1、Designation: D6657 14a1Standard Test Method forpH of Wet Blue1This standard is issued under the fixed designation D6657; 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 t
2、he year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEParagraph 9.1.3 was added editorially in November 2014.1. Scope1.1 This test method covers the determination of the pH ofall types of wet blue and wet white.1.2 For pH of wet
3、white, the procedure is identical, substi-tute wet white for wet blue in the standard method.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, as
4、sociated 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:2D6659 Practice for Sampling and Preparation of Wet Blue
5、for 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. Terminology3.1 Definitions of Term Specific to this Standard:3.1.1 The pH of a solution has been
6、defined as the negativelogarithm of the hydrogen ion activity. A solution of pH 7 isneutral at 24 C. Lower numbers indicate increasing acidity;higher numbers, increasing alkalinity.4. Significance and Use4.1 This test method is designed to measure the pH of adistilled-water extract of wet blue. This
7、 is considered to be ameasure of the acidity or alkalinity of the wet blue. Excessiveacidity or alkalinity may have a deleterious effect on the agingcharacteristics of wet blue and the leather made from it.4.2 This test method is suitable for development, control,and service evaluation of wet blue.5
8、. Apparatus5.1 Electronic pH Meter, with a suitable electrode. Themeter shall have an accuracy of at least 0.01 pH unit andreproducibility of 0.05 pH unit.5.2 Analytical Balance, sensitive to 0.01 g or greater.6. Reagents6.1 Purity of WaterUnless otherwise indicated, referencesto water shall be unde
9、rstood to mean distilled water or water ofequal purity. Distilled water shall have a pH value of not lessthan 5.5 nor more than 7.0 and shall give a residue of not morethan 0.5 mg, when 100 mL is evaporated and dried in aplatinum dish.6.2 Commercially Standardized pH Solutions3:6.2.1 Alkaline Phosph
10、ate Buffer Solution (0.01 M trisodiumphosphate, pH = 11.72 at 25 C)Dissolve 1.42 g of anhy-drous disodium hydrogen phosphate (Na2HPO4) in 100 mL ofa 0.1 N carbonate-free solution of sodium hydroxide (NaOH)and dilute to 1 L with water.6.2.2 Borax Buffer Solution (0.01 M, pH = 9.18 at 25C)Dissolve 3.8
11、1 g of sodium tetraborate decahydrate(Na2B4O7 10H2O) in water and dilute to 1 L.6.2.3 Hydrochloric Acid (pH = 1.10 at 25 C)Add2gofconcentrated hydrochloric acid (HCl, sp gr 1.19) to 450 g ofwater. Standardize and dilute to 0.1 N.6.2.4 Phosphate Buffer Solution (0.025 M with respect toeach phosphate,
12、 salt pH = 6.86 at 2.5 C)Dissolve 3.40 g ofmonobasic potassium phosphate (KH2PO4) and 3.55 g ofanhydrous dibasic sodium phosphate (Na2HPO4) in water anddilute to 1 L.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.02 on
13、 Wet Blue.Current edition approved May 1, 2014. Published June 2014. Originallyapproved in 2001. Last previous edition approved in 2014 as D6657 - 14. DOI:10.1520/D6657-14AE01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. Fo
14、r Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Commercial buffer salts and solutions prepared in accordance with NationalBureau of Standards recommendations are sold by reputable laboratory supplyhouses and may be used.Copyright AS
15、TM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.2.5 Potassium Hydrogen Phthalate Buffer Solution (0.05M, pH = 4.01 at 25 C)Dissolve 10.21 g of potassiumhydrogen phthalate (KHC8H4O4) in water and dilute to 1 L.7. Test Specimen7.1 The specimen sh
16、all consist of a composite sampleprepared according to Practice D6659.7.1.1 Practice D6659Sample Preparation Method A (asreceived in wet state, diced): use 10 6 1g.7.1.2 Practice D6659Sample Preparation Method B(oven or air dried, ground): use2-5g.8. Standardization8.1 Use manufacturers directions f
17、or establishing two pointstandardization with standard pH solutions that read on eitherside of the anticipated pH of the solution to be tested. Washelectrodes by immersing in three changes of water and estab-lish a fresh liquid junction after blotting electrodes if usingsleeve type electrode prior t
18、o testing each solution.8.2 Check for electrode drift with either of the buffers andrestandardize if necessary.9. Procedure9.1 Weigh the specimen to the nearest 0.01 g and transfer toa 250 mL Erlenmeyer flask.9.1.1 If specimen was obtained as in 7.1.1 add water in theamount of ten times the mass of
19、the specimen.9.1.2 If specimen was obtained as in 7.1.2 add water in theamount of twenty times the mass of the specimen.9.1.3 Stopper the flask and agitate thoroughly. Let stand atthe Standard Laboratory Temperature, 23.0 6 1C (73.4 61.8F), with occasional agitation for not less than 4 nor morethan
20、24 h. Agitate thoroughly and if necessary transfer to aclean beaker or decant if possible.9.2 Determine the pH of the wet blue water mixture orsolution, reading the meter to the closest 0.05 unit.9.3 If a pH difference figure (Delta pH) is desired, removea 5 ml to 10 ml aliquot of the liquid into a
21、beaker and dilute tenfold. Mix well and determine the pH. Calculate the differencein pH from the initial reading.NOTE 1If the pH difference figure is 0.7 or greater, it is an indicationthat strong free acid is present.10. Report10.1 Report the following information:10.1.1 The pH of the sample shall
22、be reported to the nearest0.05 pH unit.10.1.2 The pH difference figure (Delta pH) shall be reportedto the nearest 0.05 pH unit.11. Precision and Bias11.1 This test method is adopted from the leather tanningindustry where it has long been in use and approved fordissemination as a standard method befo
23、re the inclusion ofprecision and bias statements was mandated. The pH of wetblue can change significantly over time after removal from thechrome-tanning vessel. This change happens because chemicalreactions involving the basicity of the chromium sulfatecomplex continue to occur within the wet blue.
