ASTM C471M-24

Standard Test Methods for Chemical Analysis of Gypsum and Gypsum Products (Metric)

SCOPE
1.1 These test methods cover the chemical analysis of gypsum and gypsum panel products, including gypsum ready-mixed plaster, gypsum wood-fibered plaster, and gypsum concrete.  
1.2 These test methods appear in the following order:    
Sections  
Preparation of Sample  
4  
Complete Procedure  
5 – 16  
Alternative Procedure for Analysis of Free Water in  
17  
Gypsum Using a Moisture Balance  
Alternative Procedure for Analysis of Combined Water in  
18  
Gypsum Using a Moisture Balance  
Alternative Procedure for Analysis of Organic Material  
20  
and Carbon Dioxide in Gypsum by High Temperature  
Weight Loss  
Alternative Procedure for Analysis for Calcium Sulfate by  
21  
Ammonium Acetate Method  
Alternative Procedure for Analysis for Sodium Chloride by  
22  
the Coulometric Method  
Determination of Sand in Set Plaster  
23  
Wood-fiber Content in Wood-fiber Gypsum Plaster  
24  
Optional Procedure for Analysis for Sodium by the Atomic  
25  
Absorption Method  
Optional Procedure for Analysis for Sodium by Flame  
26  
Photometry  
Determination of Orthorhombic Cyclooctasulfur (S8) in  
27  
Ggypsum Panel Products—General Provisions  
Determination of Orthorhombic Cyclooctasulfur (S8) in  
28  
Gypsum Panel Products by Gas Chromatograph  
Equipped with a Mass Spectrometer (GS/MS)  
Determination of Orthorhombic Cyclooctasulfur (S8) in  
29  
Gypsum Panel Products by Gas Chromatograph  
Equipped with an Electron Capture Detector (GC/ECD)  
Determination of Orthorhombic Cyclooctasulfur (S8) in  
30  
Gypsum Panel Products by High-performance Liquid  
Chromatograph Equipped with and Ultraviolet Detector  
(HPLC/UV)  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in these test methods.  
1.4 These text of this test method references notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.  
1.5 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.  
1.6 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-Mar-2024
• ICS: 91.100.10 - Cement. Gypsum. Lime. Mortar
• Technical Committee: C11 - Gypsum and Related Building Materials and Systems
• Drafting Committee: C11.01 - Specifications and Test Methods for Gypsum Products

Relations

• Replaces: ASTM C471M-20ae1 - Standard Test Methods for Chemical Analysis of Gypsum and Gypsum Products (Metric)
• Effective Date: 01-Apr-2024
• Refers: ASTM C317/C317M-24 - Standard Specification for Gypsum Concrete
• Effective Date: 01-Apr-2024
• Refers: ASTM C317/C317M-00(2019) - Standard Specification for Gypsum Concrete
• Effective Date: 01-Oct-2019
• Referred By: ASTM C1396/C1396M-17 - Standard Specification for Gypsum Board
• Effective Date: 01-Apr-2024
• Referred By: ASTM C452-21 - Standard Test Method for Potential Expansion of Portland-Cement Mortars Exposed to Sulfate
• Effective Date: 01-Apr-2024
• Referred By: ASTM C563-20 - Standard Guide for Approximation of Optimum SO<inf>3</inf> in Hydraulic Cement
• Effective Date: 01-Apr-2024
• Referred By: ASTM D8155-17(2023) - Standard Practice for Shake Extraction of Solid Mining and Metallurgical Processing Waste with Water
• Effective Date: 01-Apr-2024
• Referred By: ASTM C61/C61M-00(2020) - Standard Specification for Gypsum Keene's Cement
• Effective Date: 01-Apr-2024
• Referred By: ASTM C22/C22M-00(2021) - Standard Specification for Gypsum
• Effective Date: 01-Apr-2024
• Referred By: ASTM C35-01(2019) - Standard Specification for Inorganic Aggregates for Use in Gypsum Plaster
• Effective Date: 01-Apr-2024
• Referred By: ASTM D3987-12(2020) - Standard Practice for Shake Extraction of Solid Waste with Water
• Effective Date: 01-Apr-2024
• Referred By: ASTM C28/C28M-10(2020) - Standard Specification for Gypsum Plasters
• Effective Date: 01-Apr-2024
• Referred By: ASTM E3355-23 - Standard Guide for Characterization of Coal Combustion Products (CCPs) in Storage Area(s) for Beneficial Use
• Effective Date: 01-Apr-2024
• Referred By: ASTM C59/C59M-00(2020) - Standard Specification for Gypsum Casting Plaster and Gypsum Molding Plaster
• Effective Date: 01-Apr-2024
• Referred By: ASTM D34-08(2023) - Standard Guide for Chemical Analysis of White Pigments
• Effective Date: 01-Apr-2024

Overview

ASTM C471M-24: Standard Test Methods for Chemical Analysis of Gypsum and Gypsum Products (Metric) is an internationally recognized ASTM standard that establishes robust chemical analysis methods for a variety of gypsum-based materials. These include gypsum ready-mixed plaster, gypsum wood-fibered plaster, gypsum concrete, and gypsum panel products. By specifying test methods using SI (metric) units, this standard supports consistent, reliable quality control and specification compliance across global supply chains.

The standard covers detailed procedures for sample preparation, comprehensive analyses of basic and optional chemical components, and guidance on alternative testing methods utilizing advanced instrumentation. It is designed for testing laboratories, manufacturers, specifiers, and quality professionals involved with gypsum materials and related products.

Key Topics

• Sample Preparation: Guidelines for collecting, drying, crushing, sieving, and rehydrating gypsum samples to prepare for analysis, ensuring sample integrity and consistency.
• Free and Combined Water Content: Methods to determine both physically free and chemically bound water in gypsum products, critical for understanding material purity and performance.
• Analysis of Key Chemical Components:
  • Calcium Sulfate (CaSO₄): Determination by various methods, including ammonium acetate extraction.
  • Sodium Chloride (NaCl): Procedures including coulometric titration and atomic absorption/flame photometry.
  • Organic Material and Carbon Dioxide: Assessment using high temperature weight loss procedures.
  • Sulfur Trioxide (SO₃): Gravimetric determination via barium sulfate precipitation.
  • Iron and Aluminum Oxides, Magnesium Oxide, and Silicon Dioxide: Quantification essential for product quality and regulatory compliance.
• Specialty Components:
  • Wood Fiber Content in specific gypsum plasters.
  • Orthorhombic Cyclooctasulfur (S₈): Advanced analytical techniques using GC/MS, GC/ECD, and HPLC/UV for gypsum panel products.

Applications

• Quality Control: Supports manufacturers in verifying material composition, ensuring consistency, and meeting specification requirements for gypsum products.
• Product Compliance: Enables compliance with domestic and international standards for chemical composition, improving market access and technical documentation.
• Research and Development: Facilitates R&D laboratories in analyzing new formulations, assessing purity, and investigating performance characteristics of gypsum materials.
• Regulatory Testing: Assists certifying bodies and inspection agencies in ensuring products meet safety, environmental, and health regulations.
• Forensic and Failure Analysis: Provides robust test methods for investigating material failures or inconsistencies in gypsum products.

Related Standards

ASTM C471M-24 references and is complemented by various related ASTM and international standards, including:

• ASTM C11: Terminology relating to gypsum and related building materials and systems.
• ASTM C22/C22M: Specification for gypsum.
• ASTM C28/C28M: Specification for gypsum plasters.
• ASTM C59: Specification for gypsum casting plaster and gypsum molding plaster.
• ASTM C61: Specification for gypsum Keene’s cement.
• ASTM C317/C317M: Specification for gypsum concrete.
• ASTM C778: Specification for standard sand (for plaster blends).
• ASTM C842: Specification for application of interior gypsum plaster.
• ASTM D1193: Specification for reagent water.
• ASTM E11: Specification for woven wire test sieve cloth and test sieves.
• ASTM E177: Practice for use of terms precision and bias in ASTM test methods.

Practical Value

Implementing ASTM C471M-24 test methods ensures that gypsum products-whether used for construction, finishing, or specialty applications-meet rigorous quality and performance criteria. The standard’s detailed, SI unit-based procedures facilitate consistent results, enable international trade, and support technical evaluation throughout the gypsum product lifecycle. By referencing this standard, laboratories and industry professionals can demonstrate compliance, enhance product reliability, and contribute to safe, high-quality built environments.

