1、Designation: D 6657 08Standard Test Method forpH of Wet Blue1This standard is issued under the fixed designation D 6657; 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.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 white, the procedure is identical, substi-tute wet white for
3、 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, associated with its use. It is theresponsibility of the user o
4、f 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:2D 6659 Practice for Sampling and Preparation of Wet Bluefor Physical and Chemical Tests3. Terminology3.1 Definition
5、s of Term Specific to this Standard:3.1.1 The pH of a solution has been 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
6、designed to measure the pH of adistilled-water extract of wet blue. This 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 i
7、s suitable for development, control,and service evaluation of wet blue.5. 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 Pur
8、ity of WaterUnless otherwise indicated, referencesto water shall be understood 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 aplatinu
9、m dish.6.2 Commercially Standardized pH Solutions3:6.2.1 Alkaline Phosphate 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
10、water.6.2.2 Borax Buffer Solution (0.01 M, pH = 9.18 at 25C)Dissolve 3.81 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
11、.6.2.4 Phosphate Buffer Solution (0.025 M with respect toeach phosphate, 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.6.2.5 Potassium Hydrogen Phthalate Buffer Solution (0.05M, pH
12、= 4.01 at 25 C)Dissolve 10.21 g of potassiumhydrogen phthalate (KHC8H4O4) in water and dilute 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 Wet Blue.Current edition approved Sept. 1, 2008. Published Octob
13、er 2008. Originallyapproved in 2001. Last previous edition approved in 2006 as D 6657 - 01(2006).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 Docum
14、ent 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19
15、428-2959, United States.7. Test Specimen7.1 The specimen shall consist of 10 g, 6 1 g, from acomposite sample prepared according to Practice D 6659.8. Standardization8.1 Use manufacturers directions for establishing two pointstandardization with standard pH solutions that read on eitherside of the a
16、nticipated 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 to testing each solution.8.2 Check for electrode drift with either of the buffers andrestandardize if
17、 necessary.9. Procedure9.1 Weigh the specimen to the nearest 0.01 g and transfer toa 250 mL Erlenmeyer flask. Add water in the amount of tentimes the mass of the specimen. Stopper the flask and agitatethoroughly. Let stand at the Standard Laboratory Temperature,23.0 6 1 C (73.4 6 1.8 F), with occasi
18、onal agitation for notless than 4 nor more than 24 h. Agitate thoroughly and ifnecessary transfer to a clean 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, rem
19、ovea 5 ml to 10 ml aliquot of the liquid into a 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 followin
20、g information:10.1.1 The pH of the sample shall 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 app
21、roved fordissemination as a standard method before 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 sulfat
22、ecomplex continue to occur within the wet blue. 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
23、 application.12. Keywords12.1 acidity; alkalinity; blue stock; Delta pH; pH; pHdifference; wet blue; wet whiteASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised
24、 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 be reviewed every five years andif not revised, either rea
25、pproved 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 theresponsible technical committee, which you may attend. If yo
26、u 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, 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).D6657082
