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IS0
1 N T E RN AT I O N A L ORGAN I Z AT I ON FOR STAND AR D lZATl O N
IS0 RECOMMENDATION
R 334
DETERMINATION OF TOTAL SULPHUR IN COAL
BY THE ESCHKA METHOD
1st EDITION
August 1963
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
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 Recommandation R 334, Determination of Total Sulphur in Coal by the Eschka
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 May 1958, this Draft IS0 Recommendation (No. 237) was circulated to all the IS0
Member Bodies for enquiry. It was approved by the following Member Bodies:
Austria Greece Portugal
Belgium India Romania
Burma Italy Spain
Chile Japan Turkey
Czechoslovakia Mexico United Kingdom
Denmark Netherlands U.S.S.R.
Germany New Zealand Yugoslavia
Two Member Bodies opposed the approval of the Draft:
Canada, France.
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 334 - 1963 (E)
IS0 Recommendation R 334 August 1963
DETERMINATION OF TOTAL SULPHUR IN COAL
BY THE ESCHKA METHOD
1. PRINCIPLE
The sample of coal is ignited in intimate contact with Eschka mixture in an oxidizing atmosphere,
to remove combustible matter and to convert the sulphur to sulphate. This is then extracted
and determined by one of the two following methods:
(I) Gravimetric method, by precipitation with barium chloride;
(2) Titrimetric method, by precipitation with barium chromate, followed by iodometric
determination of the chromate passing into solution.
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2. SIZE OF SAMPLE
The mass of the sample required varies according to the sulphur content of the coal and the
method chosen for determining the sulphate.
Range of total sulphur content
I
_____~~ _______~~
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Sample mass
I Gravimetric method Titrimetric method
I
grammes per cent per cent
I I
1 0.1 to 5 0.6 to 2.5
5 to 10 1.2 to 5
0.5
0.25 10 to 20 2.4 to 10
-
o. 1 5 to 25
3. APPARATUS
All graduated apparatus should be of the best analytical quality obtainable and the balance used
should be sensitive to 0.1 mg.
3.1 For both methods
3.1.1 Electrically * heated mufle furnace, with a zone of substantially uniform temperature
at 800 & 25 "C and a ventilation rate of about 5 air changes per minute (see Note 1,
page 12).
3.1.2 Crucibles of platinum or glazed porcelain, of approximately 25 ml capacity.
* Although an electrically heated muffle furnace is recommended, a gas-heated furnace may be used, if precautions are taken to prevent
contamination by sulphur that may be present in the combustion gases.
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iSO/ R 334 - 1963 (E)
3.2 For gravimetric method
3.2.1
Insulating plate, 6 mm thick, of silica or other suitable material, which fits easily in the
muffle.
3.2.2 Crucibles of fused silica or platinum, or Gooch crucibles of glazed porcelain.
4. REAGENTS
All reagents should be of analytical reagent quality, and distilled water should be used throughout.
4.1 For both methods
4.1.1 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 should
entirely pass a test sieve of 0.2 mm aperture.
4.1.2 Hydrochloric acid, relative density d 1.18.
4.1.3 Standard sulphate solution. Dissolve 0.6000 g of potassium sulphate in water and
dilute to 1000 ml.
10 ml of this solution corresponds to:
0.0080 g of barium sulphate or
1.033 ml of 0.1 N sodium thiosulphate solution.
4.2 For gravimetric method
4.2.1 Barium chloride solution, 8.5 per cent (mass/volume). Dissolve 100 g of barium
chloride dihydrate in water and dilute to 1 litre. Filter the solution through a fine-
textured double acid-washed paper.
4.2.2 Methyl red indicator solution. Dissolve 1 g of o-carboxybenzene-azo-dimethyl aniline
(methyl red) in 600 ml of ethanol or industrial spirit and dilute to 1 litre with water.
4.3 For gravimetric acid-extraction method
4.3.1 Ammonia solution, relative density d 0.88, or the nearest obtainable.
4.4 For gravimetric aqueous-extraction method and titrimetric method
4.4.1 Hydrogen peroxide, 30 per cent (mass/volume) (cclOO volumes”).
4.5 For titrimetric method
4.5.1 Potassium iodide.
4.5.2
Sodium hydroxide solution, 8 per cent (mass/volume). Dissolve 80 g of sodium hydro-
xide in water and dilute to 1 litre.
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ISO/R 334 - 1963 (E)
Barium chromate solution, 3 per cent (mass/volume). To 30 g of barium chromate
4.5.3
add 100 ml of water and 100 ml of perchloric acid (relative density d 1.54) and warm
until solution is complete. Dilute the solution to 1 litre and filter into a storage
bottle through a fine-textured, double acid-washed filter paper or a filter paper pad.
Store overnight before using.
