ASTM_D_2807_-_93_2015.pdf

Designation:D280793(Reapproved 2015)Standard 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 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 determination of chromicoxide in leathers that have been partly or completely tannedwith chromium compounds.In general the samples will con-tain between 1 and 5%chromium,calculated as chromicoxide.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.See Section 7 forspecific safety hazards.2.Referenced Documents2.1 ASTM Standards:2D2617 Test Method for Total Ash in LeatherD2813 Practice for Sampling Leather for Physical andChemical TestsE180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals(Withdrawn 2009)33.Summary of Test Method3.1 The perchloric acid method is applied to the ashobtained in Test Method D2617.In the acid digestion,anyremaining organic matter is destroyed and the chromiumoxidized to the hexavalent state.On dilution,the chromium istitrated volumetrically with thiosulfate or ferrous salt.Theperchloric acid method requires less manipulation than proce-dures based on fusion of the ash,but care must be takenbecause of potential hazards in the use of this reagent.Theperchloric acid method also tends to give low results.4.Significance and Use4.1 The procedure described is specific for chromium inleather.Vanadium is the only common interfering element andthis is rarely present in quantity.The precision and accuracy ofthe methods are usually at least as good as the sampling of theleather itself.4.2 The chromium content of leather relates to the degree oftannage obtained,and hence may be a matter for specificationin the purchase of leather.The procedure described providesadequate accuracy for this purpose.5.Apparatus5.1 Potentiometric Titration EquipmentThis is required inan alternative method for titrating chromium(Cr6+)withferrous ammonium sulfate solution.The equipment consists of:5.1.1 Stirrer.5.1.2 Calomel and Platinum Electrodes.5.1.3 PotentiometerA variety of instruments is satisfac-tory.4The most convenient common feature of these instru-ments is a null-point device(either a cathode-ray electron tubeor galvanometer)that will signal the abrupt change occurringin the potential when the end point is reached.5.2 In carrying out the titration,the electrodes are immersedin the sample,the solution agitated by the stirrer,and thepotential balanced with the galvanometer or cathode-ray tube.Titrant is added dropwise until a sharp permanent change inpotential occurs.6.Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.Unless otherwise indicated,it is intended thatall reagents shall conform to specifications of the Committee1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis Thistest method was developed in cooperation with the American Leather ChemistsAssn.Current edition approved Sept.1,2015.Published October 2015.Originallyapproved in 1969.Last previous edition approved in 2009 as D2807 93(2009)1.DOI:10.1520/D2807-93R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Satisfactory equipment include,among others the following:the Kelley,Serfass,and Fisher tritrimeters,Leeds&Northrup potentiometers,and Beckman pHmeters.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 on Analytical Reagents of the American Chemical Society,where such specifications are available.5Other grades may beused,provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated,referenceto water shall be understood to mean distilled water or water ofequal purity.6.3 Ferrous Ammonium Sulfate,Standard Solution(0.1N)Dissolve39.21gofferrousammoniumsulfate(Fe(NH4)2(SO4)