ASTM D974-08e1
(Test Method)Standard Test Method for Acid and Base Number by Color-Indicator Titration
Standard Test Method for Acid and Base Number by Color-Indicator Titration
SIGNIFICANCE AND USE
New and used petroleum products can contain basic or acidic constituents that are present as additives or as degradation products formed during service, such as oxidation products. The relative amount of these materials can be determined by titrating with acids or bases. This number, whether expressed as acid number or base number, is a measure of this amount of acidic or basic substances, respectively, in the oilalways under the conditions of the test. This number is used as a guide in the quality control of lubricating oil formulations. It is also sometimes used as a measure of lubricant degradation in service; however, any condemning limits must be empirically established.
Since a variety of oxidation products contribute to the acid number and the organic acids vary widely in corrosive properties, the test cannot be used to predict corrosiveness of an oil under service conditions. No general correlation is known between acid number and the corrosive tendency of oils toward metals. Compounded engine oils can and usually do have both acid and base numbers in this test method.
SCOPE
1.1 This test method covers the determination of acidic or basic constituents (Note 1) in petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and isopropyl alcohol. It is applicable for the determination of acids or bases whose dissociation constants in water are larger than 10−9; extremely weak acids or bases whose dissociation constants are smaller than 10−9 do not interfere. Salts react if their hydrolysis constants are larger than 10−9.
Note 1—In new and used oils, the constituents considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, and addition agents such as inhibitors and detergents. Similarly, constituents considered to have basic properties include organic and inorganic bases, amino compounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts of heavy metals, and addition agents such as inhibitors and detergents.
Note 2—This test method is not suitable for measuring the basic constituents of many basic additive-type lubricating oils. Test Method D4739 can be used for this purpose.
1.2 This test method can be used to indicate relative changes that occur in an oil during use under oxidizing conditions. Although the titration is made under definite equilibrium conditions, the method does not measure an absolute acidic or basic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid or base numbers is known.
Note 3—Oils, such as many cutting oils, rustproofing oils, and similar compounded oils, or excessively dark-colored oils, that cannot be analyzed for acid number by this test method due to obscurity of the color-indicator end point, can be analyzed by Test Method D664. The acid numbers obtained by this color-indicator test method need not be numerically the same as those obtained by Test Method D664, the base numbers obtained by this color indicator test method need not be numerically the same as those obtained by Test Method D4739, but they are generally of the same order of magnitude.
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.
A2.1.1 This test method is intended for determining the acceptability of p-naphtholbenzein indicator for use in Test Method D974 with regard to color change over a pHr range.
General Information
Relations
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
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Designation:D974–08
Designation: 139/98
Standard Test Method for
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Acid and Base Number by Color-Indicator Titration
This standard is issued under the fixed designation D974; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
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´ NOTE—Corrected terminology in 7.7.1 to match the rest of the standard text editorially in July 2010.
color-indicatorendpoint,canbeanalyzedbyTestMethodD664.Theacid
1. Scope*
numbers obtained by this color-indicator test method need not be
1.1 This test method covers the determination of acidic or
numerically the same as those obtained by Test Method D664, the base
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basic constituents (Note 1) in petroleum products and lubri-
numbers obtained by this color indicator test method need not be
cants soluble or nearly soluble in mixtures of toluene and
numerically the same as those obtained by Test Method D4739, but they
isopropylalcohol.Itisapplicableforthedeterminationofacids are generally of the same order of magnitude.
or bases whose dissociation constants in water are larger than
1.3 The values stated in SI units are to be regarded as
−9
10 ; extremely weak acids or bases whose dissociation
standard. No other units of measurement are included in this
−9
constants are smaller than 10 do not interfere. Salts react if
standard.
−9
their hydrolysis constants are larger than 10 .
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
NOTE 1—In new and used oils, the constituents considered to have
acidic characteristics include organic and inorganic acids, esters, phenolic responsibility of the user of this standard to establish appro-
compounds, lactones, resins, salts of heavy metals, and addition agents
priate safety and health practices and determine the applica-
such as inhibitors and detergents. Similarly, constituents considered to
bility of regulatory limitations prior to use.
have basic properties include organic and inorganic bases, amino com-
pounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts
2. Referenced Documents
of heavy metals, and addition agents such as inhibitors and detergents.
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2.1 ASTM Standards:
NOTE 2—This test method is not suitable for measuring the basic
D117 GuideforSampling,TestMethods,andSpecifications
constituents of many basic additive-type lubricating oils. Test Method
D4739 can be used for this purpose. for Electrical Insulating Oils of Petroleum Origin
D664 Test Method forAcid Number of Petroleum Products
1.2 Thistestmethodcanbeusedtoindicaterelativechanges
by Potentiometric Titration
that occur in an oil during use under oxidizing conditions.
D1193 Specification for Reagent Water
Although the titration is made under definite equilibrium
D4175 Terminology Relating to Petroleum, Petroleum
conditions, the method does not measure an absolute acidic or
Products, and Lubricants
basicpropertythatcanbeusedtopredictperformanceofanoil
D4739 Test Method for Base Number Determination by
under service conditions. No general relationship between
Potentiometric Hydrochloric Acid Titration
bearing corrosion and acid or base numbers is known.
NOTE 3—Oils, such as many cutting oils, rustproofing oils, and similar 3. Terminology
compounded oils, or excessively dark-colored oils, that cannot be ana-
3.1 Definitions:
lyzed for acid number by this test method due to obscurity of the
3.1.1 acid number, n—the quantity of base, expressed in
milligrams of potassium hydroxide per gram of sample that is
required to titrate a sample to a specified end point.
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This test method is under the jurisdiction of ASTM Committee D02 on
3.1.1.1 Discussion—In this test method, the indicator is
PetroleumProductsandLubricantsandisthedirectresponsibilityofSubcommittee
p-naphtholbenzeintitratedtoagreen/green-brownendpointin
D02.06 on Analysis of Lubricants.
a toluene-water-isopropanol solvent.
In the IP, this test method is under the jurisdiction of the Standardization
Committee. This test method was adopted as a joint ASTM-IP standard in 1965.
Current edition approved July 1, 2008. Published August 2008. Originally
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approved in 1948. Last previous edition approved in 2007 as D974–07. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D0974-08. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
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Statementsdefiningthistestmethod,itsmodification,anditssignificancewhen Standards volume information, refer to the standard’s Document Summary page on
applied to electrical insulat
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