The solution prepared from commercially available barium chromate should be tested
for suitability. This is done by using it to carry out duplicate determinations, by the
method described under section 5, “Procedure”, on accurately weighed portions of
between 0.13 g and 0.14 g of potassium sulphate. If the mean of the results, expressed
as a percentage of the amount of sulphur taken, is less than 99.5 or greater than 100.5,
the barium chromate should be rejected.
A satisfactory solution may be prepared by the following method: dissolve 28.92 g of
barium chloride dihydrate in 500 ml of water. Dissolve 23.00 g of potassium chromate
in 500 ml of water. Heat both solutions almost to boiling point and add the barium
chloride solution slowly to the potassium chromate solution, stirring during the addi-
tion. Boil for 5 minutes, filter by suction through a fine-textured, double acid-washed
filter paper supported in a Buchner funnel and wash with hot distilled water until the last
20 ml of the washings give no more than a faint trace of opalescence with silver nitrate
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solution.
Wash the precipitate by means of a jet of water into a 2 litre beaker, add 200 ml of
distilled water and 100 ml of perchloric acid (relative density d 1.54) and warm until
solution is complete. Dilute the solution to 1 litre with water and filter into a storage
bottle through a fine-textured, double acid-washed filter paper or a filter paper pad.
4.5.4 Sodium acetate solution, 13.6 per cent (mass/volume). Dissolve either 136 g of
anhydrous sodium acetate or 225 g of the trihydrate in water and dilute to 1 litre.
4.5.5 Sodium acetate solution, 0.9 per cent (mass/volume). Dissolve either 9 g of anhydrous
sodium acetate or 15 g of the trihydrate in water and dilute to 1 litre.
Diluted ammonia solution. Dilute the ammonia solution (4.3. I) (relative density
4.5.6
d 0.88) with an equal volume of water; dilute other strengths appropriately. Store
this solution over calcium oxide to remove carbonate.
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Sodium thiosulphate solution, approximately 0.1 N. Dissolve 25 g of sodium thio-
4.5.7
sulphate pentahydrate in freshly boiled water, add l ml of chloroform and dilute to
1000 ml with water. Standardize this solution beforeuse against 0.1 N potassium iodate
in the presence of a trace of potassium iodide.
4.5.8 Mixed indicator solution
SOLUTION A. Dissolve 0.125 g of o-carboxybenzene-azo-dimethyl aniline (methyl red)
in 60 ml of ethanol or industrial spirit and dilute to 100 ml with water.
SOLUTION B. Dissolve 0.083 g of 3 :7 bisdimethylaminophenothiazinium chloride
(methylene blue) in 100 ml of ethanol or industrial spirit. Store in a dark glass bottle.
Mix equal volumes of solution A and solution B. Do not use the mixed solution
after more than one week.
4.5.9 Phenol red indicator solution. Grind 1 g of phenol-sulphonphthalein (phenol red) with
28.4 ml of 0.4 per cent sodium hydroxide solution and dilute to 1 litre.
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IÇO/R 334 - 1!363 (E)
4.5.10 Starch indicator solution, 1 per cent (mass/volume). Suspend 1 g of soluble starch
in 5 ml of water and add the suspension rapidly to 90 ml of boiling water. Boil for
1 minute and cool. Prepare fresh daily.
5. PROCEDURE
5.1 Preparation of Solution
Before commencing the determination, mix the air-dried sample of coal, ground to pass
a sieve of 0.2 nim aperture, for at least 1 minute, preferably by mechanical means.
Cover the bottom of the 25 ml crucible uniformly with 0.5 g of the Eschka mixture (4.1.1).
Weigh accurately 1 g, 0.5 g, 0.25 g or 0.1 g of the sample (according to the expected sulphur
content and the method of determination) and mix it intimately with 2.5 g of the Eschka
mixture (4.1.1) in a suitable vessel. Transfer the mixture to the 25 ml crucible; level the
contents by tapping the crucible gently on the bench and cover the contents uniformly with
1.0 g of the Eschka mixture (4.1.1) (see Note 2, page 12).
Place the charged crucible (and any others up to the limit of the muffle capacity) in the cold
furnace and raise the temperature to 800 f 25 "C in about 1 hour, maintaining this tem-
perature for a further 1% hours. Withdraw the crucible (or crucibles) and allow to cool
(see Note 3, page 12).
Transfer the ignited mixture from the crucible to a 400 ml beaker containing 25 to
30 ml of water. If unburnt particles are present, the determination should be rejected.
Wash out the crucible thoroughly with hot water, using about 50 ml, and add the washings
to the contents of the beaker.
The determination may be completed by either of the procedures described under clauses
5.2 and 5.3.
5.2 Gravimetric method
Extract the sulphate in the residue by either of the two methods below:
Acid extraction, see clause 5.2.1
Aqueous extraction, see clause 5.2.2.
Acid extraction. Place a cover glass on the beaker and then carefully add sufficient
5.2.1
of the hydrochloric acid (4.1.2)- 17 ml will normally be required-to dissolve the solid
matter, warming the contents of the beak
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