An American National Standard

Designation: D 721 – 02a

Designation: 158/69(85)

Standard Test Method for

Oil Content of Petroleum Waxes1
This standard is issued under the fixed designation D 721; 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. Summary of Test Method

1.1 This test method covers the determination of oil in 3.1 The sample is dissolved in methyl ethyl ketone, the
petroleum waxes having a congealing point of 30°C (86°F) or solution cooled to –32°C (–25°F) to precipitate the wax, and
higher as determined in accordance with Test Method D 938, filtered. The oil content of the filtrate is determined by
and containing not more than 15 % of oil.2 evaporating the methyl ethyl ketone and weighing the residue.
1.2 The values stated in inch-pound units are to be regarded
as the standard. The values in parentheses are for information 4. Significance and Use
only. 4.1 The oil content of a wax may have significant effects on
several of its properties, such as strength, hardness, flexibility,
NOTE 1—With some types of waxes, of oil contents greater than 5%,
there may be an incompatibility with MEK resulting in the formation of scuff resistance, coefficient of friction, coefficient of expansion,
two liquid phases. If this occurs, the method is not applicable to the melting point, and oil straining. The importance of these effects
material under test. may be dependent upon the ultimate use of the wax.
1.3 This standard does not purport to address all of the 5. Apparatus
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 5.1 Filter Stick and Assembly, consisting of a 10-mm
priate safety and health practices and determine the applica- diameter sintered glass filter stick of 10 to 15 µm maximum
bility of regulatory limitations prior to use. pore diameter as determined by the method in Appendix X1,
provided with an air pressure inlet tube and delivery nozzle. It
2. Referenced Documents is provided with a ground-glass joint to fit a 25 by 170-mm test
2.1 ASTM Standards: tube. The dimensions for a suitable filtration assembly are
D 938 Test Method for Congealing Point of Petroleum shown in Fig. 1.
Waxes, Including Petrolatum3 NOTE 2—A metallic filter stick may be employed if desired. A filter
E 1 Specification for ASTM Thermometers4 stick made of stainless steel and having a 12.7–mm (1⁄2-in.) disk of 10 to
E 128 Test Method for Maximum Pore Diameter and Per- 15-µm maximum pore diameter, as determined by Test Method E 128, has
meability of Rigid Porous Filters for Laboratory Use5 been found to be satisfactory.6 The metallic apparatus is inserted into a 25
by 150–mm test tube and held in place by means of a cork.
5.2 Cooling Bath, consisting of an insulated box with 25.4
1
This test method is under the jurisdiction of ASTM Committee D02 on mm (1-in.) holes in the center to accommodate any desired
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
D02.10 on Properties of Petroleum Wax.
number of test tubes. The bath may be filled with a suitable
Current edition approved Nov. 10, 2002. Published February 2003. Originally medium such as kerosine, and may be cooled by circulating a
approved in 1943. Last previous edition approved in 2002 as D 721-02.
In the IP, this method is under the jurisdiction of the Standardization Committee.
This test method was issued as a joint ASTM-IP tentative in 1964.
This test method was prepared jointly by the Technical Association of Pulp and
Paper Industry and ASTM International.
6
This test method has been adopted for use by government agencies to replace The sole source of supply of a suitable metal filter stick with designated
Method 5431 of Federal Test Method Standard No. 79lb. porosity G known to the committee at this time is the Pall Trinity Micro Corp.,
2
This test method is being used by some laboratories for products of higher oil Route 281, Cortland, NY 13045. A list of United Kingdom suppliers can be obtained
content. from the Institute of Petroleum, 61 New Cavendish St., London, W1G 7AR, United
3
Annual Book of ASTM Standards, Vol 05.01. Kingdom. If you are aware of alternative suppliers, please provide this information
4
Annual Book of ASTM Standards, Vol 14.03. to ASTM International Headquarters. Your comments will receive careful consid-
5
Annual Book of ASTM Standards, Vol 14.02. eration at a meeting of the responsible technical committee 1, which you may attend.

