1、Designation: D5356 10 (Reapproved 2015)Standard Test Method forpH of Chrome Tanning Solutions1This standard is issued under the fixed designation D5356; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber 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 the pH ofchrome tanning solutions.1.2 The values stated in SI units are to be regarded asst
3、andard. 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 ap
4、plica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D3898 Test Method for Chromic Oxide in Basic ChromiumTanning LiquorsE70 Test Method for pH of Aqueous Solutions With theGlass Electrode3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1
5、 pH, of a solutionthe negative logarithm of thehydrogen ion activity.3.1.1.1 DiscussionA solution of pH 7 is neutral at 24C.Lower numbers indicate increasing acidity, higher numbersindicate increasing alkalinity.4. Summary of Test Method4.1 The chrome tanning liquor is diluted to a concentrationof 2
6、5.0 6 0.5 g chromic oxide equivalent per litre, allowed tocome to equilibrium and the pH is then measured with theappropriate meter. For general details of a procedure, TestMethod E70 should be consulted. The provisions of thestandard shall be governing except where the text of this testmethod speci
7、fically deviates.5. Significance and Use5.1 This test method is designed to measure the pH of achrome tanning solution which has been diluted to a specificconcentration. This is considered to be a measure of the acidityor alkalinity of the solution.5.2 This test method is suitable for quality contro
8、l in themanufacture of leather.6. Apparatus6.1 pH Meter, either battery or line-operated equipped withappropriate electrodes. The meter shall have a maximum scaledivision of 0.1 pH unit and reproducibility of 0.05 pH unit.NOTE 1Sellers list reasonably priced models having more sensitivityand greater
9、 reproducibility.7. Reagents7.1 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 the American Chemical Society,where such specifications are
10、 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.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean distilled water or w
11、ater ofequal purity.7.3 Buffer SolutionsCommercially available buffer solu-tions of 2.00 6 0.02 pH and 4.00 6 0.02 pH shall be used formeter standardization, in accordance with the manufacturersrecommendations and the provisions set forth in Test MethodE70.1This test method is under the jurisdiction
12、 of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical AnalysisCurrent edition approved Dec. 1, 2015. Published December 2015. Originallyapproved in 1993. Last previous edition approved in 2010 as D5356 10. DOI:10.1520/D5356-10R15.2For referenced ASTM st
13、andards, 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 Specifications , AmericanChemical Soci
14、ety, 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 Convention, Inc. (USPC), Rockville,MD
15、.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States18. Standardization8.1 Standardize the meter against the pH 4.00 standard, inaccordance with the manufacturers recommendations and theprovisions set forth in Test Method E70. The buffer
16、standardshall be at room temperature and the temperature compensatorshall be set at this temperature.8.2 Read the pH of the 2.00 standard with no adjustment ofthe meter. The standard shall be at a temperature no more than2C different from that at which the meter was standardizedagainst the pH 4.00 s
17、tandard, and the temperature compensatorset accordingly.8.3 If the reading of the pH 2.00 buffer does not differ bymore than 0.05 pH from the published value under thetemperature conditions, the standardization is satisfactory andthe meter ready for use. If the error exceeds 0.05 pH, the meterand el
18、ectrodes must be checked and the necessary adjustmentsmade to obtain conformity.9. Procedure9.1 The sample shall be representative of the chrometanning liquor to be tested. It shall be adjusted to an equivalentchromic oxide concentration of 25.0 6 0.5 g/L (Note 2) andallowed to stand at room tempera
19、ture for at least 60 min beforemeasuring pH in order to attain dilution equilibrium (Note 3).NOTE 2The concentration adjustment shall be based on the analysis ofthe liquor for chromium as based on Test Method D3898. In most cases,the concentration of the sample will be above 25 g chromic oxide per l
20、itreand measurement of the appropriate quantity of liquor in a graduate orweighed quantity shall be transferred to a 100-mL volumetric flask.Diluting with water at room temperature, will give sufficiently accuratedilution.NOTE 3If the dilution described in Note 2 takes place essentially atroom tempe
21、rature, the change in pH is sufficiently slight that 60-minequilibration will suffice. If it is necessary to concentrate the solution byboiling, or the original solution was hot, then the diluted sample should beheld at least 24 h before testing, or the pH test may be repeated untilconstant to 0.1 p
22、H are obtained.NOTE 4If measuring the pH of spent chrome tanning solutions, it maybe necessary to remove grease and sediment prior to measurement.9.2 After standardization of the meter (Section 8), rinse theelectrodes three times with water and remove surplus waterwith a soft, nonabrasive tissue. Do
23、 not let the electrodes dry.Immediately immerse the electrodes in the prepared sample toa depth recommended by the manufacturer, set the temperaturecompensator to the temperature of the solution (25 6 5C),allow the meter to equilibrate, and read the pH to the nearestpH unit of the meter.10. Report10
24、.1 Report the following information:10.1.1 pH of sample = A (25gCr2O3per litre)where:A = pH reading obtained in Section 9.10.1.2 pH of spent chrome tanning liquor = B (undiluted)where:B (undiluted) = pH reading obtained in Section 9.11. Keywords11.1 chrome tanning solutions; pH ; spent tanning liquo
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