General Test Procedure Melting Range and Freezing Point

Purpose
1. This procedure is applicable to all incoming Raw materials, In-process and Finished products.
Apparatus
1. Melting point apparatus
2. Thin-walled capillary glass tubes of hard glass, closed at one end
3. pestle mortar
4. Beakers
5. Test tubes
6. Water bath
7. Calibrated glass thermometer
8. Balance
Reagents
1. None
Procedure
1. Procedure for melting point determination
  1. Reduce the substance to a very fine powder.
  2. Introduce into a capillary glass tube, a sufficient quantity of the dry powder to form a compact column 4 to 6mm high.
  3. Start the melting point apparatus as per the program encoded in the apparatus for that particular material. And note down the melting point displayed on the apparatus (which is the mean of 3 readings).
  4. When a particular program is not available start heating at a rate of 10C per minute. When temperature is below 10 °C to the expected melting range of sample adjust the heating rate to about 1 °C per minute and insert the capillary tube into melting point apparatus.
  5. Melting point is the mean of three readings displayed on the display panel of the apparatus.
  6. Record the melting point.
Procedure for melting point range determination
1. Reduce the substance (previously dried at temperature below the melting point of the substance for

about 24 hours unless otherwise specified in the respective specification or testing procedure) to a

very fine powder.

1. Introduce into a capillary glass tube, a sufficient quantity of the dry powder to form a compact column

4 to 6mm high.

1. Fill a suitable liquid e.g. water for temperatures up to 60C, glycerin up to 150C, liquid paraffin for

up to 250C, silicon oil for up to 300C ; in the heating vessel.

1. Start heating the liquid in the heating vessel at a rate of 10C per minute on hot plate or suitable

heating mantle. When temperature is below 10 °C to the expected melting range of sample, remove

the thermometer and quickly attach the capillary tube to the thermometer by wetting both with a drop

of liquid and adjust the height so that the closed end of the capillary is near the middle of the

thermometer bulb. Replace the thermometer and continue heating. Adjust the heating rate to about 1

°C per minute.

1. Continue the heating and observe the temperature at which the sample begins to soften and the

temperature at which it becomes completely liquid with a clear meniscus.

1. Record the melting range (i.e. the temperature at which it starts melting and the temperature at which

it is completely melted).

Procedure for freezing point determination
1. For determining freezing point; a test tube is placed inside another test tube, the inner tube is closed

by a stopper that carries a stirrer and a thermometer fixed so that the bulb is about 15 mm above the

bottom of the tube. The stirrer is made from glass rod. The inner tube is supported centrally in a 1

liter beaker containing suitable cooling liquid to within 20mm of the top. The thermometer is

supported in the cooling bath.