SIST ISO 8658:1998
(Main)Carbonaceous materials for use in the production of aluminium -- Green and calcined coke -- Determination of trace elements by flame atomic absorption spectrometry
Carbonaceous materials for use in the production of aluminium -- Green and calcined coke -- Determination of trace elements by flame atomic absorption spectrometry
Produits carbonés utilisés pour la production de l'aluminium -- Coke cru et calciné -- Détermination des éléments-traces par spectrométrie d'absorption atomique dans la flamme
Ogljikovi materiali za proizvodnjo aluminija - Zeleni in kalcinirani koks - Določevanje elementov v sledovih s plamensko atomsko absorpcijsko spektrometrijo
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IS0
INTERNATIONAL
8658
STANDARD
First edition
1997-04-O 1
Carbonaceous materials for use in the
production of aluminium - Green and
Determination of trace
calcined coke -
elements by flame atomic absorption
spectroscopy
Produits carbon& utilis& pour la production de I’aluminium - Coke cru et
calcin6 - Dgtermination des Mments-traces par spectrom&rie
d’absorption atomique dans la flamme
Reference number
IS0 8658: 1997(E)
---------------------- Page: 1 ----------------------
IS0 8658: 1997(E)
Foreword
IS0 (the international Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 8658 was prepared by the British Standards
Institution (BSI) (as BS 6043: Part 2: Section 2.3:1989) and was adopted,
under a special “fast-track procedure”, by Technical Committee ISORC 47,
Chemistry in parallel with its approval by the IS0 member bodies
0 IS0 1997
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central @ iso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii
---------------------- Page: 2 ----------------------
IS0 8658: 1997(E)
INTERNATIONAL STANDARD @ IS0
Carbonaceous materials for use in the production of aluminium -
Green and calcined coke - Determination of trace elements by
flame atomic absorption spectroscopy
1 Scope
This International Standard describes a method for the determination of trace elements in green and calcined coke
with an ash content of not greater than 1 % (m/m) and with individual concentrations not greater than the following:
Calcium 0,025 % (mlm)
Chromium 0,005 % (m/m)
Copper 0,025 % (mlm)
Iron 0,030 % (m/m)
Lead 0,010 % (m/m)
Magnesium 0,010 % (m/m)
0,001 % (m/m)
Manganese
Nickel 0,050 % (m/m)
Silicon 0,100 % (m/m)
Vanadium 0,100 % (m/m)
0,004 % (m/m)
Zinc
NOTE - A method for the determination of ash of cokes is given in IS0 8005:1984, Carbonaceous materials used in the
production of a/uminium - Green and cakined coke - Determination of ash. However, it is essential that the ash produced by
that method not be used in the procedure of this International Standard because of the risk of contamination by trace elements.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain
registers of currently valid International Standards.
IS0 385-l :I 984, Laboratory glassware - Burettes - part I: General requirements.
IS0 835-l :I 981, Laboratory glassware - Graduated pipettes - ParI 1: General requirements,
ISO 1042: 1983, Laboratory glassware - One-mark mhmetric flasks.
IS0 3696:1987, Water for laboratory use - Specification and test methods,
IS0 6375: 1980, Carbonaceous materials for the production of aluminium - Coke for electrodes - Sampling
.
---------------------- Page: 3 ----------------------
@ IS0
IS0 8658: 1997(E)
3 Principle
A test portion sample is heated in a muffle furnace at 700 OC for IO h and the ash produced is fused with a mixture
of sodium carbonate and orthoboric acid. The melt is dissolved in dilute hydrochloric acid and the trace metal
content is analysed by flame atomic absorption spectrometry.
4 Reagents
Unless otherwise stated, use only reagents of recognized analytical grade and water complying with grade 2 of
IS0 3696.
4.1 Sodium carbonate, anhydrous.
4.2 Orthoboric acid.
4.3 Hydrochloric acid, concentrated, c(HCI) = 36 % (m/m), p = 1 ,I6 g/ml.
4.4 Lanthanum chloride solution, 100 mg La/ml, atomic absorption grade, c(LaCl3.7H20) = 267 g/l.
4.5 Standard calcium solution, 0,l mg/Cal.
Dry calcium carbonate (reagent grade) at 1 IO “C + 5 “C for 1 h and cool in a desiccator containing diphosphorus
pentoxide. Weigh 2,497 g + 0,001 g into a 250 ml beaker. Add 50 ml of water, then, a little at a time, 50 ml of
concentrated hydrochloric acid (4.3). When the solution is clear, transfer quantitatively to a 1 000 ml one-mark
volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 100 ml one-mark volumetric flask (5.6). Add
approximately 20 ml of water and 5 ml of hydrochloric acid (4.3). Dilute to the mark with water and mix.
