1、Designation: D2807 17D2807 17aStandard Test Method forChromic Oxide in Leather (Perchloric Acid Oxidation)1This standard is issued under the fixed designation D2807; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 This test method covers the determina
3、tion of chromic oxide in leathers that have been partly or completely tanned withchromium 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 include
4、d 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 responsibilityof the user of this standard to establish appropriate safety safety, health and healthenvironmental practices and determine theapplicability of regula
5、tory 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 standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recom
6、mendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D2617 Test Method for Total Ash in LeatherD2813 Practice for Sampling Leather for Physical and Chemical TestsD2868 Test Method for Nitrogen Content (Kjeldahl) and H
7、ide Substance Content of Leather, Wet Blue and Wet WhiteD3495 Test Method for Hexane Extraction of LeatherD3790 Test Method for Volatile Matter (Moisture) of Leather by Oven Drying3. Summary of Test Method3.1 The perchloric acid method is applied to the ash obtained in Test Method D2617. In the acid
8、 digestion, any remainingorganic matter is destroyed and the chromium oxidized to the hexavalent state. On dilution, the chromium is titrated volumetricallywith thiosulfate or ferrous salt. The perchloric acid method requires less manipulation than procedures based on fusion of the ash,but care must
9、 be taken because of potential hazards in the use of this reagent. The perchloric acid method also tends to give lowresults.4. Significance and Use4.1 The procedure described is specific for chromium in leather. Vanadium is the only common interfering element and this israrely present in quantity. T
10、he precision and accuracy of the methods are usually at least as good as the sampling of the leatheritself.4.2 The chromium content of leather relates to the degree of tannage obtained, and hence may be a matter for specification inthe purchase of leather. The procedure described provides adequate a
11、ccuracy for this purpose.5. Apparatus5.1 Potentiometric Titration EquipmentThis is required in an alternative method for titrating chromium (Cr6+) with ferrousammonium sulfate solution. The equipment consists of:1 This test method is under the jurisdiction of ASTM Committee D31 on Leather and is the
12、 direct responsibility of Subcommittee D31.06 on Chemical Analysis This testmethod 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 i
13、n 20152017 asD2807 93 (2015).D2807 17. DOI: 10.1520/D2807-17.10.1520/D2807-17A.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on
14、 the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users
15、 consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.1.1 Stirrer.5.1.2 Calomel an
16、d Platinum Electrodes.5.1.3 PotentiometerA variety of instruments is satisfactory.3 The most convenient common feature of these instruments is anull-point device (either a cathode-ray electron tube or galvanometer) that will signal the abrupt change occurring in the potentialwhen the end point is re
17、ached.5.1.4 In carrying out the titration, the electrodes are immersed in the sample, the solution agitated by the stirrer, and the potentialbalanced 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. Re
18、agents6.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to specifications of the Committee on Analytical Reagents of the American Chemical Society, where suchspecifications are available.4 Other grades
19、may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the accuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, reference to water shall be understood to mean distilled water, deionized water,or water o
20、f equal purity.6.3 Ferrous Ammonium Sulfate, Standard Solution (0.1 N)Dissolve 39.21 g of ferrous ammonium sulfate(Fe(NH4)2(SO4)26H2O) in water, add 25 mL of H2SO4, and dilute to 1 L.6.3.1 StandardizationDry potassium dichromate (K2Cr2O7) in an oven at 130 C for 2 h and cool in a desiccator. Weigh i
21、ntoa 250-mL glass-stoppered Erlenmeyer flask about 0.200 g of K2Cr2O7 to an accuracy of 0.0001 g. A beaker is preferred ifpotentiometric titration is used. Dissolve in 75 to 100 mL of water, add 20 mL of sulfuric acid (H2SO4, 1+1) and titrate with theferrous ammonium sulfate solution to be standardi
22、zed. Determine the end point either potentiometrically, or with 1,10-phenanthroline ferrous sulfate solution, 0.025 M,5 as indicator. The potentiometric end point is marked by a sharp decrease inoxidation potential. The indicator end point is from blue-green to a red-brown. It is preferable not to a
23、dd the indicator until theend 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 maybe retarded by storing th
24、e solution in a dark bottle and by adding a few pieces of mossy tin to the solution. However, the solutionshould be standardized daily whenever samples are being analyzed. Calculate the normality of the ferrous ammonium sulfatesolutions as follows:Normality5A/0.049033B! (1)where:A = grams of K2Cr2O7
25、 used, andB = millilitres required for titration.6.4 Nitric Acid (sp gr 1.42)Concentrated nitric acid (HNO3).6.5 Perchloric Acid (60 %)70 or 72 % perchloric acid (HClO4) may be substituted but storage is somewhat more hazardous.6.6 1,10-Phenanthroline-Ferrous Sulfate Solution (0.025 M).56.7 Phosphor
26、ic Acid (40 %)Dilute 45 mL of 85 % phosphoric acid (H3PO4) with water to 100 mL.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 (Na2S2O35H2O) in previouslyboiled wate
27、r, add 1 g of sodium carbonate (Na2CO3), and dilute to 1 L.6.9.1 StandardizationDry potassium dichromate (K2Cr2O7) in an oven at 130 C for 2 h and cool in a desiccator. Weigh intoa 250-mL glass-stoppered Erlenmeyer flask about 0.200 g of K2Cr2O7 to an accuracy of 0.0001 g. Dissolve in 50 mL of water
28、;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. Titratewith 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
29、the deep blue color changes to a clear green. Record the titration. Calculate the normalityof the thiosulfate solution as follows:Normality5A/0.049033B! (2)3 Satisfactory equipment include, among others the following: the Kelley, Serfass, and Fisher tritrimeters, Leeds chromic oxide; perchloric acid
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