*A Summary of Changes section appears at the end of this standard.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

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 D 721 – 02a
5.8 Evaporation Assembly, consisting of an evaporating
cabinet and connections, essentially as illustrated in Fig. 4, and
capable of maintaining a temperature of 35 6 1°C (95 6 2°F)
around the evaporation flask. Construct the jets with an inside
diameter of 4 6 0.2 mm for delivering a stream of clean, dry
air vertically downward into the weighing bottle. Support each
jet so that the tip is 15 6 5 mm above the surface of the liquid
at the start of the evaporation. Supply air at the rate of 2 to 3
L/min per jet, purified by passage through a tube of 10-mm
bore packed loosely to a height of 200 mm with absorbent
cotton. Periodically check the cleanliness of the air by evapo-
rating 4 mL of methyl ethyl ketone by the procedure specified
in 8.5. When the residue does not exceed 0.1 mg, the
evaporation equipment is operating satisfactorily.
5.9 Analytical Balance, capable of reproducing weights to
0.1 mg. The sensitivity should be adjusted so that 0.1 mg will
deflect the pointer one half division on the pointer scale.
5.10 Wire Stirrer—A piece of stiff wire, made of iron,
stainless steel, or Nichrome wire of about No. 20 B & S (0.9
mm in diameter) or 16 swg gage, 250 mm long. A 10-mm
diameter loop is formed at each end, and the loop at the bottom
end is bent so that the plane of the loop is perpendicular to the
wire.

All dimensions are in millimetres 6. Reagents

FIG. 1 Filter Stick 6.1 Methyl Ethyl Ketone, conforming to the specifications of
the Committee on Analytical Reagents of the American Chemi-
cal Society.7
refrigerant through coils, or by using solid carbon dioxide. A 6.2 Store the solvent over anhydrous calcium sulfate (5
suitable cooling bath to accommodate three test tubes is shown weight % of the solvent). Filter prior to use.
in Fig. 2. 6.3 Air supply, clean and filtered.
5.3 Pipet, or equivalent dispensing device capable of deliv- NOTE 3—As an alternative, it is permissible to replace all references to
ering 1 6 0.05 g of molten wax. “air” used in the solvent evaporation process with “nitrogen,” provided the
5.4 Transfer Pipet, or equivalent volume dispensing device, nitrogen is clean and filtered. It should be noted, however, that the
capable of delivering 15 6 0.06 mL. precision statements for the test method were determined using air only
5.5 Air Pressure Regulator, designed to supply air to the and that the precision associated with using nitrogen has not been
determined.
filtration assembly (8.5) at the volume and pressure required to
give an even flow of filtrate. Either the conventional pressure- 7. Sample
reducing valve or a mercury bubbler-type regulator has been
7.1 If the sample of wax is 1 kg (2 lb) or less, obtain a
found satisfactory. The latter type, illustrated in Fig. 3, consists
representative portion by melting the entire sample and stirring
of a 250-mL glass cylinder and a T-tube held in the cylinder by
thoroughly. For samples over 1 kg (2 lb), exercise special care
means of a rubber stopper grooved at the sides to permit the
to ensure obtaining a truly representative portion, bearing in
escape of excess air. The volume and pressure of the air
mind that the oil may not be distributed uniformly throughout
supplied to the filtration assembly is regulated by the depth to
the sample, and that mechanical operations may express some
which the T-tube is immersed in mercury at the bottom of the
of the oil.
cylinder. Absorbent cotton placed in the space above the
mercury prevents the loss of mercury by spattering. The air 8. Procedure
pressure regulatory is connected to the filter stick and assembly
8.1 Melt a representative portion of the sample, using a
by means of rubber tubing.
water bath or oven maintained at 70 to 100°C (158 to 212°F).
5.6 Thermometer, having a range as shown below and
As soon as the wax is completely melted, thoroughly mix.
conforming to the requirements as prescribed in Specification
Preheat the pipet or equivalent measuring device in order to
E 1, or in the Specification for IP Standard Thermometers.
Thermometer Number
Temperature Range ASTM IP
7
Reagent Chemicals, American Chemical Society Specifications, American
–37 to +21°C 71C 72C Chemical Society, Washington, DC. For suggestions on the testing of reagents not
–35 to +70°F 71F 72F listed by the American Chemical Society, see Annual Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
5.7 Weighing Bottles, conical in shape and glass-stoppered, and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
having a capacity of 15 mL. MD.

