ASTM_D_6656_-_14b.pdf

Designation:D665614bStandard Test Method forDetermination of Chromic Oxide in Wet Blue(PerchloricAcid Oxidation)1This standard is issued under the fixed designation D6656;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 wet blue that has been partly or completely tannedwith chromium compounds.In general,the samples willcontain chromium content between 1%and 5%when calcu-lated as chromic oxide expressed upon a dry basis otherwisereferred to as moisture-free basis(mfb).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 9 forspecific safety hazards.2.Referenced Documents2.1 ASTM Standards:2D6658 Test Method for Volatile Matter(Moisture)of WetBlue by Oven DryingD6659 Practice for Sampling and Preparation of Wet Bluefor Physical and Chemical TestsE180 Practice for Determining the Precision of ASTMMethods for Analysis and Testing of Industrial and Spe-cialty Chemicals(Withdrawn 2009)3E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 DefinitionsThe terms and definitions employed withinthis method are commonly used in normal laboratory practiceand require no special comment.4.Summary of Test Method4.1 The perchloric acid method may be applied to wet blue.Accurately weighed wet blue samples are digested in a blend ofconcentrated nitric acid and a prepared“oxidation mixture”consisting of sulfuric and perchloric acids.Once completed,oxidation of all tri-valent to haxavalent chrome is executed bycontrolled heating.Upon dilution,the chromium is indirectly(back)titrated volumetrically with standardized thiosulfateusing released iodine as the titrate.The perchloric acid methodrequires less manipulation than procedures based upon fusionof the ash.However,care must be taken because of potentialhazards in the use of this reagent.5.Significance and Use5.1 The procedure described is specific for chromium in wetblue.Vanadium is the only common interfering element and israrely present in quantity.The precision and accuracy of themethods are usually,at least,as good as the sampling of wetblue itself.5.2 The chromium content of wet blue is related to thedegree of tannage obtained,and hence may be a matter forspecification in the purchase of wet blue.The proceduredescribed provides adequate accuracy for this purpose.6.Apparatus6.1 Analytical Balanceaccurate and calibrated to 0.001 g.6.2 Erlenmeyer Flasks250 mL capacity or equivalent.6.3 Burette50 mL capacity of suitable calibration grade,minimum calibration of 0.1 mL.6.4 Glass Anti-Bumping Beadsor equivalent.6.5 Measuring Cylindersof 50 mL capacity or equivalent.6.6 Small Glass Filter Funnel.6.7 Dessicatorof suitable size and design and chargedwith fresh dessicant.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.02 on Wet Blue.Current edition approved Nov.1,2014.Published December 2014.Originallyapproved in 1996.Last previous edition approved in 2014 as D6656-14a.DOI:10.1520/D6656-14B.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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.8 Weighing Vesselsof suitable size and design.6.9 Drying Ovenwith accurate variable temperature con-trols.7.Reagents and Materials7.1 Purity of ReagentsAnalytical Reagent(AR)gradeshall be used in all tests.Unless otherwise indicated,it isintended that all reagents shall conform to specifications of theCommittee on Analytical Reagents of the American ChemicalSociety,where such specifications are available.4Other gradesmay be used,provided it is first ascertained that the reagent isof sufficiently high purity to permit its use without lesseningthe accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated,referenceto water shall be understood to mean distilled water or water ofequal purity.7.3 Commercial ReagentsThe use of commercially avail-able pre-standardized analytical reagents a