ASTM E126-92(1998)
(Test Method)Standard Test Method for Inspection and Verification of Hydrometers
Standard Test Method for Inspection and Verification of Hydrometers
SCOPE
1.1 This test method describes the principles, apparatus, and procedures for the inspection and verification of glass hydrometers of the constant-mass, variable-displacement type. It is intended to apply to ASTM hydrometers as well as to glass hydrometers in general.
1.2 The values stated in inch-pound units are to be regarded as the standard. The metric equivalents of inch-pound units may be approximate.
1.3 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: E 126 – 92 (Reapproved 1998)
Standard Test Method for
Inspection and Verification of Hydrometers
This standard is issued under the fixed designation E 126; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3.2.3 specific gravity, n—the ratio of the mass of a given
volume of material at a stated temperature to the mass of an
1.1 This test method describes the principles, apparatus, and
equalvolumeofgas-freedistilledwateratastatedtemperature,
procedures for the inspection and verification of glass hydrom-
expressed by
eters of the constant-mass, variable-displacement type. It is
intended to apply to ASTM hydrometers as well as to glass Specific Gravity x/x F ~or y/y C!
(2)
hydrometers in general.
1.2 The values stated in inch-pound units are to be regarded
where x is usually 60° and y is usually 15.56 °C.
as the standard. The metric equivalents of inch-pound units
3.2.4 thermo-hydrometer, n—a glass hydrometer having a
may be approximate.
thermometer combined with a hydrometer in one instrument.
1.3 This standard does not purport to address all of the
3.2.5 Other descriptions of terms relating to thermometers
safety concerns, if any, associated with its use. It is the
are included in Test Method E 77.
responsibility of the user of this standard to establish appro-
4. Significance and Use
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
4.1 Thepurposeofthistestmethodistoestablishacommon
method by which manufacturers and users of hydrometers may
2. Referenced Documents
make tests to establish the validity of their readings in use or as
2.1 ASTM Standards:
a standard for comparison of hydrometer performance for
D 1265 Practice for Sampling Liquefied Petroleum (LP)
evaluation or selection purposes, or both.
Gases—Manual Method
4.2 The goal is to provide a standard method that is simple,
E 77 Test Method for Inspection and Verification of Ther-
easily understood, and which can be performed by the end user
mometers
in the hope that it will result in a better understanding of
E 344 Terminology Relating to Thermometry and Hydrom-
hydrometers.
etry
5. Apparatus
3. Terminology
5.1 Graduated Metal Scales, of the conventional type, for
3.1 Definitions:
checking linear dimensions. If more convenient, metal tem-
3.1.1 The definitions given in Terminology E 344 apply.
plates may be used on which lines are ruled at suitable
3.2 Definitions of Terms Specific to This Standard:
distances from reference points corresponding to the maximum
3.2.1 API gravity, n—the gravity obtained from the follow-
and minimum values of the specified dimensions.
ing relationship:
5.2 Micrometers, of the conventional type, for checking
diameters.
API Gravity, deg 5 141.5/~sp gr 60/60 °F!2 131.5 (1)
5.3 Comparators, for the verification of hydrometers. Suit-
3.2.2 density, n—the mass of a unit volume of material.
able types are described in Appendix X1.
5.4 Equipment for checking the thermometers of thermo-
1 hydrometers is described in Test Method E 77.
This test method is under the jurisdiction of ASTM Committee E-20 on
Temperature Measurement and is the direct responsibility of Subcommittee E20.05
6. Reference Standards
on Liquid-in-Glass Thermometers and Hydrometers.
Current edition approved May 15, 1992. Published July 1992. Originally
6.1 Primary Standard Hydrometers—Primary standard hy-
e1
published as E 126 – 59 T. Last previous edition E 126 – 88 .
drometers should have similar dimensions and shape to the
Annual Book of ASTM Standards, Vol 05.01.
Annual Book of ASTM Standards, Vol 14.03. instruments to be tested, but more finely subdivided. For
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E 126
example, if the instruments to be tested are subdivided to ogy in calibrating hydrometers, and it will be helpful to follow
0.0005 sp gr, the primary standards would have graduations of them to such extent as the need for accuracy requires.