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: C471M − 24
Standard Test Methods for
Chemical Analysis of Gypsum and Gypsum Products
(Metric)
This standard is issued under the fixed designation C471M; 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 footnotes (excluding those in tables and figures) shall not be
considered as requirements of the standard.
1.1 These test methods cover the chemical analysis of
gypsum and gypsum panel products, including gypsum ready- 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
mixed plaster, gypsum wood-fibered plaster, and gypsum
concrete. responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.2 These test methods appear in the following order:
mine the applicability of regulatory limitations prior to use.
Sections
1.6 This international standard was developed in accor-
Preparation of Sample 4
Complete Procedure 5 – 16
dance with internationally recognized principles on standard-
Alternative Procedure for Analysis of Free Water in 17
ization established in the Decision on Principles for the
Gypsum Using a Moisture Balance
Development of International Standards, Guides and Recom-
Alternative Procedure for Analysis of Combined Water in 18
Gypsum Using a Moisture Balance
mendations issued by the World Trade Organization Technical
Alternative Procedure for Analysis of Organic Material 20
Barriers to Trade (TBT) Committee.
and Carbon Dioxide in Gypsum by High Temperature
Weight Loss
2. Referenced Documents
Alternative Procedure for Analysis for Calcium Sulfate by 21
Ammonium Acetate Method
2.1 ASTM Standards:
Alternative Procedure for Analysis for Sodium Chloride by 22
the Coulometric Method C11 Terminology Relating to Gypsum and Related Building
Determination of Sand in Set Plaster 23
Materials and Systems
Wood-fiber Content in Wood-fiber Gypsum Plaster 24
C22/C22M Specification for Gypsum
Optional Procedure for Analysis for Sodium by the Atomic 25
Absorption Method
C28/C28M Specification for Gypsum Plasters
Optional Procedure for Analysis for Sodium by Flame 26
C59 Specification for Gypsum Casting Plaster and Gypsum
Photometry
Molding Plaster
Determination of Orthorhombic Cyclooctasulfur (S ) in 27
Ggypsum Panel Products—General Provisions
C61 Specification for Gypsum Keene’s Cement
Determination of Orthorhombic Cyclooctasulfur (S ) in 28
C317/C317M Specification for Gypsum Concrete
Gypsum Panel Products by Gas Chromatograph
C778 Specification for Standard Sand
Equipped with a Mass Spectrometer (GS/MS)
Determination of Orthorhombic Cyclooctasulfur (S ) in 29 C842 Specification for Application of Interior Gypsum Plas-
Gypsum Panel Products by Gas Chromatograph
ter
Equipped with an Electron Capture Detector (GC/ECD)
D1193 Specification for Reagent Water
Determination of Orthorhombic Cyclooctasulfur (S ) in 30
Gypsum Panel Products by High-performance Liquid
D1428 Test Method for Test for Sodium and Potassium In
Chromatograph Equipped with and Ultraviolet Detector
Water and Water-Formed Deposits by Flame Photometry
(HPLC ⁄UV)
(Withdrawn 1989)
1.3 The values stated in SI units are to be regarded as
D2013 Practice for Preparing Coal Samples for Analysis
standard. No other units of measurement are included in these
E11 Specification for Woven Wire Test Sieve Cloth and Test
test methods.
Sieves
1.4 These text of this test method references notes and
E177 Practice for Use of the Terms Precision and Bias in
footnotes that provide explanatory material. These notes and
ASTM Test Methods
These test methods are under the jurisdiction of ASTM Committee C11 on
Gypsum and Related Building Materials and Systems and are the direct responsi- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
bility of Subcommittee C11.01 on Specifications and Test Methods for Gypsum contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Products. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2024. Published April 2024. Originally the ASTM website.
ɛ1 3
approved in 1961. Last previous edition approved in 2020 as C471M – 20a . DOI: The last approved version of this historical standard is referenced on
10.1520/C0471M-24. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C471M − 24
E691 Practice for Conducting an Interlaboratory Study to 4.3.1 Gypsum Ready-mixed Plaster or Gypsum Wood-
Determine the Precision of a Test Method fibered Plaster—Screen the dried sample through a 150 μm
(No. 100) sieve (see Note 1) and discard the residue retained on
3. Terminology the sieve. Reweigh the remaining sample and calculate the
percentage of the dried sample. Reduce the sample in accor-
3.1 Definitions:
dance with 4.1.5. Thoroughly blend and rehydrate the speci-
3.1.1 For definitions of terms used in these test methods,
men in accordance with 4.1.4.
refer to Terminology C11.
3.2 Definitions of Terms Specific to This Standard:
NOTE 1—Detailed requirements for this sieve are given in Specification
E11.
3.2.1 calibration standard, n—a chemical mixture contain-
ing a known quantity of the analyte used to relate the measured
4.3.2 Gypsum Neat Plaster or Gypsum Gauging Plaster—
analytical signal to the concentration of the analyte.
Reduce the dried sample in accordance with 4.1.5. Thoroughly
3.2.2 dried sample, n—a sample devoid of free water. blend and rehydrate the specimen in accordance with 4.1.4.
3.2.3 internal standard, n—a chemical used in the quantifi-
4.4 Gypsum Casting and Molding Plaster (Specification
cation of S by monitoring and adjusting for minor variances in
8 C59)—Reduce the dried sample in accordance with 4.1.5.
instrument performance.
Thoroughly blend and rehydrate the specimen in accordance
with 4.1.4.
3.2.4 riffle, n—a hand feed sample divider device that
divides the sample into parts of approximately the same
4.5 Gypsum Keene’s Cement (Specification C61)—Reduce
weight. (D2013)
the dried sample in accordance with 4.1.5. Blend in no more
3.2.5 sample as received, n—a representative portion of raw
than 1 % molding plaster or K SO and rehydrate the specimen
2 4
gypsum or gypsum product in the state received by the testing in accordance with 4.1.4.
laboratory, including aggregates, impurities, and water content.
4.6 Gypsum Concrete (Specification C317/C317M)—
3.2.6 surrogate standard, n—a chemical used to account for
Screen the dried sample through a 150 μm (No. 100) sieve (see
extraction efficiency of S .
Note 1) and discard the residue retained on the sieve. Reweigh
the remaining sample and calculate the percentage of the dried
4. Preparation of Sample
sample. Reduce the sample in accordance with 4.1.5. Thor-
oughly blend and rehydrate the specimen in accordance with
4.1 General Procedures—Details of sample preparation will
4.1.4.
vary according to the type of material being tested.
4.1.1 Sample as Received—Use a sufficient amount of
4.7 Gypsum Panel Products—Cut or break the dried sample
sample such that, after sieving, not less than 50 g of sample
into small pieces. Using a mortar and pestle, strike the pieces
will remain for testing. Weigh the entire sample immediately
of the sample to loosen the paper face. Remove the pieces of
after opening the container in which the material was received.
paper by hand as they are separated from the core of the
This will become the weight of the sample as received.
gypsum board. Carefully scrape any remaining powder from
4.1.2 Drying—Dry the sample in accordance with Section 7.
the paper. When all the paper has been removed from the
This will be the weight of the dried sample.
pieces of the sample, reduce the sample in accordance with
4.1.3 Crushing and Grinding—Crush and grind the sample
4.1.5.
by hand with a mortar and pestle or by mechanical crushing
and grinding equipment to pass a 250 μm (No. 60) sieve. Take
COMPLETE PROCEDURE
care, particularly with mechanical equipment, not to expose the
sample to temperatures of more than 52 °C. Clean the
5. Apparatus
equipment thoroughly between samples. Thoroughly remix the
ground sample and store it in an airtight container to avoid
5.1 Analytical Balance—Capable of weighing the weighing
contamination.
bottles, lids, and samples.
4.1.4 Rehydrating—Thoroughly blend and rehydrate
5.2 Balance—Capable of weighing not less than 100 g at a
samples which contain calcium sulfate in forms other than
precision of 0.001 g.
CaSO · 2H O and natural anhydrite. Place the sample in
4 2
distilled water and keep it wet for not less than 48 h. Dry the
5.3 Drying Oven—A mechanical convection oven set at
hydrated sample in an oven at 45 °C 6 3 °C to constant weight 45 °C 6 3 °C.
and recrush or grind it in accordance with 4.1.3.
5.4 Desiccator—Capable of being tightly sealed and con-
4.1.5 Sample Reduction—Thoroughly mix and reduce large
taining calcium chloride or equivalent desiccant.
samples as required by quartering or by the use of a riffle to
5.5 Calcining Oven or Furnace—Capable of achieving and
obtain a specimen of approximately 50 g.
maintaining temperatures to not less than 1000 °C.
4.2 Gypsum (Specification C22/C22M)—Gypsum samples
5.6 Weighing Bottles—Borosilicate glass or ceramic con-
will be received in the form of rocks or powder, or both. If
tainers with tightly sealable lids.
necessary crush and reduce the entire dried sample in accor-
dance with 4.1.3 and 4.1.5.
5.7 Hot Plate—A controllable hot plate capable of heating
4.3 Gypsum Plaster (Specification C28/C28M): casseroles to approximately 120 °C.
C471M − 24
5.8 Porcelain Casseroles—With a capacity of 50 mL to 6.1.16 Sulfuric Acid (1 + 6)—Carefully mix one volume of
100 mL. H SO (sp gr 1.84) with six volumes of water.
2 4
6.1.17 Nitric Acid (0.1 N)—Mix 1.4 mL of HNO (sp gr
5.9 Filtering Funnels.
1.42) with 200 mL of water.
5.10 Filter Paper.
6.1.18 Phenolphthalein Indicator Solution—Dissolve 0.25 g
5.11 Porcelain Crucibles. of phenolphthalein in 30 mL of methanol and dilute to 50 mL
with water.
5.12 Mortar and Pestle.
6.1.19 Sodium Hydroxide Solution (0.1 N)—Dissolve 1 g of
5.13 Mechanical Jaw Crusher—Capable of crushing gyp-
sodium hydroxide (NaOH) in 250 mL of water.
sum rocks up to 50 mm diameter.
6.1.20 Water—Reagent water shall be in accordance with
Specification D1193, type II. Specification D1193 gives the
5.14 Mechanical Grinder—Burr mill or equivalent capable
following values for type II grade water.
of grinding the granular output of the jaw crusher specified in
5.13.
Electrical conductivity, max, μS/cm at 298 K (25-C) 1.0
Electrical resistivity, min, MΩ·cm at 298 K (25-C) 1.0
Total organic carbon (TOC), max, μg/L 50.0
6. Reagents
Sodium, max, μg/L 5.0
Chlorides max, μg/L 5.0
6.1 Purity of Reagents—Use reagent grade chemicals in all
Total silica, max, μg/L 5.0
tests. Unless otherwise indicated, use reagents that conform to
the specifications of the Committee on Analytical Reagents of
7. Free Water
the American Chemical Society, where such specifications are
