ASTM D6656-14b
(Test Method)Standard Test Method for Determination of Chromic Oxide in Wet Blue (Perchloric Acid Oxidation)
Standard Test Method for Determination of Chromic Oxide in Wet Blue (Perchloric Acid Oxidation)
SIGNIFICANCE AND USE
5.1 The procedure described is specific for chromium in wet blue. Vanadium is the only common interfering element and is rarely present in quantity. The precision and accuracy of the methods are usually, at least, as good as the sampling of wet blue itself.
5.2 The chromium content of wet blue is related to the degree of tannage obtained, and hence may be a matter for specification in the purchase of wet blue. The procedure described provides adequate accuracy for this purpose.
SCOPE
1.1 This test method covers the determination of chromic oxide in wet blue that has been partly or completely tanned with chromium compounds. In general, the samples will contain chromium content between 1 % and 5 % when calculated as chromic oxide expressed upon a dry basis otherwise referred to as moisture-free basis (mfb).
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. See Section 9 for specific safety hazards.
General Information
Relations
Buy Standard
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6656 − 14b
StandardTest Method for
Determination of Chromic Oxide in Wet Blue (Perchloric
Acid Oxidation)
This standard is issued under the fixed designation D6656; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
3.1 Definitions—The terms and definitions employed within
1.1 This test method covers the determination of chromic
this method are commonly used in normal laboratory practice
oxide in wet blue that has been partly or completely tanned
and require no special comment.
with chromium compounds. In general, the samples will
contain chromium content between 1 % and 5 % when calcu-
lated as chromic oxide expressed upon a dry basis otherwise 4. Summary of Test Method
referred to as moisture-free basis (mfb).
4.1 The perchloric acid method may be applied to wet blue.
Accuratelyweighedwetbluesamplesaredigestedinablendof
1.2 The values stated in SI units are to be regarded as
concentrated nitric acid and a prepared “oxidation mixture”
standard. No other units of measurement are included in this
consisting of sulfuric and perchloric acids. Once completed,
standard.
oxidation of all tri-valent to haxavalent chrome is executed by
1.3 This standard does not purport to address all of the
controlled heating. Upon dilution, the chromium is indirectly
safety concerns, if any, associated with its use. It is the
(back) titrated volumetrically with standardized thiosulfate
responsibility of the user of this standard to establish appro-
using released iodine as the titrate. The perchloric acid method
priate safety and health practices and determine the applica-
requires less manipulation than procedures based upon fusion
bility of regulatory limitations prior to use. See Section 9 for
of the ash. However, care must be taken because of potential
specific safety hazards.
hazards in the use of this reagent.
2. Referenced Documents
5. Significance and Use
2.1 ASTM Standards:
5.1 The procedure described is specific for chromium in wet
D6658 Test Method for Volatile Matter (Moisture) of Wet
blue. Vanadium is the only common interfering element and is
Blue by Oven Drying
rarely present in quantity. The precision and accuracy of the
D6659 Practice for Sampling and Preparation of Wet Blue
methods are usually, at least, as good as the sampling of wet
for Physical and Chemical Tests
blue itself.
E180 Practice for Determining the Precision of ASTM
5.2 The chromium content of wet blue is related to the
Methods for Analysis and Testing of Industrial and Spe-
degree of tannage obtained, and hence may be a matter for
cialty Chemicals (Withdrawn 2009)
specification in the purchase of wet blue. The procedure
E177 Practice for Use of the Terms Precision and Bias in
described provides adequate accuracy for this purpose.
ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to
6. Apparatus
Determine the Precision of a Test Method
6.1 Analytical Balance—accurate and calibrated to 0.001 g.
6.2 Erlenmeyer Flasks—250 mL capacity or equivalent.
This test method is under the jurisdiction ofASTM Committee D31 on Leather
6.3 Burette—50 mL capacity of suitable calibration grade,
and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
minimum calibration of 0.1 mL.
