ASTM_D_2868_-_10_2015.pdf

Designation:D286810(Reapproved 2015)Standard Test Method forNitrogen Content(Kjeldahl)and Hide Substance Content ofLeather,Wet Blue and Wet White1This standard is issued under the fixed designation D2868;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 the nitro-gen content of all types of leather,wet blue and wet white.Thenitrogen content is used to calculate the hide substance(proteinfiber)content of leather,wet blue and wet white.NOTE1The original test method for leather was essentially acomposite of Method 6441 of Federal Test Method Standard No.311 andMethod B5 of the American Leather Chemists Association.NOTE2Melamine,if present in bonded leather,could give anartificially high value for the calculation of protein fiber.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:2D2813 Practice for Sampling Leather for Physical andChemical TestsD6659 Practice for Sampling and Preparation of Wet Bluefor Physical and Chemical TestsE177 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.Summary of Test Method3.1 The specimen prepared according to an accepted proce-dure(see Note 3)is digested with acid in the presence of acatalyst to convert the nitrogen to ammonium ion.The ammo-nium ion formed is nonvolatile under these highly acidconditions.NOTE3For leather use specimen prepared per Practice D2813.Forwet blue and wet white,use specimen prepared per Practice D6659.3.2 The acid mixture is then made alkaline and the ammonialiberated is distilled into either a boric acid solution whichabsorbs the ammonia,or a sulfuric acid solution which absorbsthe ammonia.3.3 When the boric acid solution is used,the amount ofammonia in the boric acid is then determined by back titrationwith standardized acid using a sharp color change indicator(green to purple)to determine the end point.When the sulfuricacid solution is used,the amount of ammonia in the sulfuricacid solution is then determined by back titration with stan-dardized base using a sharp color change indicator(purple togreen-blue)to determine the end point.4.Significance and Use4.1 The nitrogen content as determined by this test methodis normally considered to be related to the amount of hidesubstance(protein fiber)present in the leather sample.A factorof 5.62 is normally used to calculate the hide substance fromthe nitrogen content.4.1.1 The 5.62 factor represents the average result of manyanalyses of animal hides,but it cannot be considered to beaccurate since it varies somewhat from hide to hide of the sametype,from type of hide to type of hide,and also with thethickness of hide retained in the final leather(split thickness ascompared to original hide thickness).As a result of thesevariations,the true factor for any given leather may beexpected to vary from 5.44 to 5.80 or about 63%.34.2 A given leather sample may contain nitrogenous sub-stances other than hide substance(protein fiber)which will be1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on ChemicalAnalysis.Thistest method was developed in cooperation with the American Leather ChemistsAssn.(Standard Method B5 1954).Current edition approved Dec.1,2015.Published December 2015.Originallyapproved in 1970.Last previous edition approved in 2010 as D2868 10.DOI:10.1520/D2868-10R15.2For 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.3Dahl,S.,“Determination of Hide Substance in the Kjeldahl Method,”inChemistry and Technology of Leather,Vol 4,Reinhold Publishing Co.,New York,NY,1965.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 analyzed for by this test method,such as resins,dyestuffs,etc.,that contain nitrogen.Therefore,although this test method isfairly accurate for determining the nitrogen content of leather,its use for determining hide substance may result in largeerrors.4.3 The hide substance value derived from this