1、Designation: D 6019 96 (Reapproved 2006)Test Method forDetermination of Chromic Oxide in Basic ChromiumTanning Liquors (Ammonium Persulfate Oxidation)1This standard is issued under the fixed designation D 6019; the number immediately following the designation indicates the year oforiginal adoption o
2、r, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of chromicoxide in chrome tanning l
3、iquors, either simple, with addedaluminum or zirconium, or with the usual masking complexingagents.1.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of
4、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 sol
5、ution 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 qual
6、ity 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 P
7、urity 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 on Analytical Reagents of The American Chemical Society,where such specifications are available.2Other grades may beus
8、ed, 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 or water ofequal purity.4.3 Ammonium P
9、ersulfate20 % solution 100 gm of per-sulfate into 500 mL water.4.4 Starch Indicator, 1 %Make a paste of1gofsolublestarch in about 10 mL of water, add 90 mL water, and boil for1 min with stirring. Cool and add one drop of chloroform. Thesolution is subject to decomposition and should be renewed ifa d
10、eep blue color is not obtained on addition of one drop ofindicator to a solution of 1 drop tincture of iodine in 100 mLof water.4.5 Sodium Thiosulfate Solution, 0.1 NDissolve 24.85 gof Na2S2O35H2O in water, add1gNa2CO3, and dilute to 1 L.4.5.1 StandardizationDry potassium dichromate(K2Cr2O7) in an o
11、ven 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 mL water, add 15 mL 1:4 hydrochloric acid, 20mL of 10 % potassium iodide solution, stopper the flask, andallow to stand 5 mi
12、n 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 1 % starchsolution, and continue titrating until the deep blue colorchanges to a clear green. Record the titration.normality of sodium thiosulfate 5weight po
13、tassium dichromate0.04903 3 mL titration(1)The thiosulfate solution is quite stable but should be restan-dardized at least once a month.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 edi
14、tion approved Oct. 1, 2006. Published November 2006. Originallyapproved in 1996. Last previous edition approved in 2001 as D 6019 - 96(2001).2Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted b
15、y 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con
16、shohocken, PA 19428-2959, United States.4.6 Potassium Dichromate,K2Cr2O7, primary standardgrade.4.7 Potassium Iodide, 6 %Dissolve6gKIin100mLwater.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 gm of AgNo3in 100mL w
17、ater.4.10 Potassium Permanganate, 1 %Dissolve5gofKMnO3in 500 mL water.5. Procedure5.1 Weigh 11 to 12 g, to the nearest 0.1 mg, of the chrometanning material to be analyzed.5.2 Quantitatively transfer to a 500 mL volumetric flask.Dilute to the mark and mix thoroughly.5.3 Pipet 25 mL aliquots into eac
18、h of 500 mL Erlenmeyerflasks. Run in triplicate.5.4 Add 10 mL concentrated sulfuric acid. (WarningThisshould be done in a hood. Heat and fumes will be generated.)5.5 Carefully add 200 mL deionized water. Add 8 mL of1 % silver nitrate and ten drops of approximately 1 % potas-sium permangante. Add 50
19、mL of 20 % solution of ammoniumpersulfate.5.6 Bring to a boil. At this stage a permanganate colorshould develop (pink to a purple color). If the permanganatecolor fails to develop, remove from heat and carefully addsmall amounts of additional persulfate. If necessary, continueaddition of persulfate
20、until the permanganate color is perma-nent. This color will not develop until all of the chromium isoxidized. Continue boiling for 20 min.5.7 Add 10 mL of 1:1 hydrochloric acid. This is to destroythe permanganate. If the pink color does not fade after 5 min,add an additional amount of 1:1 HCl. The c
21、olor is yellow at thisstage. Precipitated silver chloride will also be present. Boil for10 min. Total boiling time should be between 30 to 40 min.5.8 Remove from heat and cool in water bath (65 to 70F).5.9 Titrate with sodium thiosulfate using potassium iodideand starch indicator in the usual manner
22、.6. Calculation6.1 Calculate the chromic oxide in the liquor as follows:Cr2O3% 5A 3 N 3 0.02533W3V253 100 (2)where:A = the number of millilitres of standard thiosulfate (orferrous sulfate) required to titrate the 25 mLaliquot ofthe specimen,N = the normality of the thiosulfate (or ferrous sulfate)so
23、lution,W = the weight of the specimen before dilution, g, andV = the volume to which W was diluted, mL.6.2 Unless otherwise specified, test two 25 mL aliquotsfrom the diluted specimen.6.3 The chromic oxide in the sample for the test shall be theaverage of the test results obtained from the two aliqu
24、otstested.6.4 Record the chromic oxide in the sample to the nearest0.1 %.7. Precision and Bias7.1 PrecisionThe precision of test results obtained withina laboratory (repeatability conditions) was obtained under thedefined conditions of the test method. Based on three dailyrepetitions on each of thre
25、e days a maximum range of 0.12 %absolute and a standard deviation of 0.052 was obtained. Theprecision of test results obtained in different laboratories(reproducibility conditions) is a range of the average ofdeterminations for fourteen laboratories of 0.27 % absolute andthe standard deviation was 0
26、.071.7.2 BiasPotassium dichromate, a primary standard, wasused to determine bias. The chemical was treated with theoxidation procedure to determine any extraneous oxidation/reduction that may be occurring. Additionally, by applying therecovery factor to the results of the test results, errors instan
27、dardization might be nullified. The average recovery forten laboratories was 99.89 % with a standard deviation of 0.54.The average standard deviation for an individual laboratorywas 0.26.8. Keywords8.1 basic chromium tanning liquors; chrome oxideASTM International takes no position respecting the va
28、lidity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is su
29、bject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headqu
30、arters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This stand
31、ard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 6019 96 (2006)2
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