ASTM D6656-01(2006)
(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).
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 for specific safety hazards.
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Designation:D6656–01(Reapproved 2006)
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 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
1.2 This standard does not purport to address all of the (back) titrated volumetrically with standardized thiosulfate
safety concerns, if any, associated with its use. It is the using released iodine as the titrate. The perchloric acid method
responsibility of the user of this standard to establish appro- requires less manipulation than procedures based upon fusion
priate safety and health practices and determine the applica- of the ash. However, care must be taken because of potential
bility of regulatory limitations prior to use. See Section 9 for hazards in the use of this reagent.
specific safety hazards.
5. Significance and Use
2. Referenced Documents
5.1 The procedure described is specific for chromium in wet
2.1 ASTM Standards: blue. Vanadium is the only common interfering element and is
D6658 Test Method for Volatile Matter (Moisture) of Wet rarely present in quantity. The precision and accuracy of the
Blue by Oven Drying methods are usually, at least, as good as the sampling of wet
D6659 Practice for Sampling and Preparation of Wet Blue blue itself.
for Physical and Chemical Tests 5.2 The chromium content of wet blue is related to the
E180 Practice for Determining the Precision of ASTM degree of tannage obtained, and hence may be a matter for
Methods for Analysis and Testing of Industrial and Spe- specification in the purchase of wet blue. The procedure
cialty Chemicals described provides adequate accuracy for this purpose.
3. Terminology 6. Apparatus
3.1 Definitions—Thetermsanddefinitionsemployedwithin 6.1 Analytical Balance—accurate and calibrated to 0.001 g.
this method are commonly used in normal laboratory practice 6.2 Erlenmeyer Flasks—250 ml capacity or equivalent.
and require no special comment. 6.3 Burette—50 ml capacity of suitable calibration grade,
minimum calibration of 0.1 ml.
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 ml capacity or equivalent.
and is the direct responsibility of Subcommittee D31.02 on Blue Stock.
6.6 Small Glass Filter Funnel.
Current edition approved Oct. 1, 2006. Published November 2006. Originally
approved in 1996. Last previous edition approved in 2001 as D6656 - 01. DOI:
6.7 Dessicator—of suitable size and design and charged
10.1520/D6656-01R06.
with fresh dessicant.
Annual Book of ASTM Standards, Vol 15.04.
6.8 Weighing Vessels—of suitable size and design.
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 6.9 Drying Oven—with accurate variable temperature con-
Standards volume information, refer to the standard’s Document Summary page on
trols.
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6656–01 (2006)
7. Reagents and Materials 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
7.1 Purity of Reagents—Analytical Reagent (AR) grade
the dark. Titrate with the thiosulfate solution that is to be
shall be used in all tests. Unless otherwise indicated, it is
standardized. When the solution color has faded to brownish-
intended that all reagents shall conform to specifications of the
green, add 2 ml of 2 % starch solution and continue titrating
Committee on Analytical Reagents of the American Chemical
until the deep blue color changes to a clear green. Record the
Society, where such specifications are available. Other grades
volume of titrant used. Calculate the Normality of the thiosul-
may be used, provided it is first ascertained that the reagent is
fate solution as follows:
of sufficiently high purity to permit its use without lessening
the accuracy of the determination. Normality 5 A 4 0.04903 3 B!
~
7.2 Purity of Water—Unless otherwise indicated, reference
where:
to water shall be understood to mean distilled water or water of
A = grams of K Cr O used, and
2 2 7
equal purity.
B = ml required for titration.
7.3 Commercial Reagents—The use of commercially avail-
8.2 Shelf Life—The thiosulfate solution is relatively stable.
able pre-standardized analytical reagents and solutions is
However, it should be re-standardized at least once every
appropriate, providing those reagents and solutions have been
month. Alternatively, a commercially available pre-
prepared according to and conform to the previously men-
standardized analytical solution may be substituted.
tioned specifications (see 7.1).
7.4 Nitric Acid—(HNO ), 70 % w/w.
9. Hazards
7.5 PerchloricAcid—(HClO ), 60-62 % w/w. 70 % or 72 %
9.1 Chemicals used can be harmful and/or explosive.
w/w perchloric acid may be substituted; however, storage is
9.2 The improper use of perchloric acid can lead to violent
somewhat more hazardous.
and serious explosions. In general, these can be traced to
7.6 Sulfuric Acid—(H SO ), 96-98 % w/w.
2 4
situations where concentrated perchloric acid has come in
7.7 Potassium Iodide—(KI), 99-100 % purity.
contact with organic or easily oxidized materials.
7.8 Potassium Iodide Solution—(KI), 10 % w/w. Dissolve
9.3 The exact procedures given must be followed and the
10g(6 0.1 g) of potassium iodide into 100 ml of water.
digestion, once started, should be kept from possible contact
7.9 Starch Indicator Solution—2 % or equivalent. Prepared
with other organic matter. The digestion should never be
according to accepted procedures available in analytical hand-
allowed to boil dry. The perchloric acid should never be used
books.
without the accompanying use of nitric and sulfuric acids.
7.10 Oxidizing Mixture—Mix 1666 ml of concentrated
9.4 Any spills involving perchloric acid should be flushed
sulfuric acid into an appropriate glass container that contains
with water and a liquid acid neutralizer.
2500mlofperchloricacidusingextremecautionwhileadding.
9.5 The use of a perchloric acid hood, reserved for perchlo-
Cool the mixture to room temperature before use.
ric acid digestion, equipped with wash-down facilities and
7.11 PhosphoricAcid—(H PO ),40 %w/w.Dilute45mlof
3 4
constru
...
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