Why seal capillary tube for melting point of exo?

Sealing a capillary tube for melting point determination of a compound is essential to prevent contamination and ensure an accurate measurement. By sealing the tube, the sample is protected from moisture and air, which could alter its properties and affect the melting point. Additionally, sealing helps maintain a uniform environment during the heating process, allowing for a more precise observation of the melting behavior of the substance.