.
desired, a second gas supply (diluent gas) with its control and
measurement devices may be needed to mix with the gas from
6.2 Sulfur dioxide (SO ) permeation tubes are relatively
the permeation tube chamber. Equipment of this kind is
insensitive to interferences.
available commercially. A typical system contains a thermo-
6.3 Nitrogen dioxide (NO ) permeation tubes are sensitive
electrically temperature-controlled permeation tube chamber
to moisture, hence they should be stored in dry atmospheres
with temperature control within 60.1 °C over the range from
and used with relatively dry carrier gases (<10 % relative
15 °C to 35 °C. Such equipment is well suited to field usage.
humidity). Permeation of moisture into the contents of a tube
may damage the walls and also cause progressive decreases in
7.3 A typical system for laboratory use that can be as-
the permeation rate. Moisture incorporated in the contents
sembled from readily available parts is shown schematically in
during manufacture can cause the same effect (4).
Fig. 1. The parts required are described in the following
subsections.
6.4 Hydrogen sulfide (H S) permeation tubes may turn
7.3.1 Flowmeters—Several, sufficient to cover the range
white during use in the presence of oxygen because of inverse
permeation and formation of collodial sulfur. This phenom- from 0 L⁄min to 15 L⁄min, calibrated by Practice D3195.
enon may affect the permeation rate, if severe, hence is a
7.3.2 Copper Tubing—Approximately 1 m long [3 ft] by
reason for recalibration. However, in an inert gas stream, the
6.25 mm [0.25 in.] in outside diameter for use as a heat
tubes are relatively stable.
exchanger in the water bath.
6.5 Materials of construction shall be compatible with the 7.3.3 Ball Joints (Ungreased) and Tubing, for the necessary
connections. Butt seals may also be used made with inert
contents of the tube. For instance, some fluorocarbons may
cause FEP tubes to swell and possibly to rupture. materials such as polyethylene.
D3609 − 22
NOTE 1—This system is constructed from readily available laboratory equipment.
NOTE 2—Warning—If the room temperature is significantly different from that of the water bath, a small difference in temperature between the bath
and the condensor containing the permeation tube can exist. In this event, the temperature indicated by the thermometer in the condensor should be used
as that of the permeation tube, rather than that of the water bath.
FIG. 2 Typical System for Laboratory Use
7.3.4 Mixing Bulb, to ensure adequate mixing of the perme- A specially constructed constant temperature chamber may be
ated gas and the diluent gas stream. A Kjeldahl trap is used or, if more convenient, the weight loss occurring during
recommended.
use of the tube in the actual flow system (7.2 and 7.3) can be
7.3.5 Long Condenser, with large bore in which a thermom-
measured. In the latter case, place the tube in its chamber
eter and a permeation tube can be inserted.
(condenser) and run the system as described in Section 10.
7.3.6 Temperature Controlled Water Bath—About 8-L [2-
Remove the tube at 24-h intervals and weigh on a semimicro
gal] capacity, capable of 60.1 °C or better water temperature
analytical balance. Handle the tube with gloves or forceps to
control, with a variable temperature control range from about
minimize pickup of moisture or grease. Remove the tube for
15 °C to 35 °C, preferably equipped with a positive displace-
only the minimum time required for the weighing.
ment type recirculating pump with at least 1-L/min liquid flow
Furthermore, it is advisable to conduct the w
...

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: D3609 − 00 (Reapproved 2014) D3609 − 22
Standard Practice for
Calibration Techniques Using Permeation Tubes
This standard is issued under the fixed designation D3609; 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.
1. Scope
1.1 This practice describes a means for using permeation tubes for dynamically calibrating instruments, analyzers, and analytical
procedures used in measuring concentrations of gases or vapors in atmospheres (1, 2).
1.2 Typical materials that may be sealed in permeation tubes include: sulfur dioxide, nitrogen dioxide, hydrogen sulfide, chlorine,
ammonia, propane, and butane (1).
1.3 The values stated in SI units are to be regarded as standard.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D1356 Terminology Relating to Sampling and Analysis of Atmospheres
D3195 Practice for Rotameter Calibration
E1 Specification for ASTM Liquid-in-Glass Thermometers
E2251 Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
3. Terminology
3.1 Definitions—Refer to Terminology D1356.
4. Summary of Practice
4.1 A liquefiable gas, when enclosed in an inert plastic tube, escapes by permeating the tubing wall at a constant, reproducible,
temperature-dependent rate.
This practice is under the jurisdiction of ASTM Committee D22 on Air Quality and is the direct responsibility of Subcommittee D22.01 on Quality Control.
Current edition approved Sept. 1, 2014Nov. 1, 2022. Published September 2014December 2022. Originally approved in 1977. Last previous edition approved in 20102014
as D3609 – 00 (2010).(2014). DOI: 10.1520/D3609-00R14.10.1520/D3609-22.
The boldface numbers in parentheses refer to a 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 [e-mail]. 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
D3609 − 22
4.2 Permeation tubes are calibrated gravimetrically, with the weight loss of the tube equated to the weight of the escaping material.
4.3 Permeation tubes are held at constant temperature in a carrier-gas stream of dry air or nitrogen to produce a gas concentration
dependent on the permeation rate and the flow of the carrier gas.
