Apparatus: A setup comprising a heating bath, thermometer, and assembly of a melting point tube. (Perforation of the rubber stopper and installation of the melting point determination device)

Procedure: (Demonstration) a. Drying and Grinding of the Sample:

  • Ensure the sample is thoroughly dried and ground.

b. Sample Loading:

  • Cut a capillary tube with sealed ends to a length of approximately 10-12 cm.
  • Insert one open end into the sample powder, loading it to a height of about 3-4 mm.
  • Invert and tap gently to compact the sample, leaving a final height of 2-3 mm.

c. Attachment to Thermometer:

  • Affix the capillary tube containing the sample to the thermometer. Ensure the sample portion is in the middle of the mercury bulb.

d. Placement in Heating Bath:

  • Place the assembly into the heating bath. Ensure the mercury bulb of the thermometer is in the middle of the bath, not touching the bottom or deviating from the surface of the bath liquid.

e. Rough Melting Point Determination:

  • Begin heating at a relatively fast rate, typically 4-5°C per minute, until the sample melts. Note the thermometer reading at this point for reference during the melting point determination.

f. Heating and Temperature Control:

  • Gradually increase the temperature. Initially, the heating rate can be faster. When the temperature is approximately 15°C below the rough side melting point, control the heating rate to 1-2°C per minute.

g. Observation of Melting Point:

  • Observe the melting point, noting two critical stages:
    • Onset of Melting (Initial Melting): Contraction of the solid; when the sample begins to collapse and a liquid phase appears.
    • Complete Melting: Disappearance of the solid into a transparent liquid.

h. Recording Results:

  • Record the melting point range, from the onset of melting to complete melting temperature.

i. Multiple Data and Repetition:

  • Perform the procedure at least twice, using a new sample-loaded melting point tube for the second run. The bath temperature should be at least 20°C below the melting point before insertion.
By 向阳 翟


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