7.1 Significance and Use—The free water analysis deter-
available. If it is necessary to use other grades, first ascertain
mines the amount of free water contained in the sample as
that the reagent is of sufficiently high purity so that its use will
opposed to chemically combined water, and prepares the
not lessen the accuracy of the determination.
sample for further analysis.
6.1.1 Ammonium Chloride (NH Cl).
6.1.2 Ammonium Hydroxide (sp gr 0.90)—Concentrated
7.2 Procedure:
ammonium hydroxide (NH OH).
7.2.1 Weigh a sample of the material as received of not less
6.1.3 Ammonium Nitrate (25 g/L)—Dissolve 25 g of ammo-
than 50 g to a precision of 0.001 g and spread it out in a thin
nium nitrate (NH NO ) in water and dilute to 1 L.
layer in a suitable vessel. Place in an oven and dry at 45 °C 6
4 3
6.1.4 Ammonium Oxalate ((NH ) C O ).
4 2 2 4 3 °C until constant mass has been obtained. The samples are to
6.1.5 Barium Chloride (100 g/L)—Dissolve 100 g of barium
be cooled in a desiccator prior to each weighing. The loss of
chloride (BaCl ·2H O) in water and dilute to 1 L.
2 2 weight corresponds to the free water.
6.1.6 Calcium Chloride (CaCl )—Anhydrous Calcium
7.2.2 Retain the sample in a sealed container or in the
Chloride with a combined water of not more than 5 %.
desiccator for further analysis.
6.1.7 Hydrochloric Acid (sp gr 1.19)—Concentrated hydro-
7.3 Calculation and Report—Calculate and report loss in
chloric acid (HCl).
weight as a percentage of the sample as received or of the dried
6.1.8 Hydrochloric Acid (1 + 4)—Mix one volume of HCl
sample as required.
(sp gr 1.19) with four volumes of water.
7.4 Precision and Bias:
6.1.9 Hydrochloric Acid (1 + 5)—Mix one volume of HCl
7.4.1 The precision of this test method is based on an
(sp gr 1.19) with five volumes of water.
interlaboratory study of Test Methods C471M in 2020. Each of
6.1.10 Nitric Acid (sp gr 1.42)—Concentrated nitric acid
ten volunteer laboratories analyzed two different gypsum
(HNO ).
sample types. Every “test result” represents an individual
6.1.11 Potassium Chromate Solution (100 g/L)—Dissolve
determination, and all participants reported five test results per
5 g of potassium chromate (K CrO ) in 50 mL of water, mix,
2 4
material. Practice E691 was followed for the design and
add ten drops of 0.05 N silver nitrate (AgNO ) solution, allow
analysis of the data; the details are given in ASTM Research
to stand for 5 min, and filter.
Report No. C11-2000.
6.1.12 Potassium Permanganate (5.6339 g/L)—Dissolve
7.4.1.1 Repeatability (r)—The difference between repetitive
5.6339 g of potassium permanganate (KMnO ) in water and
results obtained by the same operator in a given laboratory
dilute to 1 L.
applying the same test method with the same apparatus under
6.1.13 Silver Nitrate, Standard Solution (0.05 N)—Prepare
constant operating conditions on identical test material within
and standardize a 0.05 N silver nitrate (AgNO ) solution.
short intervals of time would in the long run, in the normal and
6.1.14 Sodium Ammonium Phosphate—(NaNH HPO ).
4 4
correct operation of the test method, exceed the following
6.1.15 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric
values only in one case in 20.
acid (H SO ).
2 4
(1) Repeatability can be interpreted as maximum difference
between two results, obtained under repeatability conditions,
ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, 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, Supporting data have been filed at ASTM International Headquarters and may
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma- be obtained by requesting Research Report RR:C11-2000. Contact ASTM Customer
copeial Convention, Inc. (USPC), Rockville, MD. Service at [e-mail].
C471M − 24
that is accepted as plausible due to random causes under 8.3.3 Place the specimens in the calcining oven with the lids
normal and correct operation of the test method. placed loosely on each bottle or crucible for 2 h or until
(2) Repeatability limits are listed in Table 1.
constant weight has been obtained.
7.4.1.2 Reproducibility (R)—The difference between two
8.3.4 Place the lids tightly on the weighing bottles, remove
single and independent results obtained by different operators
from the oven, and place in the desiccator to cool to room
applying the same test method in different laboratories using
temperature.
different apparatus on identical test material would, in the long
8.3.5 Weigh each specimen to a precision of 0.0001 g and
run, in the normal and correct operation of the test method,
record the weights.
exceed the following values only in one case in 20.
8.3.6 Retain the residues for carbon dioxide analysis.
(1) Reproducibility can be interpreted as maximum differ-
ence between two results, obtained under reproducibility
8.4 Calculation and Report—Calculate and report the aver-
conditions, that is accepted as plausible due to random causes
age loss in weight of the three specimens as a percentage of the
under normal and correct operation of the test method.
sample as received or of the dried sample, as required, to the
(2) Reproducibility limits are listed in Table 1.
nearest 0.001 g and record the tare weights.
7.4.1.3 The above terms (repeatability limit and reproduc-
8.5 Precision and Bias:
ibility limit) are used as specified in Practice E177.
7.4.1.4 Any judgment in accordance with statements 7.4.1.1 8.5.1 The precision of this test method is based on an
and 7.4.1.2 would have an approximate 95 % probability of interlaboratory study of Test Methods C471M in 2020. Each of
being correct. ten volunteer laboratories analyzed two different gypsum
7.4.2 Bias—At the time of the study, there was no accepted
sample types. Every “test result” represents an individual
reference material suitable for determining the bias for this test determination, and all participants reported five test results per
method, therefore no statement on bias is being made.
material. Practice E691 was followed for the design and
7.4.3 The precision statement was determined through sta- analysis of the data; the details are given in ASTM Research
tistical examination of 278 results, from ten participating
Report No. C11-2000.
laboratories, on two types of gypsum materials.
8.5.1.1 Repeatability (r)—The difference between repetitive
7.4.4 To judge the equivalency of two test results, it is
results obtained by the same operator in a given laboratory
recommended to choose the material closest in characteristics
applying the same test method with the same apparatus under
to the test material.
constant operating conditions on identical test material within
short intervals of time would in the long run, in the normal and
8. Combined Water
correct operation of the test method, exceed the following
8.1 Significance and Use—The combined water analysis
values only in one case in 20.
determines the percent of chemically combined water and is
(1) Repeatability can be interpreted as maximum difference
used to calculate the purity of gypsum or the amount of
between two results, obtained under repeatability conditions,
gypsum or gypsum plaster in gypsum products.
that is accepted as plausible due to random causes under
normal and correct operation of the test method.
8.2 Interferences—Some materials, such as organic and
(2) Repeatability limits are listed in Table 2.
hydrated compounds that decompose within the same tempera-
ture range as gypsum, will cause high results. When the 8.5.1.2 Reproducibility (R)—The difference between two
maximum temperature is exceeded, some carbonates undergo
single and independent results obtained by different operators
decomposition, which will result in high results.
applying the same test method in different laboratories using
different apparatus on identical test material would, in the long
8.3 Procedure:
run, in the normal and correct operation of the test method,
8.3.1 For each sample, place three weighing bottles with
exceed the following values only in one case in 20.
lids in the preheated calcining oven or furnace and heat for 2 h
(1) Reproducibility can be interpreted as maximum differ-
at 215 °C to 230 °C. Place in the desiccator and allow to cool
ence between two results, obtained under reproducibility
to room temperature. Weigh the bottles and lids to the nearest
conditions, that is accepted as plausible due to random causes
0.0001 g and record the tare weights.
under normal and correct operation of the test method.
8.3.2 Weigh out three specimens of approximately 5 g each
(2) Reproducibility limits are listed in Table 2.
of the sample as prepared in Section 4 and dried in Section 7
to a precision of 0.0001 g in the previously tared weighing 8.5.1.3 The above terms (repeatability limit and reproduc-
bottles and record the total weight with lids. ibility limit) are used as specified in Practice E177.
TABLE 1 Free Water (in Accordance With Section 7)
Repeatability Reproducibility
Number of Repeatability Reproducibility
A
Average Standard Standard
Material Laboratories Limit Limit
Deviation Deviation
n x¯ s s r R
r R
Natural Gypsum 10 1.906 0.287 0.287 0.803 0.803
Flue Gas Desulphogypsum (FGD) 10 9.909 0.281 0.514 0.786 1.440
A
The average of the laboratories’ calculated averages.
C471M − 24
TABLE 2 Combined Water (in Accordance with Section 8)
Number Repeatability Reproducibility
Repeatability Reproducibility
A
of Average Standard Standard
Material Limit Limit
Laboratories Deviation Deviation
n x¯ s s r R
r R
Natural Gypsum 9 19.291 0.129 0.129 0.363 0.363
Flue Gas Desulphogypsum (FGD) 9 19.364 0.195 0.279 0.547 0.782
A
The average of the laboratories’ calculated averages.
8.5.1.4 Any judgment in accordance with statements 8.5.1.1 9.4.3 Erlenmeyer Flask C, 250 mL, 24/20 ground-glass
and 8.5.1.2 would have an approximate 95 % probability of joint.
being correct.
9.4.4 Separatory Funnel D, with ground glass stopper and
8.5.2 Bias—At the time of the study, there was no accepted
interchangeable hollow ground-glass joint. A delivery tube
reference material suitable for determining the bias for this test
bent at the end extends into the sample flask approximately
method, therefore no statement on bias is being made.
15 mm from the bottom and is used to introduce acid into flask.
8.5.3 The precision statement was determined through sta-
9.4.5 Condenser E.
tistical examination of 278 results, from ten participating
9.4.6 Gas-washing Bottle F, 250 mL, with fitted disk con-
laboratories, on two types of gypsum materials.
taining distilled water to retain most of the acid volatilized
8.5.4 To judge the equivalency of two test results, it is
from the alkalimeter.
recommended to choose the material closest in characteristics
9.4.7 U-Tube G, containing mossy zinc to remove the last
to the test material.
traces of HCl.
9. Carbon Dioxide
9.4.8 Gas-washing Bottle H, 250 mL, with fritted disk,
