MIL-DTL-10866E
4.2.4.6.1.3 Thermometer. The thermometer shall be of the partial immersion type and be
capable of detecting the proper range in accordance with ASTM E 1.
4.2.4.6.1.4 Sieve. A 125-micron (µm) sieve used in preparation of the standard sample
and of samples of material to be tested shall meet the requirements of ASTM E 11.
4.2.4.6.2 Standard sample.
4.2.4.6.2.1 Chemical composition. The standard sample shall be homogeneous and of
the same basic chemical composition as the unknown to be analyzed. This condition is satisfied
when both materials are quite pure, or when both the standard and the unknown have been made
by the same industrial process. Significant deviations from identity in chemical composition
lead to some loss of precision.
4.2.4.6.2.2 Particle size. The standard sample must be uniformly blended, and particle
size must be fine enough so that a test specimen of approximately 0.1 gram will yield
reproducible melting point data. In preparing a standard sample from coarse crystalline material
the sample should be ground fine, passed through a 125-µm sieve, and blended thoroughly
before subdividing and storing for use in the test.
4.2.4.6.2.3 Storage. The standard sample shall be stored under such conditions that its
quality will not deteriorate. This is vital to the success of the method, since deterioration of the
standard sample may cause lowered initial melting temperature, which will result in falsely high
indications of the purity of the materials under test. Many chemicals are somewhat hygroscopic,
and it may be agreed that the standard or both the standard and the sample are to be conditioned
by appropriate means before the initial melting point is determined.
4.2.4.6.3 Sampling. A bulk sample shall be withdrawn by means appropriate to the
processing, shipment, or storage conditions. This bulk sample shall be blended and subdivided,
with grinding steps where appropriate, until a blended sample of 1 to 10 grams with a particle
size passing 125-µm sieve is obtained.
4.2.4.6.4 Procedure.
a. Grind approximately 0.1-gram test specimens of the standard sample and of the
unknown sample as finely as possible in mortars or on pieces of flat glass with spatulas. Charge
the melting point capillary tubes with the finely ground test specimens to form packed columns in
the bottom of the tubes from 3 to 4 mm in height. The capillary tubes are packed tightly by adding
the powdered test specimen in three or four increments, ensuring each increment is well packed.
b. Preheat the oil bath to approximately 15 °C below the expected melting range. Then
adjust the temperature rise rate to 1 ± 0.2 °C per minute during the actual melting of the sample.
c. Without removing the thermometer from the heating bath, place the packed capillary
tubes containing the standard and unknown sample in the heating bath when the temperature is
about 5 °C below the expected initial melting point. Hold the packed capillary tubes adjacent to
the thermometer bulb in such a way that they and the thermometer bulb are at a uniform
temperature.
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