Current edition approved Nov. 1, 2014. Published December 2014. Originally
approved in 1996. Last previous edition approved in 2014 as D6656 - 14a. DOI:
6.4 Glass Anti-Bumping Beads—or equivalent.
10.1520/D6656-14B.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
6.5 Measuring Cylinders—of 50 mLcapacity or equivalent.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on 6.6 Small Glass Filter Funnel.
the ASTM website.
6.7 Dessicator—of suitable size and design and charged
The last approved version of this historical standard is referenced on
www.astm.org. with fresh dessicant.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6656 − 14b
6.8 Weighing Vessels—of suitable size and design. 7.16 Sodium Thiosulfate Standard Solution—(Na S O ),
2 2 3
0.1N (6 0.0002). Dissolve 24.85 g of sodium thiosulfate
6.9 Drying Oven—with accurate variable temperature con-
(Na S O ·5H O) in previously boiled water, add 1.00 g of
2 2 3 2
trols.
sodium carbonate (Na CO ) and dilute to 1000 mL.
2 3
7. Reagents and Materials
8. Standardization
7.1 Purity of Reagents—Analytical Reagent (AR) grade
8.1 Dry potassium dichromate (K Cr O ) in an oven at 130
2 2 3
shall be used in all tests. Unless otherwise indicated, it is
°C for 2 h and cool in a dessicator. Once cool, weigh about 0.2
intended that all reagents shall conform to specifications of the
g(6 0.0001 g) of this dry potassium dichromate into a clean
Committee on Analytical Reagents of the American Chemical
250 ml, glass-stoppered Erlenmeyer flask. Dissolve in 50 mL
Society, where such specifications are available. Other grades
water; add 4 ml of hydrochloric acid (HCl, 1:1) and 20 ml of
may be used, provided it is first ascertained that the reagent is
KI solution. Stopper the flask and allow to stand for 5 min. in
of sufficiently high purity to permit its use without lessening
the dark. Titrate with the thiosulfate solution that is to be
the accuracy of the determination.
standardized. When the solution color has faded to brownish-
7.2 Purity of Water—Unless otherwise indicated, reference green, add 2 ml of 2 % starch solution and continue titrating
until the deep blue color changes to a clear green. Record the
to water shall be understood to mean distilled water or water of
equal purity. volume of titrant used. Calculate the Normality of the thiosul-
fate solution as follows:
7.3 Commercial Reagents—The use of commercially avail-
able pre-standardized analytical reagents and solutions is Normality 5 A÷~0.04903 3B!
appropriate, providing those reagents and solutions have been
where:
prepared according to and conform to the previously men-
A = grams of K Cr O used, and
2 2 7
tioned specifications (see 7.1).
B = ml required for titration.
7.4 Nitric Acid—(HNO ), 70 % w/w.
8.2 Shelf Life—The thiosulfate solution is relatively stable.
7.5 Perchloric Acid—(HClO ), 60-62 % w/w. 70 % or 72 %
4 However, it should be re-standardized at least once every
w/w perchloric acid may be substituted; however, storage is
month. Alternatively, a commercially available pre-
somewhat more hazardous.
standardized analytical solution may be substituted.
7.6 Sulfuric Acid—(H SO ), 96-98 % w/w.
2 4
9. Hazards
7.7 Potassium Iodide—(KI), 99-100 % purity.
9.1 Chemicals used can be harmful or explosive, or both.
7.8 Potassium Iodide Solution—(KI), 10 % w/w. Dissolve
9.2 The improper use of perchloric acid can lead to violent
10g(6 0.1 g) of potassium iodide into 100 ml of water.
and serious explosions. In general, these can be traced to
situations where concentrated perchloric acid has come in
7.9 Starch Indicator Solution—2 % or equivalent. Prepared
contact with organic or easily oxidized materials.
according to accepted procedures available in analytical hand-
books.