containing concentrated H SO and trap I, to remove any SO
2 4 3
9.1 Summary of Test Method—The sample is decomposed
mist that is carried over.
with HCl and the liberated CO is passed through a series of
9.4.9 Absorption Bulb J, containing Anhydrone to remove
scrubbers to remove water and sulfides. The CO is absorbed
last traces of water vapor.
with Ascarite, a special sodium hydroxide absorbent, and the
gain in weight of the absorption tube is determined and 9.4.10 CO Absorption Bulb, containing Ascarite filled as
calculated as percent CO . follows: On the bottom of the bulb, place a layer of glass wool
extending above the bottom outlet and on top of this a layer of
9.2 Significance and Use—The carbon dioxide analysis is
Anhydrone approximately 10 mm thick; immediately above
useful in estimating carbonates and organic carbon for chemi-
this place another layer of glass wool, then add Ascarite to
cal balance.
almost fill the bulb. Place a top layer of Anhydrone approxi-
9.3 Special Reagents:
mately 10 mm thick on top of the Ascarite and top it off with
9.3.1 Magnesium Perchlorate Desiccant—For drying.
a covering of glass wool.
9.3.2 Sodium Hydroxide Absorbent—A coarse sodium hy-
9.4.11 U-guard Tube L, filled with Anhydrone in left side
droxide coated silica.
and Ascarite in right side.
9.4 Special Apparatus—The apparatus illustrated in Fig. 1
9.4.12 Purifying Jar M, Fleming, containing H SO .
2 4
consists of the following:
9.5 Procedure:
9.4.1 Purifying Jar A, Fleming, containing sulfuric acid.
9.4.2 Drying Tube B, U-shaped with side arms and glass- 9.5.1 After drying as described in Section 8 place the
stoppers. Side arms are shaped to hold rubber tubing. Contains residue obtained in the 250 mL Erlenmeyer flask (C). Connect
Anhydrone on left side and Ascarite on right side. the flask to the apparatus as shown in Fig. 1. Purge the system
FIG. 1 Apparatus for Carbon Dioxide Analysis
C471M − 24
free of carbon dioxide by passing a current of CO -free air not less than 20 min to do the evaporation. Make a blank
through the apparatus for 10 min to 15 min. determination with one casserole in parallel. Cool to room
temperature.
9.5.2 Weigh the absorption bulb to 0.0001 g and attach it to
10.3.3 Add enough hydrochloric acid (sp gr 1.19) to wet the
the train. Remove the glass stopper from the separatory funnel,
solid residue. Add 20 mL of water, boil and filter through filter
place 50 mL of dilute HCl (1 + 1) in the separatory funnel (D),
paper. Wash the filter paper thoroughly using not less than
and replace the stopper with the interchangeable hollow
100 mL of room temperature water to render the precipitate
ground-glass joint through which passes a tube for admitting
chloride free. The most effective washing technique is to use
purified air. Open the stopcock of the separatory funnel and
many small quantities of wash water rather than fill the funnel
admit air through the top of the funnel to force the hydrochloric
to the brim two or three times. Test the filtrate for chloride by
acid into the Erlenmeyer flask (C).
collecting a small amount and adding a few drops of 0.1
9.5.3 Start cold water circulating through the condenser (E)
normal silver nitrate (AgNO ) solution. A white precipitate
and, with CO -free air passing at a moderate rate through the 3
indicates more washing is needed. Discard this test solution.
absorption train, place a small hot plate or gas burner under the
10.3.4 Place all the filtrate back in the same casserole.
sample flask and boil for approximately 2 min. Remove the hot
Evaporate to dryness and heat to 120 °C for 1 h and cool. To
plate and continue the flow of purified air at approximately
the cooled casserole add enough HCl (sp gr 1.19) to wet the
three bubbles per second for 10 min to sweep the apparatus free
solid residue. Add 50 mL of water and boil.
of CO . Close the absorption bulb, disconnect it from the train
10.3.5 Wash the second contents of the casserole through
and weigh, opening the stopper momentarily to equalize the
another filter paper. Thoroughly wash the residue in the filter
pressure. Use a second absorption bulb as counterpoise in all
paper until chloride free as in 10.3.3. Retain the filtrate for the
weighings unless a single pan balance is used.
iron and aluminum oxide analysis.
9.6 Calculation—Calculate the percent CO to the dried
10.3.6 Dry sufficient crucibles by placing in a cold muffle
sample as follows:
furnace during warm up or by placing in a drying oven for
% CO 5 A 2 B /C × 100 1 2 D (1) 15 min to 20 min, then placing in a 900 °C muffle furnace.
~~ ! !~ !
Cool crucibles to room temperature in a desiccator.
where:
10.3.7 Transfer both filter papers to a tared crucible and char
A = mass of absorption bulb + CO g,
slowly without flaming. Burn off all the carbon and ignite in a
B = mass of absorption bulb before the run, g,
muffle furnace at 900 °C for 15 min.
C = mass of specimen, g, and
10.3.8 Cool the crucibles in a desiccator and weigh to the
D = percent combined water as determined in Section 8 as
nearest 0.0001 g.
a decimal.
10.4 Calculation and Report—Calculate the average weight
Calculate the percent CO to the sample as received as
of the three precipitates and report as silicon dioxide (SiO )
follows:
and other insoluble matter to the percentage of sample as
% CO 5 E~1 2 F! (2)
2 received or to the dried sample as required.
where: 10.5 Precision and Bias—Neither the precision nor the bias
for the silicon dioxide and other acid insoluble matter has been
E = result of Eq 1, and
determined.
F = percent free water as determined in Section 7 as a
decimal.
11. Iron and Aluminum Oxides
9.7 Precision and Bias—Neither the precision nor the bias
11.1 Significance and Use—The iron and aluminum oxides
for the carbon dioxide analysis has been determined.
(Fe O + Al O ) analysis is used to determine the quantity of
2 3 2 3
these metal oxides in gypsum or gypsum products.
10. Silicon Dioxide and Other Acid Insoluble Matter
11.2 Procedure—To the filtrate, obtained as described in
10.1 Summary of Test Method—The gypsum and other acid
Section 10, add a few drops of nitric acid (HNO ), and boil to
soluble components of the sample are dissolved in dilute
ensure oxidation of the iron. Add 2 g of ammonium chloride
hydrochloric acid (HCl). The residue is weighed and calculated
(NH Cl) previously dissolved in water. Make alkaline with
as silicon dioxide and other acid insoluble matter.
ammonium hydroxide (NH OH). Digest hot for a few minutes
10.2 Significance and Use—The silicon dioxide and other
until the precipitate coagulates. Filter, wash, ignite the precipi-
acid insoluble matter analysis determines and is used to report
tate at 1000 °C for 30 min or to constant weight in a muffle
the percentage of one of the inert impurities in gypsum and
furnace and weigh as Fe O + Al O . Save the filtrate for the
2 3 2 3
gypsum products.
CaO analysis.
10.3 Procedure—Perform in triplicate.
NOTE 2—The addition of a pinch of ashless filter paper pulp will aid in
the filtration of the precipitate.
10.3.1 Weigh approximately 1 g of the specimen prepared in
Section 4 to the nearest 0.0001 g.
11.3 Calculation—Calculate Fe O + Al O to the percent-
2 3 2 3
10.3.2 Place the specimen in a porcelain casserole. Add age of sample as received or the dried sample as required. This
approximately 50 mL of 1 + 5 hydrochloric acid. Evaporate precipitate may be further treated to separate the two oxides,
slowly and carefully to apparent dryness on a hot plate. Take but this is generally unnecessary.
C471M − 24
11.4 Precision and Bias—Neither the precision nor the bias chloride (BaCl ). The precipitate is filtered and weighed as
for the iron and aluminum oxides analysis has been deter- barium sulfate (BaSO ) and the sulfur trioxide (SO ) equiva-
4 3
mined. lent is calculated.
14.2 Significance and Use—The specification for gypsum
12. Calcium Oxide
and some gypsum products specifies the amount of calcium
12.1 Significance and Use—The calcium oxide (CaO) sulfate (CaSO ) required, either in the dihydrate (CaSO ·
4 4
analysis is used to determine the amount of CaO and calculate 2H O) or hemihydrate (CaSO · ⁄2 H O) form. This procedure
2 4 2
the amount of calcium carbonate (CaCO ) in gypsum and assumes that an insignificant amount of sulfate other than
gypsum products. calcium sulfate is present. This test method is used to deter-
mine compliance to the gypsum and gypsum product specifi-
12.2 Procedure:
cations. It is also commonly used in quality control work.
12.2.1 To the filtrate obtained as described in Section 11 add
5 g of ammonium oxalate ((NH ) C O ) dissolved in water. 14.3 Interference—This test method has been developed for
4 2 2 4
Digest hot for 30 min, making sure that the solution is always natural gypsum and for impurities generally found associated
with natural gypsum. Synthetic gypsum will sometimes have
alkaline with NH OH. Filter, wash, and ignite the precipitate at
1000 °C for 2 h to constant weight in a platinum crucible in a an additional number of interfering elements and compounds,
and if so, this procedure will not give accurate results. This test
muffle furnace.
method has a number of interferences that theoretically affect
12.2.2 Alternative Method—To the filtrate obtained as de-
the results. Co-precipitation and occlusion are problems if the
scribed in Section 11, add 5 g of (NH ) C O dissolved in
4 2 2 4
solution is either too acidic or too basic. Calculations using
water. Digest hot for 30 min, making sure that the solution is
SO analysis are most accurate on samples that are known to be
always alkaline with NH OH. Filter and wash, transfer the
4 3
completely hydrated or completely dehydrated.
precipitate to a beaker, and wash the filter paper with hot
H SO (1 + 6), catching the washing in the same beaker. Heat
2 4
14.4 Procedure:
gently to complete solution, adding more H SO if necessary.
2 4
14.4.1 Having properly selected and prepared the samples
While still warm, titrate with potassium permanganate
as specified in Section 4, weigh a representative specimen of
(KMnO ) solution (5.6339 g/L) until the pink color persists.
approximately 0.5 g, to the nearest 0.0001 g.
12.3 Calculation—The number of milliliters of KMnO
14.4.2 Place the weighed sample into a 400 mL beaker. Add
solution used gives directly the percentage of lime in the dried
50 mL of HCl (1 + 5). Boil and disperse with the flattened end
sample. Calculate the CaO to the percentage of sample as
of a glass rod while stirring until the sample is completely
received or the dried sample as required.
broken down. Add approximately 100 mL boiling water and
continue boiling for 15 min, with this step to be extended as
12.4 Precision and Bias—Neither the precision nor the bias
required, so the combined boiling time is not less than 1 h.