4.6 Standard chromium solution, 0,l mg Cr/ml.
Wash, by decantation, approximately I,2 g of chromium metal of minimum purity 99,9 % (m/m) with dilute
hydrochloric acid [c(HCI) = 1 mol/l], then wash with water and dry in an air-circulating oven maintained at
1 IO OC k 5 “C for IO min. Weigh 1 g + 0,001 g of the dried chromium into a 250 ml beaker containing about 50 ml of
water. Slowly add 50 ml of concentrated hydrochloric acid (4.3). After dissolution, transfer quantitatively to a
1 000 ml one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 100 ml one-mark volumetric flask (5.6). Add
approximately 20 ml of water and 5 ml of concentrated hydrochloric acid. Dilute to the mark with water and mix.
Store in a polythene bottle.
4.7 Standard copper solution, 1 mg Cu/ml.
Wash, by decantation, approximately I,2 g of copper metal of minimum purity 99,9 % (m/m) with dilute nitric acid
[c(HNOs) = 2 mol/l], then wash with water and dry in an air-circulating oven maintained at 1 IO OC + 5 OC for IO min.
Weigh 1 g + 0,001 g of the dried copper into a 250 ml beaker containing about 25 ml of water. Slowly add 35 ml of
concentrated nitric acid (p = I,42 g/ml). After dissolution, transfer quantitatively to a 1 000 ml one-mark volumetric
flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
4.8 Standard iron solution, 1 mg Fe/ml.
Weigh 1 g + 0,001 g of iron of minimum purity 99,9 % (m/m) into a 250 ml beaker and add 25 ml of water. Carefully
add 50 ml of concentrated hydrochloric acid (4.3). After dissolution, transfer quantitatively to a 1 000 ml one-mark
volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
2
---------------------- Page: 4 ----------------------
@ IS0 OS0 8658: 1997(E)
4.9 Standard magnesium solution, 0,Ol mg Mg/ml.
Weigh 1 g + 0,001 g of magnesium of minimum purity 99,9 % (m/m) into a 250 ml beaker and add 50 ml of water.
Carefully add 50 ml of concentrated hydrochloric acid (4.3). After dissolution, transfer quantitatively to a 1 000 ml
one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 1 000 ml one-mark volumetric flask (5.6). Add
approximately 50 ml of water and 45 ml of concentrated hydrochloric acid (4.3). Dilute to the mark with water and
mix.
4.10 Standard manganese solution, 0,l mg Mn/ml.
Wash, by decantation, approximately I,2 g of manganese metal of minimum purity 99,9 % (m/m) with dilute nitric
dcid [c(HNOs) = 2 mol/l], then wash with water and dry in an air air-circulating oven maintained at 110 “C & 5 “C for
IO min. Weigh 1 g + 0,001 g of the dried manganese into a 250 ml beaker containing about 25 ml of water. Slowly
add 35 ml of concentrated nitric acid (p = I,42 g/ml). After dissolution, transfer quantitatively to a 1 000 ml one-mark
volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 100 ml one-mark volumetric flask (5.6). Add
I,42 g/ml). Dilute to the mark with water and
approximately 50 ml of water and 3 ml of concentrated nitric acid (p =
mix.
4.11 Standard nickel solution, 1 mg Ni/ml.
Weigh 1 g + 0,001 g of nickel of minimum purity 99,9 % (mfm) into a 250 ml beaker and add 25 ml of water.
Carefully add 35 ml of concentrated nitric acid (p = II ,42 g/ml), and heat to dissolve. After dissolution, transfer
quantitatively to a 1 000 ml one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a
polythene bottle.
