Melting point apparatus. Magnified view, through a lens, of a sample being analysed for its melting point in a melting point apparatus. The crystals of the sample (orange, in sample tube) are being slowly electrically heated until they melt. The temperature will be obtained from a thermometer (not seen). Several readings will be averaged and compared with standard literature values. In this case the sample is a 2,4-dinitrophenylhydrazone, a product of a reaction to test for the presence of an aldehyde or ketone. The melting point of this product depends on the original chemical being tested for, in this case the aldehyde ethanal.