for the calcium oxide analysis has been determined.
14.4.3 Using filter paper, filter into a clean 600 mL flask and
rinse the 400 mL beaker thoroughly with hot distilled water.
13. Magnesium Oxide
Carefully wash the sides of the 400 mL beaker while wiping
13.1 Significance and Use—The magnesium oxide (MgO)
the insides with a rubber-tipped glass rod making sure all
analysis is used to determine the amount of MgO and calculate
splatters and insoluble are washed into the filter paper. Dry and
the amount of magnesium carbonate MgCO in gypsum and
burn off the filter paper leaving the residue to be dried and
gypsum products.
weighed for insoluble matter, if this test method is not
otherwise.
13.2 Procedure—To the filtrate obtained as described in
12.2.1 or 12.2.2, add enough water to give a total volume of
14.4.4 Dilute the filtrate to 400 mL to 500 mL. Add one to
approximately 600 mL. Cool, and add 10 mL of NH OH and two drops of 0.1 % methyl red indicator. Prepare a 400 mL to
5 g of sodium ammonium phosphate (NaNH HPO ) dissolved
500 mL sample of 0.05 to 0.1 N HCl. Add one to two drops of
4 4
in water. Stir vigorously until a precipitate begins to form. Let
0.1 % methyl red indicator. Compare the color of this solution
stand overnight. Filter, using a Gooch crucible, and wash with
to the color of the filtrate. Dilute the filtrate or add HCl (1 + 5)
NH NO solution. Ignite at 1000 °C for 2 h to constant weight
solution as necessary to match the pH of the 0.05 to 0.1 N HCl
4 3
in a muffle furnace.
solution.
14.4.5 Boil the filtrate solution and add 20 mL of near-
13.3 Calculation—Multiply this weight by 0.36207 to find
boiling 10 % barium chloride solution, preferably with the help
the weight of magnesium oxide (MgO). Calculate the MgO to
of a pipette, drop by drop while stirring. The barium chloride
the percentage of sample as received or to the dried sample as
solution should be prepared not less than one day before use.
required.
Continue boiling the solution for 10 min to 15 min and digest
13.4 Precision and Bias—Neither the precision nor the bias
hot for 3 h or until the precipitate settles.
for the magnesium oxide analysis has been determined.
14.4.6 Filter and wash with approximately 125 mL to
150 mL of hot water to render the precipitate chloride free. Test
14. Sulfur Trioxide
the filtrate for chloride by collecting a small amount and adding
14.1 Summary of Test Method—In this test method, sulfate a few drops of 0.1 N AgNO solution. A white precipitate
is precipitated from an acid solution of the gypsum with barium indicates more washing is needed. Alternately, use filtering
C471M − 24
crucibles for quick filtering if the particular crucibles to be used sample to give the net titration. A 1 mL net titration is
are tested prior to use by refiltering the filtrate from the equivalent to 0.002923 g of sodium chloride (NaCl). Calculate
crucibles with filter paper, and no more than 2 mg is collected the NaCl as a percentage of the sample as received or the dried
on the filter paper. sample as required.
14.4.7 Ignite the precipitate and paper in a tared crucible,
15.4 Precision and Bias—Neither the precision nor the bias
and slowly char the paper without inflaming. Burn off all the
for the chloride analysis has been determined.
carbon and ignite in a muffle furnace at 800 °C to 900 °C or
using bright red heat over a Bunsen burner for 15 min to 20
16. Report
min. Dry the filtering crucibles by placing in a cold muffle
16.1 Report the results obtained in the analysis as follows:
furnace during warm-up or in a drying oven prior to igniting in
a muffle furnace at 800 °C to 900 °C for 15 min to 20 min.
%
Free water .
NOTE 3—Thoroughly cleans crucibles before each use and heat in a
Combined water .
furnace at 800 °C to 900 °C and cool in a desiccator before taring.
Carbon dioxide (CO ) .
14.4.8 Cool all crucibles in a desiccator and weigh to the
Silicon dioxide (SiO ) and insoluble matter .
Iron and aluminum oxides (Fe O + Al O ) .
nearest 0.0001 g. 2 3 2 3
Lime (CaO) .
14.5 Calculation—Multiply the weight of the precipitate by
Magnesium oxide (MgO) .
Sulfur trioxide (SO ) .
0.343 to determine the weight of sulfur trioxide (SO ). Calcu-
Sodium chloride (NaCl) .
late the SO to the percentage of sample as received or to the
3 Total 100.00 ±
dried sample as required.
14.6 Precision and Bias—Neither the precision nor the bias
NOTE 4—Since it is frequently advisable to recalculate the results
obtained in the chemical analysis in order that they may be more
for the sulfur trioxide analysis has been determined.
enlightening, the following is submitted for consideration:
15. Chlorides (1) Multiply the percentage of combined water by 4.778 to obtain
purity or percentage gypsum. To calculate the percentage of CaSO · ⁄2
15.1 Significance and Use—Small amounts of chlorides in
H O in plasters, multiply the percentage of gypsum by 0.8430.
gypsum or gypsum products often have a detrimental effect on
(2) Multiply the percentage of combined water by 2.222 to obtain the
their use. This procedure is used to measure the amount of amount of SO combined as gypsum.
(3) Subtract the result obtained in (2) from the total SO found by
chlorides present and report it as sodium chloride. 3
analysis to obtain the excess SO .
15.2 Procedure:
(4) Multiply the excess SO by 1.700 to obtain the percentage
anhydrite, CaSO .
15.2.1 Weigh approximately 20.0 g of sample as prepared in
(5) Multiply the percentage of gypsum found in (1) by 0.3257 to obtain
Section 4 to 0.001 g and transfer to a 400 mL beaker. Add
the percentage of CaO combined as gypsum.
150 mL of water, stir, and heat to just below the boiling point.
(6) Multiply the percentage of anhydrite found in (4) by 0.4119 to
Cover with a watch glass and maintain at just below boiling
obtain the percentage of CaO combined as anhydrite.
(not less than 80 °C) for 1 h with occasional stirring. Filter with
(7) Add (5) and (6) together. Then subtract this result from the total
CaO percentage found by analysis.
suction on a Buchner funnel fitted with a medium filter paper.
(8) Multiply the excess CaO percentage by 1.785 to obtain the
Wash the residue with four 20 mL portions of hot water.
percentage of calcium carbonate.
15.2.2 Add two drops of phenolphthalein indicator solution
(9) Multiply the percentage of MgO by 2.091 to obtain the percentage
to the filtrate. If the filtrate fails to turn pink, add 0.1 N NaOH
of magnesium carbonate.
solution dropwise with stirring until a faint pink color devel-
NOTE 5—Having made the calculations in Note 4, the results may be
ops. Add 0.1 N HNO dropwise until the pink color just
reported as follows:
disappears.
%
15.2.3 If the chloride content is very low, transfer the entire
Gypsum (CaSO ·2H O) .
4 2
filtrate quantitatively to a 400 mL beaker and proceed as
Anhydrite (CaSO natural and manufactured) (Note 4) .
Silicon dioxide and insoluble (SiO + Ins.) .
described in 15.2.4. If larger amounts of chloride are expected, 2
Iron and aluminum oxide (R O ) .
2 3
transfer the filtrate quantitatively to a 250 mL volumetric flask,
Calcium carbonate (CaCO ) .
cool to room temperature, and dilute to 250 mL. Take a suitable
Magnesium carbonate (MgCO ) .
Magnesium oxide (MgO) .
aliquot, transfer to a 400 mL beaker, and dilute to a volume of
Sulfur trioxide (SO ) .
100 mL to 250 mL.
Sodium chloride (NaCl) .
15.2.4 Place the beaker containing the sample on a white
Total 100.00 ±
surface, add 0.5 mL (ten drops) of K CrO solution and titrate
2 4
with AgNO solution using a micro buret having a 10 mL
NOTE 6—The presence of the different forms of CaSO may be
capacity and graduated in divisions of 0.02 mL. Titrate until a
determined by a microscopic examination. A paper titled “Gypsum
faint but definite orange color is visible. Analysis with the Polarizing Microscope” containing suggested methods
can be found in ASTM STP 861.
15.2.5 Perform a blank titration using the same volume of
water as the sample volume and the same amount of K CrO
2 4
solution. Titrate to the same color as obtained with the sample.
Green, George W., “Gypsum Analysis with the Polarizing Microscope,” The
15.3 Calculation—Subtract the volume of AgNO solution
3 Chemistry and Technology of Gypsum, ASTM STP 861, ASTM International, 1984,
used for the blank titration from the volume used for the pp. 22–47.
C471M − 24
17. Alternative Procedure for Analysis of Free Water in 17.5.1.1 Repeatability (r)—The difference between repeti-
Gypsum Using Moisture Balance tive results obtained by the same operator in a given laboratory
applying the same test method with the same apparatus under
17.1 Significance and Use—The free water analysis deter-
constant operating conditions on identical test material within
mines the amount of free water contained in the sample as
short intervals of time would in the long run, in the normal and
opposed to chemically combined water, and prepares the
correct operation of the test method, exceed the following
sample for further analysis.
values only in one case in 20.
17.2 Equipment—A programmable moisture balance, ca-
(1) Repeatability can be interpreted as maximum difference
pable of temperature control of 61 °C to at least 200 °C. The
between two results, obtained under repeatability conditions,
moisture balance must be capable of measuring a minimum of
that is accepted as plausible due to random causes under
0.01 % loss in weight and be able to bring the temperature of
normal and correct operation of the test method.
an empty tray from ambient conditions up to 200 °C.
(2) Repeatability limits are listed in Table 3.
17.2.1 Equipment Setup—Implement a test program for
17.5.1.2 Reproducibility (R)—The difference between two
“free water” that takes a sample of 5 g to 8 g from an initial
single and independent results obtained by different operators
temperature to 45 °C at the maximum rate of temperature rise
applying the same test method in different laboratories using
and holds the temperature at 45 °C for up to two hours. The
different apparatus on identical test material would, in the long
initial temperature shall be defined as a temperature of 20 °C to
run, in the normal and correct operation of the test method,
30 °C.
exceed the following values only in one case in 20.
17.3 Procedure:
(1) Reproducibility can be interpreted as maximum differ-
17.3.1 Prior to beginning the test, both the moisture balance
ence between two results, obtained under reproducibility
and sample temperature must be less than 30 °C. Note that
conditions, that is accepted as plausible due to random causes
some phases of gypsum are metastable in humidity and as
under normal and correct operation of the test method.
such, samples should be stored to minimize changes due to
(2) Reproducibility limits are listed in Table 3.
environmental conditions.
17.5.1.3 The above terms (repeatabi
...

