ASTM D2807-93(2003)
(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 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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 2003)
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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 4. Significance and Use
1.1 This test method covers the determination of chromic 4.1 The procedure described is specific for chromium in
oxide in leathers that have been partly or completely tanned leather. Vanadium is the only common interfering element and
with chromium compounds. In general the samples will con- this is rarely present in quantity.The precision and accuracy of
tain between 1 and 5% chromium, calculated as chromic the methods are usually at least as good as the sampling of the
oxide. leather itself.
1.2 This standard does not purport to address all of the 4.2 Thechromiumcontentofleatherrelatestothedegreeof
safety concerns, if any, associated with its use. It is the tannage obtained, and hence may be a matter for specification
responsibility of the user of this standard to establish appro- in the purchase of leather. The procedure described provides
priate safety and health practices and determine the applica- adequate accuracy for this purpose.
bility of regulatory limitations prior to use. See Section 7 for
5. Apparatus
specific safety hazards.
5.1 Potentiometric Titration Equipment—Thisisrequiredin
6+
2. Referenced Documents
an alternative method for titrating chromium (Cr ) with
2.1 ASTM Standards: ferrousammoniumsulfatesolution.Theequipmentconsistsof:
D2617 Test Method for Total Ash in Leather 5.1.1 Stirrer.
D2813 Practice for Sampling Leather for Physical and 5.1.2 Calomel and Platinum Electrodes.
Chemical Tests 5.1.3 Potentiometer—A variety of instruments is satisfac-
E180 Practice for Determining the Precision of ASTM tory. The most convenient common feature of these instru-
Methods for Analysis and Testing of Industrial Specialty ments is a null-point device (either a cathode-ray electron tube
Chemicals or galvanometer) that will signal the abrupt change occurring
in the potential when the end point is reached.
3. Summary of Test Method
5.2 Incarryingoutthetitration,theelectrodesareimmersed
3.1 The perchloric acid method is applied to the ash in the sample, the solution agitated by the stirrer, and the
obtained in Test Method D2617. In the acid digestion, any
potential balanced with the galvanometer or cathode-ray tube.
remaining organic matter is destroyed and the chromium Titrant is added dropwise until a sharp permanent change in
oxidized to the hexavalent state. On dilution, the chromium is
potential occurs.
titrated volumetrically with thiosulfate or ferrous salt. The
6. Reagents
perchloric acid method requires less manipulation than proce-
dures based on fusion of the ash, but care must be taken 6.1 Purity of Reagents—Reagent grade chemicals shall be
because of potential hazards in the use of this reagent. The used in all tests. Unless otherwise indicated, it is intended that
perchloric acid method also tends to give low results. 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
ThistestmethodisunderthejurisdictionofASTMCommitteeD31onLeather
sufficiently high purity to permit its use without lessening the
and is the direct responsibility of Subcommittee D31.06 on ChemicalAnalysisThis
accuracy of the determination.
test method was developed in cooperation with the American Leather Chemists
Assn.
Current edition approved May 10, 2003. Published June 2003. Originally
approved in 1969. Last previous edition approved in 1998 as D2807–93 (1998). Satisfactory equipment include, among others the following: the Kelley,
Annual Book of ASTM Standards, Vol 15.04. Serfass,andFishertritrimeters,Leeds&Northruppotentiometers,andBeckmanpH
Annual Book of ASTM Standards, Vol 15.05. meters.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D2807–93 (2003)
6.2 Purity of Water—Unless otherwise indicated, reference 6.9.1 Standardization—Dry potassium dichromate
towatershallbeunderstoodtomeandistilledwaterorwaterof (K Cr O )inanovenat130°Cfor2handcoolinadesiccator.
2 2 7
equal purity. Weigh into a 250-mL glass-stoppered Erlenmeyer flask about
6.3 Ferrous Ammonium Sulfate, Standard Solution (0.1 0.200 g of K Cr O to an accuracy of 0.0001 g. Dissolve in 50
2 2 7
N)—Dissolve 39.21 g of ferrous ammonium sulfate mLofwater;add4mLofhydrochloricacid(HCl,1+1)20mL
(Fe(NH ) (SO ) ·6H O) in water, add 25 mL of H SO , ofKIsolution,stoppertheflask,andallowtostand5mininthe
4 2 4 2 2 2 4
anddilute to 1 L. dark. Titrate with the thiosulfate solution to be standardized.
6.3.1 Standardization—Dry potassium dichromate When the color of the solution has faded to a brownish-green,
(K Cr O )inanovenat130°Cfor2handcoolinadesiccator. add2mLof2%starchsolutionandcontinuetitratinguntilthe
2 2 7
Weigh into a 250-mL glass-stoppered Erlenmeyer flask about deep blue color changes to a clear green. Record the titration.
0.200 g of K Cr O to an accuracy of 0.0001 g. A beaker is Calculate the normality of the thiosulfate solution as follows:
2 2 7
preferred if potentiometric titration is used. Dissolve in 75 to
Normality 5 A/~0.04903 3 B! (2)
100mLofwater,add20mLofsulfuricacid(H SO ,1+1)and
2 4
titrate with the ferrous ammonium sulfate solution to be
where:
standardized. Determine the end point either potentiometri-
A = grams of K Cr O used, and
cally, or with 1,10-phenanthroline ferrous sulfate solution, 2 2 7
6 B = millilitres required for titration.
0.025 M, as indicator.The potentiometric end point is marked
6.9.2 The thiosulfate solution is quite stable but should be
by a sharp decrease in oxidation potential. The indicator end
restandardized at least once a month.
point is from blue-green to a red-brown. It is preferable not to
6.10 Starch Indicator Solution, prepared according to ac-
add the indicator until the end point is approaching, as
cepted procedures available in analytical handbooks.
evidencedbythedisappearanceofayellowish-greencolorand
6.11 Sulfuric Acid (sp gr 1.84)—Concentrated sulfuric acid
a gradual change to blue-green.
(H SO ).
2 4
6.3.2 The titer of the ferrous ammonium sulfate solution
decreases slowly because of oxidation of ferrous iron. This
7. Hazards
change may be retarded by storing the solution in a dark bottle
and by adding a few pieces of mossy tin to the solution.
7.1 The improper use of HClO can lead to violent and
However, the solution should be standardized daily whenever
serious explosions. In general, these can be traced to situations
samples are being analyzed. Calculate the normality of the
whereconcentratedHClO hascomeincontactwithorganicor
ferrous ammonium sulfate solutions as follows:
easily oxidized materials.
7.2 The exact procedures given must be followed and the
Normality 5 A/ 0.04903 3 B! (1)
~
digestions, once started, should be kept from possible contact
with other organic matter. The digestions should never be
where:
allowed to boil dry. HClO should never be used without
A = grams of K Cr O used, and
2 2 7
accompanying use of HNO and H SO .
3 2 4
B = millilitres required for titration.
7.3 AllspillsinvolvingHClO shouldbeflushedwithwater.
6.4 Nitric Acid (sp gr 1.42)—Concentrated nitric acid
Rags, sawdust, and other organic materials should never be
(HNO ).
us
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