A pure white crystalline compound was found to melt at 112.5-113.0oC when taken on a melting point apparatus, and on further heating, the liquid was found to turn brown at ca. 145-150 oC. The capillary containing the melted compound was set aside to cool, and resolidify. When the sample was retried, using the same capillary the sample melted at 133.6-154.5oC. Why is the melting point higher than 112°, and the range so wide?