The determination of the melting point is of great importance in the
identity test, since many substances can be determined by their melting
point.
The purity of substances can also be qualitatively measured via
melting point. A well-defined melting point is only given for 100
percent pure substances. Due to impurities, such as impurities or
dopants, most substances have a melting interval (beginning of the melt
to completion of the melt) of a few degrees Celsius. Even impurities
during the manufacture of chemicals cause this melting point to expand
to a melting interval. As a result, most substances that are examined
with a melting point meter have a melting interval. This effect is used
to identify the degree of impurity of the substance.