ASTM D6657-14ae1

Standard Test Method for pH of Wet Blue

SIGNIFICANCE AND USE
4.1 This test method is designed to measure the pH of a distilled-water extract of wet blue. This is considered to be a measure of the acidity or alkalinity of the wet blue. Excessive acidity or alkalinity may have a deleterious effect on the aging characteristics 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.
SCOPE
1.1 This test method covers the determination of the pH of all types of wet blue and wet white.  
1.2 For pH of wet white, the procedure is identical, substitute wet white for wet blue in the standard method.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Apr-2014
• ICS: 59.140.10 - Processes and auxiliary materials
• Technical Committee: D31 - Leather
• Drafting Committee: D31.02 - Wet Blue

Relations

• Replaces: ASTM D6657-14a - Standard Test Method for pH of Wet Blue
• Effective Date: 01-May-2014

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation: D6657 − 14a
StandardTest Method for
pH of Wet Blue
This standard is issued under the fixed designation D6657; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Paragraph 9.1.3 was added editorially in November 2014.
1. Scope measure of the acidity or alkalinity of the wet blue. Excessive
acidity or alkalinity may have a deleterious effect on the aging
1.1 This test method covers the determination of the pH of
characteristics of wet blue and the leather made from it.
all types of wet blue and wet white.
4.2 This test method is suitable for development, control,
1.2 For pH of wet white, the procedure is identical, substi-
and service evaluation of wet blue.
tute wet white for wet blue in the standard method.
1.3 The values stated in SI units are to be regarded as
5. Apparatus
standard. No other units of measurement are included in this
5.1 Electronic pH Meter, with a suitable electrode. The
standard.
meter shall have an accuracy of at least 0.01 pH unit and
1.4 This standard does not purport to address all of the
reproducibility of 0.05 pH unit.
safety concerns, if any, associated with its use. It is the
5.2 Analytical Balance, sensitive to 0.01 g or greater.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
6. Reagents
bility of regulatory limitations prior to use.
6.1 Purity of Water—Unless otherwise indicated, references
2. Referenced Documents
to water shall be understood to mean distilled water or water of
2.1 ASTM Standards:
equal purity. Distilled water shall have a pH value of not less
D6659 Practice for Sampling and Preparation of Wet Blue
than 5.5 nor more than 7.0 and shall give a residue of not more
for Physical and Chemical Tests
than 0.5 mg, when 100 mL is evaporated and dried in a
E177 Practice for Use of the Terms Precision and Bias in
platinum dish.
ASTM Test Methods
6.2 Commercially Standardized pH Solutions :
E691 Practice for Conducting an Interlaboratory Study to
6.2.1 Alkaline Phosphate Buffer Solution (0.01 M trisodium
Determine the Precision of a Test Method
phosphate, pH = 11.72 at 25 °C)—Dissolve 1.42 g of anhy-
drous disodium hydrogen phosphate (Na HPO ) in 100 mL of
3. Terminology
2 4
a 0.1 N carbonate-free solution of sodium hydroxide (NaOH)
3.1 Definitions of Term Specific to this Standard:
and dilute to 1 L with water.
3.1.1 The pH of a solution has been defined as the negative
6.2.2 Borax Buffer Solution (0.01 M, pH = 9.18 at 25
logarithm of the hydrogen ion activity. A solution of pH 7 is
°C)—Dissolve 3.81 g of sodium tetraborate decahydrate
neutral at 24 °C. Lower numbers indicate increasing acidity;
(Na B O · 10H O) in water and dilute to 1 L.
2 4 7 2
higher numbers, increasing alkalinity.
6.2.3 Hydrochloric Acid (pH = 1.10 at 25 °C)—Add2gof
concentrated hydrochloric acid (HCl, sp gr 1.19) to 450 g of
4. Significance and Use
water. Standardize and dilute to 0.1 N.
4.1 This test method is designed to measure the pH of a
6.2.4 Phosphate Buffer Solution (0.025 M with respect to
distilled-water extract of wet blue. This is considered to be a
each phosphate, salt pH = 6.86 at 2.5 °C)—Dissolve 3.40 g of
monobasic potassium phosphate (KH PO ) and 3.55 g of
2 4
This test method is under the jurisdiction ofASTM Committee D31 on Leather
anhydrous dibasic sodium phosphate (Na HPO ) in water and
2 4
and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
dilute to 1 L.
Current edition approved May 1, 2014. Published June 2014. Originally