9.3 The exact procedures given must be followed and the
digestion, once started, should be kept from possible contact
7.10 Oxidizing Mixture—Mix 1666 mL of concentrated
with other organic matter. The digestion should never be
sulfuric acid into an appropriate glass container that contains
allowed to boil dry. The perchloric acid should never be used
2500 mL of perchloric acid using extreme caution while
without the accompanying use of nitric and sulfuric acids.
adding. Cool the mixture to room temperature before use.
NOTE 1—The reagents may be added individually according to 11.3.1.
9.4 Any spills involving perchloric acid should be flushed
7.11 Phosphoric Acid—(H PO ), 40 % w/w. Dilute 45 mL with water and a liquid acid neutralizer.
3 4
of 85 % phosphoric acid with water to 100 ml.
9.5 The use of a perchloric acid hood, reserved for perchlo-
ric acid digestion, equipped with wash-down facilities and
7.12 Hydrochloric Acid—(HCl, 1:1 dilution of 37 %, w/w).
Used in standardization of thiosulfate solution. constructed entirely of non-porous inorganic material is re-
quired.
7.13 Potassium Dichromate—(K Cr O ). Used in standard-
2 2 7
9.6 Perchloric acid bottles should be stored on a ceramic or
ization of thiosulfate solution.
non-porous tray or shelf and never on a wooden or pervious
7.14 Sodium Carbonate—(Na CO ). Used in preparation of
2 3
shelf.
thiosulfate solution.
9.7 Perchloric acid must not be permitted to go dry in the
7.15 Sodium Thiosulfate—(Na S O ·5H O). Used to pre-
2 2 3 2
presence of organics, metals or metal salts.
pare thiosulfate solution.
9.8 It is advisable to keep only a one pound (0.45 kg) bottle
of acid in a working area.
Reagent Chemicals, American Chemical Society Specifications , American
10. Test Specimens
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
listed by the American Chemical Society, see Analar Standards for Laboratory
10.1 The test specimen shall be 3-5 g of wet blue from a
Chemicals, BDH Ltd. Poole, Dorset, UK and the United States Pharmacopoeia and
composite sample prepared according to Practice D6659 and
National Formulary, U.S. Pharmacopoeial Convention, Inc. (USPC), Rockville,
MD. weighed to an accuracy of 0.001 g.
D6656 − 14b
11. Procedure
E = 0.025332 = chromic oxide (Cr O ) equivalence
2 3
weight per milliliter (g/mL),
11.1 Accurately weigh between 3 and5g(6 0.001 g) of the
W = weight of original wet blue specimen (as received) in
prepared wet blue sample into a 250 mL Erlenmeyer flask.
grams (g), and
Record the weight to the nearest 0.001 g.
100 = conversion to percent.
11.2 Using extreme care, add 20 mL of nitric acid (HNO )
12.2 The above calculation provides the Cr O content of
2 3
to the flask.
the wet blue on an “as received” basis. Since the chromium
11.3 Next, carefully and slowly add 25 mLof the Oxidizing
content of wet blue is expressed upon a dry (moisture-free)
Mixture
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6656 − 14a D6656 − 14b
Standard Test Method for
Determination of Chromic Oxide in Wet Blue (Perchloric
Acid Oxidation)
This standard is issued under the fixed designation D6656; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of chromic oxide in wet blue that has been partly or completely tanned with
chromium compounds. In general, the samples will contain chromium content between 1 % and 5 % when calculated as chromic
oxide expressed upon a dry basis otherwise referred to as moisture-free basis (mfb).
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. See Section 9 for specific safety hazards.
2. Referenced Documents
2.1 ASTM Standards:
D6658 Test Method for Volatile Matter (Moisture) of Wet Blue by Oven Drying
D6659 Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
E180 Practice for Determining the Precision of ASTM Methods for Analysis and Testing of Industrial and Specialty Chemicals
(Withdrawn 2009)
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions—The terms and definitions employed within this method are commonly used in normal laboratory practice and
require no special comment.