4.12 Standard lead solution, 1 mg Pb/ml.
Weigh 1 g + 0,001 g of lead of minimum purity 99,9 % (m/m) into a 250 ml beaker and add 25 ml of water. Carefully
add 35 ml of concentrated nitric acid (p = I,42 g/ml), and heat to dissolve. After dissolution, transfer quantitatively to
a 1 000 ml one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
4.13 Standard silicon solution, 1 mg Si/ml.
into a platinum dish or large platinum crucible, weigh 2,139 g of silica of minimum purity 99,9 % (m/m) and 6 g of
anhydrous sodium carbonate (4.1), and mix well with a platinum spatula. Carefully fuse the mixture over a flame
until a transparent melt is obtained. Allow to cool, add warm water, heat gently until completely dissolved and
transfer quantitatively to a 400 ml PTFE beaker. Allow to cool. Dilute the solution to about 300 ml with water,
transfer quantitatively to a 1 000 ml one-mark volumetric flask (5.6), dilute to the mark with water and mix.
Immediately transfer this solution to a screw-cap polythene bottle.
Discard this solution after one month.
4.14 Standard vanadium solution, 1 mg V/ml.
Heat vanadium(V) oxide of minimum purity 999 % (m/m) in a covered platinum crucible (5.9) at 500 “C + IO OC for
30 min and cool in a desiccator. Weigh 1,785 g of the dried material and dissolve in a slight excess of sodium
hydroxide solution [c(NaOH) = 1 mol/l] in a PTFE beaker, then dilute to about 250 ml with water. Carefully add, a
little at a time, concentrated sulfuric acid [c(O,5 H2S04) = 9 mol/l], until the solution is just acid to litmus paper, then
add a further 5 ml. Cool to room temperature, transfer PO a 1 000 ml one-mark volumetric flask (5.6), dilute to the
mark with water and mix.
---------------------- Page: 5 ----------------------
@ IS0
IS0 8658: 1997(E)
4.15 Standard zinc solution, 0,ll mg Zn/ml.
Weigh 1 g + 0,001 g of zinc of minimum purity 99,9 % (m/m) into a 100 ml beaker and add 25 ml of water. Carefully
add 25 ml of concentrated hydrochloric acid (4.3) and heat to dissolve. After dissolution, transfer the solution
quantitatively to a 1 000 ml one-mark volumetric flask (5.6), dilute to the mark with water and mix.
Using a one-mark pipette (5.8), transfer 10 ml of this solution to a 100 ml one-mark volumetric flask (5.6), add about
20 ml water an
...
SLOVENSKI STANDARD
SIST ISO 8658:1998
01-januar-1998
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VSHNWURPHWULMR
Carbonaceous materials for use in the production of aluminium -- Green and calcined
coke -- Determination of trace elements by flame atomic absorption spectrometry
Produits carbonés utilisés pour la production de l'aluminium -- Coke cru et calciné --
Détermination des éléments-traces par spectrométrie d'absorption atomique dans la
flamme
Ta slovenski standard je istoveten z: ISO 8658:1997
ICS:
71.100.10 Materiali za proizvodnjo Materials for aluminium
aluminija production
SIST ISO 8658:1998 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 8658:1998
---------------------- Page: 2 ----------------------
SIST ISO 8658:1998
IS0
INTERNATIONAL
8658
STANDARD
First edition
1997-04-O 1
Carbonaceous materials for use in the
production of aluminium - Green and
Determination of trace
calcined coke -
elements by flame atomic absorption
spectroscopy
Produits carbon& utilis& pour la production de I’aluminium - Coke cru et
calcin6 - Dgtermination des Mments-traces par spectrom&rie
d’absorption atomique dans la flamme
Reference number
IS0 8658: 1997(E)
---------------------- Page: 3 ----------------------
SIST ISO 8658:1998
IS0 8658: 1997(E)
Foreword
IS0 (the international Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 8658 was prepared by the British Standards
Institution (BSI) (as BS 6043: Part 2: Section 2.3:1989) and was adopted,
under a special “fast-track procedure”, by Technical Committee ISORC 47,
Chemistry in parallel with its approval by the IS0 member bodies
0 IS0 1997
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central @ iso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii
---------------------- Page: 4 ----------------------
SIST ISO 8658:1998
IS0 8658: 1997(E)
INTERNATIONAL STANDARD @ IS0
Carbonaceous materials for use in the production of aluminium -
Green and calcined coke - Determination of trace elements by
flame atomic absorption spectroscopy
1 Scope
This International Standard describes a method for the determination of trace elements in green and calcined coke
with an ash content of not greater than 1 % (m/m) and with individual concentrations not greater than the following:
Calcium 0,025 % (mlm)
Chromium 0,005 % (m/m)
Copper 0,025 % (mlm)
Iron 0,030 % (m/m)
Lead 0,010 % (m/m)
Magnesium 0,010 % (m/m)
0,001 % (m/m)
Manganese
Nickel 0,050 % (m/m)
Silicon 0,100 % (m/m)
Vanadium 0,100 % (m/m)
0,004 % (m/m)
Zinc
NOTE - A method for the determination of ash of cokes is given in IS0 8005:1984, Carbonaceous materials used in the
production of a/uminium - Green and cakined coke - Determination of ash. However, it is essential that the ash produced by
that method not be used in the procedure of this International Standard because of the risk of contamination by trace elements.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
International Standard. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain
registers of currently valid International Standards.
