Common issues

Solvent effects

As well as inpurities in the crystal matrix causing the melting point range to be depressed (or widened), the presence of solvents, and especially water, can result in the melting point range being less than ideal. It is a good idea to ensure that compounds have had sufficient opportunity to dry (eg spreading out on a watch glass, or allowing to dry for a period of time over a vacuum a sinter, or using a dessicator or vacuum dessicator) prior to recording the melting point range. Care should however be taken with compounds which are deliquescent, as these compounds have the reverse issue, and melting point values will become worse over time as the compounds absorb water (or other solvents) over time.

Decomposition range

Some compounds don't turn into liquids when heated, but decompose instead. For these a decomposition range would be recorded instead of a melting range.