approved in 2001. Last previous edition approved in 2014 as D6657 - 14. DOI:
10.1520/D6657-14AE01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Commercial buffer salts and solutions prepared in accordance with National
Standards volume information, refer to the standard’s Document Summary page on Bureau of Standards recommendations are sold by reputable laboratory supply
the ASTM website. houses and may be used.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6657 − 14a
6.2.5 Potassium Hydrogen Phthalate Buffer Solution (0.05 reactions involving the basicity of the chromium sulfate
M, pH = 4.01 at 25 °C)—Dissolve 10.21 g of potassium complex continue to occur within the wet blue. The amount
hydrogen phthalate (KHC H O ) in water and dilute to 1 L. and rate of these pH changes is dependent on the specific
8 4 4
processes and materials used to manufacture the wet blue. The
7. Test Specimen
user is cautioned to verify that the precision and bias (or
reproducibility) of this method is adequate for the contem-
7.1 The specimen shall consist of a composite sample
plated application.
prepared according to Practice D6659.
7.1.1 Practice D6659—Sample Preparation Method A (as
11.2 A real world precision statement was determined
received in wet state, diced): use 10 61g.
through statistical examination of 145 results from 9
7.1.2 Practice D6659—Sample Preparation Method B
laboratories,on16materialsovernearly2years.PracticeE691
(oven or air dried, ground): use2-5g.
was followed for the design and analysis of the data.The terms
below (repeatability and reproducibility) are used as specified
8. Standardization
in Practice E177.
8.1 Use manufacturer’s directions for establishing two point
11.2.1 Repeatability (r)—The difference between repetitive
standardization with standard pH solutions that read on either
results obtained by the same operator in a given laboratory
side of the anticipated pH of the solution to be tested. Wash
applying the same test method with the same apparatus under
electrodes by immersing in three changes of water and estab-
constant operating conditions on identical test material within
lish a fresh liquid junction after blotting electrodes if using
short intervals of time would in the long run, in the normal and
sleeve type electrode prior to testing each solution.
correct operation of the test method, exceed the following
values only in one case in 20.
8.2 Check for electrode drift with either of the buffers and
11.2.2 Reproducibility (R)—the difference between two
restandardize if necessary.
single and independent results obtained by different operators
9. Procedure applying the same test method in different laboratories using
different apparatus on identical test material would, in the long
9.1 Weigh the specimen to the nearest 0.01 g and transfer to
run, in the normal and correct operation of the test method,
a 250 mL Erlenmeyer flask.
exceed the following values only in one case in 20.
9.1.1 If specimen was obtained as in 7.1.1 add water in the
Repeatability (r) Reproducibility (R)
amount of ten times t
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D6657 − 14a D6657 − 14a
Standard Test Method for
pH of Wet Blue
This standard is issued under the fixed designation D6657; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Paragraph 9.1.3 was added editorially in November 2014.
1. Scope
1.1 This test method covers the determination of the pH of all types of wet blue and wet white.
1.2 For pH of wet white, the procedure is identical, substitute wet white for wet blue in the standard method.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D6659 Practice for Sampling and Preparation of Wet Blue for Physical and Chemical Tests
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions of Term Specific to this Standard:
3.1.1 The pH of a solution has been defined as the negative logarithm of the hydrogen ion activity. A solution of pH 7 is neutral
at 24 °C. Lower numbers indicate increasing acidity; higher numbers, increasing alkalinity.
4. Significance and Use
4.1 This test method is designed to measure the pH of a distilled-water extract of wet blue. This is considered to be a measure
of the acidity or alkalinity of the wet blue. Excessive acidity or alkalinity may have a deleterious effect on the aging characteristics
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. Apparatus