5. Significance and Use
5.1 Most analytical methods used in air pollutant measurements are comparative in nature and require calibration or
standardization, or both, often with known blends of the gas of interest. Since many of the important air pollutants are reactive
and unstable, it is difficult to store them as standard mixtures of known concentration for extended calibration purposes. An
alternative is to prepare dynamically standard blends as required. This procedure is simplified if a constant source of the gas of
interest can be provided. Permeation tubes provide this constant source, if properly calibrated and if maintained at constant
temperature. Permeation tubes have been specified as reference calibration sources, for certain analytical procedures, by the
Environmental Protection Agency (3).
NOTE 1—This system has the advantage of smaller uncertainty of the temperature of the permeation tube.
FIG. 1 Optional System for Laboratory Use of a Permeation Tube
6. Interferences and Precautions
6.1 Permeation tubes are essentially devices to provide a constant rate of emission of a specific gaseous substance over period of
time. They consist of a two-phase (gas-liquid) system to maintain a constant vapor pressure (at constant temperature) which is the
driving force for emission of the gas through a semipermeable membrane (tube walls). They can be expected to maintain a constant
emission rate that is temperature dependent as long as a significant amount of liquid is present in the device. The liquid shall be
pure, else its composition may change during the life time of the tube, due to differential evaporation, with consequent vapor
pressure changes. Care must also be exercised that the diffusion membrane (tube walls) is not damaged or altered during use. The
contents of permeation tubes are under relatively high pressure. Accordingly, there is the possibility of violent rupture of tube walls
under high temperature exposure. Permeation rates have temperature coefficients up to 10 % per degree Celsius. When temperature
coefficients are large, above 3 % per degree Celsius, stringent temperature control is required. Furthermore permeation tubes
exhibit temperature hysteresis so that they must be temperature equilibrated from 2 to 24 h before use, depending upon the
temperature differential between storage and use (4). It is important that permeation tubes are filled with anhydrous constituents
of high purity. They shall be handled with care to minimize contact with moisture, oil, and foreign substances.
D3609 − 22
6.2 Sulfur dioxide (SO ) permeation tubes are relatively insensitive to interferences.
6.3 Nitrogen dioxide (NO ) permeation tubes are sensitive to moisture, hence they should be stored in dry atmospheres and used
with relatively dry carrier gases (<10 % relative humidity). Permeation of moisture into the contents of a tube may damage the
walls and also cause progressive decreases in the permeation rate. Moisture incorporated in the contents during manufacture can
cause the same effect (4).
6.4 Hydrogen sulfide (H S) permeation tubes may turn white during use in the presence of oxygen because of inverse permeation
and formation of collodial sulfur. This phenomenon may affect the permeation rate, if severe, hence is a reason for recalibration.
However, in an inert gas stream, the tubes are relatively stable.
6.5 Materials of construction shall be compatible with the contents of the tube. For instance, some fluorocarbons may cause FEP
tubes to swell and possibly to rupture.
7. Apparatus
7.1 Permeation Tube sized in accordance with and calibrated to concentrations needed or expected for the analysis method. The
user should check calibration as described in Section 9.1.
7.2 Flow and Temperature Control System—Prepare or purchase a system that will dry the carrier gas, and control and measure
its flow as it passes over the permeation tube that is being held at constant temperature. If lower concentrations are desired, a
second gas supply (diluent gas) with its control and measurement devices may be needed to mix with the gas from the permeation
tube chamber. Equipment of this kind is available commercially. A typical system contains a thermoelectrically temperature-
controlled permeation tube chamber with temperature control within 60.1°C60.1 °C over the range from 1515 °C to 35°C.35 °C.
Such equipment is well suited to field usage.
7.3 A typical system for laboratory use that can be assembled from readily available parts is shown schematically in Fig. 1. The
parts required are described in the following subsections.
7.3.1 Flowmeters—Several, sufficient to cover the range from 00 L ⁄min to 1515 L L/min, ⁄min, calibrated by Practice D3195.
7.3.2 Copper Tubing—Approximately 1 m long [3 ft] by 6.25 mm [0.25 in.] in outside diameter for use as a heat exchanger in
the water bath.
7.3.3 Ball Joints (Ungreased) and Tubing, for the necessary connections. Butt seals may also be used made with inert materials
such as polyethylene.
7.3.4 Mixing Bulb, to ensure adequate mixing of the permeated gas and the diluent gas stream. A Kjeldahl trap is recommended.
7.3.5 Long Condenser, with large bore in which a thermometer and a permeation tube can be inserted.
7.3.6 Temperature Controlled Water Bath—About 8-L [2-gal] capacity, capable of 60.1°C60.1 °C or better water temperature
control, with a variable temperature control range from about 1515 °C to 35°C,35 °C, preferably equipped with a positive
displacement type recirculating pump with at least 1-L/min liquid flow rate to supply water to the condenser.
7.3.7 Thermometer, ASTM No. 91C (see Specification E1), ASTM No. S91C (see Specification E2251), or equivalent, calibrated
to 60.1°C.60.1 °C.
7.3.8 Mercury Barometer. Barometer.
7.4 An alternate system is shown in Fig. 2. It has the advantage of lower uncertainty of the temperature of the permeation tube.
The required parts are described in the figure.
D3609 − 22
NOTE 1—This system is constructed from readily available laboratory equipment.
NOTE 2—Warning—If the room temperature is significantly different from that of the water bath, a small difference in temperature between the bath
and the condensor containing the permeation tube can exist. In this event, the temperature indicated by the thermometer in the condensor should be used
as that of the permeation tube, rather than that of the water bath.
FIG. 2 Typical System for Laboratory Use
8. Reagents and Materials
8.1 Carrier Gas or Diluent Gas for Flow Over Permeation Tube—Cylinder of dry nitrogen or pure, dry air, or purified room air
(charcoal
...