The melting point of a solid is the temperature at which the substance begins to change from a solid to a liquid. Pure organic compounds have very defined melting points. Through the use of these melting points, the purity of the compound can be determined. Contaminants normally lower the melting point and broaden the melting point range (the temperature at which melting starts and the temperature at which the substance is melted). Narrow range melting points are normally indicative of the purity of an organic compound. Extremely pure compounds have ranges of 0.1 to 0.3 °C. Commercially available compounds (technical grade) have ranges of
2-3 °C. The normal laboratory grade organic (ACS) compounds have a 1°C range. The larger the melting point range, the less pure the compound.