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.
´1
Designation: C471M − 20a C471M − 24
Standard Test Methods for
Chemical Analysis of Gypsum and Gypsum Products
(Metric)
This standard is issued under the fixed designation C471M; 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.
ε NOTE—The title of Table 2 was editorially corrected in May 2021.
1. Scope
1.1 These test methods cover the chemical analysis of gypsum and gypsum panel products, including gypsum ready-mixed plaster,
gypsum wood-fibered plaster, and gypsum concrete.
1.2 These test methods appear in the following order:
Sections
Preparation of Sample 4
Complete Procedure 5 – 16
Alternative Procedure for Analysis of Free Water in 17
Gypsum Using a Moisture Balance
Alternative Procedure for Analysis of Combined Water in 18
Gypsum Using a Moisture Balance
Alternative Procedure for Analysis of Organic Material 19
Alternative Procedure for Analysis of Organic Material 20
and Carbon Dioxide in Gypsum by High Temperature
Weight Loss
Alternative Procedure for Analysis for Calcium Sulfate by 20
Alternative Procedure for Analysis for Calcium Sulfate by 21
Ammonium Acetate Method
Alternative Procedure for Analysis for Sodium Chloride by 21
Alternative Procedure for Analysis for Sodium Chloride by 22
the Coulometric Method
Determination of Sand in Set Plaster 22
Determination of Sand in Set Plaster 23
Wood-fiber Content in Wood-fiber Gypsum Plaster 23
Wood-fiber Content in Wood-fiber Gypsum Plaster 24
Optional Procedure for Analysis for Sodium by the Atomic 24
Optional Procedure for Analysis for Sodium by the Atomic 25
Absorption Method
Optional Procedure for Analysis for Sodium by Flame 25
Optional Procedure for Analysis for Sodium by Flame 26
Photometry
Determination of Orthorhombic Cyclooctasulfur (S ) in 26
Determination of Orthorhombic Cyclooctasulfur (S ) in 27
Ggypsum Panel Products—General Provisions
Determination of Orthorhombic Cyclooctasulfur (S ) in 27
Determination of Orthorhombic Cyclooctasulfur (S ) in 28
Gypsum Panel Products by Gas Chromatograph
Equipped with a Mass Spectrometer (GS/MS)
These test methods are under the jurisdiction of ASTM Committee C11 on Gypsum and Related Building Materials and Systems and are the direct responsibility of
Subcommittee C11.01 on Specifications and Test Methods for Gypsum Products.
Current edition approved Dec. 1, 2020April 1, 2024. Published January 2021April 2024. Originally approved in 1961. Last previous edition approved in 2020 as
ɛ1
C471M – 20.C471M – 20a . DOI: 10.1520/C0471M-20AE01.10.1520/C0471M-24.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C471M − 24
Determination of Orthorhombic Cyclooctasulfur (S ) in 28
Determination of Orthorhombic Cyclooctasulfur (S ) in 29
Gypsum Panel Products by Gas Chromatograph
Equipped with an Electron Capture Detector (GC/ECD)
Determination of Orthorhombic Cyclooctasulfur (S ) in 29
Determination of Orthorhombic Cyclooctasulfur (S ) in 30
Gypsum Panel Products by High-performance Liquid
Chromatograph Equipped with and Ultraviolet Detector
(HPLC ⁄UV)
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in these test methods.
1.4 These text of this test method references notes and footnotes that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered as requirements of the standard.
1.5 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.
1.6 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:
C11 Terminology Relating to Gypsum and Related Building Materials and Systems
C22/C22M Specification for Gypsum
C28/C28M Specification for Gypsum Plasters
C59 Specification for Gypsum Casting Plaster and Gypsum Molding Plaster
C61 Specification for Gypsum Keene’s Cement
C317/C317M Specification for Gypsum Concrete
C778 Specification for Standard Sand
C842 Specification for Application of Interior Gypsum Plaster
D1193 Specification for Reagent Water
D1428 Test Method for Test for Sodium and Potassium In Water and Water-Formed Deposits by Flame Photometry (Withdrawn
1989)
D2013 Practice for Preparing Coal Samples for Analysis
E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in these test methods, refer to Terminology C11.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 calibration standard, n—a chemical mixture containing a known quantity of the analyte used to relate the measured
analytical signal to the concentration of the analyte.
3.2.2 dried sample, n—a sample devoid of free water.
3.2.3 internal standard, n—a chemical used in the quantification of S by monitoring and adjusting for minor variances in
instrument performance.
3.2.4 riffle, n—a hand feed sample divider device that divides the sample into parts of approximately the same weight. (D2013)
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.
The last approved version of this historical standard is referenced on www.astm.org.
C471M − 24
3.2.5 sample as received, n—a representative portion of raw gypsum or gypsum product in the state received by the testing
laboratory, including aggregates, impurities, and water content.
3.2.6 surrogate standard, n—a chemical used to account for extraction efficiency of S .
4. Preparation of Sample
4.1 General Procedures—Details of sample preparation will vary according to the type of material being tested.
4.1.1 Sample as Received—Use a sufficient amount of sample such that, after sieving, not less than 50 g of sample will remain
for testing. Weigh the entire sample immediately after opening the container in which the material was received. This will become
the weight of the sample as received.
4.1.2 Drying—Dry the sample in accordance with Section 7. This will be the weight of the dried sample.
4.1.3 Crushing and Grinding—Crush and grind the sample by hand with a mortar and pestle or by mechanical crushing and
grinding equipment to pass a 250 μm (No. 60) sieve. Take care, particularly with mechanical equipment, not to expose the sample
to temperatures of more than 52 °C. Clean the equipment thoroughly between samples. Thoroughly remix the ground sample and
store it in an airtight container to avoid contamination.
4.1.4 Rehydrating—Thoroughly blend and rehydrate samples which contain calcium sulfate in forms other than CaSO · 2H O and
4 2
natural anhydrite. Place the sample in distilled water and keep it wet for not less than 48 h. Dry the hydrated sample in an oven
at 4545 °C 6 3 °C to constant weight and recrush or grind it in accordance with 4.1.3.
4.1.5 Sample Reduction—Thoroughly mix and reduce large samples as required by quartering or by the use of a riffle to obtain
a specimen of approximately 50 g.
4.2 Gypsum (Specification C22/C22M)—Gypsum samples will be received in the form of rocks or powder, or both. If necessary
crush and reduce the entire dried sample in accordance with 4.1.3 and 4.1.5.
4.3 Gypsum Plaster (Specification C28/C28M):
4.3.1 Gypsum Ready-mixed Plaster or Gypsum Wood-fibered Plaster—Screen the dried sample through a 150 μm (No. 100) sieve
(see Note 1) and discard the residue retained on the sieve. Reweigh the remaining sample and calculate the percentage of the dried
sample. Reduce the sample in accordance with 4.1.5. Thoroughly blend and rehydrate the specimen in accordance with 4.1.4.
NOTE 1—Detailed requirements for this sieve are given in Specification E11.
4.3.2 Gypsum Neat Plaster or Gypsum Gauging Plaster—Reduce the dried sample in accordance with 4.1.5. Thoroughly blend
and rehydrate the specimen in accordance with 4.1.4.
4.4 Gypsum Casting and Molding Plaster (Specification C59)—Reduce the dried sample in accordance with 4.1.5. Thoroughly
blend and rehydrate the specimen in accordance with 4.1.4.
4.5 Gypsum Keene’s Cement (Specification C61)—Reduce the dried sample in accordance with 4.1.5. Blend in no more than 1 %
molding plaster or K SO and rehydrate the specimen in accordance with 4.1.4.
2 4
4.6 Gypsum Concrete (Specification C317/C317M)—Screen the dried sample through a 150 μm (No. 100) sieve (see Note 1) and
discard the residue retained on the sieve. Reweigh the remaining sample and calculate the percentage of the dried sample. Reduce
the sample in accordance with 4.1.5. Thoroughly blend and rehydrate the specimen in accordance with 4.1.4.
4.7 Gypsum Panel Products—Cut or break the dried sample into small pieces. Using a mortar and pestle, strike the pieces of the
C471M − 24
sample to loosen the paper face. Remove the pieces of paper by hand as they are separated from the core of the gypsum board.
Carefully scrape any remaining powder from the paper. When all the paper has been removed from the pieces of the sample, reduce
the sample in accordance with 4.1.5.
COMPLETE PROCEDURE
5. Apparatus
5.1 Analytical Balance—Capable of weighing the weighing bottles, lids, and samples.
5.2 Balance—Capable of weighing not less than 100 g at a precision of 0.001 g.
5.3 Drying Oven—A mechanical convection oven set at 4545 °C 6 3 °C.
5.4 Desiccator—Capable of being tightly sealed and containing calcium chloride or equivalent desiccant.
5.5 Calcining Oven or Furnace—Capable of achieving and maintaining temperatures to not less than 1000 °C.
5.6 Weighing Bottles—Borosilicate glass or ceramic containers with tightly sealable lids.
5.7 Hot Plate—A controllable hot plate capable of heating casseroles to approximately 120 °C.
5.8 Porcelain Casseroles—With a capacity of 50 to 100 mL.50 mL to 100 mL.
5.9 Filtering Funnels.
5.10 Filter Paper.
5.11 Porcelain Crucibles.
5.12 Mortar and Pestle.
5.13 Mechanical Jaw Crusher—Capable of crushing gypsum rocks up to 50 mm diameter.
5.14 Mechanical Grinder—Burr mill or equivalent capable of grinding the granular output of the jaw crusher specified in 5.13.
6. Reagents
6.1 Purity of Reagents—Use reagent grade chemicals in all tests. Unless otherwise indicated, use reagents that conform to the
specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are
available. If it is necessary to use other grades, first ascertain that the reagent is of sufficiently high purity so that its use will not
lessen the accuracy of the determination.
6.1.1 Ammonium Chloride (NH Cl).
6.1.2 Ammonium Hydroxide (sp gr 0.90)—Concentrated ammonium hydroxide (NH OH).
6.1.3 Ammonium Nitrate (25 g/L)—Dissolve 25 g of ammonium nitrate (NH NO ) in water and dilute to 1 L.
4 3
Reagent Chemicals, American Chemical Society Specifications,ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, 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. Pharmacopeial Convention, Inc. (USPC),
Rockville, MD.
C471M − 24
6.1.4 Ammonium Oxalate ((NH ) C O ).
4 2 2 4
6.1.5 Barium Chloride (100 g/L)—Dissolve 100 g of barium chloride (BaCl ·2H O) in water and dilute to 1 L.
2 2
6.1.6 Calcium Chloride (CaCl )—Anhydrous Calcium Chloride with a combined water of not more than 5 %.
6.1.7 Hydrochloric Acid (sp gr 1.19)—Concentrated hydrochloric acid (HCl).
6.1.8 Hydrochloric Acid (1 + 4)—Mix one volume of HCl (sp gr 1.19) with four volumes of water.
6.1.9 Hydrochloric Acid (1 + 5)—Mix one volume of HCl (sp gr 1.19) with five volumes of water.
6.1.10 Nitric Acid (sp gr 1.42)—Concentrated nitric acid (HNO ).
6.1.11 Potassium Chromate Solution (100 g/L)—Dissolve 5 g of potassium chromate (K CrO ) in 50 mL of water, mix, add ten
2 4
drops of 0.05 N silver nitrate (AgNO ) solution, allow to stand for 5 min, and filter.
6.1.12 Potassium Permanganate (5.6339 g/L)—Dissolve 5.6339 g of potassium permanganate (KMnO ) in water and dilute to 1
L.
6.1.13 Silver Nitrate, Standard Solution (0.05 N)—Prepare and standardize a 0.05 N silver nitrate (AgNO ) solution.
6.1.14 Sodium Ammonium Phosphate—(NaNH HPO ).
4 4
6.1.15 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid (H SO ).
2 4
6.1.16 Sulfuric Acid (1 + 6)—Carefully mix one volume of H SO (sp gr 1.84) with six volumes of water.
2 4
6.1.17 Nitric Acid (0.1 N)—Mix 1.4 mL of HNO (sp gr 1.42) with 200 mL of water.
6.1.18 Phenolphthalein Indicator Solution—Dissolve 0.25 g of phenolphthalein in 30 mL of methanol and dilute to 50 mL with
water.
6.1.19 Sodium Hydroxide Solution (0.1 N)—Dissolve 1 g of sodium hydroxide (NaOH) in 250 mL of water.
6.1.20 Water—Reagent water shall be in accordance with Specification D1193, type II. Specification D1193 gives the following
values for type II grade water.
Electrical conductivity, max, μS/cm at 298 K (25-C) 1.0
Electrical resistivity, min, MΩ·cm at 298 K (25-C) 1.0
Total organic carbon (TOC), max, μg/L 50.0
Sodium, max, μg/L 5.0
Chlorides max, μg/L 5.0
Total silica, max, μg/L 5.0
7. Free Water
7.1 Significance and Use—The free water analysis determines the amount of free water contained in the sample as opposed to
chemically combined water, and prepares the sample for further analysis.
7.2 Procedure:
7.2.1 Weigh a sample of the material as received of not less than 50 g to a precision of 0.001 g and spread it out in a thin layer
in a suitable vessel. Place in an oven and dry at 4545 °C 6 3 °C until constant mass has been obtained. The samples are to be
cooled in a desiccator prior to each weighing. The loss of weight corresponds to the free water.
7.2.2 Retain the sample in a sealed container or in the desiccator for further analysis.
C471M − 24
7.3 Calculation and Report—Calculate and report loss in weight as a percentage of the sample as received or of the dried sample
as required.
7.4 Precision and Bias:
7.4.1 The precision of this test method is based on an interlaboratory study of Test Methods C471M in 2020. Each of ten volunteer
laboratories analyzed two different gypsum sample types. Every “test result” represents an individual determination, and all
participants reported five test results per material. Practice E691 was followed for the design and analysis of the data; the details
are given in ASTM Research Report No. C11-2000.
7.4.1.1 Repeatability (r)—The difference between repetitive results obtained by the same operator in a given laboratory applying
the same test method with the same apparatus under constant operating conditions on identical test material within short intervals
