ASTM D6656-01(2010)e1
(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
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.
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.
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Designation: D6656 − 01 (Reapproved2010)
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.
´ NOTE—The SI statement was added and the Subcommittee name corrected in footnote 1 in November 2010.
1. Scope 4. Summary of Test Method
1.1 This test method covers the determination of chromic 4.1 The perchloric acid method may be applied to wet blue.
oxide in wet blue that has been partly or completely tanned
Accuratelyweighedwetbluesamplesaredigestedinablendof
with chromium compounds. In general, the samples will concentrated nitric acid and a prepared “oxidation mixture”
contain chromium content between 1 % and 5 % when calcu-
consisting of sulfuric and perchloric acids. Once completed,
lated as chromic oxide expressed upon a dry basis otherwise oxidation of all tri-valent to haxavalent chrome is executed by
referred to as moisture-free basis (mfb).
controlled heating. Upon dilution, the chromium is indirectly
(back) titrated volumetrically with standardized thiosulfate
1.2 The values stated in SI units are to be regarded as
using released iodine as the titrate. The perchloric acid method
standard. No other units of measurement are included in this
requires less manipulation than procedures based upon fusion
standard.
of the ash. However, care must be taken because of potential
1.3 This standard does not purport to address all of the
hazards in the use of this reagent.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5. Significance and Use
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. See Section 9 for 5.1 The procedure described is specific for chromium in wet
blue. Vanadium is the only common interfering element and is
specific safety hazards.
rarely present in quantity. The precision and accuracy of the
2. Referenced Documents
methods are usually, at least, as good as the sampling of wet
2.1 ASTM Standards:
blue itself.
D6658 Test Method for Volatile Matter (Moisture) of Wet
5.2 The chromium content of wet blue is related to the
Blue by Oven Drying
degree of tannage obtained, and hence may be a matter for
D6659 Practice for Sampling and Preparation of Wet Blue
specification in the purchase of wet blue. The procedure
for Physical and Chemical Tests
described provides adequate accuracy for this purpose.
E180 Practice for Determining the Precision of ASTM
Methods for Analysis and Testing of Industrial and Spe-
6. Apparatus
cialty Chemicals (Withdrawn 2009)
6.1 Analytical Balance—accurate and calibrated to 0.001 g.
3. Terminology
6.2 Erlenmeyer Flasks—250 mL capacity or equivalent.
3.1 Definitions—The terms and definitions employed within
6.3 Burette—50 mL capacity of suitable calibration grade,
this method are commonly used in normal laboratory practice
minimum calibration of 0.1 mL.
and require no special comment.
6.4 Glass Anti-Bumping Beads—or equivalent.
This test method is under the jurisdiction ofASTM Committee D31 on Leather
6.5 Measuring Cylinders—of 50 mLcapacity or equivalent.
and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
Current edition approved Oct. 1, 2010. Published November 2010. Originally
6.6 Small Glass Filter Funnel.
approved in 1996. Last previous edition approved in 2006 as D6656 - 02 (2006).
DOI: 10.1520/D6656-01R10E01. 6.7 Dessicator—of suitable size and design and charged
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
with fresh dessicant.
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 6.8 Weighing Vessels—of suitable size and design.
the ASTM website.
6.9 Drying Oven—with accurate variable temperature con-
The last approved version of this historical standard is referenced on
www.astm.org. trols.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D6656 − 01 (2010)
7. Reagents and Materials 8. Standardization
8.1 Dry potassium dichromate (K Cr O ) in an oven at 130
7.1 Purity of Reagents—Analytical Reagent (AR) grade
2 2 3
°C for 2 h and cool in a dessicator. Once cool, weigh about 0.2
shall be used in all tests. Unless otherwise indicated, it is
g(6 0.0001 g) of this dry potassium dichromate into a clean
intended that all reagents shall conform to specifications of the
250 ml, glass-stoppered Erlenmeyer flask. Dissolve in 50 mL
Committee on Analytical Reagents of the American Chemical
water; add 4 ml of hydrochloric acid (HCl, 1:1) and 20 ml of
Society, where such specifications are available. Other grades
KI solution. Stopper the flask and allow to stand for 5 min. in
may be used, provided it is first ascertained that the reagent is
the dark. Titrate with the thiosulfate solution that is to be
of sufficiently high purity to permit its use without lessening
standardized. When the solution color has faded to brownish-
the accuracy of the determination.
green, add 2 ml of 2 % starch solution and continue titrating
7.2 Purity of Water—Unless otherwise indicated, reference
until the deep blue color changes to a clear green. Record the
to water shall be understood to mean distilled water or water of
volume of titrant used. Calculate the Normality of the thiosul-
equal purity.
fate solution as follows:
7.3 Commercial Reagents—The use of commercially avail-
Normality 5 A÷ 0.04903 3B
~ !
able pre-standardized analytical reagents and solutions is
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.
However, it should be re-standardized at least once every
7.5 Perchloric Acid—(HClO ), 60-62 % w/w. 70 % or 72 %
month. Alternatively, a commercially available pre-
w/w perchloric acid may be substituted; however, storage is
standardized analytical solution may be substituted.
somewhat more hazardous.
9. Hazards
7.6 Sulfuric Acid—(H SO ), 96-98 % w/w.
2 4
9.1 Chemicals used can be harmful or explosive, or both.
7.7 Potassium Iodide—(KI), 99-100 % purity.
9.2 The improper use of perchloric acid can lead to violent
7.8 Potassium Iodide Solution—(KI), 10 % w/w. Dissolve
and serious explosions. In general, these can be traced to
10g(6 0.1 g) of potassium iodide into 100 ml of water.
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-
9.3 The exact procedures given must be followed and the
books.
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.
addin
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