Melting Point of Naphthalene

Take a small capillary tube, fill, it with naphthalene powder and seal its mouth. Attach the capillary to the bulb of a thermometer and put the assembly into water bath (Fig. 4.3). Heat the water slowly and note down the temperature at which naphthalene melts. Compare it with the value given in Table. Can you guess if the given sample is pure? Pure materials melt at ideal melting point whereas impure materials dont.