4. Summary of Test Method
4.1 The perchloric acid method may be applied to wet blue. Accurately weighed wet blue samples are digested in a blend of
concentrated nitric acid and a prepared “oxidation mixture” consisting of sulfuric and perchloric acids. Once completed, oxidation
of all tri-valent to haxavalent chrome is executed by controlled heating. Upon dilution, the chromium is indirectly (back) titrated
volumetrically with standardized thiosulfate using released iodine as the titrate. The perchloric acid method requires less
manipulation than procedures based upon fusion of the ash. However, care must be taken because of potential hazards in the use
of this reagent.
5. Significance and Use
5.1 The procedure described is specific for chromium in wet blue. Vanadium is the only common interfering element and is
rarely present in quantity. The precision and accuracy of the methods are usually, at least, as good as the sampling of wet blue itself.
5.2 The chromium content of wet blue is related to the degree of tannage obtained, and hence may be a matter for specification
in the purchase of wet blue. The procedure described provides adequate accuracy for this purpose.
This test method is under the jurisdiction of ASTM Committee D31 on Leather and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
Current edition approved May 1, 2014Nov. 1, 2014. Published June 2014December 2014. Originally approved in 1996. Last previous edition approved in 2014 as
D6656 - 14.D6656 - 14a. DOI: 10.1520/D6656-14A.10.1520/D6656-14B.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6656 − 14b
6. Apparatus
6.1 Analytical Balance—accurate and calibrated to 0.001 g.
6.2 Erlenmeyer Flasks—250 mL capacity or equivalent.
6.3 Burette—50 mL capacity of suitable calibration grade, minimum calibration of 0.1 mL.
6.4 Glass Anti-Bumping Beads—or equivalent.
6.5 Measuring Cylinders—of 50 mL capacity or equivalent.
6.6 Small Glass Filter Funnel.
6.7 Dessicator—of suitable size and design and charged with fresh dessicant.
6.8 Weighing Vessels—of suitable size and design.
6.9 Drying Oven—with accurate variable temperature controls.
7. Reagents and Materials
7.1 Purity of Reagents—Analytical Reagent (AR) grade shall be used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
7.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean distilled water or water of equal
purity.
7.3 Commercial Reagents—The use of commercially available pre-standardized analytical reagents and solutions is appropriate,
providing those reagents and solutions have been prepared according to and conform to the previously mentioned specifications
(see 7.1).
7.4 Nitric Acid—(HNO ), 70 % w/w.
7.5 Perchloric Acid—(HClO ), 60-62 % w/w. 70 % or 72 % w/w perchloric acid may be substituted; however, storage is
somewhat more hazardous.
7.6 Sulfuric Acid—(H SO ), 96-98 % w/w.
2 4
7.7 Potassium Iodide—(KI), 99-100 % purity.
7.8 Potassium Iodide Solution—(KI), 10 % w/w. Dissolve 10 g (6 0.1 g) of potassium iodide into 100 ml of water.
7.9 Starch Indicator Solution—2 % or equivalent. Prepared according to accepted procedures available in analytical handbooks.
7.10 Oxidizing Mixture—Mix 1666 mL of concentrated sulfuric acid into an appropriate glass container that contains 2500 mL
of perchloric acid using extreme caution while adding. Cool the mixture to room temperature before use.
NOTE 1—The reagents may be added individually according to 11.3.1.
