1、Designation: D 3898 93 (Reapproved 2003)Standard Test Method forChromic Oxide in Basic Chromium Tanning Liquors1This standard is issued under the fixed designation D 3898; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 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 liquors, either simple, with addedalumin
3、um or zirconium, or with the usual masking complexingagents.1.2 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-b
4、ility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 2807 Test Method for Chromic Oxide in Leather (Per-chloric Acid Oxidation)23. Summary of Test Method3.1 The solution is oxidized with sodium peroxide until thechromium is completely converted to the chromate ion
5、. 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 is titratedwith standardized sodium thiosulfate.4. Significance and Use4.1 The procedure described is for the quality c
6、ontrol 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 degree of tannage, andhence may be a matter for specification in the purchase ofleather.5. Interferences5.1 The test method
7、 is generally the most accurate andconvenient for the purpose. However, if the liquor containsiron or copper, which interfere with the sodium thiosulfatetitration, or complex organic or inorganic reducing agents(sodium thiosulfate, for example) which are not oxidized byalkaline peroxide but reduce h
8、exavalent chromium on acidifi-cation, an alternate procedure must be used. The perchloricacid method described in Test Method D 2807, using theferrous sulfate titration, is suitable, although the results ob-tained may be one to two percent low.6. Reagents and Materials6.1 Purity of ReagentsReagent g
9、rade 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.3Other grades may beused, provided it is first a
10、scertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean distilled water or water ofequal purity.6.3 Sodium Peroxide, (Na2O2). Store in o
11、riginal 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. Thesolution is subject to decomposition and should be renewed ifa deep blue color is not obtained on addition of 1
12、drop ofindicator to a solution of 1 drop tincture of iodine in 100 mLof water.6.5 Sodium Thiosulfate Solution, 0.1 NDissolve 24.85 gof Na2S2O35 H2O in water, add1gNa2CO3, and dilute to 1 L.6.5.1 StandardizationDry potassium dichromate(K2Cr2O7) in an oven at 130C for 2 h and cool in a desiccator.Weig
13、h 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 min in the dark. Titrate with the sodiumthiosulfate
14、to be standardized. When the color of the solution1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis. Thistest method was developed in cooperation with the American Leather ChemistsAssoc.Current edi
15、tion approved May 10, 2003. Published June 2003. Originallyapproved in 1991. Last previous edition approved in 1998 as D 3898 93 (1998).2Annual Book of ASTM Standards, Vol 15.04.3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on
16、 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 Convention, Inc. (USPC), Rockville,MD.1Copyright ASTM International, 100 Bar
17、r Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.has 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 thiosulfate 5weight potassium dichromate0.0490
18、3 3 mL 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. Dilute 250 mL concentratedhydrochloric acid
19、(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. Transfer a 25 mL aliquot to a500 mL Erlenmeyer
20、 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 few boiling granulesor glass beads and boi
21、l 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 to stand in the darkfor 5 min. Titrate wit
22、h 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. Calculate results as describedin Section 8.8.
23、Calculation8.1 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 mL aliquot ofthe specimen,N = the normality of the thiosulfate (or ferrous sulfate)solut
24、ion,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 results obtained from the two aliquots
25、tested.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 Reproducibility between laboratories on the samefact
26、orial 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 not yield biased results.9.2.2 On the fou
27、r 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 connection with any item mentionedin t
28、his 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 responsible technical committee and must
29、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 Headquarters. Your comments will receive careful consideration at a meeting of there
30、sponsible 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 standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700,
31、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 3898 93 (2003)2