IS0 385-l :I 984, Laboratory glassware - Burettes - part I: General requirements.
IS0 835-l :I 981, Laboratory glassware - Graduated pipettes - ParI 1: General requirements,
ISO 1042: 1983, Laboratory glassware - One-mark mhmetric flasks.
IS0 3696:1987, Water for laboratory use - Specification and test methods,
IS0 6375: 1980, Carbonaceous materials for the production of aluminium - Coke for electrodes - Sampling
.
---------------------- Page: 5 ----------------------
SIST ISO 8658:1998
@ IS0
IS0 8658: 1997(E)
3 Principle
A test portion sample is heated in a muffle furnace at 700 OC for IO h and the ash produced is fused with a mixture
of sodium carbonate and orthoboric acid. The melt is dissolved in dilute hydrochloric acid and the trace metal
content is analysed by flame atomic absorption spectrometry.
4 Reagents
Unless otherwise stated, use only reagents of recognized analytical grade and water complying with grade 2 of
IS0 3696.
4.1 Sodium carbonate, anhydrous.
4.2 Orthoboric acid.
4.3 Hydrochloric acid, concentrated, c(HCI) = 36 % (m/m), p = 1 ,I6 g/ml.
4.4 Lanthanum chloride solution, 100 mg La/ml, atomic absorption grade, c(LaCl3.7H20) = 267 g/l.
4.5 Standard calcium solution, 0,l mg/Cal.
Dry calcium carbonate (reagent grade) at 1 IO “C + 5 “C for 1 h and cool in a desiccator containing diphosphorus
pentoxide. Weigh 2,497 g + 0,001 g into a 250 ml beaker. Add 50 ml of water, then, a little at a time, 50 ml of
concentrated hydrochloric acid (4.3). When the solution is clear, transfer quantitatively to a 1 000 ml one-mark
volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 100 ml one-mark volumetric flask (5.6). Add
approximately 20 ml of water and 5 ml of hydrochloric acid (4.3). Dilute to the mark with water and mix.
4.6 Standard chromium solution, 0,l mg Cr/ml.
Wash, by decantation, approximately I,2 g of chromium metal of minimum purity 99,9 % (m/m) with dilute
hydrochloric acid [c(HCI) = 1 mol/l], then wash with water and dry in an air-circulating oven maintained at
1 IO OC k 5 “C for IO min. Weigh 1 g + 0,001 g of the dried chromium into a 250 ml beaker containing about 50 ml of
water. Slowly add 50 ml of concentrated hydrochloric acid (4.3). After dissolution, transfer quantitatively to a
1 000 ml one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 100 ml one-mark volumetric flask (5.6). Add
approximately 20 ml of water and 5 ml of concentrated hydrochloric acid. Dilute to the mark with water and mix.
Store in a polythene bottle.
4.7 Standard copper solution, 1 mg Cu/ml.
Wash, by decantation, approximately I,2 g of copper metal of minimum purity 99,9 % (m/m) with dilute nitric acid
[c(HNOs) = 2 mol/l], then wash with water and dry in an air-circulating oven maintained at 1 IO OC + 5 OC for IO min.
