Information from a melting point range

Melting points are always reported as a range, from the temperature at which melting was first observed to begin until the temperature at which melting was complete. The melting point range can be compared to previously reported data for a compound (unless the compound is novel), for both the absolute value and also the range over which the compound melted. 

For a compound of regular purity, such as a solid which has been recrystallised or purified by flash column chromatography, the melting point range is typically a couple of degrees Celcius, and with the upper value very close (or the same as) those reported in the literature. Unpurified compounds, would usually have a suppressed melting point, and a wider range (maybe 5 °C would be typical).

Reporting a range

Melting point ranges should be reported with appropriate precision and units. Whilst many melting point apparatus may report to a 0.1 °C, it is unlikely that this is a realistic level of precision unless a melting point has been recorded very slowly. Typically ranges are rounded to 1 °C. The literature melting point range is usually reported alongside, along with a reference to the source. Often the recrystallisation solvent is reported in brackets alongside the melting point, unless this information is provided in a procedure directly accompanying the data.

For example, a melting point range for benzoic acid (recrystallised from water) might be reported as:

Benzoic acid: MP 120-122 °C (water) lit: 121-125 °C (Sigma Aldrich).