FED-STD-228A
Method 8321.1
18 APRIL 2014
SPECIFIC GRAVITY; PYCNOMETER
1. SCOPE
1.1 This method is intended for use in determining the specific gravity of rubber insulating compounds
and sheaths. It is particularly applicable when the specimen is not in the form of one solid and continuous
piece. It is not as rapid as method 8322 but is considered more accurate.
2. SPECIMEN
2.1 The specimen should consist of approximately 1 gram of the insulation or sheath taken from the
inspection unit.
3. APPARATUS AND REAGENTS
3.1 The apparatus and reagents shall be as follows:
3.1.1 An analytical balance and weights.
3.1.2 A pycnometer.
3.1.3 Ninety-five percent ethyl alcohol.
4. PROCEDURE
4.1 Unless otherwise specified in the detail specification, the determination shall be made at a
temperature of 25° ± 0.5°C (77° ± 1°F), unless the coefficient of expansion of the rubber compound is
known, in which case, the determination may be made at any convenient temperature and the value
corrected to 25°C.
4.2 The specimen shall be weighed to the nearest 0.1 mg. and the weight recorded as W1.
4.3 The pycnometer shall be filled with 95 percent alcohol, weighed to the nearest 0.1 milligram and the
weight recorded as W2.
4.4 The specimen shall then be placed in the pycnometer which shall be filled with alcohol and the whole
weighed to the nearest 0.1 milligram, and the weight recorded as W3.
5. RESULT
5.1 The specific gravity of the specimen at 25°/4° C shall be calculated as follows:
Specific gravity (25°/4°C) = 0.9971 x W1 x specific gravity of alcohol at 25°/25° C
W1-(W2-W3)
where:
W1=weight of the specimen, grams.
W2=weight of pycnometer filled with alcohol, grams.
W3=weight of pycnometer filled with specimen and alcohol, grams.
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