2
 D 721 – 02a

All dimensions are in millimetres (inches)

FIG. 2 Cooling Bath

prevent the solidification of wax in the tip, and withdraw a the stirrer. Remove the test tube from the ice bath, wipe dry on
portion of the sample as soon as possible after the wax has the outside with a cloth, and weigh to the nearest 0.1 g.
melted. The mass of wax transferred to the test tube must be
1.00 6 0.05 g. Allow the test tube to cool, and weigh to the NOTE 6—During this operation the loss of solvent through vaporiza-
tions should be less than 1%. The weight of the solvent is therefore
nearest 1 mg. practically a constant, and after a few samples are weighed, this weight,
NOTE 4—The weight of a test tube which is cleaned by means of approximately 11.9 g, can be used as a constant factor.
solvents will not vary to a significant extent. Therefore, a tare weight may
be obtained and used repeatedly.
8.3 Insert the thermometer into the test tube and place the
test tube containing the wax-solvent slurry in the cooling bath,
8.2 Pipet 15 mL of methyl ethyl ketone into the test tube and which is maintained at –34.5 6 0.3°C (–30 6 2°F). During this
place the latter just up to the level of its contents in a hot water chilling operation it is important that stirring by means of the
or steam bath. Heat the solvent wax mixture, stirring up and thermometer be almost continuous, in order to maintain a
down with the wire stirrer, until a homogeneous solution is slurry of uniform consistency as the wax precipitates. Do not
obtained. Exercise care to avoid loss of solvent by prolonged allow the wax to set up of the walls of cooling vessel nor
boiling. permit any lumps of wax crystals to form. Continue stirring
NOTE 5—Very high-melting wax samples may not form clear solutions. until the temperature reaches –31.7 6 0.3°C (–25 6 0.5°F).
Stir until the undissolved material is well dispersed as a fine cloud. 8.4 Remove the thermometer from the tube and allow it to
8.2.1 Plunge the test tube into an 800-mL beaker of ice drain momentarily into the tube; then immediately immerse in
water and continue to stir until the contents are cold. Remove the mixture the clean dry filter stick which has previously been

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 D 721 – 02a
evaporation procedure, using a 5-min evaporation period
instead of 30 min, until the loss between successive weighings
is not over 0.2 mg.
9. Calculation
9.1 Calculate the amount of oil in the wax as follows:
Oil in wax, weight % 5 ~100 AC/BD!– 0.15 (1)

where:
A = weight of oil residue, g,
B = weight of wax sample, g,
C = weight of solvent, g, obtained by subtracting weight
of test tube plus wax sample (8.1) from weight of
test tube and contents (8.2),
D = weight of solvent evaporated, g, obtained by sub-
tracting weight of weighing bottle plus oil residue
from weight of weighing bottle plus filtrate (7.5),
and
0.15 = average factor correcting for the solubility of wax in
All dimensions are in millimetres the solvent at –32°C (–25°F).
FIG. 3 Air Pressure Regulator
10. Report
cooled by placing it in a test tube and holding at –34.5 6 1°C 10.1 Report the result as oil content, Test Method D 721. If
(–30 6 2°F) in the cooling bath for a minimum of 10 min. Seat the result is negative, report as zero.
the ground-glass joint of the filter so as to make an airtight seal. 11. Precision and Bias
Place an unstoppered weighing bottle, previously weighed
together with the glass stopper to the nearest 0.1 mg, under the 11.1 Precision—The precision of this test method as deter-
delivery nozzle of the filtration assembly. mined by statistical examination of interlaboratory results is as
follows:
NOTE 7—Take every precaution to ensure the accuracy of the weight of 11.1.1 Repeatability—The difference between two test re-
the stoppered weighing bottle. Prior to determining this weight, rinse the sults, obtained by the same operator with the same apparatus
clean, dry weighing bottle and stopper with methyl ethyl ketone, wipe dry
on the outside with a cloth, and place in the evaporation assembly to dry
under constant operating conditions on identical test material,
for about 5 min. Then remove the weighing bottle and stopper, place near would in the long run, in the normal and correct operation of
the balance, and allow to stand for 10 min prior to weighing. Stopper the the test method, exceed the following values only in one case
bottle during this cooling period. Once the weighing bottle and stopper in twenty:
have been dried in the evaporation assembly, lift only with forceps. Take 0.06 1 8% of the mean
care to remove and replace the glass stopper with a light touch.
11.1.2 Reproducibility—The difference between two single
8.5 Apply air pressure to the filtration assembly, and imme-
and independent results obtained by different operators work-
diately collect about 4 mL of filtrate in the weighing bottle.
ing in different laboratories on identical test material would, in
Release the air pressure to permit the liquid to drain back
the long run, in the normal and correct operation of the test
slowly from the delivery nozzle. Remove the weighing bottle
method, exceed the following values only in one case in
immediately, and stopper and weigh to the nearest 10 mg
twenty:
without waiting for it to come to room temperature. Unstopper
the weighing bottle and place it under one of the jets in the 0.2 1 11% of the mean
evaporation assembly maintained at 35 6 1°C (95 6 2°F), with 11.2 Bias—The procedure in this test method has no bias
the air jet centered inside the neck, and the tip 15 6 5 mm because the value of oil content can be defined only in terms of
above the surface of the liquid. After the solvent has evapo- a test method.
rated, which usually takes less than 30 min, remove the bottle
and stopper, and place them near the balance. Allow to stand 12. Keywords
for 10 min and weigh to the nearest 0.1 mg. Repeat the 12.1 oil content; petroleum wax; wax

