1、Designation: D3898 93 (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 l
2、ast 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
3、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 theresp
4、onsibility 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 Te
5、st 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
6、 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 deg
7、ree 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 organ
8、ic 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
9、, 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 on Analytical Reagents of
10、 The American 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, referen
11、ceto 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 of1gofsolublestarch in about 10 mL of water, add 90 mL water and boil for1 min with stirring. Cool and add 1 drop of chloroform
12、. 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 responsibil
13、ity 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/D389
14、8-93R15.2For 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 Specifi
15、cations , 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 Conven
16、tion, Inc. (USPC), Rockville,MD.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.5 Sodium Thiosulfate Solution , 0.1 NDissolve 24.85 gof Na2S2O35 H2O in water, add1gNa2CO3, and dilute to 1 L.6.5.1 StandardizationDry potassium dichrom
17、ate(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 mL water, add 15 mL 1:4 hydrochloric acid, 20mL of 10 % potassium iodide solution, stopper the flask and
18、allow 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 1 % starch solutionand continue titrating until the deep blue color changes to aclear green. Record the titration.normality of sodium thio
19、sulfate 5weight potassium dichromate0.04903 3mL titration(1)The thiosulfate solution is quite stable but should be restan-dardized at least once a month.6.6 Potassium Dichromate, K2Cr2O7, Primary StandardGrade.6.7 Potassium Iodide, 10 %. Dissolve 10 g KI in 100 mLwater.6.8 Hydrochloric Acid, 1:4. Di
20、lute 250 mL concentratedhydrochloric acid (sp gr 1.19) to 1 L with water.7. Procedure7.1 Weigh the liquor to the nearest milligram before dilu-tion. The specimen shall consist of a weighed quantity of theliquor diluted to a definite volume containing from 0.003 to0.004 g of Cr2O3per millilitre. Tran
21、sfer a 25 mL aliquot to a500 mL Erlenmeyer flask and dilute to approximately 250 mL.Add sodium peroxide, about1gatatime, with swirling, untilall green color or green precipitate has disappeared, and thesolution becomes a clear yellow. (The presence of a whitepercipitate is of no consequence.) Add a
22、few boiling granulesor glass beads and boil gently for at least 30 min to destroyperoxide. Cool, dilute to 250 mL, and add 1:4 hydrochloricacid until the yellow color changes to orange. Add an addi-tional 25 mL of 1:4 hydrochloric acid, 20 mL of potassiumiodide solution and stopper the flask.Allow t
23、o stand in the darkfor 5 min. Titrate with 0.1 N sodium thiosulfate standardized asdescribed in 6.4.1. When the color of the solution has faded toa brownish-green, add 2 mL of 1 % starch solution andcontinue the titration until the deep blue color changes to aclear green. Record the titration. Calcu
24、late results as describedin Section 8.8. Calculation8.1 Calculate the chromic oxide in the liquor as follows:Cr2O3,%5A 3 N 30.02533W3V253100 (2)where:A = the number of millilitres of standard thiosulfate (orferrous sulfate) required to titrate the 25 mL aliquot ofthe specimen,N = the normality of th
25、e thiosulfate (or ferrous sulfate)solution,W = the weight of the specimen before dilution, g, andV = the volume to which W was diluted, mL.8.2 Unless otherwise specified, test two 25 mL aliquotsfrom the diluted specimen.8.3 The chromic oxide in the sample for the test shall be theaverage of the test
26、 results obtained from the two aliquotstested.8.4 Record the chromic oxide in the sample to the nearest0.1 %.9. Precision and Bias9.1 Precision:9.1.1 Repeatability on triplicate runs by four laboratories onfour samples shows an estimated deviation of 0.17 % of thechromium present.9.1.2 Reproducibili
27、ty between laboratories on the samefactorial experiment shows an estimated standard deviationamounting to 0.9 % of the chromium present.9.2 Bias:9.2.1 The average result of the factorial experiment aboveshows a bias of +0.07 % of the chromium present and, henceon the average, the test method does no
28、t yield biased results.9.2.2 On the four samples studied, the standard deviationdue to variation in composition was 0.35 % of the chromiumpresent.10. Keywords10.1 basic chromium tanning liquors; chrome oxideASTM International takes no position respecting the validity of any patent rights asserted in
29、 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 subject to revision at any time by the re
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32、l, 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). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 93 (2015)2
