How to Determine Melting Point of a Substance

thiele tube
We know the melting point of different substances. But ever you questioned how the melting point of a substance is determined. There are various method to determine the melting point. Thiele’s tube containing paraffin oil is a popular method and widely used in laboratories.

Determination of melting point

Steps that you have to follow

#1 We need a capillary tube which is about 5 to 6 cm long having a diameter of 1 mm. This capillary tube is sealed at one end by heating on a burner.

#2 Take compound on a white paper. Divide the compound finely using glass rod. Fill the capillary tube with the finely divided compound.

#3 We need a thermometer to measure melting point. The capillary tube with the sealed end at the bulb of the thermometer is tied using thread.

#4 The Theil’s tube is filled with paraffin oil which has a high boiling point more than 370-degree Celsius. Thermometer with tied capillary is immersed in the paraffin oil.

#5 The bulb of the thermometer is near the side arm of the Theile’s tube which is clamped to a stand.

#6 The triangular sidearm of the Thiele’s tube is heated maintaining uniform temperature due to convection current.

#7 When the substance in the capillary tube starts melting, heating is discontinued.

#8 The temperature at which the substance melts completely is recorded which is the melting point of the substance

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