ASTM D3913-93(1998)
(Test Method)Standard Test Method for Acidity in Basic Chromium Tanning Liquors
Standard Test Method for Acidity in Basic Chromium Tanning Liquors
SCOPE
1.1 This test method covers the determination of the titratable acidity of chromium tanning liquors. By titratable acidity is meant not only free acidity, which is rarely present, but also anions combined with weakly basic cations such as Chromium (III), which can be titrated with base at the phenolphthalein end point.
1.2 This standard does not purport to address all of the safety problems, 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.
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Designation: D 3913 – 93 (Reapproved 1998)
Standard Test Method for
Acidity in Basic Chromium Tanning Liquors
This standard is issued under the fixed designation D 3913; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 5. Interferences
1.1 This test method covers the determination of the titrat- 5.1 Although for most purposes, the results of this analysis
able acidity of chromium tanning liquors. By titratable acidity are intended to give a measure of the acid anions associated
is meant not only free acidity, which is rarely present, but also with chromium, it should be mentioned that any weak basic
anions combined with weakly basic cations such as Chromium cation will behave similarly. Hence, aluminum, zirconium,
(III), which can be titrated with base at the phenolphthalein end ferric iron, and weak organic bases will all yield salts with
point. acidity titratable by this test method. A discussion of the effect
1.2 This standard does not purport to address all of the of these interferences has been published.
safety concerns, if any, associated with its use. It is the 5.2 If there are anions which form very stable complexes
responsibility of the user of this standard to establish appro- with chromium present in the solution, the titration:
priate safety and health practices and determine the applica-
~x1 y232 2
@CrOH X ~H O! # 1 ~3 2 X!OH
x y 2 62x2y
bility of regulatory limitations prior to use.
Cr~OH! 1 X 1 ~6 2 x 2 y!H O (1)
3 y 2
2. Referenced Documents
where:
2.1 ASTM Standards:
X 5 stable complexes,
D 3898 Test Method for Chromic Oxide in Basic Chro-
will not go to completion at the phenolphthalein endpoint and
mium Tanning Liquors
the acidity reported will be low. Large excess of oxalate or
E 180 Practice for Determining the Precision of ASTM
complexing anions of lesser affinity used for masking effect
Methods for the Analysis and Testing of Industrial Chemi-
will introduce this error. To obviate this, an entirely different
cals
method has been developed in which the hydroxyl groups are
titrated and the chromium is completely complexed by oxalate.
3. Summary of Test Method
This is generally referred to as the Lehigh method and may be
6,7
3.1 A sample of suitable size is taken by diluting and
used if complex ions are present in interfering amount.
aliquoting, if necessary. The sample is then heated to boiling
6. Reagents and Materials
and titrated hot to the first appearance of a pink color, stable to
boiling in the supernatant solution, as determined by viewing
6.1 Purity of Reagents—Reagent grade chemicals shall be
the settled solution against the rim of a porcelain dish, or
used in all tests. Unless otherwise specified, it is intended that
against the light in a tall beaker or Erlenmeyer flask.
all reagents shall conform to the specifications of the Commit-
tee on Analytical Reagents of the American Chemical Society,
4. Significance and Use
where such specifications are available. Other grades may be
4.1 The acidity of a chrome tanning liquor, as determined by
used, provided it is first ascertained that the reagent is of
this test method, is rarely employed as such. This result is
sufficient high purity to permit its use without lessening the
normally combined with the results of a chromium analysis
accuracy of the determination.
(see Test Method D 3898) to determine a property of the liquor
6.2 Purity of Water—Unless otherwise specified, reference
called basicity. This property, equal to the percentage by which
anions in a normal chromic salt have been replaced by
hydroxyl in the solution being analyzed, is closely related to
Hartford, W. H., JALCA, Vol 56, 1961, p. 568.
the tanning behavior of the solution. Thorstensen, T. C., and Theis, E. R., JALCA, Vol 47, 1952, p. 583.
Theis, E. R., and Thorstensen , T. C., Journal International Society Leather
Trade Chemists, Vol 31, 1947, p. 124.
Serfass, E. J., Theis, E. R., and Clark, A., Jr., The Journal of the Leather
This test method is under the jurisdiction of ASTM Committee D-31 on Leather
Chemists Association, Vol 42, 1947, p. 360.
and is the direct responsibility of Subcommittee D31.06 on Chemical Analysis-
Reagent Chemicals, American Chemical Society Specifications, American
General Methods. This test method was developed in cooperation with the American
Leather Chemists Assoc. Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Current edition approved Jan. 15, 1993. Published March 1993. Originally listed by the American Chemical Society, see Analar Standards for Laboratory
published as D 3913 – 91. Last previous edition D 3913 – 91. Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Annual Book of ASTM Standards, Vol 15.04. and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
Annual Book of ASTM Standards, Vol 15.05. MD.
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NOTICE: This standard has either been superceded and replaced by a new version or d
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