ASTM D2807-17a

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Designation: D2807 − 17 D2807 − 17a
Standard Test Method for
Chromic Oxide in Leather (Perchloric Acid Oxidation)
This standard is issued under the fixed designation D2807; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. 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 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 safety, health and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. See Section 7 for specific safety hazards.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D2617 Test Method for Total Ash in Leather
D2813 Practice for Sampling Leather for Physical and Chemical Tests
D2868 Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather, Wet Blue and Wet White
D3495 Test Method for Hexane Extraction of Leather
D3790 Test Method for Volatile Matter (Moisture) of Leather by Oven Drying
3. Summary of Test Method
3.1 The perchloric acid method is applied to the ash obtained in Test Method D2617. In the acid digestion, any remaining
organic matter is destroyed and the chromium oxidized to the hexavalent state. On dilution, the chromium is titrated volumetrically
with thiosulfate or ferrous salt. The perchloric acid method requires less manipulation than procedures based on fusion of the ash,
but care must be taken because of potential hazards in the use of this reagent. The perchloric acid method also tends to give low
results.
4. Significance and Use
4.1 The procedure described is specific for chromium in leather. Vanadium is the only common interfering element and this is
rarely present in quantity. The precision and accuracy of the methods are usually at least as good as the sampling of the leather
itself.
4.2 The chromium content of leather relates to the degree of tannage obtained, and hence may be a matter for specification in
the purchase of leather. The procedure described provides adequate accuracy for this purpose.
5. Apparatus
6+
5.1 Potentiometric Titration Equipment—This is required in an alternative method for titrating chromium (Cr ) with ferrous
ammonium sulfate solution. The equipment consists of:
This test method is under the jurisdiction of ASTM Committee D31 on Leather and is the direct responsibility of Subcommittee D31.06 on Chemical Analysis This test
method was developed in cooperation with the American Leather Chemists Assn.
Current edition approved April 1, 2017Sept. 1, 2017. Published May 2017September 2017. Originally approved in 1969. Last previous edition approved in 20152017 as
D2807 – 93 (2015).D2807 – 17. DOI: 10.1520/D2807-17.10.1520/D2807-17A.
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.
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D2807 − 17a
5.1.1 Stirrer.
5.1.2 Calomel and Platinum Electrodes.
5.1.3 Potentiometer—A variety of instruments is satisfactory. The most convenient common feature of these instruments is a
null-point device (either a cathode-ray electron tube or galvanometer) that will signal the abrupt change occurring in the potential
when the end point is reached.
5.1.4 In carrying out the titration, the electrodes are immersed in the sample, the solution agitated by the stirrer, and the potential
balanced with the galvanometer or cathode-ray tube. Titrant is added dropwise until a sharp permanent change in potential occurs.
5.2 Perchloric Acid Hood.
6. Reagents
6.1 Purity of Reagents—Reagent grade chemicals 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.
6.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean distilled water, deionized water,
or water of equal purity.
6.3 Ferrous Ammonium Sulfate, Standard Solution (0.1 N)—Dissolve 39.21 g of ferrous ammonium sulfate
(Fe(NH ) (SO ) ·6H O) in water, add 25 mL of H SO , and dilute to 1 L.
4 2 4 2 2 2 4
6.3.1 Standardization—Dry potassium dichromate (K Cr O ) in an oven at 130 °C for 2 h and cool in a desiccator. Weigh into
2 2 7
a 250-mL glass-stoppered Erlenmeyer flask about 0.200 g of K Cr O to an accuracy of 0.0001 g. A beaker is preferred if
2 2 7
potentiometric titration is used. Dissolve in 75 to 100 mL of water, add 20 mL of sulfuric acid (H SO , 1+1) and titrate with the
2 4
ferrous ammonium sulfate solution to be standardized. Determine the end point either potentiometrically, or with 1,10-
phenanthroline ferrous sulfate solution, 0.025 M, as indicator. The potentiometric end point is marked by a sharp decrease in
oxidation potential. The indicator end point is from blue-green to a red-brown. It is preferable not to add the indicator until the
end point is approaching, as evidenced by the disappearance of a yellowish-green color and a gradual change to blue-green.
6.3.2 The titer of the ferrous ammonium sulfate solution decreases slowly because of oxidation of ferrous iron. This change may
be retarded by storing the solution in a dark bottle and by adding a few pieces of mossy tin to the solution. However, the solution
should be standardized daily whenever samples are being analyzed. Calculate the normality of the ferrous ammonium sulfate
solutions as follows:
Normality 5 A/~0.04903 3B! (1)
where:
A = grams of K Cr O used, and
2 2 7
B = millilitres required for titration.
6.4 Nitric Acid (sp gr 1.42)—Concentrated nitric acid (HNO ).
6.5 Perchloric Acid (60 %)—70 or 72 % perchloric acid (HClO ) may be substituted but storage is somewhat more hazardous.
6.6 1,10-Phenanthroline-Ferrous Sulfate Solution (0.025 M).
6.7 Phosphoric Acid (40 %)—Dilute 45 mL of 85 % phosphoric acid (H PO ) with water to 100 mL.
3 4
6.8 Potassium Iodide Solution (10 %)—Dissolve 10 g of potassium iodide (KI) in 100 mL of water.
6.9 Sodium Thiosulfate, Standard Solution (0.1 N)—Dissolve 24.85 g of sodium thiosulfate (Na S O ·5H O) in previously
2 2 3 2
boiled water, add 1 g of sodium carbonate (Na CO ), and dilute to 1 L.
2 3
6.9.1 Standardization—Dry potassium dichromate (K Cr O ) in an oven at 130 °C for 2 h and cool in a desiccator. Weigh into
2 2 7
a 250-mL glass-stoppered Erlenmeyer flask about 0.200 g of K Cr O to an accuracy of 0.0001 g. Dissolve in 50 mL of water;
2 2 7
add 4 mL of hydrochloric acid (HCl, 1+1) 20 mL of KI solution, stopper the flask, and allow to stand 5 min in the dark. Titrate
with the thiosulfate solution to be standardized. When the color of the solution has faded to a brownish-green, add 2 mL of 2 %
starch solution and continue titrating until the deep blue color changes to a clear green. Record the titration. Calculate the normality
of the thiosulfate solution as follows:
Normality 5 A/ 0.04903 3B (2)
~ !
Satisfactory equipment include, among others the following: the Kelley, Serfass, and Fisher tritrimeters, Leeds & Northrup potentiometers, and Beckman pH meters.
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, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
A satisfactory reagent, Ferroin, is manufactured by the G. Frederick Smith Chemical Co., Columbus, Ohio.commercially availabl
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