of time would in the long run, in the normal and correct operation of the test method, exceed the following values only in one case
in 20.
(1) Repeatability can be interpreted as maximum difference between two results, obtained under repeatability conditions, that
is accepted as plausible due to random causes under normal and correct operation of the test method.
(2) Repeatability limits are listed in Table 1.
7.4.1.2 Reproducibility (R)—The difference between two single and independent results obtained by different operators applying
the same test method in different laboratories using different apparatus on identical test material would, in the long run, in the
normal and correct operation of the test method, exceed the following values only in one case in 20.
(1) Reproducibility can be interpreted as maximum difference between two results, obtained under reproducibility conditions,
that is accepted as plausible due to random causes under normal and correct operation of the test method.
(2) Reproducibility limits are listed in Table 1.
7.4.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.
7.4.1.4 Any judgment in accordance with statements 7.4.1.1 and 7.4.1.2 would have an approximate 95 % probability of being
correct.
7.4.2 Bias—At the time of the study, there was no accepted reference material suitable for determining the bias for this test method,
therefore no statement on bias is being made.
7.4.3 The precision statement was determined through statistical examination of 278 results, from ten participating laboratories,
on two types of gypsum materials.
7.4.4 To judge the equivalency of two test results, it is recommended to choose the material closest in characteristics to the test
material.
8. Combined Water
8.1 Significance and Use—The combined water analysis determines the percent of chemically combined water and is used to
calculate the purity of gypsum or the amount of gypsum or gypsum plaster in gypsum products.
TABLE 1 Free Water (in Accordance With Section 7)
Repeatability Reproducibility
Number of Repeatability Reproducibility
A
Average Standard Standard
Material Laboratories Limit Limit
Deviation Deviation
n x¯ s s r R
r R
Natural Gypsum 10 1.906 0.287 0.287 0.803 0.803
Flue Gas Desulphogypsum (FGD) 10 9.909 0.281 0.514 0.786 1.440
A
The average of the laboratories’ calculated averages.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:C11-2000. Contact ASTM Customer
Service at [e-mail].
C471M − 24
8.2 Interferences—Some materials, such as organic and hydrated compounds that decompose within the same temperature range
as gypsum, will cause high results. When the maximum temperature is exceeded, some carbonates undergo decomposition, which
will result in high results.
8.3 Procedure:
8.3.1 For each sample, place three weighing bottles with lids in the preheated calcining oven or furnace and heat for 2 h at
215215 °C to 230 °C. Place in the desiccator and allow to cool to room temperature. Weigh the bottles and lids to the nearest 0.0001
g and record the tare weights.
8.3.2 Weigh out three specimens of approximately 5 g each of the sample as prepared in Section 4 and dried in Section 7 to a
precision of 0.0001 g in the previously tared weighing bottles and record the total weight with lids.
8.3.3 Place the specimens in the calcining oven with the lids placed loosely on each bottle or crucible for 2 h or until constant
weight has been obtained.
8.3.4 Place the lids tightly on the weighing bottles, remove from the oven, and place in the desiccator to cool to room temperature.
8.3.5 Weigh each specimen to a precision of 0.0001 g and record the weights.
8.3.6 Retain the residues for carbon dioxide analysis.
8.4 Calculation and Report—Calculate and report the average loss in weight of the three specimens as a percentage of the sample
as received or of the dried sample, as required, to the nearest 0.001 g and record the tare weights.
8.5 Precision and Bias:
8.5.1 The precision of this test method is based on an interlaboratory study of Test Methods C471M in 2020. Each of ten volunteer
laboratories analyzed two different gypsum sample types. Every “test result” represents an individual determination, and all
participants reported five test results per material. Practice E691 was followed for the design and analysis of the data; the details
are given in ASTM Research Report No. C11-2000.
8.5.1.1 Repeatability (r)—The difference between repetitive results obtained by the same operator in a given laboratory applying
the same test method with the same apparatus under constant operating conditions on identical test material within short intervals
of time would in the long run, in the normal and correct operation of the test method, exceed the following values only in one case
in 20.
(1) Repeatability can be interpreted as maximum difference between two results, obtained under repeatability conditions, that
is accepted as plausible due to random causes under normal and correct operation of the test method.
(2) Repeatability limits are listed in Table 2.
8.5.1.2 Reproducibility (R)—The difference between two single and independent results obtained by different operators applying
the same test method in different laboratories using different apparatus on identical test material would, in the long run, in the
normal and correct operation of the test method, exceed the following values only in one case in 20.
(1) Reproducibility can be interpreted as maximum difference between two results, obtained under reproducibility conditions,
that is accepted as plausible due to random causes under normal and correct operation of the test method.
(2) Reproducibility limits are listed in Table 2.
†
TABLE 2 Combined Water (in Accordance with Section 8)
Number Repeatability Reproducibility
Repeatability Reproducibility
A
of Average Standard Standard
Material Limit Limit
Laboratories Deviation Deviation
n x¯ s s r R
r R
Natural Gypsum 9 19.291 0.129 0.129 0.363 0.363
Flue Gas Desulphogypsum (FGD) 9 19.364 0.195 0.279 0.547 0.782
† Editorially corrected.
A
The average of the laboratories’ calculated averages.
C471M − 24
8.5.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.
8.5.1.4 Any judgment in accordance with statements 8.5.1.1 and 8.5.1.2 would have an approximate 95 % probability of being
correct.
8.5.2 Bias—At the time of the study, there was no accepted reference material suitable for determining the bias for this test method,
therefore no statement on bias is being made.
8.5.3 The precision statement was determined through statistical examination of 278 results, from ten participating laboratories,
on two types of gypsum materials.
8.5.4 To judge the equivalency of two test results, it is recommended to choose the material closest in characteristics to the test
material.
9. Carbon Dioxide
9.1 Summary of Test Method—The sample is decomposed with HCl and the liberated CO is passed through a series of scrubbers
to remove water and sulfides. The CO is absorbed with Ascarite, a special sodium hydroxide absorbent, and the gain in weight
of the absorption tube is determined and calculated as percent CO .
9.2 Significance and Use—The carbon dioxide analysis is useful in estimating carbonates and organic carbon for chemical balance.
9.3 Special Reagents:
9.3.1 Magnesium Perchlorate Desiccant—For drying.
9.3.2 Sodium Hydroxide Absorbent—A coarse sodium hydroxide coated silica.
9.4 Special Apparatus—The apparatus illustrated in Fig. 1 consists of the following:
9.4.1 Purifying Jar A, Fleming, containing sulfuric acid.
9.4.2 Drying Tube B, U-shaped with side arms and glass-stoppers. Side arms are shaped to hold rubber tubing. Contains
Anhydrone on left side and Ascarite on right side.
9.4.3 Erlenmeyer Flask C, 250 mL, 24/20 ground-glass joint.
9.4.4 Separatory Funnel D, with ground glass stopper and interchangeable hollow ground-glass joint. A delivery tube bent at the
end extends into the sample flask approximately 15 mm from the bottom and is used to introduce acid into flask.
9.4.5 Condenser E.
FIG. 1 Apparatus for Carbon Dioxide Analysis
C471M − 24
9.4.6 Gas-washing Bottle F, 250 mL, with fitted disk containing distilled water to retain most of the acid volatilized from the
alkalimeter.
9.4.7 U-Tube G, containing mossy zinc to remove the last traces of HCl.
9.4.8 Gas-washing Bottle H, 250 mL, with fritted disk, containing concentrated H SO and trap I, to remove any SO mist that
2 4 3
is carried over.
9.4.9 Absorption Bulb J, containing Anhydrone to remove last traces of water vapor.
9.4.10 CO Absorption Bulb, containing Ascarite filled as follows: On the bottom of the bulb, place a layer of glass wool extending
above the bottom outlet and on top of this a layer of Anhydrone approximately 10 mm thick; immediately above this place another
layer of glass wool, then add Ascarite to almost fill the bulb. Place a top layer of Anhydrone approximately 10 mm thick on top
of the Ascarite and top it off with a covering of glass wool.
9.4.11 U-guard Tube L, filled with Anhydrone in left side and Ascarite in right side.
9.4.12 Purifying Jar M, Fleming, containing H SO .
2 4
9.5 Procedure:
9.5.1 After drying as described in Section 8 place the residue obtained in the 250 mL Erlenmeyer flask (C). Connect the flask to
the apparatus as shown in Fig. 1. Purge the system free of carbon dioxide by passing a current of CO -free air through the apparatus
for 1010 min to 15 min.
9.5.2 Weigh the absorption bulb to 0.0001 g and attach it to the train. Remove the glass stopper from the separatory funnel, place
50 mL of dilute HCl (1 + 1) in the separatory funnel (D), and replace the stopper with the interchangeable hollow ground-glass
joint through which passes a tube for admitting purified air. Open the stopcock of the separatory funnel and admit air through the
top of the funnel to force the hydrochloric acid into the Erlenmeyer flask (C).
9.5.3 Start cold water circulating through the condenser (E) and, with CO -free air passing at a moderate rate through the
absorption train, place a small hot plate or gas burner under the sample flask and boil for approximately 2 min. Remove the hot
plate and continue the flow of purified air at approximately three bubbles per second for 10 min to sweep the apparatus free of
CO . Close the absorption bulb, disconnect it from the train and weigh, opening the stopper momentarily to equalize the pressure.
Use a second absorption bulb as counterpoise in all weighings unless a single pan balance is used.
9.6 Calculation—Calculate the percent CO to the dried sample as follows:
%CO 5 A 2 B /C ×100 12 D (1)
~~ ! !~ !
where:
A = mass of absorption bulb + CO g,
B = mass of absorption bulb before the run, g,
C = mass of specimen, g, and
D = percent combined water as determined in Section 8 as a decimal.
Calculate the percent CO to the sample as received as follows:
%CO 5 E~12F! (2)
where:
E = result of Eq 1, and
F = percent free water as determined in Section 7 as a decimal.
9.7 Precision and Bias—Neither the precision nor the bias for the carbon dioxide analysis has been determined.
C471M − 24
10. Silicon Dioxide and Other Acid Insoluble Matter
10.1 Summary of Test Method—The gypsum and other acid soluble components of the sample are dissolved in dilute hydrochloric
acid (HCl). The residue is weighed and calculated as silicon dioxide and other acid insoluble matter.
10.2 Significance and Use—The silicon dioxide and other acid insoluble matter analysis determines and is used to report the
percentage of one of the inert impurities in gypsum and gypsum products.
10.3 Procedure—Perform in triplicate.
10.3.1 Weigh approximately 1 g of the specimen prepared in Section 4 to the nearest 0.0001 g.
10.3.2 Place the specimen in a porcelain casserole. Add approximately 50 mL of 1 + 5 hydrochloric acid. Evaporate slowly and
carefully to apparent dryness on a hot plate. Take not less than 20 min to do the evaporation. Make a blank determination with
one casserole in parallel. Cool to room temperature.
10.3.3 Add enough hydrochloric acid (sp gr 1.19) to wet the solid residue. Add 20 mL of water, boil and filter through filter paper.
Wash the filter paper thoroughly using not less than 100 mL of room temperature water to render the precipitate chloride free. The
most effective washing technique is to use many small quantities of wash water rather than fill the funnel to the brim two or three
times. Test the filtrate for chloride by collecting a small amount and adding a few drops of 0.1 normal silver nitrate (AgNO )
solution. A white precipitate indicates more washing is needed. Discard this test solution.
10.3.4 Place all the filtrate back in the same casserole. Evaporate to dryness and heat to 120 °C for 1 h and cool. To the cooled
casserole add enough HCl (sp gr 1.19) to wet the solid residue. Add 50 mL of water and boil.
10.3.5 Wash the second contents of the casserole through another filter paper. Thoroughly wash the residue in the filter paper until
chloride free as in 10.3.3. Retain the filtrate for the iron and aluminum oxide analysis.
10.3.6 Dry sufficient crucibles by placing in a cold muffle furnace during warm up or by placing in a drying oven for 1515 min
to 20 min, then placing in a 900 °C muffle furnace. Cool crucibles to room temperature in a desiccator.
10.3.7 Transfer both filter papers to a tared crucible and char slowly without flaming. Burn off all the carbon and ignite in a muffle
furnace at 900 °C for 15 min.
10.3.8 Cool the crucibles in a desiccator and weigh to the nearest 0.0001 g.
10.4 Calculation and Report—Calculate the average weight of the three precipitates and report as silicon dioxide (SiO ) and other
insoluble matter to the percentage of sample as received or to the dried sample as required.
10.5 Precision and Bias—Neither the precision nor the bias for the silicon dioxide and other acid insoluble matter has been
determined.
11. Iron and Aluminum Oxides
