The measurement of melting points is a relatively straightforward procedure that is carried out to determine the purity of a compound or to assist with its identification. A pure compound will melt over a relatively narrow temperature range, impurities both lowering temperature and widening the range over which it melts. The apparatus used to measure melting points can be simple oil baths to 'hot-stage' apparatus where the melting process is observed with the aid of a microscope. In each case the range of temperatures a compound melts is recorded and compared with known data.