ASTM_D_6019_-_15.pdf

Designation:D601915Test Method forDetermination of Chromic Oxide in Basic ChromiumTanning Liquors(Ammonium Persulfate Oxidation)1This standard is issued under the fixed designation D6019;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.Summary of Test Method2.1 The solution is oxidized with ammonium persulfateuntil the chromium is completely converted to the chromateion.The solution is boiled to complete oxidation of organicmaterials and to destroy excess ammonium persulfate;it is thencooled and acidified.Potassium iodide is added,and theliberated iodine is titrated with standardized sodium thiosul-fate.3.Significance and Use3.1 The procedure described is for the quality control formanufacturing liquors and specifications for the purchase ofsuch liquors.3.2 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.4.Reagents and Materials4.1 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.2Other 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.4.2 Purity of WaterUnless otherwise indicated,referenceto water shall be understood to mean distilled water,deionizedwater or water of equal purity.4.3 Ammonium Persulfate20%solution 100 g of persul-fate into 500 mL water.4.3.1 Alternatively,ammonium persulfate may be added in5.5 as solid form using plastic scoopula.4.4 Starch Indicator,2%Make a paste of 2 g of solublestarch in about 10 mL of water,add 90 mL water,and boil for1 min with stirring.Cool.Refrigerate after use.The solution issubject to decomposition and should be renewed if a deep bluecolor is not obtained on addition of one drop of indicator to asolution of 1 drop tincture of iodine in 100 mL of water.4.5 Sodium Thiosulfate Solution,0.1 NDissolve 24.85 gof Na2S2O35H2O in water,add 1 g Na2CO3,and dilute to 1 L.4.5.1 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 flask,andallow to stand 5 min in the dark.Titrate with the sodiumthiosulfate to be standardized.When the color of the solutionhas faded to a brownish-green,add 2 mL of 2%starchsolution,and continue titrating until the deep blue colorchanges to a clear green.Record the titration.normality of sodium thiosulfate5weight potassium dichromate0.049033mL titration(1)1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis.Current edition approved Dec.1,2015.Published January 2016.Originallyapproved in 1996.Last previous edition approved in 2010 as D6019 10.DOI:10.1520/D6019-15.2Reagent 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.Pharmacopeial Convention,Inc.(USPC),Rockville,MD.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 The thiosulfate solution is quite stable but should be restan-dardized at least once a month.4.6 Potassium Dichromate,K2Cr2O7,primary standardgrade.4.7 Potassium Iodide,10%Dissolve 10 g KI in 100 mLwater.4.8 Hydrochloric Acid,1:1Dilute 250 mL concentratedhydrochloric acid(sp gr 1.19)in 250 mL water.4.9 Silver Nitrate,1%Dissolve 1 g of AgNO3in 100 mLwater.4.10 Potassium Permanganate,1%Dissolve 1 g ofKMnO3in 100 mL water.5.Procedure5.1 Weigh 11 to 12 g,to the nearest 0.1 mg,of the chrome