Melting point s can be "sharp" where the phase change occurs at a particular temperature, or the solid may soften and then melt over a range of temperatures. Conventionally melting point refers to the sharp melting point, and this is exhibited by pure chemical compounds that do not decompose. Slip melting point usually refers to a technique for measuring the point at which a waxy solid "slips" in a tube -waxy solids such as hydrocarbons produced from petroleum oil are mixture and melt over a range and this is near reproducible way of obtaining a diagnostic single "melt" temperature for the mixture.