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IS0
I N T ERN AT I O N A L O RG A N I ZAT I ON FOR STAN DARD I ZAT I O N
IS0 R ECO M M EN DATI O N
R 331
DETERMINATION OF MOISTURE
IN THE ANALYSIS SAMPLE OF COAL
BY THE DIRECT GRAVIMETRIC METHOD
1st EDITION
August 1 963
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by the national standards organization of that country, being
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For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 331, Determination of Moisture in the Analysis Sample of
Coal by the Direct Gravimetric Method, was drawn up by Technical Committee ISO/TC 27,
Solid Mineral Fuels, the Secretariat of which is held by the British Standards Institution (B.S.I.),
Work on this question by the Technical Committee began in 1950 and led, in 1957, to the
adoption of a Draft IS0 Recommendation.
In February 1958, this Draft IS0 Recommendation (No. 21 I) was circulated to all the IS0
Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial
nature, by the following Member Bodies:
Austria
Israel Romania
Bulgaria Italy Spain
Y
Burma Japan Turkey
Canada
Netherlands United Kingdom
Chile
New Zealand U.S.A.
Czechoslovakia
Poland U. S. S. R.
Denmark Portugal Yugoslavia
France Republic
Germany of South Africa
India
One Member Body opposed the approval of the Draft :
Belgium.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council,
which decided, in August 1963, to accept it as an IS0 RECOMMENDATION.
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ISO/R 331-1963 (E) I
IS0 Recommendation R 331 August 1963
DETERMINATION OF MOISTURE
IN THE ANALYSIS SAMPLE OF COAL
BY THE DIRECT GRAVIMETRIC METHOD
1. INTRODUCTION
Two direct methods are available for the determination of moisture in the analysis sample of coal:
(1) a gravimetric method, in which the moisture is determined in an atmosphere of nitrogen, and
(2) a volumetric method,* in which the moisture is determined by distillation.
This IS0 Recommendation describes the direct gravimetric method.
Since coal is hygroscopic, its moisture will vary with change of humidity of the atmosphere, and
the moisture in the analysis sample, therefore, should be determined whenever portions are weighed
out for other analytical determinations, e.g. volatile matter, calorific value, carbon and hydrogen etc.
If all the portions taken for analysis are weighed out on the same day and at about the same time,
and if the analyses are proceeded with without delay, one determination of moisture will suffice.
2. PRINCIPLE
Coal is heated at 105 to 110 "C in a stream of oxygen-free, dry nitrogen and the moisture driven
The increase in weight of the
off is collected in an absorption tube containing a desiccant.
absorption tube (after deducting the result of a separate blank determination) is due to moist-
ure in the coal (see Note below).
NOTE. - If suitable precautions are taken against re-absorption of moisture by the dried coal, the
loss in weight of the sample may be measured and compared with the gain in weight of the
absorption tube. This procedure is of advantage in discriminating between coals which are rich
in absorbed gases and those which are not.
Sa IS0 Recommendation R 348, Determination of Moisture in the Analysis Sample of Coal by the Direct Volumetric Method.
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I IÇO/R 331-1963 (E)
3. APPARATUS
The balance used should be sensitive to 0.1 mg.
3.1 Source of heat, such that a glass retort tube is maintained at a constant and uniform temper-
ature within the range 105 to 110 OC. A convenient source is e.g. an electrically heated and
thermostatically controlled aluminium block oven.
3.2 Drying tower, packed with a desiccant to dry the stream of nitrogen entering the retort tube.
3.3 Howmeters, capable of measuring a flow rate sufficient to maintain two atmosphere changes
per minute in the retort tube. If a pressure drop over a constriction is used as a means of
measuring flow rate, the manometer liquid should be a non-volatile oil.
3.4 Retort tubes. Glass retort tubes of about 50 ml capacity, having a suitable inlet for dry
nitrogen and an outlet for moisture-laden nitrogen, and capable of holding 1 g of the sample,
spread out in a uniform layer either in the retort tube itself or in a boat which is inserted
into the tube.
3.5 Boats (if employed), of non-oxidizable material, such as glass or glazed porcelain.
3.6 Absorption tubes, of a suitable design and able to contain sufficient desiccant to remove the
moisture completely from the nitrogen stream.
4. REAGENTS
4.1 Desiccant. A suitable desiccant is e.g. dry magnes-Jm perchlorate (see Note below). It is
important that the same desiccant be used in both the drying tower and the absorption tubes,
since the incoming nitrogen and the gas leaving the system should be dried to exactly the
same degree.
J
NOTE. - Attention is drawn to the care needed in handling magnesium perchlorate. When
exhausted, it should be washed down the sink with a current of water.
4.2 Nitrogen. With a maximum oxygen content of 30 parts per million (see Appendix, page 7).
5. PROCEDURE
Before commencing the determination, mix the air-dried sample of coal, crushed to pass a sieve
of 0.2 mm aperture, for at least one minute, preferably by mechanical means.
Adjust the flow rate of the nitrogen (4.2) passing through the drying tower and flowmeter so as to
give two atmosphere changes per minute through the retort tube. Connect an empty retort tube to a
closed absorption tube and to the
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