Weigh 1 g + 0,001 g of the dried copper into a 250 ml beaker containing about 25 ml of water. Slowly add 35 ml of
concentrated nitric acid (p = I,42 g/ml). After dissolution, transfer quantitatively to a 1 000 ml one-mark volumetric
flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
4.8 Standard iron solution, 1 mg Fe/ml.
Weigh 1 g + 0,001 g of iron of minimum purity 99,9 % (m/m) into a 250 ml beaker and add 25 ml of water. Carefully
add 50 ml of concentrated hydrochloric acid (4.3). After dissolution, transfer quantitatively to a 1 000 ml one-mark
volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
2
---------------------- Page: 6 ----------------------
SIST ISO 8658:1998
@ IS0 OS0 8658: 1997(E)
4.9 Standard magnesium solution, 0,Ol mg Mg/ml.
Weigh 1 g + 0,001 g of magnesium of minimum purity 99,9 % (m/m) into a 250 ml beaker and add 50 ml of water.
Carefully add 50 ml of concentrated hydrochloric acid (4.3). After dissolution, transfer quantitatively to a 1 000 ml
one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 1 000 ml one-mark volumetric flask (5.6). Add
approximately 50 ml of water and 45 ml of concentrated hydrochloric acid (4.3). Dilute to the mark with water and
mix.
4.10 Standard manganese solution, 0,l mg Mn/ml.
Wash, by decantation, approximately I,2 g of manganese metal of minimum purity 99,9 % (m/m) with dilute nitric
dcid [c(HNOs) = 2 mol/l], then wash with water and dry in an air air-circulating oven maintained at 110 “C & 5 “C for
IO min. Weigh 1 g + 0,001 g of the dried manganese into a 250 ml beaker containing about 25 ml of water. Slowly
add 35 ml of concentrated nitric acid (p = I,42 g/ml). After dissolution, transfer quantitatively to a 1 000 ml one-mark
volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
Using a one-mark pipette (5.8), transfer IO ml of this solution to a 100 ml one-mark volumetric flask (5.6). Add
I,42 g/ml). Dilute to the mark with water and
approximately 50 ml of water and 3 ml of concentrated nitric acid (p =
mix.
4.11 Standard nickel solution, 1 mg Ni/ml.
Weigh 1 g + 0,001 g of nickel of minimum purity 99,9 % (mfm) into a 250 ml beaker and add 25 ml of water.
Carefully add 35 ml of concentrated nitric acid (p = II ,42 g/ml), and heat to dissolve. After dissolution, transfer
quantitatively to a 1 000 ml one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a
polythene bottle.
4.12 Standard lead solution, 1 mg Pb/ml.
Weigh 1 g + 0,001 g of lead of minimum purity 99,9 % (m/m) into a 250 ml beaker and add 25 ml of water. Carefully
add 35 ml of concentrated nitric acid (p = I,42 g/ml), and heat to dissolve. After dissolution, transfer quantitatively to
a 1 000 ml one-mark volumetric flask (5.6). Dilute to the mark with water and mix. Store in a polythene bottle.
4.13 Standard silicon solution, 1 mg Si/ml.
into a platinum dish or large platinum crucible, weigh 2,139 g of silica of minimum purity 99,9 % (m/m) and 6 g of
anhydrous sodium carbonate (4.1), and mix well with a platinum spatula. Carefully fuse the mixture over a flame
until a transparent melt is obtained. Allow to cool, add warm water, heat gently until completely dissolved and
transfer quantitatively to a 400 ml PTFE beaker. Allow to cool. Dilute the solution to about 300 ml with water,
transfer quantitatively to a 1 000 ml one-mark volumetric flask (5.6), dilute to the mark with water and mix.
Immediately transfer this solution to a screw-cap polythene bottle.
Discard this solution after one month.
4.14 Standard vanadium solution, 1 mg V/ml.
Heat vanadium(V) oxide of minimum purity 999 % (m/m) in a covered platinum crucible (5.9) at 500 “C + IO OC for
30 min and cool in a desiccator. Weigh 1,785 g of the dried material and dissolve in a slight excess of sodium
hydroxide solution [c(NaOH) = 1 mol/l] in a PTFE beaker, then dilute to about 250 ml with water. Carefully add, a
little at a time, concentrated sulfuric acid [c(O,5 H2S04) = 9 mol/l], until the solution is just acid to litmus paper, then
add a further 5 ml. Cool to room te
...
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