ISO 418:2001

INTERNATIONAL ISO
STANDARD 418
Third edition
2001-12-15
Photography — Processing chemicals —
Specifications for anhydrous sodium sulfite
Photographie — Produits chimiques de traitement — Spécifications
relatives au sulfite de sodium anhydre

Reference number
©
ISO 2001
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ii © ISO 2001 – All rights reserved

Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references.1
3 General.1
3.1 Physical properties.1
3.2 Hazardous properties.1
3.3 Storage.1
4 Requirements.2
5 Reagents and glassware.2
6 Sampling.2
7 Test methods .2
7.1 Assay .2
7.2 Mass fraction of insoluble matter (as a precipitate of calcium, magnesium and ammonium
hydroxides) .5
7.3 Mass fraction of heavy metals .5
7.4 Mass fraction of iron .5
7.5 Alkalinity (as Na CO ).5
2 3
7.6 Reaction to ammoniacal silver nitrate.6
7.7 Mass fraction of thiosulfate (as Na S O ).6
2 2 3
7.8 Appearance of solution.7
Table 1 — Summary of requirements .2

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 418 was prepared by Technical Committee ISO/TC 42, Photography.
This third edition cancels and replaces the second edition (ISO 418:1994), of which it constitutes a technical
revision.
iv © ISO 2001 – All rights reserved

Introduction
This International Standard is one of a series that establishes criteria of purity for chemicals used in processing
photographic materials. General test methods and procedures cited in this International Standard are compiled in
ISO 10349-1.
This International Standard is intended for use by individuals with a working knowledge of analytical techniques,
which may not always be the case. Some of the procedures utilize caustic, toxic, or otherwise hazardous
chemicals. Safe laboratory practice for the handling of chemicals requires the use of safety glasses or goggles and,
in some cases, other protective apparel such as rubber gloves, face masks or aprons. Normal precautions for the
safe performance of any chemical procedure shall be exercised at all times, but specific details have been
provided for hazardous materials. Hazard warnings designated by a letter enclosed in angle brackets, 〈 〉 , are used
as a reminder in those steps detailing handling operations and are defined in ISO 10349-1. More detailed
information regarding hazards, handling and use of these chemicals may be available from the manufacturer.
This International Standard provides chemical and physical requirements for the suitability of a photographic-grade
chemical. The tests correlate with undesirable photographic effects. Purity requirements are set as low as possible
consistent with these photographic effects. These criteria are considered to be the minimum requirements
necessary to assure sufficient purity for use in photographic processing solutions, except that if the purity of a
commonly available grade of chemical exceeds photographic processing requirements and if there is no economic
penalty in its use, the purity requirements have been set to take advantage of the availability of the higher-quality
material.
Every effort has been made to keep the number of requirements to a minimum. Inert impurities are limited to
amounts that will not unduly reduce the assay. All tests are performed on samples “as received” to reflect the
condition of materials furnished for use. Although the ultimate criterion for suitability of such a chemical is its
successful performance in an appropriate use test, the shorter, more economical test methods described in this
International Standard are generally adequate.
Assay procedures have been included in all cases where a satisfactory method is available. An effective assay
requirement serves not only as a safeguard of chemical purity, but also as a valuable complement to the identity
test. Identity tests have been included whenever a possibility exists that another chemical or mixture of chemicals
could pass the other tests.
All requirements listed in clause 4 are mandatory. The physical appearance of the material and any footnotes are
for general information only and are not part of the requirements.
Efforts have been made to employ tests that are capable of being run in any normally equipped laboratory and,
whenever possible, to avoid tests that require highly specialized equipment or techniques. Instrumental methods
have been specified only as alternative methods or alone in those cases where no other satisfactory method is
available.
Over the past few years, great improvements have been made in instrumentation for various analyses. Where such
techniques have equivalent or greater precision, they may be used in place of the tests described in this
International Standard. Correlation of such alternative procedures with the given method is the responsibility of the
user. In case of disagreement in results, the method called for in the specification shall prevail. Where a
requirement states “to pass test”, however, alternative methods shall not be used.

INTERNATIONAL STANDARD ISO 418:2001(E)

Photography — Processing chemicals — Specifications for
anhydrous sodium sulfite
1 Scope
This International Standard establishes criteria for the purity of photographic-grade anhydrous sodium sulfite and
specifies the tests to be used to determine the purity.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 10349-1:1992, Photography — Photographic-grade chemicals — Test methods — Part 1: General.
ISO 10349-3:1992, Photography — Photographic-grade chemicals — Test methods — Part 3: Determination of
matter insol
...