ISO 334:2020

INTERNATIONAL ISO
STANDARD 334
Fourth edition
2020-08
Coal and coke — Determination of
total sulfur — Eschka method
Charbon et coke — Dosage du soufre total — Méthode Eschka
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Preparation of test sample . 2
8 Procedure. 3
8.1 Test portion . 3
8.1.1 For coal . 3
8.1.2 For coke . . . 3
8.2 Charging the crucible . . 3
8.3 Ignition . 4
8.3.1 For coal . 4
8.3.2 For coke . . . 4
8.4 Recovering the residue . 4
8.5 Extraction . 4
8.6 Precipitation of barium sulfate . 4
8.7 Blank testing . 5
9 Expression of results . 5
10 Precision . 6
10.1 Repeatability limit . 6
10.2 Reproducibility limit . 6
11 Test report . 6
Annex A (informative) Derivation of factors used in the calculation in Clause 9 .7
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5,
Methods of analysis.
This fourth edition cancels and replaces the third edition (ISO 334:2013), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— updating of referenced documents;
— amending of Introduction;
— adding of the provision of terms and definitions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

Introduction
The objective of this document is to provide a reference method for determining the total sulfur content
in coal and coke with Eschka method.
Instrumental methods for a more rapid determination of total sulfur are now available. If such a method
is to be used, it is important to demonstrate that the method is free from bias, when compared to this
reference method, and will give levels of repeatability and reproducibility which are the same as, or
better than, those quoted for the reference method (see Clause 10).
INTERNATIONAL STANDARD ISO 334:2020(E)
Coal and coke — Determination of total sulfur — Eschka
method
1 Scope
This document specifies a reference method for determining the total sulfur content of hard coal, brown
coals and lignites, and coke by the Eschka method.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample
ISO 1170, Coal and coke — Calculation of analyses to different bases
ISO 5068-2, Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric
method for moisture in the analysis sample
ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test
sample by drying in nitrogen
ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples
ISO 18283, Hard coal and coke — Manual sampling
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Principle
A test portion is ignited in intimate contact with the Eschka mixture in an oxidizing atmosphere at
800 °C to remove combustible matter and to convert the sulfur to sulfate. This is then extracted with
hydrochloric acid solution and determined gravimetrically by precipitation with barium chloride.
5 Reagents
WARNING — Care should be exercised when handling the reagents, many of which are toxic and
corrosive.
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
distilled water or water of equivalent purity.
5.1 Eschka mixture.
Mix two parts by mass of light calcined magnesium oxide with one part by mass of anhydrous sodium (or
potassium) carbonate. The mixture shall entirely pass a test sieve of 212 μm nominal size of openings.
5.2 Hydrochloric acid.
Concentrated ρ approximately 1,18 g/ml, mass fraction approximately 36 %.
5.3 Potassium sulfate solution.
Weigh, to the nearest 0,1 mg, about 2 g of potassium sulfate, previously dried at a temperature of 105 °C
to 110 °C. Dissolve in water and dilute to 1 l.
5.4 Barium chloride, approximately 85 g/l solution.
Dissolve 100 g of barium chloride dihydrate in water and dilute to 1 l. Filter before use through a close-
textured, doubly acid-washed filter paper or filter-paper pad.
5.5 Methyl red indicator solution.
Dissolve 1 g of 2-(4-dimethylaminophenylazo) benzoic acid sodium salt (methyl red) in 1 l of water.
5.6 Ammonia, concentrated solution, mass fraction not less than 25 %.
5.7 Silver nitrate, 17 g/l solution.
Dissolve 17 g of silver nitrate in water and dilute to 1 l. Store in a dark, glass bottle.
6 Apparatus
6.1 Analytical balance, capable of weighing to the nearest 0,1 mg.
6.2 Graduated glassware, conforming to the requirements for class A in the international standards
prepared by ISO/TC 48.
6.3 Electrically heated muffle furnace, capable of being maintained at a temperature of
800 °C ± 25 °C. The ventilation through the muffle furnace shall be such as to give about five air changes
per minute.
6.4 Crucible, of platinum, silica, or glazed porcelain, of capacity approximately 25 ml.
6.5 Flat plate, 6 mm thick, of silica (or other suitable refractory material) which fits easily into the
muffle furnace (6.3).
6.6 Gooch crucible, of glazed porcelain or sintered glass.
6.7 Air oven, capable of being maintained at a temperature of 130 °C ± 10 °C.
7 Preparation of test sample
The sample shall be the general analysis test sample, prepared to a nominal top size of 212 μm by the
preparation procedures specified in ISO 13909-4 or ISO 18283.
2 © ISO 2020 – All rights reserved

The sample should be brought in moisture equilibrium with the laboratory atmosphere by exposure
in a thin layer on a tray. Exposure time shall be kept to a minimum (this is particularly important for
brown coals and lignites).
The sample shall be thoroughly mixed for at least 1 min immediately before analysis, preferably by
mechanical means.
If the results are to be calculated other than on an "air-dried" basis (see Clause 9), then, after weighing
the test portion (see 8.1), determine the moisture content using a further portion of the test sample by
th
...