24、The amountand rate of these pH changes is dependent on the specificprocesses and materials used to manufacture the wet blue. Theuser is cautioned to verify that the precision and bias (orreproducibility) of this method is adequate for the contem-plated application.11.2 A real world precision stateme
25、nt was determinedthrough statistical examination4of 145 results from 9laboratories, on 16 materials over nearly 2 years. Practice E691was followed for the design and analysis of the data. The termsbelow (repeatability and reproducibility) are used as specifiedin Practice E177.11.2.1 Repeatability (r
26、)The difference between repetitiveresults obtained by the same operator in a given laboratoryapplying the same test method with the same apparatus underconstant operating conditions on identical test material withinshort intervals of time would in the long run, in the normal andcorrect operation of
27、the test method, exceed the followingvalues only in one case in 20.11.2.2 Reproducibility (R)the difference between twosingle and independent results obtained by different operatorsapplying the same test method in different laboratories usingdifferent apparatus on identical test material would, in t
28、he longrun, in the normal and correct operation of the test method,exceed the following values only in one case in 20.Repeatability (r) Reproducibility (R)0.04 0.2911.3 The precision of this test method is based on anintralaboratoy study of ASTM WK40322, New Standard TestMethod for the Determination
29、 of pH in Wet Blue and WetWhite, conducted in 2012. Nine laboratories participated in thisstudy, testing 16 Wet Blue samples. Every “test result” repre-sents an individual determination. The laboratories were askedto report a single test result for 13 materials and duplicate testresults for 3 materi
30、als. Except for the absence of replicate testresults from all of the study materials, Practice E691 wasfollowed for the design and analysis of the data; the details aregive in an ASTM research report.411.3.1 Repeatability (r)The difference between repetitiveresults obtained by the same operator in a
31、 given laboratoryapplying the same test method with the same apparatus underconstant operating conditions on identical test material withinshort intervals of time would in the long run, in the normal andcorrect operation of the test method, exceed the followingvalues only in one case in 20.11.3.1.1
32、Repeatability can be interpreted as maximum dif-ference between two results, obtained under repeatabilityconditions, that is accepted as plausible due to random causesunder normal and correct operation of the test method.11.3.1.2 Repeatability limits are listed in Table 1.11.3.2 Reproducibility (R)T
33、he difference between twosingle and independent results obtained by different operatorsapplying the same test method in different laboratories using4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D31-1021. ContactASTM CustomerSe
34、rvice at serviceastm.org.D6657 14a12different apparatus on identical test material would, in the longrun, in the normal and correct operation of the test method,exceed the following values only in one case in 20.11.3.2.1 Reproducibility can be interpreted as maximumdifference between two results, ob
35、tained under reproducibilityconditions, that is accepted as plausible due to random causesunder normal and correct operation of the test method.11.3.2.2 Reproducibility limits are listed in Table 1.11.3.3 The above terms (repeatability limit and reproduc-ibility limit) are used as specified in Pract
36、ice E177.11.3.4 Any judgment in accordance with 11.3.1 wouldnormally have an approximate 95 % probability of beingcorrect, however the precision statistics obtained in this ILSmust not be treated as exact mathematical quantities which areapplicable to all circumstances and uses. The limited numberof
37、 materials for which replicate results were reported essen-tially guarantees that there will be times when differencesgreater than predicted by the ILS results will arise, sometimeswith considerably greater or smaller frequency than the 95 %probability limit would imply. Consider the repeatability l
38、imitas a guide, and the associated probability of 95 % as only arough indicator of what can be expected.11.4 BiasNo information can be presented on the bias ofthe procedure in Test Method D6657 for measuring pH becauseno material having an accepted reference value was included inthe analysis.11.5 Th
39、e precision statement was determined through sta-tistical examination of 145 results, from 9 laboratories, on 16materials over nearly 2 years.12. Keywords12.1 acidity; alkalinity; blue stock; Delta pH; pH; pHdifference; wet blue; wet whiteASTM International takes no position respecting the validity
40、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 subject t
41、o 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 Headquarters.
42、 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 standard is
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44、m.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:/ 1 pHMaterial AverageAxRepeat-abilityStandardDeviationSrReproduc-ibilitySta
45、ndardDeviationSRRepeat-abilityLimitrReproduc-ibility LimitRWet Blue 12412 3.54 0.18 0.50Wet Blue 13112 3.35 0.11 0.30Wet Blue 11912 3.55 0.09 0.24Wet Blue 122211 3.45 0.18 0.50Wet Blue 22112 3.47 0.12 0.32Wet Blue 2513 3.60 0.12 0.33Wet Blue 31312 3.58 0.02 0.06Wet Blue 41812 3.68 0.05 0.15Wet Blue
46、51612 3.67 0.06 0.17Wet Blue 62812 3.43 0.13 0.35Wet Blue 81512 3.54 0.09 0.24Wet Blue 92412 3.70 0.07 0.18Wet Blue 41313 3.55 0.12 0.33Wet Blue 61313 3.60 0.00 0.06 0.01 0.18Wet Blue 8713 3.58 0.03 0.16 0.08 0.46Wet Blue 92513 3.62 0.01 0.13 0.03 0.37Average 3.56 0.01 0.10 0.04 0.29AThe average of the laboratories calculated averages.D6657 14a13
