The melting point determined by the capillary method is the temperature at which the last solid particle of a compact column of a substance in a tube passes into the liquid phase.
Unless otherwise prescribed, dry the finely powdered substance in vacuum and over anhydrous silica gel R for 24 h or at a temperature specified in the monograph
Transfer a quantity of the dried powder by tapping the tube on a hard surface (ensure the capillary tube bottom is not damaged or cracked).
The capillary tube closed at one end and dimensions suitable for the apparatus used.
Raise the temperature of the instrument to about 10 °C below the presumed melting point and then adjust the rate of heating to about 1 °C/min.
When the temperature is 5 °C below the presumed melting point, correctly introduce the capillary tube into the instrument.
Record the temperature at which the last particle passes into the liquid phase