ISO 5068-1:2025
(Main)Brown coals and lignites — Determination of moisture — Part 1: Indirect gravimetric method for total moisture
Brown coals and lignites — Determination of moisture — Part 1: Indirect gravimetric method for total moisture
This document specifies two methods for determination of the total moisture of brown coals and lignites using an indirect gravimetric single-stage method and a two-stage method.
Charbons bruns et lignites — Détermination de l'humidité — Partie 1: Méthode gravimétrique indirecte pour l'humidité totale
General Information
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Standards Content (Sample)
International
Standard
ISO 5068-1
Second edition
Brown coals and lignites —
2025-05
Determination of moisture —
Part 1:
Indirect gravimetric method for
total moisture
Charbons bruns et lignites — Détermination de l'humidité —
Partie 1: Méthode gravimétrique indirecte pour l'humidité totale
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
4.1 Single-stage method .1
4.2 Two-stage method .1
5 Reagent . 2
6 Apparatus . 2
7 Sample . 4
7.1 General .4
7.2 Single-stage method .4
7.3 Two-stage method .4
8 Procedure . 5
8.1 Single-stage method .5
8.2 Two stage method .5
8.2.1 Air dry loss moisture .5
8.2.2 Residual moisture .5
9 Expression of results . 6
9.1 Single-stage method — Total moisture .6
9.2 Two-stage method .6
9.2.1 Air dry loss moisture .6
9.2.2 Residual moisture .6
9.2.3 Total moisture .7
10 Precision of method . 7
10.1 Repeatability .7
10.2 Reproducibility critical difference .7
11 Test report . 7
Annex A (informative) Nitrogen-purification train . 8
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 5, Methods
of analysis.
This second edition cancels and replaces the first edition (ISO 5068-1:2007), which has been technically
revised.
The main changes are as follows:
— referenced documents have been updated;
— terms and definitions have been updated;
— the test report has been updated.
A list of all parts in the ISO 5068 series can be found on the ISO website.
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
International Standard ISO 5068-1:2025(en)
Brown coals and lignites — Determination of moisture —
Part 1:
Indirect gravimetric method for total moisture
1 Scope
This document specifies two methods for determination of the total moisture of brown coals and lignites
using an indirect gravimetric single-stage method and a two-stage 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 1213-2, Coal and coke — Vocabulary — Part 2: Terms relating to sampling, testing and analysis
ISO 13909-4, Coal and coke — Mechanical sampling — Part 4: Preparation of test samples of coal
ISO 18283, Coal and coke — Manual sampling
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1213-2 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
4.1 Single-stage method
A sample, prepared using a closed mill, is dried to a constant mass at a temperature of 105 °C to 110 °C in an
atmosphere of nitrogen. The total moisture mass fraction is calculated from the loss in mass of the sample.
4.2 Two-stage method
At the first stage, the coarsely ground sample is dried either at ambient temperature or at a higher
temperature not exceeding 40 °C, to reach equilibrium with the surrounding atmosphere. At the second
stage, the sample dried in an air atmosphere (air-dry sample) is crushed and dried to a constant mass at
a temperature of 105 °C to 110 °C in an atmosphere of nitrogen. The total moisture is calculated from the
losses in mass during the two drying stages.
5 Reagent
5.1 Desiccant, fresh or freshly regenerated and preferably self-indicating.
Suitable desiccants are magnesium perchlorate and silica gel.
WARNING — Magnesium perchlorate is a strong oxidizing agent. Do no attempt to regenerate the
absorbent. Do not permit contact with organic materials or reducing agent.
5.2 Nitrogen, high-purity, dry with a maximum oxygen volume fraction of 30 µl/l.
NOTE Commercial nitrogen of this purity is available. See Annex A for details.
6 Apparatus
6.1 Oven, nitrogen-flushed, capable of being controlled by a temperature of 105 °C to 110 °C and with the
additional provision for passing a current of dry nitrogen through it at a flow rate about 15 times the oven
volume per hour.
Before using a new oven, carry out a temperature profile through the interior and take care to insert samples
only where the temperature is known to be 105 °C to 110 °C.
A suitable oven is illustrated in Figure 1.
Dimensions in millimetres
Key
1 nitrogen outlet
2 space for heating element
3 tube for temperature-measuring device
4 copper gauze, having apertures of nominal size 0,25 mm
5 nitrogen inlet
Figure 1 — Typical nitrogen oven
6.2 Drying cabinet, capable of being controlled at a temperature of 30 °C to 40 °C and with provision for
venting.
6.3 Tray, non-corrodible, of such dimensions that the loading of the sample layer does not exceed 1 g/cm .
6.4 Dish, a shallow dish of silica or glass, with ground edges and fitted with a ground-glass cover, or of a
non-corrodible, heat-resistant material with a well-fitting lid.
The diameter of the dish shall be such that the mass of coal layer does not exceed 0,25 g/cm for 10 g of
the sample.
6.5 Balances, sensitive to 0,01 g and to 0,001 g.
6.6 Flow meter, capable of measuring the rate of flow nitrogen through the oven.
6.7 Drying tower, 500 ml capacity, packed with magnesium perchlorate or silica gel for drying the
nitrogen.
6.8 Cooling vessel, for example, a desiccator without desiccant, containing a metal plate, preferably of
aluminium or copper.
The vessel may be provided with a means to pass nitrogen through it or with desiccant in it during the
cooling period.
7 Sample
7.1
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