To determine the melting point of the unknown substance if approximate melting point is not known, it is better to make or fill two capillaries with the same substance. The temp of the heating liquid bath may then be raised fairly rapidly using one capillary tube in order to determine the melting point approximately, the bath is then allowed to cool about 30deg C and second capillary tube is substituted for the first and accurate determination is made .It should be noted that a second determination of melting should not be made as the bath liquid cools by observing temperature at which the molten material in the capillary tube solidifies. This is because in many cases the substance may partially decomposed or some changes in its crystalline form which may change its melting point.