5.1 Electronic pH Meter, with a suitable electrode. The meter shall have an accuracy of at least 0.01 pH unit and reproducibility
of 0.05 pH unit.
5.2 Analytical Balance, sensitive to 0.01 g or greater.
6. Reagents
6.1 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean distilled water or water of
equal purity. Distilled water shall have a pH value of not less than 5.5 nor more than 7.0 and shall give a residue of not more than
0.5 mg, when 100 mL is evaporated and dried in a platinum dish.
This test method is under the jurisdiction of ASTM Committee D31 on Leather and is the direct responsibility of Subcommittee D31.02 on Wet Blue.
Current edition approved May 1, 2014. Published June 2014. Originally approved in 2001. Last previous edition approved in 2014 as D6657 - 14. DOI:
10.1520/D6657-14A.10.1520/D6657-14AE01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6657 − 14a
6.2 Commercially Standardized pH Solutions :
6.2.1 Alkaline Phosphate Buffer Solution (0.01 M trisodium phosphate, pH = 11.72 at 25 °C)—Dissolve 1.42 g of anhydrous
disodium hydrogen phosphate (Na HPO ) in 100 mL of a 0.1 N carbonate-free solution of sodium hydroxide (NaOH) and dilute
2 4
to 1 L with water.
6.2.2 Borax Buffer Solution (0.01 M, pH = 9.18 at 25 °C)—Dissolve 3.81 g of sodium tetraborate decahydrate (Na B O ·
2 4 7
10H O) in water and dilute to 1 L.
6.2.3 Hydrochloric Acid (pH = 1.10 at 25 °C)—Add 2 g of concentrated hydrochloric acid (HCl, sp gr 1.19) to 450 g of water.
Standardize and dilute to 0.1 N.
6.2.4 Phosphate Buffer Solution (0.025 M with respect to each phosphate, salt pH = 6.86 at 2.5 °C)—Dissolve 3.40 g of
monobasic potassium phosphate (KH PO ) and 3.55 g of anhydrous dibasic sodium phosphate (Na HPO ) in water and dilute to
2 4 2 4
1 L.
6.2.5 Potassium Hydrogen Phthalate Buffer Solution (0.05 M, pH = 4.01 at 25 °C)—Dissolve 10.21 g of potassium hydrogen
phthalate (KHC H O ) in water and dilute to 1 L.
8 4 4
7. Test Specimen
7.1 The specimen shall consist of a composite sample prepared according to Practice D6659.
7.1.1 Practice D6659—Sample Preparation Method A (as received in wet state, diced): use 10 6 1 g.
7.1.2 Practice D6659—Sample Preparation Method B (oven or air dried, ground): use 2 - 5 g.
8. Standardization
8.1 Use manufacturer’s directions for establishing two point standardization with standard pH solutions that read on either side
of the anticipated pH of the solution to be tested. Wash electrodes by immersing in three changes of water and establish a fresh
liquid junction after blotting electrodes if using sleeve type electrode prior to testing each solution.
8.2 Check for electrode drift with either of the buffers and restandardize if necessary.
9. Procedure
9.1 Weigh the specimen to the nearest 0.01 g and transfer to a 250 mL Erlenmeyer flask.
9.1.1 If specimen was obtained as in 7.1.1 add water in the amount of ten times the mass of the specimen.
9.1.2 If specimen was obtained as in 7.1.2 add water in the amount of twenty times the mass of the specimen.
9.1.3 Stopper the flask and agitate thoroughly. Let stand at the Standard Laboratory Temperature, 23.0 6 1°C (73.4 6 1.8°F),
with occasional agitation for not less than 4 nor more than 24 h. Agitate thoroughly and if necessary transfer to a clean beaker or
decant if possible.
9.2 Determine the pH of the wet blue water mixture or solution, reading the meter to the closest 0.05 unit.
9.3 If a pH difference figure (Delta pH) is desired, remove a 5 ml to 10 ml aliquot of the liquid into a beaker and dilute ten fold.
Mix well and determine the pH. Calculate the difference in pH from the initial reading.
NOTE 1—If the pH difference figure is 0.7 or greater, it is an indication that strong free acid is present.
10. Report
10.1 Report the following information:
10.1.1 The pH of the sample shall be reported to the nearest 0.05 pH unit.
10.1.2 The pH difference figure (Delta pH) shall be reported to the nearest 0.05 pH unit.
11. Precision and Bias
11.1 This test method is adopted from the leather tanning industry where it has long been in use and approved for dissemination
as a standard method before the inclusion of precision and bias statements was mandated. The pH of wet blue can change
significantly over time after removal from the chrome-tanning vessel. This change happens because chemical reactions involving
the basicity of the chromium sulfate complex continue to occur within the wet blue. The amount and rate of t
...