0.0002 or 0.0001 sp gr. Primary standards must be calibrated
7.2.1.1 In order that readings shall be uniform and repro-
by a laboratory (such as the National Institute of Standards and
ducible, the hydrometer must be clean, dry, and at the tem-
Technology) capable of testing instruments of such precision.
perature of the liquid before immersing to take a reading. It is
Corrections must be stated to one tenth of a scale division.
particularly important that the stem be clean so that the liquid
Primary standards should be reverified at regular intervals.
will rise uniformly around the stem and merge into an
NOTE 1—The specific gravities of liquids used in testing hydrometers imperceptible film on the stem.
may be obtained by hydrostatic weighing instead of by the use of primary
7.2.1.2 Cleanliness—The readiness with which proper
standards as described above. Details of the hydrostatic weighing appa-
cleanlinesscanbeobtaineddependssomewhatonthecharacter
ratus can be found in the Dictionary of Applied Physics or “Density of
of the liquid. Certain liquids, such as mineral oils and strong
Solids and Liquids.”
alcoholic mixtures, adhere to the stem very readily. In such
6.2 Secondary Standard Hydrometers—Secondary standard
cases, wiping with a lint-free cloth moistened with acetone or
hydrometers are more suitable and have adequate sensitivity
alcohol and drying immediately before each reading is usually
for most work. These standards should have similar dimen-
sufficient. On the other hand, with weak aqueous solutions of
sions and shape to the instruments to be verified, and should
sugar, salts, acids, and alcohol, scrupulous cleaning of the stem
have the same graduation interval. Thus, one standard may be
is required. For such liquids, two methods for preparing
used to check the entire range of the instrument to be tested.
instruments for testing are in common use. In one method,
Secondarystandardsshallbeverifiedagainstprimarystandards
hydrometers are dipped in a mixture of one part concentrated
by a laboratory competent to conduct such tests, with correc-
sulfuric acid and two parts fuming sulfuric acid, thoroughly
tions stated to one-tenth scale division. Reverification should
rinsedwithwater,anddriedbywipingwithacleancloth.Inthe
be done at regular intervals.
other method, hydrometers are washed with soap and water,
dried, and wiped with a cloth moistened with alcohol to
7. Procedure
remove any residual soap film. The stems can usually be kept
7.1 Dimensional Inspection:
clean during the testing by wiping with a lint-free cloth
7.1.1 Check the lineal dimensions and diameters by com-
moistened with alcohol (preferably absolute) and drying before
paring the hydrometer with the appropriate device described in
each reading.
5.1 and 5.2.
7.1.2 Inspect the hydrometers for correctness of graduation
7.2.1.3 Influence of Temperature—In order that a hydrom-
spacing.API and Baumé hydrometers are graduated with equal
etermaycorrectlyindicatethedensityorstrengthofaspecified
spacing. The interval between graduations of density and
liquid, it is essential that the liquid be uniform throughout and
specific gravity hydrometers is smaller near the bottom of the
at the temperature specified on the instrument. In comparing
scale. The proper spacing can be obtained from the following
two hydrometers having the same standard temperature and
formula:
made of the same type of glass, however, the temperature of
l 5 L 3 d /d 3 ~d 2 d !/~d 2 d ! the liquid need not be considered since the correction required
2 1 2 1
(3)
due to variation from the standard temperature is the same for
both instruments. But the temperatures of the liquid, the
where:
hydrometers, and the surrounding atmosphere should be nearly
l 5 distance from the top line to any line, d, between the
equal during the observation; otherwise, the temperature of the
top and the bottom,
liquid will be changing, causing differences in density. To
L 5 distance between the top and the bottom graduations
ensure uniformity in the liquid, thorough mixing is required
of the scale,
shortly before the observations are made.
d 5 density, or specific gravity, of the bottom line, and
d 5 density, or specific gravity, of the top line.
1 7.2.1.4 InfluenceofSurfaceTension—Whenahydrometeris
7.1.3 Check the scale of alcoholometers graduated to read
floated in a liquid, a small quantity of the liquid rises about the
percent of alcohol by weight or by volume by comparison with
stem to form a meniscus. This liquid adhering to the stem
the values for master scales given in the “Standard Density and
above the general level of the liquid in which the instrument is
Volumetric Tables.” .
floating has the same effect as adding to the mass of the
7.2 Verification:
hydrometer, thus increasing the depth of immersion.
7.2.1 General Considerations—The details of procedure
7.2.1.5 Because a hydrometer will indicate differently in
described in the following paragraphs are, in general, the ones
two liquids having the same density but different surface
employed at the National Institute of Standards and Technol-
tensions, and since surface tension is a specific property of
liquids, it is necessary to specify the liquid for which a
hydrometer is intended. Although hydrometers of equivalent
Dictionary of Applied Physics, MacMillan and Co., London, Vol 3, p. 439. dimensions may be compared, without error, in a liquid
“Density of Solids and Liquids,” National Institute of Standards and Technol-
differinginsurfacetensionfromthespecifiedliquid,theresults
ogy, Circular No. 487.
6 of comparisons of dissimilar instruments in such a liquid must
“Standard Density and Volumetric Tables,” National Institute of Standards and
Technology, Circular, No. 19. be corrected for the effect of the surface tension.
E 126
7.2.1.6 In many liquids spontaneous changes in surface 7.2.2.1 Use either of the comparators described in X1.1 and
tension occur due to the formation of surface films of impuri- X1.2.
ties, which may come from the apparatus, the liquid, or the air. 7.2.2.2 Introduce into the comparator a sufficien
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