ASTM_D_3898_-_93_2015.pdf

Designation:D389893(Reapproved 2015)Standard Test Method forChromic Oxide in Basic Chromium Tanning Liquors1This standard is issued under the fixed designation D3898;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.1.Scope1.1 This test method covers the determination of chromicoxide in chrome tanning liquors,either simple,with addedaluminum or zirconium,or with the usual masking complexingagents.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.2.Referenced Documents2.1 ASTM Standards:2D2807 Test Method for Chromic Oxide in Leather(Perchlo-ric Acid Oxidation)3.Summary of Test Method3.1 The solution is oxidized with sodium peroxide until thechromium is completely converted to the chromate ion.Thesolution is boiled to complete oxidation of organic materialsand to destroy excess peroxide;it is then cooled and acidified.Potassium iodide is added and the liberated iodine is titratedwith standardized sodium thiosulfate.4.Significance and Use4.1 The procedure described is for the quality control formanufacturing liquors and specifications for the purchase ofsuch liquors.4.2 The chromium content of the liquors determines theamount to be used to obtain the desired degree of tannage,andhence may be a matter for specification in the purchase ofleather.5.Interferences5.1 The test method is generally the most accurate andconvenient for the purpose.However,if the liquor containsiron or copper,which interfere with the sodium thiosulfatetitration,or complex organic or inorganic reducing agents(sodium thiosulfate,for example)which are not oxidized byalkaline peroxide but reduce hexavalent chromium onacidification,an alternate procedure must be used.The per-chloric acid method described in Test Method D2807,using theferrous sulfate titration,is suitable,although the results ob-tained may be one to two percent low.6.Reagents and Materials6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.Unless otherwise indicated,it is intended thatall reagents shall conform to the specifications of the Commit-tee onAnalytical Reagents of TheAmerican Chemical Society,where such specifications are available.3Other 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 Sodium Peroxide,(Na2O2).Store in original metal can.6.4 Starch Indicator,1%Make a paste of 1 g of solublestarch in about 10 mL of water,add 90 mL water and boil for1 min with stirring.Cool and add 1 drop of chloroform.Thesolution is subject to decomposition and should be renewed ifa deep blue color is not obtained on addition of 1 drop ofindicator to a solution of 1 drop tincture of iodine in 100 mLof water.1This 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 ChemistsAssoc.Current edition approved Sept.1,2015.Published October 2015.Originallyapproved in 1991.Last previous edition approved in 2009 as D3898 93(2009).DOI:10.1520/D3898-93R15.2For 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.3Reagent Chemicals,American Chemical Society Specifications,AmericanChemical Society,Washington,DC.For suggestions on the testing of reagents notlisted by the American Chemical Society,see Analar Standards for LaboratoryChemicals,BDH Ltd.,Poole,Dorset,U.K.,and the United States Pharmacopeiaand National Formulary,U.S.Pharmaceutical Convention,Inc.(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.5 Sodium Thiosulfate Solution,0.1 NDissolve 24.85 gof Na2S2O35 H2O in water,add 1 g Na2CO3,and dilute to 1 L.6.5.1 StandardizationDrypotassiumdichromate(K2Cr2O7)in an oven at 130C for 2 h and cool in a desiccator.Weigh into a glass stoppered Erlenmeyer flask(500 mL)about0.2 g of potassium dichromate to an accuracy of 0.1 mg.Dissolve in 250 mLwater,add 15 mL1:4 hydrochloric acid,20mL of 10%potassium iodide solution,stopper the