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IS0
I N T ERN AT1 O N A L O RG A N IZ AT I O N FOR STAN DARD I ZATl O N
IS0 RECOMMENDATION
R 333
DETERMINATION OF NITROGEN IN COAL
BY THE SEMI-MICRO KJELDAHL METHOD
1st EDITION
August 1963
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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 Recommendation R 333, Determination of Nitrogen in Coal by the Semi-niicro
Kjeldahl 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 1951 and led, in 1957, to the
adoption of a Draft IS0 Recommendation.
In April 1958, this Draft 1SO Recommendation (No. 223) was circulated to all the IS0
Member Bodies for enquiry. It was approved by the following Member Bodies:
Austria Germany Portugal
Belgium
India Republic of South Africa
Burma Italy
Romania
Canada Japan Spain
Chile Mexico Turkey
Czechoslovakia Netherlands United Kingdom
Denmark New Zealand U.S.S.R.
France Poland Yugoslavia
No Member Body opposed the approval of the Draft.
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 333 - 1963 (E)
IS0 Recommendation R 333 August 1963
DETERMINATION OF NITROGEN IN COAL
BY THE SEMI-MICRO KJELDAHL METHOD
1. PRINCIPLE
Coal (see Note below) is heated with concentrated sulphuric acid in the presence of a mixed
catalyst to convert the nitrogen into ammonium sulphate, from which the ammonia, released by
steam distillation from alkaline solution, is absorbed in boric acid and determined by titration
with sulphuric acid.
NOTE.- In bituminous coals and anthracite, the nitrogen is fairly uniformly distributed, even
when the seam is banded; in some lignites the nitrogen varies in the different bands of the seam,
and sampling difficulties make it undesirable to employ a semi-micro method using only a 0.1 g
sample, so that the Kjeldahl method using a 1 g sample should be used for such banded lignites.
2. APPARATUS
All volumetric apparatus should be of the best analytical quality obtainable, and the balance used
should be sensitive to 0.1 mg.
2.1 Digestion flask. A flask of borosilicate glass, of bulb capacity 50 ml, preferably pistol-
shaped, with a light borosilicate blown-glass bulb which is a loose fit in the neck of the
flask, to prevent loss of acid.
2.2 Distillation apparatus. A suitable water steam distillation apparatus of borosilicate glass,
fitted with a splash head to arrest the passage of any entrained sodium hydroxide from the
distillation flask (see Fig. 1, page 4).
2.3 Receiver. A wide-necked, flat-bottomed conical flask, of 100 ml capacity.
2.4 Burette, of 25 ml capacity.
2.5 Heating arrangement, to heat simultaneously one or more flasks inclined at about 35" from
the vertical. A suitable arrangement is illustrated in Figure 2 and in the Table, page 6.
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ISO/R 333 - 1963 (E)
FIG. 1. - Suitable distillation apparatus
Splash head
Condenser
1- outlet
apparatus
Condenser
1- inlet
Drain plug
100 rnl conical flask 2-
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ISO/R 333 - 1963 (E)
3. REAGENTS
All reagents should be of analytical reagent quality, and distilled water should be used throughout.
3.1 Mixed catalyst, containing by mass -
32 parts of anhydrous potassium sulphate,
1 part of selenium powder, and
5 parts of mercuric sulphate.
Grind the above reagents in a mortar and mix them thoroughly.
3.2 Sucrose.
3.3 Sulphuric acid, relative density d 1.84.
'U
3.4 Boric acid solution, saturated. Dissolve 60 g of boric acid in 1 litre of hot water, cool and
allow to mature for three days before decanting the clear liquid.
3.5 Alkaline sodium sulphide solution. Dissolve 20 g of sodium sulphide (Na2S*9H,O) in water,
and dilute to 50 ml; add a solution of 240 g of sodium hydroxide in 600 ml of water, and
mix well.
3.6 Sulphuric acid, 0.01 N.
3.7 Mixed indicator solution:
SOLUTION A. - Dissolve O. 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 solutions A and B. Do not use the mixed solution after more than
one week.
4. PROCEDURE
Before commencing the determination, mix the air-dried sample of coal, ground to pass a sieve of
0.2 mm aperture, for at least 1 minute, preferably by mechanical means.
Weigh to the nearest 0.1 mg about 0.10 g of the sample, transfer carefully to the digestion flask,
add 2.0 g of the mixed catalyst (3.1) and shake to mix. Add 4 ml of the sulphuric acid (3.3) and
mix again.
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ISO/R 333 - 1!W (F)
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