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 D 721 – 02a

All dimensions are in millimetres (inches)

FIG. 4 Evaporation Assembly

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 D 721 – 02a

APPENDIX

(Nonmandatory Information)

X1. METHOD OF TEST FOR MEASUREMENT OF MAXIMUM PORE DIAMETER OF RIGID POROUS FILTERS

X1.1 Scope X1.5.2 Thoroughly wet the clean filter to be tested by

X1.1.1 This method covers the determination of the accept- soaking it in distilled water.
ability of porous filter sticks used for filtration in Test Method X1.5.3 Assemble the apparatus as shown in Fig. X1.1.
D 721. This method establishes the maximum pore diameter Apply pressure slowly from a source of clean air.
and also provides a means of detecting and measuring changes X1.5.4 Immerse the filter just below the surface of the
which occur form continued use. water.
NOTE X1.2—If a head of liquid exists above the surface of the filter, the
X1.2 Definition back pressure produced must be deducted from the observed pressure.
X1.2.1 maximum pore diameter—the diameter in microme- X1.5.5 Increase the air pressure to 10 mm below the
ters of the largest opening in the filter. acceptable pressure limit and then at a slow uniform rate of
NOTE X1.1—It is recognized that the maximum pore diameter as about 3 mm Hg/min until the first bubble passes through the
defined herein does not necessarily indicate the physical dimensions of the filter. This can be conveniently observed by placing the beaker
largest pore in the filter. It is further recognized that the pores are highly or test tube over a mirror. Read the manometer when the first
irregular in shape. Because of the irregularity in shape and other
bubble passes off the underside of the filter.
phenomena characteristic of filtration, a filter may be expected to retain all
particles larger than the maximum pore diameter as defined and deter- X1.6 Calculation
mined herein, and will generally retain particles which are much smaller
than the determined diameter. X1.6.1 Calculate the pore diameter as follows:
D 5 2180/p
X1.3 Summary of Method
X1.3.1 The filter is cleaned and wetted with water. It is then where:
immersed in water and air pressure is applied against its upper D = pore diameter, µm, and
surface until the first bubble of air passes through the filter. The p = manometer reading, mm Hg.
maximum pore diameter is calculated from the surface tension NOTE X1.3—From this equation, pressure corresponding to the upper
of water and the applied pressure. and lower limits of the specified pore diameters can be calculated. These
pressures may be used for acceptance testing.
X1.4 Apparatus
X1.4.1 Pressure Measuring Device, mercury-filled manom-
eter or equivalent, capable of measuring pressures in incre-
ments of 0.5 mm of Hg.
X1.4.2 Air Supply, clean and filtered.
X1.4.3 Air Pressure Regulator, needle-valve type.
X1.4.4 Drying Oven.
X1.5 Procedure
X1.5.1 Clean the filter sticks by soaking in concentrated
hydrochloric acid, and then wash them with distilled water.
Rinse with acetone, air dry, and place in drying oven at 220°F FIG. X1.1 Assembly of Apparatus for Checking Pore Diameter or
(105°C) for 30 min. Filter Sticks

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 D 721 – 02a
SUMMARY OF CHANGES

Committee D02.10 has identified the location of selected changes to this standard since the last issue
(D 721–02) that may impact the use of this standard.

(1) Updated the thermometer chart in 5.6 to include the ASTM (3) Added a new Note 3.
71C thermometer as an equivalent to the IP 72C thermometer.
(2) Added 6.3 to align with air supply requirements in
Appendix X1.

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