1、Designation: D 6657 01 (Reapproved 2006)Standard 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 paren
2、theses 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 the pH ofall types of wet blue.1.2 This standard does not purport to address all of thesafety concerns,
3、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-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 6659 Practice for Sampling and Preparation
4、of Wet Bluefor Physical and Chemical Tests3. Terminology3.1 Definitions 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,
5、 increasing alkalinity.4. Significance and Use4.1 This test method is 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 agingcharacter
6、istics 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. 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
7、 Analytical Balance, sensitive to 0.01 g or greater.6. Reagents6.1 Purity 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 o
8、f 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 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 car
9、bonate-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 3.81 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 ac
10、id (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, 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
11、 to 1 L.6.2.5 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 shall consist of 10 g, 6 1 g, from acomposite sample prepared according to Practice D 6659.8. St
12、andardization8.1 Use manufacturers directions for 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 e
13、lectrodes if usingsleeve type electrode prior to testing each solution.1This test method is under the jurisdiction of ASTM Committee D31 on Leatherand is the direct responsibility of Subcommittee D31.02 on Blue Stock.Current edition approved Oct. 1, 2006. Published November 2006. Originallyapproved
14、in 2001. Last previous edition approved in 2001 as D 6657 - 01.2For 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 websit
15、e.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 19428-2959, United States.8.2 Check
16、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. Add water in the amount of tentimes the mass of the specimen. Stopper the flask and agitatethoroughly. Let stand at the Stan
17、dard Laboratory Temperature,23.0 6 1 C (73.4 6 1.8 F), with occasional 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
18、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 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 indicationt
19、hat strong free acid is present.10. Report10.1 Report the following 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
20、 the leather tanningindustry where it has long been in use and approved 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 becau
21、se chemicalreactions involving the basicity of the chromium sulfatecomplex 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 (o
22、rreproducibility) of this method is adequate for the contem-plated application.12. Keywords12.1 acidity; alkalinity; blue stock; Delta pH; pH; pHdifference; wet blueASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this
23、 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 be
24、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 therespo
25、nsible 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, Wes
26、t 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 6657 01 (2006)2