7.11 Phosphoric Acid—(H PO ), 40 % w/w. Dilute 45 mL of 85 % phosphoric acid with water to 100 ml.
3 4
7.12 Hydrochloric Acid—(HCl, 1:1 dilution of 37 %, w/w). Used in standardization of thiosulfate solution.
7.13 Potassium Dichromate—(K Cr O ). Used in standardization of thiosulfate solution.
2 2 7
7.14 Sodium Carbonate—(Na CO ). Used in preparation of thiosulfate solution.
2 3
7.15 Sodium Thiosulfate—(Na S O · 5H O). Used to prepare thiosulfate solution.
2 2 3 2
7.16 Sodium Thiosulfate Standard Solution—(Na S O ), 0.1N (6 0.0002). Dissolve 24.85 g of sodium thiosulfate (Na S O ·
2 2 3 2 2 3
5H O) in previously boiled water, add 1.00 g of sodium carbonate (Na CO ) and dilute to 1000 mL.
2 2 3
8. Standardization
8.1 Dry potassium dichromate (K Cr O ) in an oven at 130 °C for 2 h and cool in a dessicator. Once cool, weigh about 0.2 g
2 2 3
(6 0.0001 g) of this dry potassium dichromate into a clean 250 ml, glass-stoppered Erlenmeyer flask. Dissolve in 50 mL water;
add 4 ml of hydrochloric acid (HCl, 1:1) and 20 ml of KI solution. Stopper the flask and allow to stand for 5 min. in the dark.
Titrate with the thiosulfate solution that is to be standardized. When the solution color has faded to brownish-green, add 2 ml of
2 % starch solution and continue titrating until the deep blue color changes to a clear green. Record the volume of titrant used.
Calculate the Normality of the thiosulfate solution as follows:
Reagent Chemicals, American Chemical Society Specifications , American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed by
the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd. Poole, Dorset, UK and the United States Pharmacopoeia and National
Formulary, U.S. Pharmacopoeial Convention, Inc. (USPC), Rockville, MD.
D6656 − 14b
Normality 5 A÷ 0.04903 3B
~ !
where:
A = grams of K Cr O used, and
2 2 7
B = ml required for titration.
8.2 Shelf Life—The thiosulfate solution is relatively stable. However, it should be re-standardized at least once every month.
Alternatively, a commercially available pre-standardized analytical solution may be substituted.
9. Hazards
9.1 Chemicals used can be harmful or explosive, or both.
9.2 The improper use of perchloric acid can lead to violent and serious explosions. In general, these can be traced to situations
where concentrated perchloric acid has come in contact with organic or easily oxidized materials.
9.3 The exact procedures given must be followed and the digestion, once started, should be kept from possible contact with
other organic matter. The digestion should never be allowed to boil dry. The perchloric acid should never be used without the
accompanying use of nitric and sulfuric acids.
9.4 Any spills involving perchloric acid should be flushed with water and a liquid acid neutralizer.
9.5 The use of a perchloric acid hood, reserved for perchloric acid digestion, equipped with wash-down facilities and
constructed entirely of non-porous inorganic material is required.
9.6 Perchloric acid bottles should be stored on a ceramic or non-porous tray or shelf and never on a wooden or pervious shelf.
9.7 Perchloric acid must not be permitted to go dry in the presence of organics, metals or metal salts.
9.8 It is advisable to keep only a one pound (0.45 kg) bottle of acid in a working area.
10. Test Specimens
10.1 The test specimen shall be 3-5 g of wet blue from a composite sample prepared according to Practice D6659 and weighed
to an accuracy of 0.001 g.
11. Procedure
11.1 Accurately weigh between 3 and 5 g (6 0.001 g) of the prepared wet blue sample into a 250 mL Erlenmeyer flask. Record
the weight to the nearest 0.001 g.
11.2 Using extreme care, add 20 mL of nitric acid (HNO ) to the flask.
11.3 Next, carefully and slowly add 25 mL of the Oxidizing Mixture to the flask.
11.3.1 Alternatively, add in this order: 20 mL HNO , 15 mL HC1O , and 10 mL H SO .
3 4 2 4
11.4 Add a few glass anti-bumping beads (these will allow the solution to boil evenly), then place the filter funnel into the neck
of the flask.
11.5 Under the
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.