INTERNATIONAL ISO
STANDARD 334
Fourth edition
2020-08
Coal and coke — Determination of
total sulfur — Eschka method
Charbon et coke — Dosage du soufre total — Méthode Eschka
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents . 1
6 Apparatus . 2
7 Preparation of test sample . 2
8 Procedure. 3
8.1 Test portion . 3
8.1.1 For coal . 3
8.1.2 For coke . . . 3
8.2 Charging the crucible . . 3
8.3 Ignition . 4
8.3.1 For coal . 4
8.3.2 For coke . . . 4
8.4 Recovering the residue . 4
8.5 Extraction . 4
8.6 Precipitation of barium sulfate . 4
8.7 Blank testing . 5
9 Expression of results . 5
10 Precision . 6
10.1 Repeatability limit . 6
10.2 Reproducibility limit . 6
11 Test report . 6
Annex A (informative) Derivation of factors used in the calculation in Clause 9 .7
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5,
Methods of analysis.
This fourth edition cancels and replaces the third edition (ISO 334:2013), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— updating of referenced documents;
— amending of Introduction;
— adding of the provision of terms and definitions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

Introduction
The objective of this document is to provide a reference method for determining the total sulfur content
in coal and coke with Eschka method.
Instrumental methods for a more rapid determination of total sulfur are now available. If such a method
is to be used, it is important to demonstrate that the method is free from bias, when compared to this
reference method, and will give levels of repeatability and reproducibility which are the same as, or
better than, those quoted for the reference method (see Clause 10).
INTERNATIONAL STANDARD ISO 334:2020(E)
Coal and coke — Determination of total sulfur — Eschka
method
1 Scope
This document specifies a reference method for determining the total sulfur content of hard coal, brown
coals and lignites, and coke by the Eschka method.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample
ISO 1170, Coal and coke — Calculation of analyses to different bases
ISO 5068-2, Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric
method for moisture in the analysis sample
ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test
sample by drying in nitrogen
ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples
ISO 18283, Hard coal and coke — Manual sampling
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Principle
A test portion is ignited in intimate contact with the Eschka mixture in an oxidizing atmosphere at
800 °C to remove combustible matter and to convert the sulfur to sulfate. This is then extracted with
hydrochloric acid solution and determined gravimetrically by precipitation with barium chloride.
5 Reagents
WARNING — Care should be exercised when handling the reagents, many of which are toxic and
corrosive.
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
distilled water or water of equivalent purity.
5.1 Eschka mixture.
Mix two parts by mass of light calcined magnesium oxide with one part by mass of anhydrous sodium (or
potassium) carbonate. The mixture shall entirely pass a test sieve of 212 μm nominal size of openings.
5.2 Hydrochloric acid.
Concentrated ρ approximately 1,18 g/ml, mass fraction approximately 36 %.
5.3 Potassium sulfate solution.
Weigh, to the nearest 0,1 mg, about 2 g of potassium sulfate, previously dried at a temperature of 105 °C
to 110 °C. Dissolve in water and dilute to 1 l.
5.4 Barium chloride, approximately 85 g/l solution.
Dissolve 100 g of barium chloride dihydrate in water and dilute to 1 l. Filter before use through a close-
textured, doubly acid-washed filter paper or filter-paper pad.
5.5 Methyl red indicator solution.
Dissolve 1 g of 2-(4-dimethylaminophenylazo) benzoic acid sodium salt (methyl red) in 1 l of water.
5.6 Ammonia, concentrated solution, mass fraction not less than 25 %.
5.7 Silver nitrate, 17 g/l solution.
Dissolve 17 g of silver nitrate in water and dilute to 1 l. Store in a dark, glass bottle.
6 Apparatus
6.1 Analytical balance, capable of weighing to the nearest 0,1 mg.
6.2 Graduated glassware, conforming to the requirements for class A in the international standards
prepared by ISO/TC 48.
6.3 Electrically heated muffle furnace, capable of being maintained at a temperature of
800 °C ± 25 °C. The ventilation through the muffle furnace shall be such as to give about five air changes
per minute.
6.4 Crucible, of platinum, silica, or glazed porcelain, of capacity approximately 25 ml.
6.5 Flat plate, 6 mm thick, of silica (or other suitable refractory material) which fits easily into the
muffle furnace (6.3).
6.6 Gooch crucible, of glazed porcelain or sintered glass.
6.7 Air oven, capable of being maintained at a temperature of 130 °C ± 10 °C.
7 Preparation of test sample
The sample shall be the general analysis test sample, prepared to a nominal top size of 212 μm by the
preparation procedures specified in ISO 13909-4 or ISO 18283.
2 © ISO 2020 – All rights reserved

The sample should be brought in moisture equilibrium with the laboratory atmosphere by exposure
in a thin layer on a tray. Exposure time shall be kept to a minimum (this is particularly important for
brown coals and lignites).
The sample shall be thoroughly mixed for at least 1 min immediately before analysis, preferably by
mechanical means.
If the results are to be calculated other than on an "air-dried" basis (see Clause 9), then, after weighing
the test portion (see 8.1), determine the moisture content using a further portion of the test sample by
th
...