ASTM D2807-93(2009)e1
(Test Method)Standard Test Method for Chromic Oxide in Leather (Perchloric Acid Oxidation)
Standard Test Method for Chromic Oxide in Leather (Perchloric Acid Oxidation)
SIGNIFICANCE AND USE
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.
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.
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 and health practices and determine the applicability of regulatory limitations prior to use. See Section 7 for specific safety hazards.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D2807 − 93(Reapproved 2009)
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.Anumber 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 Department of Defense.
´ NOTE—Added research report information to Section 12 editorially in September 2010.
1. Scope remaining organic matter is destroyed and the chromium
oxidized to the hexavalent state. On dilution, the chromium is
1.1 This test method covers the determination of chromic
titrated volumetrically with thiosulfate or ferrous salt. The
oxide in leathers that have been partly or completely tanned
perchloric acid method requires less manipulation than proce-
with chromium compounds. In general the samples will con-
dures based on fusion of the ash, but care must be taken
tain between 1 and 5% chromium, calculated as chromic
because of potential hazards in the use of this reagent. The
oxide.
perchloric acid method also tends to give low results.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
4. Significance and Use
standard.
4.1 The procedure described is specific for chromium in
1.3 This standard does not purport to address all of the
leather. Vanadium is the only common interfering element and
safety concerns, if any, associated with its use. It is the
thisisrarelypresentinquantity.Theprecisionandaccuracyof
responsibility of the user of this standard to establish appro-
the methods are usually at least as good as the sampling of the
priate safety and health practices and determine the applica-
leather itself.
bility of regulatory limitations prior to use. See Section 7 for
4.2 Thechromiumcontentofleatherrelatestothedegreeof
specific safety hazards.
tannage obtained, and hence may be a matter for specification
2. Referenced Documents in the purchase of leather. The procedure described provides
2 adequate accuracy for this purpose.
2.1 ASTM Standards:
D2617Test Method for Total Ash in Leather
5. Apparatus
D2813Practice for Sampling Leather for Physical and
Chemical Tests 5.1 Potentiometric Titration Equipment—Thisisrequiredin
6+
an alternative method for titrating chromium (Cr ) with
E180Practice for Determining the Precision of ASTM
Methods for Analysis and Testing of Industrial and Spe- ferrousammoniumsulfatesolution.Theequipmentconsistsof:
cialty Chemicals (Withdrawn 2009) 5.1.1 Stirrer.
5.1.2 Calomel and Platinum Electrodes.
3. Summary of Test Method
5.1.3 Potentiometer—A variety of instruments is satisfac-
tory. The most convenient common feature of these instru-
3.1 The perchloric acid method is applied to the ash
ments is a null-point device (either a cathode-ray electron tube
obtained in Test Method D2617. In the acid digestion, any
or galvanometer) that will signal the abrupt change occurring
in the potential when the end point is reached.
ThistestmethodisunderthejurisdictionofASTMCommitteeD31onLeather
5.2 Incarryingoutthetitration,theelectrodesareimmersed
and is the direct responsibility of Subcommittee D31.06 on ChemicalAnalysisThis
test method was developed in cooperation with the American Leather Chemists in the sample, the solution agitated by the stirrer, and the
Assn.
potential balanced with the galvanometer or cathode-ray tube.
Current edition approved April 1, 2009. Published July 2009. Originally
Titrant is added dropwise until a sharp permanent change in
approved in 1969. Last previous edition approved in 2003 as D2807–93 (2003).
potential occurs.
DOI: 10.1520/D2807-93R09E01.
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. Satisfactory equipment include, among others the following: the Kelley,
The last approved version of this historical standard is referenced on Serfass,andFishertritrimeters,Leeds&Northruppotentiometers,andBeckmanpH
www.astm.org. meters.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D2807 − 93 (2009)
6. Reagents 6.6 1,10-Phenanthroline-Ferrous Sulfate Solution (0.025
M).
