ASTM D2807-93(1998)
(Test Method)Standard Test Method for Chromic Oxide in Leather (Perchloric Acid Oxidation)
Standard Test Method for Chromic Oxide in Leather (Perchloric Acid Oxidation)
SCOPE
1.1 This test method covers the determination of chromic oxide in leathers that have been partly or completely tanned with chromium compounds. In general the samples will contain between 1 and 5% chromium, calculated as chromic oxide.
1.2 This standard does not purport to address the safety problems, 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 7 for specific safety hazards.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: D 2807 – 93 (Reapproved 1998)
Standard Test Method for
Chromic Oxide in Leather (Perchloric Acid Oxidation)
This standard is issued under the fixed designation D 2807; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope this is rarely present in quantity. The precision and accuracy of
the methods are usually at least as good as the sampling of the
1.1 This test method covers the determination of chromic
leather itself.
oxide in leathers that have been partly or completely tanned
4.2 The chromium content of leather relates to the degree of
with chromium compounds. In general the samples will con-
tannage obtained, and hence may be a matter for specification
tain between 1 and 5 % chromium, calculated as chromic
in the purchase of leather. The procedure described provides
oxide.
adequate accuracy for this purpose.
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
5. Apparatus
responsibility of the user of this standard to establish appro-
5.1 Potentiometric Titration Equipment—This is required in
priate safety and health practices and determine the applica-
6+
an alternative method for titrating chromium (Cr ) with
bility of regulatory limitations prior to use. See Section 7 for
ferrous ammonium sulfate solution. The equipment consists of:
specific safety hazards.
5.1.1 Stirrer.
2. Referenced Documents 5.1.2 Calomel and Platinum Electrodes.
5.1.3 Potentiometer—A variety of instruments is satisfac-
2.1 ASTM Standards:
tory. The most convenient common feature of these instru-
D 2617 Test Method for Total Ash in Leather
ments is a null-point device (either a cathode-ray electron tube
D 2813 Practice for Sampling Leather for Physical and
or galvanometer) that will signal the abrupt change occurring
Chemical Tests
in the potential when the end point is reached.
E 180 Practice for Determining the Precision of ASTM
5.2 In carrying out the titration, the electrodes are immersed
Methods for Analysis and Testing of Industrial Chemicals
in the sample, the solution agitated by the stirrer, and the
3. Summary of Test Method
potential balanced with the galvanometer or cathode-ray tube.
Titrant is added dropwise until a sharp permanent change in
3.1 The perchloric acid method is applied to the ash
potential occurs.
obtained in Test Method D 2617. In the acid digestion, any
remaining organic matter is destroyed and the chromium
6. Reagents
oxidized to the hexavalent state. On dilution, the chromium is
6.1 Purity of Reagents—Reagent grade chemicals shall be
titrated volumetrically with thiosulfate or ferrous salt. The
used in all tests. Unless otherwise indicated, it is intended that
perchloric acid method requires less manipulation than proce-
all reagents shall conform to specifications of the Committee
dures based on fusion of the ash, but care must be taken
on Analytical Reagents of the American Chemical Society,
because of potential hazards in the use of this reagent. The
where such specifications are available. Other grades may be
perchloric acid method also tends to give low results.
used, provided it is first ascertained that the reagent is of
4. Significance and Use sufficiently high purity to permit its use without lessening the
accuracy of the determination.
4.1 The procedure described is specific for chromium in
leather. Vanadium is the only common interfering element and
Satisfactory equipment include, among others the following: the Kelley,
This test method is under the jurisdiction of ASTM Committee D-31 on Serfass, and Fisher tritrimeters, Leeds & Northrup potentiometers, and Beckman pH
Leather, and is the direct responsibility of Subcommittee D31.06 on Chemical meters.
Analysis—General Methods. This test method was developed in cooperation with Reagent Chemicals, American Chemical Society Specifications, American
the American Leather Chemists Assn. Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Current edition approved Jan. 15, 1993. Published March 1993. Originally listed by the American Chemical Society, see Analar Standards for Laboratory
published as D 2807 – 69 T. Last previous edition D 2807 – 78 (1991). Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Annual Book of ASTM Standards, Vol 15.04. and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
Annual Book of ASTM Standards, Vol 15.05. MD.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2807 – 93 (1998)
6.2 Purity of Water—Unless otherwise indicated, reference of KI solution, stopper the flask, and allow to stand 5 min in the
to water shall be understood to mean distilled water or water of dark. Titrate with the thiosulfate solution to be standardized.
equal purity. When the color of the solution has faded to a brownish-green,
6.3 Ferrous Ammonium Sulfate, Standard Solution (0.1 add 2 mL of 2 % starch solution and continue titrating until the
N)—Dissolve 39.21 g of ferrous ammonium sulfate deep blue color changes to a clear green. Record the titration.
(Fe(NH ) (SO ) ·6H O) in water, add 25 mL of H SO , Calculate the normality of the thiosulfate solution as follows:
4 2 4 2 2 2 4
anddilute to 1 L.
Normality 5 A/~0.04903 3 B! (2)
6.3.1 Standardization—Dry potassium dichromate
(K Cr O ) in an oven at 130°C for 2 h and cool in a desiccator.
2 2 7
where:
Weigh into a 250-mL glass-stoppered Erlenmeyer flask about
A = grams of K Cr O used, and
0.200 g of K Cr O to an accuracy of 0.0001 g. A beaker is 2 2 7
2 2 7
B = millilitres required for titration.
preferred if potentiometric titration is used. Dissolve in 75 to
6.9.2 The thiosulfate solution is quite stable but should be
100 mL of water, add 20 mL of sulfuric acid (H SO , 1+1) and
2 4
restandardized at least once a month.
titrate with the ferrous ammonium sulfate solution to be
6.10 Starch Indicator Solution, prepared according to ac-
standardized. Determine the end point either potentiometri-
cepted procedures available in analytical handbooks.
cally, or with 1,10-phenanthroline ferrous sulfate solution,
6.11 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid
0.025 M, as indicator. The potentiometric end point is marked
(H SO ).
2 4
by a sharp decrease in oxidation potential. The indicator end
point is from blue-green to a red-brown. It is preferable not to
7. Hazards
add the indicator until the end point is approaching, as
7.1 The improper use of HClO can lead to violent and
evidenced by the disappearance of a yellowish-green color and
serious explosions. In general, these can be traced to situations
a gradual change to blue-green.
where concentrated HClO has come in contact with organic or
6.3.2 The titer of the ferrous ammonium sulfate solution
easily oxidized materials.
decreases slowly because of oxidation of ferrous iron. This
7.2 The exact procedures given must be followed and the
change may be retarded by storing the solution in a dark bottle
digestions, once started, should be kept from possible contact
and by adding a few pieces of mossy tin to the solution.
with other organic matter. The digestions should never be
However, the solution should be standardized daily whenever
allowed to boil dry. HClO should never be used without
samples are being analyzed. Calculate the normality of the
accompanying use of HNO and H SO .
3 2 4
ferrous ammonium sulfate solutions as follows:
7.3 All spills involving HClO should be flushed with water.
Normality 5 A/~0.04903 3 B! (1)
Rags, sawdust, and other organic materials should never be
used to mop up spilled acid.
7.4
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