11.1 Significance and Use—The iron and aluminum oxides (Fe O + Al O ) analysis is used to determine the quantity of these
2 3 2 3
metal oxides in gypsum or gypsum products.
11.2 Procedure—To the filtrate, obtained as described in Section 10, add a few drops of nitric acid (HNO ), and boil to ensure
oxidation of the iron. Add 2 g of ammonium chloride (NH Cl) previously dissolved in water. Make alkaline with ammonium
hydroxide (NH OH). Digest hot for a few minutes until the precipitate coagulates. Filter, wash, ignite the precipitate at 1000 °C
for 30 min or to constant weight in a muffle furnace and weigh as Fe O + Al O . Save the filtrate for the CaO analysis.
2 3 2 3
NOTE 2—The addition of a pinch of ashless filter paper pulp will aid in the filtration of the precipitate.
11.3 Calculation—Calculate Fe O + Al O to the percentage of sample as received or the dried sample as required. This
2 3 2 3
precipitate may be further treated to separate the two oxides, but this is generally unnecessary.
C471M − 24
11.4 Precision and Bias—Neither the precision nor the bias for the iron and aluminum oxides analysis has been determined.
12. Calcium Oxide
12.1 Significance and Use—The calcium oxide (CaO) analysis is used to determine the amount of CaO and calculate the amount
of calcium carbonate (CaCO ) in gypsum and gypsum products.
12.2 Procedure:
12.2.1 To the filtrate obtained as described in Section 11 add 5 g of ammonium oxalate ((NH ) C O ) dissolved in water. Digest
4 2 2 4
hot for 30 min, making sure that the solution is always alkaline with NH OH. Filter, wash, and ignite the precipitate at 1000 °C
for 2 h to constant weight in a platinum crucible in a muffle furnace.
12.2.2 Alternative Method—To the filtrate obtained as described in Section 11, add 5 g of (NH ) C O dissolved in water. Digest
4 2 2 4
hot for 30 min, making sure that the solution is always alkaline with NH OH. Filter and wash, transfer the precipitate to a beaker,
and wash the filter paper with hot H SO (1 + 6), catching the washing in the same beaker. Heat gently to complete solution, adding
2 4
more H SO if necessary. While still warm, titrate with potassium permanganate (KMnO ) solution (5.6339 g/L) until the pink
2 4 4
color persists.
12.3 Calculation—The number of milliliters of KMnO solution used gives directly the percentage of lime in the dried sample.
Calculate the CaO to the percentage of sample as received or the dried sample as required.
12.4 Precision and Bias—Neither the precision nor the bias for the calcium oxide analysis has been determined.
13. Magnesium Oxide
13.1 Significance and Use—The magnesium oxide (MgO) analysis is used to determine the amount of MgO and calculate the
amount of magnesium carbonate MgCO in gypsum and gypsum products.
13.2 Procedure—To the filtrate obtained as described in 12.2.1 or 12.2.2, add enough water to give a total volume of
approximately 600 mL. Cool, and add 10 mL of NH OH and 5 g of sodium ammonium phosphate (NaNH HPO ) dissolved in
4 4 4
water. Stir vigorously until a precipitate begins to form. Let stand overnight. Filter, using a Gooch crucible, and wash with NH NO
4 3
solution. Ignite at 1000 °C for 2 h to constant weight in a muffle furnace.
13.3 Calculation—Multiply this weight by 0.36207 to find the weight of magnesium oxide (MgO). Calculate the MgO to the
percentage of sample as received or to the dried sample as required.
13.4 Precision and Bias—Neither the precision nor the bias for the magnesium oxide analysis has been determined.
14. Sulfur Trioxide
14.1 Summary of Test Method—In this test method, sulfate is precipitated from an acid solution of the gypsum with barium
chloride (BaCl ). The precipitate is filtered and weighed as barium sulfate (BaSO ) and the sulfur trioxide (SO ) equivalent is
2 4 3
calculated.
14.2 Significance and Use—The specification for gypsum and some gypsum products specifies the amount of calcium sulfate
(CaSO ) required, either in the dihydrate (CaSO · 2H O) or hemihydrate (CaSO · ⁄2 H O) form. This procedure assumes that
4 4 2 4 2
an insignificant amount of sulfate other than calcium sulfate is present. This test method is used to determine compliance to the
gypsum and gypsum product specifications. It is also commonly used in quality control work.
14.3 Interference—This test method has been developed for natural gypsum and for impurities generally found associated with
natural gypsum. Synthetic gypsum will sometimes have an additional number of interfering elements and compounds, and if so,
this procedure will not give accurate results. This test method has a number of interferences that theoretically affect the results.
Co-precipitation and occlusion are problems if the solution is either too acidic or too basic. Calculations using SO analysis are
most accurate on samples that are known to be completely hydrated or completely dehydrated.
C471M − 24
14.4 Procedure:
14.4.1 Having properly selected and prepared the samples as specified in Section 4, weigh a representative specimen of
approximately 0.5 g, to the nearest 0.0001 g.
14.4.2 Place the weighed sample into a 400 mL beaker. Add 50 mL of HCl (1 + 5). Boil and disperse with the flattened end of
a glass rod while stirring until the sample is completely broken down. Add approximately 100 mL boiling water and continue
boiling for 15 min, with this step to be extended as required, so the combined boiling time is not less than 1 h.
14.4.3 Using filter paper, filter into a clean 600 mL flask and rinse the 400 mL beaker thoroughly with hot distilled water. Carefully
wash the sides of the 400 mL beaker while wiping the insides with a rubber-tipped glass rod making sure all splatters and insoluble
are washed into the filter paper. Dry and burn off the filter paper leaving the residue to be dried and weighed for insoluble matter,
if this test method is not otherwise .otherwise.
14.4.4 Dilute the filtrate to 400400 mL to 500 mL. Add one to two drops of 0.1 % methyl red indicator. Prepare a 400400 mL to
500 mL sample of 0.05 to 0.1 N HCl. Add one to two drops of 0.1 % methyl red indicator. Compare the color of this solution to
the color of the filtrate. Dilute the filtrate or add HCl (1 + 5) solution as necessary to match the pH of the 0.05 to 0.1 N HCl
solution.
14.4.5 Boil the filtrate solution and add 20 mL of near-boiling 10 % barium chloride solution, preferably with the help of a pipette,
drop by drop while stirring. The barium chloride solution should be prepared not less than one day before use. Continue boiling
the solution for 1010 min to 15 min and digest hot for 3 h or until the precipitate settles.
14.4.6 Filter and wash with approximately 125 to 150 mL 125 mL to 150 mL of hot water to render the precipitate chloride free.
Test the filtrate for chloride by collecting a small amount and adding a few drops of 0.1 N AgNO solution. A white precipitate
indicates more washing is needed. Alternately, use filtering crucibles for quick filtering if the particular crucibles to be used are
tested prior to use by refiltering the filtrate from the crucibles with filter paper, and no more than 2 mg is collected on the filter
paper.
14.4.7 Ignite the precipitate and paper in a tared crucible, and slowly char the paper without inflaming. Burn off all the carbon
and ignite in a muffle furnace at 800800 °C to 900 °C or using bright red heat over a Bunsen burner for 1515 min to 20 min. Dry
the filtering crucibles by placing in a cold muffle furnace during warm-up or in a drying oven prior to igniting in a muffle furnace
at 800800 °C to 900 °C for 1515 min to 20 min.
NOTE 3—Thoroughly cleans crucibles before each use and heat in a furnace at 800800 °C to 900 °C and cool in a desiccator before taring.
14.4.8 Cool all crucibles in a desiccator and weigh to the nearest 0.0001 g.
14.5 Calculation—Multiply the weight of the precipitate by 0.343 to determine the weight of sulfur trioxide (SO ). Calculate the
SO to the percentage of sample as received or to the dried sample as required.
14.6 Precision and Bias—Neither the precision nor the bias for the sulfur trioxide analysis has been determined.
15. Chlorides
15.1 Significance and Use—Small amounts of chlorides in gypsum or gypsum products often have a detrimental effect on their
use. This procedure is used to measure the amount of chlorides present and report it as sodium chloride.
15.2 Procedure:
15.2.1 Weigh approximately 20.0 g of sample as prepared in Section 4 to 0.001 g and transfer to a 400 mL beaker. Add 150 mL
of water, stir, and heat to just below the boiling point. Cover with a watch glass and maintain at just below boiling (not less than
80 °C) for 1 h with occasional stirring. Filter with suction on a Buchner funnel fitted with a medium filter paper. Wash the residue
with four 20 mL portions of hot water.
C471M − 24
15.2.2 Add two drops of phenolphthalein indicator solution to the filtrate. If the filtrate fails to turn pink, add 0.1 N NaOH solution
dropwise with stirring until a faint pink color develops. Add 0.1 N HNO dropwise until the pink color just disappears.
15.2.3 If the chloride content is very low, transfer the entire filtrate quantitatively to a 400 mL beaker and proceed as described
in 15.2.4. If larger amounts of chloride are expected, transfer the filtrate quantitatively to a 250 mL volumetric flask, cool to room
temperature, and dilute to 250 mL. Take a suitable aliquot, transfer to a 400 mL beaker, and dilute to a volume of 100100 mL to
250 mL.
15.2.4 Place the beaker containing the sample on a white surface, add 0.5 mL (ten drops) of K CrO solution and titrate with
2 4
AgNO solution using a micro buret having a 10 mL capacity and graduated in divisions of 0.02 mL. Titrate until a faint but definite
orange color is visible.
15.2.5 Perform a blank titration using the same volume of water as the sample volume and the same amount of K CrO solution.
2 4
Titrate to the same color as obtained with the sample.
15.3 Calculation—Subtract the volume of AgNO solution used for the blank titration from the volume used for the sample to give
the net titration. A 1 mL net titration is equivalent to 0.002923 g of sodium chloride (NaCl). Calculate the NaCl as a percentage
of the sample as received or the dried sample as required.
15.4 Precision and Bias—Neither the precision nor the bias for the chloride analysis has been determined.
16. Report
16.1 Report the results obtained in the analysis as follows:
%
Free water .
Combined water .
Carbon dioxide (CO ) .
Silicon dioxide (SiO ) and insoluble matter .
Iron and aluminum oxides (Fe O + Al O ) .
2 3 2 3
Lime (CaO) .
Magnesium oxide (MgO) .
Sulfur trioxide (SO ) .
Sodium chloride (NaCl) .
Total 100.00 ±
NOTE 4—Since it is frequently advisable to recalculate the results obtained in the chemical analysis in order that they may be more enlightening, the
following is submitted for consideration:
(1) Multiply the percentage of combined water by 4.778 to obtain purity or percentage gypsum. To calculate the percentage of CaSO · ⁄2 H O in
4 2
plasters, multiply the percentage of gypsum by 0.8430.
(2) Multiply the percentage of combined water by 2.222 to obtain the amount of SO combined as gypsum.
(3) Subtract the result obtained in (2) from the total SO found by analysis to obtain the excess SO .
3 3
(4) Multiply the excess SO by 1.700 to obtain the percentage anhydrite, CaSO .
3 4
(5) Multiply the percentage of gypsum found in (1) by 0.3257 to obtain the percentage of CaO combined as gypsum.
(6) Multiply the percentage of anhydrite found in (4) by 0.4119 to obtain the percentage of CaO combined as anhydrite.
(7) Add (5) and (6) together. Then subtract this result from the total CaO percentage found by analysis.
(8) Multiply the excess CaO percentage by 1.785 to obtain the percentage of calcium carbonate.
(9) Multiply the percentage of MgO by 2.091 to obtain the percentage of magnesium carbonate.
NOTE 5—Having made the calculations in Note 4, the results may be reported as follows:
%
Gypsum (CaSO ·2H O) .
4 2
Anhydrite (CaSO natural and manufactured) (Note 4) .
Silicon dioxide and insoluble (SiO + Ins.) .
Iron and aluminum oxide (R O ) .
2 3
Calcium carbonate (CaCO ) .
Magnesium carbonate (MgCO ) .
Magnesium oxide (MgO) .
Sulfur trioxide (SO ) .
Sodium chloride (NaCl) .
C471M − 24
Total 100.00 ±
NOTE 6—The presence of the different forms of CaSO may be determined by a microscopic examination. A paper titled “Gypsum Analysis with the
Polarizing Microscope” containing suggested methods can be found in ASTM STP 861.
17. Alternative Procedure for Analysis of Free Water in Gypsum Using Moisture Balance
17.1 Significance and Use—The free water analysis determines the amount of free water contained in the sample as opposed to
chemically combined water, and prepares the sample for further analysis.
17.2 Equipment—A programmable moisture balance, capable of temperature control of 61 °C to at least 200 °C. The moisture
balance must be capable of measuring a minimum of 0.01 % loss in weight and be able to bring the temperature of an empty tray
from ambient conditions up to 200 °C.
17.2.1 Equipment Setup—Implement a test program for “free water” that takes a sample of 55 g to 8 g from an initial temperature
to 45 °C at the maximum rate of temperature rise and holds the temperature at 45 °C for up to two hours. The initial temperature
shall be defined as a temperature of 2020 °C to 30 °C.
17.3 Procedure:
17.3.1 Prior to beginning the test, both the moisture balance and sample temperature must be less than 30 °C. Note that some
phases of gypsum are metastable in humidity and as such, samples should be stored to minimize changes due to environmental
conditions.
17.3.2 Weigh and evenly distribute 55 g to 8 g of a sample of the material as received in a clean tared pan in the moisture balance.
Run the described free water test program until a constant mass is reac
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