6.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
6.7 Phosphoric Acid (40 % )—Dilute 45 mL of 85% phos-
all reagents shall conform to specifications of the Committee
phoric acid (H PO ) with water to 100 mL.
3 4
on Analytical Reagents of the American Chemical Society,
6.8 Potassium Iodide Solution (10 %)—Dissolve 10 g of
where such specifications are available. Other grades may be
potassium iodide (KI) in 100 mL of water.
used, provided it is first ascertained that the reagent is of
6.9 Sodium Thiosulfate, Standard Solution (0.1 N)—
sufficiently high purity to permit its use without lessening the
accuracy of the determination. Dissolve 24.85 g of sodium thiosulfate (Na S O ·5H O) in
2 2 3 2
previously boiled water, add 1 g of sodium carbonate
6.2 Purity of Water—Unless otherwise indicated, reference
(Na CO ), and dilute to 1 L.
2 3
towatershallbeunderstoodtomeandistilledwaterorwaterof
6.9.1 Standardization—Dry potassium dichromate
equal purity.
(K Cr O )inanovenat130°Cfor2handcoolinadesiccator.
2 2 7
6.3 Ferrous Ammonium Sulfate, Standard Solution (0.1
Weigh into a 250-mL glass-stoppered Erlenmeyer flask about
N)—Dissolve 39.21 g of ferrous ammonium sulfate
0.200 g of K Cr O to an accuracy of 0.0001 g. Dissolve in 50
2 2 7
(Fe(NH ) (SO ) ·6H O) in water, add 25 mL of H SO ,
4 2 4 2 2 2 4
mLofwater;add4mLofhydrochloricacid(HCl,1+1)20mL
anddilute to 1 L.
ofKIsolution,stoppertheflask,andallowtostand5mininthe
6.3.1 Standardization—Dry potassium dichromate
dark. Titrate with the thiosulfate solution to be standardized.
(K Cr O )inanovenat130°Cfor2handcoolinadesiccator.
2 2 7
When the color of the solution has faded to a brownish-green,
Weigh into a 250-mL glass-stoppered Erlenmeyer flask about
add2mLof2%starchsolutionandcontinuetitratinguntilthe
0.200 g of K Cr O to an accuracy of 0.0001 g. A beaker is
2 2 7
deep blue color changes to a clear green. Record the titration.
preferred if potentiometric titration is used. Dissolve in 75 to
Calculate the normality of the thiosulfate solution as follows:
100mLofwater,add20mLofsulfuricacid(H SO ,1+1)and
2 4
Normality 5 A/ 0.04903 3 B (2)
~ !
titrate with the ferrous ammonium sulfate solution to be
standardized. Determine the end point either
where:
potentiometrically, or with 1,10-phenanthroline ferrous sulfate
A = grams of K Cr O used, and
2 2 7
solution, 0.025 M, as indicator. The potentiometric end point
B = millilitres required for titration.
is marked by a sharp decrease in oxidation potential. The
6.9.2 The thiosulfate solution is quite stable but should be
indicator end point is from blue-green to a red-brown. It is
restandardized at least once a month.
preferable not to add the indicator until the end point is
approaching, as evidenced by the disappearance of a
6.10 Starch Indicator Solution, prepared according to ac-
yellowish-green color and a gradual change to blue-green.
cepted procedures available in analytical handbooks.
6.3.2 The titer of the ferrous ammonium sulfate solution
6.11 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid
decreases slowly because of oxidation of ferrous iron. This
(H SO ).
2 4
change may be retarded by storing the solution in a dark bottle
and by adding a few pieces of mossy tin to the solution.
7. Hazards
However, the solution should be standardized daily whenever
samples are being analyzed. Calculate the normality of the
7.1 The improper use of HClO can lead to violent and
ferrous ammonium sulfate solutions as follows:
serious explosions. In general, these can be traced to situations
whereconcentratedHClO hascomeincontactw
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